Heinrich Kunel Replika

©1997 Brent H. Van Arsdell

©1997 Brent H. Van Arsdell

Brent H.Van Arsdell

Solar power is great, but there are other environmentally friendly ways besides PV systems to pump water, run a fan, or charge your batteries. Besides, if you live in a cloudy part of the world and you want to get off grid, you'll need a way to top off your batteries on days when the sun doesn't shine. If you're looking for a good way to supplement your home power system you should consider a Stirling engine.

Robinson Stirling Engine

Above: A Robinson type engine for low power uses.

Heinrich Kunel

Above: A Robinson type engine for low power uses.

Above: ACivil War era Rider-Ericsson Stirling cycle engine restored by Charles Mac Arthur.

A Stirling engine shares some traits with the engine in your car. Stirling engines use heat supplied from the outside rather than from burning fuel inside the engine itself. The air inside the cylinders is alternately heated and cooled to make the force that powers the pistons. Stirlings can be made to run on solar power, wood chips, cow chips, or just about any heat source you can imagine. The illustrations shows the basic principles. One end of the engine is kept hot and the other side is kept cold. In the middle of the engine is a mechanism to move the air from the cold side to the hot side.

One difficulty with understanding Stirling engines is that there are literally hundreds of different mechanical configurations. But all that really matters is that the hot side stays hot, the cold side stays cold, and the air moves back and forth between sides. When the air moves to the hot side it expands and pushes on the piston. When it return to the cold side it contracts and pulls on the piston. An Introduction to Stirling Engines, available from American Stirling, is probably the best introductory guide book available.

To get a feel for what you can do with a Stirling engine today you need to know a short history. Stirling engines were invented in 1816 by the Reverend Robert Stirling

who was a minister of the Church of Scotland. The steam engines of the day tended to explode, often killing people nearby. Stirling engines wouldn't explode.

The trouble was that in a Stirling engine, the hot side of the engine heats up to the average temperature of the flame and stays hot. Cast iron was the only material readily available when Stirling engines were first made, but when cast iron is heated to almost red hot, it oxidizes fairly quickly and the engines would break. In spite of the trouble with cast iron, tens of thousands of Stirling engines were built up until about 1914 as pumping engines, general purpose engines, or to run fans.

Free Breeze Fan

Above: Free Breeze fan runs on top of wood stove.

It just so happens that the Stirling engine cycle is the most efficient engine cycle. That doesn't mean that any given Stirling engine is very efficient, but they can be. Some research engines have reached an incredibly high efficiency of 40%. For comparison, a good car engine is about 25% efficient. Stirling engines like to run at one power setting, so applications like pumping water, running a fan, or charging batteries are a particularly good use.

Above: Ryder-Ericsson with pump, 500 gallons per hour to 50 feet.

There has been a lot of very good modern research on Stirling engines, and companies are developing them for combined heat and power applications. Two companies may bring products to the market within two years or so. South Power, a company in New Zealand, has a promising design that is optimized for heating and remote power applications along with producing auxiliary power on yachts. In Denmark, Sigma Elektroteknisk A.S. seems likely to market a Stirling engine specifically intended for home power use, but it won't be available until at least next year.

A good Stirling engine design that is available now is the ST05 G Stirling engine designed by German engineer Dieter Viebach. Herr Viebach has designed a 300 to 500 watt Stirling engine that is intended to be powered by burning wood chips, propane, or your favorite renewable energy source. Casting kits are available for under $1,000 and complete engines without burners, alternators, or cooling systems are

Key to Stirling Engine

Crank Shaft

Fly Wheel

Key to Stirling Engine

Crank Shaft

Fly Wheel

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Heat Source mMMMMMM

Heat Source

Stirling Engines

Compression Phase

Compression Phase

Stirling Burner Design

Heating Phase available for under $5,000. If you speak German or can get a German translator on the line, give him a call. Herr Viebach sells the casting kits or will put you in touch with a machinist friend who can build you a complete engine.

You may be able to find a Stirling engine solution to your home power needs a lot closer to home. Why not use an antique Stirling engine? Stirling engines (then called hot air engines) were very popular at the turn of the century for several reasons: they were reliable, safe, and could be made to run on just about any fuel. If you don't need huge amounts of power, an antique or perhaps a reproduction may solve your problem.

A down side to heating a home with a wood stove is that it can get too hot right next to the stove while the rest of the room stays cold. The Mealtime Stove company in Ontario, Canada builds a Stirling powered fan that you simply place on the hot surface of your wood stove. It will put out a nice gentle breeze that circulates the warm air through the entire room. The fan is available in the United States from the American Stirling Company.

Cooling Phase

Do you need a fan to keep cool in the summertime? Kenneth Rhodes can build you a replica of an alcohol-fired 1906 Lake Breeze fan. If you want an engine to keep a small battery system topped off, Ken can build you a scale model of a Robinson type Stirling engine that comes complete with a propane burner. He can build full size engines too.

The simplest choice for some applications may be to buy an antique Stirling engine and get it running. These engines were built

Heating Phase

Hot Air

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Expansion Phase

Revolution

Cold Air

Expansion Phase

Cooling Phase

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