From wind turbines to solar photovoltaic cells, sustainable business ventures have produced a plethora of well-tested methods for converting renewable energy into electricity. Though much remains to be done when it comes to actually replacing coal and other fossil fuel-based electricity with a clean energy grid, there is little doubt that the technology to do so exists. A far greater challenge has been finding a truly renewable and sustainable energy source capable of replacing the petroleum-based liquid fuels used to power motor vehicles and aircraft. But scientists at the California Institute of Technology may finally be closing in on a solution.