4 Advantages of Using Drone Surveying to Create Orthophotos of Solar Power Plants

At solar power plants, the site is extensive and there are many items to inspect, such as terrain, the extent of site development, rows of mounting racks, access roads, drainage facilities, fences, slopes, and surrounding vegetation. Walking the site to check is important, but there are limits to quickly getting an overview of a large area and sharing the same situation among stakeholders. One useful approach is to create orthophotos from photos taken by drone surveying, making it easy to view the entire site like a map.

An orthoimage is an image created by correcting multiple photographs taken from above through photogrammetric processing and similar methods, reducing apparent displacement caused by camera angle and terrain relief so that it can be used like a plan view. Unlike ordinary aerial photographs, it makes it easier to understand on-site positional relationships and can be used for before-and-after construction comparisons, progress monitoring, maintenance management, and explanatory materials for stakeholders. However, because the achievable accuracy and purposes vary depending on the creation method, how control points are placed, and the shooting conditions, it is important not to treat it as an all-purpose deliverable but to position it correctly according to the intended use.

This article outlines four main advantages of using drone surveying to create orthomosaic images of solar power plants and discusses how to apply them in practice.

Table of Contents

• Why Orthoimagery Is Required at Solar Power Plants

• Benefit 1: Easier to grasp the entire site in a single image

• Advantage 2: Makes it easier to compare changes before and after construction and across different time periods

• Benefit 3: Makes it easier to explain matters and build consensus among stakeholders

• Benefit 4 Easy to use as records for maintenance management and troubleshooting

• Basic Photography and Surveying Considerations for Creating Orthophotos

• Practical Approaches to Utilizing Drone Surveys for Solar Power Plants

Why Orthophotos Are Required at Solar Power Plants

On solar power plant sites, there are many occasions when the planned drawings are compared with the actual on-site conditions. Before site preparation, it is necessary to verify the existing topography, access routes, drainage direction, surrounding roads, and the relationship with adjacent properties. During construction, you must monitor the progress of the development area, racking foundations, panel layout, cable routes, access/maintenance roads, temporary yards, and so on. Even after construction, it is necessary to continuously observe vegetation growth, slope conditions, clogging of drainage facilities, deterioration of pathways, and changes in the surrounding environment.

If you try to manage these using only on-site photos, it can become difficult to understand the photo locations and orientations, and when you look back later it may be hard to determine exactly which spot was photographed. In particular, solar power plants have repeating rows of mounting racks and panels, so partial photos often make it difficult to identify locations. Access roads, drainage channels, and areas near fences may also have few landmarks, so it takes effort to grasp the whole picture using only a photo ledger.

Ortho images are useful materials for addressing such challenges. Because they allow the entire site to be viewed from above, they make it easy to grasp at a glance the positional relationships of equipment and topography. Another advantage is that, when overlaid with existing-condition drawings, layout plans, construction plans, inspection records, and reports, they make it easier to identify discrepancies between actual site conditions and the plans.

By utilizing drone surveying, you can efficiently obtain wide-area information that is difficult to capture by walking and photographing alone. Areas that are hard to view from the ground—such as the upper parts of slopes, the backs of panel rows, low spots where drainage tends to concentrate, and conditions near site boundaries—become easier to understand when observed from above. Of course, orthophotos alone cannot fully determine ground conditions or the integrity of structures, but they are effective as materials for narrowing down locations that require inspection.

At solar power plants, multiple stakeholders—design, construction, surveying, maintenance, clients, landowners, and partner companies—handle the same site information. Even topics that are prone to misunderstandings when explained only in words can be discussed while concretely showing locations and extents using orthophoto images. The larger the site, the greater the value of being able to confirm things while looking at the same screen.

Therefore, orthophotos are not merely attractive aerial imagery but should be regarded as practical documents for streamlining site management of solar power plants. In particular, regularly recording the same area through drone surveys makes it easier to verify site changes afterwards and to use the images when explaining construction quality and maintenance.

Benefit 1: Easier to grasp the entire site with a single image

The first advantage of using drone surveying to create orthoimages of solar power plants is that it makes it easier to grasp the entire site as a single image. Solar power plants cover large areas, and looking from the ground alone can make it difficult to understand their overall shape and layout. This is especially true for plants on sloping terrain, in mountainous areas, on reclaimed or developed land, or those divided into multiple sections, where walking the site can still take a long time before the overall connections are understood.

Conventional ground-level photographs are well suited for recording conditions from a single viewpoint. However, because each photo has a different shooting direction and sense of distance, they can be unsuitable for verifying relationships across a wide area. For example, the positional relationship between rows of mounting racks and access roads, the connection between drainage channels and slopes, the relationship between power conditioner installation locations and cable routes, and the relative distance between fences and adjacent land are difficult to judge from individual photos alone.

With an orthoimage, you can view the site from above, making it easier to intuitively understand the overall layout of the site. It becomes easy to grasp which direction slopes extend, where pathways are, which areas have panels installed, and where uncompleted sections or leftover materials remain. By first understanding the overall picture of the site, it also becomes easier to plan the sequence of inspections, surveys, and construction checks.

Orthophotos are also useful as a starting point for existing-condition maps. Although they serve a different role from precise design drawings or survey maps, using them as background maps to check the site’s appearance and equipment layout makes meetings and site inspections easier to carry out. The ability to visually confirm ground surface conditions that are difficult to discern from drawings alone, the presence or absence of vegetation, material storage areas, vehicle access routes, and the locations of temporary structures is a practical advantage.

At solar power plants, it is important to grasp on-site conditions before construction. By understanding the pre-development topography, existing roads, drainage outlets, trees, and the relationships with adjacent buildings and farmland, you increase the information available for developing construction plans. With orthomosaic images from drone surveys, it is also easier to confirm wide-area conditions that are easily overlooked during field inspections, improving the accuracy of preparations before entering the site.

Being able to view the entire site in a single image even during construction is highly valuable. It provides an overview of differences in progress by work section, temporary storage locations for materials, movement paths of heavy machinery and vehicles, uncompleted areas, and places where work is concentrated, making it easier to revise work plans. It is a heavy burden for site managers to walk and inspect the entire area every day, but creating orthophotos through regular drone surveys enables efficient checking of the condition of a large site.

Furthermore, orthophotos are materials that are easy for people unfamiliar with the site to understand. When explaining the situation to stakeholders who are not based on site—such as clients, internal management departments, or partner companies—it can be difficult to convey information using only text or partial photographs. By using orthophotos, you can concretely show the site extent, equipment layout, and work locations, making it easier to align the premises for your explanation.

However, even when using orthophotos to understand the site as a whole, attention must be paid to the images’ positional accuracy and the time they were captured. For applications that require positional accuracy, it is necessary to establish appropriate control points and check points and to produce the images after confirming the coordinate system. Also, if construction has progressed after the images were taken, the images will serve as records of a past state. It is important to clearly indicate when the images were taken and to manage them so they are not confused with the site’s current conditions.

Benefit 2 Easier to compare changes before and after construction and across different time periods

The second advantage is that it becomes easier to compare conditions before and after construction and changes over time. At solar power plants, the site condition changes significantly over time due to site development, foundation construction, racking installation, panel installation, electrical equipment work, exterior works, drainage improvements, weeding, repairs, and so on. Recording these changes and making them available for later review is important for construction management and maintenance.

Regularly photographing the same area with drone surveying and keeping the images as orthomosaic images makes it easier to visually compare changes over time. By placing side by side the vacant lot before construction, the condition before grading, the terrain after grading, the layout after racking installation, and the completed state after panel installation, you can grasp where and how changes occurred. The key difference is that records that tend to remain as points in ground-level photos can be preserved as areas.

Comparing before and after construction makes it easier to check whether the developed area deviates significantly from the plan, whether the location of management roads is as expected, whether drainage facilities are placed where needed, and whether there are any issues with the positions of fences and gates. Of course, separate surveying and inspection are required for detailed verification of as-built conditions and structural checks, but orthophotos are useful as materials for understanding overall consistency.

Comparisons over time are also useful for monitoring progress during construction. For example, you can visually confirm changes such as mounting frames installed in sections that were unconstructed at the time of the previous shoot, material storage yards being relocated, access roads being improved, and the scope of drainage works expanding. Details that are difficult to convey in text-only progress reports become easier to understand when images are compared.

Comparing changes is also useful for troubleshooting. If sediment runoff is observed after heavy rain, comparing it with past ortho images makes it easier to determine the extent to which the ground surface has changed. If vegetation has become overgrown and may affect the area around panels, comparing with past images also makes it easier to understand how the vegetation has spread. Rather than taking images only after an anomaly occurs, keeping records during normal conditions increases the information available for assessing changes.

In solar power plants, long-term maintenance continues even after completion. Not only the generation equipment itself, but changes to the ground surface, drainage, slopes, access roads, and surrounding trees can affect plant operations. By producing orthophotos regularly, it becomes easier to track site changes over years and to inform inspection and repair planning.

To make comparisons effective, it is important to keep imaging conditions as consistent as possible. If flight altitude, coverage area, photo overlap, time of capture, solar elevation, or weather change significantly, the appearance of the images will also change. It can be difficult to make conditions exactly the same, but at a minimum it is important to capture the same area with consistent quality and manage the data in the same coordinate system. When the purpose is to compare changes, care must be taken not to mistake differences from the previous time that are due to image creation conditions for actual on-site changes.

When using orthophotos as comparative reference materials, it is helpful in practice to record the acquisition date, coverage area, creation conditions, presence or absence of ground control points, coordinate system, and intended use. Even if only the images remain later, you may be unable to make a proper judgment if the conditions are unknown. For drone surveys of solar power plants, it is important to manage not only the deliverables themselves but also the information needed to correctly interpret those deliverables.

Benefit 3: Makes it easier to explain and build consensus among stakeholders

The third advantage is that it makes it easier to explain matters and build consensus among stakeholders. The planning, construction, and maintenance of solar power plants involve many stakeholders. Project owners, designers, contractors, surveyors, electrical contractors, maintenance personnel, landowners, and those involved in administrative consultations all view the site from different perspectives. Therefore, even when they are talking about the same location, the area or condition they have in mind may differ.

Orthoimages help reduce this misalignment in understanding. Based on an aerial image of the entire site, you can explain by specifically pointing out this parcel, this service road, this drainage channel, this slope, and the area along this fence, making it easier to align the assumptions of the discussion. Spatial relationships that are hard to convey through text or verbal explanation alone become easier to understand when shown on an image.

Especially at solar power plants, because similar rows of panels extend continuously, even people familiar with the site can take time to pinpoint a location. An orthophoto makes it easier to explain by linking to row numbers, plot names, access roads, equipment locations, and so on. It also allows you to clearly define the area in question when sharing locations where abnormalities were found during inspections, places that need repair, or places that require additional checks.

During the construction phase, it becomes easier to use for progress reporting and work-section coordination. For example, you can use images to confirm which areas of land development have been completed, which plots are progressing with mounting-structure installation, where materials are being stored, and whether vehicle traffic routes are obstructed. Even if stakeholders cannot gather on site, sharing the situation using ortho images can improve the efficiency of meetings.

Orthophotos are also effective as reporting materials for clients. Having materials that provide an overview of the entire site makes it easier to explain progress and issues. Compared with presenting only individual photos, they make it easier to show what is happening and where, so those receiving the report can more easily understand the situation. If necessary, annotating the orthophoto with inspection areas and points of concern increases its usefulness as explanatory material.

Orthophotos can also be useful when explaining matters to landowners and nearby stakeholders. For example, when explaining the location of an access route, conditions near boundaries, drainage flow, or the extent of vegetation management, it can be difficult to understand positional relationships from on-site photos alone. Using orthophotos makes it easier to show which part of the overall site you are referring to.

However, when using orthoimages in explanatory materials, wording that avoids causing misunderstanding is necessary. Because orthoimages are visually easy to interpret, there is a risk of overestimating the conclusions that can be drawn from what is visible on the image. For example, it is not appropriate to determine boundaries or rights relationships, or to judge the safety of structures, based solely on the area visible in the image. Boundary confirmation, legal judgments, detailed design verification, and structural evaluations each require surveying, drawings, on-site inspections, and expert judgments appropriate to their respective purposes.

Also, when sharing with stakeholders, it is important to clearly indicate the date the images were taken and their purpose. Treating old images as representing the current situation can lead to misunderstandings about the areas that have been completed or the parts that have been modified. In shared materials, it is safest to clearly state the date of capture, the coverage area, the purpose of creation, and the assumptions about positional accuracy.

Orthoimages are not only materials that help provide an accurate understanding of a site, but also materials that enhance the quality of communication. On sites that are large, involve many stakeholders, and require long-term management—such as solar power plants—the ability to make decisions while viewing the same information is itself of great value.

Advantage 4 Easy to use as records for maintenance and troubleshooting

The fourth advantage is that it can be easily used as a record for maintenance and fault checks. A solar power plant is not finished once construction is complete. Even after operations begin, it is necessary to continuously inspect the generation equipment, mounting racks, foundations, maintenance roads, drainage systems, fences, slopes, vegetation, and the surrounding environment. The larger the site, the more important it becomes to record where and when inspections were carried out and where any changes occurred.

Using orthophotos for maintenance management enables recording the condition of an entire power plant on an areal basis. During on-site inspections, information can become biased toward the routes walked and the locations photographed by the personnel in charge. In contrast, orthophotos obtained by drone surveying preserve the entire imaging coverage as a single record, making it easier to review the overall condition of the site later.

One of the items frequently checked in operation and maintenance is vegetation growth. At solar power plants, vegetation can make work around the panels more difficult, raise concerns about shading, and make it harder to inspect fences and drainage facilities. If orthophotos are produced periodically, it becomes easier to get an overview of the extent of vegetation spread and the condition around access roads. While images alone cannot definitively determine impacts on power generation, they provide clues for on-site inspections and for prioritizing weed-control plans.

They can also be used to inspect drainage facilities and slopes. After heavy rain, surface scouring, sediment deposition, changes around drainage channels, and deterioration of access roads may occur. With orthophotos, it is easier to check changes over a wide area and to narrow down locations that should be prioritized for on-site inspection. While images alone cannot determine fine cracks or internal conditions, they are useful as an entry point for grasping overall changes.

It is also useful for checking conditions near fences and boundaries. At solar power plants, fences are often installed along the site boundary, and it is necessary to understand the positional relationship with surrounding roads, farmland, forests, rivers, and private land. Using orthophotos makes it easier to check vegetation along fences, maintenance paths, and the condition of the perimeter. When combined with on-site patrols, it is expected to reduce omissions in inspections.

Orthoimages are also useful materials for recording defects or abnormalities when they are found. By photographing details on site and indicating their positions on the orthoimage, it becomes easier to organize what is happening and where. Even if the person in charge changes, having location information on the images makes handover easier. Comparing with past records can also provide material for considering when the defect may have begun to occur.

However, even when using orthoimages for operation and maintenance, it is important not to rely on them too heavily. Some abnormalities are difficult to confirm from images. For example, the fastening condition of mounting structures, the internal condition of electrical equipment, detailed ground subsidence, internal clogging of drainage systems, and fine defects on panel surfaces require separate on-site confirmation or specialist inspections. Positioning orthoimages as materials for overall understanding, recordkeeping, comparison, and narrowing down targets for further inspection makes them easier to incorporate into practical work.

If you plan to use them continuously for operations and maintenance, it's also important to establish rules for capturing and storing images. Organizing the capture date, coverage area, file names, storage location, responsible personnel, intended use of the images, and links to related on-site photos and inspection records will make them easier to find later. Because solar power plants are operated for long periods, if records become dependent on individuals you may not be able to find the information you need a few years later. To make effective use of orthomosaic images from drone surveys, it's important not only to create them but also to have a system for ongoing management.

Basics of Photography and Surveying to Keep in Mind When Creating Orthophotos

Orthomosaic images are a useful deliverable, but creating them does not necessarily result in a quality that can be used in practice. When producing orthomosaic images from drone surveys of photovoltaic power plants, it is necessary to organize in advance the flight plan, ground control points, image overlap, weather, the condition of the target objects, and the intended use of the deliverables.

First, it is important to be clear about why you are creating orthophotos. The required capture area and accuracy considerations change depending on whether the purpose is to share the overall site situation, to compare before and after construction, to use them for layout checks or progress management, or to keep records for maintenance. If you shoot while the purpose is unclear, problems such as the necessary area not being captured, insufficient positional accuracy, or images being difficult to use for comparisons are likely to occur.

Consider the imaging scope not only within the solar power plant site but, as necessary, to include surrounding roads, access routes, drainage outlets, and areas that clarify the relationship with adjacent properties. Of course, rules governing flight operations, safety measures, permissions from stakeholders, and consideration for privacy are required. In the practical operation of solar power plants, roads and drainage outlets outside the site boundary can be important for management, so it is important to set the imaging scope appropriately according to the purpose.

Image overlap also affects quality. Because ortho images are created by stitching together multiple photographs, insufficient overlap between photos can easily lead to missing areas, distortions, and seam inconsistencies. In places where similar patterns repeat, such as rows of panels, processing errors can be more likely, so ensure sufficient overlap and, when necessary, adjust the shooting direction and altitude.

Setting reference points and validation points is also important. The level of control required differs depending on whether ortho images are used simply as visual material or for position verification and overlaying with drawings. For applications that require positional accuracy, it is necessary to install easily identifiable reference points on site and process the data after confirming their coordinates. It is also useful to prepare validation points to verify how well the produced deliverables match the actual site.

Weather and lighting conditions also require attention. Rain or strong winds can more easily cause safety issues and problems with image quality. During periods of strong backlighting or many shadows, the appearance of the ground surface and equipment can change, which may affect image processing and visual inspections. At solar power plants, reflections from panel surfaces can be strong, so it is important to plan the shooting time and flight direction.

On an active construction site, heavy machinery, workers, temporary structures, materials, and vehicles may appear in images. These can be useful for recording site conditions, but they may also affect the clarity and processing of orthophotos. Before capturing images, you should check the work schedule and access areas and ensure conditions are safe for flight. When flying a drone on the site, it is also essential to inform workers and secure takeoff and landing locations.

Managing deliverables is also important. Orthoimages tend to have large file sizes, and capturing them multiple times increases the amount of data. Organize them so that the date, site name, capture area, and intended use are clear, and save them linked to related photos, point clouds, drawings, and inspection records so they are easier to use later. Rather than simply creating images and leaving it at that, storing them in a state that anyone can use increases their practical value.

How to Leverage Drone Surveys of Solar Power Plants in Practice

The advantages of using drone surveying to create orthomosaic images for solar power plants can be organized into four points: grasping the entire site, comparing conditions over time, explaining to stakeholders, and keeping maintenance records. Each of these offers practical value for solar power plants that cover large areas. The strength of orthomosaic images lies in their ability to capture an overall picture that is difficult to see from ground-based checks alone and to support decision-making when combined with drawings and inspection records.

On the other hand, orthophotos are not万能. It is necessary to distinguish between information visible in the images and information that can only be determined by on-site measurements. When positional accuracy is required, control points and verification points must be handled appropriately. The safety of structures, the condition of electrical equipment, boundaries and rights, and detailed as-built judgments, among other things, should not be determined solely from orthophotos; it is important to combine verification methods according to the purpose.

To put it to practical use, the starting point is to clarify the intended purpose. Depending on whether it is used to capture site conditions before construction, to monitor progress during construction, or for maintenance and management after completion, the coverage, required accuracy, storage method, and sharing method will differ. By developing a capture plan tailored to the objective and aligning stakeholders on how to interpret the deliverables, you can increase the effectiveness of drone surveying.

Also, a mindset of continuous use is important. Rather than creating an orthomosaic image only once and stopping, accumulating records at key milestones and during regular inspections makes it easier to track changes at a solar power plant. Keeping images at times such as before construction, after site preparation, after racking installation, at completion, after the start of operation, and during periodic inspections will make it easier to explain the situation later.

At solar power plants, terrain, area, equipment layout, surrounding environment, and management challenges differ from site to site. Therefore, it is important to design how orthomosaic images from drone surveying are used to match each site's objectives. Rather than simply producing attractive images, organizing them as information that can be used for on-site decision-making leads to greater efficiency in construction management and maintenance.

Orthoimages are practical documents that let you view a large site at a glance and enable stakeholders to make decisions based on the same information. If you want to streamline understanding the current status of a solar power plant, compare construction works, keep inspection records, or prepare explanatory materials, it is worthwhile to incorporate drone surveying in a planned way after clearly defining the objectives and required accuracy. Visualizing the entire site and preserving records that are easy to manage leads to site management that is oriented toward long-term operation.