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The Size of Your System Relates to Energy Efficiency

The first step in sizing your solar system is to reduce any unnecessary power usage in your home. By doing so, you can purchase a smaller, less expensive system that will save money on the upfront cost and still make your home more energy efficient. Your local utility can be a good resource for energy efficiency tips, and it often gives rebates for replacing major energy-wasting appliances with more efficient ones such as Energy Star-rated appliances (www.energystar.gov). To reduce your consumption by half is just as good for the Earth as providing half of your energy needs with a solar system — and it’s easier on your pocketbook.

How Much Electricity can you Create?

To estimate paybacks or returns on investment, first you need to predict the amount of electricity your PV system will generate. For the simplest systems with fixed PV, minimal shading, reasonably good orientation, inclination and annual net metering, this is easy to estimate. Multiply your local annual “noon sun hours per day” (keep reading) by your PV wattage. Reduce that figure by 15 percent to 30 percent to compensate for less-than-perfect system efficiency. Now divide this total by 1,000 for the total kilowatt-hours produced by your system.

A typical value for “noon sun hours per day” in the Midwest is 4.5. In the Sun Belt, this value is slightly higher (above 6 in some areas of the desert) and in the extreme Pacific Northwest to the Upper Midwest and through New England, the value is about 4 or slightly lower. To find the average amount of sunshine in your area, go to rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/state.html. In some locations (California, for example), the electric rates vary with the season.

Learn More about Solar

Power in Mother’s Archive

Mother’s Archive contains 35 years worth of articles highlighting the hard work and creativity that characterizes the back-to-the-land lives of Mother’s readers. To read these articles, including those about solar power listed below, go to www.MotherEarth News.com and click on the “Renewable Energy” link. From there, you can view a list of the most recent articles. You also can scan the whole archive by entering the keyword “solar” into the search function.

December/January 2005, No. 207
“Affordable Super Solar Homes”

August/September 2003, No. 199
“Plug into the Sun”

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