Solar-powered Stirling engine

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“.^[1]

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.^[2] 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 a Stirling cycle engine,^[2] which operates by letting heat flow from a hot source to a cold sink to do work.^[3] 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.^[2]

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.^[4] Thermal capacity and rotating mass result in less sudden changes in output power. Experiments show the possibility of higher efficiencies.^[5]

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.

• Solar thermal energy#Dish designs
• Stirling Energy Systems