Semiconductor-based Multilayer Selective Solar Absorber for Unconcentrated Solar Thermal Energy Conversion

Area of Science:

• Materials Science
• Renewable Energy Engineering
• Optics

Background:

• Solar thermal energy conversion is crucial for industrial heating, air conditioning, and electricity generation.
• Achieving high stagnation temperatures (>200°C) with unconcentrated sunlight necessitates spectrally selective absorbers.
• These absorbers require high visible absorptivity and low thermal emissivity.

Purpose of the Study:

• To develop a novel semiconductor-based multilayer selective absorber for efficient solar thermal energy conversion.
• To demonstrate the potential of unconcentrated solar thermal systems for mid-temperature applications.

Main Methods:

• Fabrication of a semiconductor-based multilayer selective absorber.
• Characterization of optical properties (absorptance and emittance).
• Field testing to measure stagnation temperatures under unconcentrated sunlight.

Main Results:

• The absorber exhibits 76% absorptance in the solar spectrum and approximately 5% emittance in the thermal spectrum.
• Field tests achieved a peak stagnation temperature of 225°C.
• This performance is comparable to state-of-the-art selective surfaces.

Conclusions:

• The developed selective absorber effectively utilizes the bandgap energy for efficient solar absorption.
• Unconcentrated solar thermal systems can reach high temperatures, potentially exceeding 300°C with optimization.
• This technology can eliminate the need for solar concentrators in mid-temperature solar applications, such as process heat supply.