Radiative cooling materials continue to underperform compared to their
theoretical potential due to parasitic heating from contact with ambient
air. Solutions to this problem are expensive or complex to fabricate.
Here, a potentially inexpensive, simply fabricated material that
improves cooling performance by reducing parasitic heating was created
using naturally abundant salts. NaCl and KCl are not typically
considered for radiative cooling because of their high hygroscopicity
and low mechanical strength; however, these compounds are highly
infrared-transparent and can be fabricated into aerogel-like structures
to provide thermally insulating properties. Salt aerogels, described
herein, scattered (reflected) visible light, transmitted infrared
radiation, and provided thermal insulation. They were packaged into
mechanical supporting panels to avoid physical disruption and the
nanostructure was stabilized to moisture by adding anti-caking agent.
The panels were able to keep an underlying surface below ambient
temperature for a full 24-hour cycle and reduced parasitic heating rate
by more than half (compared to an uncovered surface). The panels were
able to cool a variety of underlying surfaces, even highly absorbing
surfaces that are normally well above ambient temperature during the
day. This work demonstrates an affordable, easily produced,
electricity-free cooling technology with potential to be manufactured
for large-scale practical applications.