How to streamline as-built verification of solar power plants using drone surveying

Table of Contents

• Common issues that occur during as-built verification of solar power plants

• Reasons why drone surveying can streamline as-built verification

• Key items to check during as-built verification

• Preparations to complete before on-site flights

• Basic workflow for drone surveying

• How to use survey data for as-built verification

• Points to pay attention to for maintaining accuracy

• Approach to integrating conventional verification methods

• Using data for refurbishment and maintenance

• Summary

Common Issues That Often Arise During As-built Verification of Solar Power Plants

In the construction or renovation of solar power plants, as-built verification that confirms earthworks, mounting racks, panel layouts, drainage systems, maintenance access paths, perimeter areas, and other elements have been constructed in accordance with the design and construction plan is important. As-built verification is not merely the task of checking appearance after completion. It is also the process of organizing fundamental information related to power generation efficiency, maintainability, safety, and future repair planning.

Solar power plants are sites where many pieces of equipment are arranged across a wide area, making it difficult to grasp the overall picture from ground-level inspections alone. In particular, for plants utilizing sloping terrain, reclaimed land, mountainous areas, or idle land, the range of checks expands to include ground elevation differences, embankments, drainage directions, the alignment of racking rows, and the tilt of the panel surfaces. When on-site personnel walk the site to inspect, omissions and inconsistent records are likely to occur, and even when photos are taken it can be hard to understand the positional relationships.

Another challenge in as-built inspections of solar power plants is aligning understanding among stakeholders. Because the contractor, client, designer, and maintenance manager each view the site from different perspectives, they may prioritize different points even when looking at the same location. For example, the construction team emphasizes the installation status of the mounting structures, the design team emphasizes layout and slope, and the maintenance team emphasizes the usability of access routes and drainage. For these reasons, verbal explanations or just a few site photos alone make it difficult for everyone to understand the same condition.

If as-built verification work is postponed, rework before completion can become substantial. Heights of graded surfaces, walkway widths, drainage routes, and equipment spacing, for example, may require major effort to modify after completion. Even small deviations can later surface as impacts on power generation, accessibility during inspections, ease of mowing, or problems with stormwater management.

One effective option in that context is as-built verification using drone surveying. By capturing the entire site from the air and organizing the data as images and three-dimensional data, it becomes easier to visualize the condition of large sites. Rather than completely replacing traditional ground inspections, it can be used as a complementary method to reduce omissions in site checks and to make it easier for stakeholders to make decisions while viewing the same materials.

Why Drone Surveying Can Streamline As-Built Verification

The reason drone surveying is well suited for as-built verification of solar power plants is that it provides a wide-area aerial overview. In a solar power plant, panel rows, mounting racks, access paths, fences, graded surfaces, drainage facilities, and so on are distributed across the entire site. From ground level you may be able to see the equipment directly in front of you, but it is difficult to grasp the overall layout, misalignment of rows, or trends across the whole site. By photographing from above with a drone, you can view the entire site like a single map, making it easier to detect localized irregularities.

What's important in as-built verification is to objectively record site conditions. If the person in charge relies only on impressions they had on site, the basis for later explanations will be weak. Using aerial photographs, orthophotos, point cloud data, and elevation data obtained from drone surveys makes it easier to keep a record of the post-construction condition. This makes those records useful not only as verification materials at completion but also as baseline documents for future renovation and maintenance management.

Time-saving effects can also be expected. When inspecting a large power plant on foot, just getting around can take a lot of time. This is especially burdensome in summer or on sloped terrain, where on-site inspection itself can be a strain. By using drone surveying, you can set the flight area in advance and carry out the necessary captures in one go, making it easier to organize the scope of on-site checks. It is not realistic to complete all inspections with drones alone, but because you can first obtain an overview of a wide area and extract the locations that need checking, you can focus ground inspections more effectively.

Drone surveying is also well suited to comparing as-built conditions. By overlaying design drawings, construction plans, past survey data, and pre-construction terrain data, it becomes easy to see where things are generally as planned and where there are discrepancies. In solar power plants, even small changes in the post-development terrain or racking positions can affect drainage and maintenance access routes. If comparable data are available, differences can be organized as positional and elevation deviations rather than relying on subjective judgments.

Furthermore, a major advantage is that it makes explanations to stakeholders easier. Aerial photographs and three-dimensional data are materials that even those unfamiliar with the site can understand intuitively. For clients and managers, indicating the relevant locations within an overall map communicates more effectively than lining up dozens of on-site photos. When sharing the results of as-built verification and deciding on necessary corrective actions or additional checks, drone survey data becomes an effective common reference.

Key items to check during as-built verification

In as-built verification of a solar power plant, the first step is to check the overall condition of site development. The height of the developed surface, slopes, shapes of cut-and-fill, finishing of slope faces, and the direction in which rainwater flows all affect stable operation of the plant. Especially on developed sites, if drainage does not flow as intended it can lead to muddy access roads, slope erosion, and ground deformation around the racking. By using drone surveys to identify elevation differences and changes in terrain, you can confirm broad-scale trends that are easy to overlook from the ground.

Next, verify the layout of the panel rows and racking. At a solar power plant, many racks are aligned with a consistent orientation and spacing. If the row alignment is irregular, it can affect not only appearance but also the clearance between adjacent rows, shading effects, and the ability to secure maintenance walkways. Aerial imagery makes it easier to identify row curvature, layout bias, changes in aisle width, and how the ends are finished.

The orientation and tilt of the panel surfaces are also subject to inspection. If the azimuth and angles assumed in the design differ significantly from the as-built conditions on site, it can become difficult to reconcile with power generation simulations and shading analyses. However, there are limits to definitively determining fine angles and the mounting condition of components from drone surveys alone. By combining three-dimensional data with ground-based measurements, it becomes easier to identify overall trends and locations that require additional verification.

Service access paths and inspection routes should also be checked. A power plant is not finished when construction ends; after operations begin, inspections, vegetation control, cleaning, repairs, and equipment replacements are required. If there are sections with insufficient path width, steep slopes that make work difficult, or areas prone to becoming muddy due to drainage, the burden of maintenance increases. Using drone survey data, you can obtain an aerial overview to verify the continuity of paths and accessibility to equipment.

Connections with drainage facilities and surrounding structures should not be overlooked. Gutters, catch basins, drainage channels, detention ponds, the toe of slopes, and fence lines can be difficult to assess for problems when inspected individually on site. Estimating the flow of water across the entire site from above and identifying low-lying areas and spots where water tends to accumulate can provide clues for early detection of post-construction defects. However, actual drainage capacity and ponding conditions need to be evaluated together with checks during rainfall and ground-level inspections.

Fences, gates, the perimeter, and areas near the boundary with neighboring properties are also aspects that should be documented during as-built verification. Because a solar power plant covers a large area, inspecting the perimeter takes time. If you photograph the perimeter with a drone, it becomes easier to confirm the condition of fence installation, connections to roads, elevation differences with adjacent land, and the potential for rainwater inflow from outside. When determining the boundary itself, compare with boundary documents and survey results, and verify on the ground as necessary.

Preparations to Complete Before On-Site Flights

To streamline as-built verification in drone surveying, pre-flight preparation is important. First, clarify what you want to verify. Even within as-built verification, the required shooting area and types of data change depending on whether you emphasize checking the finished surface, mounting-frame placement, or coordination with the drainage plan. If you shoot with an unclear objective, problems can arise later such as lacking photos from necessary angles, missing the areas you want to check, or insufficient reference information.

Next, organize design drawings, construction drawings, layout plans, survey maps, boundary documents, and so on in advance. Data acquired by drone can be useful for understanding the site on its own, but its value as as-built verification increases when compared with design information. You need to confirm which drawings will serve as the reference, what coordinate systems and scales the drawings use, and whether the latest changes have been incorporated.

Setting the flight area is also essential. At solar power plants, not only the site itself but also perimeter roads, drainage outlets, boundaries with adjacent properties, and access roads may need to be checked. If you only photograph the equipment within the site, it can become difficult to judge how it interfaces with the surroundings. Depending on the purpose of the as-built verification, it is important to plan the flight to include the necessary surrounding areas.

Confirmation of safety and legal aspects is also necessary. When flying a drone, check aviation laws, the flight rules of the Civil Aviation Bureau of the Ministry of Land, Infrastructure, Transport and Tourism, on-site safety rules, permission from landowners and facility managers, and consideration for surrounding third parties and vehicles. In areas with flight restrictions—such as around airports, densely populated areas, emergency-use airspace, and around events or critical facilities—you must confirm required procedures and whether flight is permitted in advance. Since photovoltaic power plants have electrical equipment, overhead lines, access roads, workers, heavy machinery, and material storage areas, it is important to check site conditions on the day of flight and decide on takeoff and landing sites and the permitted access area.

It is also necessary to organize how reference points, ground control points, and verification points are handled. When conducting as-built verification and dealing with position, dimensions, or elevation, images alone may be insufficient. By installing reference points on site as needed and confirming their positions with surveying instruments, you can increase the reliability of drone survey data. It is also important to distinguish between areas that require precision and areas intended for overall situational awareness.

Weather and capture conditions also affect the results. Strong winds, rain, dense fog, strong backlighting, and extreme shadows can impact image quality and flight safety. At solar power plants, panel surfaces tend to reflect light, so their appearance can change depending on the time of day. When using images for as-built verification, record the capture conditions to prevent misinterpretation of the data later.

Basic Procedure for Drone Surveying

As-built verification using drone surveying is most efficient when carried out in the sequence of defining objectives, flight planning, field checks, image capture, data processing, comparative checking, and report compilation. First, decide what you want to determine in this verification. For example, if you want to check the finished condition of a graded surface versus the arrangement of rows of mounting frames, the flight altitude, image overlap, placement of ground control points, and the deliverables used for verification will differ.

In the flight plan, ensure the entire power plant can be photographed with the required accuracy and coverage. If photo overlap is insufficient, data may be missing or distortions may occur during post-processing. For as-built verification, not only fine details but the continuity of the whole is important, so a plan that captures the entire target area without omission is necessary. Pay special attention to site edges and areas with elevation differences, as coverage tends to be insufficient there.

At the site, check the takeoff and landing locations, obstacles, worker traffic flow, wind conditions, and the positions of power lines and trees. At solar power plants, racking and panels are arranged in a regular pattern and may look monotonous from above, but at ground level aisles and equipment can be intricately interwoven. Secure a safe flight path and, when necessary, share flight times and access areas with the site supervisor.

In photography, we differentiate between vertical photography to grasp the overall site and oblique photography to check equipment risers, slopes, and peripheral areas. Vertical photography is suitable for orthophotos and plan comparison, while oblique photography helps capture the site's three-dimensional conditions. For as-built verification, step differences, drainage structures, and slope conditions—which are hard to discern from plan views alone—are also important, so we combine multiple shooting methods as needed.

After image capture, we generate orthophotos, three-dimensional point clouds, elevation data, and other products from the images. Orthophotos are deliverables that allow aerial photographs to be used like maps. They are suitable for checking layout, verifying pathway widths, and inspecting perimeter areas. Point cloud data can be used to understand the site in three dimensions. It is useful for confirming the height of graded surfaces, slope geometry, and the three-dimensional arrangement of mounting frames.

Finally, compare the data with design information and past records. In as-built verification, it is not enough to simply look at the captured data. Overlay the captured data with design drawings and construction plans to identify locations with discrepancies, and determine whether those discrepancies are acceptable or require additional checks. When using the results as as-built documentation for public works or documents specified by the client, confirm in advance the applicable standards, instructions from the supervising inspector, submission formats, and methods for verifying accuracy. Recheck necessary locations on the ground and proceed with corrective actions and record-keeping. By establishing this workflow, drone surveying becomes a practical means for as-built verification rather than merely photography.

How to Use Survey Data for As-built Verification

Data acquired by drone surveying should be used according to its intended purpose. The clearest way to utilize it is plan view verification using orthophotos. By organizing images of the entire power plant taken from above, you can check at a glance the alignment of panel rows, maintenance aisles, fences, drainage facilities, and the extent of earthworks. Even when positional relationships are hard to grasp in ordinary photographs, orthophotos allow verification in a way that feels close to a drawing.

When checking the placement of mounting racks and panels, verify them by overlaying the design placement lines and partition lines. This makes it easier to understand misalignment of rows, end detailing, aisle widths, and clearances between pieces of equipment. In particular, at the edges of power plants and on irregularly shaped sites, there may be areas that are difficult to lay out as designed. Using drone survey data makes it possible to identify such areas within the overall context and makes it easier for stakeholders to verify them.

For checking site surfaces and drainage, elevation data and 3D data are useful. Even places that look flat from the ground can have low areas where water tends to accumulate when viewed over a wider area. By checking changes in elevation, you can assess which direction rainwater is likely to flow and whether there are spots near pathways or racking where water is likely to pond. Actual drainage conditions require observation during rainfall and on-site verification, but you can narrow down suspicious locations in advance.

It can also be used to verify differences in as-built conditions. By acquiring data at stages such as before construction, after site preparation, after racking installation, after panel installation, and at completion, you can track construction progress and changes over time. This makes it easier to see at which stage the terrain changed, over what area work progressed, and where any changes occurred. If problems arise later, comparing with past data makes it easier to investigate the cause.

When using a report, combining an overall view with enlarged views makes it easier to understand. An overall view alone does not show details, and an enlarged view alone does not convey positional relationships. First show the relevant location within the overall view, then enlarge it and explain the condition; this sequence makes it easier to communicate to stakeholders who have not been to the site. In reports for as-built verification, it is important not only to describe the conclusions reached but also to state which materials were used as the basis for those conclusions.

Inspection results can also be used for corrective action management. By organizing points requiring verification on drone survey data and recording the results of on-site checks and the status of corrective actions, you can reduce unverified items and overlooked responses. On large sites such as solar power plants, managing corrective measures through verbal reports or individual photos alone can easily cause confusion. By organizing around data that includes location information, you can clarify the process of verification, instruction, response, and re-verification.

Points to keep in mind to maintain accuracy

When using drone surveying for as-built verification, you need to clarify your approach to accuracy. Images captured by drones are convenient, but simply taking pictures does not automatically produce high-precision survey results. Decide the accuracy required according to the objective, and put in place the shooting conditions, control points, calibration points, check points, processing methods, and verification methods needed to meet that accuracy.

First, positional accuracy and visual clarity are separate things. Even if aerial photos look good, positions can be offset when overlaid on drawings. When determining dimensions or positions during as-built verification, you need to correct the data using on-site control points or known points and confirm consistency with the design drawings. In particular, when judging locations near boundaries, equipment layouts, or drainage facilities, the method of establishing reference points is important.

Next, attention must also be paid to height accuracy. When checking the elevation or slope of a graded surface, image processing alone can produce large errors. If grass, materials, temporary structures, panels, or mounting racks are recognized as the ground surface, the data may differ from the actual ground elevation. When reviewing elevation data, confirm that the ground surface and equipment tops are not mixed, and supplement with on-site measurements as necessary.

Imaging conditions also affect accuracy. Conditions such as insufficient photo overlap, heavy shadows, strong reflections, wind causing the aircraft to be unstable, or inappropriate flight altitude can reduce the reproducibility of the data. Solar panels are highly reflective and have continuous dark surfaces, which can make it difficult for image processing to detect feature points. Photographing not only the panels themselves but also the surrounding terrain, walkways, and perimeter areas makes it easier to improve the stability of data processing.

Also, the information on the design drawings must be checked. Even if the as-built data are correct, if the drawings used for comparison are outdated or do not reflect changes, differences may be mistakenly identified. If changes occurred during construction, the parties involved need to confirm which drawing should be treated as authoritative. In as-built verification, not only the accuracy of the survey data but also the correctness of the design information being compared is equally important.

Finally, distinguish what can and cannot be determined by drone surveying. Aerial data cannot confirm bolt tightness, the condition of electrical connections, the internal condition of structural members, or the construction state of underground sections. These require separate inspections or tests. Drone surveying should be positioned as an efficient means of verifying wide-area shapes, layouts, topography, appearance, and progress, and it is practical to use it in combination with necessary on-the-ground verification.

Approach for Combining with Conventional Verification Methods

Drone surveying is convenient, but it does not eliminate the need for all traditional as-built verification. For as-built verification of photovoltaic power plants, on-site measurements, visual inspections, photographic records, construction records, and inspection documents remain important. Drone surveying is effective when used to streamline these verifications, narrow down what needs to be checked, and make explanatory materials easier to understand.

For example, you can inspect the entire site with a drone survey to identify locations where row irregularities or insufficient aisle widths are suspected. After that, measure the corresponding locations on the ground to confirm the necessary dimensions and conditions. Following this workflow makes it easier to prioritize what to check than to walk the entire site in detail on foot. The larger the power plant, the greater the effect of this preliminary assessment.

Also, conducting drone surveys at each construction stage helps with process management. If you retain data at milestones such as after site preparation, after racking installation, after panel installation, and after external works completion, you can review past conditions when you need to check later. As-built verification should not be carried out only immediately before completion; to prevent rework, checks at intermediate stages are also important.

Combining them with on-site photographs is also effective. Use drone aerial photos to show the overall location and ground photographs to show detailed conditions; doing so makes reports easier to understand. Because aerial photos alone do not reveal fine details and ground photographs alone do not show positional relationships, combining both enhances explanatory power. In particular, for areas requiring corrective action or locations under discussion, keeping a set of the overall-location photos and the detailed photos makes later verification easier.

This is a point to consider for coordination with construction records and inspection records. If you store the results of as-built verification only as standalone documents, they will be difficult to find later. By organizing the confirmation date, scope of coverage, imaging conditions, person in charge, verification results, and corrective status, the records become easier to use for future maintenance management and incident response. Drone survey data tends to be large in size, so it is advisable to decide on storage rules and naming conventions in advance.

Data Utilization That Also Supports Renovation and Maintenance

Drone survey data acquired for as-built verification of solar power plants can be used not only for checks at completion but also for operation and maintenance after operations begin. Solar power plants are facilities operated over long periods, and over time the terrain, vegetation, drainage, access routes, and perimeter conditions change. If the completion data is retained as a baseline, it becomes easier to compare the condition several years later.

For example, when checking slope changes or erosion caused by rainwater, having past three-dimensional data and aerial imagery makes it easier to grasp the extent of the changes. With only ground photos, it can be difficult to compare changes unless they were taken from the same position and angle. If the entire power plant is periodically recorded by drone surveying, you can monitor changes across the whole facility over time.

It also helps with weed control and vegetation management. At solar power plants, the growth of weeds and trees can affect inspection work and power generation efficiency. Using aerially captured data makes it easier to identify the extent of vegetation spread, locations where pathways are being blocked, and points of intrusion from the perimeter. By retaining baseline data on pathways and equipment placement during as-built confirmation, it becomes easier to plan subsequent maintenance.

It can also be used for planning refurbishment work. When considering adding panels, repairing mounting racks, adding drainage facilities, improving walkways, or implementing slope stabilization measures, it is important to understand the current topography and equipment layout. If past as-built data are available, the effort required to ascertain site conditions before renovation can be reduced. This is especially true for older power plants where existing documentation may not match current conditions, so obtaining the latest state through drone surveying is worthwhile.

It can also indirectly help with investigations into the causes of reduced power generation. Decreases in power output can be related to multiple factors such as equipment faults, soiling, shading, wiring, and weather conditions. Although drone survey data alone cannot determine the cause, it can provide material to check the causes of shading around panels, changes in terrain and vegetation, and changes in equipment layout. If data from the as-built verification are available, the initial state and the current state can be compared, making it easier to organize the starting point of the investigation.

Thus, the data obtained through as-built verification should not be considered only for the time of completion but treated as baseline data for long-term operation. Solar power plants can differ in their ability to operate stably depending on the quality of maintenance after completion. By continuously recording site conditions using drone surveying, it becomes easier to establish an information base that can be used consistently for inspections, repairs, renovations, and the preparation of explanatory materials.

Summary

As-built verification of a solar power plant requires checking many elements over a wide area, such as earthworks, mounting structures, panel layout, access routes, drainage, and the perimeter. Relying solely on ground inspections makes it difficult to grasp the overall picture, and the task is prone to missed checks and difficulty explaining findings. By using drone surveying, you can get an overview of the entire site and efficiently organize the as-built condition while comparing it with design information and past data.

In particular, plan-view checks using orthophoto images, terrain verification using three-dimensional data, and progress monitoring using time-series data are methods that align well with the practical work of solar power plants. Using aerial data makes it easier to identify disturbances in panel rows, the continuity of pathways, drainage directions, and the condition of perimeter areas. Furthermore, because stakeholders can confer while viewing the same materials, this also helps with decisions on corrective measures and the preparation of reporting documents.

On the other hand, drone surveying is not a cure-all. To ensure positional and height accuracy, establishing reference and control points, defining imaging conditions, processing data, and verifying consistency with drawings are necessary. Also, items that cannot be determined from the air—such as the electrical connection status and the internal condition of structural members—need to be confirmed on the ground or combined with other inspections. Drone surveying should be used to complement conventional verification methods and as a means to improve the efficiency and explanatory power of on-site inspections.

Data obtained from as-built verification can be used not only as records at completion but also for future maintenance and retrofit planning. By regularly documenting the condition of the power plant and enabling comparisons of changes over time, you increase the information available for maintenance decision-making. Drone surveying is an effective option for confirming the construction quality of solar power plants and establishing a management system geared toward long-term operation.

If you want to streamline as-built verification for a solar power plant, it is important to first understand the entire site and prepare survey data that can be compared with the design information. If you want to reduce the burden of on-site checks while keeping records that are easy for stakeholders to understand, organize the division of responsibilities for legal compliance, safety, accuracy, and coordination with ground inspections, and then consider a site management system that leverages drone surveying.