Our first micro hydro system

Our first hydro system was built at no cost using only reclaimed parts. At first we used an old Stuart Turner brass rotary pump, that we found at the local recycling centre, to provide the turbine. The generator is one of the permanent magnet motors that we have previously used on some cycle generators. It took a fair amount of work to modify the shaft of the motor to fix to the pump and to ensure there were no leaks but the results were worth the effort.

The pump worked okay, but we got frustrated with frequent blockages within the casing. We eventially switched to what was basically a four inch diameter plastic paddle wheel. This item was previously the cooling fan on the back of a large induction motor. It proved to be slightly more efficient than the pump impeller and it could never get blocked.

Inspired by the improvement, we decided to built a pelton wheel. Sixteen cups were fashioned from plate aluminum and rivited to a alumilum disk to form the wheel. It seems to be performing well but its 6 inch diameter is perhaps a little larger than ideal. It is also poorly balanced and causes a lot of vibration.

Having established that it is perfectly possible to use reused pumps or even make a pelton wheel using simple hand tools - we are now tempted to buy a professionally fabricated pelton wheel so that we can compare the performance differences. If we do this, we'll put our findings on this page.

With all the systems we have built so far, the top of the pipe (known as a penstock) was placed in a natural pool within the stream bed. To reduce the chance of blockages in the jet or turbine we added a filter made using fine plastic netting sacks that onions and root vegetables are often packed in. The netting was tied over a plastic bottle with holes cut in it which prevents the netting from entering the pipe and maintains a large surface area for the filter. It seemed to worked fine for a while but when the larch trees dropped their neddles we had lots of problems. Either the filter would get blocked and reduce the amount of water passing through the pipe or the needles would get through and block the turbine. Changing the turbine to one less susceptible to blockages has eliminated the problem.
We have used about 100m of plastic hose laid in the stream bed and providing about 20m of head (the height from the top of the pipe to the turbine). Unfortunately the pipe is made up of short sections and where they are joined the internal diameter is reduced. This increases the resistance and decreases the flow rate. Ideally we would have used a single piece of pipe in order to minimise resistance.

We intend to use pipe of a larger diameter in the future.
The stream and the turbine is about 200m from the Long House and we therefore needed a long run of cable to get the electricity produced to the place we would use it. We joined together a load of off-cuts of 1.5mm2 multistrand wire but were worried that such a long cable would mean large losses because of the low voltage levels we use. However when we measured the voltage at either end of the cable we found the loss was bearly detectable thanks to the low current produced. If we manage to make a more efficient system that produces more power then the power losses in transmission may become far more of an issue and we would have to consider using thicker cable or producing AC at a higher voltage.

The stream we are using is seasonal but while it is running we can produce about 18 watts (18watts * 24hours = 432watthours or ~1.5amp @ 12volts which means 36AmpHrs per day). This level of power is adequate to charge our batteries and in theory provides enough to run a laptop computer (30w) and/or a low energy lightbulb (20w) for at least 12 hours every day.
We found the whole process of creating the hydro system was surprisingly easy but could it really be that simple? While taking water from your own land is a Common Law right in this country, an abstraction license and an annual fee may be required under the Water Resources Act 1991. There are a number of exceptions, such as for private domestic water supplies like to our kitchen. We contacted the Environment Agency to find out what the situation was with our hydro system and were pleased to learn that small hydro power schemes are excempt from an annual license fee.

The amount of power we can potentially produce is fairly low, limited by the nature of our streams and landscape. We have a reletively low flow available to us and it is only the amount of head (pressure) provided by the steep valley walls that makes our tiny system viable. Despite these constraints, we should able to increase the efficiency of our system by using a more suitable turbine, a more efficient generator and a larger diameter pipe - only time will tell.

Last updated: 2011-07-05

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