6 Checks to Identify Ground Deformation at Solar Power Plants Using Drone Surveying

In the operation and maintenance of solar power plants, it is important not only to inspect the power generation equipment itself but also to continuously monitor the condition of the ground and developed surfaces that support the equipment. Especially at plants in mountainous areas, on slopes, on sites that include embankments, or at facilities with complex drainage paths, ground subsidence, scouring, cracking, slope bulging, concentration of rainwater, and unevenness around the mounting racks can progress gradually. These changes are difficult to notice on foot in the early stages, and if overlooked, maintenance response may lag behind.

Drone surveying is one method for recording the wide grounds of a solar power plant from above in a surface-wide manner, making it easier to grasp changes in terrain and around equipment. By periodically photographing the same area and comparing photos, point clouds, terrain models, orthophotos, and so on, it becomes easier to detect signs of ground deformation that are difficult to judge by visual inspection alone. In this article, we organize six checklist items that practitioners should confirm when using drone surveying to grasp ground deformation at solar power plants.

Table of Contents

• Organize the objectives for assessing ground deformation using drone surveys

• Check 1: Verify changes in settlement and surface unevenness.

• As Check 2, inspect the slope face and slope for deformation.

• As Check 3, inspect for signs of poor drainage and scouring.

• As Check 4, check the ground around the mounting rack and around the foundation.

• For Check 5, verify the differences against historical data.

• Use Check 6 to prompt on-site verification and decisions regarding repairs.

• Operational Points for Leveraging Drone Surveying in Ground Management

• Summary

Organize the objectives for assessing ground deformation using drone surveying

The purpose of checking ground deformation at photovoltaic power plants is not merely to detect abnormalities in the ground. Multiple objectives overlap, including ensuring the stable operation of power generation equipment, improving the efficiency of maintenance inspections, assessing conditions after disasters, prioritizing repairs, and maintaining management records. In particular, because solar power plants have many panels, mounting structures, foundations, cables, drainage facilities, and access roads distributed across large sites, localized ground changes can occur and be discovered late.

Ground deformations take various forms. Typical examples include settlement of developed surfaces, wave-like undulations of the ground surface, slope failures, scour around drainage ditches, collapse at the edges of embankments, soil erosion around support foundations, and ruts or steps on maintenance roads. These may sometimes occur suddenly and on a large scale, but more often they progress gradually under the influence of rain, wind, drainage, vegetation, vehicle traffic, and aging. Therefore, rather than judging based on a single inspection at one point in time, it is important to detect changes by comparing past and present conditions.

The advantage of drone surveying is that it makes it easy to record the entire site from the same perspective and at the same level of detail. Inspections conducted on foot can result in oversights depending on the inspector’s experience and walking route. In contrast, aerial photography with a drone allows wide coverage of areas such as between rows of panels, slopes, around regulating ponds, drainage paths, maintenance roads, and the perimeter. Furthermore, combining this with surveying methods that can obtain ground surface elevation information makes it easier to quantitatively grasp trends in settlement and heaving.

However, drone surveying is not foolproof. In areas where vegetation is dense, the ground surface can become difficult to see, and parts beneath panels or in the shadow of mounting racks may be hard to inspect from above. In addition, surveying accuracy depends on imaging conditions, flight planning, the placement of control points, analysis methods, and the site's lighting and terrain conditions. Therefore, to understand ground deformation, it is necessary to decide in advance what to check with drone surveying, which areas to prioritize, and which results should be followed up with on-site verification.

In practice, it is easier to operate if confirming ground deformation is positioned as part of inspection work. For example, during regular inspections, record the entire site, and after heavy rain or typhoons, focus on checking drainage routes and slopes, managing any locations where anomalies are found by linking them to site photographs and survey point information. By doing this, the results of drone surveys will not remain merely image data but will become management documents that can be used for maintenance decisions and repair planning.

Check 1: Verify changes in settlement and unevenness

The first things to check regarding ground deformation at a solar power plant are settlement and surface unevenness. Settlement refers to a change in which the ground becomes lower than the surrounding area, while surface unevenness refers to a condition where the ground surface develops irregularities or undulations. On a power plant’s development site, settlement and unevenness can occur in embankment areas, backfilled zones, around drainage facilities, on maintenance roads used by vehicles, and around foundations. Even small changes in the early stages, if left unaddressed, can lead to poor drainage, tilting of the racking, and impaired passage of work vehicles.

When using drone surveying to detect subsidence and surface irregularities, the important thing is not to rely solely on plan-view images. Aerial photographs can suggest anomalies from differences in ground color and shadows, but elevation information is necessary to verify the degree of unevenness. By creating point clouds and terrain models and checking elevation differences across the ground surface, you can more easily detect subsidence trends that are hard to perceive with the naked eye. In particular, if the same location is surveyed periodically, you can confirm the amount of change by comparing it with the previous survey.

When conducting inspections, it is important not only to view the entire power plant uniformly but also to focus on locations prone to settlement. Areas where fill was placed during site development, areas where existing valley topography was filled in, the ground above drainage pipes and culverts, the surroundings of regulating ponds and waterways, and curved sections or stopping points on access roads are all places where changes are likely to appear. By cross-checking these locations in advance against management drawings and past construction records, it becomes easier to detect anomalies when reviewing drone survey results.

When assessing settlement or surface irregularities, you should avoid drawing major conclusions from a single survey result. For example, variations in grass height, soil moisture, shadows at the time of imaging, or vehicle tracks can make the ground appear to have changed in images. Also, if flight conditions or analysis parameters differ greatly between the previous and current surveys, the appearance of differences will be affected. Therefore, when a location suspected of abnormalities is found, inspect on site the condition of the ground surface, cracks, height differences, puddles, and any impact on the mounting structures.

In practice, it is important to record the locations where settlement or unevenness is found. Summarizing the location, extent, trend of change, inspection date, site photographs, surrounding facilities, and drainage conditions makes it easier to compare during the next inspection. Changes in the ground can be difficult to assess for hazard from a single inspection, but if recorded continuously it becomes easier to distinguish whether the deformation is progressive or only a temporary surface change.

Check 2: Confirm deformations of slope faces and slopes

In solar power plants, inspecting the condition of slopes and embankments is important. Especially at plants located in mountainous areas or on sloping terrain, cut-and-fill slopes are often created during site development, and they can experience distress due to rainfall, poor drainage, changes in vegetation, or surface soil erosion. Small slope collapses or bulging may not be noticeable from a distance in the early stages, but if they progress they can lead to sediment runoff and impacts on equipment.

In drone surveying, because slopes can be inspected from above and at oblique angles, it becomes easier to identify areas that are difficult to see from the ground. Slopes not visible from the access road, slopes on the far side of panel rows, peripheral slopes, and embankment surfaces around retention ponds can also be captured in the overall record by including them in the imaging plan. In particular, slope shoulders, slope toes, areas near drainage outlets, and spots where sediment has accumulated are locations where signs of deformation are likely to appear.

When inspecting slopes, attention should be paid not only to the shape of the ground surface but also to changes in color and disturbances in vegetation. Areas where soil is exposed, traces of rainwater flowing in streaks, places where the way grass has been flattened differs from the surroundings, spots that appear locally wet, and locations where sediment has accumulated downslope can indicate surface erosion or small-scale collapse. Enlarging images taken with a drone can reveal small changes that might be overlooked during ground inspections.

However, the safety of a slope cannot be determined from images alone. What drone surveying can confirm is limited to surface geometry and visible changes. The internal condition of the ground, moisture content, the presence or absence of slip surfaces, and the functioning of drainage facilities require, as necessary, specialized investigations and on-site verification. Therefore, viewing the role of drone surveying as a means to detect areas of concern early and to narrow down locations that should be prioritized for inspection makes it easier to incorporate into practical work.

When conducting regular inspections of slopes or embankments, it is useful to ensure that images can be compared from the same angle and taken at the same time of year. Because vegetation cover and sunlight conditions vary with the seasons, judging based solely on simple visual appearance can be difficult. If possible, decide on shooting timings according to the inspection purpose—such as before the rainy season, after the rainy season, and after typhoons—to make it easier to identify trends in ground deformation.

Check 3: Inspect for signs of poor drainage and scour

Many ground deformations are related to water flow. On the site of a solar power plant, rainwater that falls on panel surfaces or graded surfaces can concentrate in specific locations. Even if the drainage plan is appropriate, over time soil, sediment, and fallen leaves can accumulate in channels and reduce drainage capacity. In addition, during heavy rainfall, flows exceeding design assumptions can occur, eroding drainage ditches, slopes, the ground beside maintenance roads, and the ground surface beneath the racking.

In drone surveying, poor drainage and signs of scour can be identified across the surface. Places where puddles tend to remain, locations where flow channels have formed on the ground surface, traces of sediment outflow, areas with deposits around drains, and places where sediment has accumulated at the toe of slopes are all points that are easy to detect from imagery. Photographing immediately after rain makes it easier to identify areas of water retention, while photographing in clear weather makes it easier to identify traces of runoff and sediment deposition.

Scour can appear in its early stages as thin grooves or streak-like traces. As it progresses, it can deeply cut into the ground surface, wash away soil around foundations, or cause the shoulders of maintenance roads to collapse. In drone images it may appear as variations in ground color or thin shadows, but it can be difficult to discern when hidden by grass or gravel. Therefore, images should be reviewed along drainage paths, and locations of concern should be inspected on site to determine their depth and extent.

When assessing drainage problems, it's important not only to note whether water is present but to consider why water accumulates in that location. Countermeasures vary depending on whether the area is lower than its surroundings, drainage channels are clogged, embankment settlement has altered the slope, or ruts from vehicle traffic have become flow paths. Confirming terrain trends with drone surveying and combining that information with the condition of on-site drainage facilities and sediment accumulation makes it easier to sort out the causes.

Also, at solar power plants, the arrangement of panel rows can cause rainwater to fall preferentially in certain locations. If rainwater falling from the panel edges continues to hit the same spot, it can erode the ground surface or create small grooves. These effects can be hard to see from aerial images alone, but by combining point clouds, oblique images, and on-site photos, it becomes easier to identify the areas where rainwater is concentrating. This information is useful for considering drainage improvements and simple repairs.

For Check 4, inspect the ground around the racking and around the foundations

When checking for ground deformation, it is necessary to focus on the areas around the mounting structures and foundations. In solar power plants, numerous mounting structures are installed on the ground, and the stability of the foundations and the condition of the surrounding ground affect the operation and maintenance of the power generation equipment. Changes such as soil being washed away around the foundations, subsidence of the ground surface, water accumulating around rows of mounting structures, or uneven settlement of the surrounding ground are items that should be checked promptly.

Drone surveying allows you to get a bird’s-eye view of the alignment of entire rows of racking and the condition of the ground surface. From the ground, attention tends to focus on each foundation individually, but from above it becomes easier to identify area-wide trends — for example, that only certain rows have disturbed ground, that multiple foundations are showing changes along the drainage flow, or that only part of the side along the access road has settled. This is especially effective at large power plants.

In ground checks around mounting structures, shadows from panels and the structures themselves can make the ground surface difficult to see. Therefore, it is important to adjust the time of day for imaging, flight altitude, and shooting direction. In addition to images taken directly overhead, acquiring oblique images when necessary can make it easier to check for soil erosion and level differences around the foundations. However, while oblique images are effective for visual inspection, if they are to be treated as survey results the analysis conditions need to be organized.

One point to be careful about around foundations is that changes on the ground surface do not necessarily appear immediately as abnormalities in the equipment. Even small scour or settlement can make the mounting structure itself appear, at first glance, to be problem-free. However, if soil erosion is repeated at the same location, it could affect the support conditions around the foundation and future maintenance work. Therefore, rather than making a one-time judgment about whether an anomaly exists, it is important to continuously check whether the changes are ongoing.

Also, the areas around the rows of mounting racks are affected by weed control and maintenance work. After mowing the vegetation, the ground surface becomes easier to see, but tire tracks from work vehicles and accumulations of cut grass can temporarily change the appearance of the ground. When reviewing drone survey results, being aware of whether on-site work occurred before or after the imaging will make it easier to distinguish ground deformation from effects caused by maintenance activities.

Check 5: Verify differences against past data

When assessing ground deformation, comparison with past data is crucial. Images or topographic data from a single point in time can make it difficult to determine whether a site has always been that way or has changed recently. By conducting regular drone surveys and accumulating data for the same area, you can verify ground changes in a time series. This is a major advantage for the operation and maintenance of solar power plants.

During change detection, we review a combination of the previous orthophoto, point cloud, terrain model, site photographs, and inspection records. Image comparisons can reveal traces of sediment runoff, changes in vegetation, the locations of puddles, and the condition of maintenance roads. Comparisons of elevation information can show trends of subsidence or uplift. In particular, comparing terrain models with each other makes it easier to identify the areas where elevation has changed.

However, when handling difference data, attention must be paid to differences in survey conditions. Changes in flight altitude, number of photos taken, ground control points, analysis settings, condition of the vegetation, weather, and sunlight conditions can affect the comparison results. For example, if the grass was short last time and has grown this time, the ground surface may appear higher. Conversely, data taken immediately after weeding may make the ground surface more visible and appear lower than before.

Therefore, when checking differences in ground deformation, it is important not to look at survey results mechanically alone, but to interpret them together with on-site conditions. Even in locations where the amount of change appears large, it may be due to vegetation or shadows. Conversely, even if the amount of change appears small, caution is necessary if it is occurring continuously along a drainage path. Using differences from drone surveys as a basis for determining the priority of on-site inspections is effective.

To leverage differences from past data, rules for data management are also important. Organizing and recording the capture date, capture area, surveying conditions, weather, control points used, analysis results, and notes on anomalies makes later comparisons easier. If file names and folder structures are inconsistent, simply locating the required data can take time. In managing ground deformation, preserving measured results in a form that can be used continuously is as important as taking the measurements.

Use as Check 6 to trigger on-site verification and repair decisions

When a drone survey finds a suspected ground deformation, the next necessary step is an on-site inspection. Aerial images and point clouds are effective for locating abnormal areas, but a field check is indispensable for the final judgment. In particular, the depth of cracks, the depth of scour, soil looseness, water flow, the condition around foundations, and impacts on work safety need to be confirmed on site.

On-site inspections can be conducted more efficiently by basing them on locations identified by drone surveys. Rather than wandering aimlessly around a large power plant, extracting areas of concern from the imagery beforehand and prioritizing which to check makes it easier to reduce inspection time. This workflow is especially effective when you need to quickly grasp the overall situation after heavy rain or a typhoon: use drone surveys to cover a wide area and focus on key locations during on-site inspections.

When making decisions about repairs, organize not only the presence or absence of abnormalities but also their progression and the extent of their impact. Even small scour can require prompt action if it is on a drainage route and has expanded compared with past data. Conversely, if it is merely surface movement of sediment and does not affect equipment or drainage, a decision may be made to monitor the situation. What is important is to record the rationale for the decision.

Repairs for ground deformation can include various measures such as cleaning drainage routes, replenishing soil and sediment, surface protection, slope protection, improvements to drainage facilities, and repairs to maintenance roads. Which measure is appropriate depends on site conditions and the cause of the deformation. Results from drone surveying can be used as documentation to describe the pre-repair condition and can also aid in post-repair verification and in considering measures to prevent recurrence.

The results of drone surveys are also effective for sharing with stakeholders. If multiple parties—such as power plant managers, maintenance personnel, contractors, and designers—can review the same images and terrain data to confirm the situation, it becomes easier to reduce differences in understanding. Areas and spatial relationships that are difficult to convey through on-site explanations alone are easier to share using aerial imagery.

Operational Points for Leveraging Drone Surveying in Ground Management

To make drone surveying effective for ground management at solar power plants, it is important to adopt an operational approach that does not end with a single flight. Ground deformation often progresses over time, so it is necessary to record it regularly and maintain a state in which changes from the previous record can be checked. The frequency of surveying varies depending on the plant’s location and risk, but keeping records during regular inspections, after heavy rain or typhoons, and before and after repairs makes management easier.

The first thing to decide in operation is the area to check each time. Clarify whether you will survey the entire power plant, focus on slopes and drainage channels, or include access roads and the perimeter. A full-site survey is suitable for grasping conditions over a wide area, but if you want to detect small deformations you need to capture the focused areas at higher resolution. Dividing flight plans according to the objective makes it easier to obtain the required results.

Another important point is to maintain conditions that make comparisons easy. If you can carry out surveys each time with similar flight altitudes, imaging coverage, reference points, and analysis conditions, it becomes easier to check differences from past data. Of course, it is difficult to make the conditions exactly the same because of weather and on-site circumstances, but even matching conditions as much as possible greatly improves the usability of the data. In particular, when assessing ground deformation, it is important to continue observing the same location using the same reference.

The timing of weed removal is also a point to consider. When checking changes on the ground surface, tall grass can make it difficult to see the condition of the ground. If possible, photographing after weeding or during periods when grass is short makes it easier to confirm settlement, erosion, cracking, and sediment accumulation. However, immediately after weeding, traces of the work or the presence of cut grass may affect the appearance, so recording the work status in the inspection records will make later assessment easier.

A system for verifying data is also important. Even if you obtain results from drone surveys, if it is not decided who will check them and from which viewpoints, anomalies can be overlooked. By organizing the viewpoints to be inspected—ground conditions, drainage, mounting structures, access roads, slopes, etc.—and by establishing a workflow for recording verification results, you can more easily stabilize inspection quality. Rather than relying solely on experienced personnel, it is important to create a state in which judgments can be shared using images and records.

Furthermore, drone surveying also aids safety management. Steep slopes, muddy areas, crumbling road shoulders, and areas around drainage facilities that are difficult to access can be dangerous if people are forced to enter them. By first checking conditions with a drone, you can grasp the overall situation before approaching hazardous locations. Of course, necessary on-site inspections should still be carried out, but drone surveying can be used as a basis for planning inspection routes and making decisions about entry.

Summary

Ground deformation at solar power plants is a critical item to check in the operation and maintenance of power generation equipment. Settlement, unevenness, slope deformation, poor drainage, scour, and soil washout around foundations can appear as small changes in the early stages. However, if detection is delayed, the scope of repairs may expand and the safety of inspections and on-site work may be affected.

By utilizing drone surveying, you can comprehensively record the entire power plant and more easily grasp the condition of the ground, drainage, slopes, and areas around mounting structures. In particular, comparing with past data makes it easier to determine whether observed changes are progressing or are only temporary surface variations. This is a major advantage for operational personnel managing large sites.

However, you should avoid concluding the safety of the ground solely from drone survey results. It is important to detect signs of anomalies in images and point clouds, confirm depth, extent, causes, and impacts on equipment through on-site inspection, and, if necessary, proceed to repairs or ongoing monitoring. Drone surveys are not a replacement for on-site inspections; they are most effective when used as a means to streamline inspections and increase the information available for decision-making.

Effective ground management for solar power plants requires continuing regular recording, checking differences against past data, on-site inspection of priority areas, and comparison of conditions before and after repairs. Implementing these practices not only enables early detection of ground deformation but also improves the accuracy of maintenance planning and facilitates information sharing among stakeholders. When incorporating drone surveying into plant maintenance, it is important to establish surveying and recording systems suited to the site while keeping in mind the six checks for ground deformation.

For a more practice-oriented assessment of ground deformation at solar power plants and to efficiently document the condition of large sites, it is advisable to organize in advance the imaging coverage, survey accuracy, analysis outputs, and the workflow for on-site verification, and to consider a drone surveying framework aligned with the inspection objectives.