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Three points for selection of inverters for off grid photovoltaic power generation systems

463 Published by admin 6月 04,2020

In order to ensure the normal operation of the off grid photovoltaic power generation system, the selection of the off grid inverter is very important. When selecting the off grid inverter, it is necessary to understand the product model, rated voltage, rated power, performance characteristics, etc. Match the photovoltaic power generation system. When selecting an off grid photovoltaic power generation inverter system, the following points should be noted:

NKD off grid inverter

1. Sufficient rated power to meet the electrical power requirements of the equipment under maximum load, as well as system expansion and access to some temporary loads.

When selecting an off grid inverter, the selection of the rated capacity of the inverter with a single device as the load is relatively simple. When the electrical equipment is a purely resistive load or the power factor is greater than 0.9, the rated capacity of the inverter is selected It can be 1.1 to 1.15 times the capacity of the electrical equipment. When the inverter is loaded with multiple devices, the selection of off grid inverter capacity should consider the possibility of simultaneous operation of electrical equipment.

For general inductive loads, such as motors, refrigerators, air conditioners, washing machines, high-power water pumps, etc., at startup, the instantaneous power may be 5 to 6 times its rated power, at this time, the inverter will withstand a large instant surge. For such systems, the rated capacity of the inverter should be left with sufficient margin to ensure that the load can be reliably started. The high-performance inverter can achieve multiple full-load starts without damaging the power devices. For their own safety, small inverters sometimes need to use soft start or current limiting start.

off grid inverter

In addition, the inverter must have a certain overload capacity. When the input voltage and output power are rated values ​​and the ambient temperature is 25°C, the continuous reliable working time of the inverter should not be less than 4h; when the input voltage is rated value, When the output power is 125% of the rated value, the safe working time of the off grid inverter should not be less than 1 minute; when the input voltage is the rated value and the output power is 150% of the rated value, the safe working time of the inverter should not be Less than 10s.

2. It should have high voltage stability. The adjustment performance of the output voltage of the off grid inverter indicates the voltage stabilizing ability of the output voltage of the photovoltaic inverter. Generally, the photovoltaic inverter products give the output voltage of the photovoltaic inverter when the DC input voltage changes within the allowable fluctuation range. The percentage of fluctuation deviation is usually called the voltage regulation rate. The high-performance photovoltaic inverter should also give the percentage of deviation of the output voltage of the photovoltaic inverter when the load changes from zero to 100%, usually called the load regulation rate. The voltage adjustment rate of a photovoltaic inverter with excellent performance should be less than or equal to ±3%, and the load adjustment rate should be less than or equal to ±6%.

In off grid photovoltaic power generation systems, batteries are used as energy storage equipment. When the battery with a nominal voltage of 12V is in a floating charge state, the terminal voltage can reach 13.5V, and the short-term overcharge state can reach 15V. The fluctuation of the battery terminal voltage can reach about 30% of the nominal voltage. This requires the inverter to have a good voltage regulation performance in order to ensure that the off grid photovoltaic power generation system is powered by a stable AC voltage.

solar combiner box

3. High efficiency under various loads. The overall efficiency represents the size of the PV inverter’s own power loss. The PV inverter with a larger capacity should also give the efficiency value under full-load operation and low-load operation. The efficiency of the inverter has an important impact on the photovoltaic power generation system to increase the effective power generation and reduce the cost of power generation. Therefore, the selection of photovoltaic inverters should be compared as much as possible, and the products with high efficiency of the whole machine should be selected. The high efficiency of the whole machine is a distinguishing feature of the inverter for photovoltaic power generation which is different from the ordinary inverter.

In order to ensure the normal operation of the off grid photovoltaic power generation system, the selection of the off grid inverter is very important. When selecting the off grid inverter, it is necessary to understand the product model, rated voltage, rated power, performance characteristics, etc. Match the photovoltaic power generation system. When selecting an off grid photovoltaic power generation inverter system, the following points should be noted:

1. Sufficient rated power to meet the electrical power requirements of the equipment under maximum load, as well as system expansion and access to some temporary loads.

When selecting an off grid inverter, the selection of the rated capacity of the inverter with a single device as the load is relatively simple. When the electrical equipment is a purely resistive load or the power factor is greater than 0.9, the rated capacity of the inverter is selected It can be 1.1 to 1.15 times the capacity of the electrical equipment. When the inverter is loaded with multiple devices, the selection of off grid inverter capacity should consider the possibility of simultaneous operation of electrical equipment.

For general inductive loads, such as motors, refrigerators, air conditioners, washing machines, high-power water pumps, etc., at startup, the instantaneous power may be 5 to 6 times its rated power, at this time, the inverter will withstand a large instant surge. For such systems, the rated capacity of the inverter should be left with sufficient margin to ensure that the load can be reliably started. The high-performance inverter can achieve multiple full-load starts without damaging the power devices. For their own safety, small inverters sometimes need to use soft start or current limiting start.

In addition, the inverter must have a certain overload capacity. When the input voltage and output power are rated values ​​and the ambient temperature is 25°C, the continuous reliable working time of the inverter should not be less than 4h; when the input voltage is rated value, When the output power is 125% of the rated value, the safe working time of the off grid inverter should not be less than 1 minute; when the input voltage is the rated value and the output power is 150% of the rated value, the safe working time of the inverter should not be Less than 10s.

2. It should have high voltage stability. The adjustment performance of the output voltage of the off grid inverter indicates the voltage stabilizing ability of the output voltage of the photovoltaic inverter. Generally, the photovoltaic inverter products give the output voltage of the photovoltaic inverter when the DC input voltage changes within the allowable fluctuation range. The percentage of fluctuation deviation is usually called the voltage regulation rate. The high-performance photovoltaic inverter should also give the percentage of deviation of the output voltage of the photovoltaic inverter when the load changes from zero to 100%, usually called the load regulation rate. The voltage adjustment rate of a photovoltaic inverter with excellent performance should be less than or equal to ±3%, and the load adjustment rate should be less than or equal to ±6%.

In off grid photovoltaic power generation systems, batteries are used as energy storage equipment. When the battery with a nominal voltage of 12V is in a floating charge state, the terminal voltage can reach 13.5V, and the short-term overcharge state can reach 15V. The fluctuation of the battery terminal voltage can reach about 30% of the nominal voltage. This requires the inverter to have a good voltage regulation performance in order to ensure that the off grid photovoltaic power generation system is powered by a stable AC voltage.

3. High efficiency under various loads. The overall efficiency represents the size of the PV inverter’s own power loss. The PV inverter with a larger capacity should also give the efficiency value under full-load operation and low-load operation. The efficiency of the inverter has an important impact on the photovoltaic power generation system to increase the effective power generation and reduce the cost of power generation. Therefore, the selection of photovoltaic inverters should be compared as much as possible, and the products with high efficiency of the whole machine should be selected. The high efficiency of the whole machine is a distinguishing feature of the inverter for photovoltaic power generation which is different from the ordinary inverter.

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