in
Iitti, Finland Run-of-the-river, or ROR, hydroelectricity is considered ideal for streams or rivers that can sustain a minimum flow or those regulated by a lake or reservoir upstream. A small dam is usually built to create a headpond ensuring that there is enough water entering the
penstock pipes that lead to the
turbines, which are at a lower elevation. through a pipe and/or tunnel leading to electricity-generating turbines, then return the water back to the river downstream. Run-of-the-river projects are dramatically different in design and appearance from conventional hydroelectric projects. Traditional hydroelectric dams store enormous quantities of water in
reservoirs, sometimes flooding large tracts of land. In contrast, run-of-river projects do not have the
disadvantages associated with reservoirs and so cause fewer environmental impacts. —run of the river, in
Sault Ste. Marie, Michigan, US. The use of the term "run-of-the-river" for power projects varies around the world. Some may consider a project run-of-the-river if power is produced with no water storage, but limited storage is considered run-of-the-river by others. Developers may mislabel a project run-of-the-river to soothe public perception about its environmental or social effects. The
European Network of Transmission System Operators for Electricity distinguishes
run-of-the-river and pondage hydropower plants, which can hold enough water to allow generation for up to 24 hours (reservoir capacity / generating capacity ≤ 24 hours), from
reservoir hydropower plants, which hold far more than 24 hours of generation without pumps. The
Bureau of Indian Standards describes run-of-the-river hydroelectricity as: Many of the larger run-of-the-river projects have been designed to a scale and generating capacity rivaling some traditional hydroelectric dams. For example, the
Beauharnois Hydroelectric Generating Station in Quebec is rated at 1,853 MW (
Megawatts). Some run-of-the-river projects are downstream of other dams and reservoirs. The reservoir was not built by the project but takes advantage of the water supplied by it. An example would be the 1995 1,436 MW
La Grande-1 generating station. Previous upstream dams and reservoirs were part of the 1980s
James Bay Project. There are also small and somewhat-mobile forms of a run-of-the-river power plants. One example is the so-called
electricity buoy, a small floating
hydroelectric power plant. Like most buoys, it is anchored to the ground, in this case in a river. The energy within the moving water propels a
power generator and thereby creates electricity. Prototypes by commercial producers are generating power on the
Middle Rhine river in Germany and on the
Danube river in Austria. == Major types ==