Researchers at the Vellore Institute of Technology (VIT), in India, have proposed a technique for mitigating partial shading in PV systems. The method is based on the Lo Shu nine-square grid of ancient Chinese mathematical tradition which was also used as a divination tool for ancient Chinese feng shui masters and is today the basis of popular sudoku puzzles.
Scientists from VIT’s Solar Energy Research Cell and School of Electrical Engineering claim their sudoku method can completely remove shading by reconfiguring installations – physically or electrically. The academics claim approaches such as maximum power point tracking (MPPT) or using appropriate converters and inverters only partially alleviate the problem.
“The use of any array reconfiguration method alters the row current in such a way that every single row carries the same current and disperses the shade occurring on the PV panel,” said the VIT group. That would mean fewer bypasses and mismatch power losses, as well as raised power output.
Lo Shu
The VIT group said the nine by nine Lo Shu matrix is directly transposed onto their PV array reconfiguration procedure. For large solar installations, the technique can be applied with smaller, three by three sub-arrays, ensuring only a few panel movements are necessary and only elements in columns with fewer interconnections need to be relocated.
Under the VIT approach, panels connected in a ‘total cross tied’ (TCT) configuration – mounted in parallel rows connected in series – are physically relocated using the Lo Shu technique, with their electrical connections unaltered. Physical relocation of panels to different rows using the Lo Shu arrangement disperses shade, thereby reducing the intensity of shade concentrated on particular areas of panels. The researchers said their approach offers the added benefit that it does not require a large number of switches and sensors.
The VIT group said array performance depends on the degree of shading as well as total occurrence.
Results
The Lo Shu method was tested on a 6.4 kW solar system under four shade patterns: short wide (SW), long wide (LW), short narrow (SN) and long narrow (LN). Under the first two, the maximum power output of a shaded panel was 5,783 W and 5,738W, respectively. For SN and LN, the returns were 5,558 W and 5,548 W, respectively. “For the considered shade pattern, the proposed LS outperformed the TCT and DS [dominance square alternative format for laying out PV arrays],” said the researchers. “For instance, the difference between the mismatch power loss of LS and TCT [was] 1,241 W, 918 W, 327 W [and] 317 W, for SW, LW, SN and LN, respectively.”
The academics claimed the new technique is more profitable than other array reconfiguration approaches and enabled savings of INR3,285 ($43.69) per year. The researchers added: “If the size is maximized and if the number of PV arrays is increased, the outcome will be higher.”
Research co-author Venkateswari Radhakrishnan told pv magazine: “This method can be successfully implemented to larger symmetrical PV arrays.”
The findings of the research are presented in the study Power enhancement of PV system via physical array reconfiguration based Lo Shu technique, published in Energy Conversion and Management and on the ScienceDirect website.
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