“This proposal delivers its ‘green’ energy at roughly twice the cost of a LA-basin gas-generated power, estimates energy expert Tom Tanton, since transmission losses from Wyoming to LA would be between 10 and 11 percent. This is surely a project that should be taken with a grain, or a chunk, of salt.”
California, trying to desalinize their drinking and irrigation water, is floating the idea of buying and storing renewable energy in a salt mine near Salt Lake City as part of a plan to get ‘green’ electrons to Los Angeles. This technology-over-economics, cost-be-damned project would use an existing Utah-to-California transmission line previously dedicated to coal-by-wire from the Intermountain Coal Power Plant.
This scheme, a joint venture by Pathfinder Energy, Magnum Energy, Dresser-Rand and Duke-American Transmission, is based on the purported success of a preexisting energy storage project in Alabama that uses compressed air stored in natural caverns to power electricity producing generators. The proposal will get an up or down next year from its sponsor Southern California Power Authority (SCPA).
Compressed Air Energy Storage
Compressed air energy storage (CAES) would use surplus (generally nighttime) wind-generated electricity to run a motor to compress air in an underground cavern. To meet on-peak demand, the pressurized air would be then released to run another turbine to regenerate electricity for transmission on a 500 kV line owned by the Southern California Power Authority. All this is envisioned to replace coal-by-wire from the 1,900-MW Intermountain plant in southern Utah, operated by Los Angeles Department of Water and Power.
This proposal would serve as an energy storage battery, like water retained behind a dam that is released to drive a hydroelectric turbine. However, this wind power “battery” is inefficient because of the inevitable energy losses of conversion and reconversion.
Also, CAES requires one kilowatt hour worth of natural gas (equivalent) to generate three kilowatt hours of electricity. Utility-scale CAES costs $60 to $160 per kilowatt hour, a cost inflator for the residential cost of electricity in California of about $0.16 per kilowatt hour.
The project would generate and store wind power that would equal twice the amount of power as Hoover Dam at peak wind periods, says SCPA, a confederation of the Los Angeles Department of Water and Power (LADWP), ten cities in the L.A. area, and the Imperial County Irrigation District, as shown on the map here (click to enlarge). The major source of power for the SCPA today is from the Intermountain coal plant.
As the SCPA phases out its reliance on dirty coal power to comply with California’s renewable energy goals, energy companies are lining up proposals to re-use SCPA’s 500-mile Path 27 powerline that transmits electricity from Utah to Southern California. The deadline for submitting proposals to the SCPA’s Request for Proposals for Renewable Energy Storage Projects is December 31, 2014.
Billionaire Los Angeles media and sports magnate Philip Anschutz has also announced plans to submit a proposal to supply Los Angeles with electricity from his existing 1,000-turbine wind farm near Saratoga, Wyoming. Anschutz is known as “The Man Who Owns LA” by The New Yorker magazine for his kingdom of entertainment and sports businesses centered in Los Angeles.
Tom Tanton, Principal Policy Advisor with the California Energy Commission from 1976 to 2000, identified these problems with the proposal. First, compressed air energy storage is not widely nor commercially available. Second, the referenced plant in Alabama is not really a commercial plant but a pilot demonstration (and the only one at that). Third, the geology is different, which is important for compressing and keeping air contained.
Gas for CAES
Tanton also says that a fossil-fuel natural-gas power would be needed to run the storage facility.
In order to use the compressed air on the generation cycle (it gets hot under compression, cold under expansion), natural gas is needed; or else some other way to heat the air. This stage of generation is basically a combustion turbine (aka gas turbine) only with the benefit of not using engine power to compress air. (In a typical combustion turbine about 2/3rds of fuel is for compression.) The released, stored air in expanding undergoes adiabatic expansion and would otherwise get quite cold.
It’s not quite true to say “a small amount of natural gas’” as proponents of the project claim says Tanton (It’s equal to about 1/3 that of a gas turbine for the same megawatt hour). Further this scheme assumes energy storage is needed for ‘backup’ not for balancing. However, a compressed air energy storage facility doesn’t respond (back and forth) quite fast enough for balancing. A facility this size would also need to be balanced (with attendant inefficiencies imposed on other power plants), or isolated from the grid.
Twice the Cost?
This proposal delivers its “green” energy at roughly twice the cost of a LA-basin gas-generated power, estimates Tanton, since transmission losses from Wyoming to LA would be between 10 and 11 percent. This is surely a project that should be taken with a grain, or a chunk, of salt.
This article is based on an email interview by the author with Tom Tanton, president of T2 & Associates.