Spectrally Selective Absorbers/Emitters for Solar Steam Generation and Radiative Cooling‐Enabled Atmospheric Water Harvesting

Abstract

Renewable energy harvesting from the sun and outer space have aroused significant interest over the past decades due to their great potential in addressing the energy crisis. Furthermore, the harvested renewable energy has benefited another global challenge, water scarcity. Both solar steam generation and passive radiative cooling‐enabled atmospheric water harvesting are promising technologies that produce freshwater in green and sustainable ways. Spectral control is extremely important to achieve high efficiency in the two complementary systems based on absorbing/emitting light in a specific wavelength range. For this reason, a broad variety of solar absorbers and IR emitters with great spectral selectivity have been developed. Although operating in different spectral regions, solar selective absorbers and IR selective emitters share similar design strategies. At this stage, it is urgent and necessary to review their progress and figure out their common optical characteristics. Herein, the fundamental mechanisms and recent progress in solar selective absorbers and IR selective emitters are summarized, and their applications in water production are reported. This review aims to identify the importance of selective absorbers/emitters and inspire more research works on selective absorbers/emitters through the summary of advances and the establishment of the connection between solar absorbers and IR emitters.

Solar Selective Absorber for Emerging Sustainable Applications

“…[54][55][56]59,60] These photothermal conversion materials have high absorption in the solar spectrum wavelength range, but also have high emission in the infrared spectrum, which inevitably causes significant heat radiative losses. [12,13] Another thermal management approach is to use SSA to minimize radiative heat losses, thus further improving the overall efficiency of the desalination system. [65] In 2016, Chen et al first introduced a commercial SSA (BlueTec etaplus) to ISSG systems, which can produce water vapor (>100 C) at below 1 sun radiation in ambient environment by suppressing convective, conductive, and radiative heat losses (Figure 7a).…”

“…[ 54–56,59,60 ] These photothermal conversion materials have high absorption in the solar spectrum wavelength range, but also have high emission in the infrared spectrum, which inevitably causes significant heat radiative losses. [ 12,13 ] Another thermal management approach is to use SSA to minimize radiative heat losses, thus further improving the overall efficiency of the desalination system. [ 65 ]…”

“…The E λ,Solar ( λ ) is the spectral solar power, and the E λ,B ( λ , T A ) is the blackbody radiation power, q Solar is the total solar irradiance (AM 1.5G, 1 kW m −2 ); σ is the Stefan−Boltzmann constant, T A is the object temperature. [ 12 ]…”

Recent Progress on the Solar‐Driven Interfacial Evaporation Based on Natural Products and Synthetic Polymers

“…Since then, the research on SSG reached a climax, scientists reviewed SSG from the design and thermal management of solar evaporation systems to the dimensions, selection structural design, and light‐absorbing layer of PMs, and published dozens of articles. [ 16–31 ] Finally, Zhu's group [ 32 ] exhibited the structural designs of interfacial solar vapor generators to improve the energy transfer efficiency and evaporation rate. Mi and his colleagues [ 33 ] also present the latest strategies in reducing salt accumulation on the evaporator for solar desalination and brine treatment.…”

Thermochromic Materials for Smart Windows: A State-of-Art Review

“…A significant portion of the energy consumption in buildings is due to heating, ventilation, and air conditioning (HVAC). Numerous studies have focused on materials with tunable optical properties to regulate and convert solar energy for different applications (Li et al, 2020a, Li et al, 2020bWang et al, 2020a;Wang et al, 2020b;Wang et al, 2020c). Since windows are substantial sources of heat to the building envelopes, recent investigations on smart windows aim to reduce energy consumption while maintaining thermal comfort for the indoor environment (Khandelwal et al, 2017;Rezaei et al, 2017).…”