Four Drone Surveying Steps for Identifying Degraded Areas in Solar Power Plants

Maintenance of solar power plants tends to require inspection of a wide range of elements, including panels, mounting structures, graded areas, drainage facilities, slopes, and access roads. Simply walking the site for inspections makes it difficult to later organize the spatial relationships and extents of deterioration, which can lead to rework when compiling reports and repair plans. Using drone surveying, you can record the entire plant from the air and more easily organize suspected areas of deterioration together with their location data. This article explains, in four steps for practitioners, the basic procedure for using drone surveying to organize deteriorated areas at solar power plants.

Table of Contents

• Clearly define the purpose of cataloging deteriorated locations using drone surveying.

• Step 1 Organize the site conditions and the items to be checked in advance

• Step 2 Determine the coverage area and flight plan

• Step 3 Interpret deterioration locations from the acquired data

• Step 4 Record in a ledger with location information to inform repair decisions

• Operational approach to reducing oversights when organizing deterioration locations

• Summary

Clarify the purpose of organizing deteriorated areas using drone surveying

The purpose of conducting drone surveys at solar power plants is not simply to take aerial photographs. What is practically important is to organize the information so that it can later be confirmed where within the plant there are suspected deterioration or abnormalities, what kind they are, and how extensive they are. If inspectors leave their observations at the site only as verbal notes or photographs, location identification can become ambiguous, causing discrepancies in understanding among facility managers, contractors, maintenance personnel, and project owners. By acquiring overhead imagery and three-dimensional terrain information with drone surveys, it becomes easier to understand where deterioration has occurred within the entire plant.

There are various types of degradation in solar power plants. Attention is required not only for the equipment itself but also for the land and surrounding structures that support the plant, such as dirt or suspected damage on panel surfaces, settlement around racking, scour around foundations, small slope failures, clogged drainage channels, ruts on access roads, overgrowth of weeds, and deformation around fences. In particular, at solar power plants installed in mountainous areas or on developed land, rainwater flow, ground changes, and vegetation conditions can affect operation and maintenance. These changes are difficult to assess from a single visual inspection, so comparison with past data and fixed-point records is important.

The advantage of drone surveying is that it makes it easy to record large areas under similar viewing conditions. Ground-based photos are effective for checking close-up views of objects, but they are limited in grasping the overall layout of a power plant and the relationships between anomalous locations. Images taken from above allow integrated confirmation of panel rows, walkways, drainage routes, slopes, and boundary areas. Also, if point clouds and elevation data are generated as needed, they can serve as material for examining ground undulations and subsidence trends, as well as deformations in embankment and cut sections. However, drone surveying alone cannot determine all deterioration. What can be confirmed from images is mainly visible changes or suspected abnormalities, and electrical faults, internal deterioration, or reductions in structural member strength need to be judged in combination with other inspection methods or specialized investigations.

Therefore, before using drone surveying, it is important to be clear about what you want to organize. Whether you want to grasp overall deterioration trends, record damage locations after a typhoon or heavy rain, determine the priority of repair work, or create location maps to attach to inspection reports, the shooting methods and the way deliverables are produced will vary accordingly. If you fly with an unclear objective, you are likely to encounter problems such as having images but lacking photos from the necessary angles, insufficient positional accuracy, or no reference standards available for comparison.

Drone surveying for organizing deterioration sites is most effective when regarded as a practical tool that connects on-site inspection, recording, sharing, and decision-making. The purpose is to record anomalies found on-site with positional information, organize them on drawings and images of the entire power plant, and create a situation in which stakeholders can consider response policies while looking at the same information. With that premise, it becomes easier to utilize surveying not as mere image capture but as a means to improve the quality of maintenance and asset management.

Please translate the following input into English.

Step 1: Organize site conditions and items to be checked in advance

The first step is to organize the inspection targets and site conditions before going to the site. Solar power plants vary from site to site in terms of site shape, panel layout, surrounding terrain, the presence or absence of maintenance roads, embankment heights, and the arrangement of drainage facilities. If you try to decide the shooting area on site without prior organization, you may miss photographing necessary locations, get too close to hazardous areas, or run out of flight time. If the purpose is specifically to identify areas of deterioration, it is especially important to decide in advance which equipment and areas to focus on.

First, what you should check is the overall layout of the power plant. Knowing the orientation of the panel rows, the locations of the substation and collector equipment, service roads, entrances and exits, fences, drainage channels, retention ponds, slopes, and boundaries with adjacent land makes it easier to plan flight routes. If there are existing site plans, as-built drawings, past inspection records, or repair histories, it is a good idea to review them in advance. Locations that have previously experienced ground subsidence, poor drainage, panel damage, slope collapse, or overgrown weeds should be priority areas to check during this photo survey.

Next, we organize the types of deterioration. For visual inspections of solar power plants, targets include cracks and dirt on panel surfaces, frame deformation, tilt of mounting structures, soil erosion around foundations, sediment accumulation in drainage channels, slope cracks, road subsidence, leaning fences, abnormalities around cable racks, and so on. However, there are items that are easy to confirm from drone images and items that are difficult to judge without close on-site inspection. Discoloration and shape changes visible from the air are easy to detect, whereas bolt loosening, fine corrosion, and internal equipment faults can be difficult to assess from images alone. Therefore, in drone surveys it is realistic to perform a broad initial assessment and link suspicious areas to ground confirmation.

As part of on-site conditions, verifying safety is essential. Solar power plants can have electrical equipment, overhead lines, trees, steep slopes, narrow passages, and areas where third parties may enter. Before flight, check whether takeoff and landing areas can be secured safely, whether you can plan routes that do not come too close to generation equipment or surrounding facilities, and whether the terrain is prone to wind effects. At plants in mountainous areas or along the coast, wind direction can change easily and terrain can disturb airflow. Because unsafe flights can lead to accidents or poor data quality, weather conditions and on-site safety checks must be prioritized.

The timing of photography also affects how degradation appears. During periods when weeds are overgrown, the ground surface and areas around the foundations can become difficult to see. Immediately after rain, puddles and poor drainage are easier to confirm, but mud and reflections can make image interpretation difficult. In periods of strong sunlight, shadows deepen and the conditions under panels and around mounting frames can become harder to observe. Depending on the objective, being mindful of the shooting timing and the sun’s angle can help obtain data that are easier to interpret later.

In the preparatory phase, decide at what unit level to manage deterioration locations. Whether you organize by panel, by panel row, by block, or by area will affect the required image resolution and the method for position management. In large power plants, trying to record every anomaly in detail makes management complex. Decide on a granularity that is easy to use for on-site maintenance, and classify issues by severity and urgency so that downstream processes run smoothly.

Step 2 Determine the imaging area and flight plan

The next step is to specify the imaging coverage and flight plan. In drone surveying used for cataloging deterioration locations, it is important to differentiate between imaging that uniformly records the entire power plant and imaging that examines areas of concern in detail. Relying only on overall imaging will lack fine detail, while relying only on detailed imaging makes spatial relationships difficult to understand. The key is to plan so that you produce data usable as an overall site map of the power plant while enabling interpretation of locations suspected of deterioration.

For overall imaging, ensure the entire power plant is recorded continuously, including panel rows, walkways, slopes, drainage facilities, and boundary areas. Shooting while maintaining a consistent altitude and image overlap makes it easier to create wide-area orthophotos and three-dimensional data in post-processing. An orthophoto is an image corrected to appear as if viewed directly from above, and it is a useful deliverable for location maps and marking degraded areas. When creating point clouds or elevation data, they provide material for checking terrain changes and height differences. In all cases, missing coverage or insufficient overlap will degrade the quality of the deliverables, so it is necessary to set the coverage area with a sufficient margin during the flight planning stage.

Detailed photography supplements areas that are difficult to discern in overall shots. For example, oblique shots taken from different angles can be effective for detecting clogging in drainage channels, cracks in slopes, soil erosion, leaning fences, subsidence of maintenance roads, and deformations around mounting racks. Step differences and side deformations that are not visible in images taken directly overhead also become easier to identify when photographed obliquely. However, solar panels are affected by reflections, and depending on the shooting angle and time of day, images can become washed out by glare or obscured by shadows. In detailed photography, it is desirable to record the necessary areas from multiple angles while taking into account reflections, shadows, and obstacles.

When positional accuracy is required, also consider how to handle reference points and control points. If you only need to organize deterioration locations into broad areas, it may be sufficient to know their positions on the images. On the other hand, if you use the data to quantify repair areas or issue construction instructions, compare with past data, or clarify positional relationships with boundaries or structures, more stable positional information will be necessary. Prepare according to your purpose, such as installing reference points on site, aligning with existing survey results, or utilizing functions that improve positioning accuracy. Explanations about accuracy should be organized together with the intended use of the deliverables to help prevent misunderstandings among stakeholders.

Flight plans should also take into account ensuring safety within the power plant. Even when flying over panels, considering possible aircraft malfunctions or strong winds, it is important to keep approaches to equipment to the minimum necessary. Select takeoff and landing locations where dust and small stones are unlikely to be stirred up and that do not impede pedestrian or vehicle traffic. If there are residences, roads, farmland, transmission facilities, or the like nearby, consideration for third parties and surrounding facilities is also required. If the plant manager, maintenance personnel, or on-site workers are present, sharing flight times and restricted access areas in advance helps avoid encroachment during work and misunderstandings. For actual flights, it is also necessary to confirm permits/approvals and safety management in accordance with aviation law, municipal rules, facility manager rules, and the surrounding environment.

When creating a shooting plan, it is important to work backwards from the intended use of the deliverables. Whether you need an overall view to attach to a report, a list of deterioration locations, images for before-and-after repair comparisons, or baseline data for the next inspection will change the required shooting density and the types of images. If the purpose is to create an asset register, images that can be easily correlated with the power plant’s zones and asset numbers are required. For repair decision-making, images that reveal the extent of deterioration, the impact on surrounding equipment, and the urgency are necessary. Solidifying an image of the deliverables before flight reduces the risk of discovering deficiencies after shooting.

Step 3 Interpret areas of deterioration from the acquired data

After shooting, interpret areas of degradation based on the acquired images and survey data. What is important here is not to immediately conclude that a change seen in an image is degradation. Images of photovoltaic power plants capture various elements such as shadows, reflections, dirt, weeds, moisture, differences in soil color, and variations in appearance due to shooting angle. Something that appears abnormal in an image may actually be a temporary shadow or a puddle. Conversely, a change that looks minor in an image may turn out to be a serious sign of degradation upon ground inspection. In interpretation, it is important to extract suspicious areas and, if necessary, follow up with on-site verification or specialist inspection.

First, review the overall images to get an overview of the condition of the entire power plant. Look for changes that are noticeable when viewing a wide area, such as misalignment of panel rows, discoloration of the ground surface, places where rainwater tends to collect, traces of sediment flow, uneven vegetation, sloughing of slopes, blockages in drainage channels, and ruts in access paths. Even if a deterioration appears to occur in isolation, it may be related to the terrain or drainage flow. For example, if the ground surface is eroded only beneath a specific row, rainwater may be concentrating from upstream. If sediment has accumulated at the base of a slope, a small collapse may be occurring at the top. For this reason, it is important to consider not only individual photos but also their connection to the surrounding area.

Next, review the detailed images and classify the types of deterioration. You may decide the classifications for each site, but in practice it is easier to organize them into equipment-related, ground-related, drainage-related, vegetation-related, and boundary-related categories. Equipment-related includes visual abnormalities around panels and racks, exposure of foundations, deformation of wiring support components, and so on. Ground-related includes settlement, level differences, scour/erosion, soil runoff, cracks, and deterioration of road surfaces. Drainage-related includes changes in watercourses, clogging of gutters and catch basins, overflow traces, and scour at drainage outlets. Vegetation-related includes overgrowth of weeds, encroachment of trees, grass covering the undersides of panels, and reduced visibility of access paths. Boundary-related includes leaning fences, deformation around gates, and inflow of soil from outside.

When interpreting findings, it is also useful to establish how to judge severity. If you separate priorities—items that require immediate on-site verification, items to be monitored until the next inspection, items to be handled by routine maintenance such as cleaning or weeding, and items to be reflected in repair plans—you make the record more actionable rather than merely archival. For example, if poor drainage is affecting the foundations around panel racks, or slope deformation might spread toward the equipment, those should be given high priority. On the other hand, minor weeds or temporary puddles can be incorporated into routine maintenance after confirming the situation.

If past data are available, comparing them with the current data is useful. If the same area was captured under similar conditions, it becomes easier to compare changes in the ground surface, the spread of weeds, changes in drainage routes, and the progression of slopes. For the initial drone survey, create baseline data, and operate so that subsequent surveys are used to check for changes; this makes it easier to explain the progression of deterioration. However, if flight altitude, angle, timing, or sunlight conditions differ significantly, comparison can become difficult. If you plan to use the data continuously, record the capture conditions and try to re-capture under as similar conditions as possible.

In addition to marking the image, it is good practice to concisely record why a location was flagged as a suspected deterioration. For example, add explanations such as evidence of soil runoff, sediment accumulation visible in drainage channels, linear changes on the slope surface, suspected scouring beneath a row of panels, or suspected settlement of a maintenance road so that another inspector can later trace the basis for the judgment. Marks on an image alone can make it hard to understand what was being considered problematic. Interpretation results should be retained together with their rationale as information to inform subsequent ground inspections and repair planning.

Step 4: Record in a ledger with location information and use it to inform repair decisions

The final step is to record the extracted deterioration locations in a register with location information and use that to inform repair decisions. Simply storing images is not enough to leverage drone survey results for maintenance management. It is necessary to organize where suspected deterioration exists, what type it is, the degree of priority, who will inspect it and when, and what the next actions are. By registering this information, inspection results become management information that can be shared among stakeholders without relying on individual memory.

The ledger records the power plant name, photo date, inspection date, location of degraded areas, management number, degradation classification, summary, judgment category, response policy, photo number, verifier, remarks, and so on. Locations should be recorded in a form that is easy to reconfirm on site, such as the plant area name, panel row number, aisle number, coordinates, and marks on images. Because coordinates alone can make it difficult for field workers to identify a location, combining positions on site plans or orthophotos with on-site landmarks increases practical usability. Assigning a management number makes it easier to link reports, photos, repair requests, and reinspection results.

To inform repair decisions, it is important to organize priorities in the register. If there are many deteriorated areas, it is not realistic to address them all at once. Based on impacts on equipment, impacts on power generation, impacts on safety, the progression of deterioration, potential for spread to surrounding areas, ease of inspection, and so on, you need to determine the order of response. For example, if poor drainage is causing scour around the racking foundations, it may be necessary to review the water flow rather than simply cleaning the drainage channels. Even a small slope collapse requires prompt on-site inspection if it is expanding with each rainfall. Recording past and current conditions side by side in the register makes it easier to explain priorities.

When preparing a report, combining an overall map and detailed photographs makes it easier to understand. The overall map should indicate where suspected deterioration is located within the power plant. Detailed photographs should allow confirmation of the condition of each location. Furthermore, assigning the same number to the register, the overall map, and the photographs makes it easier for the reader to track the information. In practice, people in multiple roles may look at the same documents—for example, managers confirming the overall picture, maintenance staff responding on-site, and contractors considering repair methods. Making the documents clear in terms of both location and content to anyone who views them is important for making the most of the drone survey results.

When creating a ledger, it is also necessary to decide the rules for updating the data. If a ledger that has been created is left unattended, old and new information will be mixed at the next inspection, making it difficult to manage. Organizing statuses such as "addressed," "under observation," "needs reinspection," "repair scheduled," and "not applicable," and recording the update date makes it easier to manage the history. If you take drone photos again after repairs, you can keep them as before-and-after comparison materials. This is also useful for reporting to the client and for internal maintenance records.

Also, it's important to make the register usable in the field. If a list created in the office is hard to use on site, it will increase the effort required during re-inspections. Including information that field workers can easily understand—such as area divisions within the plant, aisle names, methods for identifying panel rows, and routes from the entrances—will speed up reaching deteriorated locations. Orthophotos and location data obtained from drone surveys can also be used as maps to guide on-site inspections. The larger the plant, the more directly this ease of location identification translates into work efficiency.

Operational approach to reduce oversights when organizing deterioration locations

When using drone surveying to identify and manage areas of deterioration, it is desirable to incorporate it as an ongoing operation rather than ending with a single flight. Deterioration at solar power plants does not always appear all at once. Many issues progress over time: scour that advances a little with each rainfall, weeds that change seasonally, gradual spreading of slope deformations, ruts that deepen from traffic, and so on. Conducting drone surveys regularly under similar conditions makes it easier to detect changes early.

To reduce oversights, it is effective to standardize the items to be checked. If you rely solely on each inspector’s experience every time, the locations to be inspected and the criteria for judgment will change. Decide in advance the scope to be checked—panel rows, mounting foundations, drainage channels, slopes, walkways, fences, entrances and exits, surrounding boundaries, etc.—and make sure to verify them in the same order even when interpreting images after photographing. This helps reduce variability in inspection results. Especially when managing multiple power plants, using the same classifications and ledger items makes comparisons between plants easier.

Combining this with on-site visual inspection is also important. Drone surveying is well suited to efficiently understanding a wide area, but it has limits when it comes to checking fine details. By identifying suspected deterioration in the images and then performing close-up ground inspections starting with the highest-priority locations, you can increase the efficiency of field verification. Conversely, mapping anomalies found during ground inspections onto the drone imagery makes it possible to determine whether those anomalies are related to the surrounding terrain or drainage. Combining the aerial perspective with the ground-level perspective enables a more accurate understanding of the actual conditions.

When organizing areas of deterioration, how photos are taken and the naming rules are also important. If there are a large number of image files, simply locating the desired photo later can take a lot of time. Organize the shooting date, power plant name, area name, management number, etc., and make them correspond to the register so that report preparation and reinspection become easier. In maintenance management practice, it is important not only to store images but also to make clear which image corresponds to which area of deterioration.

You should also consider how to share information with stakeholders. Even if inspection personnel understand the images, if that understanding is not conveyed to the managers and contractors who make repair decisions, it will be difficult to proceed. Share the overview diagram, register, detailed photos, and response policy together so the locations and conditions of deteriorated areas are immediately clear. In particular, when multiple parties such as the power plant owner, management company, maintenance company, and construction company are involved, it is easier to reach a common understanding by discussing images with location data than by explaining only in words.

On the other hand, it is also important not to over-rely on the results of drone surveys. Images and point clouds contain useful information, but their appearance and accuracy can vary depending on weather, lighting conditions, flight altitude, aircraft performance, and analysis methods. When making a final determination about the presence or absence of deterioration, it is necessary to cross-check with on-site verification, specialist inspections, design documents, construction history, and past inspection records. Especially when decisions involve safety or structural judgments, conclusions should not be drawn from image interpretation alone; expert confirmation should be obtained as necessary.

In operational terms, drone surveying is also useful for temporary inspections after disasters. After typhoons, heavy rain, strong winds, snowfall, earthquakes, and the like, it is necessary to quickly determine where abnormalities have occurred within a power plant. Photographing the entire facility from the air before walking through a large power plant makes it possible to efficiently check for debris inflow, slope failures, flooding, fence damage, and road obstructions. If baseline data from normal conditions are available, it becomes easier to compare post-disaster changes. Recording regular inspections and temporary inspections under the same management rules increases their value as long-term maintenance records.

Summary

Using drone surveys to organize degradation locations at a solar power plant makes it possible to get an overview of anomalies and changes across a large site and, together with location information, makes them easier to manage. The important thing is not merely to take photographs, but to clarify objectives, organize inspection targets, create a capture/flight plan, record interpretation results in a ledger, and link them to repair decisions. By combining overall images of the plant, detailed photos, location information, and inspection comments, on-site verification, report preparation, and sharing with stakeholders become easier.

In practice, rather than determining deterioration solely from drone surveys, a realistic approach is to extract suspected deterioration from images and connect the necessary locations to on-the-ground verification or specialist inspections. In particular, problems such as poor drainage, ground deformation, minor slope collapses, overgrown vegetation, and subsidence of maintenance access roads become easier to understand in terms of causes and affected areas when organized while considering the overall layout of the power plant. If imaging conditions and record fields are standardized so they can be compared with past data, it becomes easier to track the progression of deterioration and to explain repair priorities.

In the maintenance and management of solar power plants, it is important to record inspection results in a way that is easy to understand and that connects to subsequent actions. Drone surveying is an effective recording method for that purpose, with strengths in wide-area inspections, location identification, and preparing shareable materials. If you want to streamline the organization of degraded areas and manage the entire flow from on-site verification to repair decisions, it is important to clarify site conditions, required accuracy, safety management, and how deliverables will be used, and then establish a system that can operate from surveying to data processing in line with actual work.