MOTHER's Small Hydroelectric Plant Revisited

MOTHER EARTH NEWS editors reflect on the successes and failures of the Eco-Village small hydroelectric plant.


| January/February 1985



091-092-03

The heart of the speed control: about $30 worth of electronics.

MOTHER EARTH NEWS EDITORS

It's been more than four years since we reported to you on the construction of a small hydroelectric plant at Eco-Village. In the meantime, we've been working steadily on refining the design to improve its performance and make it more practical. And, as our system has matured, we've learned some lessons — ones you can "go to school on" to make your own system work (and cost) right the first time.

The Crossflow Turbine

You may remember that the heart of our small hydroelectric plant is a homemade crossflow turbine that's 12 inches in diameter and 18 inches long. The device was made by slicing 72-degree sections from 4-inch Schedule 40 steel pipe and welding 20 of the arcs into end plates made of ¼ -inch mild steel. It still runs essentially unchanged: We removed it at one point and trued its circumference on a lathe, in hopes of gaining power from the tighter fit between turbine and nozzle. Unfortunately, reducing the clearance to 1/32 inch produced no detectable effect on the runner's output.

In its nearly five years of operation, our crossflow has spun away without a hitch. Even though debris from the lake has slightly bent one of the blades, the tweak hasn't noticeably affected the turbine's performance.

Maintenance has consisted solely of an annual greasing of the SCB pillow-block bearings that the 1 7/16-inch shaft rides on.

Reliable as it's been, however, we have wished that the turbine had been designed differently in the first place. Our crossflow's nozzle was sized to deliver 3.5 cubic feet per second (cfs, or about 1,500 gallons per minute) of water, and we've confirmed that discharge rate with a weir, a flow-measuring device. The problem is that we don't have a dependable 3.5-cfs supply from the 11-acre (54-acre-foot) Eco-Village lake. The system design was based on an Army Corps of Engineers estimated flow rate for Transylvania County, N.C., of 3.8 cfs per square mile. That was a mistake.

Since the Eco-Village plant went on-line, a detailed assessment of microhydropower potential in western North Carolina (sponsored by the North Carolina Alternative Energy Corporation, or NCAEC) has produced much more specific — and therefore accurate — flow figures for the region. As it happens, the Eco-Village's elevation is somewhat lower than the average for Transylvania County. And in the Southern Appalachian region, flow per square mile increases with altitude. The NCAEC report suggests that the mean flow at Eco-Village should be about 2.6 cfs per square mile, a number that jibes well with our experience.





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