Hydropower

Hydropower is electrical energy derived from falling or running water. The water pressure that is created by water is used to turn the blades of a turbine. The turbine is connected to a generator, which converts the mechanical energy into electricity.

There are two basic types of hydropower plants — those that impound water behind a dam and those that divert water into a channel parallel to the river (often called "run-of-river" hydropower plants). Hydroelectric plants can be developed at existing dams or at water control structures built for other purposes such as water level control of rivers, lakes and irrigation schemes. However, run-of-river plants usually have a lower impact on upstream and downstream environments and communities because local habitats and the flow of silt and nutrients in the river are less affected by diverting than damming water.

Hydropower is an extremely flexible source of energy. In both the run-of-river and dam systems, water is led to a vertical tube or "penstock" that delivers water to the turbines. Hydropower plants can therefore be used to respond quickly to variable demand by releasing or diverting more water. In the case of dam systems, water can also be reserved when demand is low in order to generate additional power during periods of peak demand.

Hydropower plants are often subdivided into "large" hydro that usually involve dams, and small hydro that are normally run-of river systems. There is currently no agreement in the international community as to the definition of small hydropower. The upper limit is generally regarded to be 10 MW. However, small in Canada can refer to projects of between 20 and 25 MW while in China it is as high as 50 MW.

Small hydropower systems are further defined by the scale, including mini hydro 

(<500kW — typical supply for a small factory or isolated community), micro hydro 

(<100kW — enough for one or two houses) and pico hydro (<5kW).

Small run-of-river hydropower systems generally have lower environmental and social impacts, and therefore are often preferred to larger plants that involve the construction of dams. However, large hydropower plants can have an important role in electricity generation in sites where appropriate precautions are undertaken and negative environmental and social impacts of large hydro are avoided. Hydropower plants with dams offer the ability to reserve water for electricity generation as required, making larger plants a useful source to complement the variable output of renewable energy power sources such as solar and wind energy.

Certification programs such as the Environmental Choice EcoLogo certification for low-impact hydro-electric generation, and the application of sustainability criteria such as those suggested by the International Hydropower Association, are important tools in identifying and promoting low-impact hydropower production.

Benefits:

• Hydropower is a complementary power source to more intermittent renewable energy power sources such as wind and solar because the flow can be regulated to reserve generating capacity during periods of peak demand or when the generating capacity of other renewable energy sources is limited. 
• Small hydro facilities can be integrated into existing irrigation structures, flood control and dams. Because existing structures are used, adding generating capacity only requires the construction of small engineering works.
• Small hydro production has an important role to play in providing electricity to remote communities and industries in developing countries where rural electrification via the grid is not practical.
• In Canada, hydroelectric generation can provide clean electricity and a source of income to many remote communities that would otherwise be forced to rely on diesel generation.
• Hydroelectric energy is a proven technology, and hydroelectric stations have a long life.