Happy on One Kilowatt

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We decided on a two-part system using a bucket and sediment tank. We placed the bucket under a low waterfall, covering it with a screen to filter out large debris; the strong flow clears the screen and keeps smaller sediment from settling on the bottom of the bucket, sending it along with the water, through a pipe, to a sediment tank located farther down the line.

(Admittedly, this type of system works best with a pristine stream like ours. Even so, for reliability, we installed a second water pickup point just below the bucket.)

For the sediment tank, we needed something large enough to allow silt to descend to the bottom and bubbles to rise to the top, leaving only clean water to exit at midlevel. Knowing that a vertical tank makes a better separator than a horizontal tank, we chose an oversized plastic garbage container.

We covered the outlet from the sediment tank to the hydro equipment with a fine mesh screen to prevent the passage of large particles that might clog the nozzle at the end of the pipeline. Air bubbles and turbulence move these particles to the surface of the tank, where they are drawn off along with surplus water. (The sediment tank doubles as an overflow, since much more water enters it than is needed for the hydro system. Average flow in the creek is 100 gallons a minute, while the maximum we use for the hydro system is 30 gallons per minute. Four overflow pipes lead from the top of the tank back to the stream.)

The system in place, we promptly conducted pressure and flow tests. Our measurements showed a static pressure (the pressure at the bottom of the pipeline when water is not flowing) of 155 pounds per square inch (psi). At a flow rate of 30 gallons per minute, we measured 140 psi, just right for a turbine using one nozzle, the lowest cost arrangement. While awaiting the arrival of our Harris turbo/alternator - a high-power version wound for a 24V to 28V output - we built a protective wooden shed for it beside the main creek, to allow easy dispos al of the wastewater.

One advantage of hydropower over solar - besides the 10:1 cost ratio - is that the battery bank need only be large enough to provide peak loads for starting motors, as well as to meet operating loads that exceed the alternator's capacity. (With solar, the batteries have to store power for nights and rainy days, while with hydro, you can count on continuous current production.) We started with six 12V RV batteries in series/parallel. They required excessive maintenance, however, so we switched to four 6V golf-cart batteries, still giving us 6 kilowatt-hours of storage capacity. (For more on batteries, see "The Almighty Battery," MEN, Feb/Mar 1999.)

In our type of hydro system, the alternator must continuously produce a full current (in our case 50 amps) even when we don't need it, in order to avoid wearing out the turbine. (When not being used to generate power, the turbine's speed actually doubles.) Thus, to avoid overcharging the batteries, we installed a regulator that continuously checks their voltage; when the batteries are fully charged, excess current is shunted to resistor loads. For the resistors we opted to use a bank of water heater elements, placing them with the batteries. That way, in cold weather, the excess power warms the batteries, increasing both their efficiency and life expectancy.

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