Micro hydro

The first thing is to determine if you have a suitable site. This link shows some pictures of streams and rivers, and gives an idea of the flow rate available, the minimum head that would be required, and the amount of power that might be generated. They suggest that a rough estimate of the power available is given by the formula Head X Flow X 5 = kW, where the head is in metres and the flow in cubic metres per second. The head should be at least one metre to be effective.

The piping used to carry the water to the generator is called the penstock. The article Hydro Electric Penstock Design (pdf) provides a good summary of the issues involved. It starts by examining the type of pipework available, the pressure they will have to be able to withstand and the resistance to water flow that they create. Routing of the penstock and the need for shut-off valves, vents and thrust blocks is also discussed.

Turbines used in microhydro installations fall into three categories.

• Impulse turbines are open to the air and a have a high velocity jet of water directed onto the turbine blades and are best suited to high-head, low-flow systems.
  
• Reaction turbines are fully submerged and are best suited to low-head high-flow applications
  
• Propellor turbines are like a boat propellor and work in a no-head high-flow situation.
  

One option for generating electricity from the turbine is to use an induction generator.

Boulder, Colorado, has eight hydroelectric generators incorporated into the city's municipal water system which generate enough power to provide 11 percent of the electricity needed by the city. (April 12th, 2009)

Living Off-Grid: Our Micro Hydro Alternative Energy System - Jennifer Lance gives an overview of her micro-hydro installation in California. (March 26, 2008)