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Earth Power Technology

The Future of Wind Power May Be Underground 223

Posted by samzenpus
from the blow-from-down-below dept.
Hugh Pickens writes "When the wind is blowing, it is usually the cheapest peaking power available. However utilities need consistent always-on power from large, cheap coal and nuclear power plants that are the backbone of the electric grid. Wired reports that operators are looking at Compressed Air Energy Storage (CAES) using abandoned mines and sandstones of the Midwest to store compressed-air. This converts the intermittent motions of the air into a steady power source by using it to run air compressors to pump air into an underground cave where it's stored under pressure. The first CAES plant in the United States actually went online in McIntosh, Alabama in 1991 where engineers created a geological pocket 900 feet long and up to 238 feet wide in a dome by pumping water into it to dissolve the rock salt. When the (briny) water was pumped back out, the salt resealed itself and they had an air-tight container."
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The Future of Wind Power May Be Underground

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  • Generate a Vacuum (Score:5, Interesting)

    by rally2xs (1093023) on Thursday March 11, 2010 @02:25AM (#31435218)

    Instead, build long tunnels between major cities, evacuate them down to between 0 and 3 psi, and run high speed trains through them. The trains would need very little energy to run thru the extremely thin atmosphere, and the pressure diffential can be used to generate electricity when needed. 2 birds, 1 stone.

    • Re: (Score:2, Insightful)

      It would also transmit the electricity. 3 birds, 1 stone.
    • by Avin22 (1438931) on Thursday March 11, 2010 @02:46AM (#31435318)
      2 birds, 1 very expensive stone. It would probably cost a great deal of money to build tunnels, evacuate out almost all the air, and maintain that low atmosphere. Sure, it might save some energy of running the train, but the money and resources needed to do this would greatly outweigh any benefit. We are almost certainly much better off investing in other ways of producing or saving energy.
    • by clarkkent09 (1104833) * on Thursday March 11, 2010 @03:15AM (#31435486)
      Why not just move cities closer to each other. It would be cheaper than your idea.
      • by Dr. Evil (3501)

        If you got rid of the roads, parking lots and driveways, everything would be within walking distance!

    • by SmallFurryCreature (593017) on Thursday March 11, 2010 @04:34AM (#31435784) Journal

      The problem is that trains need people on board who in general want to breath, spoiled brats they are.

      So, the train would need an oxygen supply on board, added weight and explosion risk and a LOT of oxygen because people do a lot of breathing. It would also need to scrub the CO2 out, because it is after all a closed system.

      Then the train needs to enter a normal area to let people in and out without explosive decompression.

      It can be done, but is just not worth the hassle, especially when aerodynamics don't matter all that much for a train. The nose after all is only a small part of a LOOOOOOOOOOOONG train. The carriages don't add much to wind resistance, you can in a way decrease air-resistance per carried passenger by just carrying more passengers.

      • Re: (Score:3, Informative)

        by Gordonjcp (186804)

        3psi is about atmospheric pressure at 40,000 feet - roughly where commercial airliners fly. Inside a commercial airliner the pressure altitude is around 8000-10000 feet, or about 11-10psi.

        It's not entirely a solved problem, but it's not as bad as you think.

    • by FishTankX (1539069) on Thursday March 11, 2010 @05:43AM (#31436008)

      Sadly, tunnels large enough to carry trains, as modern subways will prove, are prohibitivley expensive.

      however, compressed air is a good energy storage medium.

      Assuming a 900 foot by 300 foot by 300 foot cavern was filled with compressed air with a pressure of 300 bars, would have a potential energy of roughly 50 gigawatt hours. (source: http://www.tinaja.com/glib/energfun.pdf [tinaja.com]) Or enough to run the entire united states for about an hour. This is a massive pool of energy, and significantly more cost effective than a battery.

      HOWEVER, there lies a rub. When you compress air, you generate a massive amount of heat as the thermal energy stored in the air is highly compressed. This heat energy, unless properly reclaimed and stored (I.E. In a molten salt bath) just leaks away, stealing a huge chunk of the potential energy with it. When the air is uncompressed, there is significantly less heat energy stored in the air, and thus the expanded gas is very cold. This limits how far it can expand again, and creates a formidable problem in the form of condensation.

      What you need to do to get EFFICENT compressed air storage, is either store the heat in an efficent manner, and add it back to the compressed air. OR you can gradually warm it back up to room temperature through a heat exchanger as it expands.

      All in all, the challenges to attaining decent efficency are considerable.

      What might be an easier way to achieve the same energy storage using similar principles, is to turn that same cavern they created into a giant hydro dam. Basically, create an enclosure of equal size below it. When energy needs to be stored, pump the water up to the higher cavern. When energy needs to be released, release it through hydro turbines into the lower cavern.

      • by mprinkey (1434) on Thursday March 11, 2010 @07:54AM (#31436484)

        Um, 50 gigawatt hours is about 1.8 * 10^14 joules. That is about 43 kilotons of energy. Now think catastrophic failure. Here [wikipedia.org] is an example 1/10 the size.

        All energy storage systems...especially physical storage systems...suffer from the same problem. In order to store a useful amount of energy, they need to exist on a potentially catastrophic scale. Pump storage...where is the flood plane. Compressed air...what is the blast radius, where will the supercooled plume go, will it reach aviation altitudes? Flywheel storage...reference mythbusters with the CD on a die grinder. And while not a storage system, even geothermal power plants seem to cause geological instability.

        A few years ago, I did some modelling development for people doing salt mining for compressed air storage. (IAAMechEngineer.) At the time, I remember thinking what must the hoop stresses on a 100m cavern look like at a few hundred atmospheres? And that is rock and dirt and salt holding it together. Nothing in that system tends to behave elastically. So pressurizing and depressurizing it has to induce crack growth and eventually some geological instability. How do you do in-situ inspection of your "pressure vessel"?

        In my mind, some electrochemical process is far safer, even if it uses nasty chemical. Because you can keep the chemical apart (with 100-ft high berms if need be) until it is time to react them.

        • by blueg3 (192743)

          Since when is energy measured in kilotons?

        • by Locklin (1074657)

          Some systems can store large quantities of energy but cannot release it quickly (diesel fuel -barely burns), while others contain relatively little energy but can release it very quickly (gun powder). The quantity of storage is less important than the characteristics of the energy storage system.

        • Re: (Score:3, Insightful)

          by fgouget (925644)

          Um, 50 gigawatt hours is about 1.8 * 10^14 joules. That is about 43 kilotons of energy. Now think catastrophic failure.

          You seem to think this is a totally untested domain. However we have been doing the same sort of thing with flammable natural gas [wikipedia.org] for decades and I have not heard about any accident. So presumably the underground storage of large amounts of gas is a well tested and understood technology.

          Besides you certainly don't need or even want to store your 50 gigawatt hours of energy in just one basket. Instead you'd want multiple baskets either close to production or consumption areas.

  • Unwater Bags (Score:5, Informative)

    by Black Gold Alchemist (1747136) on Thursday March 11, 2010 @02:28AM (#31435228)
    Another solution for the large scale storage of electricity is the inflation of airtight bags deep under water. Since water is so heavy, it exerts a lot of pressure against the air, leading to a cheap method of energy storage. The problem with all compressed-air systems is that have losses due to the non-isothermal nature of the process. That means some energy is lost as heat during compression, and you don't gain it all back thanks to Carnot. The energy density by volume is quite low, unfortunately, but in this application, that's basically irrelevant.

    For the curious, the energy density of compressed gas, is 100*P*ln(P/A) kJ/m^3, where P is the maximum pressure and A is the ambient pressure. That m^3 term is in the volume when compressed.
    • Re:Unwater Bags (Score:4, Interesting)

      by superposed (308216) on Thursday March 11, 2010 @03:53AM (#31435616)

      I think the losses in the CAES system are due to the fact that it is a non-adiabatic process (a diabatic process?, i.e. one where heat can be lost from the system). When you compress the air, the temperature rises, and some heat is lost to the surrounding ground. But if the cycles are fast enough, those losses may be reduced -- i.e., you allow the air to re-expand, which cools it, and it sucks heat back from the ground. Since heat moves slowly through the ground, you may be able to get a lot of it back before it goes anywhere. The innovation in the Alabama system was to use waste heat in the turbine's exhaust gases to replace this lost heat as well.

      I think the solution you propose is isobaric (constant pressure) and isothermal (constant temperature), but still not adiabatic. Some of the energy used to compress the air is converted to heat, and that heat would be lost to the ocean instead of raising the temperature of the air.

      A better solution might be to use pre-inflated air bags (or air boxes?) attached to pulleys on the bottom of the ocean. Use a motor to pull the other end of the rope, and you would draw the air bag downward, storing energy. Play out the rope and the rising air bag would turn the motor (now acting as a generator), generating electricity. You could also do this with stones or bags of silt/gravel, just raising and lowering them from the surface.

      The problem is, you would need a lot of air bags or stones to store any significant amount of energy. If the stones or gravel have a density of 2000 kg/m^3 (similar to "Gravel, wet" according to http://www.simetric.co.uk/si_materials.htm [simetric.co.uk], higher than "Clay, wet excavated" (1600) but lower than concrete (2400)), then they will have a net weight in water of about 1000 kg/m^3 (i.e., a downward force of about 10000 Newtons per m^3). Air bags would exert a similar force upward. If you can find a near-shore location with a depth of 1 km, you could store 10000 N * 1000 m = 10 MJ of energy per cubic meter of material, which is about 3 kWh/m^3. A 100 MW wind farm (presumably closer to shore) would generate 100,000 kWh of electricity per hour when the wind is blowing, so if you wanted to store 6 hours of energy from this wind farm, you would need to raise and lower about 6 * 100,000 / 3 = 200,000 cubic meters of stone or air (e.g., 200 large chunks, each 10 meters across). I suppose it could be done...

      • Re: (Score:3, Interesting)

        by richard.cs (1062366)

        the losses in the CAES system are due to the fact that it is a non-adiabatic process

        the solution you propose is isobaric (constant pressure) and isothermal (constant temperature)

        Either an adiabatic or an isothermal process will allow high efficiency. In the adiabatic process the heat from compression is stored in the air and in principle no energy is lost through the compression and decompression. In an isothermal process all of the extra heat from the compression is transferred to some external reservoir (ocean, atmosphere, etc). If this heat is transferred back to the air when decompression occurs the air leaves the system at its original temperature (as for an adiabatic process)

        • I suppose you're right, provided the decompression happens in thermal equilibrium with the water reservoir (e.g., underwater). It's hard to see how that could be done, since the air is being fed into a turbine, but maybe it's possible.

          I think the process you propose has two elements: a possibly isothermal compression/expansion cycle, and some work done against/by the buoyancy force on the air bags.

          My proposal was to eliminate the compression/expansion cycle, and just do the work, which could have 90% roundt

    • by dangitman (862676)
      Unwater? So, is that a solid, a gas, or plasma?
    • Re:Unwater Bags (Score:4, Insightful)

      by mprinkey (1434) on Thursday March 11, 2010 @08:17AM (#31436610)

      Um, how do you intend to keep bags of air at any depth underwater? Even when highly compressed, the density ratio is going to cause buoyancy, requiring some anchoring mechanism and a bag that is structurally sound enough to handle the stresses. I don't think that you can compress air enough to get it to match the density of liquid water at any depth...the nitrogen will start to liquefy first...and that brings a whole different set of problems.

      • by khallow (566160)

        Um, how do you intend to keep bags of air at any depth underwater? Even when highly compressed, the density ratio is going to cause buoyancy, requiring some anchoring mechanism and a bag that is structurally sound enough to handle the stresses. I don't think that you can compress air enough to get it to match the density of liquid water at any depth...the nitrogen will start to liquefy first...and that brings a whole different set of problems.

        We'll keep the bags down there by using an anchoring mechanism and a bag that is structurally sound enough to handle the stresses. Another problem solved, Slashdot-style! And you need the density difference, otherwise you don't have any change in the potential energy of the system.

    • I live in Ludington, Michigan. They built a very large pumped storage plant here over 30 years ago. They pump water up into a man made lake at night when the demand is lower and reverse the process during the day when the demand is greater. So we already have a Gigawatt storage device. I have been to their observatory tower several times and it seem to be very windy there all the time. Yet after 30 years there is not even one windmill on the banks of this man made lake. Morton salts is located just a
  • by ductonius (705942) on Thursday March 11, 2010 @02:37AM (#31435274) Homepage

    The problem with these energy storage techniques for renewables is every single one of them would be more economical if they were used as load leveling systems (suck extra energy during down times, release in peak hours) rather than supply leveling systems (suck extra energy in high production hours, release it in low production hours).

    The reason for this is day-to-day and monthly power consumption is a very easy thing to predict, so we know very well how much storage we need and if it will or will not be enough. Using these systems we can level the load and allow the greenest power sources (nuclear, followed by hydro) to produce the vast majority of power we need (because they can run at near 100% 24/7).

    The wind is a very much harder thing to predict. So how much storage is needed? Who knows. What we DO know is that every single wind power station is going to need gas turbine backups for when a) the wind doesn't blow, b) demand is high and c) storage is depleted.

    Using energy storage to allow nuclear and hydro to run most economically is a far better choice than using it to level the output of wind power.

    • Re: (Score:2, Insightful)

      Compressed air is a good load leveller because of it's high power density. Superconducting energy storage is also a good load leveller, but really expensive.

      I think the best way to store the energy long term would be to make synthetic gasoline (maybe natural gas) by reacting hydrogen with carbon dioxides. There has been research in the past about the electrolysis of carbonate solutions to produce hydrocarbons.
      • AFAIK, high speed flywheel storage is the best general purpose means of storing power.

        That said, if there are geologic formations that could be exploited for compressed air storage, or topographic features that could be exploited for hydro storage, then in those situations it would make sense to do so.

        Here's an interesting exercise: coal is currently mined in the North American Rocky Mountains and shipped down to nearly sea level by train to its point of use. If these trains used regenerative braking to

      • by AB3A (192265)

        Energy storage is still very much in its infancy. There are many ways to do it and there are many risks as well.

        Basically, there are two places where such energy storage is practical. One of them is in large scales at the generation facility, the other is smaller scales at the load.

        Personally, I prefer the load side for energy storage because it offers some backup in case the power distribution system is interrupted. It is also very much an issue of research with development of electric and hybrid vehicles.

    • Re: (Score:2, Interesting)

      by Anonymous Coward

      Hydro isn't always an option, and even though nuclear would go a long way to solving these problems, it also has limitations. For one, nuclear plants need coolant, which is generally a lake or river (again, geographically specific). For another, the FUD about nuclear energy isn't going away, so a lot of suitable areas won't be considered. Now, I'm not saying wind isn't similarly limited; but I am saying that wind power may work in places where neither hydro or nuclear will (dry, arid climates leap to mind).

    • by Calinous (985536)

      Hydro can not produce 100% energy all the time, as the power plant is usually more powerful than the average water production in that basin. Also, when expecting heavy rains, the hydro plants will empty the lake behind the dam, and the power decreases due to lower water level differences (maximum power is when the lake is full, but this is bad if heavy rains come)

    • Re: (Score:3, Informative)

      by DamonHD (794830)

      "What we DO know is that every single wind power station is going to need gas turbine backups for when a) the wind doesn't blow, b) demand is high and c) storage is depleted."

      The amount needed depends on many factors such as the amount of demand control too.

      So it's a grave error to think that all wind supply needs 100% callable backup, IMHO.

      Rgds

      Damon

      • by khallow (566160)

        The amount needed depends on many factors such as the amount of demand control too.

        I was thinking this too. Demand control can be counterproductive if it ends up suppressing services frequently to a lot of customers though. Some degree of demand control improves overall reliability and value of the system and should be able to handle unusual situations (like the grandparent's concern). But if you're routinely exercising demand control (such as happened during the California electricity crisis [wikipedia.org]), then there's something wrong with your system.

        • by DamonHD (794830)

          No, not at all.

          Some demand control is emergency stuff and not to be used too often, but *normal* everyday demand control is stuff like peak shaving/shifting and frequency response and is run-of-the mill non-emergency management and could be extended and would make the grid 'stiffer' and more stable, eg:

          http://www.earth.org.uk/note-on-dynamic-demand-value.html [earth.org.uk]

          Rgds

          Damon

    • Re: (Score:3, Insightful)

      by superposed (308216)

      You are using a false dichotomy here. In fact the best approach is to use all available flexibility to improve the match between supply and demand. There is no need to smooth out either supply or demand on a one-to-one basis. Instead, you use a smaller amount of flexible assets (hydro, pumped hydro, air storage, fast-start gas generators, electric vehicle chargers, price-sensitive customers, etc.) to fill in the gaps between the two. To the extent that variations in supply and demand (or between different l

    • Re: (Score:3, Informative)

      The wind is a very much harder thing to predict. So how much storage is needed? Who knows. What we DO know is that every single wind power station is going to need gas turbine backups for when a) the wind doesn't blow, b) demand is high and c) storage is depleted.

      Many studies [wikipedia.org] have been done on this subject. You appear to be a bit confused as to the purpose of load levelling systems in proposed green energy schemes.

    • by nadaou (535365)

      where I live the major hydro generation company also owns a fleet of nearby wind turbines. when the wind is blowing within minutes they slow down or speed up the dams. when the wind isn't blowing they turn the dams on full flow. no wasteful pumping water upstream, just slow down your existing dams and conserve the lake water until you need it, and they can spin up or down the dams with the daily demand cycle too (as I guess nuclear can too, but not fossil fuel burning plants). the laws of thermodynamics tel

    • by MrKaos (858439)

      Using these systems we can level the load and allow the greenest power sources (nuclear,

      Can you please explain why nuclear power is a green power source. How is Nuclear greener than Wind power?

      Using energy storage to allow nuclear and hydro to run most economically is a far better choice than using it to level the output of wind power.

      How does compressed air storage make a Nuclear Power plant more economical? Since base load power is a function of the entire grid why is it not reasonable to find a useful

      • by khallow (566160)

        Can you please explain why nuclear power is a green power source. How is Nuclear greener than Wind power?

        If you actually look at impact on the environment, nuclear is competitive. The biggest impact by far is uranium mining and thermal heating of water sources followed distantly by the Chernobyl accident (which IMHO comprises virtually all radiation released by nuclear plants). Wind on the other hand has a much larger physical footprint per power generation and any large scale deployment will increase the amount of support infrastructure (access roads, power lines) in remote locations.

    • . Using these systems we can level the load and allow the greenest power sources (nuclear, followed by hydro) to produce the vast majority of power we need (because they can run at near 100% 24/7).

      I was going to moderate you down, but decided to respond instead.

      Nuclear power requires relatively constant output levels- it's a pain in the ass to change power levels.

      Hydro has no such issues. They can't take out more water than is being put in over the long run, but that's about it. In fact, if they ca

  • by steveha (103154) on Thursday March 11, 2010 @02:41AM (#31435292) Homepage

    The first question I thought of was, "Why not just use pumped hydro power?" Then, oddly enough, I read TFA and found the answer in it:

    The nation's largest energy storage option right now is pumped hydroelectricity. When excess electricity is present in a system, it can be used to pump water up to a reservoir. Then, when that power is needed, the water is sent through a turbine to generate electricity. The U.S. electric system has 2.5 gigawatts of pumped hydro storage capacity, but most of the good, cheap sites are already occupied, and creating new reservoirs is not environmentally benign.

    And, as noted in the summary, compressed air energy storage (CAES) been tried and it works:

    'We expect the CAES plant technology pioneered in Alabama to lead to widespread application in this country," said Robert Schainker, the manager of the Electric Power Research Institute's Energy Storage Program in a press release announcing the plant's completion. 'Three fourths of the United States has geology suitable for underground air storage. At present, more than a dozen utilities are evaluating sites for CAES application."

    steveha

    • Problem is a gigawatt isn't a measure of storage capacity, it's a rate equal to 1 billion Joules per second. Still, doing some quick calcs I conclude that this is actually a great way to store energy. I'm looking forward to better electricity prices in the future.
    • by ledow (319597)

      Not just that... pumping water is a lot harder than pumping air - just through sheer mass moved. The mass thing does affect stuff on the way out too, so air can't "push" as big a turbine as water would but everything like that just creates more strain on the equipment. Additionally, water is completely incompressible, so if you want to store 10,000 litres, you have to have 10,000 litres of space (and thus a large environmental concern and also restricts the power you can produce in a certain area. Howeve

    • Just build a second (relatively small) reservoir at the base of the dam.
      Then install additional pumps and turbines. The capacity of the main reservoir is adequate for weeks of electricity production - so the bottleneck is in the bottom reservoir and the pump/turbine capacity.

  • by Fishbulb (32296)

    Pumping stuff into the ground that isn't normally there tends to give me the willies anymore. "Stick it where the sun don't shine!" isn't such a great solution, IMO.

    Besides which, why not just build Vanadium batteries [discovermagazine.com] or invest in carbon nanotube [popularmechanics.com] ultra-capacitors [arstechnica.com] (which could have direct benefit to mobile energy storage)?

    • by Calinous (985536)

      Cost is an issue - there are plenty of old mines that can be used for compressed air storage (by the way, pumped air inside mine shafts was used as "air reservoir" for a wind tunnel - I think for the nuclear reaction-powered jet engines.

    • Why not allow the markets to compete on this? Offer up limited time subsides/tax breaks JUST for storage, but without specifying what type. The reason for doing this is that we NEED energy storage now. It would allow AE to really thrive, but would also allow us to avoid building new coal plants, though it would mean that coal plants would run more.
  • I'm curious... I wonder how high the psi could get before something broke. I mean, the weak link would definitely be the seal (one would think). I suppose you could get some pretty dense air underground... very interesting idea.
    • I'm curious... I wonder how high the psi could get before something broke. I mean, the weak link would definitely be the seal (one would think). I suppose you could get some pretty dense air underground... very interesting idea.

      It would make a great Michael Bay movie.

    • I would think you pump's maximum psi rating would be the weakest point. Nothing would break, you just couldn't pump in any more air.
      • In the event of normal operation, but in the event of catastrophic failure? Hmm, interesting. I guess when I hear new ideas (new to me anyway) the first thing I think is how they may break.

        If your seal didn't hold as you thought it would or your readings were incorrect, or there was geological instability... hmm... well, it's a novel concept. I look forward to hearing more about it someday.
    • by nido (102070) <nido56&yahoo,com> on Thursday March 11, 2010 @03:53AM (#31435614) Homepage

      I mean, the weak link would definitely be the seal (one would think).

      I, for one, think that the weak link would be the compressors. Most gas pumps just aren't especially efficient. If only someone would invent a pump that's better than current designs [wikipedia.org], the world's energy problems could be quickly solved.

      Here's what the N.Y. Times article said:

      The McIntosh plant uses an electric motor and a compressor to pressurize an underground chamber of 19 million cubic feet -- 220 feet in diameter and 1,000 feet tall -- to 1,100 pounds per square inch. The pressure may sound high, but it is only about one-fifth of what the chamber could withstand.

      The chamber in Alabama could hold 5,500 psi, but the pump is only capable of 1,100 psi. Design a better pump, and the cavern could store significantly more air.

      • I'm convinced that the air compressor was invented by some guy who was having sex doggy style and noticed that as he rapidly pulled in an out air started compressing in his partners vagina. Next time your having sex with your partner and really going at it notice how your penis works just like an air compressor forcing air into the vagina. I'm convinced that many scientific insights occur in the bedroom.
        • by swb (14022)

          Maybe when you're 20. When you're 45? That seal isn't enough to pressurize anything.

  • by Animats (122034) on Thursday March 11, 2010 @02:55AM (#31435360) Homepage

    This is the Slashdot-misunderstood version of the Wired dumbed-down version. Here's some of the more serious stuff.

    Wind Operations Dispatching Training [pjm.com]: This is the grid system operator's view of wind power.

    There's a lot going on. Since electricity deregulation, the power distribution companies don't own much generation capacity. They buy power from generating companies. So there's a market system and contracts in place. The contracts are now more long-term; the "auction every half hour" scheme California had for a few years is out of favor. Now, the planning horizon is about one day.

    There's a whole series of PJM online courses [pjm.com], and if you go through some of the basic ones, you'll be able to talk about electric power intelligently.

  • by steveha (103154) on Thursday March 11, 2010 @02:58AM (#31435384) Homepage

    As a result, the plant produces one kilowatt-hour -- or 1,000 watt-hours -- of electricity for each 870 watts consumed the previous night. In contrast, the most common mode of energy storage is pumped hydro, in which water is pumped uphill at night, and during the day a valve is turned and the water runs back down, with the pumps recapturing the mechanical energy and turning it into electricity. But in that system, each kilowatt-hour put in delivers no more than 700 or 750 watts back out again. Batteries have about the same ratio.

    I assume we should reverse those first numbers: we spend 1,000 watt-hours to gain 870 watt-hours later. Cool to see that it beats pumped hydro.

    http://www.nytimes.com/1991/09/29/business/technology-using-compressed-air-to-store-up-electricity.html [nytimes.com]

    Hydroelectric plants often cost $1,000 per kilowatt of capacity, and batteries cost far more. The cost of building the Alabama plant was about $550 per kilowatt of capacity.

    And it's cheaper than pumped hydro!

    The American plant has one new twist, however: the exhaust gases from the turbine are used to preheat the compressed air after it is brought up from the cavern. That makes it 25 percent more efficient than its German predecessor, the institute says.

    Interesting. Of course, if you use this with a wind farm, you don't get this benefit; the plant discussed here is a coal plant, with plenty of waste heat.

    The above article is from 1991. Despite all these advantages, the idea never took off before now. It saved money, but not a huge amount. But since the wind blows when it blows, not when you want it to blow, I can see this being a useful thing for a wind farm.

    steveha

    • by MattskEE (925706)

      As a result, the plant produces one kilowatt-hour -- or 1,000 watt-hours -- of electricity for each 870 watts consumed the previous night.

      Not to mention they have made the classic mistake of confusing Power and Energy. Watt-hours is an energy because it has units of Joules. Watts are in the form of Joules/second which simply represents how quickly you are transferring energy from one place or form to another.

    • Em those numbers are wrong. Even 1960s-era PSH like Turlough Hill in Ireland get in the mid to high 80s returns, and modern systems aget in the 90s very easily. As for the 1991 costing, I'll say nothing.
      • uh, no. The one-way efficiency of this tiny hydropower system is about 80%, but the only number that matters is the round-trip, which is 64%, theoretical and 63% as actually measured on-site.

        It's mighty silly to spend that kind of money up front to get such miserly returns.

        Much more so bad to even think of pumped air storage, which has to be less efficient.

  • Conversion losses (Score:3, Interesting)

    by spectrokid (660550) on Thursday March 11, 2010 @04:03AM (#31435662) Homepage
    Wind -> Electricity ->compressed air ->electricity. That should give some serious losses. On top of that, windmills have gearboxes, brakes and all kinds of complicated crap to make them run perfectly in sync with the phase of the power grid. So question is, would it not be cheaper to mount a basic compressor in the nacelle and have it run directly on the axle, then pump the air through a set of pipes. Yes pipes have losses too, but remember the main cost of the windmill is its purchase, so a cheaper design might pay off?
  • Doing it with water (Score:3, Informative)

    by mbone (558574) on Thursday March 11, 2010 @06:34AM (#31436180)

    People have been storing electrical energy using water for a long time (over a century). The basic idea is the same, but in the case of water and hydroelectric dams, the solution is easier (you just run the turbines as pumps, putting water into the resevoir instead of letting it drain out). According to the wikipedia article on Pumped-storage hydroelectricity [wikipedia.org] :


    In 2009 the United States had 21.5 GW of pumped storage generating capacity, accounting for 2.5% of baseload generating capacity. PHS generated (net) -6288 GWh of energy in 2008 ...

    In 2007 the EU had 38.3 GW net capacity of pumped storage out of a total of 140 GW of hydropower and representing 5% of total net electrical capacity in the EU.

    And, yes, people have considered [cam.ac.uk] using pumped-storage hydroelectric to even out the variation in wind power.

    I myself doubt that compressed air storage would ever amount to more than a fraction of pumped hydro-electric storage, but it might be useful in very dry or very flat regions.

  • Getting the straight poop from "Wired" is like expecting it from Fox News.

    Air--pumped storage is dead from the get-go. You compress air and a goodly percentage of the energy ends up as heat, which has to be removed from the compressor cylinder heads and is lost. Then the hot compressed air loses heat to the walls of the cavern. Then when you let the air expand, it cools off and you lose pressure from that effect too.

    A rough guess-- you lose 50% of the wind energy coming and going.

    You can do better by p

    • Re: (Score:3, Interesting)

      by s122604 (1018036)

      rough guess-- you lose 50% of the wind energy coming and going.

      Rough answer, you are wrong, RTFA and RTF Thread, particularly (#31435384) http://hardware.slashdot.org/comments.pl?sid=1578760&cid=31435384 [slashdot.org]

      You can do better by pumping water uphill, where you don't have the compressive losses.

      no, you can't, again, RTFA

      here it is 2010, and I'm still using cutesy acronyms from the early 1990s, seriously though RTFA has never been a more appropriate response

    • by ErikZ (55491) *

      What about cooling air to a liquid state and storing that?

  • The problem with AE is not AE. It is the politics behind it. We had W and the neo-cons pushed Ethanol from Corn. Why? Votes. He did just in front of the elections.
    The dems have picked Wind and Solar PV as being the 2 big winners, yet neither is really all that good. Solar PV will remain the highest costs for at least 1-2 decades to come. Neither are baseload power.
    Right now, Ethanol receives more than 50% of all the money that flows into AE. Its subsidy is actually bigger than the R&D, tax breaks, A

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