Proof of concept, Labor of love

When we first installed our evacuated tube solar hot water system, it got me thinking about the heat we had to dump because we had to keep the water tank below 170 degrees F. The other piece of intriguing information is that these tubes could attain a temperature of 375+ degrees if the glycol solution was not flowing.
As we were enjoying the abundance of solar domestic hot water available, my mind kept thinking about other potentials for this high temperature fluid. At first, I thought about steam production to run a steam engine and in turn a generator. I have done extensive prototyping of variations of steam schemes that would make a carefree power source. I never even got close. Steam power requires constant fiddling and water freezes at 32 F., not a practical source of continuous power.
A few months went by and I remembered the Stirling hot air engine.(invented in 1816) No water, no freezing, little maintenance. Not only that, but efficiencies well above steam engines. (up to 40%) My search commenced for a model Stirling motor at modest cost.
Being a machinist and needing some mental diversion, I found a kit that requires machining to assemble from Grizzly. http://grizzly.com/products/searchresults.aspx?q=stirling&new=1
The vertical kit cost 77 bucks, the premachined kit was $164. I opted for the more challenging raw kit knowing I had to convert the metric drawings and some of the material stock to decimal inches. After 3 weeks of part time machining, I got it to a testing level. I put an alcohol burner under the hot end and waited. A little nudge on the flywheel and she started spinning. WOW!
So, I went through a procedure of timing and lubricating until I achieved a speed of 1770 RPM. Wow again. I looked at the size of the flame to the output and thought, this ain't bad.
Once I had a functional engine, I thought about how to power this thing from the sun. Previously, I thought about a huge array of tubes circulating mineral oil at high temperatures to power a more powerful engine. This engine was not in that league, so a more doable solution was needed.
I had Sunda 7 foot evacuated tube with a heatpipe delivery system. The business end can approach 400 degrees when exposed to the sun. So I made an aluminum connector (heat conductor) between the output of the tube to the input of the engine. This will conduct the gathered heat into the engine. (with the aid of a heat conductive paste) I finished up at the end of the day and frantically set up the rig on a board looking at the diminishing sun.
It was already 5:30 pm and the sun was getting weak. I waited for a few minutes and spun the flywheel. It spun eagerly but eventually stopped. Again and again I nudged it hoping for something, anything. After 5 minutes or so, I nudged it and viola, it kept running. As time went by it went faster and faster. Not as fast as the alcohol burner but an impressive seven hundred-some RPM....... Success, Proof of Concept.
The video captures this moment. The video does not capture my elation. It didn't matter that it was no barnstormer, it ran from the heat of the sun. All this work leaves me with a bit of fertilizer for my brain. What I made couldn't power even a laptop, maybe a cell phone. Got that picture in your mind? How convenient.
From here, I'll think about how to upscale this deal. It might have some application, but I'm not betting on it. It will become whatever, this is how innovations evolve.
Before you get carried away with the potential, let me list the ups and downs of this apparatus:
ADVANTAGES:
> Any substantial non-petrol heat source; solar, biomass, wood, etc
> No freezing of water
> No boiler explosions (could be a bummer)
> Relatively few parts, limited wear.
> Quiet
> Clean, external combustion process.
DISADVANTAGES:
> Low power to size ratio (large engine/heavy weight to output ratio)
> Lack of off-the-shelf parts and engines ($+)
> Low torque, unless designed to make it. (at the expense of HP)
> Continuous power/speed only, hard to throttle.
> Needs 4 cylinders to start automatically. ($+, complex)
We're not going to let this stuff stop us, are we????