Operation & Maintenance Best Practices Guidelines (Version 6.0)

The previous chapter explored the range of maintenance activities conducted throughout the lifetime of a PV system. This chapter delves into the various tests performed at different maintenance intervals to ensure the optimal performance and longevity of photovoltaic (PV) systems.

At different maintenance schedules, various tests are performed to ensure optimal performance and longevity of photovoltaic (PV) systems. The maintenance schedules and typical tests are summarised in Figure 5.

There are six main tests performed throughout the PV lifecycle, each serving a specific purpose.

These tests include:

1. Intermediate site acceptance test: This test is performed after the installation is complete to exclude installation damage and establish a day-zero baseline for the PV system which provides a reference point for future performance evaluations and helps in identifying any deviations or issues that may arise over time. More information on this point can be found in the EPC Best Practices Guidelines.3

2. Final site acceptance test: This test ensures that the PV system is free from defects and is operating as expected before it is handed over to the owner or operator. More information on this point can be found SolarPower Europe’s EPC Best Practices Guidelines.

3. Annual maintenance test: These inspections are conducted at predetermined regular intervals according to original equipment manufacturer (OEM) and O&M manuals. The annual maintenance test includes a comprehensive evaluation of the PV system’s performance and condition, identifying any wear and tear or potential issues that may affect its efficiency. Regular maintenance helps in prolonging the lifespan of the system, reducing the risk of unexpected failures, and ensuring consistent energy production.

4. Technical due-diligence test: This condition-based quality check is performed for specific business purposes, such as asset transactions or refinancing. The technical due-diligence test provides an in-depth assessment of the PV system’s current state, evaluating its performance, reliability, and potential risks. This test is crucial for potential buyers, investors or lenders to make informed decisions regarding the value and viability of the PV asset.

5. Troubleshooting test: When performance issues are detected, a troubleshooting test is conducted to identify and replace defective PV modules or components. This test involves pinpointing the root cause of the problem and implementing corrective actions to restore the system’s performance. Troubleshooting tests are essential for maintaining the efficiency of the PV system and minimising downtime, ensuring that the system continues to operate at optimal levels

6. Damage evaluation test: After force majeure events, such as natural disasters or extreme weather conditions, a damage evaluation test is performed to assess the damage to the PV system. This test involves inspection of the affected components, determining the extent of the damage, and implementing necessary repairs or replacements to restore the system to its previous condition. Besides providing documentation of the damage for insurance claims and legal or financial processes, these tests document the post-recovery state of the system to ensure it is functioning properly after the damage event.

For the six tests above, there are inspection methods called EC 62446 series, which set standards for the testing, documentation, and maintenance of PV systems to ensure safety and performance. Some of these inspection models are summarised in Table 2 below.

Three key inspection methods are discussed in detail below:

String I-V Curve Scanning

String I-V Curve Scanning is an essential inspection method for evaluating the electrical performance of PV modules and strings. It helps in identifying and diagnosing performance issues, ensuring the optimal operation of the PV system. String I-V scanning is covered by the standard IEC 62446-1 on the maintenance of PV systems. Through I-V scanning, we can assess performance, identify degradation, and detects issues such as shading, soiling, and module mismatches in a string of modules. To carry out this procedure, the steps are as follow:

1. Connection: Connect the I-V curve tracer to the PV string

2. Measurement of environmental conditions:

    •  Measure the irradiance using and irradiance meter

    • Measure PV module temperature using a temperature sensor

3. Measurement: Measure the voltage and current output of the string across a range of operating conditions

4. Plotting: Plot the I-V curve to visualise the electrical performance

5. Analysis: Analyse the curve for deviations from expected performance, such as lower peak power, reduced fill factor, or abnormal knee points

6. Correction: Correct the I-V curve measurements for standard test conditions (STC) based on the measured irradiance and temperature

7. Comparison: Compare the measured I-V curve with manufacturer specifications and previous baseline measurements to identify potential issues

Electroluminescence (EL) imaging

Electroluminescence (EL) Imaging is a critical inspection method for detecting microcracks and other hidden defects in PV modules that are not visible through standard inspections. It enhances the accuracy of maintenance diagnostics, leading to more effective repairs and replacements. This technique provides a detailed view of the module’s internal health, helping to ensure the overall reliability and performance of PV systems. EL imaging is a relatively new process, whose standardisation is only happening as of 2025 with the publication of IEC TS 62446-4: Photovoltaic modules and plants - Outdoor electroluminescence imaging.

The electroluminescence procedure requires dedicated equipment including EL cameras, imaging systems and a DC power supply. The steps to implement the EL inspection include:

1. Image Capture:

   a. Ensure the PV modules are disconnected from the inverter and other DC circuits to prevent any unintended current flow

   b. Connect a suitable DC power supply to the PV modules or strings under test and apply a forward bias

   c. Position the EL camera to ensure the PV modules to be tested is within the field of view

2. Analysis: Examine the captured images for defects such as microcracks, inactive cell areas, and potential degradation

3. Comparison: Compare the EL images with baseline images or manufacturer specifications to identify and quantify defects

Inspection methods vary for EL, with different levels of complexity and various benefits and costs, which make them relevant for different typologies of PV systems from rooftops to large utilities. Mounting a camera on a tripod or framing system is among the simplest set ups, while still enabling the capture of high-quality images with sufficient exposure time. It does come with drawbacks, being labour-intensive and impractical for locations such as rooftops, tall trackers, and floating PV systems. Even with a well-designed framing system, the throughput is limited to around 1,500 to 3,000 modules per night, making it less suitable for large-scale inspections. Daylight EL imaging is another solution which relies on electrical modulation for imaging. It is more flexible, as it can be conducted during both day and nighttime. However, it is relatively slow, with a throughput of fewer than 500 modules per eight-hour shift, which limits its scalability for larger installations. Drones are rapidly emerging as a key solution for speed and flexibility, notably for hard to reach locations. Drones may be equipped with CMOS or InGaAs cameras.

• CMOS cameras are not highly sensitive to EL wavelengths, necessitating long exposure times. Stabilising a drone for several seconds in an outdoor environment poses significant challenges, resulting in a throughput of only 1,200 to 2,400 modules per eight-hour night shift

• InGaAs cameras are a highly efficient solution for EL imaging by drones, reaching a throughput of 10,000 to 15,000 modules per eight-hour night shift and delivering high-quality images, making it ideal for inspecting large-scale solar farms. However, the higher initial capital expenditure and system complexity create a higher entry barrier.

EL imaging is a versatile and highly effective method for detailed inspections of PV modules. The various technologies and methodologies associated with EL imaging allow for flexibility and scalability in its application.

Infrared (IR) thermography

Infrared thermography is a critical inspection method used to detect thermal anomalies in PV modules and other Balance of System (BOS) components, such as inverters, transformers, and electrical connections. Common issues identified through IR include hotspots, which may lead to various defects including total failure of a module. These inspections are essential for maintaining the efficiency and reliability of solar PV systems by identifying and resolving potential issues early. IT thermography inspections should comply with IEC TS 62446-3 - Photovoltaic modules and plants - Outdoor infrared thermography.

To proceed with IR measurement of PV modules, drones or aircraft equipped with thermographic cameras are typically used, enabling high throughput. During data acquisition, the drone or aircraft’s flight path is pre-programmed to cover the entirety of the solar PV asset. Thermographic images and visual photos or videos are recorded during the flyover. Alongside IR capture, additional geolocation services and 3D modelling of the entire plant may be offered.

Following data acquisition, various processing steps are necessary to establish a diagnosis of anomalies and assess the root causes of PV failures. They for instance include:

• Geolocation of PV Modules: Manual or automated location of the inspected solar PV modules, recreating the layout with precise geolocation down to individual module ID or serial number

• Thermal Anomalies Detection and Classification: Manual or automated detection of thermal anomalies, identifying affected solar PV modules on the plant’s layout

• Solar PV Module Failure Analysis: Diagnosis and root-cause analysis of solar PV module failures, linking thermal anomalies to specific failures

• Data Analytics: Basic or advanced data treatment to describe the impact of failures, including degradation trends, failure distribution, and power loss assessments

• Maintenance Implementation Plan: Recommendations for actions needed to minimise yield losses, translating findings into preventive or corrective operations

• Reporting: Standard is a presentation of results on interactive digital software solutions summarising findings, including power loss estimates and financial implications. Reports are usually housed in cloud-based platforms for easy access and comparison with previous inspections

Beyond modules, IR imaging can also be carried out on other components of the BOS, typically with the use of handheld thermographic cameras. There, the data acquisition proceeds through a detailed inspection of BOS components, such as inverters, transformers, and electrical connections, capturing thermal images of each component with the thermographic camera (which must first be set for the right temperature range). During post processing, thermal anomalies in BOS components are analysed, identifying areas of excessive heat generation.

Infrared thermography is effective for detecting thermal anomalies in PV modules and BOS components. Drones with thermographic cameras are used for rapid, large-area inspections, while handheld IR cameras are essential for detailed diagnostics, particularly for module connectors and components not visible from above. This two-step approach ensures comprehensive and accurate detection of issues, enhancing the reliability and performance of solar PV systems.

Additional Services

Table 3 presents a non-exhaustive list of additional services. For more information on whether these additional services are generally included in the O&M agreement or not, see 11.3. Scope of the O&M contract

Some of these items can be considered as a part of Preventive Maintenance. This depends on the agreement between the asset owner and the O&M service provider.

The O&M agreement can foresee services other than those pertaining to electrical and mechanical plant maintenance as per the above sections. Some of these additional services are generally included in the scope of work and the O&M annual fixed fee, and some are not.

Additional services not included in the O&M contract scope of work can be requested on demand and can either be priced per service action, or based on hourly rates applicable to the level of qualification of staff required to perform the works. These hourly rates usually escalate at the same rate as the O&M Service fee. In some cases, a binding price list for the delivery of some of these additional services can be included in the O&M contract as well.

Module Cleaning

Regular module cleaning is an important part of solar maintenance, and the problems associated with soiled modules are often underestimated. Prolonged periods of time between cleans can result in bird droppings etching modules and lichen growth, both of which can be extremely difficult to remove. The intensity and type of soiling depend heavily on the location of the solar PV system (e.g. its proximity to industrial areas, agricultural land, or railway lines). 

Module cleaning methods therefore vary from manual, to robotic and mechanical and each have their own advantages and disadvantages. The frequency of cleaning should be decided on a site-bysite basis, and it may be that certain parts of a site will need cleaning more often than other parts of the same site.

Maintenance topics related to snow mitigation for PV systems include manual and automated snow removal techniques, the use of heating elements, and the application of hydrophobic or ice-phobic coatings to prevent snow adhesion. Additionally, warranty considerations are crucial; it should be ensured that any snow mitigation methods used do not void the manufacturer’s warranty When choosing a module cleaning company, asset owners and O&M service providers should check the following:

• The suggested method of cleaning is fully in-line with the module manufacturer’s warranty and according to specifications from IEC 61215 (e.g. maximum pressure load)

• Quality of water and detergents: The modules should be cleaned with high quality, ultra-pure water, not tap, mains or borehole water. Detergents must be biodegradable and comply with local environmental regulations. Water runoffs must be planned for and ensure they don’t lead to negative environmental impacts

• H&S considerations should be made with regard to keeping staff safe on site. This should include some form of H&S accreditation and specific training for solar module cleaning, including working at height, if cleaning roof mounted modules.

Some of these items can be considered as a part of Preventive Maintenance. This depends on the agreement between the Asset Owner and the O&M service provider.

Vegetation Management

Vegetation management can represent a significant portion of the operations costs of a solar PV system. Some key items to consider in vegetation management:

• Damage Reduction: Vegetation management can reduce direct mechanical damage caused by vegetation - especially woody vegetation - growing into modules and structures. Damage can also be caused by direct shading causing hot-spot formation on modules, potentially leading to long-term module damage

• Performance Enhancement: Vegetation can cause module shading, which leads to degraded module performance. This effect is disproportionate to the amount of shading, so a small amount of shading can cause a significant amount of power loss

• Erosion Control: Vegetation is critical for soil stabilisation and avoidance of erosion damage on sites. Uncontrolled erosion can cause significant structural damage on a project over time

• Carbon Sequestration: Continuous vegetation management can assist in increasing soil carbon sequestration, especially with the use of grazing animals, who are able to fertilise the soil while enhancing soil carbon capture

• Biodiversity Enhancement: The use of natural pollinators and native vegetation can enhance local biodiversity. This can improve community engagement, lead to reduced vegetation management costs, and in some cases add revenue streams to a project

• Community engagement and social license to operate: Vegetation management can be one of the most visible maintenance activities for local communities and can affect aesthetics, noise pollution, erosion, runoff, and chemical contamination concerns. Vegetation management done well can enhance relations with the community and local councils and improve the social license to operate. Done poorly, vegetation management can cause conflict with local communities and planning councils and can lead to potential legal concern

Some options for vegetation management are outlined in Table 4 below