CAES – Lies and Damned Lies

Posted on Posted in CAES, compressed air energy storage, EPRI, wind energy

With apologies to Mark Twain, I keep thinking of his categorization of whoppers when I hear the misleading, if not willfully false, claims made for Compressed Air Energy Storage – CAES.

The Wall Street Journal has a story on the DOE grants for CAES, due to be announced soon. $60 million is planned to “promote a patented technology that stores energy until it is needed”.
First, referring to CAES as “energy storage”, is a stretch, if not downright misleading. The WSJ doesn’t mention that the compressed air is “stored” for the purpose of firing a natural gas generator! Yes, that’s true – a natural gas, greenhouse gas emitting, fossil fueled generator.
Advocates of CAES are quick to point out that using compressed air increases the efficiency of natural gas generators, from about 33% to as much as 88%, so less GHG is emitted. That’s great for fossil fueled generation, but don’t call it energy storage. However, as discussed in an earlier blog, on an energy in – energy out basis, counting the energy used to compress the air, actual energy efficiency is about 54% or less. But I digress…
Second, how can anyone compare CAES to advanced batteries – like the VRB-ESS – and conclude that it’s, “much cheaper than battery storage and far more durable”? The article quotes Robert Schainker of EPRI advising that batteries are too expensive. Elsewhere he is quoted as saying CAES costs about $700 per kWhr. If the PG&E project stays on budget – how likely is that? – then PG&E will get 10 hours at 300 MW, or 3,000 MWHrs for under $400 million, about $133 per kWhr? Wow, what a deal – if it happens. However, what about the cost of the natural gas? No information has been provided yet, but 8 million MMBtu per year seems in the ballpark. At $7 MMbtu, that’s at least $560 million over 10 years. Twice that over 20 years. And what are the O&M costs? The generators are typically completely overhauled every 10,000 hours. We need more information…
By contrast, Prudent Energy is expecting the VRB-ESS to run about $500 per kWhr for 6 hours of storage within 2 years, and much cheaper for a 10 hour system. Refurbishment at 10 years, for about $60 kWhr for a 10 hour system, will allow the ESS to run another 10 years. And, wind power can be stored and delivered as needed, without emissions, with about 75% efficiency.
One final digression – if renewable energy, subsidized by taxpayers, is used to enhance a natural gas generator, is it still “renewable”. Renewable wind power is consumed to run the air compressors. The compressed air is then released to enhance natural gas generation, turning “clean” energy into “dirty” energy. What does this do to the Renewable Portfolio Standards? Does wind energy, that is not delivered to consumers, but instead is consumed to produce natural gas fired electricity, count toward the 20% – 33% RPS?
There’s no guarantee a 300 MW CAES will or can get built as expected, or that it will ultimately cost under $400 million. However, VRB systems can begin to be installed at wind farms and end-users now. It’s more likely that 300 MW of VRB batteries can get installed in 5 years than CAES, and we won’t have to substitute wind power for natural gas.

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