120 vac loads

Burke and Ben's apartment system

roof of our two story apartment building. The unbreakable panels rest on our awning, allowing easy removal to take to the beach, UCS (Union of Concerned Scientists) information tables, or PV demonstrations and speeches as well as for instant snow removal. The panels on the roof are wired for 12 Volts DC necessitating two 50 foot runs of #10 gauge Romex to the batteries. The section running through the window and to our control system is clad in conduit. A piece of scrap Styrofoam was cut to allow the conduit to pass through the window; the window closes onto the foam. The frames of the solar panels are all grounded to an eight foot copper pole sunk into the ground on the side of the apartment.


The control board and battery box lie in one corner of our living room. We have eight 6 Volt, 220 Amp-hour Exide golf cart batteries configured for 12 Volts — a total of 880 Amp-hours capacity. We decided not to ground the negative terminal of the battery. The battery box is constructed of 12 inch wafer board, and the bottom is lined with fiberglass food trays. All seams in the box are sealed with silicone rubber. Several holes were drilled near the bottom of the box to permit air to enter. It is vented with a 4 inch diameter dryer hose out a window. We cut out a piece of scrap Styrofoam that allows the dryer hose to go through; again the window closes tight onto the foam. At night and on cloudy days we plug the hole to prevent heat loss.

Control panel

All our controls are mounted on a 12 inch plywood board in front of the battery box. The positive wire from the solar electric panels runs into one side of a double pole 30 Amp square D circuit breaker and then to a steel enclosure containing an SCI charge controller. An ammeter and voltmeter are located in the cover. The power then flows through the other half of the 30 Amp breaker and into the batteries. Coming out of the batteries, the wire runs through a 30 Amp breaker connected to a 250 watt Statpower and a 15 Amp breaker connected to our DC loads. The DC loads are wired with Romex and located close to the battery box in our living room. The ac loads are distributed throughout the whole apartment connected with extension cords.

DC refrigeration

During the warm months we use a super insulated 36 quart, 12 Volt thermoelectric cooler. (The super insulation is four inches of polystyrene for an additional


R-26 insulation.) We retrofitted the cooler with a homemade digital thermostat using Radio Shack parts and some assistance from Engineering Technical Services at the university. When the refrigerator is running it consumes about 48 Watts. However, with the thermostat it only cycles on about half the time, and even less at night when no one opens it.

This unit is our largest summertime load so it is reserved for about three days per week use, depending on the weather. We are both vegetarian so refrigeration isn't a big priority. We can get fresh vegetables at a whole food grocery about a block from us, and dried beans, pasta, grains, and rice don't need refrigeration. The unit works OK for items such as beverages and foods that that are already chilled. However it takes a very long time to cool down warm leftovers and would probably not be safe for cooling down cooked meats. It is also less efficient than a Sun Frost refrigerator which neither of us could presently afford. (Someday, though!) I hope by then compressor type refrigerators will no longer contain CFCs (ChloroFluoroCarbons).

For the winter we feel we have the best refrigerator an environmentalist could ask for. This is simply a two foot high, three foot across and three foot deep box insulated to R-13 designed to set in our window. About one fifth of the unit projects outside. A small, 1.4 W DC brushless fan blow the cold outside air through the box when the temperature in the box rises above the temperature we set the thermostat to. If the thermostat is set for 33°F, for example, and the temperature outside is 40°, the fan will circulate air, keeping the temperature at 40°. If the temperature outside is below 33°, the fan will stop running as soon as the refrigerator temperature drops to 33°, thus stopping the forced air circulation and preventing our food from freezing. We use the same digital thermostat that is used for the summer refrigerator.

Two 3 inch diameter plastic dryer hoses about two feet long lead from the back of the box allowing air to enter and exit. This serves a dual purpose. First of all it prevents water from getting in. It also serves to prevent too much outside air from circulating when the fan is not running, which would cause

Above: Burke on friendly terms with the landlady of their apartment building. The Solarex Lite photovoltaic modules mark the awning of Burke and Ben's apartment in Madison, Wisconsin.

Below: Ben sends 6 Amps of DC current into the battery via a Thermax 300 Watt, 12 VDC generator (and gets some exercise while he's at it).

Ben & Burke's Daily Energy Consumption
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