Renewable Energy From An Old Concept

During the process of researching an article about green products on photovoltaic cell systems (solar panels), I came across another way to convert the sun's light into electricity. So let's take a 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.

Sense its incarnation there have been many variations of the Stirling engine and many patents. The engine's simple design demands tinkering - everyone wants to add or change something to make it better. The engine has very few moving parts, requires only a single external heat source, is very efficient, and is quiet. With the new space age materials available, the problem of piston overheating is no longer a problem like it once was.

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 better-designed engines and new types of material, a movable (tracking) parabolic mirror, and a single Stirling engine you can produce 25 kilowatts of electricity.

In a future article about green products I will list the different solar technologies and how they compare to the competition.

Michael