Talk:Tidal power
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[edit] Corn
This article states that, "In Europe, Tide Mills have been used for nearly 1,000 years, mainly for grinding corn." The wikipedia article on maize begins, "Maize. . ., also known as corn, . . . was domesticated in Mesoamerica. It spread to the rest of the world after European contact with the Americas in the late 15th century and early 16th century. " Corn could not have been ground in Europe for nearly 1,000 years. Delirium of disorder 19:04, 10 September 2006 (UTC)
- Maize is also known as "sweetcorn". Perhaps it is known as "corn" in US slang, but noone calls it that in the UK - on account of there being something quite different already called "corn". Perhaps the maize article should be changed. Fig 21:19, 10 September 2006 (UTC)
[edit] Perpetual Motion Machines
Let's see some diagrams of machines that harness tidal power, eh?
Just wondering: the tides are caused by the moon, and the moon will never stop orbiting the earth, right? So does that make tidal power perpetual motion, or am I overlooking something?
A: The tides slow the Earth's rotation down. So the source of the tidal power will be exhausted at the precise moment when the rotation speeds of the Earth around its axis and the moon around the Earth will coincide. Then the day should last more that a month now:). Harnessing the tidal power should not, IMHO, change anything in this natural process - just some part of the energy that now is dissipated as heat will be converted to electricity or whatever.
[[ Perpetual motion machines are more about entropy (second law and all that) than "energy". "Energy" is related to entropy of course, but common use of the term "energy" (as in the "debate" about energy, or the "energy crisis") is more about the economics/practicality of harnessing various phenomena (mostly chemical) to do what we humans consider useful "work" (e.g. turn the wheels of a car). In other words, there's plenty of "energy" to go about - if we could tap into the rest mass energy of a fistful of rocks, we'd be fine. With "renewable" we mean tapping into processes in nature (rainfall, sunshine, wind, tides, geotherms) that are not noticeably affected by us tapping into them. --Psm 23:00, 29 July 2005 (UTC)]]
[edit] Deceleration of the earths/moons orbit
Why would the earth and moon decelerate in a vacum? Surely after 4 billion years of decellerating would cause all sorts of problems! As the earth is decellerating in one direction, surely the tides would 'sit' on certain coast.
I was taught that the gravity due to the sun and moon on a side of the earth at any one time causes the sea to swell (cuasing the earth to appear elliptical), hence creating two tides per 24 hours. If this is so then we are not taking energy out of the movement of the moon and sun, but out of these movements in the sea.
A: The earth and moon do theoretically slow down as they are moving in a constantly changing path. However you a correct, the decelleration of the earth has very little effect on the tides, more dominant forces include the Coriolis effect, energy form the sun, tidal resonance, funneling, atmospheric pressure, high & low pressure reigons...
To conclude to say that the root of tidal motion is due to the decelleration of the Earth and the Moons orbit is misleading - in some schools it would be termed "wrong".
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- Wikipedia says "The root source of the energy comes from the slow deceleration of the Earth's rotation. The Moon gains energy from this interaction and is slowly receding from the Earth."
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- I don't think this is right. Is the following argument correct?
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- The moon is moving away from the earth and gaining potential energy. As angular momentum must be conserved the moon will also slow down, so as it moves out it will lose kinetic energy. The Kinetic energy lost is greater than the potential energy gained, this energy is tranferred into tides on the earth. The earth's rotation has nothing to do with it. Mike Young 15:18, 16 January 2007 (UTC)
- There is some confusion here. The tides raised on the earth by the moon, and vice versa, both cause a large amount of energy to be transformed into heat (by friction action in water and rock). That energy has to come from somewhere. It comes from the kinetic energy of the earth-moon system; therefore, the kinetic energy of the earth-moon system is decreasing as it is slowly transformed into heat by tidal friction. However, the total angular momentum of the earth-moon system has to stay the same, because momentum cannot be transformed into anything else. The only way for the kinetic energy of a system to decrease while the angular momentum stays constant is for the bodies to move further apart. Hence, the moon is receding very slowly, and the spin of both the earth and moon are also slowing. At the moment, the earth's rotation is 1 day, the moon's 28 days, and the month is 28 days. Everything will finally equalise and be stable when all three values are the same. However, this will take longer than the solar system will last, since the earth-moon system will be disrupted when the sun dies... Fig 10:42, 17 January 2007 (UTC)
Do you know what proportion of the energy comes from the rotational energy of the earth (the fact the earth is spinning) and what proportion from the Kinetic energy of the moon?
Also when equiplibrium is reached there will still be tides caused by the sun, I presume this comes from the rotational energy of th earth. Mike Young 14:30, 17 January 2007 (UTC)
- I dont know the proportion, no. I would imagine that is difficult to calculate. Off the top of my head, I seem to remember seeing that the day and month would stabilise at ~40 days. Regarding solar tides, everything that is happening in the earth-moon system is also happening to a very much smaller degree in the sun-earth system. But the sun will be long dead before that effect is noticeable! Fig 19:27, 17 January 2007 (UTC)
[edit] Tidal harness
Someone might want to merge tidal harness with this article or visa versa as they appear to be talking about the same thing.--GD 10:28, 26 Sep 2004 (UTC)
So the energy is only "considered inexhaustible within a human timeframe". We mean, then, that it isn't really inexhaustible, just "considered" so?. The "human timeframe" part: do we mean it will run out in a century or two or something? Weaselling for weaselling's sake. Couldn't this be stated with more conviction? --Wetman 11:41, 24 Oct 2004 (UTC)
It's "more than enough energy" or more energy than we can possibly hope to convert using our lousy tidal power barrages. --Evgeni Sergeev 11:45, 24 Oct 2004 (UTC)
No, it isn't really inexaustible. If we look from the universe's point of view, energy is just moving around, changing forms, not being created, nor destroyed. When we use non-renewable energy, like fossil fuels, we extract energy at a much faster rate than it is being stored. This means our supply will run out eventualy, but quite soon, actually. When we extract energy from Sun's rays, we know that the Sun will be there whether we extract this energy or not. The Sun is independent of devices to get the energy -- it will radiate the same amount of energy whether or not we convert some of it into electricity. It will run out of energy too, but not due to our activities. Now, tidal power is different to the Sun, as when we are building a tidal barrage, we are increasing the friction (well, not quite, we are increasing the impedance) of water movement around the Earth. Thus we are contributing to the Earth's rotation slowing down. Yet if we perform rigorous calculations, using mass of the Earth, its angular velocity and the maximum amount of energy we are taking away, we will get a contribution of a very small change in angular velocity in a very large number of years. This is much more like the Sun example, than the fossil fuels example, so we call this renewable energy.
Now, it is "considered" inexaustible within a human timeframe because we don't know how long the human timeframe will last for. Personally I believe that once we invent decent AI, we will spread out over the galaxy, and only a huge catastrophy will stop us then. This is probably fantasy to you, but I'd like to see a proof if you insist that the human timeframe is short. --130.95.128.58 01:35, 26 Oct 2004 (UTC)
The article writes: "Tidal power schemes have a very high capital cost and a very low running cost. As a result, a tidal power scheme, will not produce returns for decades after it is built. Clearly, investors will not participate in tidal power projects."
Anybody care to try to put some numbers to this? Especially since this statement looks naive. What does "returns" mean? IRR above T-bills at some set of assumptions? E.g. given where the technology is today, what would a kwh cost that's produced using some of these schemes.
The energy issue is all about cost, and in particular trade-offs between capital investments and energy yield.
--Psm 22:40, 29 July 2005 (UTC)
The term "renewable" when referring to energy says more about modern environmental sensibilities than it does with science. The very word is misleading. Who or what is doing the "renewing?" The sun? The sun is just a big gravitationally confined fusion reactor. Yet earth based fusion enery is not generally referred to as "renewable." Geothermal energy is often referred to as "renewable" and/or "sustainable" yet nothing is "renewing" it and eventually the earth will cool off and become geologically dead. For that matter there is nothing intrinsically renewable about the sun either. Eventually it'll cool off and we'll have to find some alternative.
Stealing energy from the earth's or moon's kinetic energy is just as much a one way process as digging coal out of the ground and burning it. There is much more energy available from orbital mechanics than there is from coal, of course, and it doesn't produce as much smoke. But it is a form of irreversible consumption nonetheless.
[[Wikimonster 19:50, 26 October 2005 (UTC)]]
Olla i think it's worth noting thtat even the one (french) tidal cetral that was operational when i was in highschool is enough to stop the earths rotation, in a limited period (like 1000 years). Since this argument against tidal power is nowhere noted, and an outburst of building of these plants seems the case, i want to point out that the word sustainable is a complete misfit here.
[edit] Tom and Wendy?
I couldn't be more ignorant about the subject, so I'm hesitant to just delete the section, but the Tom and Wendy and the Random Clueless Person section is just vandalism, right? --Bsteger 04:34, 25 February 2006 (UTC)
[edit] citation for mathematical modeling
can anyone provide a cite for this? would be very helpful to the article. Anlace 17:16, 8 June 2006 (UTC)
[edit] Accidental delete?
Edit: [18:51, 13 July 2006 Groovyjoker] removed a large amount of code and a big table. I presume it was accidental rather than vandalism, so I have added the missing code back in.
[edit] Citation for Ebb and Flow In One Basin
The diagrams don't make any sense---the text reads like original research. Clean-up, or delete?
[edit] "Former USSR"?
The article declares, "suitable locations are found in ... the former USSR." Why not just say Russia, or Eastern Europe? Seems a bit out of place. Trappleton 05:01, 11 August 2006 (UTC)
[edit] Blue energy
can someone have a look at Blue Energy Tidal power [[2]]. ? "The vertical axis turbine technology, which has been around since the 1920's, but held back for political reasons,?" However, i would like an advise on the statements made by this CA company, question is related to the naming of the article Blue energy. thanks. Mion 08:07, 8 October 2006 (UTC)
A: advice about which of Blue Energy's statements are you seeking? For me, as an electrical engineer, the technology looks entirely feasible, actually it has been done and more capacity should be built. Other companies with less direct names are in this business, too. "Political reasons" may have been in play, maybe similar to the electric railways in the U.S. that were bought up and closed down by automotive companies to remove competition. 90% of decision-making is said to be based on economic considerations. The article Blue energy should, IMHO, be presenting both the saline technology and tidal power as blue energy, on an equal footing. Bernd in Japan 08:32, 22 December 2006 (UTC)
[edit] Pictures
this page is so so boring need more pictures. —The preceding unsigned comment was added by 203.14.53.46 (talk)
[edit] Vandalism?
I think that there is a form of vandalism on this page. It states "Wikipedia is not a reliable source dont use it==Dam==". I do not have the experience to fix it myself, so if someone else can do it that would be wonderful. Wikipedia is very helpful and all users know the risks. I don't think that comment is appropriate. Thank you very much. 70.240.204.149 00:08, 6 March 2007 (UTC)
[edit] More information
Hello Could you please add more info on this page thank you —The preceding unsigned comment was added by 124.186.4.37 (talk) 06:38, 23 March 2007 (UTC).
