Michael Kanellos
In Iowa, Compressed Air to Be Source of Electricity July 1, 2008 at 9:05 AM
Talk about your power burp.
The Department of Energy, Sandia National Labs, and a host of municipal utilities in the Midwest are in the midst of designing a compressed air generation plant in Iowa. The plant is expected to be operational by 2012 and produce 268 megawatts of power or 50 hours of power storage. That could enough to save a municipal utility $5 million a year.
It works like this. Air compressors force air into underground caves. When power is needed, the air gets released to power a turbine, which generates electricity. The air compressors can run on fossil fuels or wind power. The technique uses about 50 percent of the natural gas that a normal natural gas power plant would use, so greenhouse gases would be cut there.
Powering the compressors with wind turbines would of course generate even fewer greenhouse gas emissions. More importantly, the power generated from the turbines at night could run the compressors. Wind turbines tend to be somewhat active at night and utilities don’t know what to do with that power since few people are awake to use it. Storing night energy in caves gives them an opportunity to generate cheaper power during peak times.
VCs, by the way, are hot for storage. Industrial battery and flywheel companies like Deeya have received investments in recent months. Solar thermal plants are investing in molten salt facilities that can store heat.
Two compressed air facilities exist: a 17-year-old facility in McIntosh, Alabama and a 30-year-old plant in Germany. Both of these are in salt domes. The Iowa facility will be in an aquifier. The DOE and Sandia are also inspecting sites in Ohio.
So if it’s so good, how come it’s not more popular? Power was cheap until a few years ago. Thus, no one was really motivated to do this. Building a compressed air facility requires extensive geological surveys. One small, select leak and that playground built over the site is swirling around in the air like a balloon.
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How does use 50% of the natural gas of a power plant? It’s storage, which inherently has some inefficiencies. So, you get less energy out than you put in. And the energy you are putting in is electricity - presumably generated by a natural gas plant. Something doesn’t add up. Is the 50% emissions cut when you use wind to power it?
Craig
ditto on the 50% natural gas thing…
Why do we need to use geological formations? Is it too expensive to build tanks? What is the input and output efficiency of compressed air storage?
It uses 50 percent of the energy that a natural gas plant would use to produce the same amount of power, in theory. in other words, if you had them side by side in a John Henry contest, natural gas generators combined with compressors would use have the fossil fuels a natural gas power plant would to produce the same amount of power.
Tanks? too small and costly. You need massive underground capacity. A similar issue comes up with carbon sequestration. Some like the idea of turning it into baking soda, but the volumes of co2 coming out would result in a lot of powder, say critics. Imagine the amount of steel that would be required for air tanks. Then again, it’s in its infancy so who knows what will happen.
Michael - still doesn’t make sense. To produce 1W of electricity from the compressed air system requires more than 1 W input. And that input is coming from a natural gas generator! How can that be better than using the 1W from the natural gas generator directly?
The benefit of this system is the storage, and the ability to shift energy use from peak to off-peak times (saving money, but not reducing emissions). Or being able to better integrate wind (which would have a net emissions reduction).
Maybe I’m still missing the point…
C
A lot of it comes down to efficiencies. Sandia is basically saying they can extract more power out of this system than you would a standard natural gas plant for the same input. In other words, you use half the gas for this for the same amount of power. The pump puts the air underground but the earth maintains the pressure on it. You have losses in gas plants too. It’s equivalent to having a better wind turbine. Storage is a key issue, but they also claim better performance. Of course, it also doesn’t exist yet so who knows if the mathematical models will bear out in reality.
I’ll have to agree to disagree on this one… Seems to me it’s simple conservation of energy. You have to generate electricity to pump the air underground. Unless you are extracting energy from the earth (which you aren’t in this case), you are going to get less energy out than you put in.
So, it’s always going to be more efficient to use the electricity directly, versus using it to pump air into the ground, and release it to generate electricity. That’s true wether or not the electricity is generated via natural gas, coal, wind, or solar. You lose in the storage.
Compressed air is only storage - it’s not generation. Unlike geothermal, which does extract energy from the earth…
But you’re not generating power directly in a natural gas plant. You’re using the gas to crank a turbine to produce electricity. If you flared the gas directly, that would be different. in any event, I’ve got more calls into the lab and we will see what they say.
Criag,
A power plant needs to run at a set capacity to produce power efficiently. Power demand ALMOST NEVER meets optimal operating capacity — the excess capacity in existing power plants is simply wasted. Storing excess capacity allows you to use it on demand, and the cost is very low because it was previously waste.
Steve Pluvia
[...] to accounts by Sandia National Laboratory and Greentech Media, Sandia along with DOE and over 100 municipal utilities in the Midwest are collaborating on a CAES [...]
[...] Department of Energy, Sandia National Labs, and several Midwestern utilities are already at work designing a compressed air storage system for a plant in Iowa scheduled for completion by [...]
This is just a guess, but from the article they are talking about running these air compressors at night when energy is being generated but not used. This process would allow at least a portion of that energy to be stored and then released during peak times.