In a hundread years, the French, being that they never give up on anything that isn't war related, will have perfected the Fusion reactor - plenty of heavy hydrogen in the sea, and there's about 27,000 fissing-fusion bombs around the world that'll be useless once the worlds fully globalised. Renewables such as wind, tidle, geothermal, hydro and solar will be used to balence the load. (IE, stop votage peaks, just are they are used today).
Fossil fuels will be well finished. God, the world consumes so much fossil fuels today, and with China and India just begining to start burning the stuff (with a combined population of 3 times that of the present western world) that's a lot of extra oil/fosil fuel consumers, and I reckon they'll not be the mainstream energy source in the next 30years time. no ways, we simply don't have enough.