Choosing a Turbine/Generator

Several different types of microhydro tur­bine/ generators are available. Your choice

minimize maintenance, Harris also offers a brushless permanent magnet generator* These units cost about $700 more, but use larger, more sturdy bearings that last two to three times longer* This greatly reduces maintenance and replacement costs* It is well worth the extra cost*

Harris turbines are for applications with 50 feet or more of head* They pro­duce from 1 kWh to 35 kWh per day,
depending on the model and site* The unit (generator) has an instantaneous output of about 2,500 watts — enough to start most appliances and power tools* Harris microhydro turbines come in 24- and 48-volt models and are manufactured in the United States*

For low-head systems that channel a lot of water through a turbine with little head (that is, on flatter sites), you may want to consider a Low Head Stream Engine (Figure 10-9) or one of the newest micro­hydro turbine/generators, the Jack Rabbit (Figure 10-10)* The Stream Engine is a brushless permanent magnet generator with sealed bearings that minimize main­tenance* These units operate in sites with heads that range from 5 to 400 feet that have flow rates from 5 to 300 gallons per minute (although flow rates above 150 gpm provide very little additional power)* Although set-up can be a bit tricky, the unit is virtually maintenance-free* Output voltages are 12, 24, and 48 volts* They’re manufactured in Canada*

The Jack Rabbit is an unusual micro­hydro turbine and generator* As shown in Figure 10-10, this submarine-like device consists of a submersible propeller and generator in a waterproof casing that’s suspended in a stream in at least 13 inches of water* The generator operates at low speeds, ideally around 9 miles per hour, or equivalent to a slow jog* Water flowing

past the device causes the propeller to spin*

In slow-moving streams, water Hows can be increased by piling rocks or heavy timbers to create a funnel with the wide end facing upstream* This channels water into the narrow end of the funnel, which greatly increases its speed. (This phenom­enon is known as the Venturi effect) The Jack Rabbit is placed at the narrow part of the funnel where the water is flowing most rapidly, optimizing the performance of the generator*

Jack Rabbits are low-capacity micro­hydro turbines that produce 100 watts of continuous power in a 9-mile-per-hour stream — or about 2.4 kWh of electric­ity per day — and slightly less in a slower stream* Jack Rabbits are rugged and require very little maintenance* The heavy-duty aluminum blades are not easily damaged* If struck by a log and bent, the propeller blades can be hammered back into shape* Another advantage of the Jack Rabbit is that it requires no pipeline, a feature that can save you a lot of money* Electrical lines from the generators (mounted securely in a stream) carry the current to the house* Jack Rabbits come in 12- and 24-volt models and are made in Great Britain. Proceed with caution with these, however* Word from users is that the power output is very low, and there are other problems that may make them a dubious choice*

Finally, the Low Head Stream Engine, with a turbo-type runner, is for use in sites that offer intermediate characteris­tics* They operate in areas with drops of 2 to 10 feet and flows ranging from 200 to

1.0 gallons per minute* Peak output is

1.0 watts, meaning that a turbine oper­ating in a good site will provide 24 kWh of electricity per day*

To learn more about these systems, I strongly recommend that you consult John Schaeffers book, Solar Living Source Book* It provides a good overview of the subject and a lot of valuable informa­tion on the various microhydro turbines, including pricing* Remember, as Dan New points out, that The turbine should be designed to match your specific head and flow* Proper selection requires con­siderable expertise.”

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