So-called residential photovoltaic (PV) systems are installed on the roofs of rural households. They are purchased like consumer goods. After installation, the power station can be connected to the national grid. A portion of the electricity generated is used primarily for the household's own consumption during the day, while any surplus is fed back into the national grid and sold at the local benchmark price for coal. Hence the name "residential PV."
With the booming growth of the residential solar power market, more and more solar companies and distributors are entering the field. Of course, various problems will inevitably arise during the residential solar power generation process, and "illnesses" are unavoidable. How do we diagnose and treat these minor issues? The following is a summary of common problems and solutions for residential solar inverters.
1. The indicator light on the photovoltaic inverter is not displaying.
Fault analysis: There is no DC input; the inverter LCD is powered by DC.
Possible reasons:
(1) Insufficient module voltage. The inverter's operating voltage is 100V to 500V. The inverter will not work if the voltage is below 100V. The module voltage is related to the solar irradiance.
(2) The PV input terminals are reversed. The PV terminals have positive and negative poles, which must correspond to each other and cannot be reversed with other groups.
(3) The DC switch is not closed.
(4) When components are connected in series, one of the connectors is not properly connected.
(5) A component is short-circuited, causing other components to also fail to work.
Solution
After using a multimeter in voltage mode, measure the inverter's DC input voltage. When the voltage is normal, the total voltage is the sum of the voltages of all components. If there is no voltage, check the DC switch, terminals, cable connectors, and components in sequence to ensure they are functioning correctly. If there are multiple components, connect and test them individually. If the inverter has been used for a period of time without a known cause, the problem likely lies in the inverter's hardware circuitry; contact the manufacturer's after-sales service.
2. The photovoltaic inverter is not connected to the grid, and the screen displays "mains power not connected".
Fault symptom: The inverter is not connected to the grid, and the screen displays "mains power not connected".
Fault analysis: The inverter is not connected to the power grid.
Possible reasons:
(1) The AC switch is not closed.
(2) The inverter's AC output terminal is not connected.
(3) When wiring, the upper row of inverter output terminals was loosened.
Solution
Use a multimeter in voltage mode to measure the AC output voltage of the inverter. Under normal circumstances, the output terminals should have 220V or 380V. If not, check in turn whether the wiring terminals are loose, whether the AC switch is closed, and whether the leakage protection switch is open.
3. The screen displays high PV voltage.
Fault Analysis: DC Voltage Overload Alarm
Possible cause: Too many components are connected in series, causing the voltage to exceed the inverter's voltage.
Solution
Due to the temperature characteristics of the components, the lower the temperature, the higher the voltage. The input voltage range for single-phase string inverters is 100-500V, and it is recommended that the voltage after stringing be between 350-400V. The input voltage range for three-phase string inverters is 250-800V, and it is recommended that the voltage after stringing be between 600-650V. Within this voltage range, the inverter efficiency is high, and it can generate electricity even when irradiance is low in the morning and evening, without exceeding the inverter's voltage limit, triggering an alarm and causing shutdown.
4. The screen displays that the PV insulation resistance is too low.
Fault Analysis: The grounding insulation resistance of the photovoltaic system is less than 2 megohms.
Possible causes: Short circuits to ground or damaged insulation in the solar panels, junction boxes, DC cables, inverters, AC cables, or terminals. Loose PV terminals and AC wiring housings, leading to water ingress.
Solution
Disconnect the power grid and the inverter, then check the resistance of each component's wires to ground in turn to find the problem point and replace it.
5. Excessive leakage current in screen display output
Fault Analysis: Excessive Leakage Current
Solution
Remove the PV array input and then check the external AC power grid. Disconnect both the DC and AC terminals and allow the inverter to power off for at least 30 minutes. If it can recover on its own, continue using it. If it cannot recover, contact after-sales technical engineers.
6. The screen displays that the mains voltage is out of range.
Fault Analysis: Grid voltage is too high. Increased grid impedance means the photovoltaic power generation at the user side cannot absorb the load. When transmitted, the excessive impedance causes the inverter output voltage to be too high, triggering inverter protection shutdown or derating operation.
Solution
(1) Increase the size of the output cable, because the thicker the cable, the lower the impedance.
(2) The closer the inverter is to the grid connection point, the shorter the cable and the lower the impedance.
