Wind power technology is already relatively mature, producing electricity under almost profitable conditions. Current machines can develop powers from 1.25 to 2.5 MW. The rotors fitted on 2.5 MW machines have a span of up to 80 m .
Virtually all high-power wind turbines have a three-blade rotor, which offers higher efficiency than two-blade rotors, without making construction of the wind turbine overcomplicated.
Wind energy is almost competitive, the cost price of the electricity produced being in the region of D 50/MWh. The main drawback with wind energy lies in the fact that it is intermittent and cannot be modulated to match demand. Intermittent operation must be compensated by the grid, which limits the share of electricity that can be supplied by wind energy.
In the future, the price of fossil fuels, together with constraints on CO2 emissions, should make wind energy more competitive.
Recently, the development of wind energy, especially within the European Union, has been supported by a voluntary policy, imposing an attractive buy-back price. The installed power has therefore increased considerably over the last few years, especially within the European Union.
The global figure reached 74 GW in 2006 and 94 MW in 2007. The installed power in Germany reached 22 GW in 2006. The two other European leaders are Spain with 11.6 GW and Denmark with 3.1 GW installed in 2006. In the USA, the installed capacity in 2006 was at the same level as in Spain.
We can expect to see offshore projects developing in the future, despite higher costs, to take advantage of stronger and more regular winds and also to avoid the visual and sound nuisance associated with land-based constructions. Denmark already has an offshore installed power of 400 MW. Germany is considering the installation of offshore sites which will produce 10 GW in 2015 and 20 GW in 2020.
In addition to wind energy production at sea, there is a revival of interest in the possibility of using sea movements [currents, waves), a field which has been studied for many years. There are various ways of harnessing the energy from the sea:
- Mechanical energy of the waves, tides or sea currents exploited by water turbines similar to wind turbines, but located under the sea.
- Thermal energy of the seas in the inter-tropical regions, based on the temperature difference between surface water and deep water.
- Energy of the salinity gradients based on the difference in salinity between fresh water and sea water.
Due to the difficulties in producing and transporting the energy produced, developments in this field have not gone beyond the stage of design, isolated facilities (the Rance tidal power plant) or prototypes (wave energy and water turbines). For the time being, offshore production of wind energy seems to be the only option feasible on a large-scale basis.
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