Mother's $10-per-square-foot (or less!) Earth Sheltered House: Part III

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A TRICKLE FROM A TRICKLE

One of the limitations imposed by a 12-volt electrical system is that the source of electricity must be close to the point of use. Because greater amperage is required at low voltage to suit the same power demand met with 120 volts, line losses can quickly become a serious problem. We're fortunate, then, to have a stream running no more than 30 feet from our house's back door, so—by placing a mini-hydroelectric station on a diversion pipe feeding into one of our ponds—we were able to get the generator within 15 feet of the back door.

The power generation system consists of a 4-1/2" pelton wheel driving a converted automobile alternator . . . and was built by Don Harris (Dept. TMEN, 632 Swanton Road, Davenport, California 95017). We're using about 20 gallons of water per minute (which is roughly 2/3 of the mean flow rate for the stream), with a total drop of 36 feet, to produce just short of 40 watts. Though this is a comparatively small amount of electricity, it is sustainable for 24 hours per day through roughly 3/4 of the year. Thus, during that operating period, it produces a little less than a kilowatt-hour per day . . . or the equivalent, in our area, of the output from six 35-watt photovoltaic panels.

This amount of power should be adequate for lighting, intermittent use of small appliances, and even a modest amount of water heating. During periods when we need more juice than the system can produce, the deficit will be made up by a 5,000-watt Honda generator that's located in a shed off the chicken coop/greenhouse. Though the device does, of course, burn fossil fuel, its great power output (as compared to our hydro system) means that it should seldom have to be run for long . . . and the water-cooled, two-cylinder engine is both fuel-efficient and quiet. What's more, plans are in the works now to scavenge waste heat from the motor-generator's cooling system to help keep our fowl and rabbits cozy in winter.

Any illusions we may have had about boosting the output from the hydro system were laid aside when we discovered just how low our fall of water actually is. We'd anticipated having as much as 70 feet of head—in fact, that's the pressure Harris Hydro planned on when it put together the system—so the 36 feet that we ended up with was a serious comedown. Don's instructions suggested that the system we were using should achieve about 40% efficiency if the fall were greater than 70 feet. (Harris also makes a unit with a permanent magnet alternator that achieves higher overall efficiency.) Pelton wheels are designed to use high heads, and they're never specified for use at lower than 50 feet. At our site, then, the Harris Hydro system is out of its element . . . but working amazingly well despite all odds!

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