Compressed Air Energy Storage
I have always been a big fan of wind power. But one of the knocks on wind is that it is intermittent. Since electrical demand probably won’t match up very well with wind fluctuations, installed wind capacity does not displace conventional power generation in a 1 to 1 ratio. For example, I have seen it claimed that 2,000 megawatts of installed wind energy still requires 1,800 megawatts of standby power for when the wind isn’t blowing. (1)
Clearly a storage system is needed. During times of high wind flow and low demand, the excess energy could be stored in something akin to a giant battery. When the wind isn’t blowing, users would pull from the “battery”. I have given a lot of thought over the past couple of years as to just what form such a storage system would take. I could envision several different options. One, air could be compressed into a storage system and then discharged through a turbine as needed. Two, water could be pumped uphill, and then be allowed to flow back through a turbine as needed. Three, water could be split to hydrogen and oxygen. I don’t like this option as much, because most electrolysis is inefficient and hydrogen storage is problematic.
(Incidentally, a variation of this third option was recently brought to my attention, in which excess wind power is used to make methanol, ethanol, or even ammonium nitrate fertilizer. For an excellent comprehensive overview of this option, combined with an impressive overview of wind energy potential in the Great Lakes area, see David Bradley’s report A Great Potential: The Great Lakes as a Regional Renewable Energy Source.)
Imagine my surprise this weekend to learn that while I have been daydreaming about a wind energy storage system, someone is in the process of doing it. Furthermore, others have previously blogged on it. I felt a bit like Rip van Winkle after waking up from his long nap. How could I have missed such an important development? The storage system is called compressed air energy storage (CAES). A January article from MSNBC explains the concept in Store wind power for later use? Cities bet on it:
A group of Iowa cities intends to not only harness the wind, but also capture it, store it underground and use it to help make electricity when demand peaks.
Members of the Iowa Association of Municipal Utilities have invested in a proposed power plant that would use wind turbines to drive compressed air into underground aquifers. The air would be released to generate electricity when needed.
The plant will use power from its own wind turbines, supplemented by cheaper electricity bought at off-peak times, to force air into rock formations at least 2,000 feet underground.
Current plans call for pressurized storage of tens of billions of cubic feet of air in rock formations deep underground. (2)
If you think I was surprised by that, imagine my surprise upon reading this from the same article:
Only two other underground compressed air plants are in operation. A plant in Huntorf, Germany, was built more than 23 years ago and a plant in McIntosh, Ala., is 11 years old. Both store compressed air in underground salt caverns.
Iowa’s project is unique in that it would use wind power to store the air and combine it with massive underground storage capacity.
The Germany and Alabama plants store hundreds of thousands of cubic feet of air in a thermos-bottle shaped container installed in the salt mines. The Iowa project would use naturally occurring pockets embedded in sand or sandstone formations sealed by shale or other rock.
So, a plant in Alabama has been using compressed air storage successfully for 11 years, and I didn’t know about it until this weekend. The only difference is that they aren’t using wind to do it. The Iowa plant will be the first to do that, but others will probably follow.
To be sure, such a storage system is not universally applicable. You need some kind of large, airtight, underground cavern. There are a lot of these in the United States, but they need to be located near a source of wind. Although, now that I think about it, I see no reason such a system couldn’t also be paired with solar or tidal generation systems, storing their excess energy using the same concept.
The plant is scheduled to come online in 2010. I wish them great success, and look forward to hearing reports after they start up.