5 Tips for Preserving Comparative On-site Photos of Solar Power Plants with Drone Surveys

In the operation and maintenance of solar power plants, it is important to continuously record site conditions and make it easier to identify differences from the previous inspection. Panel soiling, changes around the mounting racks, vegetation growth, drainage conditions, and deformations of slopes and developed land can be difficult to assess from a single photo. One useful method is to record site comparison photos using drone surveying. Combining aerial photos, oblique photos taken under consistent conditions, point clouds, and orthomosaic images makes it easier to explain changes at the site.

Table of Contents

• Clarify the purpose of preserving on-site comparison photos using drone surveying.

• Set shooting conditions so that comparisons can be made at the same position and angle.

• Consolidate reference points and management information into records that can be retrieved later.

• Explain changes by combining point clouds, orthophotos, and photographs

• Set up operational rules that are easy to use for regular inspections and reporting.

• Summary: Comparable photos are the basis for on-site decision-making

Clarify the purpose of retaining on-site comparison photos through drone surveying

When taking on-site comparison photos at a solar power plant, the first thing to decide is what you want to compare. Simply photographing the entire site makes it difficult, when reviewing the photos later, to understand what was important or what you were trying to evaluate. Solar power plants, in particular, cover large areas and have many inspection targets, such as panel rows, access aisles, slopes, drainage channels, fences, and equipment areas. If you shoot without a clear purpose for the record, you may end up with many photos that are difficult to use for reporting or decision-making.

The purposes of on-site comparison photos can be broadly categorized as understanding changes, explaining inspection results, sharing among stakeholders, and preventing future problems. For example, if you want to compare conditions before and after mowing, you need photos that show the height and extent of weed growth. For checks after a typhoon or heavy rain, photos that can confirm poor drainage, sediment runoff, abnormalities around panels, and leaning fences are required. On sites during construction or renovation, records that allow comparison of progress at each stage, changes in material storage areas, and the condition of racks and walkways are useful.

When comparing solar power plant sites, ground-level photos alone can make it difficult to grasp the overall picture. Shooting from the ground makes it hard to see the depth of panel rows and conditions near site boundaries, and the view can vary greatly depending on the photographer’s position. Using drone surveying allows an aerial overview of the entire site and makes it easier to continuously record the same area. This not only helps identify local anomalies but also makes it easier to confirm trends and changes across the whole site.

However, not all photos taken by drones are suitable for comparison. To make photos usable for comparison, you need to match how the scene appears between the previous and current shots. If flight altitude, camera orientation, shooting area, time of day, weather, or distance to the subject differ greatly, places that have only small actual changes can appear to have changed significantly. Conversely, even if important changes are captured, if the composition is too different from the previous photo, it becomes difficult to judge the magnitude of the change.

Therefore, the purpose of retaining site comparison photos must be directly reflected in the shooting plan. The required shooting method varies depending on whether you want to see overall changes, changes to specific equipment, changes in natural conditions such as vegetation or sediment, or the progress of construction or repairs. If the purpose is an overall comparison, aerial photos that capture the entire site within a consistent frame will be the focus. If the purpose is detailed inspection, it is easier to understand by combining ground-level photos and low-altitude oblique photos.

In practice, it is important to treat on-site comparison photos not just as “evidence of inspection” but as “input for subsequent decision-making.” If keeping photos becomes an end in itself, the number of shots and storage tasks will increase, creating a heavier management burden. By being aware of which photo enables whom to judge what, you can narrow down the locations and frequency that need to be photographed. Even when incorporating drone surveys of solar power plants into operations, the starting point is to clarify the role of comparison photos in line with the site’s management objectives.

When determining the purpose of comparison photos, it is effective to consider not only the on-site personnel but also the perspectives of those who will view the photos—such as the management company, the plant owner, the construction contractor, and the maintenance and inspection staff. Small changes that may seem minor to on-site personnel can become important factors for decision-making for stakeholders checking the situation from a remote location. Conversely, things that are obvious on site may not be conveyed to someone who only sees the photos. If you regard comparison photos as records meant to communicate the situation to people who are unfamiliar with the site, the necessary shooting range and how to explain things will become clear.

Also, the purpose of keeping comparison photos is not something you decide once and then finish. As you continue operations, you will learn which locations are frequently checked, which receive many inquiries, and which are prone to problems. Based on that information, it is important to review the photo locations and the items you record. Solar power plants look different depending on the season and are affected by vegetation growth, rainfall, snowfall, strong winds, and other factors. Start with a standard photography plan, and adjust how you keep comparison photos to match the site’s characteristics so that you end up with records that are practical for day-to-day operations.

Determine shooting conditions that allow comparison from the same position and angle

A major factor affecting the quality of on-site comparison photos is whether they were taken from the same position and angle. When you place the previous and current photos side by side, if the shooting position or angle differs significantly, you cannot determine whether the cause of the change is an actual site change or a difference in shooting conditions. At solar power plants, because the rows of panels are arranged regularly, even a slight change in angle can alter how shadows appear and how the rows overlap. If you plan to use the images as comparison photos, it is important to standardize the shooting conditions as much as possible.

In drone surveying, you can photograph a defined area from the air, but when using images as comparison photos, you need to be mindful of consistency rather than just flying the drone. By deciding in advance the flight altitude, direction of travel, camera orientation, shooting interval, and target area, it becomes easier to capture images under similar conditions in subsequent sessions. If you can fly the same plan each time, it becomes easier to track changes across the whole site over time and to use the images in reports and inspection records.

Particularly important is the shooting direction that serves as the reference for comparison. At solar power plants, the most effective viewing direction varies depending on the orientation and tilt of the panels, the arrangement of access paths, and the shape of the site. Whether you shoot along the rows of panels, across the rows, or centered on the site boundary will change what information is visible. For example, if you want to compare the growth of grass between rows, photos taken only along the rows can be hard to discern. If you want to see changes in drainage channels or slopes, photos taken at an angle to the subject can make it easier to grasp a sense of depth.

When setting shooting conditions, it's easier to organize things by separating the roles of overhead (vertical) photos and oblique photos. Overhead photos are suited to capturing the overall site layout, the spread of vegetation, the positional relationships of pathways and equipment, and the extent of soil or standing water. Oblique photos, by contrast, are effective at conveying rack tilt, the condition of slopes, fence deformation, and the three-dimensional situation around equipment. Rather than relying on one type, combining them according to the purpose produces records that are easier to compare.

Time of day is another condition that must not be overlooked. At solar power plants, the sun’s position greatly affects how shadows lengthen. If you photograph during times when shadows are long, the shadows of the panels and mounts can cover the ground surface, making it difficult to see the condition of the grass and changes in the ground. Conversely, when the sunlight is too strong, the contrast between light and dark becomes large and details can be hard to discern. Although it is difficult to match conditions exactly every time, for comparison it is desirable to photograph at as close a time of day and under as similar weather conditions as possible.

Weather also affects comparison photos. The appearance of the ground and panel surfaces changes between sunny and cloudy conditions. After rain, puddles and wet soil become noticeable, giving a different impression than when dry. Depending on the purpose of on-site comparisons, it can be effective to intentionally record post-rain conditions. For checking drainage conditions and sediment runoff, photos taken after rainfall as well as photos taken under normal conditions can be important material for decision-making. However, because treating routine inspection comparison photos and post-disaster confirmation photos by the same criteria can cause confusion, it is important to separate the shooting purposes in the records.

In comparative photography using drone surveying, reproducibility of the flight route is also important. If the operator chooses shooting positions by feel each time, the coverage will be slightly shifted even if the photos look similar. If possible, establish routes for routine inspection photography in advance and record them in the same order to make management easier. Separating routes for photographing the entire site, routes for photographing priority areas, and routes for post-disaster checks makes it easier to capture images suited to each purpose.

What you want to avoid in comparison photos is a situation where assessments vary depending on the photographer. If one person focuses on shooting near the entrance while another takes more photos of the center of the panel, chronological comparisons become difficult. To ensure records remain consistent even when personnel change, it is effective to map shooting positions and directions onto site drawings and management documents. When managing shooting locations by name, don’t rely only on broad names like "north slope" or "south drainage channel"; decide from which direction and what to include in the frame so it will be less confusing when you review them later.

Shooting from the same position and angle is not just to make the photos look good. It is a prerequisite for explaining whether changes have occurred. When the conditions of the previous photo and the current photo are similar, it becomes easier to compare the spread of vegetation, ground subsidence, soil movement, fence deformation, muddiness of pathways, and so on. Those receiving the report can also more easily understand site changes by looking at the differences between the photos. In drone surveys of solar power plants, not only the technique of shooting but also designing to record under the same conditions increases practical value.

Consolidate reference points and management information to make records searchable later

On-site comparison photos are often reviewed not only immediately after being taken but also months or years later. What becomes important then is ensuring that the photos can be found afterward. No matter how clear a photo is, if the shooting location, shooting date, target equipment, and purpose of the shot are unknown, its value as comparison material decreases. At solar power plants, rows of similar panels and walkways often continue, so it can be difficult to identify the location from photos alone. That is why it is essential to record reference points and management information together.

The term "reference point" has a technical connotation in surveying, but in site comparison photos it becomes easier to understand if you think of it as a marker for aligning the positional relationships in photos. Managing easily verifiable on-site features—such as structures, fence corners, intersections of walkways, areas around equipment, and the ends of drainage channels—as reference points makes it easier to find the same location during the next shoot. When handling position information in drone surveying, it becomes easier to link photos, point clouds, and orthophotos to the site's positions, making them easier to organize as comparison materials.

However, relying solely on on-site landmarks carries the risk that those landmarks may change or be removed in the future. Material storage areas, temporary structures, signs, and vegetation can vary with the seasons or with construction, making them unstable as reference points. When managing comparison photos, it is desirable to use locations or equipment that are as unlikely to change as possible as reference points. Linking photos to management-used information such as power plant sections, panel row numbers, aisle numbers, and equipment numbers makes them easier to share among stakeholders.

Basic photo management information includes the date taken, time taken, photographer, subject, purpose, shooting direction, site name, and section name. If you record these items consistently for every photo, it becomes easier to search for images later. For example, if you can classify them as "photos taken of the north-facing slope during the spring routine inspection," "photos taken to check drainage channels after a typhoon," or "photos for comparing before and after grass cutting," you can reduce the time needed to find the necessary photos. This kind of organization becomes even more important at sites where large numbers of photos accumulate.

File names and folder structures also have significant practical importance. Simply saving photos after shooting makes them increasingly difficult to find over time. Organizing them so that the site name, date, inspection type, and shooting area are identifiable will make them easier for multiple people to handle. Especially when managing multiple solar power plants, ambiguous plant or section names can result in photos being mixed with those from other sites. To prevent the organization method from changing each time you shoot, it is effective to decide on a naming convention in advance.

Photos and data obtained from drone surveys tend to contain more information than ground-based photographs. By combining overall photos, divided photos, oblique photos, point cloud data, and orthophotos, you can record site conditions from multiple perspectives. On the other hand, the more data you have, the greater the effort required to manage it. If you don't decide which data will serve as the official reference for comparisons and which photos are supplementary, you can easily become confused when preparing reports. Simply distinguishing and storing reference photos for comparison and supplementary photos will make operations considerably easier.

To make site comparison photos easier to use later, you need to manage them together with location information and comments rather than as standalone images. Even if you can identify the place shown in a photo, it is insufficient as a basis for decision-making if you don't know why it was taken. For example, even for photos of the same drainage channel, the points to look for change depending on whether the photo was taken as part of a routine inspection or to check conditions after heavy rain. Adding concise on-site comments makes it easier to recall the situation when reviewing the photos later.

When writing comments, it is important not to rely solely on subjective expressions. Phrases such as "quite bad" or "seems fine" can be interpreted differently by different people in charge. If you record observations together with comparison photos, it is easier to convey your point if you focus on facts that can be verified in the photos, such as "the grass has spread toward the walkway compared to last time," "some sediment has accumulated in part of the drainage channel," or "a gap is visible at the bottom of the fence." Whether judgment or countermeasures are necessary should be organized separately based on the photos and factual records to improve the transparency of the report.

Also, to make records that can be found later, it is important that all stakeholders use the same rules. If unique names or abbreviations understood only by on-site staff are used, confusion will arise when another person takes over. In managing solar power plants, data are often accumulated over long periods, so person-dependent management should be avoided. Ideally, the photo location, section name, equipment name, storage location, and the notation used in reports should be standardized as much as possible so that anyone can understand the place and purpose.

In using drone surveying for solar power plants, not only the accuracy of the imagery but also the accuracy of data management directly determines outcomes. Even if you record site changes with photographs, they lose much of their value if you cannot retrieve them when needed. Aligning reference points and management information may seem like a mundane task, but it is a crucial step in turning comparative photos into records that can be used in practical operations.

Describe changes by combining point clouds, orthophotos, and photographs

Site comparison photos are visually easy-to-understand records, but there are changes that cannot be fully explained by photographs alone. At solar power plants, there are situations where three-dimensional information is relevant to assessment, such as slight deformations of slopes, irregularities in the ground surface, movement of soil, elevation differences around drainage channels, and the spread of vegetation. In such cases, combining point clouds and orthomosaic images acquired by drone surveys with photographs makes it easier to explain changes on site.

Ortho images can be used as images that make aerial photographs easier to handle like maps. With ordinary oblique or aerial photographs, it can be difficult to understand positional relationships because of the camera angle and terrain. By using ortho images, it's easier to confirm planimetric arrangements such as the overall site layout, rows of panels, walkways, drainage channels, fences, and slopes. They also make it easier to explain the overall situation when comparing the extent of grass growth, areas of sediment accumulation, and the locations of puddles.

On the other hand, point clouds are useful for confirming three-dimensional shapes. They help to grasp elevation differences, bulges, and changes in slope that are difficult to discern in photographs. For example, if part of a slope may be beginning to fail, it can appear in photos only as differences in color or shadow. By using point clouds in combination, it becomes easier to confirm changes in shape three-dimensionally, which increases the persuasive power of on-site explanations. However, because point clouds alone can make it difficult to convey surface texture, color, and the detailed condition of equipment on site, combining them with photographs is effective.

When using them as comparison materials, it becomes easier to understand if you consider the roles of photographs, orthoimages, and point clouds separately. Photographs intuitively convey the appearance of the site. Orthoimages indicate positional relationships and extents. Point clouds are used to check changes in shape and elevation. By combining these three, it becomes easier to explain "where", "over what area", and "how" changes at the site are occurring.

For example, when checking the mowing area, ground-level photos alone can make it difficult to see how far the grass has spread across the entire site. Using aerial photos or orthophotos captured by a drone makes it easier to understand the overall distribution of the grass. Additionally, attaching oblique photos of key areas can convey the grass height and proximity to equipment. This provides records that are easy to use for before-and-after comparisons of mowing and for planning the scope of the next work.

Combining methods is highly effective when checking drainage conditions. If you photograph from above after heavy rain to capture places where water tends to pool, you can see which areas of the site are affected. By confirming positions on the orthophoto and, if necessary, recording the condition around drainage channels and catch basins with oblique photos, it becomes easier to explain the situation to relevant parties. If point clouds are available, they also serve as a reference for identifying low-lying terrain and areas prone to water accumulation.

Drone surveying is also useful for comparing construction and repairs. For example, recording the same area—such as the ground after land development, the condition after installation of mounting frames, before and after pathway maintenance, and before and after drainage channel repairs—allows you to confirm changes at each stage. If you keep orthophotos as well as photographs, it becomes easier to check the positional relationships of the construction or repair areas later. For stakeholders who cannot visit the site, aerial comparison materials provide an easy-to-understand way to convey the situation.

However, using point clouds and orthoimages does not automatically enable correct judgments. Appearance varies depending on data creation conditions, capture area, resolution, weather, shadows, ground surface conditions, and so on. In areas with dense vegetation, the ground surface can be difficult to see, and areas under panels or in the shadows of mounting racks can be hard to confirm. When using them as comparative material, it is important to understand which areas can be verified from the data and which are difficult to verify, and to combine them with on-site inspections and ground-level photographs.

In comparative materials, clarity is also important. Point clouds and ortho images contain a large amount of information, so they can be difficult for people not familiar with a technical perspective. In reports and shared materials, rather than showing detailed data right away, it is effective to first indicate the location with an overall photograph or ortho image, and then explain the condition with photos of key areas. If necessary, placing the previous and current images side by side and supplementing them with text describing the changed areas makes it easier for readers to make judgments.

The purpose of site comparison photos is not to leave behind pretty images, but to preserve information that can be used for on-site decision making. By combining point clouds and orthophotos, you can supplement positional relationships and shape changes that are hard to convey with photos alone. In the operation and maintenance of solar power plants, comparison materials are required in various situations such as routine inspections, post-disaster checks, repair planning, and reporting to stakeholders. By effectively combining data from drone surveying, it becomes easier to explain the condition of the site more objectively.

Establish user-friendly operational rules for periodic inspections and reporting

To continuously utilize on-site comparison photos, you need operational rules that prevent the person in charge from getting confused each time they shoot. Even if the first few sessions are conducted carefully, when inspection duties get busy the shooting coverage may change or photo organization may be postponed. In solar power plant management, continuity is crucial. Because comparison photos are records that link the previous and the current, and the current and the next, their value diminishes if operations are not stable.

The first thing to decide in the operational rules is the frequency of imaging. You should clarify whether to image at each regular inspection, seasonally, or only additionally after typhoons or heavy rain. At solar power plants there are several timings when changes occur, such as vegetation growth, rainfall, strong winds, snowfall, and construction or repairs. It is not necessary to conduct detailed drone surveys at every one of these times, but keeping baseline photos for normal conditions and separate inspection photos for abnormal events makes comparisons easier.

The next thing to decide is the priority of the targets to be photographed. In a large power plant, photographing every area at the same density each time becomes burdensome. Therefore, it is easier to manage if you separate the areas that must be photographed for overall inspection from the areas that are photographed as needed for focused inspection. For overall inspection, cover the entire site, main access routes, rows of panels, the perimeter, and the drainage system. For focused inspection, target locations that have had past faults, areas where vegetation tends to grow, places where water tends to pool, slopes, and areas near boundaries.

To make reports easier to use, it is important to standardize the procedures for organizing photos after shooting. Simply storing photos as taken will make preparing reports time-consuming. By separating, for each inspection, overall photos, photos of key areas, comparison photos, and supplementary photos, you can more easily retrieve the materials you need. When placing previous photos and current photos side by side, if the shooting locations and subjects are aligned, creating the report materials will go smoothly.

In reports, it is easier to understand if you separate facts that can be confirmed from photos and the judgments of the person in charge. For example, the fact "compared with the previous inspection, the grass in the north walkway has spread" and the proposed action "consider including it in the mowing scope before the next inspection" are easier for readers to understand if written separately. On-site comparison photos are used as evidence to support judgments. Rather than just attaching photos, briefly explain which part you looked at and what you judged, as this helps align understanding among stakeholders.

If incorporated into regular inspections, safety-related operational measures are also indispensable. Solar power plants include electrical equipment, mounting racks, access ways, slopes, fences, and surrounding roads. When flying drones, operations must be carried out after confirming on-site safety checks, the surrounding environment, weather conditions, the locations of personnel, and the facility management rules. On days with strong winds or poor visibility, it is important not to force filming and to consider rescheduling. Even for the sake of keeping comparative photographs, operations that compromise safety should be avoided.

Also, photographs taken and survey data may include the power plant’s equipment layout and management information. When deciding where to share or store them, care must be taken to prevent them from being inadvertently disseminated beyond authorized parties. While on-site comparison photos are convenient, they are also management documents that contain facility information. For peace of mind, clarify the scope of access according to the intended use—such as internal sharing, sharing with partner companies, or reporting to the owner.

Operational rules that are too detailed won't be sustained. Requiring many fields for every photo and complex processing each time increases the burden on on-site staff. The important thing is to clearly define the minimum items to collect and to create a system that can be continued without undue effort. If the date taken, site name, section name, subject of the photo, purpose of comparison, and differences from the previous time are recorded, the result will be a record that is practical and easy to use in daily operations. Adding detailed data as needed makes it easier to continue.

To maintain the same quality when personnel change, it is effective to document the imaging procedures. Briefly summarizing which points to shoot from, what altitudes and directions to use as guidelines, which photos to include in reports, and where to store them after capture will make handovers easier. Because managing a solar power plant is a long-term task, it is important to avoid relying too heavily on individual experience. When introducing drone surveying, considering not only equipment and technology but also how to integrate it into daily operations leads to better results.

When you accumulate comparative photos that are easy to use in reports, the quality of site management improves. By comparing them with past photos, it becomes easier to notice trends in changes. You can identify places where grass grows easily, spots where water tends to pool after rain, areas where soil and sediment are likely to move, and locations around the perimeter fence that require inspection. This information is useful when considering inspection plans and prioritizing maintenance work. Drone surveys of solar power plants become more practically useful when used not as one-off photo shoots but as a continuous site management system.

Summary: Photos that can be compared form the foundation for on-site decision-making

When preserving on-site comparison photos of solar power plants using drone surveying, it is important not to simply take a large number of photos, but to record them in a way that allows later comparison. Decide on the purpose, standardize shooting conditions, organize reference points and management information, combine point clouds and orthophotos, and incorporate the process into regular inspections—by doing so, photos will transform from mere records into materials for decision-making. If you have comparison photos that accurately convey changes on site, it becomes easier to share the situation with remote stakeholders and to advance considerations for maintenance and repairs.

At solar power plants, not only panels and mounting structures but also vegetation, drainage, slopes, access paths, the perimeter, and areas around equipment are elements that change over time. There are limits to managing these solely with ground-level photos. By utilizing drone surveying, you can obtain an aerial overview of the entire site while focusing on recording the specific areas you need. If previous and current photos can be compared under the same conditions, it becomes easier to explain whether changes have occurred and the extent of those changes.

On the other hand, using drones does not automatically produce good comparison materials. If the shooting purpose, location, angle, storage method, and reporting workflow are not organized, the photos may multiply but become records that are difficult to use. What matters in practice is designing the entire process from shooting to sharing as a single workflow. This is especially essential on sites where multiple personnel are involved, where the management method must be clear to anyone.

Site comparison photos are useful not only when problems occur but also for improving the quality of everyday management. Being able to understand past conditions makes it easier to identify areas that change rapidly or require attention. It also makes explaining inspection results easier and reduces differences in perception among stakeholders. If you want to continuously record on-site changes in maintenance of a solar power plant, consider using drone surveying that emphasizes consistency of image capture and data management.

If you want to keep site comparison photos in a form that is more useful for practical work, it is important to consider photography, surveying, data organization, and sharing as an integrated process. To clearly record the condition of a solar power plant from above and make it useful for inspections and reporting, decide the purpose of the comparison in advance and establish procedures that allow shooting under the same conditions. By accumulating records that can be reviewed continuously, it becomes easier to create comparison materials that are convenient for on-site decision-making.