A previous article covered the remarkable growth of Spanish wind and the success in incorporating this electricity into Spain's grid. It focused on the periods in November when wind provided much of the country's electricity, peaking at almost 54% in the early morning of 8 November 2009. Wind was almost 23% of the Spanish total electricity production during the month of November, beating nuclear for the first time. Solar also grew rapidly in 2009, up from 1% in 2008 to 3% of national output. The effect on CO2 emissions from power generation was striking. Carbon dioxide output fell by over a sixth, largely as a result of the growth in renewables.
Those who oppose the growth of wind in countries like the UK often say that renewables are so unreliable that conventional power stations have to operate at the same time, just in case the wind drops. They say that therefore wind or solar have no effect on CO2 emissions. Spain's 2009 figures demonstrate that this is not true.
Spanish electricity consumption fell by about 4.3% in 2009 because of the poor state of the country's economy. The output from renewables – excluding hydro – was up 22% over the year. So we would expect carbon dioxide emissions to fall somewhat. But the decrease was magnified by the substantial fall in coal and gas use in power stations. Coal was down 24% and gas 9%. In total, the CO2 output from the country's power generation sector was down 17% on the year. The Spanish electricity producers association wrote (30 December 2009) about the fall in CO2 emissions and its relation to rising renewable production saying 'Paralelamente, las emisiones de CO2 descendieron en torno al 17%' (In parallel, CO2 emissions fell an overall 17%).
This data should provide the strongest possible rebuttal to those who claim that wind power doesn’t reduce CO2 emissions
Footnote  The original article said that wind output increased by 23%. In the comments below, Vinny correctly points out that the 22% was for renewables within Spain's 'Special Regime', which includes solar as well as wind. I've changed the article to reflect Vinny's correction.