Hydroelectric power is the energy derived from flowing water. The energy in the water is generated by the Sun; the water in seas and oceans is heated by the Sun and evaporates, rising up into the atmosphere.
When it falls as rain on higher ground, it has gained potential energy – it has the potential to fall at speed which is kinetic energy (energy from movement).
This energy can be tapped either from running rivers or from man-made reservoirs where stored water is allowed to flow down through a tunnel.
UK developments are likely to focus on small-scale, ‘run-of-river’ projects due to their lower environmental impact and smaller spatial requirement.
How it works
The water flows over a turbine and the power of the water makes the turbine rotate. The turbine is connected to a generator that converts this energy into electrical energy, the form we use in homes and businesses.
Source: Unites States Army Corps of Engineers
In a 'run-of-river' scheme the energy from the flowing river water is captured. The flow can be controlled or enhanced using a variety of techniques including landscaping the river or installing a weir.
There are also 'run-of-river' diversion schemes where water is channelled away from the main body of water and diverted to a powerhouse containing a turbine and generator. Having flowed through the turbine the water either flows back to the river or to an alternative watercourse. Diversions schemes can also be incorporated in to storage schemes.
A 'storage' scheme commonly consists of a reservoir created by a dam. The dam raises the level of the water to create a hydrostatic head. This is the difference between the level of the water in the reservoir, on one side of the dam, and the lower level of water on the other side. When electricity is required gates are opened in the dam which causes the water to flow from the higher body of water to the lower body of water. The flowing water causes turbines, attached to generators, to turn and electricity to be generated. It is common for the turbine and generator to be located within the dam itself. The amount of energy created depends on the height of the hydrostatic head.
A 'pumped storage' scheme works using the same principles as a storage scheme but incorporates two reservoirs – an upper reservoir and a lower reservoir. When demand for electricity is low, electricity is used to pump water from the lower reservoir to the upper reservoir. When demand is high the water flows from the upper reservoir to the lower reservoir, using gravity, and causes turbines en route to turn. The turbines are attached to generators and electricity is generated.
Pumped storage is not considered to be a form of renewable energy because it uses electricity to pump water from the lower reservoir to the upper reservoir.
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