6.1.3 Geographical assessment

Hydropower is the largest and most mature application of renewable energy, with some 678,000MW of installed capacity worldwide, producing over 22% of the world's electricity (2564TWh/yr) in 1998. Of this, 27,900MW is at small-scale sites, generating 115TWh/year. In Western Europe, hydropower contributed 520TWh of electricity in 1998, or about 19% of EU electricity (avoiding thereby the emission of some 70 million tonnes of CO₂ annually). Despite the large existing hydropower capacity, there is still much room for further development as most assessments assume this is only around 10% of the total world viable hydro potential.

 

6.2 TECHNICAL OUTLINE

6.2.1 From water to electricity

Hydropower systems convert the energy of flowing water into mechanical power, and then usually into electricity. The water flows via a channel or penstock to a waterwheel or turbine where it strikes the bucket of the wheel, causing the shaft of the waterwheel or turbine to rotate. When generating electricity, the rotating shaft is connected to an alternator or generator. The electrical energy produced may be used directly, stored in batteries, or inverted to produce utility-quality electricity.
The amount of power a specific hydropower site can produce depends on its head, i.e. the height H (m) through which the water falls, and the flow rate. The head determines the useful potential energy of a site (PE = m·g·H). The flow of the river is the volume of water (m³) which passes a cross section of the river per second (Q m³/s).

The gross theoretical power (P kW) available is then given by:
P = 9.81 × Q × H

This available power will be converted by the hydro turbine into mechanical power. As the turbine and the rest of the electro-mechanical equipment have efficiencies lower than 100% (usually 90 to 95%), the electric power generated will be less than the available gross power.