Maintenance is an important criterion when installing solar systems. Proper maintenance ensures the system's optimum work capacity. In other words, its working conditions and its life is sustained for as long as possible. Solar systems can indeed be easily maintained when compared to diesel generators however they are not maintenance-free. This article will cover the preventative maintenance of major components of a PV system. First, we go through the major components in a solar system and its functions and then provide a checklist for reference.
Array Installation and wiring
The panels have to be properly installed in such a way that maximum sunlight reaches the panels because even with a little bit of shading on one of the panels, the energy output of your entire photovoltaic array will be less. The array is often thought to be maintenance-free, but regular inspections must be carried out to ensure their performance is good. A visual inspection of the module should be done to check out for cracks, discolorations dirt accumulations, etc. If any obvious defects are found they should be noted down so that they can be monitored in the future.
Figure 1: Cleaning of rooftop solar panels
The conditions of module mounting, the wiring should be checked. Item to observe should include proper grounding of the array mounts, proper insulation of module wiring, whether the grounded conductors are properly installed and the array mounts are properly secured and sealed. Adequate precautions have to take while doing maintenance on solar panels when they are located on rooftops as there is a risk of falling off.
DC Connections
In a large solar photovoltaic (PV) array, multiple solar modules are connected in series in a string to build the voltage up to proper levels for the inverter. Multiple strings of solar modules are then combined in parallel to multiply the string output currents to higher levels for input into the inverter. The combiner box combines all these strings. Also known as the DC box, it is generally used in larger commercial and utility plants. The DC box consists of overcurrent protection fuse assemblies for the strings and combines them into a single main output. In case of overcurrent and overvoltage, these DC boxes protect the inverters from getting damaged.
Wire size
Two common conductor materials used in commercial/residential PV installations are copper and aluminum. The cables can be solid or stranded. Copper wires are sized using the gauge scale. Lower the gauge number higher the current it can handle safely. Commercial solar panels generally use 10-gauge wires. This allows 30 amps of current to flow from a single panel. For multiple panels, a combiner set is needed to safely transfer the power to the charge controller. The figure below shows the kind of wire gauge used in a typical PV system.
Figure 2: Typical wire gauge used in a solar PV system
Wiring installations should be checked for cracks and deterioration of the insulation material. Inspections for any corrosion or burning must also be done. If found then they have to be consulted with the installers and all ground wires must also be properly checked for any damage.
Utility External Disconnect Switch (UEDS)
A Utility External Disconnect Switch (UEDS) is a disconnect device that the utility uses to isolate a PV system to prevent it from accidentally sending power to the utility grid during routine or emergency maintenance. They should easily visible and accessible. Disconnects come in a variety of sizes, from 30amp up to 800amp, so proper planning of your system is necessary to determine which disconnect sizes you need
Figure 3: Utility meter and the AC disconnect switch
Switching this off will disconnect the system from the utility. The loads will operate the same as in case of a power failure.
Charge controllers
A charge controller is a regulator that prevents the batteries from getting over charged. It monitors the current and voltage coming from the panels and going to the batteries. It has to be made sure the condition of the charge controllers is fine to ensure proper monitoring of the battery voltage. The wires from the charge controller to the battery bank can generally be the same or larger gauge than the main set from the PV array. Some charge controllers tend to lower the voltage coming from the panels and tend to increase the current going to the batteries. So proper caution must be taken in selecting the correct wire size. It has to be made sure in case of an off-grid system the charge controllers are grounded for protection.
Battery maintenance
A battery is a device that stores electrical charges. Batteries should be checked and properly maintained to extend their life. It needs to be made sure that the terminals of the batteries are protected from shorting, they are labelled properly with safety procedures. It also involves checking the cell electrolyte level for correct acid volume once a month if it is an acid battery. Another important measure in determining the state of the battery is the state of voltage. After measuring each battery's voltage, it should be recorded and maintained in a log sheet. It is very important to match the gauge and the wire lengths when combining batteries in a battery bank. If this is not done, then the battery bank’s life can be shortened and resulting in safety issues.
Figure 4: Battery bank for solar PV system
Inverters
While solar panels are responsible for generating electricity, it is the inverters that convert the power and feed it to the home appliances / the grid. Good performance by the inverters is therefore very important. Solar Inverters have display panels that indicate the system and current inverter performance. Solar inverters may run through some problems and oftentimes, these issues are easy to fix.
Figure 5: A Solar inverter
Improper loading is one problem where this happens because of the damage to the fuses. Another probability is due to the tripping of the breakers. Proper care must be taken to ensure the inverters don’t come in contact with dust or water. The disconnects are properly labelled and the inverter is properly grounded.
The checklist mentioned here is a reference provided by AE Solar that provides a detailed inspection of every component of the installed PV system. A maintenance check-up on a routine basis like every year has to be done to ensure the system is in perfect working condition.