Preparing Your Land for Hydroelectric Power

If your goal is residential hydroelectricity, then it's time to get familiar with flow duration, the weir method and other measuing tools.

| January/February 1986

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    An example flow-duration table, which is useful in figuring out which hydroelectric mill to select.
    MOTHER EARTH NEWS STAFF
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    Hydroelcetric power can be a great way to reduce utility dependence — but it also requires careful planning.
    PHOTO: MOTHER EARTH NEWS STAFF
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    A flow-duration curve, which is derived from raw data and is easy to analyze.
    MOTHER EARTH NEWS STAFF

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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 EARTH NEWS' unit (shown in the attached image gallery) to huge utility-owned 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 would be worth your 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.

Play Surveyor With Your Land's Water

Measuring fall is a straightforward matter, whether the situation calls for crude or sophisticated methods. At a site with a dam — such as our 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 develop 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.

Understand Elements of Power

The quantity of water available is just as important as fall is in determining the amount of power available at a site (before equipment efficiency is considered). In fact, the two are multiplied in the basic hydropower formula: power = (flow x head) / conversion factor.






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