A system architecture that boosts the energy conservation capacity of passive cooling technology has been developed and tested by researchers from the State University of New York at Buffalo, University of Wisconsin and King Abdullah University of Science and Technology (Saudi Arabia). A prototype device was demonstrated to cool interior spaces without using electricity and to capture solar energy to heat water.

Two solar spectrally selective mirrors composed of 10 thin layers of silver and silicon dioxide and arranged in a V-shape absorb incoming sunlight, turning solar power from visible and near-infrared waves into heat. The mirrors also reflect mid-infrared waves from a vertical box placed between them and serving as a thermal emitter, radiating the associated heat skyward.

The device lowered the temperature inside a test unit by more than 12° C under direct sunlight and by more than 14° C in a simulated nighttime test. The mirrors also harnessed sufficient solar energy to heat water to about 60° C, and the thermal radiation from both sides of the vertically aligned emitter was coupled to the heat sink to realize a record-high local cooling power density of 273.3 W/m² in the laboratory.

The system described in Cell Reports Physical Science was only 70 cm² but the researchers are confident that the structure can be scaled up to cover rooftops and contribute to reduced fossil fuel consumption for heating and cooling.

The double-sided system features a thermally insulated box with V-shape solar spectrally selective plates. Source: Lyu Zhou et al.