One of the main arguments against a widespread switch to renewable energy is dealing with intermittency: if the wind isn’t blowing, or the sun isn’t shining, no power gets generated. So we need to have a backup source, say a gas power station, to fill in the gaps. Just maintaining it increases cost enormously, so you might as well run it full time.
However, there seems to be some good news on this front. This article on the thinkprogress site describes a new generation of wind turbines which include a storage battery so that excess electricity can be stored for the lean times (I can’t see for how long though). They also employ some more advanced technology to take account of weather forecasting and the state of the power grid to optimise how they run.
So: some good news on this front. Let’s hope we can get some of these installed in the UK.