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How do pv modules affect rooftop pv generation?

How do pv modules affect rooftop pv generation?
Update Time:2020-03-09

1.Dust effect of components


For the long-term operation of photovoltaic power system, the impact of dust accumulation on the panel can not be underestimated.The dust on the surface of the panel has the function of reflection, scattering and absorption of solar radiation, which can reduce the solar transmittance, resulting in the solar radiation received by the panel is reduced, the output power is also reduced, and its effect is proportional to the cumulative thickness of dust.


(1)temperature influenceAt present, photovoltaic power stations mostly use silicon solar cell modules, which are very sensitive to temperature. With the accumulation of dust on the surface of the modules, the heat transfer resistance of the photovoltaic modules is increased, which becomes the heat insulation layer on the photovoltaic modules and affects their heat dissipation.The current and voltage of some single cells in solar cell modules have changed.As a result, the product of local current and voltage of solar cell modules increases, resulting in local temperature rise on these modules.The defects of some single cells in solar cell modules may cause the components to heat up locally when working, which is called "hot spot effect".When the hot plate effect reaches a certain level, the solder joints on the module melt and destroy the grid line, resulting in the scrapping of the whole solar cell module.According to industry data, the hot spot effect reduces the actual life of solar cell modules by at least 10%.


(2)occlusion effectDust is attached to the surface of the panel, which will block, absorb and reflect light.The most important one is the blocking effect on light, which affects the absorption of light by photovoltaic panels, thus affecting the efficiency of photovoltaic power generation.Dust deposition in the panel component by the smooth surface, the first will make the panel surface light transmittance decreased;Secondly, the incident Angle of some light will be changed, resulting in uneven propagation of light in the glass cover.Studies have shown that under the same conditions, the output power of clean panel components is at least 5% higher than that of grime components, and the higher the amount of grime, the greater the degradation of component output performance.


(3)corrosion effectThe surface of photovoltaic panel is mostly made of glass. When wet acid or alkaline dust is attached to the surface of the glass cover, the glass surface will be slowly eroded, resulting in potholes on the surface, resulting in diffuse reflection of light on the surface of the cover, and the spread uniformity in the glass will be destroyed.The rougher the cover of the photovoltaic module is, the smaller the energy of refracting light is, and the energy actually reaching the surface of the photovoltaic cell decreases, resulting in the decrease of the generation of the photovoltaic cell.And rough, sticky surfaces with adhesive residues are more likely to accumulate dust than smoother surfaces.And the dust itself will absorb dust, once the initial dust exists, it will lead to more dust accumulation, accelerating the decline of photovoltaic cell power generation.


 

2.How to detect the components from the inverter end?


Group is string of monitoring technology in inverter components input, current sensor and voltage detection device installation, detect each group of voltage and current value, through the analysis of the voltage and current of each group, so as to determine whether each string of operation of the apparently normal, if any abnormal timely according to the alarm code, and precise positioning abnormal group list.And can upload the fault record to the monitoring system, so that the operation and maintenance personnel can timely find the fault.Although the cluster monitoring technology increases the cost a little, it is still insignificant for the whole photovoltaic system, but it plays a big role:


(1)early component problems, such as component dust, lobes, component scratches, hot spots and other problems, were found in a timely manner, which were not obvious at the early stage. However, by detecting the difference of current and voltage between adjacent groups, it was possible to analyze whether there were faults in the group strings.Timely handling to avoid greater losses.


(2)when the system fails, no professional on-site detection is needed to quickly determine the fault type, accurately locate the group string, and timely solve the problem by operation and maintenance personnel to minimize the loss.


 

3.Component cleaning


(1)manual cleaningManual dry cleaning component: manual dry cleaning is the use of long hair mop with special cleaning agent for cleaning, the use of oil electrostatic dust agent.Mainly USES the electrostatic adsorption principle, has the adsorption dust and the sand particle the function, can enhance the cleaning tool to absorb the dust decondulization ability, effectively avoids the dust sand particle flying in the cleaning.


(2)automatic cleaningSemi-automatic cleaning. At present, this kind of equipment is mainly refit with engineering vehicle as the carrier, with large power and high efficiency. The cleaning work has a good consistency of pressure on the components, and will not produce unbalanced pressure on the components, resulting in hidden cracks of the components.The automatic cleaning method is to install the cleaning device on the photovoltaic module array and realize the automatic cleaning of the photovoltaic module by the program control of the motor rotation.This cleaning method is costly and complex in design.

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