In the process of doing research for an article I did on solar green products, I came across the Stirling air engine. The engine was once called a hot air engine because it requires no internal diesel or fuel to run. Let’s take a deeper look at this unique engine that requires no fuel and has recently been adapted for use on solar collector dishes.

This system is not new; it was originally conceived in 1816 as an industrial rival to the steam engine. It has been largely underutilized for the past century. With the need for renewable energy sources caused by the overuse of the fossil fuels interest has resurged in solar designs, and it is now being designed into many new solar collector systems.

The Stirling engine has many different designs, some more efficient than others. Some designs use the two cylinder Alpha design, some the Beta single cylinder design and some the Gamma design (a variation of the beta for use in multiple cylinder applications). The beta Sterling design has a single chamber with two pistons and uses a highly efficient regenerator gas as the thermal conductor.

The operation of the Stirling engine is not complex, it only requires an external heat source. Some heat sources have been fuel, while some solar designs use a Fernell lens, and the latest source is large parabolic mirrors.

Operation is simple: the gases are heated by an external source, causing the hot gas to move toward a cold chamber, in the process, a piston is driven and a flywheel rotated. To put it simply, movement is achieved from heat expansion. A few knock-offs of the Stirling engines are small enough to fit in your hand. Others system are designed to drive electrical generators. They are a about the size of a fifty-gallon drum.

The system is ideal when a concentrated heat source is applied, in this case sunlight. The sunlight is collected with parabolic mirrors and focused on to the surface of the hot chamber, causing the chamber to be heated and the engine to start. This temperatures can be very high. You know this from, when as a child, you took a magnifying glass and focused it on a piece of paper. When done correctly the paper would get dark and then a flame would appear.

The engine and support equipment is contained in a package small enough to be suspended from the end of a metal arm, much like the design of satellite TV systems but on a much larger scale. Some systems are producing 25K watts of power and have been installed and operational for a couple of years.

I will compare the different solar technologies in a later article. For now, I need to lay a foundational understanding of each of the green products used to produce power so a comparison can be made.

Michael

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