A Solar Engine: Run an External Combustion Engine on Solar Power

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PHOTO: MOTHER EARTH NEWS STAFF
This external combustion engine runs on solar energy.

We all know (or should know) that the internal combustion engines in our automobiles, tractors, lawn mowers, etc., are called “internal combustion” engines because they combust (burn) their fuels internally (inside the powerplants).

And a few of us even know that the old-timey steam engine is an external combustion engine . . . because its fuel is burned outside the cylinders in which its drive pistons operate.

What a good many of us don’t know, however, is that — over the years — [1] a number of other kinds of both internal and external combustion engines have been invented, [2] one of these external combustion powerplants operates on something known as the “Stirling cycle,” and [3] inventor John Ericsson built and successfully ran a Stirling engine on nothing but sunshine away back in 1872. (See. And you thought all this solar energy business was something new!)

At any rate, MOTHER’s researchers recently bought a very small Stirling-cycle engine for $31 from Solar Engines. And, after running it with heat from an external alcohol flame for a while, someone said, “Hey! I betcha we could operate this little dude on solar energy.”

Well, we just happened to have a 1-square-foot Fresnel concentrating lens handy. So the guys in the shop quickly rigged up a little frame of scrap lumber to hold the lens and the tiny powerplant so that when the former was aimed at the sun it’d focus a hot spot directly on the latter’s drive cylinder.

  • Published on May 1, 1978
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