Converting The Sun's Heat Into Electricity

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 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.

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.

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.

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

Michael