The UK currently generates about 1.5 percent of its electricity from hydroelectric schemes. Although further large scale development potential is limited, there is scope for exploiting our remaining small scale hydro resources in a sustainable way.
Understanding hydroelectric power
Hydroelectric power is the energy derived from flowing water. This can be from rivers or man made installations, where water flows from a high level reservoir down through a tunnel and away from a dam.
Turbines placed within the flow of water extract its kinetic energy and convert it to mechanical energy. This causes the turbines to rotate at high speed, driving a generator that converts the mechanical energy into electrical energy.
The amount of hydroelectric power generated depends on the water flow and the vertical distance the water falls.
Types of hydroelectric schemes
There are 3 main types of hydroelectric schemes in use in the UK:
- Storage schemes – In storage schemes, a dam impounds water in a reservoir that feeds the turbine and generator that are usually located within the dam itself.
- Run of river schemes – Run of river schemes use the natural flow of a river, where a weir can enhance the continuity of the flow. Both storage and run of river schemes can be diversion schemes, where water is channeled from a river, lake or dammed reservoir to a remote powerhouse containing the turbine and generator.
- Pumped storage – Pumped storage incorporates two reservoirs. At times of low demand, generally at night, electricity is used to pump water from the lower to the upper basin. This water is then released to create power at a time when demand, and therefore price, is high. Pumped storage is very good for improving overall energy efficiency.
UK use of hydroelectricity
There are 3 main categories used to define the output from hydroelectric power:
- Large scale capacity: hydro plant producing more than 5 megawatts
- Small scale capacity: hydro plant producing less than 5 megawatts
- Micro scale capacity: hydro plant producing less than 50 kilowatts
The total hydroelectric installed capacity in the UK at the end of 2011 was approximately 1676 megawatts, which is around 1.9 percent of the current total UK generating capacity and.
Hydroelectric power’s contribution to our renewables targets
The UK currently generates about 1.5 percent of its electricity from hydroelectric schemes – most of which are large scale schemes in Scotland.
Hydroelectric energy uses proven and efficient technology; the most modern plants have energy conversion efficiencies of 90 percent and above. Hydro has a typical load factor of 35 percent to 40 percent.
It is unlikely we will see again the scale of development witnessed in the UK in the 1950s and 1960s. Opportunities to use this technology on a large scale are now limited, not only because of environmental concerns but also because many of the most economically attractive sites for schemes have already been used.