Researchers from Trina Solar and China’s Nanchang University claim that they have verified that sunscreen contact solar modules only perform better than topcon modules when fewer than three cells are shaded in a substring. Their findings were published in a peer-reviewed scientific article.
Scientists from Trinasolar’s State Key Laboratory of Photovoltaic Science and Technology (SKL) and Nanchang University in China have carried out a series of simulations to compare the performance of return contact (BC) solar cells with top concels under shadow conditions.
The research group explained that their goal was not to investigate the performance on both cell types from an inverted bias perspective, but rather to consider the output characteristics of the BC technology at module level by integrating the module format, diode and actual shadow conditions.
For example, the reverse bias is caused when an individual cell is shaded and other cells in the module try to push through a higher stream. Recent research has shown that this can cause damage to the shaded cell and can also lead to an increase in temperature, causing further damage.
The team started with the assumption that BC panels perform better under shadow conditions, because tunneling occurs in the PN junction at the back of the BC cell when the inverted bias voltage increases and achieves a critical value. This helps to bring the flow of the shaded cell into line with those of non-scaled cells, the researchers said that the impact of shadow at module level reduces.
In perc and topcon devices, on the other hand, P-type and the N-type doped area are separated by the Siliconensubstraat, making it difficult for the PN connection of the front contact cell to break down under shade.
“Whether the output characteristics of BC modules in actual shadow scenarios are superior to those of cell modules with front contact, have not yet achieved a uniform understanding among both module consumers and researchers,” the scientists said. “Our work fills the current research gap and offers important references for engineering design and market investments.”
The simulation series was carried out, assuming that standard experimental circumstances are adopted, with the irradiation set at 1,000 W/m2 And the temperature at 25 C. A black opaque plastic plate was used to shade both topcon and BC panels in three scenarios: a cell shadow on a single module, short driving shadow on all 12 modules and long-sided driving shadow on all 12 tested modules.
The first analysis was aimed at the relative differences in normalized capacity between the Topcon string and BC string before and after shadow. It showed that the critical breakdown voltage of BC cells is lower, which means that these devices will deliver more “more likely” when they are subject to reverse bias voltage.
Further shadow experiments with different degrees on a single cell, with the shadow area ranging from 0% to 100%, were carried out and reportedly demonstrated that BC modules only perform better than Topcon modules when fewer than three cells are shaded in a substring.
“BC modules perform better than Topcon if the number of shaded cells is less than 3, while their power issue after this threshold becomes identical,” said the academics. “This is determined by the breakdown voltage of the 5 V BC cell and the total negative bias of 15 V required for bypass -diode -activation.”
They also concluded that, in PV projects on Nuts scale where shadow is often more than negligible, the performance of the two cell technologies are identical.
“For short shadow, the mismatch in the substrings is consistent, and neither the shaded BC cells nor topcon cells are located in an inverted proposed state, so the power output performance of the two are the same,” they concluded. “In the case of long shade, the output characteristic curves of the two modules are completely identical, both present a stepped bimodal curve, so their wealth export performance is the same.”
Their findings are available in the study “Food output performance Analysis of rear contact photovoltaic module under actual field shadow conditions: a comparison with Topcon Photovoltaic module“Which was recently published in Solar energy.
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