Spanish scientists claim to have created a new, two-dimensional material which can reduce heat in electronic devices which suffer critical heating during operation, such as solar modules.
The paper A Self-Assembled 2D Thermofunctional Material for Radiative Cooling, published in Small, describes the material as an inexpensive solution made of a single layer of silica microspheres self‐assembled on a soda‐lime glass. The material, developed by researchers from the Catalan Institute of Nanoscience and Nanotechnology and the Instituto de Ciencia de Materiales de Madrid, is said to significantly reduce heat as it cools the surface on which it is placed. The cooling occurs, the scientists say, without energy consumption or gas emissions.
The researchers claim their translucent thermal emitter has enabled them to reduce the daytime temperature of a silicon wafer by around 14 degrees Celsius and added, the reduction can reach 19 degrees Celsius if the structure of the material is backed with a silver layer. According to the scientists, the emissivity of the single-layer colloidal structure of the material, and its radiative cooling power, can also be increased by using an f-SiO2 (silicon dioxide) bulk substrate.
Without the new material, such cooling tops out at 5 degrees Celsius, according to the scientists who developed it. “The cooling power of this simple radiative cooler under direct sunlight is found to be 350 W/m2 when applied to hot surfaces with relative temperatures of 50 K above the ambient,” states the paper.
How does radiative cooling work?
Radiative cooling is the principle all objects on Earth tend to emit part of the heat they receive from the sun’s infrared radiation. The atmosphere pushes that heat back to Earth, except for infrared wavelengths, which can escape the atmosphere. What the scientists claim to have created is a material that emits infrared wavelengths.
“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 Spanish team said.
Research into radiative cooling of solar cells has increased in recent years. A recent study on the matter stated investigating the effect of enhanced radiative cooling on solar cells used in commercial PV was imperative. Its authors said, however, such studies had produced little return to date. “Simulation results revealed that the solar cell temperature could only be reduced by 1.75 K even in the ideal case,” they said.
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Won’t it result in the reduction of light absorption by solar cells eventually as the material is a translucent thermal emitter?????
What about the self cleaning aspect of
these upgrades panels?
“The cooling power of this simple radiative cooler under direct sunlight is found to be 350 W/m2 when applied to hot surfaces with relative temperatures of 50 K above the ambient,” states the paper.
But solar cells do not have a 50 K temperature rise unless they are reverse-biased (hot-spot condition). A typical 15.6cm2 solar cell receives 24W of insolation and delivers about 4W in electrical power, leaving 20W of thermal energy to be radiated and conducted away. Typical full-sun heating is about 25 K, not 50 K. (This is based on NOCT numbers from manufacturers, which typically state an operating temperature of 45C in a 25C environment, at 800W/m2. Full sun is 1000W/m^2, so expected temperature rise in full sun would be 20C/0.8 = 25C = 25K.)
If the cooling efficiency scales with temperature differential, the expected radiative cooling would be 175W/m2, or about 4.26W per 15.6cm2 cell. That would reduce the thermal load about 20%, for a temperature reduction of about 5K. That would net about 2.5% in power, so it would have to be pretty cheap to be worth it, I would think. And if it blocks any light, it’s likely a net loss rather than a gain.
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