Site Assesment for Alternative Energy

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Whether you already own property or are simply in the market for it, the alternative-energy potential of a particular piece of turf ought to be as much a part of your thoughts as are access, flooding, septic-field percolation, the soil's bearing capacity, and the view. Good solar or wind potential can return thousands of dollars per year in energy savings—or even in income from power sold to your area utility—and can offer your family security in a future of uncertain energy availability.

In the simplest sense, an energy site assessment is just a matter of figuring out how much, when, and where. As you'll see over the next few pages, the first part of the question is a straightforward matter of measurement, whether you perform it yourself or consult tables prepared by someone else. Determining at any given instant the amount of power available isn't difficult, when compared to figuring "when" and "where."

Predicting performance at some point in the future ("when") is much more difficult because solar energy—and wind is essentially a solar-driven phenomenon—is by its nature variable.

Likewise, "where" can introduce large uncertainties into the estimation of energy potential, particularly with the more ephemeral sources, solar and wind.

Thus a useful alternative-energy site assessment should be composed about equally of' careful measurement and an understanding of the limitations on accuracy. Do your best, but don't overestimate the reliability of your best. And when you use the numbers, err on the side that will keep your lights lit and your house warm (or cool).

SOLAR

In a solar site survey, "how much" is insolation (including that which shines directly, that which is reflected, and that which is scattered by the atmosphere-called diffuse); "where" is local cloud cover and site shading; and "when" consists of seasonal and annual variations in both how much and where. Enthusiasm for solar over the last 15 years has produced a great deal of information about this resource . . . and those data can prove valuable to you.

More than is the case with wind, the way that solar energy arrives has much to do with the success of attempts to develop it. As you do a solar site assessment, then, keep in mind that you're looking for more than just whether it's worthwhile to develop your site or how much energy might be available. The nature of the resource will suggest the best hardware. For example, different sorts of collection systems are best for capturing direct or diffuse radiation, for coping with extensive shading from trees or buildings, and for making do in areas with a high degree of uncertainty in cloudiness, degree-days, and expected sunshine. It's beyond the scope of this minimanual to tell you how to design a system from the data you acquire, but we will try to suggest some of the directions in which the information might lead you.