5 Perspectives on Using Drone Surveying to Inspect Access Routes for Solar Power Plants

At solar power plants, not only the layout of the generation equipment and the amount of power produced, but also the condition of the access roads used for material delivery and maintenance inspections greatly affects stable operation. Whether panels, mounting structures, cables, substation equipment, heavy machinery, and maintenance vehicles can pass safely influences not only construction but also post‑completion maintenance and disaster recovery. Especially for solar power plants installed in mountainous areas, on slopes, on developed sites, or on land converted from agricultural use, it can take considerable time to assess access-road width, gradient, pavement condition, drainage, and surrounding obstacles from the ground alone.

One of the easy-to-use methods for that is drone surveying. By taking an aerial overview of the entire access route and combining photos, videos, orthophotos, and 3D data according to the purpose, it becomes easier to reduce omissions in on-site checks. However, drone surveying is not a cure-all that will reveal everything just by flying. It is important to organize the viewpoints to be checked according to the objective and to use it in conjunction with ground inspections, design drawings, and vehicle conditions.

Table of Contents

• Reasons why drone surveying is useful for checking delivery routes

• Viewpoint 1: Confirm the width and alignment of the delivery access road from above

• Perspective 2: Assess vehicle traffic risk by understanding gradients and elevation differences

• Perspective 3: Identify road surface conditions and poor drainage early

• Viewpoint 4: Check clearance of surrounding obstacles and the work yard

• Perspective 5: Organize as records that can be used after construction and during maintenance

• Precautions When Using Drone Surveys to Verify Delivery Access Routes

• Summary

Why Drone Surveys Are Useful for Verifying Access Routes

Access roads at a solar power plant serve multiple functions, including the perimeter road around the plant, internal site paths, access routes to material storage areas, and management access paths used for equipment inspections. Before construction, they are necessary to determine whether material delivery vehicles and heavy machinery can safely enter. During construction, they are used to review delivery plans and adjust temporary traffic routes. After completion, they are important for confirming whether maintenance and inspection vehicles can pass without problems and whether restoration crews can access the site in the event of a disaster.

Inspecting the access route by walking it at ground level is effective because you can directly observe small surface irregularities, mud, clogged side drains, ruts, and the like. However, the overall curvature of the access route, how it connects within the site, its positional relationship with slopes and drainage channels, and the continuity of narrow sections can be difficult to grasp from a ground-level view alone. The larger the site, the more likely it is that the locations you checked will be misaligned with those on the drawings, and the harder it may be later to identify where photos were taken.

Using drone surveying, you can continuously monitor access routes from above. Photos and videos taken from height make it easier to comprehensively grasp changes in road width, sightlines around curves, the positional relationship with material storage areas, and the sense of distance to power generation equipment. Furthermore, if you create terrain data with the necessary precision controls, it also helps confirm gradients and elevation differences. Another major advantage is that by overlaying and organizing information obtained from ground inspections with aerial records, it becomes easier to align understanding among site stakeholders.

At solar power plants, post-development topography, rainwater flow, weed growth, and slope conditions affect the usability of access roads. Especially in mountainous or sloped areas, poor drainage and weakened road shoulders can impede vehicle traffic. Conducting drone surveys to confirm the overall picture makes it easier to organize potential repair locations and areas of concern in advance, rather than responding ad hoc after problems occur.

Moreover, inspecting the access road is not a one-time task. There are multiple times when checks should be made: before construction, during construction, before completion, after operations begin, and after typhoons or heavy rains. Keeping records from drone surveys in chronological order makes it easier to compare whether ruts have formed in areas that were previously fine, whether drainage ditches have been filled in, or whether sediment has flowed in from slopes. Treating the access road not merely as a passage but as an important asset to be managed that supports power plant operations leads to a stable maintenance regime.

Viewpoint 1: Confirm the width and alignment of the access route from above

When checking the access route, the first things to confirm are whether there is sufficient width for vehicle traffic and whether the road alignment is reasonable. At solar power plants, material transport vehicles, work vehicles, heavy equipment, and inspection vehicles enter and exit during construction. Even after completion, vehicles may need to access the site for maintenance work or equipment replacement. Even if on-site passageways appear passable at first glance, there can be insufficient clearance for actual vehicle traffic at curves, near gates, along embankments, beside drainage ditches, or close to rows of panels.

With drone surveying, you can photograph the entire access route from above and get an overhead view of narrowed sections and sharp curves. A location that appears to be a single narrow point from the ground can, when seen from above, have a sequence of curves or grades before and after it. In such places, vehicles may need to perform maneuvers when entering—such as multi-point turns or backing up—or may end up too close to the shoulder. Checking the road alignment from above makes it easier to verify not only the simple width but also to anticipate how vehicles will move through it.

When checking roadway width, it is important to first clarify the conditions of the vehicles that will be used on site. The required clearance varies depending on whether you assume only small maintenance vehicles or also the delivery of large construction vehicles and heavy machinery during construction. Even when using images and terrain data obtained from drone surveys, you should not simply judge whether an area is wide or narrow; you need to assess it together with the width of the vehicles expected to pass, turning maneuvers, load overhang, whether vehicles can pass each other, and the availability of pull-out or refuge areas.

What particularly requires attention is the entrance portion of the access road. Where the public road or existing roads lead into the power plant site, gates, side ditches, utility poles, signs, fences, vegetation, changes in level, and the like affect passage conditions. Shooting the area around the entrance from above with a drone makes it easier to confirm the approach angle and how the on-site access roads connect. However, because the area near the entrance is related to road traffic and third-party passage, it is also necessary to ensure flight safety and be considerate of the filming range.

During alignment checks of the access road, we also check the clearances on the inside and outside of curves. If slopes, drainage ditches, fences, power conditioners, or other equipment are close to the inside of a curve, there is a risk of contact when vehicles pass. If there are weak shoulder sections on the outside, there is a danger of subsidence or wheel drop when a vehicle drifts outward. Recording areas of concern on overhead images created by drone surveys makes it easier to share specific locations among the contractor, the management company, and maintenance personnel.

Also, the alignment of the access route needs to be checked in relation to the material storage area and the work yard. Even if the access route is passable, if vehicles cannot be stopped safely at the location where materials are to be unloaded, on-site work will be delayed. Inside a power plant, rows of panels and mounting racks are arranged neatly, which can make it difficult to distinguish the boundaries between passageways and workspaces. Checking from above makes it easier to visualize how far vehicles can enter, where they will stop, and in which direction they will exit.

The results of checks on widths and alignments are more useful if organized and correlated with drawings and management documents rather than merely saved as site photos. For example, by classifying areas such as entrances, sharp curves, narrow sections, passing places, and zones near material storage, and linking them to site numbers or management numbers, issuing repair instructions or conducting rechecks later will go more smoothly. Drone surveying should be used to confirm access routes as continuous routes rather than as isolated points.

Perspective 2: Assess vehicle traffic risk by understanding gradients and elevation differences

At the access roads to solar power plants, it is essential to check not only the width but also the grade and elevation differences. Especially for plants located in mountainous or hilly areas, the site may include steep passages or boundaries between cut and fill. Even routes that were usable during construction can become problematic after rainfall if mud forms or the road surface is eroded, impairing a vehicle’s ability to climb or brake. Even roads that maintenance and inspection personnel use routinely can change significantly under wet conditions or when carrying loads.

When terrain data is acquired through drone surveying, it becomes easier to verify the longitudinal elevation differences of access routes and their relationship with the surrounding topography. A slope that appears gentle in photos may actually have a section where the gradient becomes steep. Conversely, a spot that feels abrupt on the ground might have a nearby, gentler detour route. Understanding the terrain from above increases the basis for decision-making when considering delivery plans and maintenance access routes.

When checking gradients, it is important not just to look at the numbers but to anticipate conditions during vehicle passage. On uphill sections, road surface condition, load weight, the presence of curves, and whether there are stopping points will have an impact. On downhill sections, braking distance, road slipperiness, drainage flow, and the distance to side ditches or embankments become issues. If there are gates or sharp curves partway along the gradient, temporary stops or maneuvering may be required, increasing strain on vehicles and operational risk.

When using drone surveying to determine elevation differences, it is effective to look not only at the access road but also at the surrounding drainage directions. Areas where water collects from higher to lower ground can experience road surface washouts or mud accumulation after rain. If water pools in low sections of a passage, the roadbed can become weaker than it appears. Checking the relationship between slope and drainage can help prevent obstructions to traffic.

In sites with significant elevation changes, safety management during material delivery requires attention. When vehicles loaded with panels, mounting-frame components, or similar items travel over sloped terrain, you must account for potential load shifts and changes in vehicle stability. If one side of an access road is a slope or there is not enough room on the shoulder, a road that simply connects through cannot be considered a safe delivery route. Observing from above with a drone allows you to comprehensively grasp the positional relationships between the road, slopes, retaining walls, drainage channels, and equipment.

Also, elevation differences in access routes affect post-construction maintenance work. When inspection personnel enter the site regularly, paths with steep slopes or many steps impact travel time and safety. For fault repairs or emergency responses, it is important whether vehicles carrying the necessary equipment can get close to the site. By identifying hard-to-pass sections in advance with drone surveys, you can plan separate routes for routine inspections and for emergencies.

However, elevation differences and slope information obtained from drone surveys can vary in accuracy depending on measurement conditions and processing methods. When using them for important decisions, it is safer to combine them with ground surveys or on-site measurements as necessary. Especially in locations directly related to boundaries, structures, drainage facilities, or judgments about vehicle access, you should not rely solely on drone data but adopt an approach of combining it with on-site verification. Drone surveying is effective for grasping the overall picture, but for final decisions it is important to carefully confirm on-site conditions.

Perspective 3: Detect Road Surface Conditions and Poor Drainage Early

The usability of access roads is largely determined by the condition of the road surface. Paths at solar power plants may be paved, covered with crushed stone, unpaved dirt roads, or used as maintenance tracks after site development. Even if they are passable immediately after construction, rainwater, repeated vehicle traffic, weed overgrowth, and sediment inflow can gradually create ruts, uneven sections, muddy patches, and scour. When inspecting access roads, it is important to be able to detect these changes early.

In drone surveying, because you can capture access roads over a wide area, it becomes easier to spot differences in pavement color, wet spots, places where sediment has washed in, and sections with continuous ruts. On-the-ground inspections tend to concentrate attention on the pavement immediately in front of you, but from above it is easier to see where water is coming from, where it is collecting, and where it is crossing the route. Aerial inspections by drone are particularly effective for checks after heavy rain or typhoons.

Poor drainage is one factor that accelerates the deterioration of access roads. If conditions such as clogged side ditches, sediment accumulating around catch basins, standing water on the pavement, or muddy water flowing in from slopes persist, the load-bearing capacity of the route is likely to decline. When vehicles pass, ruts deepen, and if water collects in those ruts, a vicious cycle of further deterioration occurs. Using drone surveys to check drainage paths and identify problem areas early helps when assessing the scope of repairs and the risk of work stoppages.

When inspecting the condition of the road surface, also check the positional relationship with the power generation equipment. If rows of panels, racking, electrical equipment, cable routes, or fences are located near the access road, rainwater or sediment movement may affect the equipment. For example, if water collects in a low section of a walkway and there are equipment foundations or cable risers nearby, this becomes a long-term maintenance concern. Being able to verify the layout of the access road and equipment simultaneously by drone is a benefit unique to solar power plants.

The overgrowth of weeds cannot be overlooked when inspecting access roads. When grass grows, the location of the road shoulder, side ditches, changes in elevation, and muddy patches become harder to see. This can make the width available for vehicle passage appear narrower than it actually is, and can also make it harder for inspectors to notice abnormalities in the road surface. Aerial photography makes it easier to identify vegetation encroaching onto the passage and the extent of grass covering drainage facilities. Drone records are also useful when prioritizing weed removal and shoulder maintenance.

Also, the appearance of the road surface changes with the season and weather. Sections that are difficult to see on clear days may reveal puddles or mud clearly after rainfall. Conversely, there is also a risk of judging conditions as excessively bad if you only look immediately after rain. To understand the actual condition of the access road, it is important to record the date and time of inspection, the weather, any rainfall immediately beforehand, and the road surface condition at the time of imaging. When using drone survey results, it is also necessary to make clear when and under what conditions the data were acquired.

When checking road surfaces and drainage, it's important not just to identify abnormalities but to translate them into follow-up actions. Organizing locations into those that need repairs, those that can be improved by cleaning, those that only require continued observation, and those that should be flagged for caution during vehicle traffic will produce materials that are practical for field work. By marking points of concern on drone survey images and combining them with ground photos and inspection notes, it becomes easier to communicate the situation to stakeholders who have not visited the site.

Viewpoint 4: Verify clearance for surrounding obstacles and the work yard

When verifying access routes, not only the road itself but also surrounding obstacles and the available space in the work yard are important. Within the site of a solar power plant there are panels, mounting structures, electrical equipment, fences, gates, drainage facilities, slopes, vegetation, and existing structures. Even if the access route is secured, if there is insufficient space for vehicle passage, unloading, or heavy machinery operations, the efficiency of construction and maintenance will decrease. Drone surveying allows confirmation of the access route together with surrounding facilities, which helps when planning work.

First, you should check where vehicles will stop and where unloading will occur. When a delivery vehicle stops on a passage, you need to consider whether other vehicles can pass, whether workers can move safely, and whether there is space to temporarily store materials. In a confined power plant, temporarily blocking a passage can bring the entire operation to a halt. Checking potential work yard locations from above makes it easier to identify which areas have room and which are likely to become congested.

Next, it is also necessary to take overhead lines and nearby structures into account. There may be power lines, communication lines, trees, buildings, signs, lighting poles, and so on around the power plant. By photographing from above with a drone, you can check whether there are obstacles along the access routes that might affect the movement of vehicles and heavy machinery. However, thin objects such as overhead lines can be difficult to see depending on shooting conditions, so it is important not to judge based on drone images alone and to combine them with ground inspections.

The location of fences and gates is also important when checking delivery routes. The ease of delivery operations varies depending on the gate’s opening direction, the width of the opening, the angle at which vehicles enter, lock management, and the availability of waiting space. Checking the area around the entrance from above allows you to sort out the connection to roads outside the site, how to access internal site passages, and the clearance before and after the gate. Especially when multiple parties will be coming and going during the construction period, it is effective to plan the delivery routes and waiting areas in advance so that vehicles do not accumulate around the entrance.

In solar power plants, the spaces between panel rows and the perimeter pathways are sometimes used as maintenance routes. Where pathway width is limited, if service vehicles get too close to the equipment there is a risk of collision. By using drone surveys to confirm the relationship between equipment layout and pathways, it becomes easier to delineate areas where vehicles should enter and areas where items must be carried by hand. This applies not only to maintenance inspections but also to work planning for component replacements and disaster recovery.

When inspecting a work yard, you must not overlook ground conditions. Even areas that look wide open from above may in reality have soft ground, poor drainage, slopes, level differences, or dense vegetation, making them difficult to use as material storage areas. By extracting candidate sites with drone surveying and then checking pavement and ground conditions on the ground, you can improve the efficiency of on-site investigations. Rather than walking aimlessly across a large site, narrowing down priority inspection points from the air is a practical advantage.

Furthermore, checking for surrounding obstacles also contributes to safety management. During delivery operations, vehicles, workers, heavy equipment, and materials can concentrate in the same area. On blind curves, in narrow passages, along slopes, or where equipment is in close proximity, guidance and access restrictions may be necessary to prevent accidents or collisions. Using aerial images captured by drones makes it easier to explain hazardous areas to stakeholders and can be used in pre-work briefings.

Perspective 5: Organize as records usable after construction and during maintenance

Checking access routes with drone surveying is more effective when the data are organized as records that can be used later, not just for seeing the site once. At solar power plants, multiple stakeholders—construction contractors, clients, management companies, maintenance personnel, electrical contractors, and others—are involved on-site at different times. If the condition of access routes is shared only via photos or verbally, it can be difficult to tell which location is being discussed. Organizing based on aerial records makes it easier to create a shared understanding.

When using recordings as records, it is important to clarify the imaging scope and the items to be checked. Organizing separately the entire access route, entrances, steep gradient sections, narrow sections, areas with poor drainage, material storage areas, work yards, locations near equipment, and so on, will make the records easier to use when reviewed later. Even if you only save images and videos captured by a drone, their value as practical documentation diminishes if it is not clear where attention should be focused. It is important to organize the material so that the points of concern can be explained in accordance with the purpose of the inspection.

Records taken before construction are useful for planning deliveries. They can organize which routes materials will be brought in through, where vehicles should wait, where unloading will take place, and which locations require on-site inspection. Records during construction can be used to manage changes to temporary access routes, pavement deterioration, relocation of material storage areas, and to review heavy-equipment movement paths. Records taken before completion are effective for checking the condition of delivery and management access routes prior to handover and for transferring information to maintenance personnel.

During the post-construction maintenance phase, drone surveys can be used as records for regular inspections. By checking the access routes together with inspections of the power generation equipment, it becomes easier to detect early changes that could lead to obstructions to traffic. For example, you can compare ruts, sediment inflow, overgrowth of weeds, shoulder collapses, and the formation of puddles that were not present in previous aerial images. Even if on-site personnel change, having past aerial images available makes it easy to understand the changes.

Records are also important for post-disaster inspections. After heavy rain, typhoons, earthquakes, or snowfall, it may be necessary to quickly determine whether access roads can be used. Even if there is an abnormality in power generation equipment, recovery work will be delayed if the access road is impassable. If you have drone survey records from normal conditions, comparing them with post-disaster images makes it easier to identify where sediment inflow or road surface damage has occurred. Comparing with past records also helps prioritize recovery work.

In organizing records, file names and management methods must not be neglected. If they do not indicate the capture date, target area, inspection purpose, site name, or section name, you will not be able to find them when needed. When images, videos, drawings, inspection notes, and repair records are stored separately, stakeholders find it difficult to follow the situation. Drone surveying outputs should be kept in a searchable format on the assumption that they will be used continuously as materials for access route management.

When sharing records with stakeholders, it is effective to prepare explanatory materials that anyone can understand, not just the technical data. Even stakeholders who are not familiar with three-dimensional data or surveying results will find it easier to understand if you provide materials that indicate areas of concern on aerial photographs. Because issues with access routes involve multiple disciplines—civil engineering, electrical, maintenance, and management—being able to communicate using shared visual information is a major advantage.

Precautions when Using Drone Surveying for Access Route Verification

Drone surveying is a convenient tool, but there are several precautions when using it to inspect access routes for solar power plants. First, proper flight planning and ensuring safety are prerequisites. Around the power plant there may be power lines, transmission towers, trees, slopes, fences, workers, vehicles, and neighboring facilities. Flying without confirming site conditions can lead to contact, crashes, or impacts on third parties. It is necessary to organize in advance the allowable flight area, takeoff and landing locations, emergency procedures, and notification of relevant parties.

Next, it is important to note that photographing alone does not necessarily ensure sufficient surveying accuracy. Aerial photos or videos can be effective when used only to grasp, as reference information, the width and slope of an access road. However, when they are used for repair design, quantity estimation, detailed elevation control, or decisions involving boundaries or structures, data must be acquired by methods that meet the required accuracy. The reliability of the results varies depending on factors such as the placement of control points, shooting altitude, overlap rate, ground verification, and data processing conditions.

At solar power plants, reflections from panels and the extensive repetition of similarly shaped equipment are also points to watch for when verifying data. Because similar scenery repeats, photos can be mislocated or it can become unclear which aisle was photographed. When taking pictures, it is important to consciously record elements that make locating the position easy, such as entrances, junctions, equipment sections, the perimeter, and management numbers. Combining these with ground-level photos and notes as needed will make later verification easier.

Consideration must also be given to weather and time of day. Flying in strong winds or rain poses safety issues, and depending on the angle of sunlight, shadows and reflections can make it difficult to see the condition of the road surface. If you want to check for poor drainage on the access road, you may want to inspect conditions after rain, but flight conditions may be poor. Depending on the purpose, it is advisable to plan operations suited to the site, such as separating general inspections in clear weather from focused inspections after rainfall.

Also, it is important not to make a definitive determination about whether delivery/access is possible based solely on drone survey results. Many factors affect vehicle passage, such as road width, gradient, pavement strength, turning, loading conditions, weather, driving route, and guidance/escort arrangements. A drone can confirm only some of these. Even if there appears to be no problem from above, there may be uneven surfaces, mud, soft ground, or hard-to-see obstacles on the ground. Conversely, places that look narrow from above may actually pose no problem for passage. For the final decision, it is important to combine on-site inspection with consultation among the relevant parties.

Attention to information management is also necessary. Information on the location of a solar power plant, equipment layout, access roads, and electrical equipment should be handled carefully from a management perspective. You should not casually share captured data with anyone outside the relevant parties, decide on storage locations and the scope of sharing, and be mindful of avoiding unnecessary third parties appearing in images. When using the results of drone surveys in operations, it is reassuring to establish operational rules that cover not only data capture but also how the data are handled.

Additionally, it is important to clarify the purpose of verifying the access route from the outset. The area that needs to be photographed and the required deliverables will differ depending on whether the goal is to create a materials delivery plan before construction, to perform a pre-completion check, to improve the efficiency of maintenance inspections, or to confirm passability after a disaster. Photographing a wide area while the purpose remains vague will only increase data volume and produce results that are difficult to use in practice. Organizing the perspectives you want to verify in advance and converting them into materials that can be used on site is the basic step to effectively utilizing drone surveying.

Summary

When inspecting access roads for photovoltaic power plants, it is important not only to simply check whether vehicles can pass, but to comprehensively assess road width, alignment, gradient, pavement, drainage, surrounding obstacles, work yards, and record management. Access roads are an important piece of infrastructure that support not only the transport of materials during construction but also maintenance inspections, equipment replacement, and disaster recovery after completion. Leaving sections that are difficult to pass unattended can lead to reduced work efficiency and safety risks, so early inspection and continuous management are required.

Drone surveying allows continuous monitoring of access routes from above, making it easier to verify overall connectivity that ground inspections alone can easily overlook. Because it provides an aerial overview of narrow sections, sharp curves, steep gradients, locations prone to poor drainage, and the available space in work yards, it aids in construction and maintenance planning. Furthermore, by keeping time-series records, it becomes easier to compare changes in pavement condition and the surrounding environment, which can also be used as a basis for decisions on repairs and inspections.

However, it is not appropriate to judge everything about an access route solely from drone surveys. Pavement bearing capacity, minor level differences, soft spots, obstacles, and the actual movement of vehicles need to be combined with on-the-ground inspections and confirmations from stakeholders. Drones are an effective means of grasping the overall picture, identifying problem areas, and creating easily shareable records. By combining drone surveys with on-site verification, access route management can be made more practical for field use.

When using drone surveying at solar power plants to check access routes, it is important to proceed with a clear understanding of what you want to verify, what deliverables you want to produce, and with whom you will share them. By organizing data with an eye toward pre-construction planning, pre-completion verification, maintenance during operation, and post-disaster inspections, you can more easily improve the overall management quality of the plant. Visualizing the condition of access routes in an easy-to-understand way and retaining it in a form usable for on-site decision-making is the practical value of applying drone surveying to solar power plants.