A device that gets scorching hot as it captures and traps much of the sun's energy using a greenhouse-like approach could usher in an era of inexpensive electricity from the sun.
The breakthrough comes from a sunlight-absorbing material made of photonic crystals that are arranged to prevent the escape of most of the energy it captures from direct sunlight.
In this case, infrared radiation from the sun enters the device through holes in the surface, but the reflected rays are blocked when they try to escape, explains Peter Bermel, an electronics researcher working on the device at the Massachusetts Institute of Technology.
This blockage is achieved by a geometry that limits re-radiation of the sun's rays to a narrow range of angles — the solar disk and region right around the sun. The rest of the rays stay in the device and heat it up.
All this concentrated heat is focused on the production of high-energy photons, which are used to generate electricity via a thermophotovoltaic device.
Conventional photovoltaic cells are limited in their ability to convert sunlight into electricity due to the inefficient conversion of the broad spectrum of sunlight that hits the cells. That's because heat is absorbed across a broad range of wavelengths and then tailored to generate the high-energy photons needed to generate electricity. The approach, Bermel said, could reach efficiencies of 35 to 36 percent, which is higher than the Shockley-Queisser limit.
Thermophotovoltaic devices have existed since the 1950s, but the concentration of sunlight is traditionally done with giant and expensive arrays of mirrors. Bermel's approach, by contrast, can be made with inexpensive chip-manufacturing technology, he said.
A major expense, though, will come in the equipment needed to track the sun so that the device is always getting direct sunlight to take advantage of the selective-angle