Notes from Windward: #68


Parabolic Trough Solar Collector

  April 21:

     While we plan on deploying a wide range of renewable energy options to supply Windward's year-round energy needs, we expect to generate the bulk of our energy using parabolic solar trough collectors. Since Windward averages better than 200 sunny days a year, and an insolation of a kilowatt per square meter, PTSCs are an attractive, low-cost way to generate heat and power at the village level.

a field of PTSC's

     You don't hear a lot of talk about PTSC systems, but they've actually been on-line and generating power for more than a decade--it's a mature technology well suited to meeting a community's energy needs. Like wind power, the primary expense comes in the up front cost of construction, thereby making this an ideal opportunity for some creative re-use.

Annie drills the edge tubing to match the keel

     Twenty years ago, most home satellite dishes were 10 1/2' in diameter, a size long since replaced as the signals moved up to a higher-frequency, thereby allowing them to be work with the smaller dishes that you see these days. Although they're long out of date, there are a lot of them out there standing their lonely vigil in the countryside--just waiting to be re-incarnated as solar energy systems.

     In order to make a parabolic trough, the first thing you need is a frame to shape your reflector into a parabola. Fortunately, the arms that form these obsolete spherical dishes can be disassembled and reassembled on a central keel to create the trough shape we need.

T-Rex takes shape

     As the trough began to take shape, Annie observed that it was looking a bit like Tyrannosaurus Rex's rib cage, so we've taken to calling this design, "T-Rex". When complete, the trough will focus more than seven square meters of sunlight on a mono-tube boiler to provide steam for the PowerLab.

  June 4:

     Finally tracked down an source for some surplus 4'x10' 24 guage galvanized sheet metal to form the trough's reflector. These days it's not just the higher price of materials that has to be dealt with, it's also the increased cost of transporting large pieces of metal.

Orly tries out an air rachet gun

     But before we could take the work truck to town to pick up the steel, we had to first deal with the fact that we hadn't got around to replacing its snow tires with summer wheels. The tires had been mounted using heavy air ratches by the guys at Les Schwab, a really incredible dealership that's always taken great care of us, with the result that getting the tires off was a bit of a challenge.

it took Orly's full weight to break the lug nuts loose

     When neither the large star wrench nor our air ratchet could break the lug nuts loose, we raised the ante by getting out the 3/4" socket set. By jumping up and down on the ratchet handle, Orly was finally able to loosen the nuts. After that, the air ratchet made short work of the task of removing the snow tires and mounting the summer tires.

sheets of 24 guage galvanized steel

     With the truck road-legal again, we headed to town dropping off a load of trash at the transfer station, picking up a ton of hay for the sheep and goats, and four 4'x10' sheets of galvanized steel to use to form the actual refectors for the parabolic trough. That's enough steel to focus 14 kilowatts of heat on a sunny day, and this time of year, we have lots of those.

Notes From Windward - Index - Vol. 68