Well there is still wind and hydro power plants. The problem is that all the clean alternatives cannot generate power every hour of every day in the year. 
If you look back 15 years though, technology has come very far. Someone will invent something that actually works to sort this issue out at an affordable price.

I am not too worried, we still have plenty of time left to go over to clean energy since only some cities are badly polluted, most of the planet is still fine for now.