Arizona State University (ASU)

There are two primary methods for capturing and using sunlight today: direct conversion of sunlight to electricity using photovoltaic (PV) solar panels, or focusing sunlight onto a fluid that is used to drive a steam turbine in concentrated solar power (CSP) systems. Storing hot fluid in CSP systems is a less expensive way to generate electricity when the sun is not shining compared to storing electrical energy from PV in batteries. However, PV uses just part of the solar spectrum at high efficiency, while CSP systems use the entire solar spectrum but at low efficiency. Combining the best elements of these two technologies could provide a means to get the most out of the full solar spectrum, generating both electricity and storable heat (for later use) within the same system. Developing hybrid solar energy systems that perform both functions at the same time could provide electricity at cost comparable to traditional sources, whether the sun is shining or not.

Arizona State University (ASU) is developing a hybrid solar energy system that modifies a CSP trough design, replacing the curved mirror with solar cells that collect both direct and diffuse rays of a portion of sunlight while reflecting the rest of the direct sunlight to a thermal absorber to generate heat. Electricity from the solar cells can be used immediately while the heat can be stored for later use. Today’s CSP systems offer low overall efficiency because they collect only direct sunlight, or the light that comes in a straight beam from the sun. ASU’s technology could increase the amount of light that can be converted to electricity by collecting diffuse sunlight, or light that has been scattered by the atmosphere, clouds, and off the earth. By integrating curved solar cells into a hybrid trough system, ASU will effectively split the solar spectrum and use each portion of the spectrum in the most efficient way possible. Diffuse and some direct sunlight are converted into electricity in the solar cells, while the unused portion of the direct sunlight is reflected for conversion to heat.

If successful, ASU’s hybrid solar energy system could offer a 50% boost in efficiency compared to the efficiency of existing CSP systems by capturing and converting different portions of the solar spectrum using the most suitable approach for each.