Carbon emissions

Directives to reduce emissions of CO₂ are used to push forward wind development, despite its being a diffuse, intermittent, and highly variable source of energy – and therefore necessarily expensive and land-use intensive. The ability of wind turbines to reduce CO₂ emissions in the power sector (never mind transportation, heating, animal agriculture, and deforestation, and let alone population growth) 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 balance (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. 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 might also consider that electricity consumption increases every year, not only in already “industrialized” countries, but especially in “developing” countries. Wind and solar (being diffuse, intermittent, and variable and therefore expensive to harness to any large degree) can not meet that growing demand. At best, they might slightly slow the growth of other more reliable and cheaper sources, but they can not halt them, let alone reduce them.

(Note: In the USA, production of electricity from coal has decreased. It has been replaced by natural gas.)

See also

• Climate change
• Renewable energy credits