Talk:Intermittent power source/Archive 1

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Intermittent power sources - new page in need of editing

This page was established to shorten a significant and long portion of the Wind Energy article, and to allow for more in-depth discussion of this subject here. In need of editing. Contributions welcome. --Gregalton 09:42, 17 November 2006 (UTC)

Nota bene: There has been considerable discussion of intermittency in the talk pages for Wind Energy. For further background, you may wish to look there (until they are moved to this talk page).--Gregalton 12:43, 17 November 2006 (UTC)

Thanks for your efforts, Greg. I've pulled the discussion from the Wind Power talk page on this topic below. Skyemoor 13:52, 17 November 2006 (UTC)

I've just reorganised the long section on intermittency of wind. This section needs to be checked for references, NPOV, and other issues, but hopefully this regrouping of the issues will make it easier to edit further and make the arguments more coherent. There is some duplication that can be better seen now. Other "to-dos": it could really use more on variability of other power sources, especially renewables, i.e. solar and potentially water. At present, this is really a page about wind variability and comparisons would be useful.--Gregalton 21:59, 19 November 2006 (UTC)

Suggestions

This is a very well done article. Covers all of the key points (at least with respect to wind intermittency), with out a lot of gratitous POV (which I found a lot in the main Wind Power article). One nit-pick: the term "base capacity factor" is not really a common or recognized term in my part of the world (U.S.). I would suggest using the term "capacity credit" or "peak load capacity factor" (or at least mention their common usage) to describe the concept of how much power wind generates (or is expected to generate) during peak-load hours. Also, any kind of dispatched resource is also "variable" and "intermittent" (that is, a combustion turbine is cycled up and down, and occasionally trips-off), so I'm not sure either is more or less "correct" when discussing these issues. I agree the "intermittent" is the most commonly recognized term, and appropriately used, but I would suggest the much more descriptive "non-dispatchible", since that's what we're really talking about here. Windyone 21:43, 19 January 2007 (UTC)

Thank you for your suggestion! When you feel an article needs improvement, please feel free to make those changes. Wikipedia is a wiki, so anyone can edit almost any article by simply following the Edit this page link at the top. You don't even need to log in (although there are many reasons why you might want to). The Wikipedia community encourages you to be bold in updating pages. Don't worry too much about making honest mistakes — they're likely to be found and corrected quickly. If you're not sure how editing works, check out how to edit a page, or use the sandbox to try out your editing skills. New contributors are always welcome. 〈REDVEЯS〉 21:46, 19 January 2007 (UTC)

Intermittency - an over stated problem?

[edit] Frequency Service and Reserve Service

this is a usefull link.... http://www.ukerc.ac.uk/content/view/258/852 looking at the actual intermittency / variability of wind in the UK,

Another useful contribution - looks at renewable power, largely wind over a vast area. – a European/Transeuropean Example –

Dipl.-Phys. G. Czisch, Prof. Dr.-Ing. J. Schmid

Institut für Solare Energieversorgungstechnik (ISET), Kassel, Germany

Phone/Fax: (+49) 561-7294-359/100, E-Mail: gczisch@iset.uni-kassel.de


http://www.google.co.uk/search?hl=en&q=windpower++europe+interconnected+grid+sahara&btnG=Search&meta=



The national grid in the UK already is a massive user of technology to cope with the existing intermittency introduced by power stations themselves, at an industrial scale - up to 2 GW of load can be lost instantaneously by frequency sensitive relays switching of steelworks etc, which is matched over a 20 minute cycle by up to 2 GW of quite small emergency diesel generators. (These are already owned and paid for, for use as emergency generators by eg hospitals, water companies etc)

For a complete description of this complex but robust system, in use for many years, see for example "Emergency Diesel Standby Generator’s Potential Contribution to Dealing With Renewable Energy Sources Intermittency And Variability" - a talk by David Andrews, Energy Manager at Wessex Water a large utility who, along with other similar companies, work closely with the UK National Grid to provide this service. This was given at the Open University Seminar " Coping with Variability - Integrating Renewables into the Electricity System - A one day conference on Tuesday January 24th at the Open University, Milton Keynes." 24th Jan 2006 .

http://eeru.open.ac.uk/conferences.htm

For Wiki article based on the above: http://en.wikipedia.org/wiki/How_the_UK_National_Grid_is_presently_controlled


Up to 5 GW of such diesel generation is also used in France for similar purposes, but the fact of the widespread existing use of these techniques seem to be relatively unknown even by the pro wind lobby.

There is no reason why this type of simple and proven scheme should not be increased in scope to cope with even the intermittency introduced by a close to 100% (in terms of annual energy delivered from wind power), which would in fact be less than the intermittency already inherent due to the unreliability of large power stations - for example in the UK Sizewell B can impose an instantaneous cut in generation of 1.2 GW, which is far more severe than the swings which could occur in a 100% UK wind scenario.

http://david-andrews-wind-energy.wikispaces.com/

I don't think the intermittency problem is about load, but about supply; what would happen if all power plants were replaced by wind, and the wind can't provide adequate power for hours or days at a time. — Omegatron 21:22, 7 November 2006 (UTC)

1...If all the power plants were augmented, ( not replaced) by sufficient turbines for 100% wind, then all that happens is that sufficient of the power stations, which have all been retained, are simply started up to provide the power for the 5% or so of the year when there is insufficient wind. Remember they have already been built, and paid for and the bulk of the cost of a power station, is the fuel - 96%. So keeping it idle, is in fact very cheap. The cost of keeping a UK power station idle can be worked out from the Spark Spread,

http://en.wikipedia.org/wiki/Spark_spread#Clean_spread

which is the published profit of a power station, and is about 0.75p/kWhEngineman 21:59, 8 November 2006 (UTC)

The point of mentioning load, is to show that routinely large grid systems shed load as a matter of course to cope with the existing inherent intermittency of the power stations, surprisingly, this fact is not apparently well known to wind power experts.Engineman 21:59, 8 November 2006 (UTC)

The intermittency problem is about load and supply, like supply and demand. Load can vary dramatically, and it is precisely the peak events (three-sigma and above) that cause problems,

I do not think this statement is true - a large drop in power supply is more stressful on a system at times of low load than the same drop at high load, simply because it will be a bigger proportion of the capacity. Peak load is not itself a problem provided you have built enough plant to deal with it.Engineman 21:59, 8 November 2006 (UTC)

Also load changes, although they can be a bit bigger, are much slower than the loss of a power station, so they are not the ruling issue. It’s the unreliability of the power stations which determines the size of sheddable load available and spinning reserve, not the variability of the load Engineman 21:59, 8 November 2006 (UTC)

In the context of wind, the intermittency problem is peak load coming at times of low supply from non-dispatchable sources, i.e. wind. So having "enough plant" is not enough - it also depends on what type of plant. Load shedding is also essential, but it is also not without cost. --Gregalton 08:20, 9 November 2006 (UTC) even if they occur quite rarely. While I agree with you that supply is also the issue, it is a red herring to discuss "what if all power plants were replaced by wind", since there are almost no systems with penetration above 10%.

No - I think you have got this wrong. If there is not enought wind at peak times, during a 100% wind scenario, you just start up the old power stations that have been kept fully manned and on standby. This is not expensive since the major cost of running a power station is the fuel cost. Engineman 22:30, 13 November 2006 (UTC)

Wind increases variability of supply (or of net load, if one prefers); the question is how much it may cost to compensate for this - presumably while holding system integrity constant.

Frequency Service is very cheap - £7k/MW per year, which amounts to say £7000/1000kw x 8760 x 60% = 0.133p/kWh in the UK at the present - look it up on the National Grid website.

Other supply sources or reduced volatility of demand (by peak demand management) are both potential means to compensate. As noted in the text, the scenario of "wind providing inadequate power" (presumably what is meant is significantly below projected norms) becomes less likely as spatial diversity between wind farms grows. --Gregalton 22:57, 7 November 2006 (UTC)

I beg to differ - it does not seem logical to say that a 100 % wind is a red herring simply because there is no existing penetration above 10%, when what is being seriously proposed is precisely that 100 % wind, (ie enough to generate over a year the same amount of power that the grid delivers to customer) is a practicable scenario.Engineman 21:20, 8 November 2006 (UTC)

Here I disagree on two points: a) I don't think 100% is actually being considered seriously anywhere,

2. It is - I am demonstrating it is a feasible goal here. No one has so far advanced any logical or factual arguements to discount it. Wind will be utterly insignificant, and relegated to a side show, unless the proponents of wind power wake up to the fact that it is perfectly possible to have 100% in terms of annual energy supply from wind. If wind proponents do not step up to this challenge, then entrenched vested interests will continue to push the unfeasible in the long term of fossil or nuclear power, and policy makers who are not technical will continue to dismiss it as a sideshow.Engineman 21:37, 9 November 2006 (UTC)

at least in the foreseeable future, precisely because it is so far away, but that is my opinion; and b) Opponents and critics of wind power frequently cite what I think is a specious argument, to wit, "wind has problems that mean that it can't provide 100% of power." Whether or not that statement is true (the answer is not true or false, but one of trade-offs),

I disagree, it is demonstrably false.

it does not mean that wind could not provide substantially more with few problems. In other words, saying "wind has problems providing 100% of power" is a red herring often used to distract from the point that wind could be expanded considerably before intermittency (or other problems) became a serious issue.--Gregalton 08:20, 9 November 2006 (UTC)

OK I see your point, so I would say that it is, to coin a phrase, then it is a false red herring - becauaw wind does not have any more problems in providing 100% than say nuclear. In order to have 30% nuclear in UK we had to build the 2 GW Dinorwig pumped storage scheme, no other purpose than to help nuclear, and to install a large amount of off peak storage heating systems. And that links back to my point in para I have labelled 2 - unless this is exposed as a false red herring then the opponents will have achieved there aim in cnfusing policy makers.Engineman 21:37, 9 November 2006 (UTC)

I would, in all due respect, dispute the figures above about diesel and unreliability of large power stations. I do not know about the UK Sizewell B, but in Ontario, 1.2 GW is about 3.5-5% of peak demand of about 25 GW. While this would be a severe loss at peak demand, in many other instances it would be manageable (assuming not completely instantaneous)

The loss of Sizewell B, or any large power station, is completely instantaneous - as soon as the breakers open, and is entirely unpredictable and can therefore happen at any time - peak or not at peak - this scenario is typical to all power grids worldwide, in one form or another. All power stations are unreliable in that they can all immediately fail, totally and without warning. No matter how reliable a power plant is, it can still fail – maybe only once in 10 years, but that possibility is what determines the measures taken to cope with the intermittency, even if the power stations are highly reliable. The wind is intrinsically in these terms more reliable than a power station and the more you have the more reliable they become, simply because all wind turbines spread over a large areas can’t suddenly all stop at once.Engineman 21:59, 8 November 2006 (UTC)

Your point on sizing the backup for unreliability or instantaneous events (often the loss of the single largest plant) is good, and I had intended to underscore that wind is better on this point (losses occur gradually, except in the case of transmission line failure, which is true of most types of generation). That said, saying wind is "more reliable" is not very precise here - it's a different reliability/variability profile. Nuclear, for example, is reliable >90% of the time with little variability, but disruption events could take the whole plant offline (total failure); geographically spread wind has almost no probability of total failure, but much higher variability (and no ability to dispatch). In this sense, wind is quite reliably variable. Nuclear's reliability/variability profile also has weaknesses for certain uses (good for base, poor dispatchability). --Gregalton 08:20, 9 November 2006 (UTC)

OK I agree with your points here - but a matter of terminology I think. You can see what I mean....the sudden changes in supply due to 100% wind would be much less in UK say, and presumably any where else, than the sudden failure of a large unit. Slow changes, down to zero wind, can easily be coped with by the gradual starting up of existing fossil units, which will only need to be used a few days per year. If you work out the cost of this, using the published spark spread, it is very low - about -0.75p/kWh.

- there is 6 MW + of hydropower capacity. At any 100% wind scenario - which I assume to mean 100% of power is expected to come from wind, on average, meaning nameplate wind capacity would be 3.5-5X average daily demand and about 100-300X greater than current installed capacity - intermittency/variability would be massive. Backup diesel capacity for this would be enormously expensive.

Clarifiication. The back up in a 100% scenario comes from the existing fossil plant which are retained, diesels woud be used for only a small fraction of the total load on the grid and only for a few hours for any sudden change, as is standard practice in the UK and France, and the US. Diesel back up is widespread in the US - for exampel Cayhoga Falls substation has about 15 x 1.4 Caterpillare diesels installed - and there are 100s more across the US.Engineman 21:37, 9 November 2006 (UTC)

No it wouldn't be enormously expensive - not if you utilize diesels that have already been paid for as emergency generators for e.g. hospitals, offices etc, and which have to be paralellable in order for them to be tested. Since they are only used a few hour per year, the fuel cost is very low comparatively.Engineman 21:59, 8 November 2006 (UTC)

I don’t see where the 100 – 300x greater than current installed capacity comes from? The installed capacity of exisiting power stations on the UK National Grid, is about 70 GW say, and to entirely generate the total annual output of this system would need about 102 GWEngineman 21:59, 8 November 2006 (UTC)pk,

If using existing diesel plants, I would agree. To invest in extra diesel for this purpose, quite expensive. As for my 100-300X figure, very rough calculation for Ontario, based on the following: wind production 20-35% of nameplate capacity (you say 40% for UK, adjust as needed), existing nameplate about 1% of peak demand, some "extra" wind required to allow for variability. If current nameplate is 1%, 100X increase is conservative. --Gregalton 08:20, 9 November 2006 (UTC)I get it but it misses the point.Engineman 21:37, 9 November 2006 (UTC)

Don't get me wrong, much higher penetration than the current <1% nameplate capacity / peak demand should be easy, but 100% seems a ridiculous target, (I disagree on good grounds and I see no evidence to disprove my assertion Engineman 21:37, 9 November 2006 (UTC)particularly if diesel backup was to be considered. (sorry but you seem to be still missing my point - the bulk back up comes from the fossil stations already built. Only a small fraction needs to be diesel, and they ahve already been builtEngineman) Also, my understanding is that France uses primarily nuclear power, has low A/C usage, and given the low marginal cost of base load, diesel back-up may make sense; in different conditions, diesel may not be realistic, i.e. almost anywhere else.

Diesels are widely used for this purpose in the UK, and France and USA and I don’t doubt many other large grid systems. Denmark is about to start doing it.Engineman

Would you explain why you assert that 100% wind is a ridiculous target - what are your reasons for saying that? Diesel back up is not being promoted in the way you imply - if you look at the original paper which explains how the UK grid works, you will see that diesel is already widely used.

Why do you say that the intermittency would be massive? In fact it can easily be shown to be not so using a thought experiment - if you imagine sufficient wind capacity spread around the coast of the uk to generate 100% of units supplied to UK over the year, and consider wind patterns and the speed at which they propagate, (50 mph?) it soon becomes obvious that even with 100% wind the rate of change of the total output of all the turbines is in fact quite slow. Graham Sinden has studied the variability of wind turbine output and found it to be very low, by looking at the simultaneous wind speed variation of weather stations over the UK for the last 30 years. And you have to compare this with the rate of change of supply when Sizewell B trips in the UK. This is a loss of 1.2 GW in zero time, whereas the rate of change of 1% of the output of the required 102 GW of distributed wind power would only achieve this change over a few minutes in the worst case.Engineman 21:20, 8 November 2006 (UTC)

I think it is a ridiculous target at present because no-one is anywhere near that; capacity (to build the turbines and site), intermittency, and other issues compound it. (sorry but that strikes me as a very strange position, to have targets only based on what you have alredy achieved. by that token it would be absurd for Kennedy to have a target in 58 to put a man on the moon on the grounds that one hadn't even been put into orbit.Engineman 21:37, 9 November 2006 (UTC)I also don't believe that any one technology is likely to be appropriate for most grids, (well what other carbon free sourse is there?Engineman 21:37, 9 November 2006 (UTC))except perhaps hydro where the appropriate geological conditions obtain (pretty rare, but no unheard of).

That said, 20% in many jurisdictions should not be problematic, and considerably more in many others. If you stick at 20 % then policy makers will say, this is a side show, we are going to go totally nuclear or clean coal, niether of which is viable in the long termEngineman 21:37, 9 November 2006 (UTC)) That is entirely respectable and would represent a massive increase over existing capacity, a significant contribution to a reduction in pollution and global warming, energy security, etc. As for the figures on the UK's variability of wind, I'm not familiar with this study. Every study I have seen for other jurisdictions suggests that variability does increase, and very significantly (massively?) at high penetration levels, even for fairly large geographic areas; ( can you cite any study which shows this?- its plainly untrueEngineman 21:37, 9 November 2006 (UTC))current storage technology (and costs associated) mean that installing storage specifically (you don't need storage - you install EHVDC cables and import and export power to neighbouring areas to suit - as does Norway to Germany and Denmark, and the Dutch connection currently being built to FranceEngineman 21:37, 9 November 2006 (UTC)) to cope with intermittency of wind raises the costs significantly for projected high penetrations. (this is simply not true in any significant senseEngineman 21:37, 9 November 2006 (UTC)) Over the longer term, I grant that this may change. --Gregalton 08:20, 9 November 2006 (UTC)

That said, I agree with the opening point in this section, even if for different reasons. Intermittency is potentially a very big problem at high penetrations, but penetration is below 10% in most places, and only 20-odd percent in Denmark. This subject is the bogeyman of wind power - much feared, rarely seen.--Gregalton 23:00, 7 November 2006 (UTC)
My first question is what is the capacity factor of existing costal wind turbines in the UK?

About 40%.....Engineman 23:19, 8 November 2006 (UTC)


In the US, the best wind farms typically operate at 40% capacity factor.  Compare that to a conventional steam generator which typically have a 80-90% capacity factor.  Even with many, many turbines distributed over a large geographic area, a 70% capacity factor would be quite impressive.

Don't undertstand the logic here? About 102 GW of wind at 40% roughly replaces the total annual output of the UK grid, with its peak load of about 60 GW - what's the problem and where does the 70% capacity factor come from?Engineman 23:19, 8 November 2006 (UTC)

Another thought experiment: imagine 102 GW of wind replacing average annual load of 40 GW (approximately) at the 40% capacity figure, with base (minimum) demand of 30 GW, assuming half of peak. Wind might have variability between 20-60 GW output, even with good spatial diversity (feel free to adjust assumptions), as wind speeds over the UK have some correlation. Unfortunately, that output is uncorrelated with demand/load. So there would be instances (albeit infrequent) where wind is 40 GW short (max demand minus minimum output), and there will be instances where wind output is 30 GW above system needs. The swing from one to the other may not happen in a single day, but it is still a wide range. Of course, load shedding, storage, power export, and other solutions are possible (including simply disconnecting the wind turbines for a period), but they all involve additional costs or lower revenue; the higher the proportion of wind, the higher these costs. This is, of course, simplistic analysis, but it does give an indication of the potential scale of the issue. (Even if wind's variability can be reduced to 30-50 GW output, which strikes me as low, the range is still 30 GW short / 20 GW over). Even if the system is quite flexible, it implies a large additional capacity to deal with the surplus/deficit, which (with current tech) would raise the overall cost of wind substantially.--Gregalton 10:15, 9 November 2006 (UTC)

That is a good summary of the issues. But the cost of EHVDC cables is very low nowadays - the longest one currenlty is 1500 kM, so all one does is to export the surplus and re-import it as required. Even without wind power, the cables will have significant savings simply due to the reductino in total capacity. If you don;t like cables, there are numerous other forms of cheap storage - off peak heat, deffereing or advancing fridges etc.Engineman 21:37, 9 November 2006 (UTC)

Gregalton, thanks for the above as it very clearly states the issue. If you look at Graham Sindens paper you will see that it is in fact very rare to have the 102GW of notional turbines operating flat out for very long, so the period when you have to do something with the excess, and the quantity is quite small comparatively speaking.

Any short term over generation, could easily be dealt with in a number of very cheap ways. For example, install a 3 kw resistance water heater in each of 20 million UK homes connected by a frequency sensitive switch. That would give 60 GW of instantaneous storage or load deferral. About 5 million UK homes already have 10 kW storage space heaters and these could be similarly flexed - at present they are on dumb timers, but again they could easily be switched to cascaded frequency control ( so they all come on and off in progression). That gives you another 50 GW of instantaneous storage for several days. By the way, these were only introduced in the 60s to cope with the then percieved intermittency and inflexibility of nuclear power, along with the 2 GW of pumped storage at Dinorwig/ Ffestiniog. See also Frequency Service and Reserve Service

Then we have David Hirst's technology of advancing or deferring fridges, freezers etc which gives another 10 GW and this is just some cheap electronics in a plug.

There is also the issue that for 102 GW of wind, Sinden shows that there is always some wind generation somewhere, so infact it some portion of wind counts as 100% reliable basedload, meaning we can retire some existing plants with the attendant savings.Engineman 22:42, 13 November 2006 (UTC)

Another question I have is why would a 1.2 GW unit trip cause under-frequency load shedding?

Well it just does - lose output and the frquency must start to fall as soon as load exceeds generation....National Grid frequency service loads are then automatically shed in direct proportion to the fall in frequency...Engineman 23:25, 8 November 2006 (UTC)Engineman 23:19, 8 November 2006 (UTC)

While this is a large unit, if the loss of this unit is the most severe contingency, the power system should be carrying sufficient operating reserves to suffer the loss of the unit without the loss of load.

That is simply not the case. The UK and the US national grid has certain large users who are contracted and qutie happy to have there load shed under just such an eventuality They find it cheaper than spinning reserveEngineman 22:42, 13 November 2006 (UTC).User:Engineman|Engineman]] 23:19, 8 November 2006 (UTC)

If the UK doesn't require this type of operating procedures on their system, my guess is that the variable nature of wind generation without sufficient operating reserves would result in frequency deviations, possibly resulting in load shedding. Doublee 22:56, 8 November 2006 (UTC)

Errrr that is the whole point of what I have been saying- the UK system is designed to do just that - load shed as Hz falls. Look up Freqency Service and Reserve Service. User:Engineman|Engineman]] 23:19, 8 November 2006 (UTC)

My understanding is that the profile of wind power generation (the power curve) is also problematic. More specifically, wind's median power output is significantly lower than the average, because power output rises geometrically with wind speed (put another way, periods of high wind contribute more to the average output than average wind periods). Even over a large area, even with 30-40% average capacity, the base component would have to be lower. For example, I have seen the figure of 20% (of nameplate) being used as capacity contribution fairly frequently; while this is probably conservative, this would mean far more wind would be needed to provide base load than the 25-40% capacity factor indicates. Not much of an issue at low-to-medium penetrations, a very big issue at high penetrations. When I look at the output of wind farms in Ontario (www.ieso.ca, look at hourly generation data), this is supported: lots of periods of output at 10-20% capacity, then some periods where 60-80%, resulting in the average capacity; unfortunately, the peak output tends to be at times of lower demand (night-time), and the lower output at times of higher demand (daytime and summer). That said, the 10% appears pretty reliable. (Usual disclaimers on this data, Ontario is not representative, not enough geographical diversity, not enough historical data, this is not a proper statistical study, etc., etc.)--Gregalton 08:20, 9 November 2006 (UTC)

Again I think you have missed my point a bit....if there is no wind, you simply start up the old power stations you have already built. They don't cost much to keep on standby.Engineman 21:37, 9 November 2006 (UTC)

Engineman, a few quick points...
1) It would make it much more like a discussion, and readable by others, if you could interject as separate paragraphs rather than editing within sentences. It is no longer possible to figure out what's what here, and may not be useful to anyone.(I was tempted to just revert to the previous version, just so it would be readable - if you were able to edit back so that your comments are separate, that would be helpful.) I think the discussion should also attempt to determine what meets the standards for inclusion in the main page, and we may have gotten away from that.
2) I think we are departing from different reference points and different assumptions. My background is economics/public policy/finance, areas where the cost and revenue matter. For wind power, the criticism I see and hear frequently is that a) it is not viable (or very expensive) at high penetrations and therefore b) wind is not a complete solution. As I've stated, I think part b is specious (no other form of energy is held to this test). Part a requires more data and experience than currently possible, and depends on market structure and a number of other factors, but is also many years out; that said, there are serious issues.
3) There are a number of credible studies (i.e. by system operators) stating clearly that there are minimal issues at levels up to 20%. See, for example, http://www.ieso.ca/imoweb/pubs/marketreports/OPA-Report-200610-1.pdf. In this study, and with existing systems, however, going substantially further (here to about 33%) would cause some problems (too much wind power when not needed seems to be biggest issue, but based on existing generation profiles); you asked for a citation, here it is. I have not seen any studies suggesting going above 50% would be easy or cost-free, but look forward to seeing citations; I have seen studies that "show" that costs grow substantially at higher levels. (And note: if wind annual capacity is 40%, the penetration level needs to be 2.5X higher to meet annual consumption, and I certainly haven't seen studies on implications of 250% penetration levels)

What frustrates me is that people talk about "problems" which implies it is unknown or insurmountable as to how to deal with it. I claim that the alleged problems with high penetrations are simply technical issues that can be dealt with in known ways at low cost.

I did not intend for it to imply it is unknown or insurmountable, and don't think that is the meaning of "problems." If you prefer, "challenges." And, what I question is the extent to which these are technical issues that can be done at "low cost." How much? My point is that the costs are unknown, and that the solutions may make high penetrations uneconomical.

I don't know of any citations looking at 100% apart from my own very rough and ready (never the less I believe robust) attempts. But where are the citations to show it is not possible?

This does not require much research. Search google for "wind power maximum penetration limit", lots of hits. To pick at random one study, see http://www.ucc.ie/ucc/depts/civil/staff/brian/EWEC03.pdf . For Ireland, they find that approximately 60% penetration (very rough figure) "the curtailment of the last wind turbine is such that it will operate for only a few hours per year during periods of maximum demand. Clearly this would be uneconomic" (My bold). (To explain, curtailment would be points at which wind turbines would no longer be producing electricity for sale - they may be physically shut down or spun with generator disconnected or by other means). Of course, plenty of potential solutions exist, Ireland may be a special case, etc, but it remains a challenge. You can also look for deCarolis and Keith, "The Costs of Wind's Variability: Is There a Threshold?", The Electricity Journal, which has a more theoretical approach to looking at the costs. Hence, the prima facie case exists that above some level, wind may be uneconomic, even if technically possible.--Gregalton 07:35, 13 November 2006 (UTC)
Your own rough and ready calculations are interesting, but this is original research. While it's interesting, it's distinct from verifiable outside expertise. Apart from that, I personally don't find it to be "proof" or not subject to dispute (for example, maintaining all existing plants unused would only cost 0.2 pence / kWh? If current production costs, for example, 4 pence, to me this would imply that fuel makes up 95% of current operating expenses.

Gregalton - look up Spark Spread - published figures show that the profit a power station makes is £7-9 / kWh. Revers that back to how much they would have to be paid, if they didn;t run, and its about 0.75p/kW h. There is no dispute - Spark spreads are widrly published.Engineman 22:52, 13 November 2006 (UTC)

Sounds high, and just not convincing - to me). At any rate, this is not the place to question your numbers, or for original research, but to attempt to determine what is "encyclopedic" enough - i.e. verifiable - to merit inclusion in this main page. Others should weigh in, but I return to the main point: the claim that 100% wind generation can be achieved economically is not proven or verifiable. Conversely, the claim that 20% is believed to be feasible is, if not proven, sufficiently credible. --Gregalton 07:35, 13 November 2006 (UTC)

4) In my view, the evidence that 20% penetration causes no major issues is reasonably credible, and 20% is not a "side show" - would be more than existing hydropower worldwide, and probably nuclear. Since world penetration is ca. 1%, penetration can be increased significantly in most jurisdictions before this issue becomes relevant (pace Denmark). It will also take a long time to get to 20%, and technology and experience will develop further after that point, and increases beyond that may prove economical and reasonable. Denmark will hopefully show the way. [Note that Denmark's "20%" penetration is in fact only 1-2% on the international grid that they depend on so heavily. Kerberos 17:15, 16 November 2006 (UTC)]
5) But the evidence that 100% can be done economically and reasonably is not "proven", as you have asserted, or at least, I haven't seen it. I do not see the statistical evidence that suggests there would only be a few days per year with too little/too much wind (even completely uncorrelated wind resources have this problem).

Look at Graham Sindens work in the UK. Oxford Universitey and the recent UKERC study. But in any case the exact number of days doesn't really matter since the costs of using the exisitng power stations as back up is so low. See Spark spread and Triads.

I do not see the financial numbers behind the solutions. I see issues with, for example, exporting large amounts of wind - to where? Countirs where it is not windy at that time. Engineman 12:12, 12 November 2006 (UTC) Will they pay? Well Germany and Norway have been doing it for years. Engineman 12:12, 12 November 2006 (UTC)How much? Do they have wind too? at these large distance they are largelyuncorrelatedEngineman 12:12, 12 November 2006 (UTC) The storage solutions, from what I have seen, are either not there or quite expensive domestic hot water and domestic space heating - happens in New Zealnd alreadyEngineman 12:12, 12 November 2006 (UTC) . To people financing wind farms, or paying for the cable, or running the systems, these issues matter a lot. Like the poeple who are payoing for the Dutch - Norway interrconnector, and the 20 year old Mid germany to Norway, or the UK France interconnector?Engineman 12:12, 12 November 2006 (UTC)

Ok I'll agree I haven't proven it in that strict sense - but overall I think I have shown it pretty unlikely that economic solutions cannot be found. Massive inter regional power flows already occur for other reasons.

6) Thanks for the information on diesel backup. This appears to be more significant than I thought.--Gregalton

07:28, 10 November 2006 (UTC)

Greg - thanks for the points. I'll re-edit this in the next few days.


To sum up in reference to the header: Intermittency of wind is potentially a big problem at high penetrations but the problem is overstated at low-to-medium penetrations. Since few grids have penetration above 10%, the problem of intermittency is overstated at present, and for most reasonable projections about wind penetration in the medium term. --Gregalton 08:24, 9 November 2006 (UTC)

Can you give any quantitive reasons to qualify and justify the assertion that it is a big problem? To put it into context,when the nuclear industry started in the UK in the 60s, some would have said that the inflexibilyt of nuclear would create BIG PROBLEMS. They were solved by a) building Dinorwic, 2 GW of flex plant, b) the cross channel interconnector - 2 GW c) massive expansion of night storage heaters.

I beleive I have disproved this (potential problem at high penetrations), becasue at 100% penetration, the max rate of change is less than that caused by the exisitn power stations.Engineman 21:37, 9 November 2006 (UTC))

Minnkota Power Cooperative, Inc. headquartered in Grand Forks, North Dakota, USA, has been successfully utilizing a load management system based on ripple control since the late 1970s.

What began as a simple tool to control peak demand during the winter – the share of electric heating loads on the Minnkota system is substantial – turned out to be a highly reliable and cost-saving instrument for the utility in recent decades. The primary driver for Minnkota’s decision to utilize load management by ripple control was the mature and well-proven technology, as well as the guaranteed signal reception at the customer’s home, school, farm or business where the various switching commands must be executed precisely.

Today, Minnkota is actively controlling a 40 percent share of its wintertime load during peak-use conditions, typically when economically priced power is not available to serve the off-peak loads. The load management system allows Minnkota to offer a competitive wholesale power rate to the 11 member-owner distribution cooperatives in eastern North Dakota and northwestern Minnesota.

Hours of control have increased from an average of 30-40 hours per heating season in the past to approximately 400 hours a year. Customers are strongly encouraged to have properly sized and operational alternate fuel backup heating systems to carry them through control times.

As a service to off-peak customers, Minnkota displays the actual status of the load management system on its Web site, www.minnkota.com. Off-peak heating remains the best energy value in the Minnkota service area.

Minnkota is sourcing its Load Management equipment from a variety of highly reliable suppliers.

Facts:

Area of Supply: 34,500-square miles Number of customers: More than 117,000 Summer Peak Load: 500 MW Winter Peak Load: 650 MW Own Generation Capacity: 528 Third Party Generation Capacity: 16


I was not referring to max rate of change, but others can decide whether this issue has been "disproven". --Gregalton 07:28, 10 November 2006 (UTC)

Due to unawareness on how to reply in a wiki thread, this thread is too difficult to follow. Please use new lines and colons (one more than the previous comment) in order to provide the indentation that makes a thread readable. Otherwise, you will have wasted your time trying to communicate your ideas. Skyemoor 12:47, 10 November 2006 (UTC)

I would suggest moving this entire section on intermittency and variability to a new page, leaving just a summary here of the main issues. It is a complex topic and appears to be important enough to merit the change. It would also reduce the amount of editing on a fairly important page, and have the more detailed editing work going on there. Any opinions? --Gregalton 19:01, 12 November 2006 (UTC)

Good idea I think. Engineman 10:27, 14 November 2006 (UTC)

I'm fine with that, as it involves any intermittent power source, not just wind. One further point; if overproduction is an issue at times, the excess could be used in ramped-up hydrogen production. Skyemoor 10:37, 14 November 2006 (UTC)

Pricing limitations?

I'm not sure what this statement means, "Many grids also use energy pricing to influence supply and demand (increasing prices to encourage increased supply and lower demand), 'but pricing solutions are incomplete solutions due to different time frames needed to find "market pricing" solutions and the operation of the grid.

"Real time" spot pricing can be one effective means to limit demand during low generation points (i.e. wind speed falls off, skies become overcast in a region, drought reduces hydropower rates/reserves, etc). Hence, the price could change for an hour, a day, a week, and so forth. It can be tied in with DSM/Load Shed management systems to reduce demand (i.e., electric hot water heaters go to 115F instead of 125F, A/C units go to lower duty cycle, etc). Skyemoor 12:32, 18 November 2006 (UTC)

The statement was intended to convey that no system uses pricing alone to ensure reliability, due to lags in adjustment to prices, etc. In other words, even the most "market-oriented" grid pricing systems are ultimately highly regulated. In comparison to, say, the banana trade - if Company X imports more bananas in week Y than anyone wants to eat, the bananas spoil and X is out the money. Contrast with electricity - systems exist to ensure that everyone participating follow quite precise rules, that are enforced using non-price mechanisms.--Gregalton 15:05, 18 November 2006 (UTC)

I'm still not sure I understand what is trying to be communicated. See if my markup begins to approach what you are saying. (and please use indentation in the Talk page, using one more colon than the person before you). Some interesting links on spot pricing are;

Skyemoor 10:18, 19 November 2006 (UTC)

I have no difficulty with the phrasing you used in the page. Again, the issue I'm trying to address is simply that a pure pricing solution is insufficient, and even so-called "deregulated" markets have quite specific rules for participants. In economic terms, a "market-clearing" solution might occasionally not be found without intervention, and is effectively enforced. Perhaps this is an issue that does not need to be addressed here at all.--Gregalton 11:26, 19 November 2006 (UTC)


There will not be one overall solution, but a set of solutions (i.e., storage, DSM, pricing, etc). Skyemoor 12:12, 19 November 2006 (UTC)

Cost of export transmission capacity

There is an assertion in the "maximum penetration" section that export transmission capacity is "cheap". This seems to me to need a reference or costing as a function of scale. For example, Ontario-Quebec link gives one instance of a 1,250 MW link to be built between Ontario and Quebec will cost over $800 million (Canadian), or approximately $640,000 per MW. Now, I do not make any assertion that this is the cheapest possible, or comparable, and it is only one datapoint. But "cheap" clearly needs to be defined better. Note that if wind power costs approximately $1-$2 million per MW of nameplate capacity, it would also seem to not be cheap relative to the cost of generating capacity for wind, it could potentially affect the economics of wind quite substantially.--Gregalton 21:37, 21 November 2006 (UTC)

One question is why was the link built in the first place ? presumably a case in terms of avoiding building more power stations in either grid, and sharing diversity savings. So the same applied to any interconnection - there are large savings availalbe by joining up grids in terms of reduction in total capacity and spinning reserve. Once built they aid the penetration of wind power.

If they are built purely to help wind power then the above beneftis acrrue.

Also, the $640,000 per MW isnet to be compared to each MW of installed capacity, but the surplus that has to be exported at peak, which will only be a fraction of the installed capacity of the windfarms.Engineman 20:51, 21 November 2006 (UTC)

I am not trying to deny reasons why the link was built in this case, and there are undoubtedly good reasons to do so; I'm simply attempting to determine whether, in the context of an NPOV article, stating that building export transmission lines is "cheap" is justifiable. It's rather vague and does not sound convincing.--Gregalton 21:37, 21 November 2006 (UTC)
I also understand there are many, many benefits to joining up the grids, but we know it does not happen all the time - presumably one reason is that it is not always (sufficiently) "cheap", or justified by the benefits. As far as your second point (to be compared to the export at peak), I agree: but what scale of export capacity, at what cost, in the scenario mentioned.--Gregalton 21:39, 21 November 2006 (UTC)

Fair point.... I guess I am saying that in the context under discussion, interinking of grids is highly economic ie a mix of the appropriate amount of cables will improve the overall economics of wind. Have a look at Project Genie.....Engineman 19:40, 24 November 2006 (UTC)

I am not arguing that the appropriate amount of cables would not improve the economics of wind; if interlinking the grids were free, it would be an easy decision. The question I am trying to get at is whether the cables themselves are economically justified. You have asserted they are "cheap"; I'm not sure that is verifiable.--Gregalton 23:30, 24 November 2006 (UTC)
Gregalton - thats a hard one to answer - but presumably the 1500 km EHVDC running up Africa, bringin power from a hydro resource to a copper mine is justifiable economically so presumably that would apply elswhere - likewise the UK cross channel link? Engineman 22:41, 25 November 2006 (UTC)
If it is a hard one to answer, it may be because it is unverifiable. As for the Africa case, saying it is justifiable in one place and hence presumably so elsewhere - well, it's just not really a complete argument or verification. The assertion was that it was "cheap".--Gregalton 19:08, 26 November 2006 (UTC)
A separate point: I'm not convinced your most recent edits are neutral or verifiable, let alone factual accuracy (to my knowledge, there are no 660 MW turbines). In addition, you've changed the meaning and context of the text enough that I'm tempted to simply revert to the previous version. Grateful you look at your edits again, in general.--Gregalton 23:30, 24 November 2006 (UTC)
Fine - I've revisited them hopefully my edits are now neutral. However from my perspective the original article was not neutral iether - the text seemed to me to be written from the POV of how grids are operated at the moment - ie dispatchable plant meeting a diurnally changing load. In this context variable but reliable plant are seen as a challenge. But there is no reason I have been presented with to show that the operating philosophy could not be modified so that dispatchable plant are merely operated to make up any short fall which will happen from time to time.
I suppose the grid operating principles could be modified. But that does not sound to me like a verifiable article. As to whether the existing article is neutral, this (the talk page) is, at any rate, probably the right place to have the discussion. The article seems to address (very broadly speaking) the issues that intermittent/variable sources of power present in the context of existing grids. If it "should be" about other grids, fair enough, but that seems to me to present a challenge for verification.--Gregalton 19:08, 26 November 2006 (UTC)
Gregalton - I was referring to the 660 MW steam turbines on the UK national grid) Engineman 22:06, 25 November 2006 (UTC)
In particular, you refer to reliability and variability as if they were the same thing. Again, a wind plant might be reliable, but extremely variable (no sudden total loss, considerable swings in output), but other types of generation may be invariate (little change in output) but have lower reliability than wind (more likelihood of total loss). It's not that one is bad, they just have different implications. These need to be clarified to get NPV.--Gregalton 23:30, 24 November 2006 (UTC)
I think we are slightly at cross purpose here - I am saying that for a large penetration, and hence a large number of wind turbines, the net output is very reliable (albeit variable - not the same thing) - it cannot in agreggate change nearly as quickly as iether a tv load pick up, or the loss of two large plants. You seem to interpret my comments as being at the individual wind plant level which they are not - I would not attempt to argue that a single wind turbine is more reliable than a large steam setEngineman 22:06, 25 November 2006 (UTC)
I have looked at the studies you cite. There still seems to be large variability likely. Is there some conclusion you're drawing from this that I'm missing? The figure you cited only goes to a 30% penetration, you're talking several times higher.--Gregalton 19:08, 26 November 2006 (UTC)
I agree, the studies you cite don't fully back your argument. The ECI study actually states that for 10% of UK electricity demand being met by wind an additional 700 MW of operating reserves would be needed in response to the variablity of the wind generation. That isn't a total of 700 MW, but an ADDITIONAL 700 MW above the current requirement. That seems to indicate that variablity and reliability are very closely related, if not the same. An additional note, the report also states that as the wind penetration increases, balancing costs will rise. Also, the report indicates that overall total system costs will increase proportionally with the increase in wind penetration, accounting for balancing and fuel cost savings. I do have two problems with the report. 1) The data used was AVERAGE HOURLY wind speed. Hourly is great, but doesn't present a true picture. If the average is 20kph, there very well could have been a 40kph gust and a 0kph gust. That uncaptured data could change results. 2) The wind data was compensated to account for hub heights at 80m, yet the assumptions used weren't disclosed. While the conversion may be 100% accurate, that could be another variable which would alter the results and conclusions.Doublee 23:06, 29 November 2006 (UTC)
I would agree with Gregalton in that there is only focus on the individual plant reliability. Due to the distributed nature and sheer number of turbines, wind farms will always give some output. However, the additions severely minimize the dispatchable nature of traditional power plants versus the fact that wind farms cannot be dispatched AT ALL. The output is variable, and while can be predicted, since when are weather forecasts accurate in a day ahead/next 12 hour timeframe? The loss of 2 plants simultaneously (1200 MW) in North America is considered a double-contingency and therefore does not require reserves to be carried for it. Also, a 660 MW plant contingency does not necessarily require 660 MW of reserves to be carried. It most likely will be less as the governor action of the units on-line with spinning reserve will arrest the frequency decline at around 59.5 Hz (in North America) You don't need 660 MW of spinning reserve to keep frequency above 59.5 Hz. I don't agree with the edits and think they should be reverted. As an operations and planning engineer with a US utility, the discussions so far tell me that no one contributing to these discussions works in operations or planning. Many of the arguments are theoretical and don't jive with how the power system is operated and assumes that DSM is guaranteed and very prevalent. DSM is a solution, but in the US, you can't require people to be on DSM.Doublee 15:54, 25 November 2006 (UTC)
The input of someone with the right background would be very warmly appreciated.--Gregalton 19:08, 26 November 2006 (UTC)

Doublee - I did not say that a large quantity of wind turbines produces a despatchable output. I am pointing out the conventional plant can easily follow the slowly changing aggregate output of a very large number of turbines - this is no more than a power system already does.

I have only focussed on individual plant 660 MW plant reliability becasue that is what the UK National Grid does, and I have compared that to the reliablility of the equivilant number of wind turbines.

Why do you only quote a 12 hour forecasing time frame? Weather forecasting is pretty accurate for wind speed 12 hours ahead, but obvously you can refine your forecasts as time goes on, until eventually you are forecasting 6, hours, 3, 1 hour, then 15 minutes, 5 minutes etc. What's the difficulty? That's what our UK already grid does - it is well known that UK National Grid study the tv guide and make adjustments in readiness for predictions that are only a few minutes / seconds ahead for say half time in a foot ball match. The best form of forecasting would be the actual output of the aggregate wind turbines themselves - what the UK's or the US's aggregate output is in one hour, is most likely to be being produced one hour later.

Regarding DSM - it is not compulsory in the UK, where my comments apply - there is a market mechanism and people are paid to make up to 2 GW of DSM available - automatically switchable load and diesel engines- this is extremely cheap and could be readily extended. The more the Grid wants, the more money they offer. It is my understanding that there is commercial DSM in the USA as well? I used to work for Caterpillar and there were a large number of diesel sets installed on US substations for this purpose Cayhoga Falls was one I recall where there were about 10 x 2 MW sets. Pesumably in response to some market mechanism?

I note you have wind turbines as being not dispatchable AT ALL (your emphasis) implying presumably that I have stated or think they are. I fully understand that point and have nowhere said or implied that they are dispatchable. So I assume you are misinterpretting my point(s) somewhere along the line.Engineman 21:34, 25 November 2006 (UTC)

For DSM and other, I think the question is at least partly of scale. How much extra DSM and other solutions would be needed and would it be "extremely cheap" as stated above? Is this verifiable? DSM in many places (Ontario, for one) is nowhere near the scale that they think is needed now. Therefore, it may not be easy or cheap.--Gregalton 19:08, 26 November 2006 (UTC)
In the UK DSM - is about 2.25 GW out of a peak demand of around 60 GW, and this is used in preference to spinning reserve or Dinorwig pumped storage - 2 GW - (the largest such scheme in the world I beleive). So since this is market based it (DSM) is presumably the cheapest. See

http://en.wikipedia.org/wiki/Reserve_service

Ontario could consider setting up a market for DSM as we have done in the UK and this will encourage people to enter the market.

Ontario should certainly do a number of things better. My point, however, was a) the amount that may be required of this with high levels of wind may be substantially higher than is needed now (when they are primarily trying to deal with short-term shortfalls at times of peak demand, which is likely events of a couple of hours); b) it may not be as cheap and easy as you are stating; and c) the "cost" of this may grow with scale. All three of these are serious issues. I don't know enough, obviously, of the UK case to compare the background or why it was done, but you yourself made the point that this was done partly because of the large nuclear installation. This may imply it was not the cheapest market solution at the time (although it could be now, marginal cost vs average cost).--Gregalton 21:23, 30 November 2006 (UTC)

Participants are paid around £7k per MW (ie not per MWh) per year, and there are around 2250 MW of such DSM capacity. Since the total annual sales of power in the UK is around 3x10exp11 kWh, this means the cost of this DSM is around 0.005p/kWh

Based on previous posts, the cost seems to be off. The Reserve Service page that is linked to indicates that the £7k per MW does NOT include fuel and operating costs. It does state that National Grid will pay these costs. Previous posts have stated that fuel accounts for 96% of power costs, so the £7k figure is probably significantly understated.Doublee 22:26, 29 November 2006 (UTC)
We are talking about two different things here. The cost of a large coal fired station, then the fuel cost is about 96% of the running cost. Reserve service largely uses small deisels which I would not call power stations, and have been built for other reasons ie emergency standby generators. Exact fees are confidential, but some players earn about £7k profit, after fuel and maintenance. The fuel and maintenance cost have to be bid in, and then these are paid for by NGT, leaving a £7k profit which is essentailly a capacity charge. There is a page on the National grid Reserve Service site which gives a scatter graph of the bid pairs.
On the variability of wind and the cost of the potential solutions, particularly cables (notwithstanding the docs you sent me separately) it still seems that there is not enough verifiable information to support the conclusions and pricing info. We should begin to edit to simply reformulate as possible solutions whose viability is not yet demonstrated on the scale that would seem to be required at extremely high penetrations.--Gregalton 21:23, 30 November 2006 (UTC)
Gregalton - sorry not sure what you mean hear - "conclusions and pricing info" please explain. Engineman 15:49, 1 December 2006 (UTC) ie are you querying my estimate of the cost of the UK transmission network, at 0.2p/kWh (which presumably includes 1/2 the 2 GW cross channel link)?
My point is that if it costs 0.2p/kWh for the entire UK high voltage grid, which shifts around up to 60 GW, it won't cost much more to connect say 10 - 20 GW into Europe. Its not exactly expensive to lay cables on the sea bed, and the North Sea and Russia is criss crossed with natural gas pipe lines which I daresay are much more expensive per unit energy tranmitted than cables.
I am not questioning the original figure, I am questioning its relevance. A four-lane highway in Northern Ontario may not cost much more per kilometer, and yet still be much more expensive per passenger. If 10-20 GW had to be built for peak events of a few day per year, that would be a different pricing proposition. At extremes, it may be more cost-efficient to spill rather than build transmission capacity. In the most simple terms, 0.2p/kWh is perhaps achievable over a 60GW national grid, yet end up being orders of magnitude more expensive in another context. Note that it is entirely possible that the expensive part may be building/extending/reinforcing the land-based grid to get to the sea-based drop off points. These discussions do not bring to bear an actual usage/sizing/scale analysis that would make this info verifiable for inclusion here.--Gregalton 20:11, 1 December 2006 (UTC)

OK I take your point - I will have a dig around and see what I can come up with. But it still seems self evident to me that such cables, at a certain level will be economic simply because that is the reason most of those linking up European and other grids have been constructed. These are not continuous base load flow, but bi directional therefore often zero generally depending on the time of day and season, so are not fully utilised, nevertheless economic.

It is evident that at some level they are justified, the question is what level. But under your 100% wind scenario a) the level required may be substantially higher and more expensive and b) if cables need to be built and laid specifically to integrate wind, it may raise the marginal cost (lower the marginal revenues) of wind significantly at such high penetrations.--Gregalton 20:53, 3 December 2006 (UTC)

Yes I agree with your summary - 100% wind definitely won't be the optimum economic solution, but there seems to be so much emphasis/exageration on the supposed insurmountable issue of intermittency it is worth examining the extreme.

An interesting link is

http://eeru.open.ac.uk/natta/docs/12.%20BrianHurley.ppt

which is presumably underlined by some detailed economic evaluation, since Airtricity are a major player. They are proposing to cover the seas around Europe with turbines and cables.

I think the situation is very similar to district heating grids, where in Germany and Scandinavia, it is found that if 50% of the peak heat load is met by combined heat and power plant, the rest peaking boilers, then 90% of the heat delivered comes from the CHP.

It may be worth examining the extreme, but it seems out of place on the article page. This section still does not reflect a NPOV. Sorry to harp on that.--Gregalton 17:02, 6 December 2006 (UTC)
Gregalton - sorry could you specify which bit you are still not happy with. ThanksEngineman 20:36, 6 December 2006 (UTC) I've re-edited the first section which is hopefully now more NOPV....Engineman 21:05, 6 December 2006 (UTC)
The section entitled "maximum penetration limits" has significant portions that do not represent a neutral point of view; much is not verifiable; and at least some of it constitutes original research. These are the three content policies of wikipedia: see http://en.wikipedia.org/wiki/Wikipedia:Neutral_point_of_view. It should be edited to correspond to these policies.--Gregalton 21:28, 6 December 2006 (UTC)

Just want to chime in to say you chaps are doing a smashing job; keep up the good work! Skyemoor 23:42, 6 December 2006 (UTC)

Oh, and there are some energy storage approaches that use caverns to store compressed air. Skyemoor 23:42, 6 December 2006 (UTC)

Thanks Skymoor.....

Gregalton, I am getting some firm figures from ABB but verbally the cost of a 1 GW link to Europe is apparenlty about 300m Euros - which I find hard to believe, but confirmation apparenlty coming. Watch this space. —The preceding unsigned comment was added by Engineman (talk • contribs) 21:23, 7 December 2006 (UTC).

Why is that hard to believe? What is the distance? If it is an asychronous link (HVDC), that is the most expensive option, but controllable. A synchronous link will be cheaper, but since you would be talking undersea cables, the cost will increase signficantly due to the added engineering and specialized materials/technical issues (voltage rise/drop in cables for various loading levels). Doublee 22:09, 7 December 2006 (UTC)

Study on variability and another on transmission limitations

This study is fairly skeptical on wind variability in Ontario, by a fairly respected research group: http://www.energyprobe.org/energyprobe/articles/EPreviewofwindpowerresults.pdf . I'll be right up front about the caveats: very short time frame of study, not much geographical dispersion yet, etc. That said, it noted a few very problematic figures: 18% of the time during summer, wind generation was insignificant (less than 2%); other studies over-optimistic on attainable geographic diversity (due to wind resources very far from demand centres); high correlations between wind farms; quite large variability in output in short time frames; poor fit with demand. Again, this is from a very limited number of farms, but is at least based on publicly-available data.

This other presentation looks at the very serious issues with transmission, again in Ontario. There are a few interesting bits that come out: a) adding additional capacity, even variable, to areas with excess load is a no-brainer, and particularly when transmission constraints exist; b) adding supply to places with excess supply and limited transmission is "not a good fit", and the cost / time-frames / planning issues involved not easy to resolve. Since the places with excess load will often be urban centres, the issue for wind is serious, and at least in Ontario, the places with good wind resources are precisely those that have excess supply and limited transmission (out). http://www.theimo.com/imoweb/pubs/marketreports/WP_20061024-CanWEA-WindTransAvailablity.pdf --Gregalton 17:00, 6 December 2006 (UTC)

General Focus vs. UK Focus

In my opinion, there is too much focus on the UK system and the particular features of that system. The challenges that the UK faces are very different than the challenges of, say, North America or South America. I think that content relating to a specific system should be organized and grouped together, and content which is general should be grouped appropriately. Example: The UK is a winter peaking system, mainly at night, which correlates well to wind output based on historical data. Conversely, the US is primarily (except for isolated individual utilities) a summer peaking system, due to high air conditioner load and hot weather. Load is highest during the day in the summer, when wind generation output is typically at its lowest based on historical data and operational experience. The challenges, solutions, costs, etc. are very different between systems and should be separated within the page. Doublee 23:41, 6 December 2006 (UTC)

Doublee. Totally agree with your points. I think that low carbon solutions will vary from country to country / continenet to continent depending on their specific circumstances. But the UK is nevertheless a good example of where local conditions in Europe indicate that a very high penetration may be economic. I don;t know much about Canada, but I would have thought a solutoin there would more likely be hyro and biomass from all those trees, but not something I am familiar with.Engineman 21:20, 7 December 2006 (UTC)
My point is UK issues are UK issues and not applicable to the US. Therefore those UK issues/specific solutions should be included in a UK specific section. Many points made on the Wikipedia page are UK specific and not general enough to be applicable to many different systems. From a US perspective the UK example, solutions, costs, etc. has no applicablity to the US, and unless it is grouped that way the reader is being misinformed if the distinction is not made. Doublee 21:37, 7 December 2006 (UTC)
Doublee - just so I'm clear - your example above was meant to be a good example, since it refers to general principles using a specific example, correct? I would also agree that the text should be general, with examples where appropriate (which will, to some degree, come from where people have knowledge, but we should try to keep it as broad as possible). There are places where the text goes well beyond that. And where necessary, separate pages can be done for wind in the U.K., etc. And: feel free to edit! Be bold! Engineman: not clear what your point is. This page is only indirectly about what mix of low carbon solutions is appropriate for each locale.--Gregalton 14:39, 8 December 2006 (UTC)
My primary concern is with the "Maximum Penetration Limits" section as the content in that section is exclusively related to the UK. Many of the points made do not apply or correlate with the US system or issues. They are points that are exclusive to the UK, and should be in a section about the UK. I would think that the page should be about what research has been published regarding the challenges and solutions to intermittent power sources, not challenges and solutions for specific systems. Doublee 17:03, 8 December 2006 (UTC)


Layout

Great work so far! I may jump in again to help with balancing out wind vs. everything else. Skyemoor 11:03, 10 December 2006 (UTC)

Please do. More technical info and references would be greatly appreciated, as well as "balance." --Gregalton 12:09, 10 December 2006 (UTC)
I have tried to clean up a few sections. If you are looking for suggestions, the penetration section could use an introduction that lays out the terms and definitions of what is meant by penetration, figures and their meaning, and editing of the "list of ideas" format that looks weak.--Gregalton 12:42, 10 December 2006 (UTC)
Answered my own request by writing an intro to penetration. Section could use more editing down, however.--Gregalton 10:31, 11 December 2006 (UTC)
Sorry to be away for so long. I've jumped back in making many tweaks here and there; for the most part, everything is looking very promising. Let me know if I've gone overboard anywhere. --Skyemoor 18:19, 27 March 2007 (UTC)
Much appreciated. Keep going. I still think the last section (high penetration scenario) is too close to original research and blue-skying, which I don't think appropriate here. But given sensitivity of others, would be grateful for another set of eyes. Best, --Gregalton 19:41, 27 March 2007 (UTC)

Removed unverified

I have removed the following: "For example in the UK which has a peak demand of 60 GW, the 2GW Dinorwig pumped storage and a 2GW cross channel link, the grid nevertheless has to permanently have reserves to deal with the simultaneous loss of 2 x 660 MW sets, 1.32GW, Sizewell B nuclear power station, which can and does fail. By contrast, if (in the UK) 102 GW, nameplate sum, of wind turbines (circa 30,000 machines) were installed and were at any time producing for example 40 GW, then clearly this output cannot suddenly change by 1.32GW from 40 GW to 41.32 GW or to 38.68 GW in the time it takes for the breakers on Sizewell to open. To this extent it is clear that the greater the penetration of variable and intermittent plant, the more reliable in this sense does the aggregate output become."

I have put this back because it is not unverified - the stats on the UK grid are contained at: Control of the National Grid (UK) Max loss of load is at Sources of intermittency on the UK National Grid

Sources of intermittency on the UK National Grid

I do not understand the reason the example was taken out. The fact is as the hypothetical example shows, the instantaneous rate of change of 40 GW is far lower than that which the UK, and therefore by extension many other grids will be faced with. Therefore, it is unarguable (i think) that 40 GW of wind, is in many respects more reliable than 40 GW of conventional 1 or 2 GW plant.

The ramping issue is a quite different one, and again simple hypothetical examples indicate they are no more severe than at the end of large football match. Engineman 16:03, 1 April 2007 (UTC)

This para on reliability seems to me unverified, highly hypothetical and too specific to the UK. It also seems to be a straw man argument on "reliability". Although the (hypothetical) 40GW could not instantaneously lose 1.32 GW, figures from existing plant do suggest that losing 10, 20, or 30% of this level of wind generation in an hour or a few hours would be entirely possible. So the "single event" loss - which I don't recall anyone ever stating as the test of reliability or as a key issue in intermittency - may not be likely/possible, but very significant ramping demands would exist in this (hypothetical) scenario. At any rate, I don't believe this assertion/denial text belongs here: the assertion of reliability as a problem was not made, and the argument to disprove the assertion is not verified from outside sources.--Gregalton 17:51, 10 December 2006 (UTC)

Engineman: welcome back. Please put your comments/replies in a given section below the most recent comment. It makes it easier for other readers in a linear timespace sort of way.
Please see [[[original research, synthesis of published works]. You make a conclusion that it is "unarguably" so. I have not seen a similar conclusion elsewhere, and don't think it's unarguable. You can settle the issue by giving a credible reference that makes this conclusion. Otherwise, it's original research.
Separately from verifiability, I think it is too specific to the UK. I'm not disputing the numbers cited about the UK system that are sourced, just whether they are needed here. See the discussion section below where others have commented that it is too UK focused. Best, --Gregalton 17:55, 1 April 2007 (UTC)

Hi Greg - thanks for your editing tips - I will try to follow,

Perhaps I am being thick, but the point I am trying to counter, is the widely made claim or assumption that very large penetrations of wind power are less reliable, and therefore expensive in the sense of needing more back up, than conventional systems - the wind protagonists claim is that large penetrations would simply use the back up that is already their for other reasons - ie the existing power stations and procedures. See for example Control of the National Grid (UK)Engineman 18:47, 1 April 2007 (UTC)

My simple calculation, (in fact it doesn't need a calculation) shows (I hope !) that it is not true that large penetrations of wind do need more back up to to mechanical unreliability.

Since 40 GW of wind plant needing say 13,000 plant, and which cannot all simultaneously suffer from physical failure, or simultaneously suffer a large one way wind speed change, must be more reliable than a grid dependant on plant of unit sizes 660 MW, which can suddenly stop - that is surely unarguable.

Since the stoppage of the 660 MW has to be coped with already, then whatever measures are used can be used at no extra cost by the 40 MW of wind, So I do not see why that point needs references - its self evident. In fact surely to argue the contrary needs references - where is the evidence?


I suppose there are two strands to this.

One is that to replace the instantaneous output of say a 660 MW set, then maybe 300 x 3 MW wind sets would be needed at a particular moment in time. But hey clearly can;t all suddenly fail physically, so in fact that makes the 300 x 3 MW wind sets more reliable than a 660 MW set, so grid needs less back up.

Secondly if you were to have 40 GW of wind, on the UK system (one has to use an example one is familiar with) then the rate of change of the wind over all geographically dispersed sets obviously cannot exceed 3 GW in a few seconds, which is what the UK national grid already copes with at the end of a royal wedding or big football match, using well established methods covered in Control of the National Grid (UK)Engineman 18:49, 1 April 2007 (UTC)

Regarding the UK, Control of the National Grid (UK) - I haven't seen any where else a detailed description of how grids are controlled for sudden loss of load etc - i assume they are much the same as the UK. Most people will be surprised to learn that in the UK we can instantly shed 2 GW out of 60 GW of load, and use 2 GW of rapid start diesels. You need to understand that and the relative other numbers to understand how bogus are many of the claims of the effects of large wind penetrations.

I have no doubt the US and other large grids work in similar ways but now one has put it up yet. Best Regards.Engineman 18:59, 1 April 2007 (UTC)

Max rate of change on UK national Grid - During the last solar eclipse, the UK grid shrugged of a 3 GW surge in 3 minutes.... http://news.bbc.co.uk/1/hi/sci/tech/specials/total_eclipse/417650.stm

There's no problem putting a link to the UK national grid site, or quoting numbers when needed. The point (repeated by others) is that it ended up being a lot of detail on the UK grid - too much - when it's covered elsewhere and not strictly the issue at hand.
As for the specifics of your argument, suffice to say that I'm not convinced that what you are stating is self-evident. And I'm not arguing the contrary - I'm just asking you to provide a credible source for that claim. If there is an assertion that you're making as important as that, it should be backed up by a reference. (Put another way, if there is this widespread myth about wind at high penetrations, you're not going to convince anyone by saying it's self-evident)
And I repeat my point about the straw man argument: I'm not sure I see the issue of response to instantaneous failure as being a major controversy. When credible studies have discussed this (balancing or regulation costs, I believe they generally call it although the terminology is devilishly different every time), they've given fairly precise estimates of potential impacts and costs. Why not quote them? It will be much more authoritative than these calculations.
The ramping/operational reserve/"back up" issue seems to me to be far more serious, and covered well at [1]; you seem to be referring primarily to instantaneous/short-term power loss/demand growth, but that's not the only component of reliability. And your scenarios definitely require some references since they go so far beyond other published studies. That's all I'm saying.--Gregalton 19:33, 1 April 2007 (UTC)

A few suggestions

It's clear that a lot of work has gone into this this article, and I have made a couple of small contributions, but mainly I have found the article to be too theoretical and hypothetical for my taste. I think the article could benefit from several things:

  • a lead section that is more readable and in line with WP policy (eg., from 1-4 paragraphs long).
  • some sort of case study section to ground the whole article, maybe of the UK, since it has received some attention in the discussion above, perhaps drawing on sources such as this: http://www.ukerc.ac.uk/content/view/258/852.

I also generally agree with the comment above about over-stating the problem of intermittency with regard to renewables. It seems to me that as electricity grids become larger, and when innovative overnight storage systems (such as phase-changing salts) are used, and when combinations of solar and wind and hydropower are integrated, and when solar power is matched to summer noon peak loads in areas where there is significant demand, that intermittency problems are reduced. I think these sorts of basic measures need to be emphasized more in the article. Perhaps there could be a section which clearly deals with basic measures to deal with intermittency which don't involve backup from large fossil fuel power stations.

Unfortunately, my detailed knowledge in this area is limited, so I would invite discussion and ask for the help of others in making changes. Johnfos 23:05, 1 April 2007 (UTC)

I agree the opening section is too long - edits welcome. Case study also welcome, although I would suggest that it should be based on an existing system or very specific studies, with less emphasis on levels of penetration unseen today.
As for over-stating the problem of intermittency: this article was separated from windpower because it was getting to be the longest, partly because perhaps the most topical and controversial (certainly one of the main areas that wind is attacked in the press, despite low understanding of the issue). Certainly as experience and technology develops, the issue will (likely) become less controversial, especially if experience is good. That said, there is very little application of the innovative solutions, very little solar power (compared to wind), and apart from hydro, little truly industrial-scale storage technology currently available (and unfortunately, hydro in most places is subject to geographic limitations). Demand management is still limited in many places (even the most basic, real-time pricing, is infrequently applied). Transmission grids and choices of generation will slowly evolve, partly due to the presence of intermittent sources, partly due to other technical/economic/political considerations.
So perhaps there is a way to separate this (thinking out loud) into short/medium term solutions and long-term. A number of long-term solutions exist that could be outlined that have the potential to dramatically change the circumstances in which intermittency is discussed, and perhaps make intermittency less of an issue. In the short/medium term, I think the situation is different, and would prefer to a) emphasize that most grids can integrate substantial amounts with little difficulty, and this is very well-documented; and b) that very, very few grids are anywhere near reaching a level of wind penetration where intermittency becomes a significant issue. Reactions? --Gregalton 06:43, 2 April 2007 (UTC)

Hi Gregalton. That all sounds good to me and the new lead section is really an improvement. I will contribute what I can and may have a few questions to ask from time to time. Hope that is OK. Johnfos 06:42, 3 April 2007 (UTC)

A few more suggestions

Gregalton and Johnfox - thanks for you carefully worded responses - despite my comments belwo, i do think it is a terrific article - just too long..

I understand that Wiki is meant to be a summary of knowledge as is established elsewhere, not for opinions or research. However the balance has to be right.

At the moment, if you as a punter tried to read up on Intermittency you would be completely overwhelmed I believe.

The section is far too long and covers too many issues in unnecessary detail which make things unnecessarily complicated.

I suggest the whole thing should be drastically simplified to give the average punter - lets say a journalist, or researcher for a tv programme, a clear idea of whether intermittency is the Achilles heal of wind or not (as is routinely claimed in many newspapers and ill informed people). At the moment I am sure a journalist would come away completely baffled and have to assume that it is a big unresolved issue.

The whole issue of how example grids are controlled is covered elsewhere in Wiki and need not be repeated. (ie Control of the National Grid (UK))

The claim that intermittency is not an insurmountable technical problem and that therefore wind could come close to providing 100% of power generation is very simple and cannot be backed up by references because it hasn’t been done. But that doesn’t not mean it is not possible and obviously (says I) so for the following reasons.

1. the entire UK national grid (which is very well defined and therefore a good example, but could be any other large grid where the facts are known) were supplied by wind power - typically 140 GW, 35000 turbines, would be needed in the UK. Then self evidently, when the wind is not blowing, all the existing power stations can be started up in sequence to fill in the gaps. That is not deniable – self evidently? The cost of doing this is very roughly the Spark Spread and not overwhelmingly significant..

2. It is known that the UK Grid can easily cope with 3 GW swings in a few minutes, (last solar eclipse) and self evidently, 35,000 turbines spread around the coasts of the UK cannot all lose or gain 3 GW in 3 minutes from a change in wind speeds over the entire UK - winds simply do not change their average speed at anything like that rate. Graham Sinden’s paper (http://www.eci.ox.ac.uk/publications/downloads/sinden05-dtiwindreport.pdf ) page 8 shows that the worst rate of change due to wind variation is about 20% and is likely to occur about once per year.

So for 60 GW of capacity that is a 12 GW change in 1 hour, or a paltry 0.2GW per minute, far less than the 3 GW change in minutes due to the last eclipse..

3. Again, 60 GW of power coming from 35,000 turbines cannot all suddenly fail technically simultaneously, therefore the Grid operating at that point, would require less back up than it already has ( to cover the failure of the large 1.32 MW Sizewell set).

Consequently, it must be obvious? Self evident? The case? that intermittency even with 100% wind is not a serious technical issue for the UK even with things as they stand at the moment.

But then one has to mention all the other already existing technologies than can be readily deployed to assist a 100% wind scenario;

1. 5 Gw of existing switch able storage heaters in real time 2. Potential 3 kW x 20 million switch able in real time immersion heaters = 60 GW 3. 2 GW cross channel link 4. Potential to add 6 GW at a cost of about £1billion 5. or 40 GW at say £7billion

So it seems to me there is no doubt that the issue of intermittency does not stand in the way of 100% wind on the UK and any other large interconnected grid system.

That’s not to say it is the most desirable economic course – that remains to be settled by proper studies.

http://energydiscussiongroup.wikispaces.com/Green+light


But I think what you are saying is that simply stating the obvious is not good enough, it has to be stated somewhere else and referenced?

On the other hand, as things stand at the moment, the net effect of the intermittency article I would argue is to make most non-specialists believe that it is a serious unsolved issue and the whole thing needs to be drastically shortened I would humbly suggest.Engineman 16:37, 2 April 2007 (UTC)

I agree it should be shortened and simplified. So far, the bias has been to preserving stuff cut from the wind power page. I will take a crack at shortening/simplifying in due course, but all are welcome to do so.
And engineman: yes, what I am saying is precisely that it does need to be stated somewhere else and referenced. See Wikipedia policy on attribution, and particularly the part on original research. Unfortunately, your conclusions, costings, etc., are not obvious - at least to me. And to say that it is perhaps not the most desirable economic course is a pretty big "but...". At any rate, it really should be published somewhere else first.--Gregalton 16:50, 2 April 2007 (UTC)

Gregalton - OK I take you point now about atribution....and loook forward to your and anyone else's efforts in shortening it. I don't think i have the skills or sufficient NPOV to undertake that task. Engineman 19:25, 2 April 2007 (UTC)

Hi Gregalton and Engineman, I think we're all agreeing that the article should be shortened and simplified, so as to make it more suitable for the average reader. Great! And I think the new lead section is very good.
But I wanted to ask about the "random nature of power generation from intermittent sources". I wouldn't have thought that we were dealing with random events when considering wind and solar. Surely, the typical daily and seasonal variations are well known and can be largely anticipated. Or am I missing something here? Johnfos 06:37, 3 April 2007 (UTC)
Look forward to your contributions. As for randomness, yes, this is probably overstating. I'll try to reformulate. Probably some other subtleties lost on the cutting floor too.--Gregalton 07:16, 3 April 2007 (UTC)
I'm looking more closely at the intro where it says: "Intermittency means that generation from these sources cannot be "dispatched" to meet demand, and changes in production do not correspond with demand cycles." Is this always the case? I'm thinking about the situation in south-western USA where the solar thermal systems match the summer noon peak demand, mainly due to air-conditioning load in cities such a Las Vegas (see Solar power plants in the Mojave Desert). A similar situation occurs in Spain (see Solar power in Spain). So in these important cases the variability in solar supply matches consumer demand and is surely a good thing.
The more I think about this topic, the more I prefer the word variability instead of intermittency, and I think we really need to stress that the variability due to daily and seasonal variations with renewables is well known and can largely be anticipated.
For both of these reasons, the matching of supply and demand in key locations, and the well-known nature of the variabilty, surely means that the variability with renewables does not have to be a major problem. It is something that we should be able to manage quite readily. Johnfos 08:06, 3 April 2007 (UTC)
I agree variability is a more accurate name, but this is the word that has stuck. See the UK ERC article for a good summary [2].
And while I broadly agree with your point, I don't think we should over-do it on the predictability. Forecasting errors remain a problem, and even if there were no errors, the mediocre correlation with demand still requires solutions (for wind anyway). The numbers I look at show large variation and some pretty rapid changes.
That said, it is highly appropriate for this page to de-bunk the myths that are most prevalent (or most actively pushed): that wind (e.g.) requires "100% backup", which is both not true and not meaningful (systems require back-up, individual sources do not); and that this intermittent nature means wind has no value (replacing fuel usage is valuable in many circumstances, and particularly in greenhouse gas reductions).
I find the way the intermittency issue is pushed for systems that have close to nil penetration fascinating. Ontario, for example, has on the order of 1.25% nominal wind/peak demand, Quebec about the same. For large systems, these amounts border on rounding errors. While there may exist some rational reasons for opposing wind, at the prevailing low penetrations it's not remotely credible.--Gregalton 08:30, 3 April 2007 (UTC)
Thanks for that. I think that what is coming out here for me is that the solar power situation is a lot more predictable and manageable than the wind power situation. I think it would probably be a good idea for the article to start off with an expanded discussion of solar power variability, and how to manage that, and then move on to the more complex wind power situation. So we would start with something relatively simple and move to something more complex. Johnfos 08:43, 3 April 2007 (UTC)
I'd hate to think that we are cutting away good meat from the article. One way to keep pertinent material is to bundle it into another article, as was the genesis of this page. WP:SUMMARY helps to smooth this transition. Penetration might be one area that could benefit from such an approach. --Skyemoor 10:39, 3 April 2007 (UTC)
Broadly speaking, I think there are two ways to go with this article:
One is to keep the focus on both wind and solar, in which case substantial material on wind would need to be cut from the article, and the solar section would need to be expanded.
The second approach would be to focus just on wind power and the article could be renamed accordingly. Perhaps the title could be something like "Integrating wind power into electricity grids". Johnfos 02:09, 4 April 2007 (UTC)

Denmark - penetration?

I've been reviewing some docs, and although I see Denmark is generally listed as 20% penetration, I see here the note that it is 44% (nominal / peak demand). Can anyone confirm?--Gregalton 10:10, 3 April 2007 (UTC)

I have now added penetration figures for a few countries. I have not been able to find peak demand figures for Spain, however, which is probably also over 20%. If anyone has access to a reference for this, it would be useful.--Gregalton 06:52, 4 April 2007 (UTC)

We have a Wind power in Denmark article now, and so if anyone is inclined to make a contribution, feel free. -- Johnfos 06:18, 7 April 2007 (UTC)

"random nature of power generation from intermittent sources"

Quoted from above:

"But I wanted to ask about the "random nature of power generation from intermittent sources". I wouldn't have thought that we were dealing with random events when considering wind and solar. Surely, the typical daily and seasonal variations are well known and can be largely anticipated. Or am I missing something here? Johnfos 06:37, 3 April 2007 (UTC) "

I think it is accurate to talk about randomness - for example wind can be reliably predicted to be stronger in the UK in the winter as a general rule, but on particular days it can be as windless as a summer day.

However wind prediction techniques are now very good. At the very least you look at the average output of the turbines themselves. Sindens work shows that at the very worst you will only be 20% different in in hours time. But of course by the time you have got to an hour ahead, you will have had 59 intervening minutes to revise your prediction, so your forecasting error gets less and less.Engineman 12:36, 3 April 2007 (UTC)

This is probably a semantic issue: the wind is clearly not random (there is a system generating it that is not random in the sense of a roulette wheel). What is essentially random is our forecast error when done far enough out. I've seen this put differently, but if someone has a good way of putting this, please add.--Gregalton 13:23, 3 April 2007 (UTC)

Examination of the implications of a technically close to 100% wind generated electric power (in terms of power generated vs power used over the year) scenario in the UK

Note - the purpose of this piece is not to claim this 100% scenario as the optimum technical and economic energy supply option, merely to show that at the limit, ie close to 100% penetration, the grid is already perfectly capable of functioning reliably and absorbing any likely power swings and cope with periods of no wind at little extra (ie in comparison to pre-existing costs) cost, using existing technologies and methods.

It therefore follows, that significant, but less than 100% can also feasibly be provided. An optimum economic mix will be a combination of various renewables and load management techniques outlined below.

The intention is to use the examination of the implications to provide a simplified explanation of a very difficult subject - that is as to how, contrary to common sense, and the claims of ill informed journalists and other experts, variable, and often non existent sources of power such as wind, can nevertheless still provide the bulk of our electrical energy in a reliable and economic way.

Only careful and sophisticated academic modelling studies can determine the optimum solutions, but these are too complicated for the average reader / journalist to follow. A good and thorough example is to be found at:


http://energydiscussiongroup.wikispaces.com/Dr+Bromley%27s+model. This model by Dr Mark Barrett of University College London takes a holistic hourly view of the entire UK energy system over a year, and based on a range of assumptions, indicates that obtaining more than 95% of electricity from renewable sources is feasible for the UK, with wind being by far the largest contributor.

A major finding is that the capacity of the link with France is increased from its present 2 GW to 6 GW to allow more trade for demand-supply matching.

Further information may be found at these links:

http://www.cbes.ucl.ac.uk/projects/energyreview/Bartlett%20Response%20to%20Energy%20Review%20-%20electricity.pdf

http://www.bartlett.ucl.ac.uk/markbarrett/Energy/UKEnergy/UKElectricityGreenLight_100506.ppt


At the moment exaggeration of the issues of intermittency, unreliability and occasional non-availability is used to justify assertions that renewables in general and wind in particular, cannot realistically provide a significant proportion of future fuel and power needs, and that therefore, dangerous and uncertain other technologies must be used to solve the greenhouse gas and approaching peak oil issues. The following is intended to be a simplified explanation.


EXAMINATION OF EXTREMES FOR THE 100% WIND CASE


1. If the total annual output(around 400 TWh/y) of the entire UK national grid (which system is well defined - Control of the National Grid (UK) and therefore a good example, but could be any other large grid where the facts are known) were targeted to be supplied totally by wind power - then typically 165 GW installed capacity operating at a 30% load factor would be needed. This would then imply 47,000 turbines of 3.5 MW peak output.

(47,000 turbines should not be considered a daunting number - 250,000 aeroplanes, 250,000 tanks, the means to destroy them, were all built in a few years in Europe during WW2. Vast areas of cities and infrastructure were destroyed and rebuilt. 40,000 wind turbines is a relatively minor undertaking by comparison and we have 25 years to do it in.)

2. Under this scenario, self evidently, when the wind speeds are low, and aggregate turbine output is below the then demand on the the grid, then sufficient of the existing UK power stations can be started up in merit order sequence to make good the shortfall. The cost of providing this cover is very roughly the Spark Spread ie loss of profit and is not overwhelmingly significant - about £7/MWh compared to supply prices presently of £70/MWh. Since the power stations have already been built and paid for, the only extra cost of operating is the fuel cost. By far the largest cost of running a fossil power station is the fuel cost which cost is not incurred when they are standing idle.

3. It is known that the UK Grid can easily cope with 3 GW load swings over a few minutes, (last solar eclipse http://news.bbc.co.uk/1/low/sci/tech/specials/total_eclipse/417650.stm ) and 1800 MW load swings in seconds ( which occurred when the half time whistle blew during the World Cup match 20/6/2006 http://www.nationalgrid.com/uk/Media+Centre/PressReleases/200606pickup.htm .)

4. If at a given moment, 47,000 turbines spread around the coasts of the UK, were producing 60 GW, (the peak output experienced by the UK national grid,) they cannot all lose or gain 3 GW in 3 minutes, or 1.8 GW load in seconds from a simultaneous change in wind speeds over the entire UK. Winds simply cannot change their average speed at anything like that rate. (a 30 mph wind is by definition travelling at 30 miles per hour, so it would take 10 hours to travel 300 miles - a typical extent of UK wind farm dispersion can be 300 to 1000 miles - winds have to go somewhere since they cannot suddenly stop.) A glance at a weather map shows that winds or windless periods extend large distances - 1000s of miles, and weather systems only travel at 10s of miles per hour.

5. Graham Sinden’s paper (http://www.eci.ox.ac.uk/publications/downloads/sinden05-dtiwindreport.pdf ) page 8 shows that the maximum rate of change due to aggregate wind variation is likely to be about 20% of wind capacity per hour and is likely to occur about once per year.

6. So for 165 GW of wind capacity which may at one time be producing 60 GW of output(and this is the worst case because its the max for the UK grid) that is a 12 GW change in 1 hour, or 0.2GW per minute, far less than the 3 GW change in minutes due to the last eclipse or the 1.8 GW in seconds at the end of a football match.

Hence no conceivable rate of change of wind can induce power swings greater than the grid already has the investment in plant and control systems in place to easily deal with.

7. At any given moment, the UK National Grid has to have at least enough fast back up (ie instantaneous, in the form of spinning reserve) to cover the failure of the largest simultaneously failable sets on the system which is usually the 1.32 MW Sizewell set. See Control of the National Grid (UK)

Therefore if at a given moment, 47,000 turbines were providing 60 GW of power (max load on the UK system), because they cannot all suddenly technically fail simultaneously, the Grid operating at that point in time, would require less fast back up than is already provided for Sizewell. 60 GWE of wind would clearly require back up to cope with variation over longer periods, but that would come from the existing power stations which can be brought on at more than the max possible rate of change of wind power per hour ( 20% of 60 GW - 12 GW per hour or 0.2 GW/minute).

This back up would take the form 6 x 2.4 GW stations, being held on hot standby ( - ie boilers just about to produce steam) but capable of generating simply by increasing fuel burn. This can occur in a lot less than an hour, and the energy needed to keep a large station on hot standby is tiny compared to the power needed when generating. This amount of hot standby would only be brought on during the periods of extreme wind change which can be reliably predicted so it would be rare that this quantity would be needed. The hot standby could be further reduced by the availability of rapid start gas turbines and other measures mentioned later. The National Grid already has about 8.5 GW of plant on hot standby at the moment.Control of the National Grid (UK)


Consequently, it is technically clearly the the case that intermittency / variability of wind, even with sufficient capacity to generate close to 100% wind is not a serious technical issue for the UK even with things as they stand at the moment because the plant and methods are there already.

8.Sinden's work which looks at all UK weather station hourly wind data for the whole of the UK over 30 years, shows (http://www.eci.ox.ac.uk/publications/downloads/sinden05-dtiwindreport.pdf ) that there are no hours during the last 30 years in the UK when this number of turbines would be producing no output. However, with no extra storage, load management or strengthened interconnectors to other systems, there would be large dumping of excess output when wind generation exceeds load and corresponding shortfalls to be made up by fossil power.

There are however, already existing well used technologies that can be readily and cheaply extended or deployed in a 100% wind scenario to make the excess of wind during high wind periods usable during windless periods minimising the need for fossil fuel back up. These are merely and extension of methods already in widespread use to cope with the intermittency of existing power stations and loads.

9. As pointed out elsewhere, there are already 2 GW of existing switchable in real time loads used by the UK National Grid for load balancing under automatic frequency control relays. Basically when the frequency falls do to a load surge or power station failure, large tranches of pre-arranged load simply drop of the system. And there are already 5 GW of existing switchable in real time storage heaters which can be brought into this frequency control (see Load and generation response mechanisms http://en.wikipedia.org/wiki/Control_of_the_National_Grid_%28UK%29 to deal with up to 5 GW of variation, and to store heat for many hours or days. (Incidentally these were installed using various market based selling techniques by the electricity companies purely to cope with the inflexibility of the early nuclear programme - this is the inverse of wind's intermittency)

10.Since these storage heaters only cover a fraction of the UKs 20,000,000 housing stock these could be readily extended if required to cover the entire UK building housing stock. At 10 kW demand per house, that would give 200 GW of storage take for several hours, but storable for days.(but not all heaters and all of the margin would be available all of the time so the actually capacity for wind storage would be significantly less than this).

11. There are already in existence a large number of 3 kW hot water electric immersion heaters. If extended to the entire UK housing stock, there are potentially there are 3 kW x 20 million switch able in real time hot water immersion heaters this give a further 60 GW of instantaneous storage. These have been remotely switchable in real time in New Zealand for 30 years using ripple control. (but not all heaters and all of the margin would be available all of the time so the actual capacity for wind storage would be significantly less than this

12. There is the existing 2 GW cross channel link to Europe - again built to cope with the intermittency of nuclear power and its ability to load follow.

13. There is the potential to add a further 6 GW at a cost of about £1billion or 40 GW at say £7billion

14. Sinden's paper (http://www.eci.ox.ac.uk/publications/downloads/sinden05-dtiwindreport.pdf ) shows that it is rare that there are high winds simultaneously over the whole of the UK meaning it would be relatively rare for the output of 165GW of 47,000 turbines to exceed 100 GW. this means that virtually all surplus power could be exported at peak wind / low load times, using a £7billion 40 GW link. The output at this time has zero marginal cost, but can be sold on the continent to compete with the current marginal plant. During times of low wind on the continent it can be bought back as needed - from whoever on the continent can offer the lowest price - as there will always be someone in the same position as us - the position of either selling their marginal plant to the highest bidder or going off the system.

15. There is already an existing 2 GW pool of small privately owned diesel generators (250 kW - 2000 kW), purchased by third parties for use for emergency cover in hospitals, water works etc, already also in use on a daily basis http://en.wikipedia.org/wiki/Control_of_the_National_Grid_%28UK%29#Reserve_service_or_National_Grid_Standing_Reserve Reserve service or National Grid Standing Reserve to help balance the UK National Grid. Since these are already paid for, for other reasons, the capacity is available at very low marginal cost. There are good reasons why using these diesel sets regularly for assisting the National Grid, actually lowers the cost of owning them and operating them and makes them more reliable. Diesel generator

16. There is a further pool of 16 GW of similar emergency standby diesels, ie used in hospitals, water works etc, but not used for load management in this way, which can be brought into use in a similar way again at very low capital cost.

17 These small sets have the perhaps surprising ability to be all started simultaneously in 30 seconds to full load using present technology, and this figure could be lowered to 2 or 3 seconds were it to be desired at little extra cost.

18. Additionally there are other techniques becoming available to allow, distributed influence over the switching decisions of millions of appliances with deferrable loads such as fridges, electric cookers, electric kettles etc, to enable them to offer additional balancing and thus effectively storage. see www.rltec.com and http://en.wikipedia.org/wiki/Dynamic_Demand_(electric_power)

19. If we are serious about cutting green house gases to 20% of present levels by 2050, then we will need to seriously address transport fuel, largely coming from fossil fuels at the moment. The only feasible large scale candidate seems to be electricity which would need an expansion of wind generation capacity from about 165 GW to probably 500 GW. This would entail a massive investment in battery storage and battery exchange stations (Batteries are likely to be the cheapest storage medium - about half the cost of hydrogen for example at present).

As a hypothetical example, 20 million electric vehicles with a 3 kW bi-directional charging / output capacity would imply a 60 GW bi-directional interruptible demand / load. (but not all vehicles would be available all of the time, and not all the storage headroom would be usable, so the actual capacity available for wind storage would be significantly less than this but still large). Battery exchange stations, instead of petrol stations as range extenders would be required and would be of greater capacity perhaps twice the in-vehicle capacity and also bi directional and capable of drawing or feeding several 100 GW back into the grid.

The provision of close to 100% wind capacity as a prime goal, along with sufficient storage / load management / interconnection to deal with inevitable excesses and shortfalls is probably not the most desirable economic solution but that is not the issue here. however Hhe above simple and broad analysis of the extremes does show that it is likely to be perfectly technically and economically possible in terms of dealing with power swings, unreliability, unavailability and intermittency of wind power even. It is argued to be worth exploring simply to draw out the issues and solutions to those unfamiliar with then, and refute the exaggerated problems claimed by anti wind proponents. It then follows that a mixed Renewable Fleet, wind, solar, tidal, biomass, giving close to 100% electricy supplies from renewables would be possible and more economically optimum.

The best mix of renewables, wind, wave, tidal, bio-mass, solar, can only be settled by proper detailed half hour by half hour economic optimisation studies of the type carried out by Dr Mark Barrett of University College London (as noted above).

So far, modeling by Dr Barrett shows that 100% renewables is possible.Engineman 16:19, 7 April 2007 (UTC)


. —The preceding unsigned comment was added by Engineman (talk • contribs) 12:55, 3 April 2007 (UTC).

I'm not really clear where you're going with this. If the intent is to show wind alone could do it (with no constraints like budget), why not just size it up to 600 GW (assuming 10% base capacity credit) and spill any excess (curtail the turbines)? Technically, perfectly feasible.--Gregalton 17:30, 3 April 2007 (UTC)
If you've no objection, I'd like to retract and rephrase my comment - I didn't mean for that to sound snarky.
My point/question can be better rephrased this way: I see no underlying technical issue with 100% wind, if there are no economic constraints.
To me, the more difficult and challenging question is the combination of the economic and technical: for example, given a set of goals (X) and a set of constraints (C), what is the optimal solution? Or, in terminology less based on linear programming: if X is goal, and the following constraints (C) exist, what is the least-cost solution? If we relax certain constraints, how much does the cost change? Or, given grid P today, what would be costs/problems of adding XX% of wind to it? Etc. I'm not clear what explicit/implicit goals or constraints your scenario contains; I think if I understood that it would make more sense to me. I also find it more compelling when the scenarios are ones that might be seen in the next, for example, 5-10 years.
If your goal is to convince doubters that intermittency is a bogus issue, I think the most effective way to do so is to counter the arguments with strong real-world / academic research. Penetration is an issue? Well, countries a,b,c,d all have penetration above that, with the following results. 100% backup required? Nonsense, not the experience in these places, see paper such-and-such. Anyway, that's just my opinion.
And final thought: while I find this interesting, it really is original research; this may not be the best place for it. (Talk page definitely better than the article page though). Best, --Gregalton 10:02, 4 April 2007 (UTC)
Engineman, you clearly have a grasp of the many multi-variate aspects of this complex issue. I find your ability to develop the necessary analytical formulation refreshing. As an encyclopedia, Wikipedia can only report on what has been researched in other venues and has a restriction on Original Research here. So we have two possibilities: 1) Find a reference to a published journal/book that has already attacked this material, or 2) write it ourselves and have it published. While having education in power engineering, I have spent most of my career in systems engineering, so I don't have the credentials (or corporate connections) to publish in this field. However, I believe you do have what it takes and could identify a publication that would publish your analysis. I would be happy to be of assistance and even help co-author if needed.
To recap, we either need to find existing research on this thread topic, or we need to do it ourselves. Your thoughts? --Skyemoor 11:43, 4 April 2007 (UTC)
I agree with Skyemoor's point - various groups are working on this type of original research now. In terms of strengthening the research, I'd suggest identifying clearly what the constraints are and the goal, whatever specifically it may be. If you'd like, possibly off-line or separately, comments/feedback on what could use strengthening, happy to do so.--Gregalton 13:58, 4 April 2007 (UTC)

Skyemoor, Gregalton, I wouuld be delighted to co-operate on some sort of original research. Gregalton has my email - do we have Skymoores? By the way I have made a number of small but important changes to the foregoing - Graham Sinden was kind enought to point out a number of errors. Engineman 14:16, 5 April 2007 (UTC)

Making a few changes

I have been reading a little more of the article, and will be doing some editing, so please check what I'm doing and see what you think. As I've said before, I don't have detailed knowledge in this area so am coming from the point of view of the average reader -- a perspective which I hope is valuable and can help us get things in perspective. If there is an edit which I've done that causes a particular problem, please feel free to revert. -- Johnfos 22:38, 5 April 2007 (UTC)

Johnfos - more power to your elbow.

Concentrating solar power and storage = not intermittent

I believe the article is incorrect wrt solar. The TREC CSP proposal specifically cites the pre existing use of molten salt storage for diurnal energy storage. Thus extremely high annual load factors are available. These are proposed to be installed in the worlds deserts and connected by hvdc cables. It is nearly aways sunny in the desert.Engineman 23:54, 5 April 2007 (UTC)

http://www.trec-uk.org.uk/news.htm)

Upon re-reading I see there is a mention but it is buried away. The point, which is not obviously made is that the TREC CSP proposal effectively offers firm power for the whole of Western Europe. Anyone looking up solar energy will come away with the impression that it is intermittent which it effectively isn't(IMHO).Engineman 11:26, 6 April 2007 (UTC)

What specifically is incorrect? I don't see how it can not be called intermittent. The existence of a storage technology doesn't make it non-intermittent, and there is probably an efficiency loss. In the context of CSP/heat-fired, the issue is less important (much easier to store than straight electricity), but for photovoltaics it doesn't go away.--Gregalton 12:45, 6 April 2007 (UTC)


Greagalton - a quote from the article

"Two forms of intermittent renewable energy, wind and solar electricity generation, present challenges due to the short timeframe of changes in generation and, in many cases, the limited correlation with demand cycles."

According to the TREC people this isn't correct. Molten salt storage, already demonstrated, enables the CSP plants to produce power continually, ie 24 hour per day. If CSP with storage is going to be described as intermittent, then so to should coal fires stations which have to off for maintenance and repair several month per yearEngineman 14:28, 6 April 2007 (UTC)

Intermittency also refers to dispatchability - not the case with solar. And maintenance/repair can generally be scheduled (to some degree anyway). My point is that as far as I can tell about this technology, it amounts to a form of storage - perhaps a very effective form of storage, but storage nonetheless. I'd suggest not trying to deny intermittency, but to qualify by saying "storage technologies for concentrated heat solar provide inherent capacity to store heat and generate electricity 24 hours per day, and substantially moderate or even eliminate diurnal generating cycles." I don't know enough about the technology and the extent to which it has been proven, cost, efficiency losses, etc., to be able to say much more about it - sounds quite new. From the description, however, is it fundamentally different than sticking a hydrostorage facility next to a wind farm? (Sounds a lot easier physically but similar concept)
And of course, at penetration levels comparable to those today, intermittency of solar is not an issue and won't be for a long time.--Gregalton 15:01, 6 April 2007 (UTC)
Having read a bit more on the TREC/CSP concept: the storage is storage, and has attendant costs/engineering issues like other types of storage. CSP may be inherently more amenable to storage than e.g. wind, but it doesn't make it not intermittent. Also potentially sensitive to periods with less direct sunlight (storms, what have you).--Gregalton 19:34, 8 April 2007 (UTC)

Article by Mark Diesendorf

Short, but interesting, article from an Australian academic:

Sustainable energy has a powerful future Johnfos 02:07, 13 April 2007 (UTC)

References

We cannot use Wikipedia talk pages as references in the article. We must follow WP:V, WP:NOR, and WP:RS. Has no one published in these areas? If not, we would need to to keep this material in the article. While I am in stark agreement with the thrust of the section, having it there prematurely affects the quality of the document from an encyclopedic standpoint. I know it seems nitpicking, but relying on peer-reviewed research tremendously bolsters our position. --Skyemoor 12:08, 15 April 2007 (UTC)

Agree entirely, the max penetration part has too much unreferenced stuff. I've tried to trim but would appreciate a different set of eyes.--Gregalton 16:05, 15 April 2007 (UTC)

Recent changes

I also strongly disagree with saying that wind can be baseload in the same way as coal, based on the article in the Australian paper. There is considerable documentation from other sources that gives wind baseload credit of 10-30%, compared to figures from 80% up for coal. The peer reviewed papers provide completely different perspective, and that newspaper article was nowhere near as well researched.--Gregalton 16:09, 15 April 2007 (UTC)

Not to put too fine a point on this, but the text may actually violate copyright of the aricle quoted. Several paras are identical.--Gregalton 16:13, 15 April 2007 (UTC)

Thanks, Gregalton. I have made some changes in the light of your concerns. See what you think.

I know that Amory Lovins too is saying that baseload does not equal big thermal plant, and he compares this to telephony and computing. But, you're right, at this stage I don't have any peer-reviewed articles on this. -- Johnfos 21:56, 15 April 2007 (UTC)

What does he mean by telephony and computing? I'm not sure I understand either the comparison or the point he's trying to make.--Gregalton 04:18, 16 April 2007 (UTC)
No, I'm sorry, I think the new text is weaselly and not NPOV. "Wind is not intermittent as long as it's backed up by fossil plant." "Solar energy with storage capacity." (I'm paraphrasing). In both cases, intermittency remains an issue and the solution has just been willed into existence. Anyone skeptical reading this will see this approach as deceptive.
In addition, it contradicts and undermines the point that e.g. "back-up" energy should not be seen as dedicated to wind (see the UK ERC report), it plays a system function. --Gregalton 04:30, 16 April 2007 (UTC)

I think that for the article to be NPOV, there needs to be acknowledgement of an emerging view, held by people such as Mark Diesendorf, Amory Lovins and Jim Falk, that:

"Some renewable electricity sources have identical variability to coal-fired power stations, so they are base-load, and can be integrated into the electricity supply system without any additional back-up. Examples include:
  • Bio-energy, based on the combustion of crops and crop residues, or their gasification followed by combustion of the gas.
  • Hot dry rock geothermal power, which is being developed in Australia.
  • Solar thermal electricity, with overnight heat storage in water or rocks, or a thermochemical store.
Furthermore, the total electricity generated from a large-scale array of dispersed wind farms, located in different wind regimes, cannot be accurately described as intermittent."[3][4] -- Johnfos 05:31, 16 April 2007 (UTC)
I also agree that emerging views should be recognized - but that is different from replacing the general viewpoint. As for the notes: I would not dispute that bio-energy is not meaningfully intermittent (timescales are annual or at most seasonal), and biofuel represents (natural) storage already. Solar: to the extent I've been able to find info on this (from links provided earlier) (a) has incremental cost to deal with intermittency, so it is intermittent - just the power source may be more easily adapted to mitigation/storage, and (b) not currently deployed at high levels, if at all. In fact, all three of the baseload technologies you mention might qualify, but have limitations for application.
As for wind, I recognise this dissenting view, but it's a bit of a fudge. First, references frequently say "intermittent" is not the best word (variable would be better), but this is the term most frequently used - and the article says that explicitly. Second, the issue of how much intermittency/variability is reduced by geographic spread is already covered by most papers, but still does not remove the issue entirely - it is sleight of hand to say the issue goes away. The amount of variability is reduced due to less-than-perfect correlations, but if the correlation is greater than zero, variability remains (and very few negative correlation, so no "perfect balancing"). In practical terms, all existing grids have limits to how much variability can be reduced as penetration rises (dependent on physical distance between economically feasible wind locations), and we don't have the final info in most places of how much variation reduction there will be. The economically feasible term and sizing issues considered are important: for Canada (just for an example), there may between e.g. British Columbia and Nova Scotia be extremely low correlation, but there is also effectively little link between the grids. Within Ontario, the physical size might be enormous, but the reality is that there is an extremely small subset of the province that has wind, transmission facility and any demand located nearby. (Of course, the level of wind is still so small that it is almost a rounding error compared to the demand/supply situation and import/export, but wind's ability to contribute to peak power/baseload is limited). Finally, the proposed solution - fossil fuel backup - is just that, a solution with incremental cost.
In other words, I question a framework that says "intermittency is wrong/doesn't exist because we can deal with it." More accurate would be to say "issue exists but can be dealt with at reasonable cost." Which is what the existing WP article mostly says. (In fact, the Australian articles coincide quite well with what is said in the article, but simply puts emphasis in a different area - probably in part because so much gencapacity in Australia is coal, and hence this defines the discussion there). I think the baseload issue is a bit of a red herring: the use of wind is explicitly referred to in many publications as a fuel-use reduction technology, so even if it doesn't "replace" an existing coal/gas plant, it has some beneficial effects (pollution, for example) if it can reduce operating times from 8000 hours a year to 1000, or fuel use from 100 units to 20 units (just to make these figures up).
That said, makes sense to include the approach in those articles as a "dissenting view" or different approach. There is no "single understanding" and proponents/opponents of wind are throwing around statements without much basis (in my view, it's mostly brought up as an issue to oppose wind, but that's my perspective).
One question: there are several references to this "maximum rate of change issue." I'll admit I don't understand why this focus (and it sounds vaguely like an attempt to avoid the issue by discussing another one). I have not seen this rate-of-change issue brought up much as a serious problem anywhere. Have I missed something? It sounds like a straw man argument to me.--Gregalton 06:55, 16 April 2007 (UTC)

New Title Suggestion

I notice that the article has a new title now, Intermittent power source, which is even less descriptive of the content of the page than the old title was.

I'd like to suggest that a better title be found. Perhaps something like "Grid integration of intermittent power sources", or even better "Grid integration of variable power sources". -- Johnfos 00:26, 16 April 2007 (UTC)

I don't really understand why the name was changed, but I think that titles that are as long as you suggested are problematic. Any other suggestions?--Gregalton 04:31, 16 April 2007 (UTC)

How about "Renewable energy and intermittency" -- just four words. -- Johnfos 10:24, 25 April 2007 (UTC)

I will go ahead and make this change. "Intermittent power source" sounds too much like something related to electronic circuitry. -- Johnfos 05:40, 28 April 2007 (UTC)

No objection - hope the redirects will work all right.--Gregalton 07:45, 28 April 2007 (UTC)

Upon reflection I realised that the proposed new title was not appropriate because the issue of "intermittency" is not unique to renewables. -- Johnfos 05:35, 26 June 2007 (UTC)

maximum rate of change

quote from Gregalton "One question: there are several references to this "maximum rate of change issue." I'll admit I don't understand why this focus (and it sounds vaguely like an attempt to avoid the issue by discussing another one). I have not seen this rate-of-change issue brought up much as a serious problem anywhere. Have I missed something? It sounds like a straw man argument to me.--Gregalton 06:55, 16 April 2007 (UTC)"

The point being addressed is that opponents of wind power claim that very large penetrations of wind would make the grid unstable due to the sudden shifts in power generated as the wind speeds suddenly changed. This so it is claimed would either make the grid likely to collapse and the lights go our, or huge amounts of inefficient back up plant would have to be employed part loaded, ready to suddenly cut in when required.

but if the aggregate maximum rate of change due to wind power is less than the rate of change which already occurs - due to power station failure, or load surges then clearly the opponents argument is false.

And indeed it seems to be the case certainly from the UK experience and the work by Graham Sinden.Engineman 10:17, 18 April 2007 (UTC)

Short answer: I wasn't asking about the technical issue, I was (obliquely) suggesting I don't see this specific concern raised very much, and when raised it's easily rebutted with facts. The existing links and references, like the UK ERC and many other studies, cover this eloquently and simply: they all essentially say their systems can handle it at any achievable level of penetration in the foreseeable future, and that the costs are low (Sinden makes this point without discussing rate of change specifically - it's the balancing cost, and it's small). The argument I see more frequently is about the operating reserve required, which is not a rate of change issue as much as having sufficient capacity (in reserve) and response time to bring larger plants up. The rate of change info is not as easily interpreted in this context.
Longer answer: maximum rate of change is primarily an issue in the short term, whatever the specific term used locally is. Akin to, as you put it, a power failure at a major plant or load surge. I see few references specifically raising this issue, and think it's well covered in the references and quotes. Whne you say "
In the medium term (say, hours) the maximum rate of change is not so much the problem, but the sustained rate of change and the "capacity contribution factor" or base-load credit or whatever it's called in each place. In your scenarios (for example), max rate of change in a short time period is 20%. And the system can basically handle this; in addition it's roughly a once or twice a year phenomenon (Sinden's 20% rate of change - 3-4 times per year if we count up and down events). I'm not convinced that you can simply divide the hourly rate of change into single minutes to say the system can handle sustained periods of change like this (rather than short, binary events). The system can handle the instantaneous loss of a sizewell plant, but can it handle the loss of a sizewell-sized facility every ten minutes? (Any intra-hour changes that are more rapid? I don't see this data)
And, very high rates of change (sub-maximal) can occur regularly that are still significant. From Sinden's paper (figure five - note the log scale) the 20% events happen a couple of times a year, 15% change (up and down) events happens twenty times a year, 10% a couple of hundred. Would a 20% event be followed immediately by a 10% event? Or a 15% by a 10% (or two)? Are they randomly distributed? Would/could they coincide with a rising/peak demand cycle? This is potentially a far greater change happening more quickly than currently is dealt with.
I'd also note that Sinden's paper only considers penetration up to 20% of supplied power, presumably corresponding to about 40-60% penetration (faceplate to peak demand). The inference that the same results/tradeoffs/costs hold true for much higher penetrations is not clear to me.
A technical point about your research/calculations above: you say the average output will be 60 GW, and take the 20% change to be of this amount; Sinden's paper (figure 5) clearly says as a % of installed capacity. So in your scenario, it seems to me the max rate of change would not be 12GW but 33GW.--Gregalton 11:29, 18 April 2007 (UTC)

Good stuff Gregalton!

Regarding the repeated loss of 1.32 GW out of 25GW (lowest output on grid roughly so biggest proportion) what happens is that immediately it goes, 2GW of Frequency Service loads and 2 GW of Reserve Service generators are lost / started. Immediately the grid winds up spinning reserve to cover the 2 GW and turns it off with in 20 minutes and reverts to the status quo ante. but it will also have called on hot standby to begin generating if needed to ensure same level of spinning reserve is available. Also if needed more stations will be put on warming. In this way it could cope with repeated failures of 1.32 GW,

Don't forget that in the summer the UK grid goes every day from say maybe 35 Gw to 60 GW - (need to check my memory!) so that is 25 Gw in 12 hours - all easily do able.Covered in detail at [http://en.wikipedia.org/wiki/Control_of_the_National_Grid_%28UK%29#Reserve_service_or_National_Grid_Standing_Reserve Engineman 18:25, 18 April 2007 (UTC)

I'm aware they're not just waiting for the wind to pick up - the question is whether the increased potential swings are significant in terms of capacity to manage them; the numbers don't convince me that it's not. As per above, you say system deals with 25GW extra load in twelve hours; under your scenario and numbers (but using the installed capacity figure), could be 16GW changes in one hour a couple of hundred times a year. If it's a fall and it happens to occur during a period when demand is rising, it exacerbates the situation.
At any rate, I still think the discussion of maximum rate of change is not really the issue, and that the calculations are not entirely convincing. Quoting the various sources ("It's not a problem") is.--Gregalton 04:40, 19 April 2007 (UTC)

Gregalton: Yes you are quite right - quoting Sinden - "The most likely change in power output from a diversified wind power system from one hour to the next is less than ±2,5% of the total installed wind power capacity (Figure 5). Larger changes from one hour to the next do occur - a change in hourly output equal to around ±20% of the installed wind power capacity is likely to happen about once per year, Over the long term, around 99.98% of all hourly changes in wind power output from a diversified system will be less than ±20%. "

So once per year you are likely to get a change of 20% of 165 GW in one hour, and this is a rate of change of say 2.75 GW in a minute - similar to what the grid already deals with. So I don't see the sudden change due to wind surge a difficulty even at present. I know these are rough and ready calculations but I think the do put the issue into context. Ie we might have to double reserves - that is make sure more plant that has already been built is warmed and synchronised - that is not a major cost item. Or we simply increase the amount of demand flexibility which is extremely cheap.

Gregalton, when you say "the discussion of maximum rate of change is not really the issue" what had you in mind?Engineman 14:31, 20 April 2007 (UTC)

You are discussing maximum rate of change in the context of very short timeframes, essentially the regulation timeframe. Three problems with this: 1) I don't see much debate/concern about the minute-by-minute (regulation) timeframe. 2) Sinden's paper does not (as far as I can tell) specify that the hourly rate of changes can be generalized to the minute-by-minute context. 3) The "maximum rate of change" within a daily cycle is more an issue of an amount of reserves that has to be carried (spinning, warm, whatever); your analysis is rather "firm" that this is not a problem (you treat it as "proven" by back-of-the-envelope calculations). I don't find the analysis to be compelling, so don't think it can be considered a settled issue (barring authoritative citations on this). For example, as noted above, you mention the once-a-year outlier; as I've noted, the 10%-15% scenarios happen considerably more frequently and seem to me more problematic than the once-a-year events. It doesn't seem obvious to me at all that because the system can handle a short-term change of 2.75GW, that it can also therefore handle 30 consecutive changes of, say, 1GW per minute. For example.--Gregalton 09:14, 21 April 2007 (UTC)
Where does the basis for "Ie we might have to double reserves - that is make sure more plant that has already been built is warmed and synchronised - that is not a major cost item." come from? What type of fuels do they use? It is my understanding that coal units aren't stable without some load on the generator. Natural gas isn't so cheap (at least in the US) to ignore the cost to have a unit running without load. Diesel is more expensive than natural gas. Nuclear isn't an option, in my opinion, for an un-loaded spinning reserve. I understand many of the established plants are paid for (capital costs), but is the O&M really that cheap that they could be run for a number of hours a day simply for spinning reserve? Another question I have for Engineman is the 1.32 GW repeated loss...exactly what is the 1.32 GW number and how was it derived? Also, what is the total contracted Frequency Service load?Doublee 15:53, 26 June 2007 (UTC)

My removed text

Moreover, several conventional power stations can fail simultaneously and without warning, as occurred on 14 August 2003 in the north-eastern USA.

OMG, this is a 100%, grade A fabrication. Look at the source, the graph on the page the reference refers to is:

August 2003 Daily Nuclear Output for the Nine U.S. Nuclear
Units Affected by the 14 August 2003 Northeast Blackout

Nuclear Units AFFECTED BY the blackout. Not the other way around. The grid was disconnected, you can't keep your units running if there is no grid to supply the power to!!! This is the first and only source in the entire article I followed up, and the rest of it looks like the exact same tone, the exact same method for citing references. I hate to put up tags like POV, in fact, I never do, but if there is one article I've ever seen on Wikipedia that seriously needs it, that would be this one. The sources are POV, and they're misquoted to make them moreso. The article's topic isn't bad, and a lot could be written academically for it, but really, the majority of the article right now looks like a complete lie. -Theanphibian (talk • contribs) 02:03, 20 July 2007 (UTC)

Revisiting Issue

Looking at statements like "Moreover, several conventional power stations can fail simultaneously and without warning." I think there's a lot of work to be done, but there is truth to it, but you can't just leave it as it.

Many units of a conventional plant can fail simultaneously and without warning, but not without a common cause. Examples:

  • Kashiwazaki-Kariwa Nuclear Power Plant - Earthquake comes and shuts down all the units, this sort of this is most severe with nuclear plants, but can apply to other types as well, and I don't know of any power source that would be immune to natural disasters, but the point remains, yes, small units will hold up better because they are not as centralized
  • Common design problems - if something is discovered that's wrong with one plant, there is a high likelihood that ALL SIMILAR plants will be shut down as well. This happens quite often with nuclear plants, a design flaw or a question of the plant's ability to operate safely comes up and the government basically orders them all shut down.

I know that fossil units can be less reliable for just random shutdowns though. The nuclear reaction basically doesn't ever change unless you do something to it. Coal fired plants could have something go wrong with the machine that chops up the fuel and throws it into the boiler (I'm not an expert here). But back to the point, statements like the one above are fine, but you can't use weasel words to make the reader think that ordinary plants shut down LOTS of units at RANDOM times without a precursor, natural event, or common technical issue. -Theanphibian (talk • contribs) 02:15, 20 July 2007 (UTC)

How I think this should read

It's not a good approach to start this with a tone of attacking convential power stations by saying they're intermittent. You're assuming the opposite to start out with. A more matter-of-fact approach would be better.

Intro: should state that "all power sources are intermittent to some degree," that would be the matter of fact way of going about it, and it avoids making refutations of invisible arguments.

I would like to see the rest of it organized mostly this way:

1. Overview
2. Conventional power sources
2.1 Intermittency: Nuclear power
2.2 Intermittency: Natural gas
3. Renewable power sources
3.1 Intermittency: Hydroelectric power
3.2 Intermittency: Solar energy
3.3 ...

Of course, overview could stand to have more sections, but every section alone just needs to answer the questions

  • How intermittent is this power source
  • What kind of intermittency is this and how does that affect the grid (ie planned intermittency, unpredictable outages, does it run during peak times or when no one needs it)

As such I think it just needs to be more level, because it certainly doesn't handle all the sources in the same way. I don't think that's a POV problem, it's just kind of holding one higher than the others.

My Example

Intermittency: Nuclear power
Nuclear power is widly considered a base load power source, in that it provides a fairly constant power source. This is done because there is a clear limit of what power the plant can be ran at and the fuel costs are small compared to the capital costs. Every year or two (depending on the plant), the plant must be shut down for planned outages for about a month. This is typically done in the spring or fall when electricity demand is lower, as such, on a national scale power output from nuclear increases corresponding with demand during the peak summer and winter months. This change in output commonly occurs on a yearly scale, it is rare that nuclear power plants adjust their power output to correspond with demand on a daily basis, which would be much more likely to happen in countries where over 50% of their power comes from nuclear (such as France).

Nuclear power plants are also subject to unplanned outages that occur due to technical failures, and occasionally, acts of God. For instance, unplanned outages in the United States caused a total capacity loss of 1.7% in 2000, which is drastically improved from 11.6% in 1980.[1]


Anyway, that's where I see the article going. There's also LOTS more to be written about hydro and pumped storage, because that's where intermittency is kind of... a good thing. -Theanphibian (talk • contribs) 20:15, 8 August 2007 (UTC)

In terminology, I've introduced the term (that is used loosely later) of maneuverability, the ability to crank output up and down. In practice, each of these power sources has characteristics of intermittency (type/frequency/scale of output changes) and maneuverability (ability of the operator to adjust up and down within certain parameters). In this usage, hydro/pumped storage has 'low' intermittency (the scale is seasonal, not generally diurnal) but high maneuverability; wind 'higher' intermittency (intra-day / week fluctuations can be significant) and low maneuverability; nuclear relatively low intermittency (although scale may be problematic given the sizes of the units) and low maneuverability. Thanks for the input to the article.--Gregalton 06:39, 9 August 2007 (UTC)
That's an excellent distinction. I'm sure these terms exist as technical terms as well, I would like to get sources that cover this eventually. I do, however, contest nuclear as always having low maneuverability, those who work in nuclear propulsion are MASTERS of transients. -Theanphibian (talk • contribs) 18:13, 11 August 2007 (UTC)