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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.

The Stirling engine was originally invented and patented as an air engine by Robert Stirling in 1816. It may have been designed as a replacement for the steam engine, because the steam engines used in factories would explode frequently, causing many injuries and fatalities. These days, because of the cost of fuel and the environmental problems with coal, many new designs are incorporating the Stirling engine in solar power systems.

The Stirling engine is a heat engine that is vastly different from the internal combustion engine. It is highly efficient, operates quietly and is great at converting otherwise wasted heat into kinetic energy. Its only drawback is loss of power from internal fraction. The gasses (most often air) used inside the engine remain inside and are never expelled. With no exhaust valves like a gasoline or diesel engine and with no explosions from combustion, the engines run very quietly.

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.

With the space age list of available materials, the pistons in the hot chamber are much better designed to handle the high temperatures that would have fried previous generations. The new systems with the right mirror design and decent tracking systems are averaging up to 25 kilowatts of electricity

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

Michael Edwards has more interesting article on going green, checkout his green energy