Cooling represents a significant use of energy use in buildings. A passive cooling strategy that does not require energy input is thus in great demand. The sun is a major renewable energy resource for humans. The universe at 3 K is an ultimate heat sink. Every object sends out heat incessantly in the form of blackbody thermal radiation. Utilizing a transparency window of Earth’s atmosphere at infrared wavelengths, Dr. Zhu and collaborators previously demonstrated for the first time passive radiative cooling to below the ambient air temperature under direct sunlight, by sending heat to the cold universe. Recently, the cold universe has emerged as a new renewable resource, with key developments such as deep sub-freezing cooling, thermal management of solar cells, and cooling of buildings. However, in order to radiatively cool an object to sub-ambient temperatures, sunlight must be reflected away. It would be desirable if the two renewable energy resources–hot sun and cold universe, can be harvested synergistically. In this project, we will develop a dual energy harvester that maximizes renewable energy harvesting from the sky - utilizing both the cold universe and sunlight, for producing cooling and electricity simultaneously and from the same area.
