The Stirling Engine is oneof those endlessly fascinating technologies. Though it can exactly approximatethe Carnot Cycle â€“ theKing of heat cycle efficiency â€“ it deviates rather substantially from the idealin practical applications. So it's no surprise that while the technology hasbeen around for a couple hundred years, and currently under study in some novelapplications like poweringa cooling fan, it's never really caught on in the mainstream.

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

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

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

Though Connor says he started the website mainly as a wayto organize his own content, it's a treasure trove of information for anyoneinterested in building a solar-powered Stirling Engine of their own, including 3DCAD drawings, aparts list, and testresults. Readers following his progress have the option to post comments onthe site.

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

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

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