5.10 Operation And Maintenance Of PV Systems

Introduction

Operation and maintenance, often shortened to O&M, decide how well a solar photovoltaic system performs over its lifetime. Even a well designed and well installed system can deliver disappointing energy output if it is poorly maintained or operated in the wrong way. This chapter focuses on what happens after a PV system is installed, for both small systems at homes and large commercial or utility projects.

Goals Of Operation And Maintenance

O&M activities have several linked goals. The first is to keep energy production as close as possible to what was expected when the system was designed. The second is to protect equipment so that it lasts for many years. The third is to ensure safety for people who live, work, or move near the system, and for the technicians who work on it. Finally, good O&M helps meet financial expectations, which is especially important for projects that sell electricity or receive performance based incentives.

A useful way to think about O&M is to separate preventive actions, which try to avoid problems before they appear, from corrective actions, which react to problems once they have appeared.

Basic Performance Concepts

To judge if O&M is effective, system owners and operators need simple measures of performance. The most important are related to how much energy the system actually produces compared with how much it could have produced under the same sunlight conditions.

One widely used concept is performance ratio. It compares the actual AC energy output with the theoretical energy if the PV generator operated at its rated efficiency under the real solar irradiation that reached the modules. In simplified form, for a given period,

$$
\text{Performance ratio} = \frac{\text{Actual AC energy output}}{\text{Reference energy output based on irradiation and nominal power}}
$$

This ratio does not stay exactly fixed, but a steady and unexplained decline can signal problems such as soiling of modules, shading from new obstacles, failing components, or incorrect operation of equipment.

Energy yield is another simple concept. It expresses the energy produced per unit of installed capacity over a period, often in kWh per kW per year. Comparing the energy yield of similar systems in the same region is a practical way to see if O&M is effective.

Overview Of Preventive Maintenance

Preventive maintenance is planned work carried out regularly to reduce the risk of faults and preserve performance. For PV systems, preventive work focuses on inspections, cleaning, mechanical checks, and basic electrical checks.

For small rooftop systems, preventive maintenance can be relatively simple and infrequent, often limited to periodic visual checks, straightforward cleaning, and review of monitoring data. For large commercial or utility plants, preventive activities follow detailed schedules, with tasks at weekly, monthly, quarterly, and annual intervals. These include thorough inspections of modules, mounting structures, cabling, inverters, safety devices, and the surroundings of the plant.

The exact schedule depends on the system size, technology used, climate conditions, and local regulations or warranty requirements. For example, a system in a sandy desert climate will usually require more frequent module cleaning and inspection of moving parts than a system in a rainy temperate climate.

Corrective Maintenance And Troubleshooting

Corrective maintenance happens when something is already wrong. It can be as simple as resetting an inverter after a grid disturbance, or as complex as replacing strings of modules or power electronics.

Troubleshooting typically begins with noticing a problem. This might happen through regular monitoring, through alarms from equipment, or through manual readings that appear abnormal. Once the operator knows that the system is underperforming, they compare the behavior of different parts of the plant, check error codes, and use test instruments where necessary.

Corrective actions can include replacing defective modules or inverters, tightening or replacing damaged connectors, repairing broken mounting parts, clearing vegetation or objects that cause unexpected shade, and restoring correct settings in control software. Good record keeping of each incident and its cause helps improve future preventive maintenance planning.

Safety Principles For O&M Activities

Any O&M activity must respect safety, because PV systems deal with electricity, heights, heavy components, and sometimes harsh environments. Even in small systems, incorrect handling can cause electric shock, fire, or mechanical injuries.

PV modules produce direct current whenever they receive light. This continues even when the inverter is switched off. As a result, some parts of the system can remain energized during maintenance. Trained technicians use safe work procedures, personal protective equipment, and lockout and tagout methods to avoid accidental contact with energized parts.

Working at height is common for rooftop systems. Therefore, safe access, proper ladders or scaffolding, guardrails, and secure attachment points for harnesses are part of O&M planning. In large ground mounted plants, vehicle movement, uneven ground, and wildlife can be additional safety concerns.

For owners and users who are not trained electricians or technicians, the main safety rule is to avoid opening electrical boxes or handling wiring. Their role can focus on basic observations and cleaning that does not require dismantling or touching electrical components.

Monitoring And Data Analysis

Modern PV systems often include monitoring systems. These can range from simple displays on small inverters to full remote monitoring platforms for large plants. Monitoring is central to effective O&M because it reveals performance trends and anomalies that are not visible by eye.

Common monitored values include DC voltage and current from each string or array, AC power output, inverter status, module or ambient temperature, and sometimes solar irradiance and wind speed. For systems that feed into a grid, grid voltage and frequency at the connection point can also be monitored.

Operators use this data in two ways. First, they use real time views and alarms to see when inverters shut down or when output drops unexpectedly. Second, they use historical data to compare daily and seasonal patterns and to detect gradual changes. For instance, if several strings of modules show lower current than others under the same conditions, that may signal soiling, shading, or deterioration.

For owners of small systems, simple online or mobile applications that show daily, monthly, and yearly production are often enough. Even in this simple case, it is useful to compare current production with earlier years during similar months to spot slow declines that may point to unaddressed maintenance needs.

Visual Inspections Of Modules And Structures

Visual inspection is one of the most basic and important O&M actions. It involves looking closely at the modules, frames, mounting structures, junction boxes, and visible cables. Many problems can be seen before they cause serious loss of performance.

For modules, the operator looks for cracks in the glass, discoloration, delamination, burned spots, or broken frames. They also check for dirt accumulation, bird droppings, falling leaves, or other materials that shade parts of the module. Broken or missing clamps, loose bolts, and corrosion on metal parts of the mounting structure also require attention.

On rooftops, inspections should check that roof penetrations remain watertight and that sealing materials around mounts are intact. For ground mounted systems, the operator looks for soil erosion around foundations, tilted or misaligned structures, and excess vegetation that could reach or shade the module surfaces.

Visual inspection is usually non intrusive, but when any safety doubt appears, maintenance staff should avoid touching the defective part until they have properly disconnected and isolated the system.

Cleaning Of PV Modules

Keeping the module surface free from excessive dirt or deposits is essential. Dust, sand, bird droppings, industrial pollution, pollen, and leaves can block sunlight. This reduces the energy output of the affected modules and can also create hot spots when some cells are shaded while others remain illuminated.

The need for cleaning depends strongly on local conditions. In rainy climates, natural cleaning by rain is often enough, and cleaning may be needed only once every year or even less. In dry or dusty areas, or near agriculture, mines, or busy roads, cleaning may be required several times per year or more often.

Cleaning methods depend on the system size and location. For small rooftop systems, manual cleaning with a soft brush or sponge and clean water is common. Strong chemicals and abrasive tools should be avoided because they can damage the module surface. Cleaning is best done when modules are cool, such as in the early morning, to reduce thermal stress and avoid rapid evaporation of water that leaves residues.

In large ground mounted plants, cleaning can be more mechanized. Options include specialized vehicles with brushes or sprayers, and in some cases robotic cleaners that travel along module rows. In water scarce regions, operators may use dry cleaning with soft brushes or devices designed to minimize water use.

Electrical Checks And Preventive Testing

Although many electrical problems appear through alarms or reduced output, preventive electrical checks can detect issues earlier and increase safety. These checks should be done by qualified personnel.

One common test is measurement of open circuit voltage and short circuit current for strings, and comparison with expected values. Significant deviations can indicate connections that are loose or corroded, damaged modules, or mismatched strings. Insulation resistance tests can identify damaged cables or moisture ingress that could lead to electric shock risk or faults.

Thermal imaging with infrared cameras is a powerful non contact method. Hot spots on modules, connectors, or cables show up clearly in thermal images. These hot spots can signal poor contacts, partial shading, internal defects, or overloaded components.

Periodic verification of torque on electrical terminations and mechanical bolts helps keep connections secure. Over time, vibration, thermal expansion, and contraction can loosen screws and clamps. Re tightening them according to manufacturer specifications helps avoid arcing and overheating.

Inverter Operation And Maintenance

Inverters are central to PV systems that provide AC electricity. They convert DC power from the modules into AC power that can be used by loads or exported to the grid. Inverters also protect the system by reacting to abnormal conditions such as voltage or frequency outside permitted ranges.

O&M for inverters starts with simple things. Keeping the environment clean and adequately ventilated is essential, because inverters generate heat during operation. Dust buildup on air inlets, blocked fans, and high ambient temperatures can reduce lifetime and cause unexpected shutdowns. Regular cleaning of ventilation grilles and checking that fans are working are simple but very important tasks.

Inverters record event logs and fault codes. When a fault occurs, the O&M team reads and interprets these codes, consults manuals, and determines if a simple reset is sufficient or if deeper repair or replacement is needed. Software or firmware updates may be part of planned maintenance to improve performance, address known issues, or adapt to changing grid codes.

For string inverters, which are common in residential and commercial systems, replacing a faulty unit is often straightforward. For central inverters used in utility scale plants, O&M can involve modular replacement of parts inside the inverter, such as power modules, filters, or control boards. In both cases, safe isolation from the DC and AC sides is essential before opening any enclosure.

Managing Vegetation And Surroundings

In ground mounted and some rooftop systems, the environment around the PV installation changes over time. Plants grow, soil moves, and objects appear. These changes can affect both performance and safety.

Vegetation management is significant for ground mounted plants. Grass and shrubs must be kept at a height that does not shade the lower part of the modules or obstruct access. At the same time, complete removal of vegetation can lead to soil erosion, dust, or habitat loss. O&M strategies therefore often try to control plant height rather than remove all plants. In some contexts, grazing animals are used under supervision as a form of vegetation control.

The surroundings should be kept free of loose objects that wind could blow onto the modules or cables. For rooftop systems, O&M may include removal of branches that might fall during storms or that start to cast shade as trees grow.

In snowy climates, snow accumulation can temporarily block sunlight. Removing snow can increase winter energy yield, but it must be done carefully to avoid damaging modules and without risking the safety of workers on slippery roofs. In many cases, the design inclination of the modules helps snow slide off naturally when temperatures rise.

Record Keeping And Documentation

Good O&M involves systematic record keeping. For every PV system, there should be a maintenance log that records inspections, cleaning dates, faults, corrective actions, and any component replacements. This log is useful for warranty claims, for compliance with regulations, and for analyzing long term performance trends.

Documentation should also include the as built system layout, serial numbers of main components, wiring diagrams, and instruction manuals. Over time, as components are replaced or upgraded, records must be updated so that future technicians know the exact configuration.

For larger projects, O&M service providers may use digital maintenance management systems that schedule tasks, store reports, and integrate with performance monitoring platforms. Even for small systems, simple but consistent documentation helps ensure continuity when ownership changes or when different technicians work on the system.

O&M Considerations For Different System Scales

Although the basic principles of O&M are common, the way they are applied varies with system size and type.

For small rooftop residential systems, O&M is often part time and focused on simple tasks. The homeowner may perform regular visual checks from a safe position and follow guidance from the installer on when to call a professional. In many cases, an annual or biannual professional inspection is sufficient, and the main issues are cleaning, checking that inverters show normal status, and ensuring no new shading.

For commercial and industrial systems, O&M is more structured. These systems often require regular professional visits, remote monitoring, and more detailed reporting, because the power and financial stakes are higher. Integration with building operations, such as coordination with backup generators or energy management systems, adds operational complexity.

Utility scale solar farms require full time or dedicated O&M teams. They manage large numbers of inverters and modules, coordinate spare parts, perform scheduled testing, and follow contractual performance guarantees. In these systems, small percentage improvements in performance ratio can translate into large financial amounts, so O&M is treated as a core operation rather than a secondary task.

Contracts, Warranties, And Service Models

O&M is not only technical, it also has contractual and economic sides. Many PV system owners sign O&M contracts with specialized service companies or the original installer. These contracts define the scope of work, response times to faults, performance guarantees, and responsibilities.

Warranties for modules, inverters, and other equipment often require that O&M follow certain minimum standards. For example, a module warranty may insist on regular cleaning and prohibit the use of specific cleaning agents. An inverter warranty may require that ventilation is not blocked and that service checks are performed by approved technicians. If O&M neglects these requirements, the manufacturer can refuse warranty claims.

In some business models, especially for large projects, O&M services are bundled with performance guarantees. The service provider agrees that the system will produce at least a certain amount of energy or maintain a minimum performance ratio. If the system underperforms for reasons that fall within the provider's control, they may have to compensate the owner. These agreements create a strong incentive for careful and proactive O&M.

End Of Life And Long Term Operation

PV systems are designed to operate for decades. Over such long periods, O&M strategies can change. In early years, the focus is mainly on keeping performance high and addressing infant failures in equipment. Later, as modules age and inverters approach the end of their typical service life, O&M involves more replacements and upgrades.

Inverters usually have shorter service lives than modules. Owners may plan one or more inverter replacements within the total life of the plant. When replacing older inverters, O&M planners can consider newer models that may be more efficient or better adapted to current grid requirements.

Modules usually degrade slowly, losing a small portion of their output each year. O&M teams track this degradation through performance analysis. When energy production becomes too low compared with expectations, owners may choose to repower the system. Repowering means replacing older modules with new ones that have higher power ratings, and adapting inverters or other components if required.

Planning for end of life is also an O&M task. This includes arranging safe decommissioning practices, recycling of modules and metal structures, and disposal of components that cannot be recycled. Clear records of the materials in the system help prepare for future recycling and reduce environmental impact at the end of the system's life.

Conclusion

Operation and maintenance of PV systems is a continuous process that begins as soon as the system is commissioned and continues throughout its lifetime. Effective O&M combines regular inspection, cleaning, monitoring, preventive testing, safe corrective actions, documentation, and planning for long term changes in equipment and environment. By taking O&M seriously, system owners protect their investment, improve energy yields, and support the reliability of solar electricity as a long term element of the energy system.