The dish/Stirling system is a renewable energy source that generates power by using parabolically arranged mirrors to reflect sunlight onto a small focal receiver, thereby heating a gas chamber connected to a piston and drive shaft. The drive shaft powers a generator which produces electricity to be distributed to a grid.
Unlike conventional photovoltaic (PV) solar cells which register at between 10% and 18% efficiency, dish/Stirling systems are capable of converting around 25% of available energy from sunlight into electricity. Dish/Stirling systems are commonly called Solar Thermal Electric systems, to distinguish them from conventional solar panels. Dish/Stirling systems are mounted on motorized pedestals programmed to ensure the mirrors continue to face the sun throughout the day.
A dish/Stirling system includes two components; the solar dish, which is simply a parabolic mirror or set of mirrors, and a Stirling engine, a closed-cycle engine that operates silently using any heat source. Efficiency for the Stirling engine approaches maximum theoretical efficiency for any engine, known technically as Carnot cycle efficiency.
The Stirling engine uses a fixed volume of gas that never leaves the chamber. An alternating heating/cooling cycle ensures that there is a constant supply of cooled gas to be heated by the thermal energy source. Since there is no exhaust in a Stirling engine, they are ideal for use on stealth vehicles such as submarines. Because Stirling engines can produce electricity using any thermal energy source, dish/Stirling systems sometimes use combustion to generate heat during the night when no solar rays are available.
The Stirling engine was patented by the Scottish minister Robert Stirling on September 27, 1816, though the engine was not used in serious applications until the turn of the century. A typical dish/Stirling system today delivers a kW of power per square meter of mirror used. In late 2004, Sandia National Laboratories, in cooperation with Stirling Energy Systems, Inc., built a small prototype dish/Stirling power plant that generates enough electricity to power more than 40 homes. The prototype plant cost almost $1 million but research scientists assert that once in production, plants of similar size could cost as little as a third their this cost, making dish/Stirling systems competitive with more conventional electricity-generating systems.