WATER SITE ASSESSMENT

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If you have a stream on your property (or dream of owning a place with one), you've probably thought about hydroelectric power. However, though hydroplants can vary in size from MOTHER's two units (shown below) to huge utility-ned-dams, many waterways just aren't capable of producing significant amounts of electricity. In this, the third section of our study of alternative-energy site assessment, we'll explore ways to uncover a stream's power potential and help you learn whether it'd be worth voter while to "go with the flow."

At this time, all practical, home-scale hydroelectric equipment makes use of a fall of greater than five feet. It is the acceleration of gravity and the weight of the water that combine to produce foot-pounds (distance and weight)—the essential ingredients of power. This fall, which is most often called head or pressure head, could be obtained over a very short distance, as is the case with a dam, or it could be developed by a long run of pipe or a flume.

So, as a ground rule, if you can't find five feet of fall over a reasonable distance, waterpower won't work for you. This can be a terrible frustration if you've got a good-sized but basically horizontal stream flowing across your land; you sense that there's energy there, but there's no practical way to get at it. (If and when equipment is developed that changes this situation, you can be sure we'll let you know about it in MOTHER.)

PLAYING SURVEYOR

Measuring fall is a straightforward matter, whether the situation calls for crude or sophisticated methods. At a site with a damsuch as MOTHER's hydro site—a simple tape measure works fine. The head is the difference in elevation between the surface of the lake and the water jet that strikes the turbine. (Deciding on the latter point calls for a little planning and imagination.) No matter where the pipe that taps the lake's water supply enters the lake, the weight of water all the way to the surface bears down, producing pressure.

More often, in order to tap a watercourse for electricity, the most practical way to de velop head is to run pipe uphill and pick up the water at a higher elevation. (Then the weight of the water in the pipe bears down, producing pressure.) In this case, measuring head can get a little more complicated. If there are several hundred feet of elevation difference, you can come close enough using a topographical map. (Those parallel elevation lines are pretty darn accurate; the big problem is figuring out where you are on the map.) But for heads of less than 200 feet, you'll need to use some sort of surveying technique.

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