From the "executive summary" in "Reduction in Carbon Dioxide Emissions: Estimating the Potential Contribution from Wind-Power," by David White, commissioned by the Renewable Energy Foundation (U.K.), December 2004:
"The CO2 emissions reduction from renewable energy in an island power system must be assessed on the basis on the impact that the accommodation of wind power into the grid will have on the whole supply chain. Electricity differs from other forms of energy, and cannot be stored directly on an industrial scale. Consequently, generation and demand have to be balanced on the grid continuously, and second by second. Policy-makers appear to have only a weak grasp of this critical fact and its implications. Indeed, the accommodation of the variable output from wind turbines into the transmission system is complex and the technical challenges are barely understood outside professional circles. Fossil-fuelled capacity operating as reserve and backup is required to accompany wind generation and stabilise supplies to the consumer. That capacity is placed under particular strains when working in this supporting role because it is being used to balance a reasonably predictable but fluctuating demand with a variable and largely unpredictable output from wind turbines. Consequently, operating fossil capacity in this mode generates more CO2 per kWh generated than if operating normally. This compromising effect is very poorly understood, a fact acknowledged recently by the Council of European Energy Regulators."
