Full Spectrum Solar Energy Conversion

Conventional solar energy conversion techniques have seen tremendous success in recent years, with photovoltaics experiencing significant market penetration in locations across the world. However, these modules typically convert no more than 20% of incoming solar energy into electricity, due in large part to inefficient utilization of the entire solar spectrum. Our group is exploring alternative solar energy harvesting schemes that seek to maximize the use of every wavelength in the solar spectrum, enabling significant increases in efficiency with potential for lower cost.

In one project, we are pursuing an approach that utilizes hybrid solar energy conversion, generating electricity from high efficiency multi-junction cells in combination with the capture of sunlight as thermal energy. The highest energy (UV and visible) photons from the sun are converted into electricity via ultra-high efficiency solar cells. The lowest energy (infrared) photons from the sun are directed to a thermal receiver that heats up a molten salt to temperatures of over 500 °C. The thermal energy can then be stored until the energy is needed. This stored energy can be converted to electricity through a heat engine, similar to conventional power plants. We can dispatch this energy when electricity prices rise, providing more solar energy when demand is the highest.  The stored energy can also be used directly to provide process heat for a wide range of commercial and industrial users.

This project, funded by ARPA-E and in partnership with the University of San Diego, San Diego State University, Boeing-Spectrolab, and Otherlab, seeks to demonstrate a prototype renewable, dispatchable, low-cost, and modular energy generation system. Considering the high penetration of solar energy into some energy generation markets, the need for storing excess solar energy for use when the sun is not shining or when energy demand rises has become increasingly more pressing. Our group is principally involved with the design of a solar module that receives concentrated sunlight and uses elemental group III-V materials to generate electricity with >45% efficiency. The module also serves as a spectrum splitter, transmitting low energy infrared light that would otherwise be poorly captured by photovoltaics to a thermal receiver with integrated thermal energy storage. This hybrid solar energy converter is currently being prototyped and will be tested in the field by 2017.

“Our group is exploring alternative solar energy harvesting schemes that seek to maximize the use of every color in the full solar spectrum, enabling significant increases in efficiency with potential for lower cost.”