Some basics about photovoltaics

Sidebar by Slim Wolfe

Solar Energy – January 2003 – Colorado Central Magazine

Some basics about photovoltaic and other power systems

Do solar panels work under a cloud? Yes, but slowly: allow about twice the time as you’d need on a sunny day.

What about wind generators? They’re best when mounted on a 40-foot pole or tower, above ground turbulence. They vibrate and can be quite noisy, and your tower must be anchored and guyed. There are many models, starting at about $600 (for a roof-mounted unit supplying about 400 watts, which is suitable for supplemental power to a solar system), and additional gear may be required.

Generally, they kick in at about 7 mph windspeed and reach maximum output at about 28 mph.

Systems supplying 2 kilowatts when conditions are right are available for about $1,200 to $2,000 or more.

Will I need a back-up generator? Most people seem to have one, but I don’t.

What are the basic cost breakdowns? All figures are approximate:

A 120-watt PV panel: $600, 25-year life expectancy panels come in different sizes, outputs, and manufacturers; there are no moving parts to break, so they may last longer than 25 years. Figure 200-500 watts for a spartan cabin, 1000 or more watts for a conservative-use couple. You can always add more.

Batteries: A pair of Trojan T105 6-volt golf-cart units sell for $140; Trojan is considered top-of-the-line, this smaller size allows for ease of handling and best amps-per-dollar economy. But there are other options and lots of new technology. I have 5 pair for night, 10 pair for shop.

Charge controller: Keeps batteries up but not boiled away. 40-amp unit runs under $200, up to 5 panels (x 7 amps each) or 6 panels (x 6 amps each) could be used with it. Smaller-rated units are considerably less.

Inverter: 300-watt can be found for $100, runs sewing machine plus a few lights and stereo, but not a vacuum or a drill; 1200-watt can be found for under $300, will run a smaller circular saw; 3000-watt can be had for $500 or so, to run larger pumps, appliances 13 amps and over. Better inverters are quite a bit higher in price. Some appliances require “true-sine-wave” devices which are in the thousands, so know your needs.

Safety units: Heavy-duty fuse and holder connects to inverter, $60. Breakers for PV panels, $250. Lightning-arrester-diverter, $40 battery box at your discretion.

Pole mounts for PV panels: Prices vary. A couple of extra panels may be more economical than a high-tech mount that tracks the sun, a homemade hinged or double-hinged device is also effective.

Kit for assembling and anchoring and guying steel poles to build your wind-turbine mount: several hundred dollars.

Wire: At least $50, not including house wiring, 4 ga welding cable for larger inverters; 6-8 ga stranded copper; elsewhere, welding cable lugs (about $1 apiece) for secure connections.

The cowboy way: Free. After all, the new bourgeoisie is only doing what the cowboys have always done, namely, raising a huge cloud of dust in search of greener pastures. –S.W.