5 Perspectives for Verifying Road Level Differences at Solar Power Plants with Drone Surveying

In solar power plants, not only the panels, racking, and electrical equipment themselves, but also the condition of internal roads and maintenance pathways affect operational quality. Road level differences, even if they appear to be minor surface irregularities at first glance, can impact the drivability of patrol vehicles, the safety of inspection work, obstacles to material delivery, poor drainage, and deformation of slopes and shoulders. In particularly large plants, if inspections are carried out only on foot or by vehicle, it is easy to overlook the location and extent of level differences, and the granularity of records can vary between personnel. This is where drone surveying, which makes it easy to capture site conditions from above over an area, is useful. This article explains five viewpoints that practitioners should keep in mind when checking road level differences at solar power plants using drone surveying.

Table of Contents

• Link the purpose of verifying road level differences to inspection and maintenance management.

• Using drone surveying to map the location and areal extent of elevation changes

• Assess not only elevation differences but also the effects on drivability and drainage.

• Enhance decision accuracy by cross-checking on-site inspections with survey results.

• Manage road level differences as records that can be compared continuously.

• Summary

Link the purpose of checking road level differences to inspection and maintenance management

The purpose of checking road level differences at a solar power plant is not simply to identify where there are bumps or depressions. In practice, it is important to promptly identify locations that could hinder patrols and maintenance work, prioritize repairs, and ensure that future deterioration can be tracked. Road level differences can be a problem in various places such as internal roads, maintenance walkways, access roads for deliveries, aisles between panel rows, and workspaces around equipment. The larger the plant, the more difficult it becomes to visually inspect the entire site with the same density, and inspections that rely only on the experience of personnel tend to produce fragmented records.

The causes of road level differences include insufficient compaction during construction, concentrated rainwater, shoulder scouring, ruts from vehicle traffic, settlement of embankment sections, and sediment washout around drainage facilities. Solar power plants often occupy large sites and are facilities that are susceptible to the influence of terrain and drainage conditions. In some cases the roads themselves are unpaved or consist mainly of gravel-surfaced access roads, and after rainfall or long-term operation vertical steps and surface unevenness can become conspicuous. If these changes are left unaddressed, they may lead to vehicles bottoming out during patrols, collapse of loads during material transport, inspectors tripping, delays in movement during emergencies, and similar problems.

When using drone surveying, it is important to clarify the inspection purpose from the outset. Whether it is as-built verification at completion, part of regular inspections, damage assessment after heavy rainfall, or a comparison before and after repairs will change the scope to be inspected and the level of detail required in the records. For example, at completion it is important to check whether there are any significant discrepancies between the design road and drainage plans and the actual conditions. On the other hand, for an operating power plant you need to focus on high-traffic routes, locations where standing water has occurred in the past, and areas where shoulder collapse has been observed.

When checking road level differences, it is important not to focus too much on the height of the step itself. In actual maintenance, the severity of the issue is determined by a combination of the step’s height, length, width, surrounding slopes, drainage routes, pavement materials, direction of vehicle traffic, and workers’ movement paths. Even a small step should be prioritized for inspection if it is in a place where water tends to collect, just before a curve, or on a route frequently used for equipment inspections. Conversely, even if the numerical height difference is relatively large, if it is in an area that is not used by traffic or can be safely bypassed, immediate large-scale repairs may not be necessary.

The advantage of drone surveying is that it makes it easier to capture road level differences within the overall topography and pathway layout of a power plant. From ground-level visual inspection, you can grasp the bumps and dips directly in front of you, but it is not easy to simultaneously understand over what area those level differences continue, whether they are locations where rainwater from the surroundings collects, or where they fall along vehicle traffic routes. By photographing from above and organizing the results, including elevation information when necessary, you can confirm road level differences as surfaces rather than points. This makes it easier to consider the scope of repairs and to explain them to stakeholders.

At the stage of organizing the inspection objectives, it is advisable to share among administrators, construction personnel, and maintenance personnel what magnitude of level difference will be treated as a problem. Data obtained from drone surveying are useful, but having data alone does not automatically determine decisions. Depending on the power plant’s road width, vehicle traffic, pavement conditions, management standards, and the contractual inspection scope, it is necessary to decide what to record and what to designate as repair candidates. In particular, when compiling a report, rather than simply stating “there is a level difference,” organizing information up to which road sections and what kinds of operational issues are expected will make it easier to link to subsequent actions.

Using Drone Surveying to Identify the Location and Areal Extent of Level Differences

The main reason for using drone surveying to check road level differences at solar power plants is that it makes it easy to capture a wide area quickly and in an areal manner. On-site roads extend around the plant perimeter, between rows of panels, around transformer and substation equipment, and near the administration building and entrances, and checking all of them on foot to the same level of accuracy takes time. In particular, road level differences may appear to be localized, but in reality they can spread as continuous subsidence or shoulder deformation. With drone surveying, you can confirm changes across the entire roadway from a bird’s-eye view using continuously captured aerial images.

When checking road level differences, you must first clearly define the area of interest. Whether you target the entire power plant, only the internal roads, or include access routes and external connection roads will change the flight plan and the method for organizing results. Within the power plant there are panels, mounting racks, fences, utility poles, wiring equipment, drainage channels, and so on, all of which affect road sightlines and imaging conditions. If the road surface you want to inspect for level differences is obscured by shadows or vegetation, it becomes difficult to judge the condition from images, so attention must be paid to the shooting season and time of day.

In areal assessments, it is important to consider horizontal positions together with changes in elevation. Even with aerial photographs alone, ruts, scour, sediment accumulation, traces of puddles, and shoulder collapse can sometimes be visually confirmed. However, to grasp the magnitude of level differences, deliverables that allow verification of pavement elevation differences and slope changes are effective. By utilizing terrain models and point clouds, contour lines, and longitudinal and cross-sectional profiles produced by drone surveying, it becomes easier to determine where a level difference begins and where it continues.

However, drone surveying results include errors caused by imaging conditions and processing conditions. When checking small elevation differences, such as road level differences, the reliability of the results varies depending on image overlap, flight altitude, the arrangement of ground control points and check points, the appearance of the road surface, and the effects of vegetation and shadows. You should avoid assuming that all small bumps and depressions can be accurately judged by drone surveying alone. In practice, a realistic workflow is to extract suspicious locations from the drone survey and, if necessary, perform on-site leveling checks, staff measurements, or simple step verifications.

When recording the locations of road surface irregularities, linking them to the power plant’s internal identification number or the road section name makes subsequent work much easier. For example, expressions like “approximately X meters from the entrance of the north perimeter road,” “the aisle between panel rows in section X,” “near a drainage manhole,” or “the access road in front of the substation” that field personnel can immediately understand will make repair instructions and rechecks smoother. Simply indicating positions on drone survey outputs can cause confusion when translating them into on-site work. Combining map coordinates, positions on photographs, and on-site landmarks increases the practicality of the records.

When assessing the extent, it is important to look not only at the center of the step but also at its spread forward, backward, left and right. Road surface unevenness may result from a single point suddenly sinking, but in reality the entire pavement can be gently tilted or deformed from the road edge toward the center. Especially on crushed-stone surfaces, movement of surface stones or ruts can cause only the wheel track positions to become lower. Viewing the entire road from above makes it easier to determine whether a local repair is sufficient or whether leveling over a certain section is necessary.

Also, the positional relationship between road level differences and adjacent equipment is important. If level changes progress near rows of panels, they will affect not only passage during patrols but also the efficiency of tasks such as mowing, washing, rack inspections, and cable checks. Road level differences along a fence may impede the routes for security patrols and perimeter inspections. Level differences around substation equipment and junction boxes will also affect where inspection vehicles and material delivery vehicles can stop. Overlaying the locations of these facilities on an overall map obtained from drone surveys allows a more realistic assessment of the range of impact of the level differences.

Consider not only elevation differences but also the effects on drivability and drainage.

When evaluating road level differences, the numerical height difference is an important metric, but relying on it alone can lead to incorrect prioritization in practice. On-site roads at solar power plants may be used by inspection vehicles, light-duty work vehicles, material delivery vehicles, and mowing machines, and the impact of road level differences on vehicle operability varies depending on the situation. Even when the height of the level difference is the same, the severity of the hazard and the extent of disruption change depending on whether the difference is nearly perpendicular to the direction of travel, a gradual change in gradient, located near a curve, or partway up an incline.

When checking the results of drone surveying, it is important to look at both the longitudinal and transverse directions of the road. Longitudinal elevation steps can cause vehicles to pitch fore and aft or scrape their undersides. Transverse steps and irregularities in cross slope can lead to vehicle tilt, drifting toward the shoulder, and uneven drainage. Roads inside power plants in particular may have limited width, and settlement or collapse at the road edges can effectively reduce the usable width. Because aerial photos alone can make it difficult to determine the directionality of elevation changes, it is effective to check cross-sections derived from the terrain model.

The impact on drainage must not be overlooked. Road level differences are not merely bumps and dips; they can change the flow of water. When depressions form in the pavement, puddles can remain after rainfall, making it easier for gravel and sediment to be displaced. If there are steps or raised areas that cross the road, water may not flow in its intended direction and can concentrate in low spots. When water concentrates, scour and shoulder collapse can progress, which may in turn make the level differences even larger. At solar power plants, drainage ditches, catch basins, slopes, balancing ponds, and natural runoff paths are all related to roads, so road level differences should not be treated separately from drainage planning.

Drone surveying allows you to assess road elevation differences and the surrounding terrain together. By looking not only at the road surface but also at adjacent slopes, drainage ditches, the ground surface beneath panels, and low-lying areas within the site, it becomes easier to understand why a level difference has occurred at a given location. For example, if sediment is flowing in from one side of the road, a portion that appears to be a step may actually be a buildup caused by deposited material. Conversely, even if part of the road surface appears low, scour may be progressing where surrounding drainage converges. Using the results of drone surveying makes it easier to formulate hypotheses about these causes.

To assess traversability, it is necessary to be aware of the continuity of travel routes. Within a power plant there are multiple movement lines: the route from the entrance to the main equipment, the perimeter patrol route, management routes between panel rows, routes used in emergencies, and so on. Even if a section has a step, the priority of response differs depending on whether it can be safely passed via an alternative route or whether that path must be used to approach the main equipment. Conducting drone surveys to obtain an overhead view of the entire roadway makes it easier to confirm not only the locations of level differences but also the presence of detours and the overall condition of the travel routes.

In practice, when evaluating level differences, organizing them not simply as “high” or “low” but from the perspectives of “whether they impede passage,” “whether rainwater tends to accumulate,” and “whether they are likely to expand if left unrepaired” makes reports more useful. Especially when explaining to management companies or power plant owners, showing numbers alone may not lead to a decision. By combining plan drawings and elevation-difference materials obtained from drone surveys with on-site photos and operational concerns, it becomes easier to convey the need for repairs.

On the other hand, when assessing drivability from drone survey results, the on-site road surface conditions should also be checked. Even if images or point clouds look flat, in reality the crushed stone may be loose, the ground may be prone to becoming muddy, or the road shoulder may be difficult to see because of vegetation. Conversely, even if the data shows many small irregularities, they may not significantly impede vehicle traffic. Survey results are useful as material for decision-making, but for final maintenance management decisions they must be combined with on-site judgment.

Enhance decision accuracy by cross-checking on-site inspections with survey results

Drone surveying is effective for broadly identifying road level differences at solar power plants, but you should avoid making conclusions based solely on the results. Road level differences can appear differently depending on vegetation, shadows, pavement materials, lighting conditions during imaging, wetness after rainfall, and accumulation of soil and debris. In particular, on gravel or dirt surfaces, surface patterns and color variations can look like level differences. Conversely, actual level differences can be masked by grass or shadows. Therefore, it is important to verify and cross-check candidate locations extracted by drone surveying with on-site inspections.

In on-site checks, we first plot the locations of concern identified by drone surveys onto maps and photos so they can be reached on site without confusion. Within power plants, panel rows and roads often look similar, and photos alone can lead to misidentifying locations. Recording plot numbers, road names, equipment numbers, the direction from the entrance, and landmarks such as fences and drainage facilities together makes field verification smoother. Turning drone survey outputs into a form usable on site not only reduces work time but also helps prevent omissions during inspections.

When verifying level differences on site, perform simple measurements as needed as well as visual inspection. Checking pavement elevation differences, the depth of depressions, the width of ruts, the distance from the shoulder, and the relationship to drains and manholes can reveal discrepancies between drone survey results and actual site conditions. When using this information to make repair decisions in particular, it is desirable to record not only photos but also measurements and field notes. For locations that require numerical accuracy, adding ground surveying or checks using control points can increase the reliability of your judgments.

What is important in on-site inspections is estimating the cause of the elevation step. The necessary countermeasures differ depending on whether the pavement has simply settled, whether it appears as a step because surrounding sediment has flowed in, whether the shoulder has collapsed and narrowed the travel width, or whether pavement material has been washed out due to poor drainage. Drone surveys make it easy to grasp broad-scale topography and water flow, while on-site inspections make it easier to confirm pavement stiffness, material condition, scour depth, and sediment accumulation. By combining both sets of information, the step can be understood not as a superficial bump but as a maintenance and asset-management issue.

When reconciling survey deliverables with on-site verification, it is also important to be aware of whether any changes occurred between the date the imagery was captured and the date of on-site verification. Roads at solar power plants can change condition over a short period due to rainfall, vehicle traffic, repair work, mowing, or sediment movement. If heavy rain occurs after a drone survey, level differences may become larger or new puddles may form. Conversely, if temporary repairs have been carried out after the imagery was captured, the conditions visible on-site may not match the survey results. Recording the imagery capture date, the verification date, and the weather and road surface conditions at the time of verification in the report makes later review and judgment easier.

Verification results should be organized so that all stakeholders share the same understanding. Road level differences at power plants involve multiple responsible parties, including equipment inspection, civil maintenance, safety management, and material delivery. Rather than presenting only the technical outputs of drone surveys, compiling the target section, characteristics of the confirmed level differences, anticipated impacts, on-site inspection findings, and recommended next actions in a single flow creates a document that is easier to use in practice. When repairs are required in particular, explaining not only the stepped sections but also drainage routes and surrounding terrain helps inform measures to prevent recurrence.

Also, to improve decision accuracy, it is important to share the limitations of drone surveying with stakeholders. Drone surveying excels at capturing conditions over wide areas, but results can be uncertain in places where road surfaces are covered with grass, under the shadows of structures, in narrow passages, or in locations affected by reflections or wetness. When a strict determination of the presence or absence of small changes in elevation is required, confirmation on the ground should be assumed. Drone surveying is not a universal decision-making device; it should be positioned as a means to efficiently narrow down areas that need verification and to organize the overall picture, which will stabilize its use on site.

Managing road surface level differences as records for continuous comparison

Road level differences at solar power plants should not be treated as a one-time check; it is important to manage them as records that can be continuously compared. Level differences and surface irregularities may widen over time, or may only become noticeable during the rainy season or after typhoons. Even roads that had no problems at handover can, after several years of operation, experience displacement of surfacing materials, the emergence of drainage patterns, or the formation of ruts where vehicle traffic is concentrated. Regular use of drone surveying makes it possible to record these changes from the same perspective and use them for comparison with past conditions.

To perform continuous comparisons, it is important to standardize shooting conditions and the way results are organized as much as possible. If records are taken at completely different altitudes, coverage areas, reference standards, or output formats each time, it becomes difficult to compare them with past data. When used for periodic inspections, deciding in advance on a standard coverage area for the entire power plant, the road sections to focus on, the format for storing results, and the method for recording candidate step locations makes it easier to maintain continuous management even if personnel change. Because road level differences can include very small changes, aligning the assumptions behind the data used for comparison is particularly important.

When keeping records, it is useful in practice to manage the location, extent, condition, impacts, and response status of unevenness as a single integrated item. For example, if an unevenness is identified on a section of roadway, linking aerial imagery of the location, site photos, simple measurements, nearby drainage conditions, and repair history makes it easier to detect changes at the next inspection. Simply saving photos in folders can leave the location or the reasons for decisions unclear when reviewed later. Linking the results of drone surveys with management ledgers and inspection records makes it easier to manage the history of road unevenness.

In continuous comparisons, it is important to look not only at the amount of change but also at the trend of that change. Whether a particular unevenness is becoming slightly larger each time, worsens only after rainfall and becomes less noticeable during dry periods, or recurs after repairs will change how you consider the causes and countermeasures. For example, if an unevenness repeatedly occurs at the same location, you may need not only superficial pavement repairs but also a review of drainage routes and an inspection of the roadbed condition. If drone surveying records wide-area changes, the issue can be organized as a maintenance and management challenge for the entire power plant rather than treated as an isolated malfunction.

Managing road level differences also relates to safety management. When inspectors and contractors move around the premises, knowing in advance where level differences exist allows route warnings and work plans to take them into account. In particular, for nighttime operations, emergency checks after bad weather, delivery of heavy loads, and grass-cutting work, information about road conditions affects work safety. Recording road level differences with drone surveys makes it easier to share information before entering the site, helping to reduce risky passage and oversights.

Recording road surface unevenness also helps when considering the scope of repairs and work planning. Specific costs vary depending on site conditions and repair methods, but to judge whether repairs are necessary and what their scope should be, it is necessary to organize which sections have how much deterioration. If drone survey results are available, stakeholders can review the same drawings and images while discussing priorities. For example, areas near entrances with high traffic, access routes to power receiving and transforming equipment, and sections where poor drainage is occurring are candidates for priority inspection. If records are well organized, the need for rework during on-site explanations can also be reduced.

What you need to be careful about in continuous management is not being satisfied with merely increasing the amount of data. Even if you repeat drone surveys, unless you compare the results, make judgments, and reflect them in subsequent actions, it will not lead to improvements in maintenance. After a survey flight, it is important to establish a workflow for checking differences from the previous survey, road sections that require attention, locations that need on-site inspection, and the condition of repaired areas. If reports are prepared in the same format each time, managers will find it easier to track changes. Managing road-level differences at solar power plants requires operating surveying, inspection, repair, and reinspection as a continuous cycle.

Summary

Road surface level differences at solar power plants tend to be management items that are overlooked compared with the power generation equipment itself, but they are important elements related to patrols, maintenance, deliveries, safety management, and drainage maintenance. Even small level differences or surface irregularities should be identified early when they occur on roads with high traffic, in locations where drainage concentrates, or along routes essential for equipment inspections. By using drone surveying, you can inspect on-site roads from above across the entire area, making it easier to identify the locations and extents of level changes and their relationship to the surrounding terrain.

However, rather than determining all road surface level differences solely from drone surveys, it is important to combine them with on-site inspections and ground measurements. The way results appear can vary depending on shooting conditions, pavement condition, vegetation, shadows, and changes after rainfall. Drone surveys are effective when used as a means to efficiently extract locations that should be checked within a large power plant and to enable stakeholders to share the same information. By evaluating not only the height of level differences but also drivability, drainage, traffic routes, and repair history, you arrive at judgments that are practical and usable in the field.

Do not treat checks for road level differences as a one-off inspection; it is also important to keep them as regular comparative records. By organizing data from completion, scheduled inspections, after heavy rainfall, after repairs, and so on, it becomes easier to detect trends of widening or recurrence of level differences. In the operation and maintenance of solar power plants, managing road conditions to keep the site safe to use is as essential as inspecting the power generation equipment. If you want to efficiently check road level differences across a large site and link them to inspection records and repair decisions, creating a drone surveying system tailored to site operations is effective.