Product Abstract

This report, Volume 2 in a series, documents the construction of the first U.S. compressed-air energy storage (CAES) plant from August 1988 to May 1991. By providing valuable information on construction and cost schedules for Alabama Electric Cooperative's (AEC) plant, this report will help utilities evaluate and build CAES plants.

Background

EPRI has studied CAES, a potentially viable storage alternative, since 1975. CAES plants use both electric energy and fuel. For each kWh of electrical output, approximately 0.80 kWh compressor input plus 4570 Btu (HHV) fuel input are required. Previous experience with CAES was one 290-MW-4h German plant in service since 1978. AEC's plant improves fuel consumption by about 25%, with a first-of-a-kind recuperator. AEC selected a joint venture bidder and construction proceeded on a turnkey-contract basis. EPRI provided the following: the recuperator and specialized plant-performance instrumentation and analysis; technical and engineering support to review design and construction efforts; and an engineer of record to document project progress.

Objective

o To document the engineering record of the first U.S. CAES plant from the beginning of plant construction to acceptance by the host- utility for commercial dispatch.

o To summarize general conclusions and lessons learned about the overall plant, cavern, and turbomachinery.

Approach

EPRI's site-and-field engineer documented the AEC CAES plant's construction history in an engineering diary. Additional data from a number of sources supplemented the diary. These sources included information from engineering review meetings, from plant specifications, and site visits by key EPRI and technical-support engineers. Also adding to the data were engineering audits and extensive photography of the plant during construction. The report documented lessons for both successful activities and those needing technical solutions.

Results

ACE's construction was completed in approximately 40 months. This was two months longer than scheduled and mainly due to completion delays in the electrical/control system. Cavern construction, from initial drilling to complete solution mining proceeded smoothly in about 25 months. The recuperator was installed in April 1990. Air was first injected into the cavern in April 1991. On March 31, 1991, the generator was first synchronized and the plant was accepted for commercial dispatch on May 31, 1991. Among the lessons learned from the project are the following: a turnkey-type contract, such as AEC's contract, is cost-effective; prefabricated buildings should result in cost reduction; and extensive design evaluation should focus on the impact of emergency startup/shutdown transients on recuperator, turbomachinery, and motive-air systems. Also of interest are these observations: the recuperator and motive air systems should have full-cavern pressure to avoid using large pressure relief systems; and separate controls for compression and generation shutdowns enable repairs to one system without affecting the other.

EPRI Perspective

This first U.S. CAES plant uses a cavern (solution-mined in a salt formation) for air storage. Appropriate geology (porous- media, hardrock or salt) is available in 85% of the United States. Future plants also can take advantage of improved technology through more modern cycles, such as those involving humidified air (CASH-ES). Engineers based the turbomachinery in the AEC plant on combustion-turbine technology with turbine-inlet temperatures of 1600 degrees Fahrenheit or less. As a result of EPRI-directed work with Westinghouse and Dresser-Rand, future plants can take advantage of more modern expanders with inlet temperatures up to 2350 degrees Fahrenheit compared to the AEC plant, engineers estimate this higher inlet-temperature turbine technology can lower CAES plant costs by 20%. By outlining a method to reduce CAES-plant costs with standard components, EPRI has made further information on construction and engineering available. For more information, see EPRI report TR-103209, "Standardized CAES Plant: Design and Construction."