Waterbattery: Waterpower Storage for Microhydro
A small amount of storage in a micro hydro system can act as a battery does in an auto. A battery accumulates power slowly while the auto is running and can release it rapidly later, as when starting the engine.
The amount of energy stored in the battery is small, but the fact that it can be stored and used on demand makes it very useful. The same principle can be applied to small scale waterpower, and in some situations with dramatic results.
A little storage can make it possible to use a very small or even intermittent waterpower source to do valuable work.
Storage can also make it practical to use a shared water resource, such as an irrigation ditch, as a waterpower source.
These thoughts came to me while working at our microhydro demonstration site in the Andes near the Bolivian capital, La Paz. There we use a very small stream to run a number of machines and power tools such as a grain mill, table saw, compressor, alternator, and more.
These are all driven directly by the Watermotor, so we get about 80% of the power from the water as usable energy and therefore need relatively little water to run our machines.
Even so, the combination of dry season plus a newly installed potable water system upstream can reduce the flow to less than what we need to run some of our tools, without drying up the stream bed.
As an example, for full power operation the table saw needs about 500 liters per minute, and sometimes this is simply not available.
But actually we seldom use this saw for more than a few minutes at a time, and rarely for more than an hour or two per day.
If we can get this much power we can keep our shop in operation throughout the dry season.
How much storage would we need for this amount of use? Surprisingly little, when we check the figures.
An example : let us say the water available to us is 100 liters per minuteonly 20% of what we need to run the table saw, and we have a 6000 liter storage tank (2 x 2 x 1.5 m). This amount plus the water arriving during operation adds up to nearly 15 minutes of continuous power, and over two hours of operating time over an 10 hour workday.
In practical terms we would never run out of waterpower. Of course, this only applies to machines that are used intermittently, as are most shop tools, especially in small shops.
A tank is often a useful thing for other reasonsbathing and irrigation among them. We have been building subterranean tanks for years using ferro-cement which makes construction easy and low in cost. This technique uses woven wire (chicken wire) for reinforcing rather than steel bars. The tank walls are usually no more than 1" thick.
Ferro-cement is especially advantageous in locations where the materials must be carried to the worksite.