Slashdot Mirror

← Back to Stories (view on slashdot.org)

Cheaper Energy From Caverns of Compressed Air

Posted by samzenpus on from the fine-until-the-earth-burps dept.

An anonymous reader writes "By using the Earth's vast underground caverns to store compressed air generated by wind farms at night, several U.S. municipalities will be 'going green' by using that stored energy to generate daytime electricity on the cheap. Engineers at a National Lab think compressed air stored in underground caverns could cut in half the cost of electricity."

8 of 114 comments (clear)

  1. How Efficient is It? by TheStonepedo · · Score: 3, Insightful

    How far are the turbines from the caves? What happens if the wind that should be generating electricity for the compressors takes the day off and chooses to make an unfashionably late arrival? How much of a boost do the turbines get from the compressed air?
    I'd think with enough losses along the way (steps up/down in voltage at transformers to transmit the power to the compressors, mechanical inefficiencies of the compressors, dependence of the turbines' optimum performance on this assistance) the project, while novel, could take a while to pay for itself. I'm not suggesting that bleeding-edge science should be economically feasible - that should come after the science is established - but that efficiency should be priority number one so that the technology can become competitive with other ways to store potential energy.

    --
    I'll be your candy shop of infinite deliciousity if you'll be my discotheque of endless rump-shaking.
    1. Re:How Efficient is It? by Rakishi · · Score: 3, Insightful

      The current method as I understand it for large scale energy storage is water. Specifically http://en.wikipedia.org/wiki/Pumped_storage

      Compressed air probably less efficient but potentially cheaper to implement.

    2. Re:How Efficient is It? by dbIII · · Score: 3, Insightful

      How Efficient is It?

      Not very. The point however is to even out the load and fill the peaks, it's just another form of pump storage I suppose for places where you can't just conveniently pump water uphill. Despite the nuke lobby cry that it is all about base load the real problems are the peaks. With base load generation you have a whole lot of power being generated at night that isn't being used by anything and what is being used is lighting which mucks up the power factor. Running great big motors (like pumps) at night or resistance heating is what is usually done.

      To sum up - a lot of energy is wasted but you get to fill the peaks without needing base load generation capacity equal to peak load requirements.

      Sometimes wasting the energy is not a big deal. The ideal centuries old application for a windmill is to move enough water into a tank over the course of a week or two for use over the next week or two. With a long enough timeframe in the design it really doesn't matter if you have a few windless days or for solar a sudden cold snap. Compressed air however is a very inefficient way to store energy.

    3. Re:How Efficient is It? by Simon+Brooke · · Score: 3, Insightful

      I think they're mainly suggesting that it would be more efficient than storing the same energy in ordinary chemical batteries, which is the current method for storing energy from natural sources for times of higher demand (or lower production, in the case of solar). Presumably their calculations are based on minimizing the inefficiencies for both batteries and compressed air.

      Pumped storage systems - essentially hydroelectric systems with a top reservoir, a bottom reservoir, and a system of pumps to move water back up to the top reservoir at times of excess generating capacity - are used in the UK at Dinorwig and at Ffestiniog, and in the US at Luddington, Michigan (and probably in other places I don't know about). This is a reasonably simple, reasonably efficient system of storing energy at time of surplus production and releasing it at times of peak demand.

      --
      I'm old enough to remember when discussions on Slashdot were well informed.
  2. Re:Why air? by srjh · · Score: 2, Insightful

    This doesn't compete with geothermal or tidal generation, so it's not necessarily any "better" or "worse". It's really more of an energy storage method (like a battery) that may even be useful as a supplement to something like geothermal generation. Store the energy at night when demand is low, and release it during the day when demand is high, and you'll smooth out variations in the power supply.

    Also, you need a pressure difference to extract energy, just a high pressure is not good enough (similar to the fact that you can't extract electrical power from heat alone - you also need a cold reservoir).

  3. Comment removed by account_deleted · · Score: 2, Insightful

    Comment removed based on user account deletion

  4. Comment removed by account_deleted · · Score: 2, Insightful

    Comment removed based on user account deletion

  5. Ecofriendly? by FrostDust · · Score: 2, Insightful

    Maybe I didn't understand the article well enough, but it just seems to me like they're using energy to compress air in caverns during the night, then using that air to make energy production during the day more efficient. Unless they're violating thermodynamics here, the amount of energy gained by using this compressed air system can't be more than the amount of energy used to compress this air into the caverns.

    So, is it that only benefit here, cheaper energy costs, comes about because they're buying the energy when it's cheaper, and storing it for use when paying for this energy is more expensive?