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If you live in a mountainous area and a brook flows swiftly through your property, you can tap its energy with the miniature equivalent of a hydroelectric power station. A relatively small and simple sys tem based on a water-driven turbine and a small electric generator can supplement current from your local utility. With a larger turbine and generator, you can free yourself from commercial power sources altogether. Large systems are costly, but where utility-supplied power is not avail able and the only alternative is a gasoline- or diesel-powered generator, a home system can prove competitive. The ability of a stream to produce electric power depends on two factors: flow, the technical term for the volume of water the stream carries; and head, the drop in elevation along the portion of the watercourse where the system will be built. Where little head is available—as in a river flowing through flatlands—an ex pensive, complex dam is essential to back up the stream and create an artificial difference in water level. A mountain stream, on the other hand, often supplies sufficient head for a home hydroelectric system and needs only to be dammed with a few boulders or logs to channel sufficient flow into the system’s inlet pipe, called the penstock. Before planning a water-powered generating system, you must calculate both the head and the flow available from your stream. (Remember, however, that even streams running through private property are subject to laws regarding conservation and water rights; check with the local water resources agency be fore undertaking a hydroelectric project.) The easiest way to measure the flow of a stream no more than 7 feet wide is to interrupt it with a temporary plywood weir (opposite). The flow of a larger stream may be listed at a local U.S. Geo logical Survey office or, in Canada, at the municipal or district office responsible for natural resources. II not, you can hire a civil engineer to take flow readings. In any case, you will need monthly flow figures for an entire year to be sure that the water level does not drop too low for generating purposes during the dry sea son. Also check to see that the stream is not subject to destructive flooding. To measure the head that your stream can provide, you will need a long measuring pole marked off in 6-inch increments, a second pole exactly 5 feet long, a 50-foot steel tape, a hand-held sighting level and a helper. In general, you will need at least 50 feet of head to make home electrical generating practical. Once you have exact figures for the flow and the head, a simple formula allows you to calculate the amount of power available in the stream: Multiply the head measurement, in feet, by the flow, in cubic feet per minute; then divide the result by 708 to get the theoretical yield, in kilowatts of electric power. Because no system, no matter how efficient, will enable you to tap completely the theoretical potential of a stream, the calculated yield should be at least twice the number of kilowatts you need for your household (-- 8). You will need the head and flow figures—as well as your kilowatt requirements and a detailed description of the topography surrounding your stream— when you begin shopping for a turbine and generator. Turbine manufacturers— most of them small firms in the western United States—generally sell their equipment in complete systems, each tailored to the customer’s site and needs. The sys tem will include the turbine and either an alternating- or a direct-current generator. For systems that are to be interconnected with public utility lines, the sup plier will also include hardware and safety devices to ensure that the electricity produced is compatible with that de livered by the utility (-- 116). A hillside power plant. In this t small- scale hydroelectric system, boulders placed in the stream bed make the water pool so that it covers the water intake, which is screened to keep out fish and debris. A penstock of inexpensive plastic pipe carries the water downhill into a pre fabricated shed serving as the powerhouse, where it spins the turbine, here a many-armed type known as a Pelton wheel --. A large valve between the penstock and the turbine regulates the flow and allows the system to be shut down completely for maintenance. Beyond the turbine, water is carried out of the powerhouse into an outflow channel. In this small system, independent of a local utility, the turbine drives a DC generator, which sup plies current to a large bank of storage batteries. From the batteries, the direct current flows through an inverter, which changes it to alternating current, and then into the house. A voltage regulator, located in a control box, prevents the batteries from being overcharged. [124] GENERATOR— TURBINE HOUSING; OUTFLOW Measuring Head and Flow Using poles and a level. Have a helper hold a pole, marked at 6-inch intervals, next to the stream 50 feet up the slope from the proposed powerhouse location. Sight the pole through a hand-held sighting level supported atop a 5- foot pole at the powerhouse site. Subtract the height sighted on the calibrated pole from the 5-foot height of the support to find the change in elevation. Move the level and its support to the location of the calibrated pole, and move the calibrated pole 50 feet upslope. Take a second reading and again subtract it from 5 feet. Repeat the process, working up the slope until the calibrated pole is directly opposite the inlet location. Add all of the measured changes in elevation -- to calculate the total head. 1. Taking depth readings with a weir. Trim a 4- by-8-foot sheet of 3 plywood to a length about 1 foot greater than the stream is wide and to a width about 8 inches greater than the stream is deep. Cut a rectangular notch in one of the long sides, about half the width and depth of the stream; bevel the notch with a rasp, leaving a 1/8-inch, squared-off ledge --. Jam the weir into the stream bed, with the notch upward and the bevel facing downstream. Drive 2-by-2 stakes just downstream of the weir to brace it, and pack mud and gravel around the edges upstream to complete the seal. With the weir properly placed, the entire flow of the stream will pass through the notch. If the water overflows the notch, widen it or make it deeper. Lay a 2-by-4 board across the stream 5 feet upstream of the weir. Using a carpenter’s level placed atop a 6-foot length of 2-by-4, adjust the board with pieces of scrap wood so that its top is even with the top of the weir. With a yardstick, measure the distance between the top of the board and the surface of the backed-up water. Subtract this distance from the depth of the notch in the weir to find the depth of the water roiling over the notch. Then use the table at right to calculate the water flow. Depth in inches | Flow value Calculating the flow. Find the water depth over measure the distance between the top of the weir notch (Step 1) in the first column of the board and the surface of the backed-up water. chart above. Read across to the corresponding. Measuring Flow [125] Prev. | Next: |