REPORT #468 March 2002

Produced by the Belize Development Trust

( From Belize Culture Listserve )

There are two ways to go with solar (apart from biomass): solar PV (electric) and solar thermal. We are planning to do the latter. Use relatively low-cost solar thermal collector(s) to heat a fluid which can be stored in an insulated tank for overnight energy and run a low differential-temperature Stirling engine. Stirling engines have been around for two centuries, have a thermodynamic efficiency of the Carnot cycle (the theoretical maximum), and until recently have been largely ignored by industry. But Dean Kaman, the inventor who came out with the gyro-stabilized scooter recently, has been working on a Stirling engine during the nineties. They are not in high-volume production, hence are expensive. We plan to convert surplus chiller compressors (or similar available technology) to Stirling engine(s). Stirling engines have only a few moving parts, are reliable, quiet, and clean. Heat one end and cool the other and they run. A Stirling engine with a 1 liter displacement and 150 deg Celsius differential temperature (achieveable with low-cost solar collectors) can provide about 500 W at 50 % efficiency, compression ratio of 5, use ambient air as working fluid (really inefficient!), and run at an attainable 40 % efficiency. That's still a high output power density, way better than steam turbines.

I am also contacting several of the companies (mostly non-US) that are developing commercial fuel cell power systems for residential and small business use and volunteering to serve as a beta or protoype tester. Who knows, perhaps one of them will take us up on that offer. Someone will be the test recipient for each of these companies, why not us? It costs nothing to ask.....alll they can do is say no.

The best fuel cell site is that of Ben Wiens, the former lead fuel cell engineer for the lead fuel-cell company, Ballard, of Vancouver, BC: I signed up with PlugPower (Latham, NY) as a field test site - nothing. Maybe they don't want engineers as field testers; we might tinker with the innards.

Before recently, PEM (hydrogen) fuel cell technology was the leading contender, but the bottleneck with direct alcohol fuel cells (DAFCs) was solved, and now they are the leading contender. That's good, because ethanol is easier and safer to store than hydrogen, sugar cane can be converted to it with fermentation and distillation (no preliminary starch breakdown needed), cane is grown all over C.A., and DAFCs are not as easily fouled by contaminants as are PEMFCs. So everything is coming up roses in FCs except that they will not be in high-volume production for automobiles for a few years yet. Not a problem. Run a diesel genset (easily converted to burn ethanol) on ethanol until the fuel cells are here; then use the ethanol for the FCs with genset as backup. Ethanol chemical energy storage is easiest (cheap plastic tank) and has highest density over batteries or thermal storage. The Ewings (Ewing Energy), who are part of our Colony, build and sell (at a good price) a really rugged Yanmar diesel 5 kW genset that they have been burning converted restaurant grease in for some time. They burn nearly anything with hydrocarbon chains. (Jim Ewing, by the way, can be reached at tel: (814) 724-7736.) They have several gensets in stock, and they are new - both diesel engine and electric generator; pushbutton start is optional; hand crank standard.

I ran some calculations based on sugar cane numbers from Peter Singfield a while back and the rule of thumb is: 2 acres/person. A ten-person "colony" requires about 20 acres of cane, at 50 % processing efficiency.

So, the best energy system I can envision at this time is a hybrid system using ethanol and solar thermal for daytime use, with optional thermal backup. (Or else the ethanol can be backup.) It is cheaper than solar PV panels and batteries, which have a relatively high cost per energy stored.

Susan, I can Winzip and email you my "energy" folder. It's big. It might be better for me to dump it on CD and postal mail it. or I might send my weblink file for "energy." Whatever you want.

Dennis L. Feucht

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