Lighting IBM PC Washing Misc Power Hair DC Lighting Stereo TV Inverter
Computer Machine Tool Dryer Refrigerator 10" B&W Standby
Figure 1. The Murray's Electrical Consumption Estimate. Appliances powered by 120vac are on the left and appliances powered by 12VDC are on the right.
2,704 Watt-hours per day. This is about 1/5th of average for the grid connected American home. Roger and Ana use propane for cooking and water heating. Their 1,300 square foot home is well insulated and equipped with three systems for space heating. First is passive solar from the greenhouse attached to the south side of the house. Second is a wood fire space heater in the house's main room. And third, a propane space heater that's not often needed.
These components were selected to provide the most cost effective power for Roger and Ana. A renewable energy system is more personalized than a pair of shoes. One size does not fit all. This set of components is a specific match for their energy requirements, site and lifestyle. A system for different folks in a different location would have different amounts and types of equipment. A renewable energy system's success or failure depends on the amount and quality of the planning done before a single piece of hardware is ever purchased. Consult an individual or company with the experience necessary to see that you get the system you require without spending more than necessary.
Power Sources- Photovoltaics (PVs) & Engine
The main source of power for Roger and Ana are eight 48 Watt Kyocera PV modules. These modules convert sunlight directly into direct current electricity. Roger and Ana's array of eight PV modules produce 384 peak Watts and about 2,500 Watt-hours per average sunny day.
The 8 PV modules are mounted on a Zomeworks passive tracker. This tracker increases the average electrical output of the PV array by 25% annually. The Zomeworks trackers use the sun's heat to keep the PV array constantly facing the sun. The tracker swivels on a steel pipe set in a hole in the ground filled with concrete. The tracker has two tubes along its sides that are filled with compressed freon gas. If the tracker is not directly facing the sun, then the tubes are unevenly heated. This causes gas to move from one side of the tracker to the other. This changes the tracker's balance and it rotates to face the sun. This tracker is totally passive and requires no electricity in its operation. The Zomeworks trackers work as if by magic. Roger says one of his favorite pastimes is trying to visually catch the tracker actually moving.
As Roger and Ana's site is heavily wooded, we had to go quite a way from the house to find a good solar location for the tracker. If a tracker is to be cost effective, then it MUST have all day access to the sun. We finally settled on a clearing that required only minimal tree cutting to give the tracker all day sun. The tracker's location is about 118 feet (one way or about 240 feet round trip wire length) from the battery compartment. This long run of 12 VDC wiring required "0" gauge copper cable to efficiently transfer the low voltage energy from the PV array to the house.
The PV array is kept under control by the Heliotrope CC-60 PWM Taper Charge Controller. This device is inserted in series between the PV array and the battery pack. The function of this controller is to see that the array doesn't overcharge the batteries. The Heliotrope is user programmable and capable of handling up to 60 Amperes of array current. This controller not only protects the batteries, but also assures they are as fully charged as possible. This control works very well and we highly recommend it. See Home Power #8, page 31, for a "Things that Work!" test of the Heliotrope CC Series Charge Controllers.
Roger and Ana's system uses an engine/generator for backup power during extended cloudy periods. This generator, which Roger has used for years, is powered via gasoline and produces
4kW of either 120 or 240 vac. The generator can power loads too large for the inverter. It can also recharge the system's batteries via the charger built into the inverter. Roger and Ana's well uses a submersible 240 vac water pump to fill a large cistern which gravity flows the water to the house. The generator supplies 240 vac for the pump. Roger is investigating putting his water supply on solar too, but that's another story...
Energy Storage- Batteries
Roger and Ana's system uses six Trojan L-16W deep cycle, lead acid batteries for storing the PV produced electricity. The Trojan L-16W is a battery containing three lead-acid cells developing 350 Ampere-hours each. Each L-16W battery contains 350 Ampere-hours at 6 VDC. We combined, via series and parallel wiring, six of these batteries into a pack of 1,050 Ampere-hours at 12 Volts DC. This pack contains enough stored energy to power the system for about 5 sunless days before requiring recharging. For more details on battery sizing, recharging and maintenance see the Battery article in this issue.
One interesting feature of this system is the outside battery compartment Roger constructed. This compartment is on the outside of same wall where the inverter and ac mains panel are located inside. This allows for short wiring lengths through the wall. The battery compartment is insulated with foil backed, rigid foam insulation to keep the batteries warmer in the winter. When we were at Roger's site shooting the photos you see here, the battery compartment was a good 15° to 20°F. warmer than the outside sub-freezing temperature. The batteries stay warm because their compartment is thermally locked to the house.
Energy Conversion - Inverter/Battery Charger
Roger and Ana's system employs a Trace 2012 inverter/charger. This marvelous device converts the 12 VDC energy stored in the batteries into 120 vac housepower for appliances. This inverter is
Two views of Roger's battery compartment. Note the insulation to help the batteries stay warmer in the winter.
Photo by Brian Green
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