A PROFITABLE PRIVATE MICROHYDROELECTRIC PLANT

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The arrangement the team developed consists of a simple, fail-safe bypass that diverts water from the turbine in the event of a power failure. During normal operation, a valve in the diverter pipe is held closed by compressed air and a solenoid. But if grid power is lost, the solenoid automatically kicks open . . . releasing the air, opening the valve, and thus allowing the water to go around the turbine. When it's time to start up again, the diverter valve is closed, with the help of either a footoperated pump or a small compressor.

Two meters monitor Laurel Creek Hydro's performance. One unit registers the amount of power consumed at the site for lighting, compressor operation, etc., and the other measures the current going back into the grid. Of course, the former reading indicates the electricity charged out at BREMCO's retail rate, and the latter refers to that paid back at the contract price of about 3¢ per KWH. (This two-meter method is the most common utility-accepted arrangement.)

THE DO-IT-YOURSELF CONTINGENT

Thousands of hours of volunteer labor went into the construction of Laurel Creek Hydroelectric, and this "sweat equity" was vital to the project's maintaining an attractive "bottom line". However, careful selection of materials and equipment also played a big part in keeping costs down.

For example, Andy and Bob built the powerhouse from recycled timbers and roughcut siding in order to save on lumber costs. They also made such components as the equipment lifts, the turbine housing, the belt guards, and the control box . . . instead of purchasing them. At the intake end, no more ready-mix concrete than necessary was used. The dam was tied to bedrock with rebar . . . poured . . . then covered with hand-laid rock.

The group also showed considerable ingenuity in dealing with the often tricky problems of pipe mounting. The top three supports are made of reinforced concrete and rock, but those down the remainder of the run consist of hand-split locust poles. The posts were pounded into the ground with'a wooden sledge, and the pipe was lashed to them with cable. At one point, where the penstock had to span a small ravine at a height of 7 feet, several pairs of thick locust poles were set in concrete to support the needed bridge.

The secure mounting of the pipe is particularly important in a high-head hydro site because of a potential problem called "pipe hammer". This disturbance can occur if a valve is inadvertently shut off too quickly . . . it's akin to the banging that sometimes takes place when a tap is closed in a poorly plumbed house. However, whereas "faucet rattle" is merely annoying, even minor pipe hammer in a hydropower penstock can easily destroy a poorly mounted system.

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