Fossil fuel use has a couple of serious issues: among them are greenhouse gas emissions and diminishing supplies.  One possible replacement could be "thermochemical fuels": synthetic fuel that can harvest and store the sun's energy in chemical form via high temperature thermochemical conversion of carbon dioxide and water.

Essentially, thermochemical fuels allow solar energy to be easily transported and stored. One recent study has calculated that the entire world's supply of jet fuel in thermochemical form could be met by the production of just one country by harnessing the sun and other essential ingredients for the process. The top contenders based on high solar irradiation and low-level capital costs are the Spain, the USA, Israel, and Chile. The full study can be found here.