Micro-Hydro

Running water holds energy in two ways at once: it falls, and it keeps coming. A micro-hydro installation sets a turbine, a wheel driven by moving water, in that stream and couples it to a generator, so the flow becomes electricity. Unlike sun and wind it does not stop at dusk or wait for a gust: while the water runs, the machine runs, giving steady background supply.

Two measurements decide whether a watercourse is worth building on. Head is the vertical drop between the intake, where water is taken in, and the discharge below it; flow is the volume passing in a given time. A large drop with little water can match a generous flow over a small one, and a fall of only 1 to 8 m (3 to 26 ft) will turn a small machine where the flow is adequate. Friction inside the penstock, the pipe carrying the water down, is subtracted from the head the site offered, so a wide pipe is part of the design rather than an upgrade. Water reasonably clear of sand and silt, and a flow that is predictable rather than merely present, come first.

The easiest version is added to water already being moved, such as an irrigation pipeline or ditch, because the water is only borrowed: the volume entering the intake leaves at the discharge. Where a new diversion must be dug, permission to take the water becomes the larger part of the work. Silt is what ends these machines, wearing away the turbine wheel and the shaft seals, so sediment control decides whether a turbine reaches the twenty years good maintenance should give. The routine failure is a blocked intake: its screen is sized so water approaches slowly enough for debris to slide along rather than pin against it, and clearing it is the recurring job, mostly after storms and leaf fall. Otherwise upkeep resembles keeping an irrigation pump running. Where electricity is not wanted, the turbine can drive a pump directly with no generator at all.