Agro Fossil Free - Experimental study on a hybrid solar photothermic and radiative cooling collector equipped with a rotatable absorber/emitter plate

General Description

Taking the frigid outer space as the heat sink, a terrestrial body can cool itself to a sub-ambient temperature via radiative sky cooling (RC) scheme. However, poor seasonal and regional adaptabilities and low cooling power density of the RC technology confine its effective applications only in hot seasons and regions with RC-friendly ambient conditions. Similarly, a solar thermal collector cannot work at night and is of little value when heat is needless. To tackle these challenges, a hybrid solar photothermic and radiative cooling (PT-RC) collector equipped with a rotatable absorber/emitter panel is proposed and experimentally investigated. This dual-mode collector can flexibly switch between PT and RC to match specific energy demands in different scenarios. The daily solar thermal efficiency of the PT-RC system at zero-reduced temperature reached 50.4%, a typical level of flat-plate solar water heating systems. The PT-RC system could not provide cooling energy during most daytime hours. However, the system could easily achieve nighttime cooling, with the cooling power of the collector decreasing from about 60 to 50 W/m2 as the circulated water being continuously cooled down from around 20 to 12 °C. The average nocturnal cooling power of the PT-RC collector ranged from 30.5 to 57.5 W/m2 in a multi-night RC test. This rotatable PT-RC collector offers a new strategy to flexibly deliver heat and coldness in a renewable and environmental-friendly manner and shows the potential of smart thermal management in buildings, vehicles, agriculture, etc.