5 Steps to Conduct Safety Inspections of Solar Power Plants Using Drone Surveys

When carrying out safety inspections of solar power plants, it is necessary to walk the expansive site and identify changes in topography, slopes, drainage, areas around mounting racks, access routes, fences, and the surrounding environment. On-site walking inspections remain important, but gaining an overview of the entire plant and organizing observed changes takes time, and factors such as overgrown vegetation, muddy ground, steep slopes, and the risk of entering after disasters can make inspection work burdensome. One readily applicable method for this is safety inspection using drone surveying.

Drone surveying is characterized by its ability to record the overall condition of a power plant as a surface based on images and positional information captured from the air. It is not merely aerial photography; by continuously recording under the same conditions and cross-referencing with drawings, point clouds, orthoimages, and the like, it becomes easier to confirm changes at the site. However, simply flying a drone does not automatically complete safety verification. It is important to organize the objectives you want to verify and design the entire flow—from pre-flight preparation, on-site shooting, and data organization to evaluation and the handover of records.

Table of Contents

• The Significance of Conducting Safety Inspections of Solar Power Plants Using Drone Surveys

• Step 1 Clarify the objectives of site conditions and safety confirmation

• Step 2 Decide the scope of inspection and risk locations before flight

• Step 3 Record the overall site and details with drone surveying

• Step 4 Read candidates for changes and anomalies from the acquired data

• Step 5: Organize reports and records that lead to the next inspection

• Precautions when using drone surveying for safety checks

• Summary Solar power plant safety checks improve accuracy through continuous record-keeping

The Significance of Conducting Safety Inspections at Solar Power Plants Using Drone Surveys

The safety of a solar power plant is supported not only by the generation equipment itself but by many elements such as the site, graded surfaces, drainage routes, slopes, maintenance access roads, fences, and surrounding vegetation. Even if there is no obvious damage to panels or mounting structures, the progression of ground subsidence, poor drainage, sediment runoff, small slope failures, ruts in access roads, or reduced visibility due to weeds can affect the safety of inspection and maintenance work. When confirming a plant’s safety, it is essential to maintain a perspective of continuously monitoring the condition of the entire site, not just the equipment.

The advantage of using drone surveying is that it can record a large site from a consistent aerial viewpoint. With ground visual inspections, information tends to be biased toward the places the inspector walked and the directions they looked. By contrast, using images captured by drones makes it easier to get an overview of the entire power plant layout, the likely directions of drainage flow, changes in terrain elevation, the distances between slopes and equipment, and the continuity of maintenance access routes. Especially when inspecting after a disaster or heavy rain, it is sometimes possible to assess conditions from above before entering the site, making it easier to prevent workers from inadvertently approaching hazardous areas.

Drone surveying also has value for record-keeping. Safety checks are not completed with a single inspection; it is important to track changes by comparing the current condition with previous ones. For example, if small scours are observed on a slope surface, the priority of the response will differ depending on whether they are temporary or expand with each rainfall. Continuous records also help determine whether depressions in maintenance access routes are merely wheel ruts or signs of poor drainage or loosening of the ground.

However, it is not appropriate to determine safety based solely on the results of drone surveys. The range visible in images and point clouds is limited, and separate inspections are required for the condition inside electrical equipment, details of mounting-structure joints, the interior of foundations, and subsurface conditions. Drone surveys are effective when used as a means to efficiently extract candidate hazardous locations and to prioritize on-site inspections. Combining them with ground inspections, electrical inspections, and maintenance records makes it easier to advance overall safety verification of the power plant.

Step 1 Clarify the purpose of on-site conditions and safety checks

The first step, before flying a drone, is to clarify what will be checked for safety. Even among solar power plants, conditions vary: those installed on flat, developed land; those on mountainous or sloped terrain; those that include former reservoirs or embankments; and those along the coast that are prone to wind and salt exposure. When site conditions differ, the risks that need to be checked also change. If you capture images with an unclear objective, you may have photos left over, but they will be difficult to use later for decision-making.

Common purposes of safety checks include identifying abnormalities after disasters, performing an overall check before routine inspections, checking the condition of slopes and drainage facilities, detecting changes in topography, verifying the passability of maintenance access paths, and assessing the possibility of fallen trees or sediment inflow from the surrounding area. After heavy rain, emphasis is placed on clogged drainage channels, sediment accumulation, scouring, and traces of turbid water flow. After typhoons, checks focus on scattered debris, disturbances around panels, leaning fences, fallen trees, and anomalies around mounting racks. For daily management, look for weed overgrowth, the condition of access routes, and changes in locations that are difficult to approach during inspections.

What is important here is to distinguish between what can be checked by drone surveys and what should be checked directly on site. While images from above make it easy to grasp wide-area changes and visual abnormalities, it can be difficult to confirm things like loose bolts, electrical faults, or minor damage to cable sheathing. During the planning stage of safety checks, deciding that drone surveys will be used for overall situational awareness and extraction of potential anomalies, while detailed judgments will be made by ground checks or specialized inspections as needed, can reduce wasted effort.

It is also important to review past drawings and inspection records. If available, review the as-built site development drawings, drainage plans, past repair histories, locations that tended to retain water, places where sediment outflow was observed, and records of mowing and weed-control management before shooting. If previous drone survey data exist, plan so that you can compare the same area, the same altitude, and similar shooting conditions. For safety checks, the basis for judgment should be to look at changes over time rather than a single image from this time.

Sharing objectives among on-site stakeholders is also essential. The power plant owner, maintenance manager, surveyor, and construction manager may each view the site from different perspectives. Some prioritize equipment conditions that directly affect power generation, while others focus on safe passage for workers or the risk of sediment runoff to surrounding areas. Before conducting a drone survey, aligning which perspectives to prioritize for this safety check will make it easier to organize the survey coverage, the analysis, and how the report is written.

Step 2: Decide the inspection area and risk locations before flight

The next step is pre-flight planning. Because solar power plants have panel rows arranged regularly, at first glance everything can look the same. However, from a safety inspection perspective, there are certain areas that require particular attention. Low-lying parts of the site, places where drainage tends to collect, the bottom of slopes, the boundary between embankments and cuttings, bends in maintenance access paths, along fences, boundaries with adjacent properties, and areas near rivers or waterways are locations where changes are more likely to occur. Before the flight, review drawings and past records and decide which spots to check closely.

It may be better not to limit the inspection scope to only the plot containing the power generation equipment. For safety checks, impacts from outside the site are also important. Possible issues such as sediment flowing in from surrounding slopes, the collapse of adjacent trees, clogging of perimeter drainage channels, and stormwater entering from roads can be overlooked if you only photograph the inside of the power plant. After confirming the area in which flight is permitted and obtaining permission from relevant parties, planning to include the perimeter and the upstream side of drainage flows makes it easier to understand the risks.

In flight planning, decide the capture altitude, image overlap, shooting direction, and flight route. Data used for safety checks should be recorded not only as visual photographs but also in a form that preserves positional relationships. A lack of image overlap makes it difficult later to organize images into maps or to verify three-dimensional changes. Especially for sites with slopes or steps, some surfaces are hard to see from directly above, so combine oblique (angled) photography as needed. However, if the flight route becomes too complex, work time and the burden of safety management increase, so it is important to narrow the scope appropriately according to the objective.

Before flight, it is also necessary to carry out checks in accordance with laws and site rules. For unmanned aircraft flights, there are items to confirm depending on the location, airspace, flight method, and surrounding environment. If there are houses, roads, railways, power transmission facilities, communication equipment, schools, factories, or similar near a power plant, carefully consider the impact on third parties and access control. Even within the site, if flying during times when workers or vehicles are active, it is necessary to notify people of the flight area, secure takeoff and landing locations, and establish emergency response procedures. After a disaster, it is important to also confirm the activities of manned aircraft conducting emergency missions and whether any flight restrictions are in place, and to avoid attempting flights that would be unsafe.

Weather conditions also affect the quality of safety inspections. On windy days, the aircraft’s stability decreases and captured images are more likely to be blurred. On days with rain or fog, visibility is reduced, affecting both the aircraft and imaging equipment. At solar power plants, reflections from panel surfaces can make images hard to see depending on the time of day. For safety inspections, it is desirable to capture images under the most stable conditions possible to avoid missing potential anomalies. Even when urgent inspections are required, such as immediately after a disaster, do not attempt to fly under conditions where flight safety cannot be ensured; perform ground checks or decide to wait whenever possible.

Step 3 Record the overall site and details with drone surveying

During on-site photography, we first acquire data that captures the entire power plant. If the whole site is photographed under consistent conditions, it becomes easier to organize the images later as orthoimages and georeferenced records. For safety inspections of solar power plants, we broadly check for disturbances in panel rows, tilting of mounting racks, deformation of walkways, discoloration of the ground surface, accumulation of sediment, abnormalities around drainage channels, slope failures, deformation of perimeter fences, and so on. Continuous changes that are difficult to see from the ground are easier to notice when viewed from above.

After capturing overall shots, record detailed images of priority areas. For example, junctions of drainage channels, the foot of slopes, the ends of panel rows, low spots on maintenance walkways, and places where sediment tends to accumulate can be difficult to assess from images taken at normal altitude alone. Adjust altitude and angle within ranges that can be flown safely, and capture images that make it clear whether abnormalities are present. At this time, it is important not only to take close-up shots but also to capture images that show positional relationships with the surrounding area. If you only enlarge and photograph the abnormal area, it becomes difficult to explain the location and extent of the impact in reports.

When capturing images, pay attention to how reference position information is handled. For safety checks, being able to compare the exact same location each time is valuable. If positional shifts are large, it becomes difficult to determine whether differences from the previous time are actual changes or data misalignments. Use ground control points or known reference points as needed to make it easier to align the acquired data. In situations requiring high accuracy, it is important to consider positioning methods and reference-point installation in advance and to develop a surveying plan suited to the objectives.

At solar power plants, attention must be paid to the effects of panel reflections and shadows. Depending on the time of day, panel surfaces may appear washed out, making it difficult to see surrounding conditions. Conversely, when shadows stretch long, surface irregularities and steps on the ground may become easier to see, but small anomalies can also be hidden by those shadows. Depending on the purpose of the shooting, consider conditions suited to overall inspection and conditions that make it easier to identify irregularities and steps. If necessary, carry out supplementary shooting from multiple angles on the same day to reduce oversights.

On-site, it is important not to rely solely on images captured by drones, but to be conscious of linking any areas of concern to ground verification. During quick checks while flying or after shooting, if sediment runoff, poor drainage, fence deformation, or path collapse is suspected, add on-site photos and notes after securing safe access. Combining drone survey images with ground photographs makes it easier to convey the location, extent, and on-the-ground context of potential anomalies. Especially when considering repairs or emergency measures, records from a worker's viewpoint are useful in addition to aerial images.

Step 4 Identify changes and anomaly candidates from acquired data

After imaging, the acquired data is organized and converted into information usable for safety verification. A typical use is to organize images so the entire power plant can be viewed like a map, and to overlay them with past data and drawings for comparison. Organizing continuous aerial images clarifies the positional relationships of panel rows, walkways, drainage channels, slopes, and the perimeter. This allows changes that are easily overlooked on site to be checked through desk-based review, narrowing down the locations that require on-site inspection.

When identifying potential anomalies, interpret visual oddities as items to include in safety checks. Areas where the ground surface color has changed may be related to mud, traces of water flow, sediment accumulation, or changes in vegetation. If there are streak-like marks on a pathway, they could be ruts caused by vehicle traffic, channelization of rainwater, or surface washout. If thin linear patterns appear on a slope face, they might be signs of scour or surface flow. Disturbances along a fence can be organized as candidates such as fallen trees, sediment, animal intrusion, or external contact.

What's important is not to immediately conclude what is visible in the images. In drone survey data, shadows, reflections, vegetation, the shooting angle, and image-processing conditions can make changes appear larger than they actually are, or conversely smaller. For safety checks, managing statuses separately—such as potential anomaly, requires monitoring, confirmed on site, and addressed—makes the basis for decisions clear. For example, a location that appears to be a clogged drainage channel in an image should be treated as a subject for confirmation, not as a confirmed anomaly, until it has been verified on site.

When comparing with past data, it is important to look at changes at the same locations. Check places where the surface color has changed since the previous survey, where sediment has spread, where the shape of slopes appears to have changed, and where the width of pathways has narrowed. If possible, view the previous and current images side by side to organize the direction and extent of the changes. If you can work with point clouds or elevation data, checking changes in elevation differences makes it easier to identify potential subsidence or sediment accumulation. However, because judgments about elevation differences are affected by data accuracy and positional alignment, do not draw conclusions from numerical values alone; verify them against on-site conditions.

In safety inspections of solar power plants, we check not only for the presence of abnormalities but also whether they affect inspection and maintenance work. For example, a muddy pathway that appears to have no direct impact on the generation equipment can lead to problems such as service vehicles being unable to enter, workers being more likely to slip or fall, and difficulty approaching or reaching the site in an emergency. Overgrowth of vegetation near the perimeter fence affects not only the facility’s power generation performance but also intrusion prevention, the ability to conduct patrols, and visibility. In safety inspections, we do not focus solely on equipment damage; we also evaluate whether maintenance and management work can be carried out safely.

Step 5: Prepare reports and organize records for the next inspection

The final step is to organize the inspection results into a format usable for reporting and the next inspection. The results of drone surveying—images and point clouds—are not sufficient for site management if they are only acquired. They need to be organized so it is clear what is where, what level of attention is required, and who should check what next. A safety inspection report should clarify the overall condition of the power plant, priority inspection areas, suspected anomalies, on-site verification results, response priorities, and items to be checked at the next inspection.

In reports, combining an overall view with detailed images makes the information easier to understand. Use the overall view to indicate the locations of suspected anomalies, and use detailed images to explain their condition. For example, if a clog in a drainage channel is suspected, show where it is located within the power plant, the upstream–downstream relationship, and whether there are nearby panel rows or walkways. If the issue is a change in a slope, explain not only the area where the collapse is visible but also whether there are facilities or paths above or below it. When the positional relationships are organized, stakeholders will have less difficulty finding their way when heading to the site.

Record granularity is also important. If you share all images as-is, the recipient may spend a lot of time reviewing them and important areas can get buried. Conversely, if you excerpt too much, you may not have enough information when you want to check the situation later. In practice, a manageable approach is to retain the original data while preparing a document that organizes the inspection results for reporting. The report should include the inspection date, imaging conditions, inspection scope, the types of data used, the locations of potential anomalies, the basis for determinations, and the planned course of action.

To facilitate the next inspection, it is important to keep records that are easy to compare. To ensure the same area can be photographed next time, record the flight route, shooting altitude, shooting conditions, how reference points are handled, and the key areas to check. In safety checks, even if the current condition appears to be problem-free, changes can emerge when the same location is monitored over time. In particular, drainage, slopes, embankments, pathways, and perimeter areas are easily affected by seasonal changes and rainfall, so fixed-point comparisons are useful.

When reporting, it is also important to avoid excessive certainty. Separate and describe the areas that can be assessed from images, the areas that have been confirmed on site, and the areas that require additional verification. For example, rather than making a single definitive statement about safety, indicate that no major topographical changes were observed within the range visible in aerial imagery, but that on-site inspection is recommended because there may be sediment buildup in parts of the drainage channels—thus clarifying the evidence and the limitations. Writing in this way makes it easier for stakeholders to decide on the next course of action.

Precautions when using drone surveying for safety checks

Drone surveying is a useful tool for safety inspections of solar power plants, but it is not a panacea. First, proper management of the flight itself is required. Inside a plant there are obstacles to be aware of during flight, such as racking, cables, utility poles, transmission equipment, trees, and fences. In mountainous areas, wind can change suddenly, and near valleys or slopes this can affect the drone's stability. Even when using drone surveying for safety inspections, it is necessary to decide to postpone operations under hazardous flight conditions.

Next, pay attention to how the data looks. Solar panels are highly reflective, and their appearance changes depending on the time of capture and the angle. In areas with dense vegetation, changes on the ground surface can be obscured. In images with many shadows, areas that appear to be steps or scour may in reality be shadows. Data produced by image processing are also influenced by capture conditions and the precision of alignment. Therefore, when interpreting drone survey data, do not rush to conclusions based on images alone; combine them with ground photos and on-site verification as needed.

One practical point is not to broaden the scope of safety checks too much. If you try to examine the entire power plant in fine detail at once, the number of photos and items to check will increase too much and it will take longer to produce the report. First, decide on the main perspectives related to the plant’s safety, and separate overall inspections from focused inspections to make operations easier. Instead of checking everything to the same depth every time, for routine inspections look for overall changes, and after heavy rain or a typhoon focus on drainage and the perimeter; it is realistic to change what you check according to the purpose.

Rules for data management are also important. In drone surveying, a large number of images and location data are generated. If you do not decide on storage locations, file names, capture dates, target areas, verifiers, and correspondence with reports, it will take time to find the necessary data later. In safety checks, because comparison with past data is valuable, you must avoid situations where data exists but cannot be found, where it is unclear which area was photographed, or where comparison with the previous inspection is impossible. Deciding on an organizational method from the outset that assumes continuous operation will stabilize the quality of inspections.

Also, it is essential to align decision criteria among stakeholders. Even when viewing the same image, different personnel may have different thresholds for judging something as hazardous. Deciding in advance whether a small amount of sediment in a drainage channel should be treated as an immediate cleanup target, monitored over time, or judged after an on-site inspection will make responses after reporting less likely to vary. Drone surveying visualizes a lot of information, but how that information is interpreted and the order in which responses are taken are determined by operational rules.

Summary: Improving the accuracy of safety checks at solar power plants through continuous recording

To carry out safety inspections of solar power plants using drone surveys, it is important to design the process as a single flow that includes not only aerial photography but also defining objectives, flight planning, on-site recording, data verification, and report preparation. In Step 1, clarify site conditions and the objectives of the safety inspection, and separate the areas to be checked by drone from those that require ground inspection. In Step 2, based on drawings and past records, determine the inspection areas and risk locations. In Step 3, record the overall situation and details of priority areas, leaving data that clarifies positional relationships. In Step 4, interpret changes and candidate abnormalities from the acquired data, and organize them as items to be confirmed rather than definitive diagnoses. In Step 5, organize the records into reports and documentation usable for the next inspection.

What's important in safety checks is not to be reassured by this inspection's results alone, but to continuously track changes. The site of a solar power plant gradually changes under the influence of rain, wind, temperature, vegetation, vehicle traffic, and the surrounding environment. Small erosion, sediment build-up in drainage channels, depressions in access paths, and surface changes on slopes can be difficult to judge from a single inspection. However, if you continue recording the same locations under similar conditions, the direction of changes becomes easier to see, making it easier to take early countermeasures.

Drone surveying is an effective means of obtaining an overview of an entire power plant, determining priorities for on-site checks, and sharing the situation among stakeholders. At the same time, there are parts that cannot be seen in images and parts that should be confirmed directly on site. In safety verification practice, rather than using drone surveying as the sole basis for decisions, combining it with ground inspections, equipment inspections, past records, and the knowledge of on-site personnel enables checks that are better suited to practical operations.

If you want to carry out safety checks at solar power plants efficiently, rather than aiming for a perfect system from the start, it is better to begin by narrowing the inspection objectives and creating records that can be compared consistently over time. By preparing records that give an overall view, track priority areas, and are handed over to the next inspection, drone surveying becomes more than mere imaging—it becomes information that supports maintenance and management decisions. To continuously improve safety checks at solar power plants, it is important to establish surveying and recording systems that are easy to use on site.