A team of researchers at Massachusetts Institute of Technology (MIT) has come up with a new way to capture solar energy that makes it easier to store and be used on demand at a later time.
Making Solar Panels More Efficient
The team created a device that improves the efficiency of solar panels by using wavelengths of light that normally are wasted because they cannot be captured by conventional photovoltaic cells. In this new system, the sun heats a high-temperature material, a two-layer absorber-emitter device placed over the PV cells. The outer sunlight-facing layer, the absorber, includes an array of multi-walled carbon nanotubes that efficiently absorbs the light’s energy and turns it into heat. A bonded layer of silicon/silicon dioxide photonic crystals, the emitter, is engineered to convert the heat back into light that can then be captured by the PV cells. This allows much more of the energy in the sunlight to be turned into electricity.
This new system combines the advantages of solar photovoltaic systems, which turn sunlight directly into electricity, and solar thermal systems, beneficial for delayed use because heat is more easily stored than electricity. The basic concept has been explored for several years, according to the team.
A lot of work has been done on the theoretical design of surfaces for solar thermophotovoltaic systems (STPVs) and fabrication of single components for potential integration in these systems, says team member Andrej Lenert, an MIT graduate student who expects to be awarded his PhD in mechanical engineering this spring.
Lenert has been involved with STPV efforts at MIT ever since the university opened the Solid-State Solar Thermal Energy Conversion (S3TEC) Center in 2010, but his interest goes back even further to a radiation class.
Schematic of the planar STPV layout. Incoming solar radiation is converted to heat at the absorber; heat is selectively radiated by the emitter, and converted to electrical power at the PV cell.
The highest efficiency cells have not always been the most economical — for example a 30% efficient multijunction cell based on exotic materials such as gallium arsenide or indium selenide produced at low volume might well cost one hundred times as much as an 8% efficient amorphous silicon cell in mass production, while delivering only about four times the output.