Most people are familiar with large scale hydropower involving large dams and reservoirs. Small scale hydropower systems with are less well known but still capable of producing sufficient power for industrial or commercial use. Hydroelectric schemes have long operating lives and can last for many decades with suitable maintenance.
The amount of energy extracted by a hydroelectric facility depends firstly on the volume of water being harnessed and secondly on the difference in height between the water source and the point where it flows through the turbine. This difference in height is known as the head. In general the costs per unit of electricity of high-head schemes are lower than those of low-head schemes.
Hydroelectric power schemes require a suitable rainfall catchment area, a water intake placed above a weir or behind a dam and a sufficient drop (head) between inlet and outlet. The water is transported to a turbine in a pipe or channel and then from the outlet of the turbine it is returned to its natural course. The turbine has a mechanical or electrical connection to the load to be supplied.
‘Run-of-river’ hydroelectric plants use the natural flow of rivers with a consistent steady flow rate where a reservoir is not necessary.
Tidal range power plants use similar technology to hydroelectric power plants to generate power from the daily rise and fall of water caused by tides. For more information about tidal power see marine energy.
Electricity can also be generated on a commercial scale via the construction of pumped storage schemes that move water between reservoirs located at different elevations. Such schemes are not carbon neutral as electricity from the grid is used to pump the water uphill. The main benefit of this technology is to generate electricity at peak demand times using water that has been pumped uphill at times of lower demand. For further information on pumped storage schemes see energy storage.