Talk:Compressed-air energy storage

From Wikipedia, the free encyclopedia

The problem with your article on isothermal air compression is that it deals only in academics, not the day-to-day use of compressed air systems. Perhaps the greatest advantage of pneumatics is their safety: moving cutters can be safely cleared no other way. Material moved through pneumatic (pressure-vacuum) systems clear debris from shops so that fall accidents are far less likely. Air tools can be safely used in wet environments and explosive atmospheres where electric tools are out of the question. Air-powered vacuums can easily remove even the most dangerous radioactive materials and asbestos without the dangers of contamination seen with electrical power. Air agitated paint tanks give the finest finish ever seen. And the list goes on. The physics of compressed air use are by definition, appalling: I can think of no less efficient way to deliver power. But we use air tools constantly, particularly indexing lifts, jacks, nailers, scalers, and air-motor driven tools. Because rotary screw compressors are now on-par with diesel powered equipment in deep-shaft mines, using the exhaust for breathing air and to cool the hot environment is a real advantage. Why didn't anyone else think to mention that? —Preceding unsigned comment added by 209.244.31.59 (talk) 21:05, 17 April 2008 (UTC)



WikiProject Energy
Energy Portal
This article is within the scope of WikiProject Energy, which collaborates on articles related to energy.
B This article has been rated as b-Class on the assessment scale.
Mid This article is on a subject of mid importance within energy.

This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.

The Physics article seems completely wrong to me. By allowing the system to compress isothermally surely much of the energy is being lost? I'll check my thermo books tonightGreglocock 04:25, 21 March 2007 (UTC)

Isothermal compression and expansion represent an ideal case where exactly the same amount of heat is released to the environment as must be reintroduced into the system during expansion. In practice the compressor and air tank will heat up during compression and the engine and tank will cool down during expansion unless very large heat exchangers are fitted or the system is very small or the power level is very small. In the ideal case no energy is lost, but in practice there is the loss of friction and losses to due with not being able to use exactly the isothermal cycle. It would be good to have some real measurements for the article. --Theosch 14:14, 22 March 2007 (UTC)
I suppose my confusion arises from my assumption that reversibility=efficiency, whhich does not apply to a system that in one cycle does no work. Either way, an adiabatic compression and expansion cycle also does no net work, and stores much more energy. I agree that an isothermal process probably bears a closer resemblance to the likely cycle of this process. Greglocock 01:36, 23 March 2007 (UTC)

66kw (~90hp) to move a average car is quite high. While 90hp may be required to accelerate quickly, modern vehicles in the US can maintain 60mph with approx 20hp or ~15kw. The quick math to prove this is simple: Assuming a standard highway fuel economy of 30mpg & an almost universally accepted bsfc (brake specific fuel consumption) of 0.53 lbs/(hr*hp) for modern gasoline engines, an engine traveling 60mph will consume approx 2 gal /hr of gasoline. Gas in the US has a specific gravity of 0.73-0.75 and thus weighs approx 6 lbs, thus the engine is consuming 12 lbs of gasoline per hour. Using a BSFC of 0.53, the a vehicle traveling 60mph @ 30mpg has an average power of 22hp or 16.9kw.

Contents

[edit] Undefined variables

The calculations are helpful, but impossible to understand with undefined variables. What are P_A and P_B? The article needs to be self-contained or contain references where terms are defined. —Preceding unsigned comment added by 68.7.105.15 (talk • contribs) 03:12, 27 December 2007 (UTC)

The notation should be clear for anyone who has completed a basic college course in thermodynamics; it is assumed that the reader has at least this level of prior knowledge. See the articles on ideal gas law and Boyle's law, referenced in the section. (You did read these supplemental articles, did you not?) The equations illustrate a simple, linear relationship between pressure and volume in an ideal gas under constant temperature conditions. PA is the pressure at state "A" and PB is the pressure at state "B", corresponding to volumes VA and VB, respectively. —QuicksilverT @ 06:13, 6 February 2008 (UTC)
I sort of agree, but on balance it is probably a reasonable whinge. I'll see if the other pages have a neat table I can steal.Greg Locock (talk) 06:47, 6 February 2008 (UTC)

[edit] Talk about pressurized caverns

This article talks mostly about the feasibility of compressed air cars. I'd love to see some discussion and math about using compressed air as a large-scale means to store energy. For example, storing the energy created by solar power during the day for use at night. --Gadlen (talk) 23:23, 18 January 2008 (UTC)

[edit] Thanks for fixing things Greglock

Hey Greglock, this is happytrombonist16, the alter-ego of whatever ip address my computer was using when I posted the facts tag. I'm kinda new, so it's very possible that wasn't the right tag to use for that situation. However, it looks like you've fixed most of the things I had a problem with, so thanks! Happytrombonist16 (talk) 05:32, 27 January 2008 (UTC)

[edit] Compressed air engine‎

At the moment air engine redirects to this page. There exists an article with the much better name Compressed air engine‎. Why don't we move the air engine stuff there, and leave the physics and storage side here? Greg Locock (talk) 09:45, 7 February 2008 (UTC)

[edit] CAES article is inadequate

The original focus of this article was on the use of compressed air energy storage for utility level power generation or grid energy storage. In my opinion the current version of this article focuses too much on the use of compressed air to power vehicles and not on power generation. Details like power output and storage time for the Mclntosh and Huntofr hybrid plants are missing. The section on types of compressed storage is inadequate and depends too much on the "German AACAES project information" which understates the efficiency of the hybrid CAES plants. The hybrid plants use the stored cooled compressed air to directly feed air into a gas turbine. This replaces the compressor that is powered directly by a normal gas turbine. The efficiency of a hybrid plant should be calculated by comparing the energy required to compress the stored air versus the energy required to run the compressor inline with the expansion turbine. See http://www.eere.energy.gov/de/compressed_air.html for details. —Preceding unsigned comment added by 68.2.181.124 (talk) 21:26, 27 March 2008 (UTC)

Apart from the above, this article is at present a mess with much duplication. I'll try to have a go later. Also there is a confusion of many articles all having to do in some way with this subject but inadequately linked. --Theosch (talk) 14:08, 4 April 2008 (UTC)

[edit] Physics check

The equations given in two sections of this article do not match. In one the specific energy is given per mole, in the other per N-m3. Probably an "n" missing somewhere. This needs to be checked and corrected.--Theosch (talk) 15:27, 4 April 2008 (UTC)

The clean-up looks okay to me. I noticed that an example of energy density was deleted. It would be good to replace that with a sourced example, say comparing the energy density with liquid fuels or batteries. --Mikiemike (talk) 22:25, 4 April 2008 (UTC)
I went through the energy density comparison referencing the appropriate Wikipedia battery page. Obviously liquid fuels are so much better there is little point in pointing this out. More interesting would be the comparison of using the same pressure vessels for compressed air storage or for storing fuel gases, e.g. CNG or hydrogen. --Theosch (talk) 15:15, 6 April 2008 (UTC)

[edit] Lake or ocean storage

At first sight this looks like an intelligent suggestion. But, I have never seen a reference to it, and certainly lake storage is rather odd. This is energetically equivalent to pumping water into the lake (to raise the water level) and then using it to generate power later on. But, it is more efficiewnt and cost effective to do this directly with water than with air. So, find some cites or I'll blow it away.Greg Locock (talk) 01:00, 29 April 2008 (UTC)

[edit] Lake or ocean storage: Response to need for citations & Additional Carnot comments

I added citations, including one relating to a patent (expired or about to expire). The patent covers the same material: underwater storage bags and their advantages. As for pumping water into a lake, that's not the correct analogy for understanding the energies: highly pressurized air is useful stored energy, water sitting in a high dam is also useful, but water in a lake can't do anything. The criticism, however, may point to other problems: for example, at extreme depth, effects relating to hydrostatic equilibrium and pressure gradient force could create problematic heating and cooling and potentially catastrophic "hammer" effects (like "water hammer" in domestic plumbing). (I'll try to add some math on this - into this talk section - if I can remember the appropriate integral calculus equation to use or have the patience to rough it out with a sums table.)

Add.: I found the barometric formula here [1]. The pressure at the top of a 1000 meter column of air is 88 percent of the pressure at the bottom (whatever that is - if sitting in ocean, 100 atm); at 330 meters (at more reasonable depth for the plastic bags), the pressure is 96 percent, pretty close. Still, temperature changes of 10 to 20 deg.C could be problematic. Anthony717 (talk) 11:45, 30 April 2008 (UTC)
Add.: Perhaps the ultimate (if far-fetched and merely illustrative) solution would be a detachment of (pressure-resistant) submarines to deliver and retrieve special "packages" from the underwater storage location. Each package would be a reinforced plastic bag containing air and sand, the sand for ballast. Ideas like this show the problem with CAES generally: the potential for energy storage is huge, but the engineering problems are equally huge. Anthony717 (talk) 11:45, 30 April 2008 (UTC)

Clearly, the deep water storage system has thermal efficiency disadvantages compared to adiabatic storage. (Though ... I suppose the air bags could be insulated with "wet suits" - good for perhaps 12 hours of storage.) Carnot efficiency can only be improved by complex staged pumping, possibly with large pressurized equalization chambers (or columns) containing the necessary heat exchangers. On the other hand, energy recovery is greatly simplified by the constant pressure of the source (the turbines can be optimized for a particular intake pressure and rate of flow). Also, the huge expense of mining is eliminated. Anthony717 (talk) 04:58, 30 April 2008 (UTC)

"As for pumping water into a lake, that's not the correct analogy for understanding the energies: highly pressurized air is useful stored energy, water sitting in a high dam is also useful, but water in a lake can't do anything. " I suggest you do the maths. I am right. That is the work done in inflating the bag underwater is identically equal to the gain in potential energy of the water in the lake. Archimedes and all that. Anyway thanks for the refs, that is fine now. Greg Locock (talk) 05:56, 30 April 2008 (UTC)