Comments on: Giving serious consideration to compressed-air energy storage

By: Alan Ruffman

Alan Ruffman — Fri, 03 Jul 2009 15:56:30 +0000

RE “Sorry… CAES usually won’t work … “. Mr. Goeggel should tell that to the Hundorf, Germany CAES (321 MW), or to the MacIntosh, Alabama CAES (110 MW), facilities which have now operated for 31 and 18 years successfully. QED?

By: Geoffrey Goeggel

Geoffrey Goeggel — Fri, 02 Jan 2009 20:13:43 +0000

Sorry…CAES usually won’t work…..isince t’s all about the money! Large CAES systems loose 50% of their input energy and cost millions. Most efficient energy storage is an existing hydro-electric dam: 75% efficient and (in some cases) only 10% the cost of CAES.

By: Franco

Franco — Wed, 17 Dec 2008 22:01:14 +0000

It’s a good concept but my feeling is that it will only be an intermediate solution because it still relies on burning a fuel such as natural gas – which is used to raise the air temperature in the expansion/power section of the turbine. The compressed air (by being under pressure) serves to lower the compression requirements of the turbine, therefore reducing the amount of fuel needed. It’s basically a Brayton cycle with a nice twist.

However, pumped hydro storage will probably be the ultimate storage solution. It’s already proven, it can storage hours worth of energy with high output power. It can be built anywhere there’s a large body of water with elevated land a few hundred meters above sea level. In the States much of the available land has been used for pumped storage but in Canada there’s a lot of potential. No doubt the U.S. would find this useful.

There are environmental concerns but I think they pale in comparison with the total amount of land that is flooded by hydro-electric dams.

I worked out roughly that it would take a reservoir 45 km by 45 km by 20 meters deep, a hundred meters above sea level to supply all the electric power needed by the U.S. for 12 hours (@ 1000 GW). Now that’s only *one* pumped storage facility for *all* the U.S. which can store the off-peak power generated by wind turbines and other renewables, assuming they supply enough to power the U.S. to begin with. But more realistically I know that it’s better to have many smaller pumped storage facilities spread out, of course. It’s just to get a feel for what’s needed.

By: Samir Succar

Samir Succar — Wed, 17 Dec 2008 15:04:14 +0000

The amount of natural gas that CAES consumes is less than half of that of a gas turbine. Furthermore a baseload plant comprised of wind and CAES would have one tenth the greenhouse gas emission rate of a conventional coal plant and roughly one fifth of a natural gas combined cycle plant. The truth is that wind/CAES systems have very low fuel consumption and emissions and the coupling of wind with storage allows wind to participate in baseload markets. This means that even at very high penetrations of wind on the system we could have baseload power generated almost entirely from renewable sources.

In addition, the air is not transported to the storage volume at high temperatures. The compression train uses intercoolers so that the high pressure air is near ambient temperature at the compressor outlet (the compression would be very inefficient otherwise and injecting high temperature air would require a larger volume and introduce thermal stress)

By: Charles Barton

Charles Barton — Wed, 17 Dec 2008 03:25:03 +0000

I was sold on the CAES ideas some time ago, and then i began to investigate why it natural gas was burned in the escaping gas stream. It turns our that CAES is something of the opposite of ground source heating, The air, compressed, goes into the ground very hot, but it gives up some of the heat to the walls of the containment chamber. When the air is released it decompressed, and hence looses compression heat. As it emerges from the ground the the escaping air is chilled enough that its newly chilled humidity turns into ice. Ice flung into turbines is will break them, hence the formerly compressed air needs to be heated, and it is heated with natural gas. The scheme still contributes to global warming, but arguably less than simple natural gas generated electricity. The scheme has never been tested on a large scale.