Researchers from the University of Miskolc in Hungary have developed a passive cooling technique for photovoltaic modules which they claim is able to lower the panels' operating temperature by up to 22%.
The novel technique consists of attaching cotton wicks immersed in the water (CWIWs) to the backside of the photovoltaic module. The water is supplied to cotton wicks from top to bottom by gravity which the scientists said helps the effective absorption of cotton and reduces water consumption. “Exposure of the wetted cotton wicks to the surrounding air decreases dry air temperature and increases humidity, producing evaporating cooling that can exploit it to absorb the rising heat from the backside of the PV module,” they explained. “The technique contributes by creating a continuous cooling environment with less water consumption and better performance under hot conditions than in other studies.”
The CWs were arranged as serpentine forms avoiding any space between them. The scientists fixed them by using thermal silicon. They also placed two plastic bottles full of water at the top edge of the PV module. “The gravity-free flow of water helps transmit the water to the CWs without extra power,” they emphasized. “Thus, this method helps to distribute the water entirely from cotton wicks throughout the PV module.”
The performance of a polycrystalline solar module with a size of 0.65 m × 0.55 m and equipped with CWIWs was compared with that of a reference panel without the cooling system. They used a data logger with two voltage sensors and two current sensors. It recorded temperature, voltage, and current values every ten minutes during the experiment days. “The experiments were conducted according to climatic conditions of Basra City, Iraq, from 20 to 29 of August 2021,” the specified. “August is characterized by a sunny month with high temperatures and low humidity on most days with moderate winds.”
Through their measurements, the academics found that the PV module with CWIWs cooling showed thermal behavior closer to the ambient temperature throughout the experiment period due to evaporating cooling of CWs. “The highest temperature recorded of the PV module with the CWIWs was 46.2 C at 12:20 PM, while the ambient temperature was 43.8 C,” they stated.
Compared to the module without cooling, the CWs-equipped module had an operating temperature that was 22% lower. “The moist condition resulting from the cotton bristles immersed in water and exposed to the wind has provided appropriate cooling that enhances efficiency to 7.25% and the power yield increment about 16.3 W,” they further explained. “Using CWIWs decreases entropy generation by about 14% due to reducing the lost exergy of the PV module than the PV module without cooling.”
The Hungarian group presented the passive technique in the paper Effect of Evaporative Cooling on Photovoltaic Module Performance, which was recently published in Process Integration and Optimization for Sustainability. “The passive cooling applied in this work enhanced the performance of the PV module higher than in other similar studies, making it more reliable for application,” it concluded.
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It is quite misleading to talk about 22% lower temperature and meaning that the temperature was something like 45°C instead of 55°C. 55/45=1.22 i.e. 22%, but it is by no means 22%. In
Fahrenheit scale you get a different result. Only on a temperature scale which refers to absolute 0 temperature e.g. the Kelvin scale, such a calculation makes any sense at all (E=kT is always calculated in Kelvin) and then a decrease from 328K to 318K is just 3.1%. I wonder how the reviewer could have missed that methodological flaw.
Overall it is a nice experiment, with a small catch: many countries have water shortages, especially the hot ones, so to generate additional drinking water some countries extract it from sea water under high energy costs… Now the question is: if creation of additional drinking water is consuming additional energy and that water improves the energy creation of the solar cell, does it really pay off, or is more energy wasted at generating that water in the first place. I think that problem was not addressed and the used up water measured.
Turn this into a solar still, please.
In my limited experience (western USA), very hot and dry places are quite dusty, and that dust sticks to wet objects. Who gets to go around and clean what amounts to a bunch of air cleaners, and how much does that person get paid to do this? I believe this is why other studies chose a different path. It’s far easier and economical to treat/clean one or more closed circuit cooling towers, even if it doesn’t result in absolute peak output or efficiency.
In our rush to use solar energy has any one considered the impact of the the thermal inefficiency of solar panels at converting solar energy to electricity? We calculate the thermal impact of fossil fuels by the amount of thermal energy introduced into the environment as a result of the combustion process relative to the amount of useful electricity produced (or even better electricity converted into useful activities after transmission which accounts for end use efficiency). Solar electric panels convert solar energy into environmental thermal energy as they produce electricity as this article highlights. Thermal heat energy (heated air) is different than light energy (i.e. it is how we sense and measure global warming). Green spaces (plants) capture light and keep the environment relatively cool, solar panels and other surfaces (i.e pavement, bricks, shingles, metal roofs, etc.) tend to convert light into thermal energy that heats the environment.
An unverified source suggests that 45% of the 1000 watts/m2 that comes to the earth’s surface is converted into thermal energy by a solar panel while only 15% conventionally and up to or over 20% with new solar panels is converted to electricity. The remainder of the solar energy is reflected and let’s assume it does not get converted to thermal energy. So, the thermal efficiency of a solar panel is between 15/(15+45) to 20/(20+45) or 25% to 30.8% (I am assuming the gain in efficiency is due to converting more of the reflected energy to electricity than by reducing the thermal energy produced). 25 to 30 percent thermal efficiency is comparable to the thermal efficiency of most fossil fired energy conversion systems before we factor in transmission losses and other thermal costs such as manufacturing and installation of the thermal conversion system.
I fear we are deceiving ourselves thinking that solar electricity (photo-voltaic and solar thermal, not to mention the thermal output from the surfaces of our infrastructure) is not contributing to our climate change problems.
In addition, the following unverified website suggests that it may take 200 kWh of energy to produce a 100 Watt solar panel.
That is 2000 hours of operation at peak output of the solar panel per watt of output capacity that a solar panel must operate before it can generate enough useful electricity to offset its cost of manufacture on an energy basis. Actual hours of operation would be greater since solar panels only operate at peak capacity a fraction of the time they are in operation. One would need to investigate the types of energy inputs for manufacture and consider also the indirect energy use associated with those types of energy to get a truly accurate assessment of the environmental thermal impact of manufacturing solar panels. Similar analyses could be done for all energy systems to allow us to asses the true impact of our energy systems on a life cycle basis which is the only basis that can reveal the truth that can drive our energy policy decisions.
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