http://www.nature.com/nature/journal/v443/n7107/full/443019a.html
The Sun provides Earth with as much energy every hour as human civilization uses every year. If you are a solar-energy enthusiast, that says it all. No other energy supply could conceivably be as plentiful as the 120,000 terawatts the Sun provides ceaselessly and unbidden. If the tiniest fraction of that sunlight were to be captured by photovoltaic cells that turn it straight into electricity, there would be no need to emit any greenhouse gases from any power plant.

