The problem is usually not 4 good months but the time when you don't have renewables since the demand is still there, or even higher (during winter). And then you have problems (see Germany, which is currently the biggest polluter around because of their renewables policy). They are lucky that they have majority of energy coming from hydro, since that is quite reliable, but still, what happens if drought strikes? Not an impossible scenario in these times of global warming. How much fossil fuels are they burning yearly instead of running a nuclear power plant?
I'd be more than happy if renewables did solve all problems, but I don't see how can that work today.