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How to choose off-grid photovoltaic inverter?
- Aug 08, 2018 -

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Photovoltaic inverters, also known as power regulators and power conditioners, are an integral part of photovoltaic systems. The most important function of the PV inverter is to convert the DC power generated by the solar panel into the AC power used by the home appliance. All the electricity generated by the solar panel must be processed by the inverter to be externally output. With an inverter, you can use a DC battery to provide AC power to your appliance. Pay attention to the following points when selecting the inverter of the off-grid photovoltaic system:

1. Should have sufficient rated output capacity and load capacity. The choice of inverter must first consider having sufficient rated capacity to meet the electrical power requirements of the equipment under the maximum load. For an inverter with a single device as its load, the rated capacity is relatively simple. When the electrical equipment is purely resistive or the power factor is greater than 0.9, the rated capacity of the inverter is 1.1 to 1.15 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. It should have high voltage stability. In the off grid photovoltaic power generation system, batteries are used as energy storage devices. When the nominal voltage 12V is in the state of floating charging, the terminal voltage can reach 13.5V, and the state of short time overcharge can reach 15V. The terminal voltage of the battery can be reduced to 10.5V or lower when the load is discharged. The fluctuation of the terminal voltage of the battery can reach about 30% of the nominal voltage. This requires that the inverter has better voltage regulation performance to ensure that the PV system is supplied with a stable AC voltage.

3. It has high efficiency or high efficiency under various loads. The high efficiency of the whole machine is a notable feature of the inverter for photovoltaic power generation, which is different from the universal inverter. The actual efficiency of the 10 kW class universal 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, in the design of photovoltaic inverter, special attention should be paid to reducing the power loss and improving the efficiency of the whole machine. Therefore, this is an important measure to improve the technical and economic index of photovoltaic power generation system. The requirements for the photovoltaic power inverter for the efficiency of the whole machine are: the rated load efficiency of the lower kW inverter is more than 80% to 85%, the low load efficiency is more than 65% to 75%, the rated load efficiency of the 10kW level inverter is more than 85% to 90%, and the low load efficiency is more than 70% to 80%.

4. It should have good over current protection and short circuit protection function. During the normal operation of the photovoltaic power system, the overcurrent or short circuit of the power supply system caused by the load failure, the misoperation of the personnel and the external interference is completely possible. Photovoltaic inverter is the most sensitive to the overcurrent and short circuit of the circuit, and it is a weak link in the photovoltaic power generation system. Therefore, when selecting the inverter, it is necessary to have a good self protection function for over current and short circuit.

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