Hydrolectric generators provide the most widely used form of renewable energy on the planet. 2010 production of
3,427 terra-watt hours of hydroelectricity produced accounted for approximately 16% of global electrical
| Classification by power output
< 5,000 W
||5 KW - 100 KW
||100 KW - 10 MW ¹
over 10 MW
|¹ in North America some 25-30MW
facilities are considered small
Hydroelectric generator installations range in size from pico-hydro installations generating only a few hundred
watts to massive massive facilities like the Three Gorges Dam which produces 22,500 MW (22.5 GW). Although no
formal definition exists, typical designations of hydro generator facilites based on generating capacity are as
shown in the table at right:
Hydroelectricity Generating Methods
All hydroelectric generators require a flow of water to drive the turbine. How that water is delivered to the
turbine can vary greatly:
• Conventional: a large capacity dam is used to store water for delivery to the turbine.
• Pumped-storage: uses surplus generating capacity to pump water up into a reservoir at higher elevation
during periods of low power consumption. During periods of peak hydroelectric power demand the water is released to
flow down through turbines and increase the maximum amount of hydroelectricity that can be generated.
• Run of river: requires no reservoir, or a very minimal reservoir, depending on the scale of the
installation. The natural volume and flow of water in the river is sufficient to drive the turbine(s).
• Tidal power: Currents through restrictive inlets are created by the rise and fall of the oceans tides can be
harnessed to drive hydroelectric turbines.
• Underground: a tunnel or tunnels are bored to deliver water from a higher elevation source to a lower
Hydroelectric generator turbine types