After setting your budget, it's time to look at your average insolation. Insolation is a measure of how much sunlight your home gets (or your neighborhood gets) over the course of a typical day, and a typical year. It's most commonly measured in Watts/square meter for commercial applications, and for residential, in terms of "sun-hours". You find good insolation information at the weather bureau; your local city planning (or county planning) office may also have this information readily at hand, with results tailored for your local geography.
The amount of energy you get from the sun in a typical day depends on both the time the sun is over the horizon and how high up it is in the sky – the angle of sunlight matters, because low angle light goes through more of the atmosphere and heats up more air molecules (and disperses) before it reaches your solar panels. The optimal sun-hour is high noon; everything else will be measured in fractions of that; on average, most locations in the US get between five and eight sun hours each day; southern climates with fewer clouds in the sky, and fewer obstructions on the southern horizon tend to get more; lots of places in the Sonoran desert of Arizona can get up to nine sun hours per day reliably.
Another factor on insolation is how much it varies at different times of the year; think about this in conjunction with your power usage patterns; you may find that your solar panels provide you the least benefit when you need them most if you're using them in the winter time to try and power electric baseboard heaters.
Finally, be aware that shade will greatly reduce the effectiveness of solar panels; because of the way photovoltaic (solar cells) work) if one of them is reduced in output due to shading, the others will be as well; there are some premium panels that have built in diodes to prevent this, but try to avoid having anything provide shade to your solar array. You'll be happier with the outcome.
See the list to the right for complete information about how to build your own solar-powered system.
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About the Author
John Horning specializes in reporting on do-it-yourself solar power projects and related topics. Visit his website at DIY-Solar-Power.net.
