Components of a solar photovoltaic (PV) system
Cell, module and array: A typical photovoltaic (PV) cell produces a small electrical output ranges from 0.5W to 2W approximately. As these devices are electrical, we can boost overall output level by wiring them in series and parallel strings. Wiring PV cells in this method is called a module. Some manufacturers now manufacture “power modules,” which can generate 190W or more power. Under full sun shine conditions, a typical 190W module which is connected to a load might generate the voltage and current of approximately 27V and 7A respectively. When modules are wired in series and parallel strings, then it is called an “array.” The output of an array is designed in such a way that the output of an array can meet almost any electrical requirement of small or large scale system.
Combiner box: Desired voltage and current can be gained by wiring modules into an electrical string. All strings are combined into one electrical output in the combiner box which is then fed to the inverter.
Inverter: Inverter converts the DC output into AC as per requirement of any photovoltaic (PV) system. Electric utility grid connected inverters generate AC which is identical to the power generated by the electric utility. These inverters sense the waveform characteristics and generated voltage of the electric utility and generate the same type of AC.
The input voltage and current level of the inverter's from the array need to be checked and recorded. If the array is not generating required DC electricity, check all switches, fuses, and circuit breakers. Blown fuses should be replaced and the breakers and switches need to be reset. A specious surge might have passed through, blowing or tripping the protective devices. Loose or dirty connections and broken wires in the inverter should be checked. All connections should be clean and make them tighten. All damaged wires should be replaced. Check the array visually for obvious damage to the panels and wiring.
There are fuses for each module or sub-array string in many combiner boxes. While troubleshooting, all these fuses should be removed and the current reading and open-circuit voltage should be recorded for each circuit string. Low output voltage indicates that some panels in the series string are disconnected or defected which requires replacement. Defective bypass or blocking diodes in the modules might need to be replaced. Wrong wiring connecting the modules in the string to the combiner box, junction box or the inverter may cause low voltage. Undersized wire may cause this problem. This problem should be rectified by upgrading the wire size for the current level.
During overcast or cloudy conditions, a damaged panel or defective bypass diode can produce low output current. One or more parallel connections between modules in the string might be loose, broken, or dirty — or some parallel connections in the module might be loose, broken, or dirty. Replace a damaged module or one with internal parallel connection problems. Defective diodes should be replaced. All connections need to be tightened and clean. Shades on the array decreases output current significantly. So, in order to obtain full current output from the string, it is required to remove the source of shades from array.
Dirty modules decrease the output current. In order to restore the output current of array, these modules need to be washed. After washing, the output current should be checked again.
First of all, operating DC input voltage and current level of the inverter should be checked by a volt meter and DC ammeter respectively. After then, these data should be recorded. On the AC side, check the inverter’s output voltage and current level. A blown fuse, broken wires or a tripped breaker can cause the insufficient output power from the inverter.
Some inverters have LED displays as indicators. It is necessary to check whether these LEDs are blinking properly or not. Properly blinking LEDs should indicate the actual condition of the inverter.
True-rms reading type volt meter can be used to measure the voltage and current to measure. After measuring, the kilowatt output should be recorded. You should record the total kilowatt hours generated since it first started up which is displayed by the inverter. You can compare the PV system’s production since the last inspection by using the recorded data.
AC load side of the inverter should be measured, because load on the inverter might have too high demand of a current. In this scenario, inverter should be upgraded or loads should be reduced.
Before starting the inverter again, any ground faults should be checked and repaired after shutting down the power. Inverter can sense the voltage and frequency of the electric utility. Typically, it generates AC electricity at the same voltage and frequency. The AC output current output of the inverter fluctuates with the level of solar input on the array. If internal disconnects sense that the electric utility voltage is high or low, then it will shut down the inverter. If this problem remains, then you should contact the concerned authority of electric utility to rectify the problem. Inverter problems could also be caused by a problem on the array side of the inverter, which trips one of the internal disconnects.
How to troubleshoot a load problem
All load switches should be checked first. It should be checked whether they are turned off or placed in the wrong position. You should check and ensure that the load is plugged in. Next, the fuses and circuit breakers should be checked. If there are tripped breakers or blown fuses, the cause should be located and the faulty component should be replaced or fixed. If there are no tripped breakers or blown fuses and the load is a motor, then there might be an open circuit in the motor or an internal thermal breaker might be tripped. In this scenario, you need to plug in another load and observe its operation.
Any loose connections and broken wires should be checked. All bad wiring should be replaced. After shutting down the power, any ground faults should be checked and repaired. Fuses need to be replaced and the switches should be reset. If they blow or trip again, there might have short circuit problem, which must be located and repaired.
If the load does not operate properly, the system voltage should be checked at the load’s connection point. Too small or too long wire feeding the circuit may cause the low voltage which needs to be upgraded to reduce the voltage drop. The load might also be large enough for the wire size in the circuit. In this scenario, the size of wire need to be upgraded or the load on the circuit should be reduced.