Cooling solar farms can make them more powerful - here is the proof
It’s a common belief that a solar panel produces more energy on receiving more sunlight but that’s not always true. In fact, a report from the World Economic Forum state that photovoltaic cells on a solar panel (that trap sunlight and convert it into electricity) may start producing less energy if they get overheated.
A new study conducted by a team of researchers from the University of Utah (UU), National Renewable Energy Laboratory (NREL), and Portland State University (PSU), sheds more light on this rarely discussed aspect of solar panels. It mentions that the efficiency of a solar plant goes down by 0.5 percent. If the temperature on the surface of its photovoltaic (PV) cells increases by just one-degree Celsius from their optimal temperature.
Many solar panel manufacturers suggest that the ideal temperature for commercially used solar panels ranges between 15°C and 35°C, and the PV cells achieve the highest energy efficiency at 25°C. So, if a solar plant experiences a temperature around 50°C, it may suffer energy losses of up to 12 percent.
“Since more than 50% of PV generation capacity within the U.S. is located in warmer climates (that have temperatures ranging between 42°C to 70°C) of California, Arizona, and Nevada, understanding and finding methods to mitigate panel heating becomes crucial to the success of low-cost solar energy,” the authors note in the paper.
The current study proposes an easy and impressive way to achieve the required cooling mechanism in solar plants naturally.
The geometry of a solar farm is linked to energy efficiency
Currently, in order to maintain an optimal temperature on solar farms, the PV cell surfaces are either provided with specially designed materials or coatings, or they are cooled down using water and wind. The authors suggest that both these strategies raise the operation cost to a large extent and require ample amounts of resources, especially in the case of large solar farms that extends up to tens of square kilometers.
For instance, the Nevada Solar One plant in Boulder City uses 850 gallons of water to produce every 1000 kWh of electricity. The water is probably used for cleaning, maintenance, and cooling purposes. The researchers propose that PV cells can be saved from overheating just by changing the geometry of a solar farm.
They suggest that if all the panels in a solar farm have a proper gap between them and they are facing in the right direction. They can automatically cool themselves through convection (the process of transfer of heat from a solid surface to air or a liquid, for example, the air surrounding a campfire gets heated due to the same phenomenon) using the wind that flows around them.
The authors explained, “In this work, we propose an expanded interpretation of PV farm geometry to improve current convective cooling predictions, accounting for 3D module arrangements as canopy flow fields.”
They suggest that rather than investing huge sums of money on traditional cooling resources, farm owners can try out different solar panel configurations in their farms and compare the energy efficiencies in each case to decide the best arrangement.
There is no formula that works for all
Apart from PV cell surface temperature, the energy output of a farm depends on factors such as the environment and panel material. Moreover, other aspects such as land area, latitude, and type of surrounding vegetation could also influence the spacing and direction of panels on a farm. Therefore, no single geometrical arrangement can work on all solar farms.
The researchers further point out that “incorporating collective contributions such as module height, array spacing, and inclination through the correlation provides a more complete description of the solar farm as a canopy flow and can be applied to any existing predictive energy-cost model. Utilizing this correlation will give solar farm designers a simple way to explore a wide variety of parameters and increase potential power gains.”
During one of their experiments, when the researchers changed the panel height and increased the space between different solar panel rows while considering all the above-mentioned factors in mind. They noticed a two percent growth in the power output from the farm. They believe that their geometry-based approach has the potential to significantly improve the efficiency of solar farms and make them more sustainable than ever.
The study is published in the Journal of Renewable and Sustainable Energy.
Heat mitigation for large-scale solar photovoltaic (PV) arrays is crucial to extending lifetime and energy harvesting capacity. PV module temperature is dependent on site-specific farm geometry, yet common predictions consider panel- scale and environmental factors only. Here, we characterize convective cooling in diverse PV array designs, capturing combined effects of spatial and atmospheric variation on panel temperature and production. Parameters including row spacing, panel inclination, module height, and wind velocity are explored through wind tunnel experiments, high- resolution numerical simulations, and operating field data. A length-scale based on fractal lacunarity encapsulates all aspects of arrangement (angle, height, etc...) in a single value. When applied to Reynolds number Re within the canonical Nusselt number heat transfer correlation, lacunarity reveals a relationship between convection and farm- specific geometry. This correlation can be applied to existing and forthcoming array designs to optimize convective cooling, ultimately increasing production and PV cell life.
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