When it comes to Saudi Arabia, the “oil kingdom”, rich economy and developed tourism leap out. From another perspective, due to the wide distribution of deserts in Saudi Arabia, the maximum temperature in summer can reach more than 50 ℃, which is undoubtedly a great test for the tolerance of electromechanical equipment placed outdoors for a long time.
As we all know, it is not only cloudy and rainy days and nights, but also muggy and hot weather that restricts the efficiency of solar power generation. Therefore, it is urgent to solve the heat dissipation problem of solar panels in the desert environment, so as to avoid that the power required for cooling is higher than that of solar power generation.
It is understood that the solar cell structure is basically composed of p-type and n-type semiconductors. This structure is called PN junction. When the solar cell absorbs sunlight, the PN interface will produce electron-hole pairs.
Under the action of the built-in electric field, the stimulated electrons and the holes that lose electrons will move in the opposite direction, resulting in current and voltage; However, if the temperature increases, the recombination speed of electron-hole pairs will be accelerated and the power generation will decrease.
In this regard, King Abdullah University of science and Technology (kaust) in Saudi Arabia believes that problems caused by environmental factors should be solved by natural principles. In this regard, they have developed a cooling system for solar panels, successfully cooled solar panels and improved power generation efficiency by 19%.
Initially, they decided to use calcium chloride to solve the problem, but half of the raw material of calcium chloride is salt, which is very easy to absorb moisture, deliquescence, and dissolve in water.
Based on this, they developed a new polymer gel through calcium chloride and carbon nanotubes. When exposed to moisture, the gel absorbs calcium and water and gradually expands. The carbon nanotubes in polymer structure can not only absorb heat but also allow polymers to continuously absorb water and drain water.
After outdoor tests, they found that these gel absorbs moisture on a hot night, and releases water vapor during the daytime, just as if people sweat through heat. Researchers pointed out that this new gel can stick in various places. When the gel is glued to the back of the solar panel, the water released from the gel can cool the solar panel by about 10 degrees.
It is worth noting that outdoor heat conduction may be related to the improvement of mass conduction. They found that the efficiency of solar panels increased by 13% ~ 19%. Researchers believe that this cooling technology has great application potential and a wide range of applications, and is suitable for various environments.
In fact, gels are not new. In order to improve the energy output of solar power generation under the rising temperature, researchers have found material in recent years, which can absorb water vapor from the air and condense it into liquid water for drinking.
Among them, the best is the gel, a mixture of carbon nanotubes and calcium chloride in polymers. During the day, gelatin absorbs heat from solar panels to release steam and evaporates water to cool the solar panels.
According to statistics, the world has more than 600gw of solar power generation capacity, meeting 3% of the global power demand. This capacity is expected to increase fivefold in the next 10 years.
Most solar panels use silicon to convert light energy into electric energy, but traditional silicon cells can only convert 20% of solar energy into electric energy, and most of the rest into heat, which can raise the temperature of solar panels by 40 ℃. Whenever the temperature exceeds 25 ℃, the efficiency of solar panels will decline.
Decades ago, it was found that cooling solar panels with water can improve their conversion efficiency, but water cooling system devices require a lot of water, storage tanks, pipelines, and pumps, which is almost impossible in arid areas or developing countries lacking infrastructure.
The gel is a simple and effective way to transform existing solar panels, which can immediately improve efficiency.
Coincidentally, environmental engineers at the Hong Kong Polytechnic University also tried to use condensate as the coolant for solar panels, and its basic principle is consistent with the above.
In addition, they found that the amount of gel required to cool the solar panels depended mainly on the humidity: in a desert environment with a humidity of 35%, the cost of 1 kilogram of gel per square meter of solar panels required cooling.
In a stuffy area with a humidity of 80%, only 0.3 kilograms of gel per square meter of solar panels can be cooled. However, no matter which application scenario, the temperature of condensate solar panels has decreased by 10 ℃.
In the outdoor test, the power generation of the improved solar panels increased by an average of 15% and a maximum of 19%. They believe that the wind may enhance the cooling effect. In view of the problem that rainwater will dissolve calcium chloride in the gel and weaken its water absorbency, the research team is currently developing the second generation of gel, which is said to not be degraded even with water.
Another design is to set up a device to collect and recondense water after water evaporation. These water can be used to clean the dust accumulated on solar panels, or can be stored for drinking, so as to meet the water demand in arid areas.
