Passive cooling boost from silica microspheres
The passive cooling technique can be used for cooling solar panels, thermoelectric modules or data centres systems.
The material unveiled in a paper published in Small under the title “A Self‐Assembled 2D Thermofunctional Material for Radiative Cooling” consists of a two-dimensional self-assembled array of 8µm-diameter silica spheres reported to behave almost as an ideal infrared emitter, providing a radiative passive cooling power of up to 350 W/m2 for a hot surface.
Experimenting with the new material, the authors found that the temperature of a silicon wafer was 14 K lower during daytime when covered with the thermal emitter, reaching an average temperature difference of 19 K when the structure was backed with a silver layer. This material could passively cool any devices where an increase in temperature has drastic effects on performance, like solar panels and computer systems.
Indeed, it is estimated that cooling systems account for 15 percent of the global energy consumption and are responsible for 10% of greenhouse gas emissions. One could say that the cure is worse than the disease, as greenhouse gases generate global warming, thus requiring even more refrigeration.
The material was inspired by the Earth’s efficient temperature-regulation mechanism, named radiative sky cooling. Although the Earth is heated by the Sun, it also emits infrared radiation to the outer space, as this kind of radiation is not captured by the atmosphere. The sand grains in deserts are among the major contributors to this phenomenon, which keeps the average temperature of our planet stable as long as we do not consider human activities. The proposed material takes advantage of the same principle, like sand grains, only a million times smaller in volume.
According to the authors’ calculations, such a cooling layer could passively remove half of the heat accumulated in a typical solar panel in a regular clear day, enough to increase the relative efficiency of a solar cell by 8 percent.
Aside from use on solar panels, other conceivable applications include refrigeration of thermoelectric modules —devices that convert temperature differences into electric current—, cooling computer systems in data centres or even smart windows that would refresh themselves and their surroundings, saving air conditioning costs.
ICN2 – www.icn2.cat
ICMM-CSIC – https://icmm.csic.es
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