Solar energy is certainly the best energy source for mankind. It's absolutely inexhaustible, and it doesn't cause any significant harm to environment, unlike nuclear, coal, oil and water energy sources.
My idea is increasing the usage of solar energy globally by covering large uninhabited mountain areas with solar cell panels. It would be the most rational use for such areas, plus these solar batteries would produce much more energy than ones located on flat areas, because sun is much more intensive on big altitudes. Also these batteries could gather and transform heat into electricity.
Just imagine millions of acres of shiny solar plates providing ecologically-friendly energy for cities!