6 points to note when calculating the site area of a solar power plant using drone surveying

In the planning, construction, and operation and maintenance of solar power plants, understanding the site area influences many decisions. There are many situations where area serves as the basis for consideration—such as the extent of site preparation, panel layout, fence length, weed control area, drainage planning, management pathways, and maintenance/inspection access routes. Traditionally, it has been common to combine drawings, on-site surveys, tape measures, and surveying instruments to determine this, but in recent years drone surveying has also been used to record the entire site from above and calculate the area.

However, using images and terrain data obtained from drone surveys does not automatically produce the correct site area. The meaning of the calculated result changes depending on how boundaries are defined, the coordinate system, control points, terrain undulation, vegetation, existing facilities, and data-processing conditions. For solar power plants, site conditions can be complex, such as former forest land, reclaimed or graded sites, sloping terrain including slopes, and sites near reservoirs or waterways. Therefore, it is important to clarify "for which extent and which type of area the measurement will be used."

This article explains six practical points to be aware of when calculating the site area of a solar power plant using drone surveying. To make it useful for preliminary estimates before design, comparisons before and after construction, and confirmation of the scope of operations and maintenance, it organizes the considerations that on-site personnel should verify.

Table of Contents

• Decide in advance the purpose of calculating the site area using drone surveying.

• Note 1 Do not confuse boundary lines with management areas

• Note 2: Organize reference points and coordinate systems before flight

• Note 3: For sites that include undulations and slopes, distinguish between types of area

• Note 4 Consider obstacles and shadows specific to solar power plants

• Note 5: Cross-check the area after image processing with on-site information.

• Note 6 Keep the area calculation results in a format usable for construction and maintenance management

• Summary: Drone surveying helps visualize site area

Decide the purpose of calculating site area using drone surveying in advance

When calculating the site area for a solar power plant, the first thing you should decide is what the area will be used for. The definition of the required area changes depending on whether you simply want to know the total size of the site, confirm the extent of the land to be developed, see the area available for panel installation, or understand the area subject to weeding and maintenance.

For example, the land area recorded in the registry and the area actually managed as a solar power plant may not match. This can occur when only part of a parcel is used, when multiple parcels are combined and treated as a single plant, or when the site includes remnant forest, waterways, access roads, or slopes outside of management. If you simply trace the area visible from an aerial drone survey and calculate the area, the resulting figure may be overestimated or underestimated depending on the intended purpose.

Also, the area used during the design stage differs from the area used for post-construction management. In the design stage, the usable area where panels can be placed and the areas requiring site preparation are important. On the other hand, for operation and maintenance, the area subject to mowing inside the fence, the inspection areas around drainage facilities, and the areas affected by weeds and trees are important. When confirming the current condition of the power plant after construction, it is necessary to make judgments including the actual fence locations, access paths, rows of mounting racks, balancing ponds, drainage ditches, and slopes.

Drone surveying's strength is that it can calculate areas while visually confirming such ranges. By creating an orthophoto from aerial photographs, you can draw lines while viewing the entire site from above and verify the target area. Combining terrain data makes it easier to understand slopes and earthwork shapes. However, because of that convenience, it is important not to confuse the area you can enclose on an image with the legally or administratively defined site boundaries.

In practice, before calculating areas, organizing the intended purpose, the target scope, the required accuracy, and how the deliverables will be used can reduce rework. By distinguishing whether a rough estimate is sufficient, whether the data will be used as construction-management documentation, for stakeholder briefings, or for internal management, the necessary flight plan and the depth of on-site verification will change. In drone surveys of solar power plants, it is more important to decide in advance which operational decisions the survey results will inform than to focus on the mere act of capturing images.

Note 1: Do not confuse boundary lines with management scope

When calculating the site area of a solar power plant using drone surveying, the difference between the boundary line and the management area is what you should pay the most attention to. The boundary line relates to land rights and cadastral boundaries, and does not necessarily coincide with on-site fences or developed areas. If you directly treat fences, roads, slopes, wooded areas, field ridges, and the like visible in a drone survey as the property boundary, it can lead to incorrect area calculations.

In solar power plants, fences are sometimes installed inside the site boundary. This can be to provide a safety margin along the boundary, to secure separation from neighboring properties, to avoid existing waterways or slopes, and so on. In such cases, the area inside the fence may be valid as the maintenance and management area, but it differs from the total area of the land. Conversely, there can be parts of the land that, although owned or used, are excluded from actual power generation equipment or maintenance operations.

When calculating the site area, first clarify which line will be used as the reference. You need to decide whether to base it on the land boundary, the fence, the edge of the development, or the panel installation area. If you calculate the area with this left ambiguous, each stakeholder may interpret it differently. For example, the design team might be looking at the area available for panel placement, while the maintenance team uses it as the grass‑cutting area, which readily leads to discrepancies.

On site, boundary stakes, boundary markers, existing drawings, land area survey maps, cadastral maps, construction drawings, management drawings, and other materials are checked and cross-referenced with positions on images captured by drone surveying. However, legal determinations of boundaries should not be made based solely on drone images. When boundary confirmation is required, judgments are made by combining relevant documents and professional surveying results. Drone surveying is a means of "visualizing" boundaries to make them easier to verify, and it does not, by itself, establish rights relationships.

Also, at solar power plants there are areas that are affected by factors originating outside the site: shade from trees on neighboring land, rainwater flowing in from outside, and sediment inflow from surrounding roads. Even if these are not included in the site area, they are important items to check for operation and maintenance. Therefore, it is practical to record separately the boundary line used for area calculation and the verification area for inspection and maintenance so they are easier to use in practice.

When drawing lines on drone survey deliverables, it is also important to clearly name the lines. Expressing them separately by purpose—such as "assumed site boundary line", "management area inside the fence", "land development area", "panel layout area", and "weed-control target area"—helps prevent misunderstandings when reviewing them later. Rather than leaving only a single area figure, being able to explain which area that figure encloses is the first step to putting drone surveying into practice.

Note 2 Organize reference points and coordinate systems before flight

When calculating site area with drone surveying, organizing control points and the coordinate system before flight is indispensable. Area calculations may seem possible simply by drawing lines on the images, but the reliability of the deliverables depends on which coordinates those images are based on and the positional accuracy with which they are georeferenced. This is especially true for large sites such as solar power plants, where positional offsets can easily affect area calculations.

Control points are reference points used to align images and point clouds obtained from drone surveys to their real-world positions. By establishing clear ground targets and tying them to known coordinates, it becomes easier to minimize positional misalignment in the produced orthomosaic images and terrain data. If control points are insufficient or unevenly distributed, the images may look fine while overall scaling or rotation errors remain. Calculating area under those conditions can therefore include errors larger than they appear.

Checking the coordinate system is also important. Drawings for solar power plants may use public coordinates, site-specific local coordinates, or provisional design coordinates. When overlaying drone survey outputs onto existing drawings, if the coordinate systems do not match, boundaries and equipment positions will be shown offset. Even when calculating area alone, if you plan to compare the results later with design or construction drawings, you should decide in advance which coordinate system to use for the outputs.

Before flight, organize the positions of the control points to be used, their point names, coordinate values, height information, and how they appear on site. At solar power plants, there are panel mounting racks, fences, electrical equipment, vegetation, slopes, and so on within the site, which can make control points difficult to see in aerial photographs. Control points should be installed at locations that can be reliably identified in the captured images and should be distributed without bias across the entire flight area. Arranging them with some spread, such as near the four corners of the site and in the central area, makes it easier to verify overall consistency.

Also, in addition to establishing control points, preparing verification points helps confirm the deliverables. By separating the points used as control points for processing from the points used to verify processing results, it becomes easier to determine how closely the created data matches the actual site. If the purpose of area calculation is a rough estimate, excessive work may not be necessary; however, when the data will be used for construction or management documentation, it is safer to establish a defined verification procedure.

With drone surveying, some aspects can be adjusted in processing software after flight, but a lack of control points or errors in the coordinate system are difficult to correct later. If, after finishing field work, you find it does not match existing drawings or you cannot explain the basis for an area measurement, re-flights or re-surveys may be required. Because solar power plants are extensive and easily affected by weather, sunlight, and wind, rework can be laborious. Organizing control points and the coordinate system before flight improves not only the accuracy of area calculations but also the efficiency of the entire workflow.

Note 3: For sites with undulating terrain or slopes, separate the types of area

When considering the site area of a solar power plant, it is important not to confuse the horizontal area with the actual surface area that includes slopes. The area shown on typical plans is often treated as the horizontal projected area as seen from above. On the other hand, for onsite tasks such as mowing, slope management, weed-control measures, topsoil protection, and stormwater measures, there are situations where the area along the ground’s slope needs to be taken into account. In mountainous areas and on developed/reclaimed land, this difference affects practical decision-making.

Orthoimages produced by drone surveying are suitable for understanding positional relationships as seen from above. They make it easy to check boundaries, fences, rows of panels, pathways, drainage facilities, etc., in plan view, and are convenient deliverables for calculating horizontal projected area. However, at sites with many slopes and steep terrain, the area delineated on an orthoimage can differ from the actual extent of the ground surface that workers walk and manage. The greater the slope, the larger the area measured along the ground surface compared to the horizontal area.

For example, when creating a weed-control plan, estimating the target area using only the horizontal (plan) area can lead to underestimating the amount of work on slopes. Conversely, in design layout considerations, because they are generally based on planimetric extent, using ground surface area as-is can lead to incorrect judgments. Depending on what the area is for, you need to decide whether to use the horizontal area or to refer to an area closer to the ground surface.

In drone surveying, creating terrain data in addition to images helps to understand elevation differences and slopes. By checking gradients from the terrain data, it becomes easier to identify the extent of earthworks, drainage directions, the spread of slopes, and locations prone to sediment runoff. When the purpose of calculating site area is related to maintenance or safety management, confirming information that includes elevation differences as well as the plan view allows for judgments that are closer to practical operations.

However, when calculating area along the ground surface, attention must be paid to data density, noise, and the effects of vegetation. At sites where grass is long, surface data obtained by drone surveys may reflect the tops of the grass rather than the ground. Areas under panels and around mounting structures can also be difficult to observe directly from above. Therefore, when dealing with the surface area of slopes, it is important to clearly state the calculation conditions and, where necessary, combine them with on-site verification.

Separating and recording different types of area can also be effective. For example, organize by purpose such as the horizontal projected area of the entire site, the managed area inside the fence, the area of the panel installation zone, the weed-control target area including slopes, and the inspection range around drainage facilities. This allows designers, constructors, and maintenance personnel to use the correct figures they need for their work even when looking at the same deliverable.

Not all sites for solar power plants are flat. For effective land use, they are sometimes installed on sloped terrain or developed/graded land. When calculating site area with drone surveys, an important practical caution to prevent misunderstandings is not to treat the word "area" as a single concept, but to distinguish whether it means horizontal area, working area, or management area.

Note 4: Consider obstacles and shadows specific to solar power plants

When conducting drone surveys at solar power plants, unlike typical vacant land or agricultural fields, there are obstacles unique to power generation facilities. Panels, racking, junction boxes, collection equipment, substation equipment, fences, monitoring devices, access paths, drainage channels, and weed-control sheets are arranged across the site. Because these appear in aerial photographs, they can affect the delineation and image processing when calculating site area.

Particularly important to watch for are shadows cast by rows of panels. In solar power plants, panels are aligned in a consistent direction, so depending on the time of capture, shadows can stretch long. When shadows overlap the ground or nearby boundaries, fences or terrain edges may become hard to see in the image. If shadows are mistaken for boundaries or structures, errors can occur when tracing lines to calculate area. When choosing the time to capture, be mindful of the length and direction of shadows and select conditions that make the area you want to inspect easy to distinguish.

Also, attention must be paid to reflections on the panels. Depending on the camera angle and sunlight conditions, the panel surface can reflect strongly, making surrounding imagery difficult to see. In images with strong reflections, it can be hard to distinguish panel edges, walkways, and the ground beneath the racking. If you are only calculating the total site area, the impact may be limited, but when you need to divide the panel installation area and maintenance paths into finer sections, image clarity becomes important.

Vegetation is also a major factor in solar power plants. When photographed with overgrown grass, the lower parts of fences, drains, boundary stakes, slope shoulders, and slope toes can be hidden. If trees are on the site or neighboring land, their canopies can cover the ground and make the actual ground boundaries difficult to see. If the area calculated by drone surveying is based on the "area visible in the images," mishandling parts hidden by vegetation can lead to discrepancies with the actual on-site conditions.

For existing power plants, the ground beneath the panels cannot be seen directly from above. Small walkways under the racks and between rows of panels, drainage ditches, localized scour, subsidence, and muddy patches may not be fully identifiable from aerial photographs alone. Even if these do not greatly affect the site area itself, supplementary on-site verification may be necessary when dividing management areas or inspection ranges. Drone surveying is an efficient way to assess large areas, but it cannot completely capture parts that are not visible.

Flight conditions also affect the outcome. On windy days the aircraft’s attitude can become unstable, which can affect image overlap and sharpness. Cloudy conditions can weaken shadows and sometimes make features easier to see, but if brightness is insufficient image quality can suffer. Rain, fog, and strong backlighting also affect image quality and safety. Solar power plants are often located in open areas and can be especially exposed to wind. It is important to prioritize conditions that allow safe flight while ensuring the image quality necessary for area calculation.

As countermeasures against obstacles and shadows, it is effective to walk the site before shooting and check locations that are hard to see, areas with dense vegetation, directions where shadows are likely to extend, and places where boundaries are unclear. If necessary, take measures to temporarily make boundaries and reference points easier to identify, creating conditions that make it easier to judge them on the images after shooting. Area calculation is affected not only during the data processing stage but also by on-site preparation before shooting, which can greatly change accuracy and usability.

Note 5 Verify the area after image processing against on-site information

In drone surveying, multiple captured images are processed to produce orthophotos and terrain data. The target area is then outlined and its area calculated. However, rather than accepting the area obtained from image processing as the final value, it is important to verify it against on-site information and existing records. Even when the images look clean and the drawings well organized, discrepancies can remain due to processing conditions and field circumstances.

First, what you want to confirm is whether the ortho image is aligned with the site and existing drawings. Check multiple locations such as fence corners, road edges, drainage facilities, buildings, known points, and landmarks near boundaries. Even if some parts align, other areas may be offset. This is especially true for large solar power plants, where offsets can be noticeable at the edges or on long, narrow sites. Check the entire area used for area calculation for any bias or misalignment.

Next, verify that the outlined area matches the intended purpose. Even if you think you have enclosed space within a fence, judgment can be ambiguous at gate sections, where it connects to access roads, waterways beneath slopes, or near boundaries with adjacent land. Places that appear continuous in drone images may be divided on site by steps or structures, separating management areas. Do not decide the lines for area calculation from images alone; cross-check them with on-site photos and field notes as needed.

Comparing with existing documentation is also useful. If past survey maps, construction drawings, site development drawings, management drawings, fence layout plans, panel layout plans, etc. are available, verify whether there is any significant difference between the area calculated by the drone survey and those documents. However, if the existing documents are old or if there were design changes during construction, the documents may not match the current conditions. If a discrepancy is found, it is important not to rush to decide which is correct, but to identify the cause of the difference.

Causes of discrepancies include differences in how boundaries are defined, differences in coordinate systems, how scale and projection are handled, changes in shape after development, changes in fence position, misidentification due to vegetation, and misalignment in image processing. For example, if existing drawings show the land boundary but a drone survey encloses the area inside a fence, it is natural that the areas will not match. Conversely, if you believe you are enclosing the same area but the discrepancy is large, you need to check the digitized boundaries and the coordinates.

After calculating an area, it is important to keep not only the numerical value but also the conditions used for the calculation. Record the date the images were taken, the area that was targeted, whether reference points were used, which coordinate system was used for processing, which locations were difficult to judge on the images, and which points were supplemented by on-site verification. If this information is retained, it will be easier to explain the basis for the area measurement later.

In solar power plants, site conditions change before construction, during construction, after construction, and during operation and maintenance. Even if the land is bare immediately after site preparation, within a few months grass will grow, drainage routes may change, and repairs or additional equipment may be added. It is necessary to clarify at what point in time the area calculated by drone surveying is based. In particular, when using it for weed-control planning or for reviewing maintenance coverage, it is desirable not to continue using past area values as they are, but to reconfirm them according to changes in current conditions.

Products produced after image processing look polished and are therefore persuasive. However, to make them truly useful in practice, it is necessary to perform on-site verification, cross-check with existing documents and the responsible party’s objectives, and clarify what the numerical values actually mean. For area calculations from drone surveys, you must not simply trust the processing results; it is essential to verify them back in the context of the site.

Point 6: Record area calculation results in a format usable for construction and maintenance

Even if a site area is calculated by drone surveying, if the results are in a form that cannot be used in later stages, their practical value is diminished. At solar power plants, area information is used in many situations such as design, construction, maintenance, vegetation control, inspection, drainage management, and dealing with neighbors. Therefore, it is important to record the calculated results not simply as numbers but in a form that makes the boundaries and intended use clear to anyone.

First, clearly assign names to the area measurements in the deliverables. By separating them by purpose—"total site area", "area managed inside the fence", "panel installation area", "weed-control area", "site development area", "slope management area"—you reduce the risk of later misuse. If only a single area is listed, different viewers may interpret it differently. This is especially important for solar power plants, where the land area, equipment layout area, and actual work area may not coincide, so organizing the names is essential.

Next, make it possible to verify the calculated area on the image. Diagrams that overlay boundary lines on the orthophoto, color-coding by parcel, and annotations for excluded areas help stakeholders understand. However, overly complex representations can instead cause misunderstandings. In practice, it is more useful to separate materials that show only the areas needed for each purpose from materials that allow checking the entire area.

During the construction phase, it is useful for verifying areas such as the development extent, material storage yards, temporary roads, access routes, and around drainage facilities. By comparing drone survey results before and after construction, it becomes easier to understand differences between the plan and the actual conditions. In particular, it can be used to check whether the development extent has expanded beyond the design, whether slopes are larger than expected, and whether maintenance access routes are secured. If area information is kept together with current-condition images, it can also be used as material for on-site briefings and internal reviews.

In the maintenance phase, it helps to grasp the area subject to weed control, check inside and outside fences, organize the inspection scope of drainage facilities, and record areas affected by vegetation. At solar power plants, managing the surrounding environment is as important as the power generation equipment itself. If the target areas for mowing and weed-prevention measures are understood in terms of area, it becomes easier to plan operations. Combining drone survey results with on-site photos and inspection notes also makes comparisons with past conditions easier.

Also, it’s a good idea to define rules for updating deliverables. Rather than calculating the area only once after construction and stopping, establish a system to update them when there are changes such as site layout modifications, fence relocations, drainage improvements, panel additions, or changes to weed-control areas. If old deliverables remain, there is a risk that areas differing from current conditions will continue to be used. Organize file names, creation dates, scopes of coverage, and update histories, and manage them so the latest version is clearly identifiable.

When sharing area calculation results, attention must be paid to the number of digits and the way they are expressed. Displaying more digits than necessary can make the result appear more precise than it actually is. The accuracy of drone surveying varies depending on flight conditions, control points, image processing, and on-site conditions. If the result is for a rough estimate, indicate that it is an estimate; if it will be used for construction management or inspection documentation, be prepared to explain that the results were produced after the necessary verification procedures. Numbers are useful, but they only become practically usable information when accompanied by their rationale and assumptions.

Furthermore, it is important to align the perspectives of all stakeholders. For the client, designers, contractors, maintenance personnel, and land managers, the same term "site area" can carry different meanings. When sharing drone survey deliverables, indicating the definition of area, the scope of coverage, the date of creation, and the intended use within the documents can reduce the need for explanations. On solar power plant sites, where multiple stakeholders often use the same materials, recording practices that prevent misunderstandings are essential.

Summary Drone surveying helps visualize site area

Calculating the site area of a solar power plant using drone surveying is one way to efficiently grasp the entire site and support decision-making for design, construction, and maintenance. Because the extent can be confirmed from images taken overhead, it becomes easier to visualize existing conditions, areas of land development, the situation inside and outside fences, and the spread of access roads and slopes that are difficult to understand from drawings alone. For large sites or those with uneven terrain, another advantage is that it can supplement areas that are hard to assess from ground-level inspection alone.

On the other hand, there are cautionary points when calculating area using drone surveying. It is important not to confuse boundary lines with the management area, to organize reference points and coordinate systems, to distinguish between horizontal area and area measured along the ground surface, to take into account site conditions such as panels, shadows, and vegetation, to cross-check image-processing results with on-site information, and to leave deliverables in a form usable for downstream processes. If you handle only the numbers without clarifying these points, you may end up using an area that does not match the intended purpose.

In drone surveys of solar power plants, it's important not just to fly and take photos, but to clarify what to check, which areas to treat as measured area, and how the results will be used in operations. By changing how you interpret area depending on the objective—grasping the entire site, comparing before-and-after site development, defining weed-control zones, inspecting drainage and slopes, and verifying equipment layout—you can enhance the value of drone surveying.

For field staff, the important thing is not to let the results of area calculations end up as "clean drawings" or "standalone figures." If you save the boundary lines, current-condition images, calculation conditions, verification date, and intended use together, they become materials that are easy to use in construction management and maintenance. Stored in a form that can be compared with past conditions, they help you understand changes at the power plant and provide a basis for prioritizing inspections and maintenance.

If you want to accurately determine the site area of a solar power plant, planning drone surveys that take local conditions into account and verification procedures after calculating the area are indispensable. To efficiently understand a large solar power plant and make use of the data for construction and maintenance, it is important to organize boundaries, coordinates, topography, obstacles, on-site inspections, and recording methods as an integrated whole. By utilizing drone surveys to visualize area measurements, it becomes easier to align stakeholders' understanding and to prepare the information needed for planning and management decisions.