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.
In 2004, Canada was the top hydropower producer in the world (12% of world production). British Columbia, Manitoba, and Quebec generate more than 75% of their power through hydro-electricity.
Capturing and using hydropower
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.
Global Status and Potential of Small Hydro
China has developed more than half of the world's small hydro capacity. In 2004 alone, the country added nearly 4 GW of small hydropower. Other countries actively pursuing small hydropower include Canada, Australia, Nepal and New Zealand.
Small hydropower is often used to supply electricity in remote or autonomous locations, such as rural villages that are not connected to the electrical grid. Hydropower may replace existing diesel generators or provide a community with electricity for the first time.
According to the International Small-Hydro Atlas, about 2000 MW of installed small hydro capacity in Canada is in place, contributing about 3% to the total Canadian installed hydroelectric capacity of 67,000 MW. Ontario Power Generation has 67 hydroelectric stations in Ontario; about half of these are below 10 MW in capacity, and they contribute about 6% of Ontario's power generation. Transalta Utilities operates almost all the small-scale hydro plants in Alberta (Alberta Power has one small plant in Jasper), contributing about 5% of Alberta's total. Nova Scotia operates about 40 small hydro plants supplying about 11% of provincial capacity. New Brunswick also operates about 40 small hydro plants, which contribute about 20%.
A recently completed inventory of Canadian small hydro sites identified over 5,500 sites with a technically feasible potential of about 11,000 MW, but only about 15 per cent of these are economically feasible to develop.
Over the last decade, the small-scale hydroelectric industry has contributed about $100 million per year to the Canadian economy in manufacturing and services and added about 30 to 50 MW yearly to Canada's power supply.
- 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.
- Larger hydro plants, especially those that involve the construction of dams, can have serious impacts on local communities and the upstream and downstream environment. There are many examples of hydro plants around the world where whole communities have been moved, lost their livelihood or had their health compromised.
- Large hydro plants can play an important role in providing electricity if guidelines and best practices are applied in their design, construction and operations; local communities are involved in planning processes; and environmental and social impacts are minimized.
- Hydroelectric reservoirs present a number of challenges, including:
- reservoirs produce greenhouse gas emissions because of decaying vegetation from flooded lands, particularly in tropical regions
- reservoirs typically result in higher levels of naturally occurring mercury in water resources, which is released from land that is flooded
- silt deposits can shorten the operational lifespan of hydroelectric reservoirs.
- Small run-of-river hydro plants are not exempt from challenges including
- frazil ice (slush formed in water that is too turbulent to freeze over) and pipeline freezing must be considered
- seasonal flows affect revenues
- fish migration can be a concern in which case conservation measures (e.g., fish guidance, habitat compensation) have to be implemented.
Links for more information
- Canadian Hydropower Association
- International Association for Small Hydro
- International Hydropower Association
- International Network on Small Hydropower
- International Rivers Network
- Independent Small Power Producers Association of British Columbia
- World Commission on Dams
- International Small-Hydro Atlas
- Pollution Probe's Primer on the Technologies of Renewable Energy
- RETScreen — Small Hydro: pre-feasibility assessment and training modules