Renewable Energy Resources for Irrigation - Practices of Irrigation and On-farm Water Management - page 503

flowing stream of water, or moderate sea wave, can yield considerable amounts of
energy.

13.6.1 Forms of Water Energy

There are many forms of water energy:

• Hydroelectric energy is a term usually reserved for large-scale hydroelectric

dams. Examples are the Grand Coulee Dam in Washington State and the
Akosombo Dam in Ghana.

•

Micro-hydro systems are hydroelectric power installations that typically produce
up to 100 kW of power. They are often used in water-rich areas as a remote area
power supply (RAPS). There are many of these installations around the world,
including several delivering around 50 kW in the Solomon Islands.

• Damless hydro systems derive kinetic energy from rivers and oceans without

using a dam.

• Wave power uses the energy in waves. The waves usually make large pontoons

go up and down in the water, leaving an area with reduced wave height in the
“shadow.” Wave power has now reached commercialization.

• Tidal power captures energy from the tides in a vertical direction. Tides come in,

raise water levels in a basin, and tides roll out. Around low tide, the water in the
basin is discharged through a turbine.

• Tidal stream power captures energy from the flow of tides, usually using under-

water plant resembling a small wind turbine. Tidal stream power demonstration
projects exist, and the first commercial prototype is installed in Strangford Lough
in September 2007.

• Ocean thermal energy conversion (OTEC) uses the temperature difference

between the warmer surface of the ocean and the colder lower recesses. To this
end, it employs a cyclic heat engine. OTEC has not been field-tested on a large
scale.

• Blue energy is the reverse of desalination. This form of energy is in research.

13.6.2 Wave Energy

Waves are a free and sustainable energy resource created as wind blows over the
ocean surface. Waves are caused by wind blowing over water, and winds are gener-
ated by the sun heating the earth. Wave energy technology is very young compared
to generating electricity from wind turbines.
Water covers around three-quarters of the earth's surface. The World Energy
Council estimates that the energy that can be harvested from the world's oceans
is equal to twice the amount of electricity that the world produces now. The UK has
by far the highest potential in the European Union for converting wave energy into
electricity. The amount of energy in waves around the UK is more than the energy