Classification of Small Hydropower Stations
Small hydro can be further subdivided into mini hydro, usually defined as less than 1,000 kilowatts (kW), and micro hydro which is less than 100 kW. Micro hydro is usually the application of hydroelectric power sized for smaller communities, single families or small enterprise.
Classification of Water Turbines
Micro-hydro plants may use purpose-designed turbines or use industrial centrifugal pumps, connected in reverse to act as turbines. While these machines rarely have optimum hydraulic characteristics when operated as turbines, their low purchase cost makes them attractive for micro-hydro class installations.
Regulation of small hydro generating units may require diversion of water around the turbine, since the project may have no reservoir to store unused water. For micro-hydro schemes feeding only a few loads, a resistor bank may be used to dissipate electrical energy as heat during periods of low demand. In a sense this energy is wasted but the incremental fuel cost is negligible so there is little economic loss.
Other small hydro schemes may use tidal energy or propeller-type turbines immersed in flowing water to extract energy. Tidal schemes may require water storage or electrical energy storage to level out the intermittent (although exactly predictable) flow of power.
