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When doing the research for a article on new green products, I was unaware of many of the different ways to convert the energy of the sun into electrical power. I have written about solar cell or photovoltaic cell systems, so let’s look at another type of solar energy system.

The Stirling engine goes back to the early 1800’s, when steam was the order of the day. Steam was used to power factories, trains, and many types of work that required lots of horsepower. However, with steam came the danger of a boiler blowing up when something went wrong. Robert Stirling saw a different approach. His invention still used fire to heat the hot chamber but instead of steam, he used the heat to move pistons.

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 heat source needed to start and maintain the Stirling cycle depends on the temperature difference between the hot and cold chambers. The greater the differential between chambers, the faster the engine will operate. In some cases the difference that occurs when the cold chamber is cooled by wetting it is enough differential to start the engine.

The Stirling cycle is pretty simple. When a heat source is applied to the large end, it causes the air to expand which moves a piston. A flywheel is used to maintain movement between cycles and add a convenient place to tap the power from the engine. What is so amazing about this design is that the design is very scalable. Engines have been produced that are as small as your hand to a large as a car but the concepts remain the same.

The reason the Stirling engine works so well for a solar application is that heat from the sun can easily be concentrated to heat the hot chamber. A parabolic mirror much like that seen with the roof mounted satellite dishes is used to gather and focus the sunlight. With the sunlight focused onto the hot chamber of the engine, the temperature raises and the engine starts running. Connect the output shaft to a generator, and electricity is the product.

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

In another article on green products, I will be doing a comparison of the different types of solar energy producing products to see how they play out and if they are a viable alternative power source or just a bunch of fancy equipment.

Michael