Early next year, dozens of huge, concave mirrors will begin to sprout on a desert farm northeast of Los Angeles. Each 37-foot-diameter Stirling dish will electronically track the sun and reflect its rays onto a heat collector, where the concentrated sunlight will superheat hydrogen to 1,300�F, driving an electric generator by Stirling engine. Once the world´s largest solar-energy farm is completed, some 20,000 dishes will stretch over 4,500 acres of the Mojave Desert, producing power for up to 278,000 homes.