Stirling Energy Systems, fresh from signing a major deal with Southern California Edison for the construction of a 4,500 acre Stirling engine solar power farm, has just locked up another regional energy giant: San Diego Gas & Electric. SDG&E has just agreed to buy 300MW of power from another Stiring Energy Systems farm, with the option of expanding to 900MW. If the full installation goes forward, the Stirling farm would produce 10% of SDG&E's total power capacity -- a big step towards the company's goal of 20% renewable energy production by 2010.
The SCE Stirling farm was to be the largest solar power array in the world; the full SDG&E plan would be a bit larger, and would result in California being home to nearly two gigawatts of non-photovoltaic solar power production within the next decade.
(Via Green Car Congress)
There are two main types of Stirling engine design: the free-piston machine and the crank-driven machine. Crank-driven machines get the power out by connecting the piston to a crankshaft. This connection requires sliding seals (between piston and cylinder wall) that are NOTORIOUS for leaking. Stirling Energy Systems is using high-pressure Hydrogen as a working fluid, also NOTORIOUS for leaking from anywhere you try to contain it. Crank-driven machines are notorious for sealing, lubrication, and reliability problems.
Free-piston machines basically make the piston out of magnets, and wrap the cylinder with wire coils (this is a gross oversimplification) but the point is, there's no crankshaft. The whole pressure vessel is hermetically sealed (essentially welded shut). This design eliminates not only the lubrication problem but also the sliding seal problem and should provide much better reliability and inherently longer mean time between failures.
Stirling Energy Systems was originally an R&D arm of SoCal Edison until it was sold to a private owner in 1996, so it is natural that SoCal Edison would want to work with a familiar design and group of people to fill its Renewables Portfolio Standard.
But if you read "The Next Great Thing" by Mark Shelton, you can see that stirling engine companies have been undercut by illusory big breaks like this before. A big computer corporation invested hugely in Sunpower, Inc. to develop a Stirling-powered microchip cooler in the 90's, then cut the program, when a competing computer company also cut their Stirling-cooler program. The computer company decided to sit on the license, in case they might need it for some competitive reason in the future, so that Sunpower couldn't sell the successful cooler they'd developed, to this company or anyone else.
How many megawatts of crank-driven machines need to be installed before the sealing problems become evident and the world decides, "Solar Stirling didn't work", and the utilites can say, "Well, we tried!"
Has anyone seen any evidence that these utilites did a thorough technical review before choosing their Stirling engine provider?
What can we do, to ensure solar is given the best possible chance, and the best possible technology is employed, rather than allowing the utilities to sign with the easiest contractor, just to fill their renewable portfolio standard?