Lessons learned through installation of solar pv systems in typical Indian hot climatic zone
Solar PV systems have been employed in European countries traditionally. The technology has been quite successful has the PV modules and BOS has to work in cold and dust free climate. However recent installations in India ,which has reached close to 1300 MW , has demonstrated that in case of solar PV technology is used in typical Indian hot and humid conditions. It behaves differently as compared to how the same technology will behave in a typical cold climate of European countries
The performance of a solar PV system is governed predominately by three factors, which are temperature ,humidity and dust. On one side temperature and humidity has played a larger role in terms of performance of PV module from other side the dust level impacts the performance of BOS in the plant. When PV modules are subjected to temperature and humidity ,specially the projects implemented in the areas such as Gujrath .It was found that some of the projects have suffered a faster degradation in output ,this was because of Potential Induced Degradation (PID). Which leads to non reversible degradation of modules ,the problem of PID arises when modules are subjected negative voltage and due to high temperature and humidity .The solar cells are subjected to electrochemical reactions that leads to electro corrosion or film de-lamination in the module. This type of problem is observed specially in case of thin film technologies ,it is not that PID is observed in only thin film technology ,recently in some of the crystalline silicon technology as identified PID due to surface polarization that creates non destructive and reversible accumulation of static charge on the surface of the cells.
Another major problem which solar PV projects face is the dusty weather and equipment performance in extreme climatic conditions, demands more sophisticated BOS specially in extreme climate. Which are capable to with stand these extreme weather conditions and reliably perform for 20 years .
Sand and dust storm can cause penetration of dust in the inverter and other sensitive electronic equipment and cause problem in the functioning of the inverter. In operating solar PV system specially BOS, in a extreme weather condition require the equipment design in accordance to dust proof containers.
As shown here by the reductions in shunt resistance (Rsh), maximum power point (MPP) and open circuit voltage, PID can significantly reduce yield in PV plants.[Source: Schuetze, et al, Laboratory Study of Potential Induced Degradation of Silicon Photovoltaic Modules]
The operating temperature of inverter during summer months typically reaches to about 80°C and becomes important that the inverter voltage range is with in the array voltage range. Increased temperature of modules reduces voltage and sometime if the voltage is less than the input window voltage of the inverter it becomes the major cause of inverter tripping.
The Polarization Effect on c-Si modules can be fully mitigated by reversing the potential voltage applied. [Source: S. Pingel, et al, Potential Induced Degradation of Solar Cells and Panels]
Inverter with IP65(International Protection Rating) standards are available in the market which are capable to operate in dusty and open environment.In this article we have tried to cover the plant performance in Indian weather conditions. However there had been significant problems beyond the plant , when it was connected to grid and tripping of solar plant was regular feature at various substations due to over loading and under loading .
Dr Sanjay Vashishtha & Rishikesh Muthyal.