Portland, Ore. -- 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.
"We now have six research dishes online at Sandia National Labs running completely autonomously, turning on and tracking the sun across the sky even on unattended weekends," said Bob Liden, vice president and general manager of Stirling Energy Systems. "We have the first 40-dish 1-megawatt farm started there and plan to have it in operation by 2007."
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.
A Stirling engine converts heat into the mechanical motion of the pistons without burning fuel; no combustion takes place. The hydrogen gases inside the engine are sealed and never leave it, making the engine very quiet.
Setting the pistons in motion
The system is closed to the air, with a single connecting pipe between the piston's chambers. The heat of the sun is focused from the system's 82 mirrors onto tubes feeding a piston's chamber. As the first piston is heated, pressure goes up in the chamber, forcing the piston to go down. The second piston rises on its crankshaft, and through the connecting tube, cooler gases enter and cool off the heated chamber. As the first chamber cools, the first piston rises on its crankshaft, driving the cool piston back down. Then the cycle repeats.
Mechatronics enables three control systems to coordinate their behavior for unattended optimal performance even under changing conditions.
By monitoring and adjusting the flow between the system's heating and cooling chambers, the Stirling engine control system keeps the engine running at a constant temperature and power output of 1,800 revolutions per minute directly into a 25-kilowatt 480-volt ac generator.
The farms were perfected in Sandia National Laboratories' New Mexico desert test site under a Department of Energy program.
The DOE predicts that by 2011, Stirling solar dish farms could deliver electricity to the grid at costs comparable with traditional electricity sources. The power would come from more than 70,000 solar dishes in the Imperial Valley and Mojave Desert that would deliver more than 1,750 megawatts to southern California's grid.