6 key points to check when surveying solar power plants with drones

Surveying for solar power plants has needs such as efficiently assessing large sites, checking earthworks and panel layouts, and retaining current-condition data usable for operation and maintenance. In these situations, drone surveying can be an effective means, but simply capturing images does not directly produce accurate drawings or point clouds. If you proceed without understanding the terrain, equipment, reflections, shadows, management zones, and flight conditions specific to a power plant, you may end up with results that look good but are difficult to use for design verification or operation and maintenance.

This article explains, in six points, the precautions that practitioners searching for "太陽光発電所　測量" (solar power plant surveying) should check before conducting drone surveys. It is organized as a set of considerations useful in a wide range of situations, such as new construction, expansion planning, post-earthwork verification, assessing conditions after panel installation, inspection of drainage and slopes, and creating records for operation and maintenance.

Table of Contents

• Clarify the purpose of drone surveying in advance

• Check laws and regulations, the surrounding environment, and safety conditions before flight

• Take into account reflections and shadows specific to solar power plants

• Verify the accuracy of results using control points and validation points

• Be mindful of how panels, mounting structures, slopes, and drainage appear

• Decide how to use and manage the deliverable data

• Summary: Preparation is important to make survey results usable on site

Clearly define the purpose of drone surveying in advance

When conducting drone surveying at a solar power plant, the first thing to confirm is the purpose of the survey. If flying a drone to capture aerial images or point clouds becomes the objective in itself, the required accuracy, coverage area, flight altitude, deliverable formats, and the items to be checked become ambiguous. As a result, problems are likely to occur later, such as “there is insufficient data for this area,” “it cannot be used to verify heights,” or “it is difficult to compare with drawings.”

Surveys for solar power plants serve various purposes, including understanding current conditions before construction, confirming development plans, managing earthwork quantities, considering panel layouts, verifying positions after mounting rack installation, reviewing drainage plans, maintaining slopes and retention ponds, and creating weed-control and inspection plans. For example, if the purpose is to capture the terrain before site development, it is important to photograph at a time when surface undulations and the positions of existing structures can be easily identified. Conversely, if the purpose is to confirm conditions after panel installation, a resolution and shooting angles that make equipment layouts—panel rows, access paths, fences, substation equipment, and drainage facilities—easy to read are required.

It is also important to consider who will use the survey results and how. The required deliverables vary depending on whether a designer will use them as a terrain model, a construction manager will use them for progress checks, or a maintenance manager will use them as inspection records. In some cases, knowing the horizontal position is sufficient, while in others elevation information is important. The preparations required differ greatly between cases where verification by photograph is adequate and those where the data must be overlaid with design drawings or existing coordinate data.

Especially at solar power plants, where sites are large and similar rows of panels continue, it can be difficult to pinpoint locations later from images alone. Therefore, rather than simply considering the photography coverage as "the entire site," it is important to decide in advance which sections will be captured, at what level of precision, and what outputs will be retained. Associating the management units used on site—such as plot names, construction zone names, equipment numbers, aisle names, fence access points, service roads, and drainage routes—with survey data makes them easier to use in downstream processes.

One of the strengths of drone surveying is its ability to efficiently capture wide areas. However, capturing a larger area does not automatically make the deliverables easier to use. If you shoot with unclear objectives, the data volume can increase unnecessarily, processing time and verification work can balloon, and the accuracy and visibility of critical locations may be insufficient. Conversely, when objectives are clear, you can focus on the necessary areas, narrow down checkpoints, and more easily stabilize the quality of the deliverables.

In the pre-meeting, confirm the surveying purpose, the deliverables to be used, the required extent, the required accuracy, consistency with existing drawings, areas on-site that can be accessed, areas that cannot be photographed, and the time windows when flights are possible. Additionally, if the deliverables will be submitted to a particular recipient, it is wise to confirm early the required data formats and delivery units. Drone surveying has aspects that can be adjusted in post-processing after capture, but because it is difficult to supplement areas that were not photographed or reference points that were not checked on site later, the initial clarification of objectives affects the quality of the deliverables.

Confirm laws and regulations, the surrounding environment, and safety conditions before flight

When conducting drone surveying at solar power plants, it is essential to check not only the technical imaging conditions but also flight-related laws and regulations, the environmental conditions around the site, and safety management requirements. Solar power plants are located in various places such as mountainous areas, former farmland, reclaimed land, industrial areas, and coastal areas. If there are houses, roads, railways, power transmission lines, communication facilities, wind power equipment, forests, rivers, or agricultural land nearby, the flight plan requires sufficient consideration.

The first thing to check is whether the flight location or method falls under procedures or restrictions under the Civil Aeronautics Act. Areas around airports, airspace 150 m (492.1 ft) or more above the ground or water surface, over densely populated areas, and emergency-use airspace, among others, require confirmation of whether flight is permitted and what procedures apply. Also, depending on the flight method — such as night flights, beyond-visual-line-of-sight operations, or flights close to people or property — permissions or approvals, safety measures, notification of flight plans, and preparation of flight logs may be required. It is important to verify the latest information for each site, including aircraft registration, pilot competency certificates, aircraft certification, consent from landowners or facility managers, and rules of local governments and relevant authorities.

Solar power plants are often located on large sites, so at first glance they may appear safe to fly over. However, the plant contains high-voltage equipment, transmission equipment, overhead lines, surveillance cameras, communications antennas, access roads, fences, entry and exit points, and worker passageways. In particular, transmission lines and service connection lines are obstacles that are easy to overlook when planning aerial filming. It is important to conduct an on-site survey before flight and confirm takeoff and landing points, flight routes, potential emergency landing sites, no-entry zones, and the movement paths of service vehicles.

Also, at solar power plants, surveying is sometimes conducted while the power generation equipment is operating. If the aircraft comes into contact with panels, racking, cables, or electrical equipment during operations, it can affect not only the surveying work but also the operation of the power generation equipment. Flights in strong winds, takeoffs and landings on slopes, operating from narrow maintenance aisles, and low-altitude flights in areas surrounded by rows of panels can be riskier than expected. It is essential to coordinate with the site safety manager, clearly mark the work area, notify workers, and control access during flight operations.

Checking the wind is also important. Solar power plants are often installed on mountain slopes or open developed sites, and even if the wind feels light at ground level, it can be strong aloft. In valleys and near ridgelines, wind direction can change easily, and disturbed airflow may occur around rows of panels and embankments. If the aircraft is blown off course during flight, capture intervals and overlap can be disrupted, degrading the quality of the results and causing safety issues. Check the weather, wind speed, wind direction, sunshine, cloud movement, and the possibility of rainfall, and make a judgment to avoid flying in risky conditions.

Do not forget to consider nearby residents and adjacent properties. Some people may feel uneasy about drone noise or drones passing overhead. Even when flying within the power plant site, if nearby roads, houses, farmland, or facilities are close, provide prior notice as necessary and clearly define the flight area. In locations where people other than site personnel might enter, station assistants to monitor the surroundings and establish measures to avoid close encounters with third parties.

Pre-flight checks are not just routine inspections; they directly affect the stability of survey results. If you fly with insufficient safety conditions, the flight may be interrupted or the imaging route may have to be changed abruptly, causing uneven image overlap and coverage. By firming up the flight plan from a safety standpoint, imaging quality becomes more stable and the risk of having to re-survey is reduced. In drone surveying, collecting good data and flying safely are inseparable.

Consider reflections and shadows unique to solar power plants

In drone surveying of solar power plants, the effects of panel surface reflections and shadows must be fully taken into account. Compared with typical surveys of developed land, roads, or farmland, solar power plants have the same-shaped panels arranged over wide areas. Panels readily reflect light, and the appearance of images can change dramatically depending on the time of capture and the sun’s position. When reflections are strong, it can become difficult to discern panel boundaries, racking, and access paths in the images, which can also affect the stability of photogrammetric processing.

In drone surveying, relative positions are estimated by using the same features that appear in multiple images. However, solar panels have uniform surfaces and repeating patterns, so feature points can be unstable. Furthermore, strong reflections and blown-out highlights can cause parts of an image to lack information, making it difficult to match with adjacent images. Even aerial photos that look sharp can be unstable for processing, so caution is necessary.

Shadows are also an important factor. When panel rows, mounting racks, fences, utility poles, trees, nearby hills, or buildings cast shadows, the appearance of the ground surface and pathways changes. In particular, during periods of low solar elevation shadows lengthen, making the aisles between panels, slopes, and drainage channels harder to see. Conversely, when sunlight is very strong reflections intensify, and panel surfaces and metal components are more likely to be blown out to white. Which time of day is most suitable depends on site orientation, panel angle, topography, and season, so if possible it is reassuring to conduct test photography in advance.

In solar power plants, the approach to imaging conditions differs depending on whether you want to measure the panels themselves or the ground surface and structures around the panels. If you want to check the current layout of panels and racking rows, it is important that the panel outlines and any row misalignments can be discerned. On the other hand, if you want to understand the heights and shapes of graded surfaces, slopes, drainage channels, and maintenance paths, many areas will be hidden by the panels, so it is necessary to supplement locations where drone surveying alone is insufficient with other surveying methods.

At a power plant where panels have been installed, the surfaces visible from above are covered by the panels, making it difficult to obtain detailed elevations of the ground surface. Point clouds and surface models created by image processing essentially reflect the surfaces of objects visible from above. In other words, they do not directly represent the ground beneath the panels or the drainage conditions under the mounting structures. If you want to verify ground-surface drainage gradients, subsidence, or erosion, a combined approach using on-site inspections, ground surveys, and individual measurements at necessary locations is needed.

In shooting settings, it is important to adjust image overlap, exposure, flight altitude, and flight speed to match field conditions. When similar rows of panels continue, ensuring sufficient overlap between images and avoiding sudden changes in brightness makes it easier to improve processing stability. However, increasing overlap does not necessarily guarantee higher quality, and it also increases data volume and processing time. It is important to balance the resolution required for the purpose with the processing load.

Reflections and shadows affect not only the appearance of the results but also subsequent interpretation work. If you want to check for damage to maintenance walkways, overgrowth of weeds, blockages in drainage channels, slope deformations, or abnormalities around fences, it becomes difficult to judge from images with strong shadows. When using images as inspection records, photographing regularly in the same season or at similar times of day makes it easier to compare them with past images. If shooting conditions change significantly each time, it becomes hard to tell whether an observed difference is an actual change or merely a difference in lighting conditions.

To improve the quality of drone surveying, it's important not simply to rely on high-performance aircraft or high-resolution imagery, but to plan the survey with an understanding of the reflections, shadows, repeating patterns, and occluded areas unique to solar power plants. By being aware on site of "what is visible and what is not," you can accurately explain the limitations of the deliverables and produce data that can be used in practice without misunderstanding.

Verify the accuracy of results using control points and check points

When considering practical use of drone surveying for solar power plants, the handling of control points and check points is extremely important. Orthophotos and point clouds created from images captured by drones can be difficult to judge for accuracy from appearance alone. Even if images are neatly stitched together, coordinates may be shifted or heights may contain errors. If you plan to use them for overlaying with design drawings, verifying earthwork quantities, or managing equipment locations, you need a mechanism to confirm how reliable the deliverables are.

Control points are important markers for aligning drone survey results with the site coordinate system and existing drawings. By properly placing known points and calibration targets installed on site and ensuring they are clearly visible in the photographs, it becomes easier to align the post-processed outputs with field coordinates. At solar power plants, the site is often large and may include slopes and level changes, so if control points are clustered in one area, errors can become large in distant areas. It is important to arrange them so they surround the entire survey area and to take into account locations with significant terrain variation.

Verification points are not points used to create the deliverable, but points used to verify the accuracy of the finished deliverable. If you assess adjustment results using only control points, the processing may appear to match well. However, when actually using the deliverable, it is important to check how well it matches at points that were not used in the adjustment. Establishing verification points makes it easier to explain the overall reliability of the deliverable and helps build consensus among stakeholders.

Even when using positioning information such as RTK or PPK, verification points are not necessarily unnecessary. The stability of results changes depending on satellite positioning conditions, the handling of base stations and correction data, camera settings, image overlap, and terrain conditions. Rather than relying solely on the vehicle’s position information, it is safer to prepare on-site points that can be checked according to the objective and to be able to explain any offsets in results and variations in elevation.

In solar power plants, attention must also be paid to where reference points and verification points are placed. If markers are placed near panels or on walkways, they can become difficult to see due to reflections, shadows, service vehicles, grass, materials, and so on. Placing them too close to generating equipment or in locations that obstruct workers’ passage can create safety issues. You must choose locations that will reliably appear in captured images, can be measured accurately on site, and do not interfere with work.

Verification of elevation accuracy is particularly important for solar power plants on sloped terrain. Even if horizontal positions are correct, vertical discrepancies can affect checks of drainage gradients, slope geometry, and prepared surfaces. In drone surveying, elevation stability varies depending on imaging conditions, ground control point layout, and how the ground surface appears. After panels are installed, panel surfaces and vegetation may be interpreted as the ground surface, so it is necessary to clearly define the ranges that can and cannot be treated as ground elevation.

Consistency with existing drawings is also a point that should be checked. Design drawings, site development drawings, as-built drawings, and management drawings for a power plant may each have been created at different times or under different coordinate conditions. If a misalignment occurs when overlaying drone survey results and drawings, it is necessary to distinguish whether the cause is actual changes on site, differences in the drawings' coordinate systems, or errors in the survey results. Comparing without checking the coordinate system, reference points, elevation datum, and the drawing creation conditions can lead to incorrect conclusions.

When verifying accuracy, set the evaluation criteria according to how the deliverables will be used. For wide-area condition assessments or inspection records, coverage and legibility can be more important than fine coordinate accuracy. Conversely, if the outputs will be used for purposes closer to design changes, boundary verification, earthwork quantity calculations, or as-built control, more rigorous accuracy checks are necessary. Since drone survey results are not universally applicable, it may be necessary, depending on the required accuracy, to combine them with ground surveys or surveys of existing control points.

When delivering results, recording the control points used, check points, acquisition date, acquisition conditions, processing conditions, results of accuracy verification, and any areas requiring caution will make it easier to reuse the results later. Especially in maintenance and management, past data may be reviewed months or years later. If at that time it is not clear under what conditions the results were produced, comparison and judgment become difficult. Records of control points and check points should be treated as fundamental documentation that supports the reliability of surveying results.

Be mindful of the appearance of panels, mounting structures, slopes, and drainage

In drone surveys of solar power plants, it is important to clarify what can and cannot be seen from above. Because drones can capture a wide area from overhead, they are well suited to understanding the arrangement of panels, access roads, fences, graded surfaces, slopes, and the positional relationships of drainage facilities. However, areas beneath panels, inside racking, ground surfaces covered by grass, the interiors of dark drainage channels, and areas beneath trees may not be sufficiently confirmed from imagery alone. When using the survey deliverables, it is necessary to understand what is easy to ascertain from the data and what should be verified by other methods.

Regarding the panels, as shown in the columns, it is easy to check tilt, placement misalignment, potential damage, and relationships with surrounding obstacles; however, judging the panel surface condition in detail is affected by imaging conditions. Strong reflections or shadows can make dirt, cracks, and surface irregularities difficult to distinguish. Also, surveying results from ordinary visible images are not intended to diagnose power generation performance itself. Investigations into the causes of reduced power output and checks for electrical abnormalities should not be judged solely on survey results, but should be considered together with power generation data, inspection results, and specialized investigations as necessary.

For mounting structures, the parts visible from above are limited. Aerial imagery can help to roughly identify the rows of racks and the positions of support posts, but bolt loosening, member deformation, foundation uplift, corrosion, and the condition of joints often cannot be fully confirmed from drone survey results alone. In particular, components located at low positions and the undersides of panels are not visible in aerial images. If the objective is to verify the structural soundness of the mounting structures, it is necessary to combine close-up photography, ground-level inspection, and cross-checking with inspection records.

In slope inspections, there are situations where drone surveying is highly effective. Because wide slopes and slopes that are difficult for people to approach can be observed from above, it becomes easier to identify collapses, scouring, cracks, changes in vegetation, and traces of drainage flow. However, during periods when grass is abundant the ground surface can be difficult to see, and the surface model may end up including the height of the grass. If you want to accurately confirm the shape and deformations of a slope, it is necessary to take measures such as photographing after mowing or during seasons with less vegetation and inspecting important locations on the ground.

Checking drainage facilities is also important. At solar power plants, post-construction stormwater management becomes a major point in operation and maintenance. Drainage ditches, catch basins, retention ponds, sedimentation basins, cross drains, and culvert outlets can have their functionality reduced by sediment buildup and vegetation overgrowth. While drone surveys make it easier to grasp the overall drainage routes and terrain that facilitate water flow, they may not be able to confirm the inside of ditches or basins, or blockages in culverts. A realistic workflow is to identify potential abnormalities from aerial inspections and conduct on-the-ground inspections where necessary.

Regarding access roads and pathways, it becomes easier to grasp broad-area issues such as ruts, scouring, subsidence, muddy spots, and locations where vehicles have difficulty passing one another. During construction, it can also be used to verify the relationships between material storage areas, temporary roads, heavy equipment traffic routes, and the positions of work yards. In the maintenance stage, it is also useful for confirming the extent of vegetation control, inspection routes, and emergency access routes. However, fine differences in step heights and the firmness of the road surface are difficult to judge from images alone, so on-site verification should be performed as necessary.

Fences and areas around boundaries are also objects that must not be overlooked in surveying a solar power plant. Fallen fences, encroachment by surrounding trees, the condition of measures against wildlife damage, elevation differences with adjacent land, and the locations of maintenance access points are all important information for operation and maintenance. Drone surveying that provides an overview of the entire site makes it easier to identify changes near boundaries and problems along the perimeter. However, when carrying out legal confirmation of boundaries or parcel boundary confirmation, you should not rely solely on drone survey results; treat them carefully in conjunction with existing documents, on-site markers, ground surveys, and any required procedures.

Thus, drone surveys excel at obtaining an overall understanding of solar power plants, but they have limitations when it comes to checking details. The important thing is not to overestimate the information obtained by drones. By using aerial surveys to extract candidates for potential anomalies across the entire site, confirming critical locations on the ground, and supplementing with other survey methods as necessary, you can produce results that are usable in practice. It is important to view the panels, mounting structures, slopes, drainage, access routes, and fences as an integrated system and to organize which information will be verified by which method.

Decide in advance how to use and manage results data

In drone surveying, after image capture you can produce various deliverables such as orthomosaic images, point clouds, 3D models, contour lines, cross-sections, data for area measurement, and data for creating as-built drawings. However, having more types of deliverables does not necessarily make things more convenient. If you generate a lot of data without deciding in advance what will be used in practice, file sizes can become large, management can get complicated, and you may be unable to find what you need when you need it. It is important to decide before surveying which deliverables will be used and by whom.

In managing solar power plants, there are many situations where data must be compared across months and years. If you can overlay and review data for each stage—before site development, after site development, after panel installation, after completion, during periodic inspections, and after disasters—it becomes much easier to grasp changes. For that reason, it is necessary to clearly record the capture date, area covered, coordinate system, reference points, processing parameters used, and output names, and to store them in a way that allows later comparison. File names and folder structures that are ambiguous make it difficult to make effective use of data that was painstakingly acquired.

When overlaying deliverable data onto design drawings or management maps, check the handling of coordinate systems and scale. Even if the drone survey results were created with correct coordinates, if the coordinate conditions of the drawings being overlaid are unclear, positions may not align. If local site coordinates, public coordinates, design coordinates, and as‑built drawing coordinates are mixed, it is important to decide in advance which reference will be used to produce the results. When performing coordinate transformations, record the transformation conditions so that another person in charge can understand them.

When working with point clouds or 3D models, you need to pay attention to the data volume. Solar power plants cover large areas and tend to produce many images, so point cloud datasets can become very large. High-density data is useful for detailed inspection, but on typical business workstations it can become heavy to display or share. For maintenance and internal sharing, manage with usability in mind—for example, provide a lightweight version separate from the detailed one, split the data by sections, or use image deliverables for verification.

Also, because the deliverable data contains on-site equipment layouts and management information, attention must be paid to the scope of sharing. Information such as the power plant’s location, entrances and exits, equipment layouts, access roads, and locations of electrical equipment can require management considerations depending on how they are handled. When sharing externally, it is essential from an information-management perspective to provide only the necessary scope, exclude unnecessary information, and clarify the recipients and purposes. Survey deliverables should be regarded not merely as images but as materials related to facility management.

When using survey results for operation and maintenance, consider linking them with inspection records. For example, if you identify areas of slope deformation, clogged drainage channels, overgrown weeds, damaged fences, or scouring of walkways, linking the location on the image to the on-site inspection record makes it easier to use for the next inspection or repair planning. Rather than simply storing aerial images, establishing an operation that records anomaly locations, inspection dates, response status, and scheduled re-inspections will increase the value of drone surveying.

In delivery and internal sharing situations, materials that explain how to interpret the deliverables are also useful. By clearly stating which area was captured, which coordinate reference system was used to create the data, what level of accuracy verification was performed, and which parts cannot be treated as ground surface due to the influence of panels or vegetation, recipients are less likely to misunderstand the results. Especially when staff unfamiliar with point clouds or 3D models are reviewing them, it is important to explain the limitations and caveats of the deliverables.

Results of drone surveys are not finished once produced. They become valuable only when organized in a way that allows continuous use for power plant design, construction, operation and maintenance, inspection, and renovation planning. If you decide on the intended uses and data management methods before surveying, the necessary capture conditions and accuracy checks become clear, reducing the risk of ending up with data that cannot be used later. The larger the power plant, the more setting rules for data management leads to improved on-site efficiency.

Summary: Preparation Is Key to Making Survey Results Usable in the Field

Drone surveying of solar power plants is a convenient method for efficiently understanding large sites. Because the entire site can be viewed from above, it becomes easier to comprehensively understand site development status, panel layout, access and maintenance roads, slopes, drainage facilities, areas around fences, and so on. It can be used in many situations, such as progress checks during construction, records at completion, operation and maintenance, and post-disaster assessments.

However, drone surveying does not automatically yield accurate results simply by capturing images. If you conduct flights with unclear objectives, the required coverage and accuracy may be insufficient. Inadequate pre-flight legal checks or safety management can lead to interrupted surveys or increased risk of accidents. If reflections, shadows, and repetitive patterns unique to solar panels are not taken into account, image processing and interpretation can be affected. Furthermore, if control points and check points are not handled properly, the results may look well-presented yet still be unreliable for practical decision-making.

At solar power plants, it is also important to distinguish between information visible from above and information that is not. Areas beneath panels, fine details of the racking, the insides of drainage channels, and ground surfaces covered by vegetation may not be fully confirmed by drone surveying alone. By using drones to gain an overall understanding, verifying necessary locations on the ground, and combining that with existing drawings, power generation data, and inspection records, you can produce information that is usable on site.

Managing deliverable data is also important. Recording the acquisition date, coverage area, coordinate conditions, control points, check points, processing parameters, and any notes makes it easier to assess the results later. Solar power plants are facilities operated over a long period. Survey results should not be treated as one-off documents but organized as records that can be used for future inspections, maintenance or upgrades, and troubleshooting.

Successful drone surveying requires preparation that includes not only flight skills and image processing, but also clarifying site objectives, safety checks, control point planning, shooting conditions, and deliverable management. In particular, field practitioners who organize in advance “what to measure,” “what accuracy it will be used for,” “what area to verify,” and “what information will be supplemented by other methods” can reduce rework after surveying.

To conduct surveys of solar power plants more efficiently, it is important to establish a system in which drone surveys provide an overall view while necessary areas are supplemented by ground surveying and on-site inspections. If control points, check points, site photos, inspection records, and supplemental measurements are managed together, the results will be more usable for construction management and maintenance. The key to connecting surveying and inspection work for solar power plants to practical operations is not to leave drone surveys as mere aerial photography, but to retain positional information and records that can support on-site decision-making.