Living off the Grid, Part II: Northern Exposure

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Kip mounted the solar array on an aluminum rack purchased with the modules. The rack was pieced together and the modules fixed with 1/4 x 20 stainless steel screws and nuts. During the course of the day, the solar array may be turned a few times in order to catch the maximum amount of sunlight, so the rack is fitted with casters to permit movement.

Kip then proceeded with wiring the modules together. The back of each panel has a positive terminal at one end and a negative at the other, and each produces 48 watts of 12-volt, DC power. The terminals are then connected and eventually the wires meet in a main, waterproof junction box. The junction box is then connected to the electric components in the basement. How Kip wired his modules together made things more convenient for both him and his wallet.

It helps to think of electricity in a wire as water in a pipe. The wattage can be compared to the power of a moving stream of water. A volt is a measure of pressure and an amp is equivalent to the number of gallons flowing per minute. The wattage is always equal to force (volts) times flow (amps), or watts = amp • volts.

Kip could simply have wired all the positive terminals together with one wire and all the negatives together in another (parallel connection), which would have produced 600 watts at 12 volts and 50 amps. That would have been fine except that once the wires from the modules met in the junction box, very heavy and expensive wire would have been required to transmit those 600 watts of power at such a low voltage from the junction box to the basement. Wire size is always determined by voltage and current, and the lower the voltage and the higher the current, the more conducting material (usually copper) and thus heavier wire you'll need.

In order to avoid going broke on wire alone, Kip wanted to double the voltage coming from the array and decided to pair off and connect his modules in a hybrid of series and parallel ( see for series diagram ; above left for junction box). He used #10 UF single conductor wire for both the series and parallel connections. By always using black wire for the positive terminals and white for the negative, Kip avoided any polarity confusion during installation. When he was finished wiring his array in series, Kip was still getting 600 watts of power from his panels, but the series connections doubled the voltage to 24, reducing the amount of amps to 25. He was able then to use a 50-foot run of #6 THHN wire from the junction box to the powercenter in the basement. Kip used two junction boxes on the array of solar panels, each connecting three pairs of modules and each running a pair of #6 THHN wires to the powercenter. All the wire connections in the main junction boxes are through a split bolt connector.

Power Equipment Installation

1. The two positive and two negative #6 THHN wires are connected to the Powercenter using a convenient connector called a box lug. A box lug is a simple kind of shackle that houses a receptor hole and a tightening screw on top (see diagram on page 52). All that's necessary is a stripper to bare a short length of copper wire, which then goes in the receptor hole. The box lugs will accommodate many different gauges of wire, are color coded so the positive and negative terminals are always clear, and require no crimping tools. Box lugs are so convenient, in fact, that they are used throughout the electrical components in Kips basement.

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