A project to generate electricity from solar energy using a Stirling engine looks to create farms that will light and cool the households of millions of California customers, at a cost that by 2011 may rival what traditional sources are charging. The technology originated when Stirling Energy Systems Inc. agreed to supply Sandia National Laboratories with solar dishes in return for Sandia's addition of mechatronics to allow the dishes to track the sun. Together, Sandia (Albuquerque, N.M.) and Stirling Energy Systems (Phoenix) designed a 1-megawatt solar power substation capable of direct connections to the existing U.S. power grid. From 2007 to 2010, the Sandia program will perfect methods of ganging the substations into successively larger groups, operating at increasingly higher voltages. In California, the state government has mandated that utilities invest in renewable energy sources for at least 20 percent of their power by 2010.