A solar powered Stirling engine is a heat engine powered by a temperature gradient generated by the sun. Even though Stirling engines can run with a small temperature gradient, it is more efficient to use concentrated solar power.
The mechanical output can be used directly (e.g. pumps) or be used to create electricity.
NASA patented a type of solar-powered Stirling engine on August 3, 1976. It used solar energy to pump water from a river, lake, or stream.[1] The purpose of this apparatus is to “provide a low-cost, low-technology pump having particular utility in irrigation systems employed in underdeveloped arid regions of the earth…[using] the basic principles of the Stirling heat engine“.
One design was patented by Roelf J. Meijer in 1987.[2] His invention combines a heat engine, such as a Stirling cycle engine, with a solar dish collector to produce electricity. This apparatus consists of a large dish that concentrates solar energy to a focal point at the center of the dish. The concentrated solar energy drives Stirling cycle engine, which operates by letting heat flow from a hot source to a cold sink to do work. The work output of the Stirling cycle then drives a generator to create electric power. Moreover, for optimal heat collection, Meijer’s solar-powered engine requires that the dish always point directly at the sun so no shadows are in the solar dish collector. This presented issues because, for the apparatus to have a complete range of motion, lubrication and rotational systems are necessary, and may compromise structural stability.
Around 2010, a company called Sunvention Solar Energy created a device similar to the NASA design that they say can pump 100,000 gallons per day, purely off of solar energy and the Stirling cycle, and costing only US$1,250. This apparatus, much like the others, used a large solar dish to collect heat from the sun to create a high temperature source, and also used low temperature water from a nearby stream as its low temperature source. This provided a great temperature range, which in turn provided more power. The apparatus pumped the water into nearby crop fields, providing a “low-cost, low-technology pump having particular utility in irrigation systems employed in underdeveloped arid regions of the earth.”
Solar-powered Stirling engines are in some situations more efficient in generating electrical energy than solar panels.[3] Thermal capacity and rotating mass result in less sudden changes in output power. Experiments show the possibility of higher efficiencies.[4]
Solar-powered Stirling engines are less scalable than solar panels.They are also more complex than a solar-electric system.
Solar-powered Stirling engines can have a secondary heat source (e.g. Gas), allowing operation during night and when the sky is clouded.