Directives to reduce emissions of CO₂ from burning carbon-based fuels (coal, oil, natural gas) are used to push forward wind energy, despite its being a diffuse, intermittent, and highly variable source of energy – and therefore necessarily expensive, inefficient, and land intensive. The ability of wind turbines to reduce CO₂ emissions in the power sector (never mind transportation, heating, animal agriculture, deforestation, and ocean pollution, and let alone population growth and urbanization) is only assumed and never tested.
Wind energy is credited with reducing CO₂ in a one-to-one substitution from the average mix of other electricity generators on a grid. The assumption is that 1 kWh of wind energy prevents the CO₂ emissions of 1 kWh produced by other sources. But that ignores many variables.
First, the average mix of other sources does not reflect which sources are most likely to be ramped down in response to wind energy production. Where there is adequate hydropower, for example, that is the source most likely to be modulated, and thus there are no CO₂ savings. Otherwise, quickly responding natural gas plants – and smaller coal plants – are the usual sources that are modulated. And that causes them to operate less efficiently, that is, with more CO₂ emissions in relation to their energy production.
Furthermore, combined-cycle natural gas turbines are almost twice as efficient as open-cycle gas turbines, but only the latter can respond quickly enough to be used to balance the fluctuations of wind energy. The result is that although the expansion of wind energy drives a corresponding expansion of gas plants for balancing (and burning natural gas emits much less particulates as well as half the CO₂ as burning coal), it also requires that those gas plants operate as open-cycle instead of the much more efficient combined-cycle. In the end, wind + OCGT does not represent a substantial reduction of CO₂ over CCGT alone. It could even increase emissions.
Finally, thermal plants (coal and nuclear) can ramp down their production by simply diverting the steam away from the generating turbines. Thus their production is reduced but not their fuel consumption and consequent emissions. They do so because it can take many hours, even days, to warm up again. This is particularly relevant to those that provide “operating reserve”. Their presence on the grid – burning fuel but not generating electricity – allows the integration of a small amount of wind energy by using these plants to balance its highly variable and intermittent production. Obviously, there would be no reduction in the emissions from these plants as they simply switch production on and off while continuing to burn fuel.
One must also consider that electricity consumption increases every year, not only in already “industrialized” countries, but especially in “developing” countries. New capacity has to be supplied by reliable and affordable sources, not intermittent, highly variable, and expensive sources such as wind.
(Note: In the USA, production of electricity from coal has decreased. It has been replaced by natural gas.)