A Scottish clergyman seems an improbable person to be an inventor, but Robert Stirling combined the two callings. In 1816, Reverend Stirling patented an engine that took his name.
Heating and Cooling Key to Engine
The simplest version of the Stirling engine has a sealed cylinder that contains a gas, usually hydrogen or helium. When the cylinder is heated from the outside, the gas expands and pushes a piston. When the gas is cooled it contracts and the piston returns to its original position.
With two cylinders linked to work in tandem, the power output of the Stirling engine is improved; one cylinder is cooling the gas while the other is heating it.
This Stirling cycle uses an external heat source, which could be anything from gasoline, to solar energy, to the heat produced by decaying plants.
Stirling Engines are Quiet but Slow to Start
The gas used inside a Stirling engine never leaves the engine, hence it is sometimes called an external combustion engine. There are no exhaust valves that vent high-pressure gases, as in a gasoline or diesel engine, and there are no explosions taking place. Because of this, Stirling engines are very quiet; they are also sluggish.
A Stirling engine takes a while to warm up before it starts producing power, and it also can’t change its power output quickly. This has restricted the usefulness of the Stirling engine to a few specialized applications, such as auxiliary power for yachts or in submarines.
Not surprisingly, the Stirling Engine Society in the United States thinks there’s a bright future for the invention: “Although there hasn’t been a successful mass-market application for the Stirling engine, some very high-power inventors are working on it.”
Global Warming Makes Stirling Engines more Popular
But, today, there is a renewed interest.
The need to cut greenhouse gas emissions has people looking for cleaner engines than the ones in cars and trucks now. Scores of people have been tinkering with Stirling engines to improve them. Models have been built that can churn out 500 horsepower with efficiencies of 30 to 45 percent. Regular gasoline engines are only 20 to 25 percent efficient. Even though the experts say the Stirling engine is unlikely to be viable as a vehicle power source it does have other applications.
World’s Largest Solar Farm to use Stirling Technology
According to an article on the Pure Energy Systems Network website (August 11, 2005) Stirling engines are being used in a 20,000 solar panel installation in Southern California:
“Combine a Stirling engine with solar as the source of heat and you have a highly efficient means of converting solar power into usable energy.
“That is what Stirling Energy Systems has been perfecting for the past 20 years.”
The technology uses solar power to operate a Stirling engine, which then rotates the collector panels to “keep the Sun’s rays focussed at greatest intensity possible.”
An old technology with a new application may revive the popularity of the Stirling engine.
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