Commissioning, Maintenance, and Troubleshooting Photovoltaic Systems Commissioning, Maintenance, and Troubleshooting Commissioning • Maintenance • Monitoring • Troubleshooting Arizona Solar Power Society www.meetup.com/arizona-solar-power-society/

A commissioning checklist should be reviewed before the initial startup of any PV system. Before any PV system is fully operated for the first time, the system should be checked thoroughly to ensure that the installation is complete and that the system is safe and ready for operation. A final checklist includes many of the same items as on maintenance, testing, and inspection checklists. See Figure 14-1. All disconnects should be in the open (OFF) position during the final checkout.

A general start-up procedure begins at the array and ends at the loads, though exact procedures may differ. The initial startup is the first time that all the system components are energized. A general start-up procedure begins at the array and ends at the loads. If there are any installation problems, this reduces the chances of causing safety hazards and damaging equipment. One at a time, each disconnect is closed and each component is switched ON, and voltage and current are compared with expected values. See Figure 14-2. (Array and battery bank voltages should be confirmed before closing their disconnects.) Meters, indicators, and displays on charge controllers and inverters are used for measuring and verifying system parameters. If at any step the system parameters are outside of the acceptable range, the startup should be aborted and troubleshooting procedures should be used to find the cause of the problem.

A detailed walkthrough allows the installer to explain the basic operation of the PV system and the maintenance requirements to the owner. For relatively simple residential interactive systems, user training may require only a short walkthrough. See Figure 14-3. If the customer observes much of the installation and commissioning processes, additional training time may not be required.

Visual module inspections involve checking for damage from physical impacts, delamination, burned internal connections, and other problems. Modules should be visually inspected for signs of any physical damage, including bent frames or broken glass. See Figure 14-4. Fractured or damaged modules should be replaced, even if they are still functioning electrically. If a damaged module is left in service, moisture may enter the module, causing dangerous shorts or ground faults. Most modules use tempered glass, which shatters into small pieces when broken from stress or impact.

Corroded grounding connections usually result from the contact of incompatible materials or extreme environments. Equipment-grounding connections at each module should be inspected for corrosion. See Figure 14-5. This type of corrosion usually results from the contact of incompatible metals, so any connections exhibiting corrosion should be replaced with the proper stainless-steel fasteners.

Periodic shading control involves trimming vegetation and cleaning a soiled array. Even a relatively small amount of shading on the array can significantly reduce electrical output. The shading analysis conducted during the site survey establishes the optimal location with the least shading. However, some conditions can change over time, resulting in increased array shading. See Figure 14-6. Routine maintenance may be required to control excessive shading.

Damp leaf debris trapped under arrays can cause mold and mildew problems. Leaves, trash, or other debris should not be permitted to collect around arrays or any other electrical equipment. When dry, these materials are a fire hazard. When damp, they attract insects and can contribute to mold or mildew problems. See Figure 14-7. In humid climates, mildew can develop in the shaded portions of a roof under standoff-mounted arrays.

Cracked or deteriorated weather sealing around attachment-point penetrations can quickly develop water leaks. Special attention should be paid to the weather sealing of roof penetrations from mounting attachment points and conduits. Sealant cracks or shrinkage, broken gaskets, and corroded metal flashings are all signs of weather sealing degradation, which can quickly result in water leaks. See Figure 14-8. Inspecting the underside of the roof from the attic (if accessible) may reveal minor water leaks not previously discovered. Water stains, soft or rotten wood, constant dampness, or insect infestation indicate possible roof leaks. Even if leaks are not found, any degradation of weather sealing should be promptly corrected by removing the old sealant materials completely and applying new sealant.

Battery enclosures should be inspected for strength, cleanliness, and adequate ventilation. The battery enclosure should be visually inspected for signs of electrolyte leakage, corrosion, or damage. Racks should be checked for adequate structural support, as well as proper placement of any straps or rails that hold batteries in place. See Figure 14-9. Trays should be checked for proper positioning beneath batteries. Also, the battery enclosure must have adequate ventilation. Obstructions that prevent airflow or otherwise clutter areas around the battery bank should be removed.

Battery terminals are particularly susceptible to corrosion and may require frequent cleaning. Any corrosion on battery terminals or connectors should be cleaned with a wire brush. See Figure 14-10. A weak solution of baking soda and water may be used to wipe down the terminals and top surfaces of open-vent lead-acid batteries as needed. Special care should be taken to ensure cleaning solutions do not enter battery cells. Terminals can be coated with petroleum jelly, grease, or special battery-terminal corrosion inhibitors as required. Also, check for adequate protection of live battery terminals, including boots or battery covers.

Battery maintenance includes checking for an adequate level of electrolyte. The electrolyte level is checked by removing the cell vent caps and comparing the level with respect to an established mark. A small flashlight is helpful to see inside the battery. Alternatively, if the battery case is partially transparent, it may be possible to see the electrolyte level from the outside. See Figure 14-11. Some batteries include an electrolyte level gauge that does not require cap removal. This gauge is a tiny captured float in contact with the electrolyte surface. When the float is visible from above through a clear window in the cap, the electrolyte level is adequate. When the electrolyte falls enough that the float cannot be seen in the window, the electrolyte is too low.

Battery watering replaces water lost from gassing during charging. Water is added directly to cells through the vent caps. Care should be taken not to overfill the cells. A funnel or large syringe can be used to add water to cells with small openings. See Figure 14-12. A special watering can with a valve on the spout to prevent against overfilling may be used. Large battery banks may use automated watering systems to administer water to each cell through a network of plastic hoses. The date and amount of water added to each cell should be recorded in maintenance records.

Battery state of charge can be related to both specific gravity and voltage. The specific gravity of the electrolyte in open-vent batteries should be checked as part of a regular maintenance schedule, and more often if problems are suspected. Specific gravity can be used to estimate battery state of charge in lead-acid batteries (though not in nickel-cadmium batteries). Open-circuit voltage can also be measured and used in conjunction with specific gravity to estimate battery state of charge. See Figure 14-13. With either method, state of charge is most accurate when the battery has been at steady-state (neither charging nor discharging) for 5 min to 10 min. After watering, specific gravity should not be measured until a charging cycle has mixed the electrolyte.

Either one of two types of hydrometers can be used to measure the specific gravity of battery electrolyte. A hydrometer is an instrument used to measure the specific gravity of a liquid. Two types of hydrometers used with battery electrolyte are the Archimedes hydrometer and the refractive index hydrometer. See Figure 14-14.

When viewing through a refractive index hydrometer, the specific gravity of the tested fluid is measured against a calibrated scale. A refractive index hydrometer, also called a refractometer, uses a prism to measure the refractive index of the electrolyte, which is related to specific gravity. The refractive index is the amount that a substance bends light that passes through it. A small drop of electrolyte is placed on the prism, and light refracts at an angle related to the density and specific gravity of the electrolyte. The user then observes the refracted light though a viewfinder on a scale calibrated in specific gravity units. See Figure 14-15. The main advantage of a refractive index hydrometer is that only a very small amount of electrolyte is required.

An infrared (IR) thermometer can measure the temperature of electrical equipment, including PV system components. Routine maintenance should include visual inspections of inverters, chargers, charge controllers, transformers, and any other electrical equipment in the PV system. This equipment requires adequate surrounding space for accessibility and airflow, which allows for heat dissipation. Therefore, equipment temperature should be measured. Infrared (IR) noncontact thermometers are ideal for this task. See Figure 14-16. Equipment at higher-than-normal temperatures requires immediate attention to address possible overloading conditions or poor airflow.

A maintenance plan includes all the necessary maintenance tasks and their respective schedules. PV-system maintenance should be carefully planned and scheduled to ensure that all necessary tasks are being performed and to minimize the time and expense required. A maintenance plan is a checklist of all required regular maintenance tasks and their recommended intervals. See Figure 14-17. Maintenance plans are developed during the design and commissioning process based on the typical maintenance requirements for the system configuration, installation type, and location. Much of this information is found in manufacturer’s recommendations.

The three most important points for measuring voltage and current information are the array output circuit, inverter output circuit, and charge controller circuit (if applicable). There are three primary locations in a PV system for measuring electrical parameters: the array output circuit, the inverter output circuit, and the battery-bank output circuit (if applicable). See Figure 14-18. Since the inverter is connected to all three circuits, most modern inverters include integrated monitoring functions as standard features. If this is not the case, external monitoring equipment can be added to measure electrical parameters. For temporary use, such as for troubleshooting, handheld test instruments are used. System designers and equipment manufacturers sometimes incorporate test points into circuits for safe and easy access by test instruments. For some installations, permanently installed meters are used.

Sensors for measuring irradiance and other parameters allow technicians to correlate PV system output with weather conditions. Including environmental parameters in monitoring allows system output to be correlated with weather conditions. These parameters usually include irradiance and ambient temperature. See Figure 14-19. For example, current output from a PV device increases proportionally with irradiance. However, if the current measurements do not correlate with the irradiance measurements, there may be a problem with the array, such as excessive shading, soiling, or blown source circuit fuses. For an accurate representation of the array’s environmental conditions, all sensors should be placed as close to the array as possible and in the same plane.

Equipment status indicators may have multiple functions. The simplest type of monitoring employs small indicator lights to show the status of components and their functions. These are usually LEDs of different colors. For example, an LED may indicate that the battery bank is fully charged, even if the charge controller also displays the actual battery-bank voltage. See Figure 14-20. Indicators on major components may indicate normal operation, ground faults, low-voltage load disconnect, battery charging, battery discharging, battery equalizing, or component malfunctions. For efficiency of space on the front panel, indicator LEDs may have multiple meanings depending on their colors (for bicolor LEDs) and the rate at which they blink.

Data-acquisition systems gather, record, and process information from many sources that can be used to observe trends or problems in PV system operation. Using computer software, this data can then be plotted to illustrate the changes of values over time. See Figure 14-21. This facilitates spotting trends and correlations between parameters. When troubleshooting, data-acquisition systems are invaluable tools. They allow the technician to review past records and identify slow trends over time or short-term events that may have impaired system performance. By connecting the computer or data-acquisition unit to the Internet, the raw data and plots can also be made available to users through web sites.

The system level includes all the components of a PV system. Troubleshooting procedures are designed to identify malfunctions by examining the system at progressively narrower levels. A troubleshooting level is the depth of examination into the equipment or processes that compose a system. Troubleshooting levels are very similar for all electrical systems, even though they may be named differently. For PV systems, the appropriate levels are the system level, subsystem level, component level, and element level. See Figure 14-22.

PV subsystems are divided by the components involved in energy production, storage, processing or conditioning, distribution, and consumption. The system is broken down into functional areas called subsystems. Subsystems may include many components, but they are all related to a particular function within the system, such as producing and controlling DC power. The subsystem level includes the energy production, storage, conditioning, distribution, and consumption functions. These functions correspond to the array, battery bank, inverter (or power conditioning unit), distribution panel, and loads, respectively. See Figure 14-23.

Most equipment manuals include troubleshooting flow charts or procedures, which narrow the possible causes of a problem by following a specific set of instructions. Research involves gathering all the relevant system documentation together, particularly equipment manuals, and finding information about normal operating parameters, specifications, compatibilities, maintenance requirements, precautions, and error codes. Some manuals include troubleshooting instructions or flow charts that may help narrow the cause of the problem. See Figure 14-24.