In most urban locations those windmills do not even generate, over their lifetimes, enough energy to cover their own manufacture. So their subsidy is a really, really, silly thing to do. It actually makes the problem worse, not better.Tim is right, this is a well understood problem with micro-generation. Assuming the people behind this plan are numerate and informed, which - partisan (and fun) sniping aside - is a reasonable assumption, then it's also reasonable to suppose they know this.
Their intention, therefore, cannot be to reduce energy use and, thereby, carbon emissions. It has long been plain that many carbon crusaders have ulterior agendas. George Monbiot, for example, is basically an anti-capitalism campaigner. But there is a suggestion in this case that while some environmentalists are not just trying to reduce carbon emission, others are not even trying to do this.
Leaving aside the merits of their, anti-capitalism, anti-globalisation, case, there is some reason to suppose that they don't really think carbon emissions are such a pressing problem.