  Radiative cooling is a passive cooling strategy with zero consumption of
electricity. Although this technology can work well during optimal atmospheric
conditions at nighttime, it is essential to achieve efficient radiative cooling
during daytime when peak cooling demand actually occurs. In this article, we
report an inexpensive planar polydimethylsiloxane (PDMS)/metal thermal emitter,
i.e., a thin film structure fabricated using fast solution coating process that
is scalable for large area manufacturing. By manipulating the beaming effect of
the thermal radiation, temperature reduction of 9.5 {\deg}C and 11.0 {\deg}C
were demonstrated in the laboratory and out-door environment, respectively. In
addition, a spectral-selective solar shelter architecture was designed and
implemented to suppress the solar input during the daytime. Due to the enhanced
directionality of the thermal emission, the dependence of the radiative cooling
performance on the surrounding environment was minimized. Out-door experiments
were performed in Buffalo NY, realizing continuous all-day radiative cooling
with an average power of ~120 W/m2 on a typical clear sunny day at Northern
United States latitudes. This practical passive cooling strategy that cools
without any electricity input could have a significant impact on global energy
consumption.
