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Most PV systems require relatively little maintenance, especially when designed appropriately for the application and installed according to best practices and with quality components. However, a modest investment in periodic inspections and maintenance ensures safety and the best possible performance. Rou tine maintenance also helps identify problems that require corrective service. The degree and frequency of maintenance required depends on the system configuration, installation type, and location. Interactive systems require the least maintenance, while stand-alone and hybrid systems, because of the inclusion of batteries or additional power sources, require maintenance that is more extensive and frequent. Manufacturers may provide maintenance guidance or procedures in their component instructions. Simple and nonhazardous maintenance can sometimes be performed by the system owner. Advanced maintenance, including troubleshooting and equipment replacement, may require the experience and expertise of a qualified installer or service technician familiar with PV systems, components, and proper safety procedures. Array maintenance includes cleaning performance-reducing dust and dirt from the module surface. Operating manuals, electrical diagrams, programming instructions and troubleshooting procedures for PV modules inverters charge controllers batteries and other major system components are usually available on line from the manufacturer’s web sites. Array Maintenance: Common maintenance tasks for arrays include module inspections, shading control, debris removal, array mount inspections, and tilt adjustments. For activities involving working around or touching modules, the array should be disabled by covering the modules or opening the array disconnect. Module Inspection. Modules should be visually inspected for signs of any physical dam age, including bent frames or broken glass. 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. Delamination is the separation of the bonded layers of glass and/or plastic encasing the PV cells of a module. Delamination allows moisture intrusion and corrosion within modules, particularly near the edges. This is visible as discolorations or bubbles in the laminate. --4. Visual module inspections involve checking for damage from physical impacts, de lamination, burned internal connections, and other problems. PHYSICAL DAMAGE; DELAMINATION; BURNED CONNECTIONS In rare cases, the internal solder connections between cells can degrade. The increased resistance causes hot spots that can burn through the back of the module and result in module failure. Problems internal to a module, such as delamination or degradation of cell connections, are typically covered under the manufacturer's warranty. When module junction boxes have removable covers, a few modules should be randomly chosen at each inspection and checked for secure wiring and moisture intrusion into the junction box. Any exposed conductors should have proper strain relief and should be neatly tied and concealed beneath the array. Conduit and fittings should be inspected for damage. Equipment-grounding connections at each module should be inspected for corrosion. 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. --5. Corroded grounding connections usually result from the contact of incompatible materials or extreme environments. Shading Control. 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 overtime, resulting in increased array shading. Routine maintenance may be required to control excessive shading. The growth of nearby trees and vegetation is an ongoing shading concern. Ground-mounted arrays may also be susceptible to shading from shrubs or long grass. These plants should be trimmed or mowed on a regular basis. The planting of trees or erection of new buildings or structures on adjacent properties may also result in additional array shading. A few municipalities and states have enacted legislation that protects the solar rights of property owners against excessive shading from adjacent properties, but in most areas there are few remedies to this situation. Excessive soiling can also cause shading. Soiling is the accumulation of dust and dirt on an array surface that shades the array and reduces electrical output. Soiling deposits may result from bird droppings, nearby industrial emissions, smoke, dust, dirt, and other atmospheric particles that settle on the array surface. Extensive soiling can reduce array output by 10% or more. The amount of soiling on an array depends on the location. Arrays mounted near dirt roads or in dusty and windy areas are more likely to become soiled. Arrays mounted next to busy roadways or airports may become soiled with hydrocarbon emissions and grime. However, even where conditions are likely to cause soiling, frequent heavy rainfall and/or a high array tilt will tend to keep modules cleaner. Soiled arrays can be cleaned by spraying the modules with a garden hose or pressure washer (with relatively low pressure). if material is stuck on a module, a soft brush and/or a light detergent may also be needed. A long-handled nonconductive brush makes it easier to reach all areas of the array surface. Direct contact with energized modules while washing must be avoided. --6. Periodic shading control involves trimming vegetation and cleaning a soiled array. SOILING; TREES --7. Damp leaf debris trapped under arrays can cause mold and mildew problems. Mold --8. Cracked or deteriorated weather sealing around attachment-point penetrations can quickly develop water leaks. Possible contact between modules and flammable materials, such as dry leaves or building materials, is the reason that ground fault protection is required for arrays mounted on buildings Debris Removal. 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. In humid climates, mildew can develop in the shaded portions of a roof under standoff-mounted arrays. Debris can be removed by hand or with a garden hose when cleaning soiled arrays. A mildew cleaner or weak bleach solution can be used to control mold and mildew. When using bleach or any sort of cleaning solution, only the recommended concentrations should be used, and any components or plants exposed to the runoff should be protected or thoroughly rinsed afterward. Array Mount Inspection. Array mounts should be inspected for any signs of corrosion or weakness. The inspection should include both the attachment of the modules to the mounting structure and the attachment of the mounting structure to the buildings or ground. 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. 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. Tilt Adjustment. Some mounting systems allow manual tilt adjustments to optimize array orientation. If adjustments are to be made seasonally, they can coincide with the biannual inspection and maintenance activities. Tilt adjustments may involve removing and replacing pins, fasteners, or clamps. The array must be properly supported and secured during and after adjustments. Battery Maintenance Batteries are usually the most maintenance- intensive components in any PV system. Regular maintenance is important to maximizing battery life and minimizing hazardous conditions, though requirements vary significantly depending on the battery design and application. Open-vent batteries are the most maintenance-intensive type of batteries because they need periodic water additions and cleaning. Sealed batteries require much less maintenance. Battery maintenance tasks include cleaning, tightening terminals, watering, and checking battery health and performance. Performance checks include specific gravity measurements, load tests, and capacity tests. Battery manufacturers usually provide detailed maintenance recommendations for their batteries. For more information, IEEE 450, Recommended Practice for Maintenance, Testing, and Replacement of Vented Lead-Acid Batteries for Stationary Applications is a useful guide for servicing batteries. Safety is of the utmost importance when per forming battery maintenance. The battery bank should be isolated from the remainder of the system by opening the battery-bank disconnect. For battery banks greater than 48 V nominal, special disconnects are required to electrically divide the battery banks into lower-voltage sections for maintenance. Special insulated tools must be used when battery terminals are exposed during maintenance. Battery Enclosure Inspection. 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. 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 Enclosures: Battery enclosures should be inspected for strength, cleanliness, and adequate ventilation. Batteries contain toxic materials and must be disposed of properly. Fortunately, nearly all of the materials in a lead-acid battery can be recycled. Batteries are typically accepted for recycling by battery manufacturers and retailers, recycling centers and hazardous waste collectors. Individual battery cases should be inspected for any cracks or distortion, as well as the cleanliness of the top surface near the terminals and vents. If battery racks, trays, or cases need cleaning, a mild soap and water solution may be used with a soft brush or rag. Terminal Inspection. Since battery terminals are made of soft lead alloys, the connections at the terminals can become loose over time. Loose connections increase the electrical resistance and voltage drop within the battery bank, resulting in unequal charge and discharge currents between individual batteries or cells. The high resistance also creates heat, which is a fire hazard, and in severe cases can overheat the battery-terminal connection until it deforms or melts. --10. Battery terminals are particularly susceptible to corrosion and may require frequent cleaning. Regular battery maintenance should include checking all terminal connections for looseness or corrosion. Any connections that move when pulled on vertically must be tightened. (Terminals should not be pulled laterally or twisted because internal battery components could be damaged.) Lock washers can be used with bolted battery terminals to prevent future loosening. The crimped lugs on battery cables should also be checked. Any corrosion on battery terminals or connectors should be cleaned with a wire brush. 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 don’t 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. Routine battery maintenance should include inspection of the safety and auxiliary equipment including personal protective equipment (PPE), fire extinguishers, smoke detectors ventilation equipment, and battery testing tools and instruments. Watering. The electrolyte in flooded, open- vent batteries must be maintained at proper levels by periodically adding water. This replaces water lost through battery gassing during charging. Water additions are required for both flooded lead-acid and flooded nickel- cadmium batteries. Pure, distilled water is recommended. Any salts and minerals dissolved in the water, even at relatively low concentrations such as in hard water from a domestic water supply, will slowly degrade a battery. Under no circumstances should acid (or base, for nickel-cadmium batteries) be added to refill a battery. The level of electrolyte must not be allowed to fall below the tops of the battery plates. Ex posed portions of the plates will oxidize, leading to premature capacity loss and battery failure. If the plates are exposed, water should be added to cover the plates. Because the electrolyte expands and the level rises slightly as the battery charges, batteries should only be completely filled or topped off after they are fully charged. Otherwise, the battery may overflow electrolyte from the cell vents when charged. The frequency of watering required depends on a number of factors. The rate of water loss increases with battery age, higher charge rates, higher regulation voltage, and higher operating temperature. Watering intervals may be extended when batteries have reserve electrolyte capacity. Advanced multistage charge control and temperature compensation reduces water loss. Excessive water loss may be due to unnecessarily frequent charging cycles caused by a faulty charge controller, failed temperature compensation, or an improper regulation setpoint. Comparatively low water loss in individual cells indicates a weak or failing cell. The cell may need either an equalization charge or to be replaced. 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. 1. 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 can not be seen in the window, the electrolyte is too low. --11. Battery maintenance includes checking for an adequate level of electrolyte. UPPER LEVEL ELECTROLYTE 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. 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. Specific Gravity Measurement. 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. 3. With either method, state of charge is most accurate when the battery has been at steady-state (neither charging nor discharging) for 5 mm to 10 mm. After watering, specific gravity should not be measured until a charging cycle has mixed the electrolyte. Watering: Battery watering replaces water lost from gassing during charging. --13. Battery state of charge can be related to both specific gravity and voltage. When taking specific gravity readings, the variations between cells are as important as the overall average of the readings. Significantly low specific gravity of individual cells indicates cell failure or shorts, which likely requires battery or cell replacement. When variations between individual cells are small (within ±0.004), an equalization charge may be required. A hydrometer is an instrument used to mea sure the specific gravity of a liquid. Two types of hydrometers used with battery electrolyte are the Archimedes hydrometer and the refractive index hydrometer. An Archimedes hydrometer is a bulb-type syringe that extracts electrolyte from the battery cell into a chamber. A float m the chamber experiences a buoyant force equivalent to the weight of the displaced electrolyte. Consequently, the float is more buoyant at higher specific gravities and floats at a higher level. The float may be a glass tube, plastic ball, or a lever attached to the side of the chamber. Marks on the side of the float or chamber are calibrated to indicate the specific gravity directly. --14. Either one of two types of hydrometers can be used to measure the specific gravity of battery electrolyte. ARCHIMEDES HYDROMETER 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. 5. The main advantage of a refractive index hydrometer is that only a very small amount of electrolyte is required. --15. When viewing through a refractive index hydrometer, the specific gravity of the tested fluid is measured against a calibrated scale. Hydrometer markings are calibrated to a specific temperature, typically 80°F (27°C). When specific gravity is measured at temperatures lower or higher than the reference temperature, a correction factor must be applied. First, the temperature of the electrolyte must be accurately measured. The adjustment of the specific gravity reading is based on the difference between the measured temperature and the reference temperature. A standard correction factor of 0.004 specific gravity units, often referred to as "points," is applied for every 10°F (5.6°C) difference. This correction factor applies regardless of the reference temperature of the hydrometer. Points are added for temperatures above the reference temperature and subtracted for temperatures below the reference temperature. For example, at 90°F (32°C), a hydrometer reading of 1.250 would be corrected to 1.254. Conversely, at 70°F (21°C), a hydrometer reading of 1.250 would be corrected to 1.246. Load Testing. The ability of a battery to maintain voltage while under load is another indication of battery condition. While a de graded battery may accept a charge, it may not perform well under load. A battery load tester is a test instrument that indicates battery health by drawing a high discharge current from a battery for a short period. The load is typically drawn at a rate of C/I or greater for no more than 15 sec. At the same time, battery voltage is measured and recorded. A minimum voltage of 9.6 V for a nominal 12 V lead-acid battery is considered acceptable for this test. Results should be recorded in a log, which helps identify long-term trends. Capacity Testing. Available battery capacity can be measured by load testing at rates comparable to those during normal system operation. Starting with a fully charged battery bank, the array is disconnected, but the system load is left connected. At regular intervals, such as every hour, the battery voltage and load current are measured and recorded. The load remains connected until the battery reaches the cutoff voltage. The total capacity is equal to the average load current multiplied by the discharge time. For example, a battery that is discharged at an average of 10 A for 8 hr delivers 80 Ah. After a capacity test, the load should be left disconnected and the array or an auxiliary charging source connected until the battery regains full state of charge. Electrical Equipment Maintenance: 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. 6. Equipment at higher-than-normal temperatures requires immediate attention to address possible overloading conditions or poor airflow. All wiring should be inspected, including conductors, terminations, conduit, and junction boxes. Disconnects, fuses, and circuit breakers should be checked for proper operation. Any exposed conductors should be checked for insulation damage, clean and secure terminals, adequate strain relief, and properly connected and supported conduits. --16. An infrared (IR) thermometer can measure the temperature of electrical equipment, including PV system components. made by Fluke. Tools and Testing Equipment: So that maintenance and troubleshooting can be conducted in a prompt and efficient manner, PV system service personnel should have certain basic tools and testing equipment available at all times. Tools: A standard PV maintenance tool kit should include screwdrivers, pliers, wire cutters, wire strippers, crimpers, wrenches and socket sets, utility knives, and flashlights. PV-specific tools include a handheld pyranometer, compass, caulking gun, and a variety of battery-maintenance equipment, as required. A variety of spare parts and materials should be readily available, including fasteners, fuses, connectors, lugs, conductors, weather sealant, lubricant, corrosion inhibitor, electrical tape, wire ties, and distilled water. Besides basic PPE, safety equipment should include a first aid kit, electrical gloves, fire-resistant clothing, hats, sunscreen, rubber gloves, and baking soda. Testing Equipment: A digital multimeter is the most important and versatile test instrument for maintenance, monitoring, and trouble shooting of electrical systems. Most models can measure voltage, current, and resistance. Other parameters, such as temperature, can also be measured, either as a built-in function or with add-on accessories. This test instrument is vital to maintaining any PV system. Other test instruments are not always required, but can be very useful. A clamp-on ammeter makes current measurements easier and safer, since the circuit does not need to be opened to take measurements. Watt-hour meters record cumulative energy and can be useful in many different ways. At the utility connection, a pair of watt-hour meters can record net energy exporting and importing. Another watt-hour meter is recommended for the inverter output, if the inverter does not already monitor energy output. On the array output circuit and the battery-bank charging circuit, ampere-hour meters are used in a manner similar to watt-hour meters. In the battery system, ampere-hour meters can also show the net energy that is in a battery, and therefore its state of charge. Maintenance Plans: 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. 7. 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. However, maintenance plans can evolve as the needs for the particular system are deter mined or changing conditions necessitate different maintenance requirements. For example, an array should normally be inspected every six to twelve months. However, if inspections reveal that soiling conditions are severe and are causing significant shading, the array may require inspection and cleaning every three months. The maintenance plan should then be changed to reflect the new requirement. It’s highly recommended that records of all maintenance tasks be kept in a maintenance log. A maintenance log is a collection of past maintenance records. The log should include the maintenance tasks completed, the date and time, results, problems encountered, and any recommendations for future maintenance, such as changes to the maintenance plan or tips for making tasks easier or more effective. Most rooftop maintenance tasks require some form of fall protection, such as warning lines. Maintenance Plan: inspect modules for damage Address array shading issues Remove debris around array Inspect array mounting system Adjust array tilt Check inverter and/or charge controller for correct settings Inspect battery enclosure Inspect battery terminals and connections Equalize batteries Water batteries Measure specific gravity of each battery cell Load-test batteries Capacity-test batteries Inspect and clean all electrical equipment Monitor system for voltage and current --17. A maintenance plan includes all the necessary maintenance tasks and their respective schedules. Next: Monitoring Prev: Commissioning |