Flexible building-integrated solar energy technologies towards carbon neutrality

In our pursuit of a sustainable future,the role of buildings in reducing carbon emissions cannot be overstated.Building energy consumption is a significant contributor to fossil energy usage and CO_(2)emissions,emphasizing the need for innovative solutions to minimize the environmental impact.With a global commitment to achieving carbon neutrality,the building sector becomes a crucial battleground in this endeavor.Solar energy,characterized by its cleanliness and near-infinite availability,holds great promise for achieving significant energy savings and reducing carbon footprints.Given the proportional energy density of solar radiation to building energy requirements,solar energy technologies are frequently integrated with buildings to foster low-energy and low-carbon strategies and propel the path to sustainability forward.

A spectrally selective surface structure for combined photothermic conversion and radiative sky cooling

The sun and outer space are the ultimate heat and cold sources for the earth,respectively.They have significant potential for renewable energy harvesting.In this paper,a spectrally selective surface structure that has a planar polydimethylsiloxane layer covering a solar absorber is conceptually proposed and optically designed for the combination of photothermic conversion(PT)and nighttime radiative sky cooling(RC).An optical simulation is conducted whose result shows that the designed surface structure(i.e.,PT-RC surface structure)has a strong solar absorption coefficient of 0.92 and simultaneously emits as a mid-infrared spectral-selective emitter with an average emissivity of 0.84 within the atmospheric window.A thermal analysis prediction reveals that the designed PTRC surface structure can be heated to 79.1℃higher than the ambient temperature in the daytime and passively cooled below the ambient temperature of approximately 10℃in the nighttime,indicating that the designed PT-RC surface structure has the potential for integrated PT conversion and nighttime RC utilization.

Effect of the spectrally selective features of the cover and emitter combination on radiative cooling performance

Radiative cooling(RC)shows good potential for building energy saving by throwing waste heat to the cosmos in a passive and sustainable manner.However,most available radiative coolers suffer from low cooling flux.The situation becomes even deteriorated in the daytime when radiative coolers are exposed to direct sunlight.To tackle this challenge,an idea of employing both a spectrally selective cover and a spectrally selective emitter is proposed in this study as an alternative approach.A comparative study is conducted among four RC modules with different spectral characteristics for the demonstration of how the spectral profiles of the cover and the emitter affects the RC performance.The results under given conditions show that the RC module with a spectrally selective cover and a spectrally selective emitter(SC/SE)reaches a net RC power of 62.4 W/m^(2)when the solar radiation is 800 W/m^(2),which is about 1.8 times that of the typical RC module with a spectrally non-selective cover and a spectrally selective emitter(n-SC/SE).When the ambient temperature is 30°C,the SC/SE based RC module realizes a daytime sub-ambient temperature reduction of 20.0°C,standing for a further temperature decrement of 9.2°C compared to the n-SC/SE based RC module.