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Precautions for inverters used in off-grid photovoltaic systems.
Feb 10, 2019

With the development of the economy and society, it is not uncommon for resources to dry up and the environment to deteriorate. The rise of the new energy concept has made photovoltaic power generation systems more and more applied to people's lives, and the world's green mountains and green waters are everyone's common wishes.

(1) It should have sufficient rated output capacity and load capacity. In order to select the inverter, it is necessary to consider having sufficient rated capacity to meet the electrical power requirements of the equipment under the maximum load. For inverters with a single device as the load, the rated capacity is relatively simple. When the electrical equipment is pure resistive load or the power factor is greater than 0.9, the rated capacity of the inverter is 1.1~1.5 of the electrical equipment capacity. Just double. When the inverter is loaded with multiple devices, the selection of the inverter capacity should consider the possibility that several consumers will work at the same time, that is, the "load simultaneous coefficient".

(2) should have high voltage stability. In off-grid photovoltaic power generation systems, batteries are used as energy storage devices. When the battery with a nominal voltage of 12V is in a floating state, the terminal voltage can reach 13.5V, and the over-charge state can reach 15V in a short time. The terminal voltage can be reduced to 10.5V or lower at the end of the battery with load discharge. The fluctuation of the battery terminal voltage can reach about 30% of the nominal voltage. This requires the inverter to have better voltage regulation performance to ensure that the photovoltaic power generation system is powered by a stable AC voltage.

(3) High efficiency or high efficiency under various loads. The high efficiency of the whole machine is a remarkable feature that distinguishes the inverter for photovoltaic power generation from the general-purpose inverter. The actual efficiency of the 10KW general-purpose inverter is only 70%~80%. When it is used in the photovoltaic power generation system, it will bring about 20%~30% of the total power loss. Therefore, the special inverter for photovoltaic power generation system should pay special attention to reduce its own power loss and improve the efficiency of the whole machine. Therefore, this is an important measure to improve the technical and economic indicators of photovoltaic power generation systems. In terms of overall machine efficiency, the requirements for inverters for photovoltaic power generation are: rated load efficiency of inverters below KW level ≥80%~85%, low load efficiency ≥65%~75%; rated load efficiency of 10KW inverters ≥85%~90%, low load efficiency ≥70%~80%.

(4) It should have good overcurrent protection and short circuit protection. During the normal operation of the photovoltaic power generation system, overcurrent or short circuit of the power supply system caused by load failure, personnel misoperation and external interference is completely possible.

The inverter is most sensitive to the overcurrent and short circuit of the external circuit and is a weak link in the photovoltaic power generation system. Therefore, when selecting an inverter, it is necessary to have a good self-protection function against overcurrent and short circuit.

(5) Easy maintenance. It is normal for a high-quality inverter to fail due to component failure after several years of operation. In addition to the manufacturer needs to have a good after-sales service system, the manufacturer is also required to have good maintainability in the inverter production process, structure and component selection. For example, the damaged components have sufficient spare parts or are easy to buy, and the interchangeability of the components is good; in the process structure, the components are easy to disassemble and replace, and the replacement is convenient. In this way, even if the inverter fails, it can quickly return to normal.

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