Introduction – Research led by the Yuan Yang, assistant professor of material science and engineering at Columbia Engineering. Along with the colleagues at the Department of the Chemistry AT Columbia University and at Stanford University, they have developed an innovative, scalable and low cost method for fabricating naming “dip and dry”. A highly efficient selective solar absorber (SSA) that can harness and convert sunlight into heat for further usage in a wide range of energy related applications, from heating water and generating steam to residential heating. The team’s method is base4d on in a news paper, “Scalable, ‘Dip-and-dry’ Fabrication of a Wide-Angle Plasmonic Selective Absorber for High-efficiency Solar-thermal Energy Conversion,” published in Advanced Materials on August 28.
Process – The authors explained that the plasmonic-nano-particle-coated foils created by their process perform as well or better than existing SSAs and manages high efficiency throughout the day, despite of the angle of the sun, due to the wide-angle design. They recommended that the simple, low-cost, and environmentally friendly process provide purposeful option to present SSA fabrication methods.
As a surface component of solar-thermal converters, SSAs are optimal because they have conflicting optical properties for solar and thermal radiation. They are fully black comparing across all colors of sunlight (from UV, to visible, to near infrared light) and can therefore soak almost all the light and become very hot. However, different from common black surfaces, they are metallic, i.e. non-emissive, when it comes to thermal radiation (mid- to far-infrared light). Heat is therefore not lost as radiation and could be adopted, for example, to heat water or generate steam.
Most SSAs are built using more sophisticated, energy-expensive, or harmful manufacturing processes such as vacuum deposition or electroplating. This enhances both the environmental footprint and cost while limiting their accessibility. As a basis for manufacturing SSAs, the dip-and-dry method is an alluring option, as it yields SSAs that are highly efficient, while bypassing the prices and environmental hazards associated with other access.
Work Experience – Working with equipments and facilities in Columbia Engineering laboratory space and the Columbia Nano Initiative (CNI), the researchers were able to formulate metal-based plasmonic SSAs using an low-cost method that can tune the SSAs to suit different operating conditions, and is compatible with industrial manufacturing methods. By dipping strips coated with a reactive metal (zinc) into a solution containing ions of a less reactive metal (copper), solar-absorbing nano-particles of copper can be easily composed on the zinc strips by a galvanic displacement reaction.
Complications – Because of its wide angle, the SSA found another long-standing problem faced by solar-absorbing surfaces is the ability to soak sunlight throughout the day from sunrise to sunset. In tests, the resulting SSAs displayed a significantly higher solar absorption at all angles than existing designs but the team plans to test other sets and combinations of metals besides zinc-copper and zinc-silver and explore ways to further increase efficiency.