Simpler Solar Power

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All PV modules produce less electricity the hotter they become, but the output reduction for amorphous PV is about half as much as it is for crystalline PV. If you use framed crystalline PV, mount the array 3 to 6 inches off the roof so it stays cooler.

The upfront cost for UniSolar’s amorphous PV is high because of the roofing to which it is bonded. But if you are putting amorphous PV on a new structure or are re-roofing an existing structure, then UniSolar standing-seam modules probably are a good choice. As PV production increases, the price of amorphous should decrease to less than crystalline modules.

The Rest of the System

The only other major component of your grid-tied nonbattery system is the inverter. The inverter changes the direct current (DC) created by the PV into the alternating current (AC) we use in North America. In a battery system, the inverter usually is sized for the maximum potential demand of your home during a power outage — and that typically makes it much larger and more expensive than nonbattery inverters that only have to be sized to handle the power produced by the PV system. The new generation of certified grid-tied, or “grid-interactive,” inverters seems reliable, but you probably should choose a high-voltage DC inverter because they are less expensive to wire. (Low-voltage inverters only are necessary under a couple of specialized conditions, where you have more than three solar arrays, persistent shade or batteries.)

Inverter power ratings refer to the maximum continuous output. As a rule of thumb, the most cost-effective nonbattery grid-tied inverters are in the 2- to 6-kilowatt range.

The Solar Payoff

The time it will take for your system to pay for itself depends on the amount of sunshine in your area; the cost of the system; local electric rates and future inflation; your state’s metering laws; your system’s type and size; and rebates and tax credits. A good installer should be able to work out all these variables for you on paper. Or once you have a system price quote, you can download the spreadsheets www.MotherEarthNews.com/downloads/simplesolar to calculate your approximate payback period and return on investment. “Payback” is the number of years it takes for your electricity savings to equal the system’s cost and maintenance.

If you live in an area where net metering is not available, a solar electric system for your home probably won’t pay for itself during your lifetime, unless the declining supply of coal and oil causes unprecedented increases in the cost of electricity. Your money may be better spent on energy- efficient home improvements.

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