Stirling Engine Solar Power Contracts Approved

An unprecedented deployment of concentrated solar thermal in California took one step closer to becoming a real project this week as state regulators gave their approval for the power purchase agreement. Completion, however, will hinge on other factors, including construction of a new proposed 100-mile long, high capacity transmission line that could cost as much as 1.4 billion dollars.

The California Public Utilities Commission (CPUC) has approved San Diego Gas & Electric’s (SDG&E) contracts to purchase 300 MW of solar power, with the potential to grow to 900 MW within 10 years. The project will be one of the largest solar facilities in the world when fully constructed and the first commercial deployment of Stirling engine-based solar concentrators. SDG&E will purchase the solar energy from Arizona-based Stirling Energy Systems. SDG&E and Stirling have agreed to a 20-year contract to first purchase 300 MW from Stirling’s SES Solar 2 facility, home to a series of Stirling solar dishes to be developed on approximately three square miles in Imperial Valley, Calif. The Stirling solar dishes use a mirrored array to focus the sun’s rays on a modern Stirling engine. Stirling engines, originally developed in 1816, have four sealed cylinders containing hydrogen or helium. When a cylinder is heated by the sun, the gas expands and pushes a piston; when it cools, the piston retreats. The mechanical action turns a generator and produces electricity. Because the cylinders are sealed, Stirling engines do not produce emissions. SDG&E has options on two future phases that could add an additional 600 MW of renewable energy and capacity to SDG&E’s resource mix. Solar energy is generally abundant during the hottest parts of the day, making it available to meet peak demand from customers. SDG&E said the Stirling projects will require additional transmission facilities to be built to bring the energy to SDG&E customers. Just days before this announcement, SDG&E filed with the CPUC explaining the need for a major new transmission line stretching over 100 miles between the San Diego region and the Imperial Valley — by 2010. SDG&E said the proposed transmission line would help to guarantee delivery of the full potential of this solar contract. SGG&E estimates the line will cost $1 billion to $1.4 billion but that the exact costs will be determined once a final proposed route and an alternate route are submitted to the CPUC in mid-2006. There was no indication whether their involvement with this new transmission line, which they’re calling the Sunrise Powerlink, would be accompanied by a CPUC request for approval of ratepayer increases. “The CPUC’s approval of our contracts is a win-win situation for our customers and the communities we serve,” said Terry Farrelly, vice president of electric and gas procurement at SDG&E. “The project will provide clean, renewable solar energy and move us closer to achieving our goal to supply 20 percent of our customers’ needs from renewable resources by 2010.”
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