The U.S. utility Pacific Gas and Electric Company (PG&E; San Francisco, California), a subsidiary of the PG&E Corporation, in December 2009 disclosed that it had contracted with a subsidiary of Santa Monica-based SolarReserve LLC for a capacity of 150 megawatts (MW) for clean solar power. According to Jonathan Marshall, Chief External Communications at PG&E Corporation and Managing Editor of the company's online publication "Next100.com", the proposed Rice Solar Energy (RSE) project will be augmented by a proven energy storage system based on molten salt. The plant is expected to be able to produce enough renewable energy for the supply of more than 60,000 average homes, starting in 2013.

A handful of companies in the solar industry are using high-tech versions of thermal storage to stabilize the output of their power plants when clouds pass overhead or when the sun goes down.

Thousands of mirrors to concentrate sun's rays onto tower-mounted receiver

If approved by state regulators, SolarReserve's power plant will be located near the unincorporated community of Rice in San Bernardino County, California. It is to use thousands of large, movable mirrors to focus the sun's rays onto a receiver in a central tower to heat four million gallons of molten salt to more than 1,000 degrees Fahrenheit (500 °C). The hot, liquid salt will flow into a storage tank and is used to heat water for a steam generator to produce electricity. According to Marshall, the stored molten salt can also provide energy during periods when sunlight dims or is not available. The ability to store heat and tap it at any time for power generation is comparable to having a huge battery or backup generator on hand to smooth out peaks and valleys of solar generation. The storage technology has been successfully demonstrated over several years in the 1990s at the U.S. Department of Energy-sponsored "Solar Two" power plant in Southern California.

Molten salt for heat storage proven technology, is being used worldwide

Molten salt is currently being used for thermal storage at the 50 megawatt (MW) capacity "Andasol 1" solar thermal power plant in Spain, the first of three sister plants designed by Solar Millennium. Abengoa Solar also has a molten salt demonstration plant and plans to use the technology in a 280 MW solar thermal power project in Arizona. Marshall reports that other companies have also expressed an interest in molten salt thermal storage, such as the Spanish company Sener and SkyFuel, based in Albuquerque. Sandia National Laboratory in Albuquerque says molten salt is ideal for capturing solar energy in power towers "because it is liquid at atmosphere pressure, it provides an efficient, low-cost medium in which to store thermal energy, its operating temperatures are compatible with todays high-pressure and high-temperature steam turbines, and it is non-flammable and nontoxic." The original commentary may be retrieved under the URL www.next100.com.

2009-12-29 | Courtesy: www.next100.com | solarserver.com © Heindl Server GmbH