Researchers at MIT are using thermophotovoltaics (TPV) to turn light into electricity. It uses photo diodes to harvest the energy and use the electricity to run electrical systems of the car. The light-based system is not meant to replace a car's engine but could run subsystems. It works by shining intense light onto new types of photo diodes to make electricity and bouncing any excess light back to the light source. It is said to be 40 - 50% efficient.
At the heart of their energy system would be a cylindrical element, such as tungsten, etched with tiny pits -- nano-holes -- so it emits intense light at selected wavelengths when heated to a high temperature, perhaps 2,200 degrees Fahrenheit (1,500 Kelvin). Special light-sensing cells, made of a new material such as gallium-antimonide, would surround the glowing element, picking up the radiated light. A highly specialized filter, set between the two, would let the most useful light wavelengths pass through to hit the photo diodes, while reflecting light of less useful wavelengths back to the heating element, pumping up the temperature. There are numerous engineering problems that need to be solved. For example, the light-collecting cells have to be cooled: Also, different materials are being tested to see which work best in terms of light emissions, light harvesting and light reflection.
For more information go to: MIT uses thermophotovoltaics to harvest energy