Microhydro Equipment & System Design

Intermediate

Inside this Article

A hydro-electric system uses the flow of water down a slope to create electrical energy.
1. Intake; 2. Screen
3. Vent Pipe
4. Penstock
5. Manifold
6. Pressure Gauge
7. Turbine
8. Alternator
8. Alternator
9 Transmission & Power Electronics

A hydro-electric system uses the flow of water down a slope to create electrical energy. The amount of energy depends on how much water is flowing, and on the height difference (head) between intake and turbine. This article covers selecting the necessary equipment, from the intake to power electronics.

1 Intake

An intake is required to channel water into the hydro system. A reservoir of water is an ideal microhydro source, but it’s not essential and most sites don’t have one. Instead, water is diverted from a flowing stream or creek into an intake that must be robust enough to withstand floods. Build a small weir or choose a natural constriction in the stream where you can catch the water.

2 Screen

A screen of sufficient area prevents things like vegetation, pebbles, and fish from entering the penstock—the pipe that carries water to the turbine. If placed deep in a very large body of static water, this screen may not need much maintenance. It may just need occasional scrubbing with a long-handled brush. Fast-moving water brings debris that must be cleaned off the screen frequently. The best solution is a sloping screen on top of a box or tank that feeds the penstock. Smooth, perforated stainless steel plate or even mesh is suitable screen material. Aquashear (Coanda-effect) screens are virtually maintenance-free if the approach velocity of the water is correctly engineered.

Divert the flow so it spills over the screen, or embed a collection tank in the bottom of the stream or at the edge of a fall. The mouth of the penstock must be large enough and deep enough in the water that it does not create a vortex and draw air.

3 Vent Pipe

A single, vertical vent downstream of the screen near the top of the penstock helps bubbles escape, prevents damage to the intake from suction if it gets blocked, and removes any trapped air from the penstock, when it is filling up. A valve is essential at the bottom of the penstock to shut off the turbine, but rarely needed at the top. If you fit a valve at the top of the penstock, put it upstream of the vent, so you can drain the penstock if desired. Valves at the turbine end of the penstock should be a type that closes slowly, to avoid pressure surges.

4 Penstock

The penstock is the engine that drives the turbine, and is the most important part of the hydro system. This pipe doesn’t just deliver water—it also provides pressure (see “Penstock Example” sidebar). The longer the penstock is, the larger its diameter must be, or friction will reduce the pressure, decreasing the energy available. Choice of pipe is a compromise between cost and efficiency—a long pipe often makes the penstock more costly than the turbine.

To make the best of limited water, try to keep penstock pressure losses below 20%. There are many online pipe friction tables and calculators for different pipe materials, but few that will factor in friction increases as pipes get older and dirtier. Oversizing the pipe is a good investment for the future.

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