There is no firm international definition of SHP, but they generally comprise hydroelectric facilities with a capacity of less than about 25-30 MW, although hydroelectric technology is basically the same regardless of generating capacity. The US DoE uses the cut-off point of 30 MW, whereas in India it is 15 MW.
Small hydro can be further subdivided into mini hydro (usually defined as <500kW) and micro hydro (<100KW).
A well-designed small hydropower system can blend with its surroundings and have minimal negative environmental impacts. Small hydropower has a huge, as yet untapped, potential in most areas of the world. The biggest advantage of SHP is that it is the only ’clean’ and renewable small source of energy available round the clock. It is free from many issues and controversies that continue to impede large hydro, such as the submergence of forests, siltation of reservoirs, rehabilitation and relocation and seismological threats. Other benefits of small hydro are user-friendliness, low cost and short planning and development periods.
In addition to these obvious benefits, SHP is especially useful in remote areas with limited or no electricity. This applies in both developed and developing countries. For example, Austria has over 1,000 small hydro plants scattered throughout its mountainous terrain. In some developing countries, rural dwellers have been able to manage the switch from firewood for cooking to electricity, thus limiting deforestation and cutting down on carbon emissions. On the macro level, rural communities have been able to attract new industries, mostly related to agriculture, owing to their ability to provide power from SHP stations. In countries such as South Africa, China and Nepal, rapid SHP development has also encouraged small, local manufacturers to support these hydropower plants.
Small hydropower is not simply a reduced version of large hydro plant. Specific equipment is necessary to meet fundamental requirements of simplicity, high-energy output, maximum reliability and easy maintenance by non-specialists. The main requirement for hydropower is to create an artificial head so that water, diverted through an intake channel or a pipe (the penstock) into a turbine, discharges back into the river downstream.