The U.S. Department of Energy is getting ready to formally on Nov. 26 put out for comment, until Dec. 31, a draft environmental assessment on a Pacific Gas and Electric test of a compressed air storage project in California.
Compressed air storage, like pumped storage hydro, offers a way to expend a certain amount of electricity to put a medium (air or water) into storage during slack power demand periods, then to release that medium to generate electricity during peak demand periods.
DOE prepared this draft environmental assessment (EA) to evaluate the potential environmental impacts of providing a financial assistance grant for up to $25m under the American Recovery and Reinvestment Act of 2009 in a cooperative agreement with Pacific Gas and Electric (PG&E) as part of the Smart Grid Demonstrations Program. The study is co-funded by DOE, the California Public Utilities Commission and the California Energy Commission.
The company proposes construction, operation, and decommissioning of an injection and withdrawal well, compression equipment, and associated temporary site facilities required to conduct pressure testing of a depleted natural gas field. PG&E proposes testing the gas field to confirm its geologic and engineering suitability for future use as the air storage reservoir for a compressed air energy storage (CAES) facility.
PG&E proposes to conduct the testing program of a geological formation located below King Island, San Joaquin County, Calif. Testing would consist of injection of air to build a subsurface bubble within the reservoir sands of the depleted King Island Gas Field, and then a series of pressure tests to further confirm the geologic suitability of the site and provide more detailed information for the engineering of a future CAES facility.
The total cost of the compression-testing project would be $20m to $25 million.
Compressed air needed to even out renewable energy production
“Renewable energy resources, such as wind and solar power, have the potential to reduce dependence on fossil fuels and greenhouse gas emissions in the electric sector,” DOE noted. “Concerns regarding climate change have spurred state regulation encouraging the integration of renewable resources into the power generating fleet. For example, under California’s existing Renewable Portfolio Standard, utilities must supply 33 percent of all electricity retail sales from eligible renewable resources by the year 2020. Much of this new generation is expected to be derived from the addition of new solar and wind power generation.
“Because wind and solar resources are by nature variable (i.e., the sun does not always shine and wind does not always blow when power is actually needed), their addition to the power generating fleet poses challenges to the reliable operation of the power distribution grid and the cost of their integration,” DOE added. “Energy storage has been identified as an important component of strategies to mitigate these effects and facilitate greater penetration of wind and solar power into the existing power generation and distribution system. CAES has been identified as a key enabling technology for expanding reliance on renewable resources for electricity production and typically provides a larger energetic return on investment when compared to many other types of storage technologies.”
CAES technology involves two major processes: air compression and underground injection for storage; and air release for electricity generation. During the air compression and storage process, electric motor-driven compressors inject air into a sealed and porous underground geological formation for storage under high pressure. During the air release phase, the high‐pressure air is released from the underground reservoir, heated using natural gas (if necessary), and expanded through sequential turbines (“expanders”), which drive an electrical generator.
Worldwide, two CAES plants using man-made caverns in salt formations—the McIntosh plant in Alabama and the Huntorf facility in Germany—have operated successfully for over 20 years, DOE pointed out.
The first phase of the feasibility study was completed in June 2013 and involved collection of core samples at depleted natural gas fields on King Island and East Island, San Joaquin County. The rock core samples were analyzed to see whether the formation would support a CAES facility, with King Island selected for the second phase. That second phase, which is the subject of this draft EA, would be to conduct pressure testing of the formation.