Following years of stagnation and bad press, hydro power is experiencing resurgence. Technologies with a lower environmental impact such as run-of-river, small hydro and low head turbines are proving to be extremely popular to both appease critics of hydro and meet energy needs. So much so that in the USA, the regulator of hydro projects, the FERC, has signed memorandum of understandings with five states, California, Colorado, Washington, Maine, and Oregon, to streamline the licensing of small projects.
Selected Types of hydropower
Impoundment uses a dam to store water. Water may be released either to meet changing electricity needs or to maintain a constant water level. These can be either high head or low head.
Run-of-river utilises the flow of water within the natural range of the river, requiring little or no impoundment. Run-of-river plants can be designed using large flow rates with low head or small flow rates with high head.
Micro hydropower Projects
These produce 100 kilowatts or less and can utilise low heads or high heads.
A portion of the river is channelled through a canal or penstock, but may require a dam.
“Pumped Storage” is another form of hydro-electric power. Pumped storage facilities use excess electrical system capacity, generally available at night, to pump water from one reservoir to another reservoir at a higher elevation. During periods of peak electrical demand, water from the higher reservoir is released to generate electricity. Although pumped storage sites are not net producers of electricity (it actually takes more electricity to pump the water up than is recovered when it is released) they are a valuable addition to electricity supply systems, because of their ability to store electricity for use at a later time when peak demands are occurring. Storage is even more valuable if intermittent sources of electricity such as solar power or wind power are hooked into a system, which is then termed “hybrid”.
The electrical storage efficiency of pumped storage devices is estimated at 80%.