5 Key Points for Monitoring Terrain Changes at Solar Power Plants with Drone Surveys

Solar power plants are sometimes installed in locations that are easily affected by terrain conditions, such as forests, reclaimed land, slopes, areas around reservoirs, and land converted from agriculture. Continuously monitoring changes in the overall site topography—not just inspecting the power generation equipment itself—is important for early detection of risks such as poor drainage, slope deformation, sediment outflow, scouring around mounting structures, and settlement of access roads. By using drone surveying, large power plants can be recorded from the air on an area-wide basis, making it easier to identify trends in change by comparing them with past topographical data.

However, drone surveying is an effective means of understanding terrain, and by itself does not determine the safety of the ground or whether repairs are necessary. By combining survey data, on-site inspections, design documents, drainage plans, and past repair history to make a judgment, it becomes information that is easy to use for power plant management.

Table of Contents

• The importance of monitoring terrain changes at solar power plants

• Key point 1: Prepare to measure under consistent conditions

• Key point 2: Observe drainage and sediment flow patterns

• Key point 3: Confirm slope and embankment deformations across surfaces

• Key point 4: Do not overlook small changes around mounting structures and access roads

• Key point 5: Organize data into a format that allows comparison with past data for decision-making

• Summary: Incorporate drone surveying into ongoing terrain management operations

The Importance of Monitoring Terrain Changes at Solar Power Plants

In managing a solar power plant, daily inspections tend to focus on power output, equipment appearance, electrical systems, weeds, fences, and drainage channels. However, the foundation that supports the stable operation of the plant is the site itself. If the ground subsides, the flow of rainwater changes, or soil and debris wash out from slopes, even if it does not immediately lead to a shutdown, the maintenance burden and the extent of repairs can increase over time.

Solar power plants in particular have panels spread over wide areas, making it difficult to view the entire site from the ground. During on-foot inspections, it's easy to notice abnormalities right in front of you, but it can be difficult to grasp trends across the whole site, how water accumulates, gradual subsidence, or the direction of soil movement. Even if on-site personnel feel something is off, without documentation that can explain it objectively, it becomes difficult to prioritize repairs or report to stakeholders.

The advantage of drone surveying is that it makes it easy to record an entire power plant from above under consistent conditions. Not only photos, but by organizing the data into orthoimages, point clouds, elevation models, contour lines, cross-sections, etc. as needed, it becomes easier to confirm changes in the terrain rather than rely on visual impressions alone. For example, it becomes easier to compare changes such as a shallow groove that was not present at the previous survey, water that should be flowing toward a drainage channel beginning to collect in a different direction, or increased accumulation near the toe of a slope.

Checking for topographic changes is not a task solely for detecting anomalies. Rather, it is meaningful to record changes while they are still small and, by monitoring their progress, use that information to inform management decisions. Trying to draw conclusions from a single survey can be influenced by differences in survey conditions, the effects of vegetation, differences in the timing of imagery, and whether the observation was made after rain or during dry conditions. By measuring continuously with the same approach and comparing results with past data, it becomes easier to judge whether a difference is merely a matter of appearance or a real topographic change that requires attention.

In terrain management for solar power plants, it is important to view the site by area rather than by point. Rather than only looking at individual anomalies such as cracks, sinkholes, scour, and sediment deposition, you check where they are concentrated on the site, whether they are related to rainwater flow, and whether they are likely to affect the racking or access and maintenance roads. Drone surveying is an effective means to assist this area-based understanding.

Key point 1: Prepare to measure under the same conditions

The first important thing when observing terrain changes at a solar power plant is to prepare so that surveys can be carried out under as similar conditions as possible each time. When comparing terrain changes, looking at only the current data is not sufficient. You need to compare it with the previous and the one before that to confirm where and to what extent changes have occurred. Therefore, if surveying conditions differ greatly each time, it becomes difficult to determine whether the differences are actual changes or simply due to differences in acquisition conditions.

First, you need to clarify the purpose of the survey. Whether you want to get a rough understanding of overall terrain changes across the power plant, focus on slope deformations, check sediment buildup around drainage channels, or verify subsidence and ruts on access roads will determine the coverage, required accuracy, flight altitude, and capture interval. If you conduct imaging with unclear objectives, you may find later that there isn’t enough data for the locations you want to compare, or that you captured an unnecessarily wide area, making processing and review take longer.

Next, decide how to handle the reference positional information. To detect terrain changes, it is important that the positions of the previous dataset and the current dataset are not significantly shifted. If you examine differences without sufficient alignment, locations that have not actually changed may appear to have changed, or conversely small changes may be overlooked. Depending on site conditions, use ground control points, check points, known points, and positioning corrections to maintain coordinate management that is suitable for comparison.

When installing reference points, choose locations within the power plant that are unlikely to move over long periods and are easy to locate during imaging. Avoid places that can be easily hidden by panel shadows or weeds, locations that may be displaced by vehicle traffic, and areas affected by drainage. Also, even when using the same reference points each time, you must confirm that the reference points themselves have not moved. If a reference point has settled or a marker has shifted, the basis for comparison will be compromised.

Timing of photography is also important. When checking terrain changes, there are appropriate times depending on the purpose, such as immediately after rain, after prolonged rainfall, after a typhoon or heavy downpour, after mowing, or following land development or repairs. For example, if you want to check for poor drainage, the condition after rainfall is informative. On the other hand, if you want to observe the surface shape as clearly as possible, it is better to shoot when there is less vegetation and the ground is more visible. Even at the same power plant, grass height and the way shadows fall change with the seasons, so you should record differences in shooting times when making comparisons.

Flight conditions are another item that should be standardized. If flight altitude, photo overlap, shooting direction, time of day, weather, solar elevation, or wind conditions change, the appearance of the generated data will change. In power plants with many panels in particular, reflections and shadows can affect image processing. Even if it is difficult to keep conditions exactly the same each time, it is important to establish standard imaging conditions and to record any changes when they occur.

Also, safety management at power plants requires attention. Check panels, mounting structures, electrical equipment, transmission facilities, fences, surrounding private land, access roads, and the movement lines of workers and vehicles, and decide the flight area and takeoff/landing locations in advance. After confirming flight rules such as the Aviation Act, approval from the facility manager, and consideration for the surrounding environment, avoid flying too close to equipment or attempting flights in strong winds. Rather than prioritizing surveying efficiency alone, establishing procedures that can be carried out safely and continuously is indispensable for long-term terrain management.

Key Point 2: Observe the flow of drainage and sediment movement

When checking topographic changes at a solar power plant, one important perspective is the flow of water. On the plant site, where rainwater enters, where it travels, and where it exits determines which areas are prone to sediment runoff, scouring, deposition, waterlogging, and slope deformation. By surveying the entire site from the air with a drone, it becomes easier to grasp how water accumulates and the directions of flow—features that are hard to notice during on-foot inspections.

Rainfall under panels and between rows of racking behaves differently from that on natural ground. Rain that falls on the panel surface can concentrate and drip at fixed points, creating narrow grooves on the surface. What begins as small streak-like changes can deepen with repeated rainfall, washing away surrounding soil and potentially affecting the piles and foundations of the racking. Even if it looks like localized soil movement from ground level, from above it may appear as a continuous occurrence along the same row.

Areas around drainage channels and side ditches should also be checked. If sediment and fallen leaves accumulate in drainage channels, water can be diverted from its normal course and spread into low-lying areas on the site. As a result, the shoulders of access roads may be eroded, water may collect at the toe of slopes, and the ground beneath panels can become muddy. Using drone surveys to check elevation differences and surface unevenness makes it easier to identify low-lying areas where water tends to gather and locations where drainage is likely to be impeded.

When observing sediment movement, it is important to check eroded areas and depositional areas together. Focusing solely on scouring does not reveal where the sediment has moved to. Conversely, looking only at deposition does not show where it came from. By viewing the power plant’s overall slope, the locations of drainage facilities, the cross slope of access roads, the orientation of slopes, and the arrangement of panel rows together, it becomes easier to infer the causes of sediment movement.

In drone surveying, it is effective to use orthophotos to check surface colors and patterns and elevation data to confirm surface undulations and flow directions. On the images, find places where the soil color has changed, where vegetation is flattened, where narrow flow channels are visible, or where gravel has been washed away, and verify those locations with the elevation data and cross-sections. Rather than judging by appearance alone, checking the slope of the terrain and the elevation differences relative to the surroundings makes it easier to organize response priorities.

Surveys conducted after rainfall may show puddles and wet areas. While this can help identify poor drainage, standing water and muddy areas can sometimes affect image processing. For that reason, it is more practical in the field to treat data for checking post-rainfall conditions separately from the standard data used to compare terrain shape. Rather than trying to use every survey for the same purpose, it is important to organize them by use: current condition assessment, change comparison, and explanation of anomalies.

On-site visual inspection is indispensable when checking drainage and sediment movement. Using drone surveying to identify areas of concern and then following up with on-foot checks improves inspection efficiency. Instead of painstakingly walking an entire large site from the start, observing the whole area from above and narrowing down places where changes are concentrated makes it easier to check important locations even with limited time.

Key Point 3: Confirm deformations of slopes and embankments across the surface

In solar power plants, flat areas are sometimes created through earthworks, or racking is installed on sloping terrain. Therefore, the condition of slopes, embankments, cuttings, slope toes, and slope shoulders are important inspection targets for terrain management. Slope deformations can appear as cracks, bulging, settlement, surface collapse, rill erosion from rainwater, and disturbed vegetation. These can be confirmed by ground inspections, but when the area is large or slopes are steep it can be difficult to grasp the overall picture.

Using drone surveying, you can record the entire slope from above and more easily determine the spatial relationships of deformations. It lets you clarify not only localized collapses but also at which elevations on the slope changes are appearing, whether there are continuous changes from the slope crest to the slope toe, and whether they are related to drainage channels or collection points. In particular, when sediment is beginning to accumulate at the slope toe, areal images and elevation data are useful for identifying where on the upper slope the material is flowing out from.

In embankment areas, gradual settlement or surface steps can become problematic. When settlement is small, it can be difficult to notice even when walking the site, but it can alter the drainage gradient of maintenance roads or cause water to pool around support structures. Creating an elevation model with drone surveying and comparing it to past data makes it easier to understand settlement trends over a wide area. However, if there is vegetation or ground surface cover, the acquired data may not accurately represent the ground itself, so assessments should be made together with on-site verification.

In comparing slopes, the way cross-sections are taken is also important. If you cut cross-sections at different locations each time, it becomes difficult to judge changes. Decide in advance on representative slope cross-sections, cross-sections where drainage tends to concentrate, cross-sections that were repaired in the past, and cross-sections near support structures or maintenance roads, and make sure you can compare the same locations so that temporal changes are easier to explain. Cross-section drawings make it easy to check for retreat of the slope shoulder, bulging in the middle of the slope, and deposition at the slope toe.

Anomalies on slopes can appear not only in topography but also in vegetation. Conditions such as grass whose color differs from the surroundings, vegetation that is sparse along particular streaks, or accumulations of flattened grass at the lower slope can provide clues to water flow or soil/sediment movement. Drone photos make it easy to detect these surface differences, but photos alone cannot determine their causes. An effective procedure is to detect anomalies in imagery, confirm the shape with elevation data, and inspect ground and drainage conditions on site.

What you want to avoid in managing slopes and embankments is simply recording discovered anomalies with a single photograph. Photos are useful for explaining the situation, but they can make it difficult to understand the extent of the occurrence and its relationship to the surrounding topography. By using drone surveying to indicate the location on an overall map and attaching cross-sections or difference maps as needed, it becomes easier to explain to stakeholders whether repairs are required and their priority. The more stakeholders there are—power producers, maintenance personnel, contractors, landowners—the more important it is to have materials that can be shared objectively.

Slope deformations, if detected early, can sometimes be addressed with small-scale drainage improvements or surface protection. However, if changes are overlooked and progress over a wide area, the impact on equipment and the scope of restoration work may become significant. Drone surveying is also effective as a means of checking the entire area without getting too close to dangerous slopes. Continuously recording signs of terrain change while ensuring safety contributes to the stable management of solar power plants.

Key Point 4: Don't Overlook Small Changes Around the Mounting Racks and Access Roads

Topographic changes at solar power plants do not occur only in obvious locations such as slopes and drainage channels. Small changes also appear in places used daily—around the racking that supports the panels, near piles and foundations, where cables run, on access roads, at vehicle turning areas, and along fences. Although each of these changes may seem minor on its own, they are details that cannot be overlooked in the operation and maintenance of the plant.

What to watch around the mounting is scouring around piles and foundations, soil washout, settlement, and concentration of rainwater. If rainwater falling from the panels continues to hit the same spot, the ground surface can be eroded along the rows of mounting structures. Also, on slopes, water flowing down from higher ground can run along the rows of mounting structures and cable routes, creating unexpected flow paths. Drone surveys from above make it easier to confirm the relationship between the rows of mounting structures and terrain changes.

On management roads, rutting, shoulder collapse, poor drainage, settlement, loss of gravel, and transverse drainage channels formed by rainwater are items inspected. Because inspection vehicles and mowing work vehicles use these roads, deterioration can affect the efficiency of routine maintenance. In particular, roads within the power plant may coincide with the site's drainage routes; when a road becomes a waterway, each rainfall can scour the road surface and cause soil and sediment to accumulate on shoulders and in low-lying areas.

To avoid missing small changes, it is important not to just look at drone survey data but to decide in advance where to check. Areas that are easy to set as regular checkpoints include rack end sections, around lower rows, places where puddles have formed in the past, bends in access roads, locations where the gradient changes, crossings with drainage channels, and roads close to slopes. Checking from the same viewpoint each time makes it easier to maintain inspection quality even if the person in charge changes.

It is also important to view topographic changes overlaid with equipment layout. Looking at topography alone can make it difficult to judge the impact on power plant management. For example, even if scour is the same depth, the priority of response changes depending on whether it occurs near a racking foundation or on bare ground away from equipment. Subsidence of maintenance roads should be assessed differently depending on whether they are primary traffic routes or seldom‑used side paths. Organizing drone survey results together with equipment layout, inspection routes, and drainage plans produces materials that are more useful in practice.

When checking terrain changes, not only the numbers but also the visual clarity of the photographs is important. When explaining to people other than the on-site staff, showing only elevation differences may not convey the situation well. Indicating the areas of change on aerial photographs and attaching enlarged views or cross-sections as needed makes it easier to share where and what is happening. In particular, when requesting decisions on repair budgets or work scheduling, it is essential to prepare materials that communicate clearly to people who have not seen the site.

One point to keep in mind is that not all changes visible in drone surveys necessarily reflect changes in the ground. Differences before and after mowing, vehicle tracks, temporary material storage areas, shadows, wet ground, fallen leaves, and similar factors can appear as changes. When processing images and performing change detection, you must avoid confusing these temporary elements with actual terrain changes. Suspect locations should be checked on site and evaluated together with record photos and notes.

Small changes are easier to deal with the sooner they are detected. It becomes possible to take actions such as correcting the direction of drainage at the stage of shallow scour, repairing when the road shoulder begins to collapse, and checking the cause when puddles start to form. Drone surveying is an effective entry point for picking up these small signs across a large power plant.

Key Point 5: Organize into a form that allows decisions to be made by comparing with past data

The value of drone surveying for managing terrain changes is realized when comparing with past data. A single survey can help grasp current conditions, but to determine whether the terrain is changing, whether the change is progressing, or whether it has stabilized after repairs, you need to compare data over time. In the maintenance of solar power plants, it is important not to let survey data end as a one-off deliverable, but to accumulate it in a form that can be compared.

The basics of comparison are to organize data using the same coordinate system, the same extent, and the same reference. If positions are misaligned between the previous and current datasets, unnecessary changes will appear on the difference map. If the capture area differs, there will be locations that cannot be compared. When the data creation conditions differ significantly, it becomes difficult to determine whether elevation differences are due to terrain changes or to differences in processing conditions. When storing survey results, recording the date of capture, flight conditions, reference points, processing conditions, site conditions, weather, the condition of vegetation, and so on will make it easier to judge when reviewing them later.

When looking at differences, it is necessary to consider not only the magnitude of the numbers but also the significance of the change. For example, even if there is a difference of a few centimeters (a few in), it may be due to vegetation or surface conditions. On the other hand, even if the amount of change is not large, caution is required if it is occurring continuously near support structure foundations or along the upper part of slopes. In evaluating terrain changes, the amount of change, the extent of occurrence, the location, the distance to equipment, the relationship to drainage, and the progression over time are all judged together.

When using this as a reporting document, it is easier to understand if you organize, for each location where changes were found, current images, past images, difference images, on-site photos, and comments. Simply writing "change detected" makes it difficult to determine the next steps. By recording at which point, in which direction, and to what extent changes are observed, and what impact they may have on equipment and inspection routes, the report becomes more useful for consideration of repairs and decisions on continued monitoring.

Also, it is important to distinguish locations that require immediate repair from those that can be monitored. If a drone survey finds many areas of change, treating them all with the same weight makes field response difficult. Locations where drainage channels are beginning to clog, where soil is flowing out from slopes, where passage on service roads is likely to be affected, and where scour is progressing around support structures should be given higher priority. On the other hand, minor changes far from equipment can be judged to be checked for progression in the next survey.

Methods of storing data are also important in practice. Survey results tend to become large in size, and if they are managed individually by the person in charge, they become difficult to locate later. It is desirable to organize them in a way that shows the year, power plant name, survey date, purpose, and type of deliverable, and to keep them accessible so that relevant parties can refer to the same materials. Managing lightweight materials for reporting separately from the original data for detailed review makes daily operations easier.

When comparing with past data, records from before and after repairs are also useful. Conducting surveys before and after work such as cleaning drainage channels, repairing slopes, placing crushed stone on maintenance roads, or backfilling scoured areas makes it easier to verify the effectiveness of measures. If changes reappear at the same location after repairs, it may indicate that the underlying cause has not been resolved by superficial fixes alone. Drone surveying can also be used to review this kind of maintenance.

A comparison of terrain changes cannot be completed by expert analysis alone. It is important that on-site personnel understand the results and can use them for subsequent inspections and repairs. Therefore, deliverables should not consist only of difficult terminology but must be organized in a way that ties directly to power plant management decisions. By producing materials that show where to look, what has changed since the last survey, and what should be checked next, drone surveying becomes not merely a photography task but a practical tool for terrain management.

Summary: Integrating Drone Surveying into Ongoing Terrain Management Operations

Topographic changes at solar power plants can sometimes appear suddenly large on a given day, but in many cases they progress as an accumulation of small changes. Narrow scour beneath panels, shallow ruts on access roads, sediment accumulation around drainage channels, surface disturbances on slopes, and slight heaving at slope toes—many of these changes are difficult to assess in their early stages. That is precisely why drone surveying, which records a wide site from the same viewpoint and allows comparison with past data, is useful.

What's important is not to let drone surveying end with a single capture of current conditions. You need to define the purpose of the survey, acquire data under the same conditions, observe drainage and sediment movement, verify slopes and embankments across their surfaces, pick up small changes around mounting frames and maintenance roads, and organize the data so it can be compared with past records. Once this workflow is in place, it's easier to explain terrain changes based on records rather than impressions.

In solar power plants, it is important to continuously monitor site conditions in the same way as inspecting generation equipment. If terrain changes can be identified early, it becomes easier to choose responses such as drainage improvements, cleaning, repairs, or ongoing monitoring. Also, for reporting to stakeholders and making repair decisions, aerial photographs, elevation data, cross-sections, and difference maps make it easier to share the site’s condition.

Drone surveying is a means to streamline terrain management for solar power plants. However, to make the results useful in practice, planning before measurement, comparison after measurement, and combining them with on-site verification are indispensable. Rather than aiming only to produce visually appealing images, connecting the work to what to check next on site, where to carry out repairs, and which changes to monitor turns the data into information useful for plant management.

If you want to continuously monitor topographic changes at a solar power plant, the first step is to establish a surveying system that safely records the entire plant and produces point clouds and terrain data that can be compared. If you want to clearly organize changes in drainage, slopes, around mounting structures, and maintenance roads, it is important to set rules for survey conditions, coordinate management, field verification, and data storage, and to utilize drone surveying as part of ongoing terrain management.