We need a mix of nuclear, clean coal with carbon capture and renewables (wind, tidal, wave, biomass etc.) and a huge expansion of urban tri-gen CHP facilities to provide district heating/cooling much more efficiently. Personally, I think the main grid supply will need base load turbine generators (hopefully nuke and clean coal) for the foreseeable future. That said, it’s surprising what painless, easy and cheap energy efficiency measures can do too.