Researchers led by Yuan Yang, assistant professor of materials science and engineering at Columbia Engineering, along with colleagues at the Department of Chemistry at Columbia University, and Stanford University have developed a new, scalable, and low-cost “dip and dry” method for fabricating a highly efficient selective solar absorber (SSA) that can harness and convert sunlight to heat for use in a wide range of energy-related applications, from heating water and generating steam to residential heating.
Researchers determined that the plasmonic-nanoparticle-coated foils created by their method perform as well or better than existing SSAs and maintain high efficiency throughout the day, regardless of the angle of the sun, due to the wide-angle design. They propose that the simple, inexpensive, and environmentally friendly process provides an appealing alternative to current SSA fabrication methods.
“We saw an unmet need for a facile, inexpensive, and sustainable method for fabricating high-performance SSAs,” said Yuan Yang. “We were pleased that our relatively simple process produced SSAs that performed on par with commercial SSAs and designs reported in other research. To our knowledge, this is the first time a plasmonic SSA has been made using such a process, and the scalability and cost of this approach brings us closer to making solar energy a practical reality for more people.”
Harvesting sunlight for renewable energy remains a primary objective for scientists. Solar-thermal converters, which can absorb light across the entire solar spectrum and convert it to heat at remarkably high efficiencies, offer a highly promising pathway for solar-energy harvesting. However, attaining high-efficiency solar-thermal conversion at low cost remains a challenge.
The selective solar absorber (SSA) developed by the researchers appears black, and thus absorptive, under sunlight (as shown on the photograph on the left). However, for thermal radiation, it behaves like a non-emissive metal mirror (reflecting the dark blue sky, as shown on the thermograph on the right), and prevents the absorbed solar energy from being radiated away and lost.
—Figure courtesy of Jyotirmoy Mandal and Yuan Yang/Columbia Engineering
With its wide angle, the SSA addressed another long-standing problem faced by solar-absorbing surfaces: the ability to absorb sunlight throughout the day from sunrise to sunset. In tests, the resulting SSAs showed a significantly higher solar absorption at all angles (~97% absorption when the sun is above, ~80% when near the horizon) than existing designs.
A low-cost and scalable approach is much sought after by various researchers,” he said. “I am excited that Yang’s research team demonstrated a scalable and environment-friendly process based on the ‘dip-and-dry’ technique. Their durable and high performance plasmonic solar absorber will find immediate applications in solar-thermal systems.”
The team plans to test other combinations of metals besides zinc-copper and zinc-silver and explore ways to further increase efficiencies. They are especially excited about the potential for the simple and affordable process to be utilized for solar conversion in developing countries.
A galvanic-displacement-reaction-based, room-temperature “dip-and-dry” technique is demonstrated for fabricating selectively solar-absorbing plasmonic-nanoparticle-coated foils (PNFs). The technique, which allows for facile tuning of the PNFs’ spectral reflectance to suit different radiative and thermal environments, yields PNFs which exhibit excellent, wide-angle solar absorptance (0.96 at 15°, to 0.97 at 35°, to 0.79 at 80°), and low hemispherical thermal emittance (0.10) without the aid of antireflection coatings. The thermal emittance is on par with those of notable selective solar absorbers (SSAs) in the literature, while the wide-angle solar absorptance surpasses those of previously reported SSAs with comparable optical selectivities. In addition, the PNFs show promising mechanical and thermal stabilities at temperatures of up to 200 °C. Along with the performance of the PNFs, the simplicity, inexpensiveness, and environmental friendliness of the “dip-and-dry” technique makes it an appealing alternative to current methods for fabricating selective solar absorbers.