When I built my new place (started back in Jan/2004) I was unable to find any commercially available CHP unit suitable. It's a long story, but thats the short version.
Anyhow, not to be put off, I built one. The design spec was that it should use "off the shelf" parts so I could maintain it, I wanted to get heat out of it for hot water and heating the house, it had to run from propane (I can't touch diesel or petrol any more - another long story), had to be remote/auto start, stop and monitored, and produce a decent, clean, stable 50Hz 240V output. It had to last at least 5 years - thats about the time I "expected" PEM/Fuelcell solutions would be viable. (ok, so I got that wrong!)
In hindsight, I still regret not getting a little rotary, but did get a 1.5 litre or thereabouts, 4-cylinder, double overhead cam, 16 valve engine from a little ford. Removed all the computer and electronics, stripped all the fuel injection off. Performed basically a LPG conversion (single fuel mixer before the throttle and inlet manifold). Replaced the fancy distributor with a more conventional one (electronic points) and coil. Added oxygen sensor, Lambda control and little gas valve in the line to maintain optimum air-fuel ratio regardless of load. Added sensor and linear actuator to the throttle butterfly to maintain the right engine speed. Built a controller to do all the remote start, stop, sequencing, monitoring of oil pressure, temperature etc, and record run hours, starts etc.
Stripped off the waterpump, the alternator and everything else that wasn't required. Added an external oil reservoir (went from 4 litres oil capacity to 10 litres - longer time between services)
Got an old industrial heat exchanger (tube in tube type) for scrap value, milled the end caps and adapted it to pass the exhaust through it to recover most of that energy.
Used a grundfos electric pump (up to 60 litres/minute) to circulate coolant through the exhaust heat exchanger, then through the block and out to my 4000 litre hot water storage.
A 1500 RPM, 14KVA, 3phase generator with AVR was coupled using a large toothed belt (timing belt, as used on drag cars for the blowers).
This thing isn't the most fuel efficient beast in the world, but it works well enough. If there was a smaller, cheap, efficient, quiet, readily available engine, I'd do this all over again using it!
