| The inexhaustible feature of solar energy is considered to be the ultimate solution to the energy crisis and the realization of green energy.An effective photovoltaic system consists of cells,photovoltaic modules and photovoltaic arrays.Due to the long-term outdoor work of photovoltaic arrays,the surface of photovoltaic modules will inevitably be dirty or occluded by some pollutants,resulting in hot spot effect,which is an important reason for power attenuation and life reduction of components.In order to improve the utilization of solar energy and obtain the maximum power of photovoltaic arrays,the current methods to avoid the harm of hot spot effect mainly include improving the series bypass protection diodes of photovoltaic arrays in partial shadows,reconfiguring the structure of photovoltaic arrays,and global maximum power tracking method of photovoltaic arrays in shadows.Although the parallel diode protection of the series batteries in traditional components can play a certain protective role,it will result in be short-circuit state of other normally working batteries and reduce the output power when the battery is blocked by a small area.The configuration of photovoltaic array structure is to reconfigure several components under large areas occlusion(such as moving clouds),however,the protection mode in the module is still dependent of parallel bypass diodes.In this paper,a new photovoltaic module was proposed,in which all cells were connected each other like a fishing net.When any each cell of the module is an abnormal state,the photocurrent could flow through the neighbor well-worked cells so that the photovoltaic output loss of the whole module was minimized as can as possible,meanwhile,the bad-worked cell could be well protected because only a small photocurrent need flow through the abnormal cell.Multisim soft[Version 13.0]was used to simulate the photovoltaic output of the series-circuit module(SM)and fishing-net module(FM)under the various experiment conditions,such as incidental light power,contaminant degree and area ratio and module dimension(cell numbers in one module).In order to validate the reliability of the simulating results,the real 6×6 array SM and FM(36 real cells,one cell area 2.5×2.5 cm2),were tested and analyzed comparatively under the same experiment condition,such as the number and position of abnormal cells or incidental natural light power.The experiment results according well with the simulating ones suggest that the FM photovoltaic output is exactly better than the SM one.By analyzing the current flow and reverse voltage characteristics of the shadowing module,we find that the power loss of the module is closely related to the reverse voltage between the shadowing cells.The output of FM is lower than that of SM when the voltage of shadow-shielding battery line is negative.A germanium diode with low on-voltage in parallel in each line of FM can effectively protect and maximize the power of the module.In order to further improve the light utilization rate of photovoltaic modules under normal operation,the conversion efficiency of the module is further improved by preparing antireflective film.Firstly,the Essential Macleod film design software was used to analyze the film and SiO2 antireflective film was prepared on top glass of the module by pull-up method.The optimum transmittance of the module glass was achieved by controlling the pull-up speed and times.At the same time,the traditional module structure was improved by removing the part of EVA layer on the surface of the battery(the same area as the size of the battery),and then a layer of antireflective film was prepared on the surface of the battery to compensate for the antireflective effect of EVA and Si3N4 on the surface of the battery.Finally,the glass,battery,part of EVA and reflective paper were packaged by hot pressing to test the photoelectric conversion efficiency.The experimental results show that the photoelectric conversion efficiency is improved about 1.5%and the CTM(cell to module)has a 0.7%gain effect. |
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