Adding an Intermediary to Enhance Solar Power
The Sun emits a great deal of energy all the time, which is why we are trying to capture and harness it for our own use. Complicating our efforts with photovoltaics, which can convert light directly to electricity, is the fact that photovoltaic materials generally respond best to one frequency or another, but the Sun's energy covers the spectrum. Researchers at MIT however have developed a system to capture more of that energy by adding an intermediary.
What MIT has built is a solar thermophotovoltaic system (STPV), and others have experimented with them before. What they do is add an intermediary that absorbs sunlight and converts it to heat. That heat is then converted back into light, but at a frequency a conventional solar cell has an easy time capturing. While previous attempts have achieved an efficiency of 1%, the MIT device has an efficiency of 3.2%. The key to this was the design of the intermediary with carbon nanotubes absorbing the sunlight and heating up, and the photonic crystal they are bonded to. That crystal was carefully engineered to emit light that matches what the photovoltaic cell can absorb.
When the researchers tested their design, they subjected it to light that was 750 times more intense than sunlight. While that sounds like a lot, previous STPV systems required concentrations thousands of times greater than natural sunlight. The researchers are confident they will be able to bring that number down further and potentially reach the 20% efficiency needed to be economically viable.