Researchers from Shanghai Polytechnic University, Shanghai Engineering Research Center of Advanced Thermal Functional Materials, and Shanghai Solar Energy Research Center Co. Ltd explored how different shade conditions impact performance of single solar cells and two-cell systems connected in series and parallel.
The results have been published by the American Institute of Physics Journal of Renewable and Sustainable Energy.
Large obstacles, like clouds and buildings, can block sunlight from reaching solar cells and even small objects, such as dust and leaves, can block sunlight from reaching solar cells. Understanding how the loss of incoming radiation affects power output is essential for optimizing photovoltaic technology, which converts light into electricity.
The researchers explored how different shade conditions impact performance of single solar cells and two-cell systems connected in series and parallel. They found that the decrease in output current of a single cell or two cells connected in parallel was nearly identical to the ratio of shade to sunlight. However, for two cells running in series, there was excess power loss.
Author Huaqing Xie, of Shanghai Polytechnic University and Shanghai Engineering Research Center of Advanced Thermal Functional Materials explained, “In the real world, photovoltaic cells are sometimes shaded by obstacles, which significantly alters the amount of incoming light. The degradation effects make power optimization difficult and result in significant power loss.”
Photovoltaics connected in series create a single path with the electrons flowing from one cell into the next. In contrast, cells in parallel provide two lanes for electrons to travel through, then recombine later. In practical applications, networks of solar cells are connected in series and parallel to expand the output current and power capability.
The team found that the decrease in output current of a single cell or two cells connected in parallel was nearly identical to the ratio of shade to sunlight. However, for two cells running in series, there was excess power loss and a rise in temperature, which can cause further output degradation. For example, with 29.6% of the series photovoltaic module in the shade, the current decreased by 57.6%.
Xie noted, “Our study indicates that many factors, including shadow area, shadows on different cells of the module, and the connection of cells and modules, may affect the performance.”
Previous studies have explored the consequences of shade on large photovoltaic modules but have largely ignored single cells and simple systems.
“In these complicated systems, shadows on one single cell may play vital role on the system output and reliability,” said Xie. “Therefore, studying single cells or a simple arrangement of two connected cells is necessary for solar panel development.”
In the future, the authors hope to examine the microscopic interaction behaviors and mechanisms in photovoltaic cells subjected to different shadows.
One would have thought that this type of research would have been done a long time ago. But serious solar aficionados have come to realize that solar cell quality has more at issue than simply area and price. The installations need maintained regularly. The designs matter. And now we know how they are wired internally has a large effect on the performance.
Knowing this will help consumers make better, more informed decisions about particular solar offerings. One day there might even be label requirements that show just what a panel actually is inside and have actual comparable ratings. Someday. Maybe.
Lets hope the folks in Shanghai keep going. Perhaps they will accumulate enough information that designs improve and perhaps a sensor might be invented to say “Wash Me!”
By Brian Westenhaus via New Energy And Fuel
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