SunCatchers use Stirling engines to capture solar energy

A type of engine invented nearly 200 years ago by a Scottish clergyman may soon provide a practical solution to capturing energy from the Sun. Called the Stirling engine, it works from an external heat source, ideal for utilizing the concentrated rays of the Sun.

Originally intended to rival the steam engine, the invention of Rev. Robert Stirling never really caught on — until now. Sterling Energy Systems of Scottsdale, AZ has used the design as the basis for its innovative SunCatcher solar energy system, using the concentrated rays from reflective dishes to drive engines capable or producing 25 kilowatts each.

The first working project is set to begin operation soon near Phoenix, AZ. The project, Maricopa Solar, LLC, is a partnership between Tessera Solar and the Salt River Project (SRP) electric utility. It will use 60 SunCatcher units to deliver 1.5 kilowatts of power for the Phoenix area power grid. SRP is committed to meet 15 percent of its retail energy needs from sustainable energy by 2025.

According to a news release from Sterling Energy Systems (SES), the Maricopa solar plant will "serve as a milestone for the development of the larger commercial projects previously announced in California and Texas totaling more than 1,600 megawatts."

Each SunCatcher unit employs a highly reflective parabolic mirror that tracks the Sun to concentrate the Sun's rays on receiver tubes containing hydrogen gas. The gas goes through an exchanger to heat an internal fluid that expands and contracts to drive a four-cylinder Stirling engine. Each engine in turn drives a generator.

SES bought original solar designs from McDonnell Douglas and Boeing in 1996, and partnered with Sandia National Laboratories in Albuquerque, NM to improve the technology over the next decade. In 2008 Sandia announced a new world record for solar efficiency had been set using the SunCatcher concept at its National Solar Thermal Test Facility (read more here).

According to SES, the SunCatcher is the most efficient solar power system, yielding a higher percentage of energy than any other present solar technology. A major advantage is that the system is scalable, that is, a large installation can begin to deliver power as soon as the first cluster of SunCatchers is installed.