6 checks to carry out post-disaster inspections of solar power plants using drone surveying

After typhoons, heavy rain, earthquakes, snowfall, or strong winds, solar power plants can experience changes that are difficult to see with the naked eye. Beyond panel damage, there are many inspection points related to the safety of generation equipment and decisions about restoration, such as tilted racking, slope failures, clogged drainage channels, scour of internal roads, and deformations around fences. Walking a large plant on foot to check everything takes time and may require approaching hazardous areas. One useful method is drone surveying, which can record conditions from above. In post-disaster inspections, it is important not simply to take photos but to organize the locations, extent, elevation differences, and amounts of change of damage and use that information to guide subsequent actions.

Table of Contents

• The safety zone that should be checked first during post-disaster inspections

• Topographic changes and subsidence to be detected by drone surveying

• Aerial perspective for inspecting anomalies in panels and mounting structures

• How to proceed without overlooking damage to drainage routes and slopes

• How to create records using point clouds and photographs that can be used for recovery decision-making

• The Importance of Preparing Baseline Data for Post-Disaster Comparisons

• Summary

Safety zones to check first during post-disaster inspections

In post-disaster inspections of solar power plants, it is important not to start by walking around the site, but to delineate the areas that can be checked safely. Immediately after heavy rain, there may be hazards such as softened ground, the top and bottom of slopes, areas around drainage ditches, and work paths that remain muddy. After strong winds or an earthquake, there may be cracked panels, deformed mounting structures, sagging cables, or collapsed fences, creating situations where you want to assess conditions before people approach. Drone surveying is one method suited to this kind of initial assessment before entering the site.

The important point here is not to assume that flying a drone will immediately complete a detailed inspection. In the initial response after a disaster, it is realistic to use it first to separate areas where people can safely approach from areas that require additional checks before approaching. Aerial photos and videos are used to identify sediment intrusion, signs of flooding, fallen trees, landslides, and major displacements of equipment, and to determine routes by which field workers can move safely. This is especially true for solar power plants located in mountainous or sloped terrain, where access paths themselves may have been washed away or road shoulders weakened. Being able to grasp the overall situation before walking on site is highly significant for improving the safety of post-disaster inspections.

When conducting drone surveys, pre-flight safety checks are indispensable. Immediately after a disaster, communications may be unstable, recovery work may be taking place nearby, and power transmission equipment or temporary materials may be in conditions different from normal. You must plan flight routes in advance, secure takeoff and landing sites safely, and conduct operations only after checking wind conditions and visibility. It is also important to confirm flight-restricted areas, third-party airspace, surrounding facilities, the status of emergency response, approval from site managers, and compliance with relevant laws and flight rules. In post-disaster inspections, not only power generation equipment but also the surrounding environment may have changed, so you may not be able to use normal flight plans as-is. Taking into account obstacles, fallen trees, collapsed slopes, and the locations of temporary vehicles, it is important to begin filming within a safe, manageable range.

In managing solar power plants, there are many situations where inspection results need to be shared with stakeholders. The information different viewers want varies—on-site staff, maintenance personnel, contractors, landowners, insurance-related parties, and so on. During the initial drone survey, it is helpful to create records that visually share where and what is happening before beginning specialized analysis. By combining wide-area overhead images, close-up images of damaged areas, and videos showing the condition of access routes, it becomes easier to convey the situation to stakeholders who cannot visit the site.

When checking safety margins, it is important not to underestimate hazardous areas. Even if it appears as minor soil erosion in a photo, the downstream side of the drainage path may actually be undercut. Even if only part of a panel row appears slightly tilted, there may be changes to the racking foundations or the ground. The purpose of using drone surveying in post-disaster inspections is not only to reduce onsite work, but to quickly identify places that may pose a risk and prioritize them. First determine locations that can be approached safely, and then proceed to detailed onsite inspections; being conscious of this flow makes it easier to balance the overall inspection’s accuracy and efficiency.

Terrain Changes and Subsidence to Monitor with Drone Surveying

One thing that is easy to overlook in post-disaster inspections of solar power plants is slight changes in the terrain. Damage such as broken panels or collapsed fences is easy to spot by eye, whereas ground subsidence, deformation of embankments, scour, and accumulation of sediment can be hard to grasp by simply walking the site. Because solar plants have panels spread over a wide area, missing a locally depressed spot or uneven drainage can allow damage to expand during the next heavy rain. Drone surveying can organize the terrain’s shape from aerial images, making it an effective means of understanding changes before and after a disaster.

When checking for terrain changes, it is not sufficient to simply look at whether something is "collapsed." You need to separately confirm the extent of the change, whether the change is close to the panel rows or racking foundations, whether it is affecting drainage direction, and whether it relates to the safety of access routes. For example, if soil is washing away around the perimeter of the plant, even if power generation is not affected right now, the next rainfall could affect fences or foundations. Conversely, localized settlement beneath panels, though hard to see from the outside, can affect racking tilt and the safety of maintenance work.

When using drone surveying to deal with terrain changes, it is important whether you can compare the data to normal-condition data. Looking only at post-disaster data makes it difficult to determine whether the area was originally low or whether it subsided because of the disaster. If you have previously acquired photos, point clouds, terrain models, or as-built survey results, it becomes easier to explain whether damage has occurred. Even if no normal-condition data exists, accurately recording the post-disaster current condition as much as possible allows it to be used as a baseline for future re-inspections or for verification after repairs.

When checking for subsidence and scour, it is also necessary to distinguish between areas where the ground surface is visible and areas where it is hard to see. At solar power plants there are parts that are difficult to judge from aerial photos alone, such as beneath panels and in the shadows of mounting racks, where weeds are overgrown, and where crushed stone is laid. Therefore, rather than treating drone survey results as absolute, it is practical to extract suspicious locations and supplement them with on-site inspections. Drones are an entry point for efficiently identifying changes over wide areas, and final judgments require a combination of on-site visual inspection, measurements, and equipment checks.

In recording terrain changes, it is important to clearly record the locations of damage. The expression "the north side has partially collapsed" alone can lead to misunderstandings in recovery instructions and when sharing information with stakeholders. By overlaying and organizing the damage extent, areas where subsidence is suspected, areas of sediment accumulation, and areas of poor drainage onto plan-view images or three-dimensional data produced by drone surveys, it becomes easier to determine the priority of subsequent work. In post-disaster response for photovoltaic power plants, judgments should include not only whether power generation has stopped but also the stability of the site and foundations. Carefully checking terrain changes helps both to prevent recurrence and to plan recovery.

Aerial Perspectives for Inspecting Abnormalities in Panels and Mounting Racks

After a disaster at a solar power plant, checking panels and mounting structures for abnormalities is also important. After strong winds, panels can lift, fastenings can loosen, and entire rows can shift. Damage from airborne debris, surface scratches from falling objects, and tilting of mounting structures after earthquakes are also items to check. Having people approach and inspect each panel one by one is necessary for detailed inspections, but it takes time to quickly ascertain whether there is damage across a large plant. By using drone surveying, you can inspect a wide area for disturbances across entire panel rows, reflections that differ from the surroundings, row tilting, and locations suspected of damage.

When viewed from above, misalignments in rows of panels can become easier to see. Rows that appear to be at the same height from the ground may, when seen from an overhead perspective, have sections that change angle or whose straightness is compromised. This may be related to changes in the support structure legs, foundations, or ground conditions. However, how things appear in images is also affected by the shooting angle and sunlight reflections. Because areas that look abnormal are not necessarily damaged, it is advisable to verify candidates extracted from drone images with on-site inspections.

Regarding abnormalities on the panel surface, some can be confirmed in visible images while others are difficult to detect. Things that are visually apparent—such as cracks, dirt, sediment adhesion, fallen branches, flying debris, and signs of inundation—can often be identified from drone photographs. On the other hand, internal electrical faults, fine cracks, and problems at connection points cannot be judged from ordinary aerial images alone. When using drone surveying for post-disaster inspections, it is more practical to aim to identify externally visible appearance abnormalities and to narrow down locations that require specialist equipment inspections.

When inspecting mounting structures, it is important to look not only at differences between rows but also at their relationship with the surrounding ground. Even if the mounting structure itself shows no major damage, if the soil around the support legs has been washed away or one side has settled, it can affect future stability. Especially at solar power plants installed on slopes, soil and debris can move downslope and accumulate beneath the mounting structures. Also, changes in drainage paths can cause water to concentrate around specific panel rows. In aerial inspections, it is important to view the mounting structures together with the ground, drainage, and slopes.

As inspection records, rather than documenting abnormal areas only with photographs, organizing the location and the condition together makes them easier to use later. For example, indicate on a map the panel rows suspected of damage, the rows where rack tilt is suspected, the areas covered by sediment, and the locations where debris has come into contact, and link close-up photos as needed. After a disaster, multiple stakeholders often act simultaneously, so verbal explanations alone tend to cause misunderstandings. Using the overhead data obtained from drone surveying as a reference makes it easier to decide which locations to prioritize for inspection, which areas to restrict access to, and which tasks to perform first.

How to Proceed Without Overlooking Damage to Drainage Routes and Slopes

In post-disaster inspections of solar power plants, checking drainage routes and slopes is especially important. Even if the power generation equipment itself shows no obvious damage, if drainage ditches are filled with sediment, catch basins around are clogged, or parts of slopes have collapsed, damage can expand with the next rainfall. Solar power plants are often installed on large developed sites, and the flow of rainwater directly affects equipment maintenance. Continuing to operate without confirming the condition of drainage after a disaster can lead to ground scouring, subsidence, sediment runoff, and impacts beyond the fence.

With drone surveying, you can get an overhead view of how water flows across an entire site. After heavy rain, you may be able to infer where water concentrated from residual surface flow paths, the direction of sediment deposition, traces of turbid water, washed-out gravel, and the way vegetation has been flattened. Damage that looks localized from the ground can sometimes be caused by a clogged drain upstream when viewed from above. Repairing only the damaged area may result in recurrence at the same location if the flow of water is not altered, so it is important to confirm drainage routes as lines.

In slope inspections, it is necessary to look not only for locations that have collapsed but also for deformations that could lead to collapse. Cracks on the slope surface, displacement of vegetation, seepage, soil bulging, settlement near the slope shoulder, and accumulation of sediment at the slope toe can all potentially lead to future deformations. However, these should not be judged solely from drone images. It is safer to record locations that appear suspicious from above and, as needed, carry out detailed on-site inspections. In particular, because the slope shoulder and slope toe can have unstable footing, assessing the situation with a drone beforehand makes it easier to reduce the risks during on-site checks.

When checking drainage facilities, it is important to inspect the inlet and outlet as a set. Even if part of a drain appears to have no problems, sediment may be clogging downstream, or water may be ponding at the downstream end. After disasters, amounts of sediment, fallen leaves, branches, and driftwood that would not occur in ordinary rain can accumulate. Track the entire drainage route using aerial photographs, and if you find signs of blockage or overtopping, confirm during on-site inspection whether removal or repairs are necessary. Including the power plant’s perimeter drainage and any outflow to adjacent land in the inspection scope can also help prevent related problems in the surrounding area.

Slopes and drainage routes are aspects where abnormalities are difficult to detect from generation figures alone. Just because power generation continues does not mean there are no issues on the site. Indeed, ground and slope deformations can progress even while equipment is operating. When using drone surveying for post-disaster inspections, it is important not to stop at confirming panel damage but to include the terrain that supports the site, drainage, and slope conditions. By treating the entire power plant as a single installation and checking where rainwater enters, where it flows, and where it exits, it becomes easier to develop recovery plans that reduce the risk of further damage.

How to create records with point clouds and photos that can be used for recovery decision-making

The purpose of conducting drone surveying for post-disaster inspections is not simply to look at the current situation and stop. It is important to leave records that can be used for recovery decisions, explaining to stakeholders, determining the scope of repairs, and creating standards for re-inspection. Even if you take a large number of photos, they become difficult to use in practice if you cannot tell the location or orientation when you review them later. Conversely, by combining photos with organized location information, overhead imagery, point clouds, and terrain models, it becomes easier to explain the extent of damage and the priorities.

Point cloud data is useful for confirming the three-dimensional shape of a site and the positional relationships of structures. It makes it easier to grasp in 3D locations where the ground may have settled after a disaster, where sediment has accumulated, or where slopes have deformed. However, creating a point cloud does not mean all decisions can be made automatically. The accuracy and density of the information that can be obtained vary depending on shooting conditions, how the ground surface appears, vegetation, shadows from panels, and analysis methods. Therefore, point clouds should be used as materials to support on-site inspections, and it is important not to rely on them as the sole basis for judgment.

When documenting with photographs, organizing them into three levels—overall, area, and close-up—makes the process easier. First, capture an overview image of the entire power plant to record the positional relationships of the damage. Next, take area photos that include the surroundings of the damaged location to document the relationships between panel rows, drainage paths, walkways, and slopes. Finally, where necessary, take close-up photos so that conditions such as cracks, sediment, deformation, blockages, and tilting can be confirmed. Recording in these staged levels makes it easier for readers to understand the situation later when compiling reports or instruction documents.

To inform recovery decisions, it is also important not to leave the locations of damage ambiguous. In solar power plants, similar rows of panels continue, so expressions like "the back row" or "near the west side" can easily lead to misunderstandings. It is necessary to organize terminology that can be commonly used on site, such as block numbers, row numbers, aisle names, compass directions, and positions relative to reference points. If location information is overlaid on the results of drone surveys, repair personnel will be less likely to get lost on site and will be able to track the same spot more easily during follow-up inspections.

It is also important to ensure that the situation before and after recovery can be compared from the same viewpoint. After emergency response following a disaster, you need to confirm that debris removal, restoration of drainage routes, slope repairs, and support-structure adjustments have been properly completed. If the shooting conditions immediately after the disaster differ greatly from those after recovery, comparison becomes difficult. Keeping records under the same flight range, the same shooting direction, and the same altitude band as much as possible will make changes easier to explain. Of course, you may not be able to match conditions exactly because of weather or safety considerations, but simply having the awareness to record with comparison in mind greatly improves the usability of the deliverables.

Records kept after a disaster are also useful for future maintenance. By accumulating information on where sediment is likely to flow, which drainage routes are prone to clogging, and which slopes are prone to deterioration, you can use it for preventive maintenance in preparation for the next heavy rain or typhoon. Drone surveying is effective not only as a one-time emergency response but also as a means of record that links routine inspections, post-disaster inspections, and post-recovery checks. Keeping a record of the power plant’s history makes it easier to carry forward knowledge of past damage and areas of concern even if on-site personnel change.

The importance of organizing baseline data to prepare for post-disaster comparisons

When conducting drone surveys after a disaster, a common challenge at many sites is the lack of reference data. If you only survey for the first time after damage has occurred, you can see the current condition, but it becomes difficult to judge how much has changed. To explain whether a spot that appears to have subsided was originally low, whether a slope that looks collapsed had that shape before, or whether sediment in a drainage path was generated by the current disaster, records from normal (pre-disaster) times are necessary. To improve the accuracy of post-disaster inspections, it is important to prepare baseline data before a disaster occurs.

Useful normal-condition data include aerial photographs of the entire power plant, survey results that show the topography, and records that reveal the layout of major equipment, drainage routes, slopes, access paths, and the condition of perimeter fences. Even if as-built documents from completion remain, mowing, repairs, drainage improvements, partial changes to site grading, and the like may have been carried out after operations began. Therefore, it is desirable to periodically retain normal-condition data that reflect the current operation and maintenance status. Recording them especially before seasons with elevated disaster risk makes post-disaster comparison easier.

In routine drone surveys, it is important to shoot with the items you want to compare after a disaster in mind. Simply keeping attractive aerial photos may be insufficient as inspection material. You need to record so that places you want to check after a disaster—panel rows, mounting structures, slopes, drainage channels, catch basins, work passages, perimeter areas, and boundaries with adjacent land—can be identified. Also, to repeatedly compare the same locations, it is effective to keep the shooting area and flight routes reasonably consistent. If you shoot under completely different conditions each time, it becomes difficult to tell whether differences are actual changes or just differences in appearance.

Maintaining baseline data during normal times also affects the speed of post-disaster response. After a disaster, many actions must be taken in a short time, such as deciding whether to stop power generation, conducting on-site inspections, reporting to stakeholders, and arranging restoration contractors. At that time, having past baseline data allows you to prioritize checks on locations that have undergone large changes. When explaining locations with no damage, it also becomes easier to show that there is little difference from normal conditions. This not only reduces unnecessary on-site inspections but also helps organize the prioritization of restoration work.

In terms of data management, it is important to record the date of capture, coverage area, weather, inspection purpose, the area checked, and whether any abnormalities were found in a way that is easy to understand. If file names and folder names are not organized, it can take time just to locate the necessary data when a disaster occurs. If you organize them chronologically—such as during normal times, immediately after a disaster, after emergency response, and after recovery is complete—it becomes easier to trace the history of changes. In the operation and maintenance of solar power plants, it is essential to continuously record the condition of the site and put in place a system that allows prompt confirmation when needed.

Data collected during normal times can be used not only after disasters but also for routine inspections. Vegetation overgrowth, clogged drainage channels, deterioration of walkways, and changes around fences can all progress gradually before a disaster occurs. By conducting regular drone surveys and recording those changes, it becomes easier to identify locations that are likely to suffer damage in the event of a disaster. To streamline post-disaster inspections, it is important not only to decide what to do after a disaster but also to determine what records to keep beforehand.

Summary

In post-disaster inspections of solar power plants, it is necessary to inspect the entire site—not only to check for damage to panels but also to include the ground, slopes, drainage routes, racking, service walkways, and the perimeter. Immediately after a disaster, hazards may remain on site, so it is important to use drone surveying to assess conditions from above and to delineate areas that can be approached safely from those that require additional inspection. At large power plants, it is difficult to inspect the whole site quickly by visual means alone, so organizing damaged locations using aerial imagery and point clouds makes it easier to improve inspection efficiency and safety.

There are six main points to check. First, determine the post-disaster safety zone and decide where on-site work can be conducted. Next, confirm topographic changes such as subsidence, scour, and sediment deposition. In addition, identify visible abnormalities in panels and racking from the air to narrow down locations that require detailed inspection. For drainage channels and slopes, it is important to check not only the damaged areas but the entire flow of water so as not to overlook causes of recurrence. On that basis, keep records usable for recovery decisions using point clouds and photographs, and finally prepare to be able to explain changes by comparing them with data from normal conditions.

Drone surveying does not complete all post-disaster inspections automatically. Its practical value increases when used in combination with on-site verification, equipment inspections, electrical checks, and decisions on repairs. This is especially true for solar power plants, where similar rows of panels extend over wide areas, so it is important to link location information with photographs and organize them. If stakeholders can share the same understanding of where and what is happening, it becomes easier to prioritize restoration work and to follow up with re-inspections and reporting.

To make post-disaster response smoother, it is essential to keep records organized during normal times. Compared with surveying for the first time after a disaster, having an understanding of the usual condition makes it easier to explain whether changes have occurred. If you periodically record an overview of the entire power plant, drainage routes, slopes, walkways, perimeter areas, and the surroundings of mounting structures, you can use them as reference material for decisions during a disaster. Incorporating post-disaster inspections into the flow of maintenance and management, rather than treating them as temporary emergency measures, leads to stable operation of the power plant.

In post-disaster inspections of solar power plants, if you want to efficiently carry out wide-area situational awareness, record damaged locations, and perform before-and-after comparisons for restoration, it is important to establish a drone surveying system that is easy to handle on site. By operating with an eye from the initial inspection response through record organization and stakeholder sharing, and by assuming the maintenance of normal-operation data, post-disaster safety confirmation, and integration with on-site inspections, it becomes easier to produce records that are useful for restoration decision-making.