A New Era in Home-Owner Hydro

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The penstock should be as short, straight, and steep as terrain permits. Avoid undulations and abrupt changes of direction. Most penstocks are polyvinyl chloride (PVC) or polyethylene pipe.

PVC is generally cheaper. Unfortunately, sunlight degrades it, and it will shatter if it freezes. A plugged penstock at minus 30 is the worst nightmare imaginable. In a perfect world, every penstock would be buried to protect it from falling trees, freezing, bears, and other mischief. But many aren't. If you intend to leave PVC on the surface, paint it before installing it. In a cold climate, be sure to insulate it with fiberglass wrap or a thick layer of straw.

Although polyethylene pipe can be more difficult to install than PVC and, in large diameters, more expensive, it is also much more frosttolerant. Where winters are frigid and the penstock won't be buried, it is the choice. Be forewarned though: Unrolling a coil of poly is like wrestling a 100-foot python.

Sizing the penstock involves a tradeoff. The smaller the pipe, the cheaper its cost. But friction (and thus power) losses increase as pipe diameter decreases. So, the longer the penstock, the larger the pipe needs to be. Most household systems have 2"-4" penstocks, although AC systems often require 6", 8", or larger.

A powerhouse doesn't have to be large or expensive. A concrete floor is nice, not essential. Plan the equipment layout so that maintenance will be convenient. And be sure to install a pressure gauge and shutoff valve upstream of the turbine. This gauge is your troubleshooting tool. (Pressure higher than normal? A turbine nozzle is plugged. Pressure too low? The problem is uphill, probably at the intake.) Powerhouses are generally sited on the stream bank, which makes them vulnerable in a flood. Make sure yours is out of the floodplain!

A complete discussion of the many kinds of hydro turbines is beyond the scope of this article. Although each type has its niche, there is a great deal of overlap. Most home-owners use either a Pelton or Turgo. (These are designs, not brand names.) At heads over 50 feet, both work well. Since a Turgo can handle more water, it's often the choice for lower heads. If you are very handy with a welding torch and want to build your own turbine, build a cross-flow—a squirrel cage-like contraption efficient across a wide range of head and flows. (MOTHER sells plans.) For more on turbines, contact the manufacturers listed below.

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