How to Verify the Area and Slope of a Solar Power Plant Using Drone Surveying

At a solar power plant, understanding the site area, panel mounting surfaces, slopes, access roads, drainage routes, and the relationships with surrounding trees and adjacent properties affects the accuracy of design, refurbishment, and operations and maintenance. In particular, area and slope relate to panel layout, racking plans, site formation conditions, drainage problems, maintenance access routes, and identifying causes of reduced power generation, so judging solely by on‑site impressions is likely to lead to oversights. By using drone surveying, even large plants can be recorded from above across the site, making it easier to verify current conditions with numerical data and drawings.

However, the area and slope obtained by drone surveying can vary in accuracy depending on capture conditions, reference points, image processing, and the condition of vegetation and structures. When using these results for construction decisions or safety judgments, it is important to confirm the assumptions behind the deliverables and, if necessary, combine them with ground surveying or on-site inspections. This article summarizes the approach to checking the area and slope of solar power plants using drone surveying, how to interpret the data, and practical points to note.

Table of Contents

• Why verifying area and slope is important for solar power plants

• Area information that can be verified with drone surveying

• Slope information that can be verified with drone surveying

• Site conditions to prepare before surveying

• Workflow for capturing images and generating data to verify area

• How to interpret elevation data to verify slope

• Practical points for verifying panel surfaces, site area, and embankments separately

• How to utilize area and slope data in design and refurbishment

• Accuracy and safety management considerations for drone surveying

• Summary

Why Area and Slope Verification Is Important for Solar Power Plants

In managing solar power plants, it is important to grasp not only the generating equipment itself but also the terrain of the entire site and the usable area. Reductions in power generation and maintenance issues are not necessarily caused only by faults in panels, wiring, or equipment; site conditions such as ground tilt, drainage flow, vegetation overgrowth, narrow maintenance access, settlement around mounting structures, and slope deformation can also have an impact.

Checking the area is not simply a matter of knowing how many square meters the site has. It is important to separately understand the area where panels can actually be installed, the passages available for maintenance and inspection, the space for heavy machinery and work vehicles, the surroundings of drainage facilities and balancing ponds, and the management areas inside and outside fences. The area shown on cadastral maps or past drawings does not necessarily match the area usable on the current site. The actual conditions may have changed due to post-development alterations in shape, added passages, slope expansions, or space changes resulting from equipment upgrades.

Checking slopes is equally important. At solar power plants, it is necessary to understand not only the orientation and tilt of the panel surfaces but also the slope of the ground itself, drainage directions, low-lying areas where rainwater tends to collect, slopes prone to soil runoff, and gradients that can impede vehicle access. In areas with steep slopes, the approach to site formation and mounting structure installation changes, and safety measures for inspections are also required. Even gentle slopes can, over a wide area, cause water to collect and lead to mud, bogging, or erosion.

Traditional on-site inspections mainly involved personnel walking the site to observe conditions and measuring only the necessary points. However, solar power plants cover large areas and have continuous rows of panels, making it difficult to grasp overall elevation changes and the continuity of slopes from the ground. Using drone surveying makes it possible to capture the entire site from above and generate orthomosaic images and three-dimensional data from the photos. This allows area and slope to be checked on drawings and makes it easier for stakeholders to share the same current site conditions.

Especially for renovation work, consideration of expansions, investigating causes of reduced power generation, post-disaster inspections, drainage improvements, weed-control planning, and checks near boundaries, it is practically useful to evaluate area and slope together. Looking at area alone makes it difficult to reflect in plans if a site is steep and hard to use. Conversely, looking at slope alone makes it hard to determine priorities and the scope of work if the area of the affected range is not known. Drone surveying has the advantage of making both easy to handle on the same dataset.

Area information that can be confirmed by drone surveying

Area information that can be confirmed by drone surveying includes not only the total site area but also detailed extents for equipment and terrain. Typical examples are a power plant's management area, panel installation areas, unused land, access paths, slopes, areas around drainage facilities, areas targeted for mowing, and management boundaries inside and outside fences. Viewing these on a single plan or orthophoto makes it easier to organize area distributions that are difficult to understand just by walking the site.

An orthoimage is an image created by correcting the distortions in photographs taken from above and stitching them together so they resemble a map. Ordinary aerial photographs show distortions in distance and shape due to camera angle and differences in terrain elevation, but converting them into an orthoimage makes it easier to confirm planar spatial relationships. At solar power plants, panel rows, mounting racks, access paths, fences, drainage channels, slopes, and surrounding roads can be seen at a glance, making orthoimages a convenient format as basic reference material for area verification.

When verifying an area, you must first define the scope of what is being managed. The site boundary of a power plant does not necessarily match the area actually being managed. If leased land, adjacent properties, access or service roads, mowing areas outside the fence, maintenance areas for drainage facilities, or similar elements are involved, it is important to decide in advance how far to measure. By overlaying the area onto images obtained by drone surveying, it becomes easier to compare the boundary on the drawings with how it appears on site.

By checking the area available for panel installation, you can assess row-by-row layouts, empty spaces, potential sites for future expansion, and areas susceptible to shading. At some power plants, unused land may remain within parts of the developed site, or there may be locations where panels are difficult to place due to slope or drainage conditions. By delineating these on orthophotos, it becomes easier to determine the practically usable area rather than simply the site area.

From a maintenance and management perspective, the area of access routes and workspaces is also important. Tasks such as mowing, inspections, cleaning, equipment replacement, and wiring checks require space for people and vehicles to move safely. If drawings can identify narrow passages, areas prone to becoming muddy after rain, or locations close to slopes, it becomes easier to plan the work. Area verification by drone surveying contributes not only to the design of power generation facilities but also to the efficiency of maintenance management.

Do not overlook confirming the areas around slopes and drainage facilities. In solar power plants, there are slopes around the developed site where rainwater gathers and where soil is prone to wash away. Measuring these zones as areas helps when deciding repair extents, mowing areas, drainage improvement extents, and inspection priority areas. Especially at large plants, sharing extents using only on-site photos can lead to misalignment in understanding, so aerial surface data is effective.

Slope information that can be verified by drone surveying

In drone surveying, you can use 3D data and elevation data created from photographs to check changes in the heights of ground surfaces and structures. Slope information is important for understanding the overall topography of a power plant. It provides clues about which direction the ground is sloping, where rainwater is likely to flow, how steep the slopes are, and whether subsidence or steps are occurring beneath rows of panels.

There are several types of slopes considered in solar power plants. First, there is the overall site topographic slope. This is to determine what kind of terrain the plant is located on: mountainous areas, hilly areas, developed land, or flat land. Next, there are local slopes near the panel installation surfaces. These relate to rack height adjustment, the alignment of panel rows, walking safety during inspections, and the flow of rainwater. Additionally, there are embankment slopes and the slopes of maintenance roads. These affect disaster risk and the safety of operation and maintenance.

To check slope, formats such as spot elevations, contour lines, shaded relief maps, and slope distribution maps are used. Spot elevations are a method for confirming the height of a specific location. Contour lines connect points of equal elevation with lines, allowing the reading of terrain undulation. Shaded relief maps display the terrain as if illuminated, making it easier to visually grasp surface irregularities. Slope distribution maps represent the gradient of the ground surface by color-coding, making it easy to compare steep and gentle areas.

At solar power plants, slope can affect power generation efficiency and maintainability. The panels’ tilt is set by the mounting racks, but if the ground slope is large, the amount of height adjustment for the racks increases and the elevation differences between rows become greater. Also, if the ground is unevenly sloped, rainwater can concentrate around certain rows or around equipment. If puddles or erosion occur, wiring, foundations, access paths, and slopes may be affected.

Slope information can also be used to investigate the causes of reduced power generation. For example, confirming the surrounding terrain, slopes, and the positions and heights of trees makes it easier to estimate the areas that are likely to be shaded depending on the season and time of day. While drone surveys alone cannot determine all impacts, understanding the terrain and equipment layout makes it easier to cross-check with power generation data and on-site inspection results.

Slopes also affect safety management. If the walkways used by inspectors, areas where grass cutting is performed, or routes used by vehicles are steep, it is necessary to review work methods and timing. After rain or snowfall, or during strong winds, slips and vehicles becoming stuck are more likely on sloped areas. Visualizing slopes with drone surveying helps with pre-work warnings and the setting of inspection routes.

Site conditions to clarify before surveying

Before checking area and slope in drone surveying, it is important to organize the on-site conditions in advance. Image capture itself can often be completed in a relatively short time, but if preparations are insufficient, problems can occur such as the required area not being captured, inability to verify accuracy, or deliverables not matching what stakeholders want. By deciding beforehand on the survey’s purpose, target area, required deliverables, and site constraints, you can reduce rework in later stages.

First, you should confirm why you are checking the area and slope. The level of detail required in the data will vary depending on whether it is pre-construction planning for a new installation, refurbishment of an existing power plant, a post-disaster inspection, an investigation into the causes of reduced power generation, or organizing the scope of operation and maintenance. For example, wide-area orthophotos are effective for a rough understanding of the site, but to check for poor drainage or subsidence you need to examine elevation differences and localized surface irregularities more carefully.

Next, clarify the survey extent. At a solar power plant, photographing only inside the fence may not be sufficient. Surrounding roads, drainage outlets, the bottom of slopes, adjacent trees, features that may cast shadows, and perimeter areas that need to be checked for management may also be included. Conversely, avoid including neighboring properties or areas with shooting restrictions without permission. It is important to align in advance among managers, owners, contractors, and maintenance personnel on how far the coverage should extend.

Consider how to handle control points and reference markers. When overlaying area and slope onto drawings or existing data, you need to align positional references. Installing easily identifiable reference markers on site and confirming their coordinates and elevations will make it easier to align the created data. Even when using platforms or positioning methods that provide high-precision location information, having on-site verifiable control points makes it easier to check and explain the deliverables.

Shooting conditions also affect the results. At solar power plants, panels tend to reflect light, and the appearance of images changes depending on the time of day and weather. Reflections, deep shadows, strong winds, rain, fog, dense vegetation, and snow cover can affect image processing and interpretation of the ground surface. If the primary purpose is area confirmation, conditions in which panels, paths, and fences are clearly visible are desirable. If the primary purpose is slope confirmation, it is also necessary to check the condition of vegetation and materials that cover the ground surface.

Preparation for safety management is also indispensable. Inside the power plant there are electrical installations, mounting racks, wiring, monitoring devices, work vehicles, and people coming and going. Before flight, confirm the takeoff and landing locations, flight altitude, flight route, emergency response measures, notification to stakeholders, and access control. If there are roads, residences, transmission facilities, trees, or slopes nearby, it is necessary to identify and assess the flight risks in advance. Depending on the flight location and flight method, confirmations, permissions, or approvals based on relevant laws and the administrator’s rules may also be required. It is a prerequisite that the plan can be implemented safely, not just that the quality of the survey results is ensured.

Workflow for Capturing Images and Creating Data to Verify Area

In drone surveys for area verification, the typical workflow is to photograph the entire power plant with a consistent overlap and stitch the images together to produce an orthomosaic. Even when the survey area is large, planning flight routes allows you to acquire consecutive photos under the same conditions. To properly verify area, it is important to prevent missed coverage, ensure image overlap, and organize the reference positional information.

In the photography plan, set the coverage area slightly larger. For features such as fences, slopes, drainage channels, and perimeter walkways, it is easier to verify them if you photograph them including the surrounding context rather than shooting right up to the boundary. You can crop out areas later, but you cannot supplement areas that were not captured during post-processing. In particular, the power plant perimeter is important for boundary verification, drainage checks, and organizing mowing areas, so confirm in advance that the necessary area is included.

Decide the flight altitude based on the required resolution and the size of the target area. Flying lower makes details easier to see, but increases the number of images to capture and lengthens processing time. Flying higher allows efficient coverage of a larger area, but fine boundaries and small pieces of equipment may become harder to discern. For area verification, it is important to ensure a resolution that can resolve panel rows, walkways, fences, drainage channels, and slope edges.

Overlap between photos is also important. In drone surveying, positional relationships are estimated by identifying the same feature points across multiple photos. Therefore, if there is insufficient overlap between photos, the connections between images can become unstable and some shapes may become distorted. At solar power plants, panels are arranged regularly and similar patterns repeat, so under certain conditions it may be difficult to identify feature points. Include walkways, the ground surface, slopes, and perimeter areas in the photography to create conditions that make data processing more stable.

When an orthophoto has been created, delineate on the map the areas you want to check. Separate the entire site, the panel installation area, access paths, slopes, unused land, areas around drainage facilities, and calculate their areas. At this stage, it is important not to rely solely on boundaries visible in the image, but to cross-check with existing drawings and management documents. Fences and paths visible on site do not necessarily coincide with legal boundaries or contractual limits. Depending on the purpose of the area verification, clarify which criteria you will use to define the boundaries.

Area data should be compiled in a form that stakeholders can readily understand. Simply presenting numbers alone can make it difficult to tell which area those measurements refer to. Overlaying the areas on an orthophoto and labeling each section makes it easier to align understanding among designers, maintenance personnel, clients, and contractors. For future comparisons, it is also useful to record the capture date, target area, survey method, handling of control points, and data creation conditions.

How to Read Elevation Data to Check Slope

To check slope, read the elevation differences of the ground surface from 3D data and elevation data created from photographs. In solar power plants, because panels and racking hide the ground surface, it can be difficult to determine ground slope from the shape seen from above alone. Therefore, it is necessary to view the data with an understanding of which data represent the ground surface and which include structures.

There are elevation datasets that represent surface heights including panels, trees, and equipment, and others that are processed to estimate heights close to the ground surface. At solar power plants, because panel surfaces cover wide areas, the generated elevation data may reflect the height of the panels. While useful for seeing the general undulation of a site, if you want to know the slope of the ground itself you need to carefully check areas where the ground surface is visible, such as walkways, spaces between panels, slopes, and the perimeter.

When reading slope, first confirm the positional relationship between high and low points. Check which direction the entire power plant slopes downward, whether the central area is shaped in a way that tends to collect water, and whether there are any steep drops on the slope side. Next, check for local irregularities. Steps or settlements between panel rows, at the ends of access roads, around drainage channels, or at the boundaries between embankments and cuttings can cause rainwater to pool or obstruct passage.

Using contour lines makes it easier to read changes in slope. Where contour lines are closely spaced, elevation changes occur over a short distance, so the slope can be judged as steep. Areas where contour lines are widely spaced are relatively gentle terrain. However, if contours are generated from data that include panels and mounting racks, the shapes of the equipment may appear as if they are part of the terrain. When the purpose is ground verification, focus assessment on parts where the ground surface can be checked, and combine with on-site surveying or ground verification as necessary.

Creating a slope distribution makes it easier to visually compare differences in gradients within a power plant. Steep slopes, gentle flat areas, pathway gradients, drainage directions, and so on can be checked on a single diagram, making it easier to select locations that should be inspected first. Especially in large power plants, simply walking the site can miss small terrain changes. Using drone surveying to grasp the overall picture and then examining any areas of concern on the ground in more detail is efficient.

When looking at slope data, it's also important not to put too much trust in the numbers. The results of drone surveying vary in accuracy depending on shooting conditions, ground control points, image overlap, the appearance of the ground surface, the condition of vegetation, and processing conditions. In particular, in areas where grass is tall, the surface of the grass may be captured as the elevation instead of the ground surface. Rather than making construction decisions based solely on slope values, it is practically safer to judge them in combination with on-site inspection, existing drawings, traces of drainage, and inspection records.

Practical points for checking panel surfaces, the site, and slopes separately

When verifying the area and slope of a solar power plant, it is important not only to look at the whole at once but also to check the panel surface, the site, and the slopes separately. Although these are within the same plant, their management purposes differ. The panel surface relates to power generation performance and equipment layout, the site relates to maintenance management and future planning, and the slopes relate to safety, drainage, and sediment runoff. By separating and organizing them according to purpose, the intended uses of the survey data become clear.

When inspecting panel surfaces, check the alignment of rows, open spaces, variations in tilt, locations prone to shading, and the relationship with the surrounding terrain. Seen from above, irregularities in panel rows and biases in layout become much easier to detect. In existing power plants, the as‑built conditions may not match the design drawings. Equipment added later, replaced panels, changes to access paths, and growth of nearby trees can alter the current layout. Confirming the present layout with a drone survey makes it easier to use as baseline documentation for retrofits and maintenance.

When checking the site, distinguish between the area to be managed as the power plant and the area that can actually be used. Even land that appears expansive in plan can include steep slopes, drainage channels, detention basins, slope faces, trees, and spaces that are difficult to use for maintenance. By separating usable areas from difficult-to-use areas on orthophotos, it becomes easier to assess potential for expansion, material storage locations, work-vehicle routes, and mowing plans.

When checking slopes, both area and inclination are important. Slopes are often not the direct installation sites for power generation equipment, but if collapse or erosion occurs they can affect panel rows, walkways, drainage facilities, and fences. Drone surveys make it easier to observe the entire slope from above and identify vegetation growth, bare ground, traces of rainwater flow, sediment accumulation, and signs of collapse. Viewed together with slope distribution and elevation differences, this makes it easier to determine inspection priorities.

From a drainage perspective, it is important to view the site and slope faces as a continuous whole. Confirm where rainwater generated within the power plant flows, where it collects, and where it discharges to the outside. If the terrain slope and the positions of drainage facilities are not aligned, water can pond or flow to unexpected locations. Elevation data from drone surveys makes it easier to estimate water flow, but actual drainage capacity and the presence of blockages must be verified on site.

When compiling inspection results, record the panel surface, the site, and the slopes separately, and ultimately integrate them into a single current-condition report. When explaining to stakeholders, mixing panel issues, land-use issues, and slope or drainage issues makes discussions hard to follow. Organizing area, slope, inspection findings, and response policy by category makes it easier for the power producer, maintenance company, design team, and construction team to make decisions.

How to Utilize Area and Slope Data in Design and Renovation

Area and slope data obtained from drone surveys are not just for verification; they are most effective when used to inform decisions on design, refurbishment, and maintenance. In solar power plants, current-condition data are needed in many situations, such as equipment renewal, panel additions, racking repairs, drainage improvements, pathway maintenance, slope repairs, and weed-control planning. Capturing the latest site conditions as numerical data and drawings helps reduce discrepancies in planning-stage estimates.

When considering new installations or expansions, it is important to understand the usable area. The total area of the site alone does not determine the actual area where panels can be placed. You must assess the area available for placement after excluding steep slopes, locations prone to shading, areas that should be left for drainage facilities and passageways, and areas that should be kept clear for operation and maintenance. By combining drone-survey orthophotos with elevation data, it becomes easier to reflect on-site conditions even at the desktop planning stage.

For renovation work, it helps verify the interfaces with existing equipment. Because existing panel rows, mounting racks, junction boxes, wiring routes, access aisles, drainage channels, fences, and so on can be inspected from above, it becomes easier to plan the work area and delivery routes. Slope data allows identification of areas that are easily accessible to heavy machinery and work vehicles, areas unsuitable for temporary storage, and areas likely to have reduced workability in rainy weather. Even aspects that are hard to explain through on-site surveys alone can be more easily conveyed to stakeholders when diagrammed data are available.

Slope information is particularly important for drainage improvement. You need to confirm where rainwater flows, which low spots tend to collect water, and whether the gradient to the drainage channels is adequate. Locations where puddles form within a power plant are not simply locally low; they can have topography that gathers water from the surrounding area. By checking overall elevation differences with drone surveys, you can review not only local countermeasures but also the drainage plan for the entire site.

For maintenance and management, it can be used to plan mowing and inspections. With area data, it becomes easier to estimate the areas to be mowed and the amount of work. With slope data, locations with a high workload or those requiring safety measures can be identified in advance. Depending on the power plant, it may be necessary to separate work methods for flat areas and slopes. If areas are divided based on drone survey results, it becomes easier to organize work plans and the scope of outsourcing.

It can also be used to help confirm the causes of decreased power generation. Although area and slope data alone cannot definitively determine the causes of reduced generation, they serve as basic reference materials for checking equipment layout, surrounding topography, potential shading, poor drainage, vegetation overgrowth, slope deformation, and the like. When combined with generation data, on-site inspections, and electrical measurements, it becomes easier to narrow down where to focus investigations. In large power plants, first grasping the overall picture leads to more efficient investigations.

Accuracy and Safety Management to Watch for in Drone Surveying

Drone surveying is a convenient method, but to use the collected data correctly, care must be taken regarding accuracy and safety management. In particular, area and slope are sometimes used for design and construction decisions, so you must verify that the accuracy is appropriate for the intended purpose. Even orthophotos or three-dimensional models that look good can affect assessments of area and slope if there are errors in position or elevation.

To ensure accuracy, clearly specify the capture conditions, control points, image processing, and validation methods. It is important to record what area was captured, at what altitude, with what degree of overlap, which reference was used for alignment, and how much offset exists relative to points that can be verified on site. Especially when overlaying existing drawings or design data, if the coordinate system or reference elevation is handled inconsistently, apparent discrepancies will occur. Before using the deliverables, you must check for differences in the references.

As points of caution specific to solar power plants, there are panel reflections and regular shapes. Panel surfaces easily reflect light, and depending on the time of shooting, overexposure or shadows can occur. Also, because identical panels are arranged in continuous rows, image processing can more easily misidentify feature points. Including shots of locations that tend to produce distinctive features—such as walkways, the ground surface, the perimeter, and slopes—makes it easier to improve the stability of processing.

When checking heights and slopes, be aware of the influence of grass and structures. In areas where grass has grown, the top of the grass rather than the ground surface may be reflected as the height. In locations with panels or racks, the data may include the height of the equipment rather than the ground. When checking slopes, be conscious of which surface you are looking at and perform supplementary on-site verification as necessary. For important construction or safety decisions, it is desirable not to rely solely on drone surveys but to combine them with ground verification.

On-site checks before flight are essential for safety management. Inside a power plant there may be electrical equipment and mounting structures, and the surroundings may include roads, buildings, trees, and transmission facilities. Flight routes, takeoff and landing sites, emergency landing locations, workers' access areas, communications status, and wind effects should be confirmed in advance. If surveying is carried out on the same day as maintenance or construction, coordinate so that the movements of people and vehicles do not interfere with the flight plan. Applicable aviation laws, rules of local governments and facility operators, and the power plant's internal safety procedures should also be confirmed beforehand.

Care must also be taken in handling deliverables. Data produced by drone surveys are useful records of current conditions, but they represent the state at the time of capture. The site changes due to vegetation growth, equipment updates, soil movement, disasters, and construction. When using past data, confirm when it was captured and whether it can still be considered representative of the current state. If you survey the same area periodically and compare the results, it becomes easier to track changes in land use, slope deformation, and drainage conditions.

Summary

Verifying the area and slope of a solar power plant by drone surveying is effective for grasping the facility’s current condition from a broad perspective and making decisions about design, renovation, and maintenance management easier. For area verification, it is important to separate and organize not only the entire site but also the panel installation area, access routes, slopes, unused land, areas around drainage facilities, and areas to be mowed. For slope verification, it is necessary to understand ground elevation differences, drainage direction, slope gradients, and the safety of work routes, and to make judgments while cross-checking with on-site inspections and existing documentation.

The advantage of drone surveying is that it can record a large power plant as an areal dataset. Overall layout, terrain continuity, drainage flows, and the condition of slopes and perimeter areas—things that are difficult to discern from ground visual inspections alone—can be confirmed as orthophotos and three-dimensional data. This makes it easier for stakeholders to review the scope of renovations, inspection priorities, and work plans while viewing the same information.

On the other hand, the results of drone surveying vary in accuracy depending on shooting conditions, control points, image processing, and the condition of vegetation and structures. Rather than taking area and slope figures at face value, it is important to confirm whether the accuracy meets the intended purpose and, if necessary, combine them with ground surveys or on-site inspections. In particular, when using the data for construction decisions, drainage improvements, or safety measures, you must clarify the data’s basis and limitations before applying it.

To make drone surveying of solar power plants useful in practice, it is important not to stop at capturing images but to compile the results into documentation that integrates area, slope, equipment layout, drainage, and maintenance scope. By understanding the current conditions, it becomes easier to identify issues at the plant and to proceed with decisions on refurbishment or maintenance. If you want to verify area and slope efficiently, consider employing drone surveying after organizing site conditions, required accuracy, safety management, and how the deliverables will be used.