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How to solve the common problems of off-grid PV system design?

- Mar 14, 2018 -

1, components, inverters, batteries to match when designing, any one can not be too large or too small, novice design, often will calculate the power consumption is too large, such as 1P air conditioning running for 12 hours, considered 10 degrees , 300W refrigerator running for 24 hours, calculated as 7.2 kWh, causing the battery capacity is too large, the system cost is too high. When designing battery capacity, it is best to have a specification that can be filled in 2 days.

2. The output of the off-grid photovoltaic power generation system is connected to the load. The phase and amplitude of the voltage and current at each output terminal of the inverter are different. The inverter does not support parallel connection of the output terminals. Do not connect the inverter output terminals together.

3. The load is a load such as an elevator and cannot be directly connected to the output of the inverter. Because the elevator is falling, the motor reverses and a back electromotive force is generated. When the inverter enters the inverter, it damages the inverter. If it is necessary to use an off-grid system, it is recommended to add a frequency converter between the inverter and the elevator motor.

4. PV micro-grid systems with complementary input from the mains need to be insulated from the components. If components have leakage currents to the ground, they will be transmitted to the mains and cause the leakage switch of the mains to trip.

5. The voltage of the module and the voltage of the battery must be matched. The PV module solar module is connected to the battery via an electronic switch. There is no device such as inductance in the middle. The voltage of the module is between 1.2 and 2.0 times the voltage of the battery. 24V battery, component input voltage between 30-50V, MPPT controller, in the middle there is a power switch and inductance circuit, the voltage of the component is between 1.2-3.5 times the battery voltage, if it is a 24V battery, The component input voltage is between 30-90V.

6, the output power of the module and the power of the controller should be similar, such as a 48V30A controller, the output power is 1440VA, the power of the module should be around 1500W. When selecting the controller, look at the voltage of the battery and then divide the power of the module by the voltage of the battery, which is the output current of the controller.

7, the battery charging current is generally 0.1C-0.2C, the maximum does not exceed 0.3C, such as a lead-acid battery 12V200AH, charging current is generally between 20A and 40A, the maximum can not exceed 60A; battery discharge current is generally 0.2 C-0.5C, maximum not more than 1C, 1 section of 12V200AH lead-acid battery, the maximum output power does not exceed 2400W, different manufacturers, different models, the specific value is not the same, when designing to obtain instructions from the manufacturer.

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