A DIY Solar-Powered Stirling Engine

The Stirling Engine is one
of those endlessly fascinating technologies. Though it can exactly approximate
the Carnot Cycle  â€“ the
King of heat cycle efficiency â€“ it deviates rather substantially from the ideal
in practical applications. So it's no surprise that while the technology has
been around for a couple hundred years, and currently under study in some novel
applications like powering
a cooling fan
, it's never really caught on in the mainstream.

Which makes it just the sort
of intriguing design challenge Engineer Doug Connor was looking to take on in
his spare time. He's learning more about the technology by building a working prototype
of a small (desktop) engine powered by sunlight, taking measurements and
figuring out how to improve the performance.

"A Stirling Engine is very
simple in construction – you've basically got two pistons and a piston and a
displacer," he says. "But the simplicity in the way it functions
notwithstanding, the simulation and analysis of one can be quite difficult."

He's capturing the diabolical, nature of the task on his
website, www.solarheatengines.com, where
he has been documenting the steps he's taken to simulate, analyze, design,
build and test a small solar-powered engine. See
photos and watch a video of his most recent design

Though Connor says he started the website mainly as a way
to organize his own content, it's a treasure trove of information for anyone
interested in building a solar-powered Stirling Engine of their own, including 3D
CAD drawings
, a
parts list
, and test
. Readers following his progress have the option to post comments on
the site.

Even if you have no plans to build a Stirling Engine, it's
a fun site to troll and get a behind-the-scenes peek at real-world design under

Connor's ultimate goal is to build something practical, and
what that ultimately comes down to is figuring out a way to scale his model and
deliver more power without driving costs up. "I showed a development engine
with a power output of about 0.1 Watt," he says, describing his experience at the Maker Faire
in Northern California in May 2008. "If I can
increase the output to 1,000 times that, I think the interest is out there."

YouTube has some great videos of small Stirling Engines in
action, like this coke can
Type in "Stirling Engine" on YouTube to see more fun stuff.

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