The Wizard's MicroPV System Richard Perez High in the snowy mountains of Oregon, the Wizard lives in a mushroom shaped dome. His small round home is about eight miles from the commercial electricity. He makes all the power he needs with a single photovoltaic panel. The Wizard's system is a prime example of what can be accomplished at very low power levels, and at very low cost. Micro Consumption = Micro System The Wizard's needs are small. He lives alone in his small cabin. The appliances in his system reflect his choices for electrical power. The main appliance is a single incandescent car tail light. This light consumes about 26 Watts (Å2.2 Amps. at 12 VDC) and is operating about four hours per day (the Wiz reads alot). The second appliance is a Shortwave/FM/AM radio receiver. This Sony radio works on 9 VDC and the Wiz uses a DC/DC converter to lower his system voltage for this radio. The radio only consumes 1.8 Watts (0.15 Amps at 12 VDC into the converter) and is operated for about eight hours per day. The third and last appliance is a coffee grinder that the Wiz powers via his small inverter. Total average power consumption for this system is about 120 Watt-hours daily. Power Source- PV This system uses a single ground mounted Kyocera J48 PV panel as its ONLY power input. There are no generators in this system. The PV panel produces about 3 Amperes of current under full sun. At the Wiz's location it makes about 200 Watt-hours daily on average. The single PV panel actually produces about 80 more Watt-hours daily than the Wizard uses. This overproduction helps refill his battery quickly after several cloudy days in a row. The panel is mounted on an EchoLiteª adjustable PV rack. The mount is fastened to a heavy wooden base which merely sits on the ground. Since the Wiz's dome is not in a good location for PVs (big shade trees all around), the panel had to be located about 75 feet from the dome. The heavy mounting base is movable and the Wiz can position his panel in different places for different seasons. This way he can work his way around the shade trees. The panel is wired to the battery directly with 10 gauge copper wire with UF insulation. There is a 20 foot loop of wire next to the panel so that it can be repositioned in a wide area. INSERT PHOTO The Wizard's mountain dome. This dome is a twelve sided stressed plywood building with a floor area of 180 square feet. The only wood above the floor is 3/8" plywood, no structural lumber was used above the floor. This dome has been withstanding the rugged Oregon weather since 1972. Also shown in this photo are the PV panel, and Buckwheat, a renewable energy powered security system. Photo by Richard Perez. Power Storage - Nicads The Wizard uses nickel-cadmium cells for power storage. This battery is composed of ten Americad HED-120 (high rate) cells wired in series. These are reconditioned nicads from Pacific West Supply in Oregon. The resulting nicad battery has a capacity of 120 Ampere-hours at 12 VDC. This battery stores enough power to last the Wizard for 12 sunless days in a row. While cloudy periods of four or five days are common here, cloudy periods longer than a week are very rare. The battery and PV system has no regulator. The only appliance in use during the day is the radio whose DC/DC converter will run at up to 32 VDC input. Hence no regulation is required because the charge rate of the PV panel (3 Amperes or a C/40 rate for the 120 Ampere-hour battery) is too low to damage the nicads. Voltage in this system gets up to 16.5 VDC on a sunny day when the nicads are full. This is fine with the nicads which bubble merrily along. The only problem encountered by the Wiz was slightly increased distilled water consumption by the cells. In the days before nicads were affordable, the Wizard used a motley assortment of lead-acid batteries. The Wizard says the nicads provide brighter incandescent light at night, less voltage depression under load, and vastly reduced "mopping up" of the cells' tops. He is very pleased with the nicads performance in his system. INSERT PHOTO The ten Americad HED-120 nickel-cadmium cells powering the Wizard's system. These reconditioned, high rate cells probably saw original service starting a diesel locomotive or such like. Now they store solar electricity. Photo by Brian Green. Power Processing - Inverter This system uses one of the new Powerstar 200 Watt inverters. Since there is a review of this inverter in this issue, I'll be brief here. This inverter converts the 12 VDC stored in the nicads into 120 vac for use in conventional appliances. The 200 watt size is ideal for the Wizard as he only uses the inverter to power a coffee grinder. Actually, the inverter is large enough (as is the rest of the system) to power larger appliances, but the Wiz ain't interested. What did it all cost? The table and chart below detail the costs of this microPV system. At around a thousand dollars, small PV systems can effectively power lights and communication in a mountain cabin. And without a generator around! INSERT ART Stand-alone PV lessons learned The Wizard has learned several lessons about using PVs as the only power source for a system. While the Wizard's system is very small, the concepts and proportions involved here apply to all systems regardless of size. ¥ The PVs should produce at least 50% more power than is consumed daily. ¥ The battery should store at least ten days of power. ¥ Keep the system simple. Parts left out cost nothing and cause no service problems. Access For more info on this microPV system, please write: The Wizard, C/O Home Power, POB 130, Hornbrook, CA 96044.