Toussaint Leads Effort to Develop Next-generation Solar Collectors

solar collectors

Thanks to a MechSE professor and a multi-institution team of experts, traditionally expensive solar energy may become affordable sooner than previously thought.

The U.S. Department of Energy SunShot Initiative has selected a team of researchers from the University of Illinois at Urbana-Champaign, the University of Michigan, and the National Renewable Energy Laboratory to develop and deploy new solar energy technology that will help to make solar energy cost-competitive with traditional forms of electricity by the end of the decade. Led by principal investigator Kimani Toussaint, an associate professor in the Mechanical Science and Engineering Department (MechSE) at Illinois, his team of researchers have received a cooperative award–one of only six awards granted nationwide–for their project on improving concentrating solar power (CSP) technologies. Read the Department of Energy press release.

CSP involves harnessing the energy of the sun by using optics to direct sunlight to a thermal energy converter, where it is subsequently transduced to electricity. The workhorse of CSP optics-based technologies currently being pursued is the parabolic trough concentrator, which employs large focusing mirrors to concentrate sunlight onto a receiver tube or pipe that contains a heat-transfer fluid, a critical component of the thermal energy converter.

The team has proposed to use a metasurface design to develop a planar focusing collector (PFC) as a potential low-cost alternative to the conventional parabolic trough concentrator. Metasurface engineering is an emerging field that uses artificially created two-dimensional, thin surfaces that are designed to exhibit properties (e.g., electromagnetic or acoustic), that are not found in nature.  For the optical spectrum this often requires the use of nanostructured materials as the building blocks for any design.

“We have a really exciting opportunity to harness the best of nanotechnology for an application that will truly impact the world’s energy portfolio,” Toussaint said. “Researchers have already demonstrated how to utilize arrays of optical nanoantennas, on a glass substrate for example, to focus light to a desired spot. The challenge will be to do this over a very broad range of optical wavelengths while mitigating potential losses. Not only would development of such a metasurface be an amazing contribution to CSP, but to this type of nanotechnology, as well.”

The design approach will result in a metalized PFC that is significantly lighter than current parabolic trough mirrors. Roll-to-roll (R2R) nanoimprint manufacturing, pioneered by project partner Jay Guo’s laboratory at the University of Michigan, will be further developed to enable scalable manufacturing of the PFC.

“The R2R-based manufacturing process has gained much attention in recent years as it promises high throughput and cost reduction in manufacturing by integrating both additive and subtractive processes in a continuous manner on a moving web,” Guo said. “The R2R nanoimprint technology inherits its high-resolution feature from traditional nanoimprint lithography, but with a speed of nanopatterning one or two orders faster. For this Energy Department funding program, R2R nanoimprint and other R2R processes will be used to scale to large areas, which will be essential in achieving the cost target of the proposed new flat CSP mirror.”

The team plans for the designed PFC to have an approximately 97% solar-weighted reflectance from 400-2000 nm and concentration ratio of 50.  The reduced surface area of the PFC and lower sensitivity to wind loads will contribute to overall cost reduction. The team aims to achieve an end target PFC cost of less than $50/m2.

According to the 2012 SunShot Vision Study, the solar collector field (i.e., collection optics) is “the single largest capital investment in a concentrated solar power (CSP) plant.”  SunShot’s bold vision is to reduce the projected levelized cost of energy contribution for the solar field to less than 2 cents/kWh by 2020, so that the solar energy cost may be reduced to 6 cents/kWh—thereby making solar energy a competitive renewable energy resource.

Upon successful completion of all three project phases the Department of Energy will have provided a total of $1.4 million to the research team.