A guest author going by Libelle posted a piece titled “Compressed Air Energy Storage – How Viable Is It?” Sunday at TheOilDrum, Canada. It’s a top-flight review of the physics and explains the thermodynamics in a quaint, easy to grasp way.

Libelle suggests that raising the elevation of water might be more effective. From here on Libelle examines the mathematics in measuring out the process of compressing the air and releasing it again in the losses of the energy inputs. While not a total loss, compressing air for later release is better than a gasoline motor but not by far. The facts behind the numbers and the calculations make the case that compressing air in a simple form isn’t particularly useful form of storage.

The basic run through offers the lessons that make up the second part of the piece. Here Libelle looks into the effects that staging the compression process might have. The advantage in doing the energy input in steps or stages of partial increases with smaller heat gains each has a considerable positive impact on the efficiency. The heat loss during compression and the heat needed to maintain volume to support pressure in releases are then the prime problems. For this article Libelle only looks to the solution of adding back fuels like natural gas to burn and expand the volume, which makes for a gas turbine drive solution.

Thanks for the math and a nice explanation of the problems. But –

Science is well on its way to using heat sources for direct to electrical generation. The nano antennae and thermoelectric researchers both have ways producible and in development that can harvest a part of the heat energy lost in compression. The thermal solar research is showing worthwhile paths to using heat sinks for storing energy for later use that could be charged in compression and discharged in depressurization. Many locations could use the cooling during depressurization as a form of energy, too. To call the whole thing off isn’t looking into technology and cross applications in any depth.

U.S. Geothermal Map

Then there is the cross to geothermal. Rather than be concerned with the heat loss, just store the compressed air with its heat in a geothermal location and add the geothermal heat, too. A look at the map of the geothermal potential across the U.S. shows a huge energy supply. Using air instead of water might prove to be a boon to many locations where water, depth, mineralization, the available latent heat and other properties would preclude a water heating solution. Moreover a hot air chamber would go far to leveling the production of wind turbine output. What added energy from geothermal heat could achieve is a study begging for research. It may also be engineered to be a closed loop system, thus becoming a nearly environmentally neutral solution.

I for one am not at all discouraged, rather I see a great potential. Viability in compressed air is only limited by the imagination and engineering prowess that is applied. It may prove to be the thing that offers a bigger output from wind than anyone had previously thought. Horizontal deep well drilling is getting better by the day. What 35,000 feet of bore looping through hot dry rock could offer a compressed air stream might surprise, very pleasantly, in the resulting energy output. With some thought others will come up with more ways to use air in harvesting heat energy for work. Just imagine, a wind turbine compresses, geothermal heats further, the flow goes through a solar array and then you have a very very hot supply. There is a lot of opportunity in compressed air geothermal energy production.


7 Comments so far

  1. ks on July 29, 2008 9:59 AM

    When I saw the article below, I became intrigued with this idea and hoped that TOD and others would take it up and assess its viability. After reading both the TOD article and yours, however, I’m still not quite sure what to make of this approach. I get that storing energy as compressed air to drive a car is not particularly efficient; but ICE’s are not either and batteries (for cars) have their issues too. From your comments, it seems you are sanguine about applications for energy storage for the grid, etc., but what about this as a different/complementary approach to powering cars?

    Thanks again for your posts.


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