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Solar cell grounding system and inverter selection design

Jan 28, 2021

Solar cell grounding system and inverter selection design

In the solar power generation system, grounding the positive and negative ends of the thin-film components can increase the service life of the components. With the inverter control, the system is also safer. There is evidence that grounding crystalline silicon can achieve the same effect. However, not every type of inverter can support the grounding of the components. The Jingfuyuan system engineer will explain the reason for this for you.


1. The purpose of solar panel grounding


(1) Safety function:


"Solar photovoltaic module grounding" is an inevitable option to ensure the safety of workers and the environment. Solar photovoltaic module In a solar photovoltaic system, it is the main component that converts sunlight energy into electrical energy, and it will continue to supply extremely large voltages. Therefore, when the solar photovoltaic module needs to be repaired or disassembled and replaced, the staff will be highly exposed to the risk of electric shock; even if the system is in a non-electric state due to a fault in the converter, the solar photovoltaic module placed outdoors still continues to supply power , So the risk of electric shock will not decrease. Especially when the solar photovoltaic modules are connected in series to form a photovoltaic array, the potential electric shock hazard faced by related workers will be caused by the accumulated voltage of all modules; not only that, whether it is commercial or domestic solar photovoltaic systems, they often need to be installed on the roof, etc. At high places, if there is no taller building in the surrounding area, the solar panels used will become the only metal body in the high place, which will increase the risk of lightning strikes.


(2) Prevent corrosion of thin film batteries and improve component life


Prevent the corrosion of the TCO conductive layer, because the TCO will be damaged after a period of operation of the thin film module. The reason is that the front glass contains about 15% sodium, and the chemical reaction of these sodium will corrode the TCO. Grounding the negative pole of the inverter input will cause the PV to generate an electric field. In this electric field, the positively charged sodium ions are adsorbed by the negative pole and stay away from the TCO layer. Because glass contains 15% sodium, the reaction of sodium and water causes TCO corrosion when the sealing is not good. Grounding the negative pole of the inverter can form an electric field, and the positively charged sodium ions will move to the negative pole to stay away from the TCO layer, which can avoid corrosion.


2. Solar panel grounding requirements for inverter


When designing, the R&D engineers of Jingfuyuan fully consider the following requirements for the inverter when the negative pole of the inverter input is grounded:


(1) DC input and AC output are electrically isolated. Inverters with power frequency transformers and inverters with high frequency transformers can be used. When the inverter is designed, the signal ground must be separated from the safety ground;


(2) Grounding circuit: Generally, the negative pole is grounded through a fuse;


(3) Detection circuit: Generally, it is a ground current Hall, which detects the current of the ground loop;


(4) Protective measures: The DC side of the inverter should be equipped with a DC relay or a circuit breaker equipped with a shunt release. When the leakage current is detected to exceed the standard, the DC side switch will be automatically disconnected.


When selecting the inverter, please note that the following inverters do not support component grounding:


(1) There is no isolated inverter.


(2) In the three-level topology, the voltage at both ends of the battery board to the ground has a fluctuation of 2 times the switching frequency, and the leakage current is large, which is not suitable for battery grounding occasions.


(3) The front-end switch of the inverter is an inverter with a load switch. There is no automatic tripping device. In case of emergency, the DC cannot be automatically disconnected. It is not suitable for battery grounding occasions.