Combined Radiative Cooling and Solar Thermal Collection: Experimental Proof of Concept

Abstract

Climate change is becoming more important day after day. The main actor to decarbonize the economy is the building stock, especially in the energy used for Domestic Hot Water (DHW), heating and cooling. The use of renewable energy sources to cover space conditioning and DHW demands is growing every year. While solar thermal energy can cover building heating and DHW demands, there is no technology with such potential and development for space cooling. In this paper, a new concept of combining radiative cooling and solar thermal collection, the Radiative Collector and Emitter (RCE), through the idea of an adaptive cover, which uses different material properties for each functionality, is for the first time experimentally tested and proved. The RCE relies on an adaptive cover that uses different material properties for each functionality: high spectral transmittance in the solar radiation band and very low spectral transmittance in the infrared band during solar collection mode, and high spectral transmittance in the atmospheric window wavelength during radiative cooling mode. Experiments were performed during the summer period in Lleida (Dry Mediterranean Continental climate). The concept was proved, demonstrating the potential of the RCE to heat up water during daylight hours and to cool down water during the night. Daily/nightly average efficiencies up to 49% and 32% were achieved for solar collection and radiative cooling, respectively.

Covering Energy Demands of Buildings with an Adaptive Radiative Collector and Emitter (AD-RCE)

“…Thus, during the day the user can decide to apply it to heat up water or cool it down, adapting to variable energy demands of the building. The RCE concept has already been demonstrated experimentally with a prototype [7] and a model has been validated [8], whereas the ad-RCE is still under development. We aim to develop and validate a new ad-RCE model and to design, build and test a new ad-RCE prototype in the following 2 years.…”

Applications of radiative sky cooling in solar energy systems: Progress, challenges, and prospects

“…Results reveal that the hybrid system can cover 54% of annual heating demand and 53% of annual cooling demand. Vall et al [127,128] proposed a black painted radiative collector and emitter, in which a glass screen was employed as the cover in the solar heating mode but was replaced by a polyethylene film in the radiative cooling mode. Experimental results suggested that average solar thermal efficiency up to 49% and radiative cooling efficiency of 32% were achieved respectively.…”

Integration of daytime radiative cooling and solar heating

“…Conversely, a combination of nighttime radiative cooling and solar heating can be found in Refs. 31 , 32 , 33 , 34 , 35 …”