It is usual to express the wind energy annual resource in terms of kWh/m2 of swept-through surface. The best sites are close to the sea coasts. As an example, we consider the case of France. There the best sites generate up to 5000 kWh/m2 per year. A 1000 m2 windmill, with a peak power of 1 MW, would yield about 5 GWh/year. Existing large windmills reach peak powers of a few MW. The average surface requirement is of the order of 8ha/MW, i. e. a production of 60 kWh/m2/year. This figure is noticeably less than that expected from photovoltaic facilities, which reach close to 300 kWh/m2/year.

For France, the production potential is estimated to be 66 TWh/year for ground-based facilities and 97 TWh/year for offshore facilities. This figure corresponds to approximately the production of 20 nuclear reactors (57 are in use at this time) and would require 100000 high power windmills with an average density of 20 windmills per km of coast. It is clear that the eco­nomically competitive potential is much less than the technically feasible potential and would depend upon the selling price as well as the environ­mental constraints. Note that since wind energy is intermittent, it can only become competitive when the facility is connected to a network. Under such conditions competitiveness is only marginal for good sites. However, the unpredictable intermittency of wind energy will make network control rather difficult, should the share of wind energy become significant. Further­more, the possibility of windless periods requires that backup electricity production systems be available. This means that wind energy is only able to save fuel but not investment. It is more adapted to fuel-intensive electricity production means, such as gas turbines, than to capital-intensive production means like nuclear reactors. It is also compatible with hydroelectricity.