The term 'micro-hydro' is usually taken to mean schemes with a power output less than 100kW. Hydro electric installations convert potential energy of water at height into kinetic energy in a turbine.
Micro hydro can roughly be split into two categories, low head (<5m head) and medium to high head.
For a medium head installation, fixed costs are around £10,000, and then variable costs are approximately £2,500/kW up to about 10kW. Hence, a 5kW domestic scheme might cost £20-£25,000.
Several different types of hydraulic turbine can be used in micro hydro installations, selection depending on the head of water, the volume of flow, and such factors as availability of local maintenance and transport of equipment to the site. For mountainous regions where a waterfall of 50 metres or more may be available, a Pelton wheel can be used. For low head installations, Francis or propeller-type turbines are used. Very low head installations of only a few metres may use propeller-type turbines in a pit. The very smallest micro hydro installations may successfully use industrial centrifugal pumps, run in reverse as prime movers; while the efficiency may not be as high as a purpose-built runner, the relatively low cost makes the projects economically feasible.
For high head applications, where there is a considerable difference in head height between the intake and the powerhouse, construction costs for the penstock can represent the bulk of the project costs for the particular installation.
For connection to the grid, similar protection devices to other micro generation technologies are required. Although micro hydro is relatively specialized, in rural areas where water is readily available via local streams and rivers, there is good potential for generation of green electricity all year round, assuming water flow in the source is not seasonal.