5 Drone Survey Items to Check Before Corrective Work at Solar Power Plants

In corrective work at solar power plants, deciding the scope of work without accurately understanding on-site conditions tends to lead to rework and additional measures. In particular, post-development terrain changes, poor drainage, slope failures, settlement around the mounting racks, and damage to maintenance access routes can be difficult to fully grasp from ground-level visual inspection alone. Drone surveying, which records the entire site from above and can organize spatial relationships and elevation differences, is useful for this. This article organizes 5 drone-surveying items to check before corrective work at solar power plants in a way that makes it easy for field personnel to judge on site.

Table of Contents

• Purpose of conducting drone surveying before remedial construction work

• As Item 1, confirm the current topography and elevation differences.

• As Item 2, check the drainage routes and areas prone to standing water

• As Item 3, check for deformation of slope faces and the edges of earthworks

• As Item 4, check for changes to the mounting structure, foundation, and surrounding walkways

• Confirm the construction scope and delivery route as Item 5

• How to Organize Drone Survey Results to Support Remedial Construction Work

• Summary

Purpose of conducting drone surveys before corrective construction

The purpose of conducting drone surveys before corrective work at a solar power plant is not simply to take site photos. The goal is to record the pre-construction conditions together with location information, making it easier for stakeholders to share where problems exist and which areas need to be repaired. Solar power plants cover large sites, with rows of panels, mounting racks, slopes, drainage facilities, maintenance walkways, fences, and other elements spread across wide areas. For that reason, simply walking the site may uncover individual anomalies, but it can be difficult to explain their positional relationships within the entire site.

In corrective construction work, multiple stakeholders may be involved, such as the contractor, power plant operator, maintenance personnel, design staff, landowners, and, in some cases, administrative authorities and neighboring stakeholders. If only those who have visited the site understand the situation, reaching agreement on the scope of work can be delayed and the conditions for estimates can become ambiguous. Creating aerial images, point clouds, and terrain models that provide an overview through drone surveying makes it easier to explain to stakeholders who have not visited the site where and what is happening.

Also, recording the condition before corrective work helps with post-construction comparisons. Improvements to poor drainage, repairs of settled areas, slope regrading, and pathway restoration all need to be checked after the work to confirm whether they were truly improved. If pre-construction records are insufficient, it becomes difficult to objectively explain the differences before and after improvement. By preserving the pre-construction condition with drone surveying, you can compare it with post-construction re-surveys and photographic records, making it easier to explain the effects of the corrective measures.

Especially at solar power plants, the flow of rainwater and slight changes in ground conditions can lead to malfunctions. If drainage becomes blocked or stagnant, muddy maintenance access paths, slope erosion, scour around foundations, and soil movement around cable routes can occur. These problems are difficult to identify by looking at a single point; it is necessary to consider the site’s overall slope, the directions of runoff collection, the locations of drainage facilities, and changes in terrain together. Drone surveying is well suited to capturing this overall picture.

However, conducting drone surveying does not automatically determine the corrective measures. Survey results must be interpreted together with site inspections, existing drawings, design conditions, construction history, and maintenance records. The important thing is not to finish the survey data as a "neat deliverable" but to organize it into a form that can be used as material for decisions on corrective work. For that purpose, before imaging or surveying you need to decide what you want to verify, what area you want to compare, and the level of accuracy with which you want to make judgments.

Although there are many points to check before corrective work at a solar power plant, in practice it is easier to organize them into five items: existing site topography, drainage, slopes, racking/foundations/walkways, and the construction area and movement lines. By checking these in order, you can not only identify problem areas but also produce surveying deliverables that support construction planning, stakeholder briefings, and post-construction verification.

Item 1: Confirm the current site topography and elevation differences

Before starting corrective work, the first things to confirm are the current topography and elevation differences. At solar power plants, the planned finished ground level from site development may not perfectly match the actual terrain. In addition, after the start of operation, rainfall, vehicle traffic, ground settlement, and soil movement can alter the terrain from its initial condition. Before performing corrective work, it is necessary to understand the current terrain and identify the locations that require repair and their priorities.

Drone surveying makes it easier to understand the overall shape and elevation differences of a site from images captured from above. Especially at large power plants, gentle slopes and low-lying areas can be difficult to notice just by walking the site. Even areas that appear flat may, overall, be low-lying places where water tends to collect. Using aerial survey results allows you to confirm elevation differences and surface undulations across the site, making it easier to determine the extent of areas requiring corrective action.

When checking the current site topography, you should not only look at high and low elevations but also consider their relationship with surrounding facilities. For example, locations such as between panel rows, at the bases of mounting racks, at the ends of maintenance access walkways, around drainage channels, along fences, and near the toe of slopes are places where terrain changes are likely to affect equipment maintenance. If water collects in low spots, it can cause settlement or muddy conditions. Conversely, raised areas can obstruct drainage flow.

If existing grading plans or as-built drawings are available, comparing them with the current terrain makes it easier to identify areas with significant changes. However, if the drawings' coordinate system, reference points, creation date, or surveying method are unclear, it is important not to judge based solely on simple differences. Old or simplified drawings may not match current conditions. Therefore, when making comparisons, confirm the reference position and elevation, and carefully assess whether the differences actually indicate changes in the terrain.

In remedial work, expanding the scope of work too much increases the burden, while making it too narrow may leave factors that cause recurrence. Measuring the existing topography makes it easier to explain how far repairs should extend. For example, instead of fixing only the single point that has settled, you can determine the area to be leveled by examining the surrounding slopes and drainage direction. This is important for stabilizing the effectiveness of the remedial work.

Also, terrain inspection relates to safety. Steps in maintenance access paths, unstable undulations near slope shoulders, and the gradients of locations where vehicles enter can lead to accidents during work or to vehicles becoming stuck. If the entire site is checked by drone surveying before corrective work, workers can identify in advance the places that require attention and the areas where heavy equipment should avoid entering. It also becomes easier to use this information for on-site safety planning.

What matters when checking the current site topography is not producing extremely detailed survey data itself, but extracting the information necessary to decide on corrective works. By organizing which areas are low, which direction water is likely to flow, and what effects there are around access paths and mounting racks, the topographic data becomes information usable for construction planning. In drone surveys of solar power plants, it is important to be mindful of both visual clarity and ease of use for on-site decision-making.

As Item 2, check the drainage routes and areas prone to standing water

One of the aspects that tends to be particularly important in corrective work at solar power plants is checking drainage routes and areas prone to standing water. Solar power plants have panels arranged over wide sites, and there are many areas where rain falls directly on the ground surface. If rainwater does not flow properly, it can lead to muddy access ways, slope erosion, scouring around foundations, sediment buildup in drainage channels, and runoff beyond the fences. Clarifying the drainage conditions before corrective work is important from the perspective of preventing recurrence.

In drone surveying, you can check the overall slope and low-lying areas of the site and estimate where rainwater is likely to flow. Actual water flow varies depending on soil type, surface conditions, grass growth, clogging of drainage facilities, rainfall amount, and so on, but topographic elevation differences are an important factor. In particular, places where water collects between rows of panels, where water flows across maintenance access aisles, and places where water stalls partway instead of heading toward drainage ditches are easier to understand when survey results are combined with on-site photographs.

When checking for areas prone to standing water, an on-site inspection immediately after rain is also useful. Surveys conducted only in clear weather can leave the ground surface dry and make water flow difficult to discern. If possible, keep photo records and field notes from after the rain and organize them by linking them to the drone survey’s location data. Confirming where puddles form, how far they spread, and the direction of any flow traces makes it easier to determine the scope of remedial works.

When checking drainage routes, we also verify whether the existing drainage facilities are functioning. Even if drains, catch basins, cross pipes, culverts, side ditches, and outfalls are installed, they will not work properly if clogged with sediment or vegetation. In addition, settlement after development or movement of sediment can prevent water from reaching the drainage facilities. By using drone surveys to confirm the terrain and inspecting the condition of drainage facilities on site, it becomes easier to determine whether cleaning will suffice or if slope corrections or additional installations are necessary.

In solar power plants, raindrops falling from the panels can cause streak-like erosion on the ground surface. If this progresses, it may affect the bases of the racks and the areas around cables. Drone imagery can sometimes reveal differences in ground color, streak-like traces, and the direction in which soil or sediment has flowed. Ground-level photos tend to provide only localized records, but viewing from above makes it easier to determine whether similar erosion is occurring across multiple rows or is concentrated in a particular slope direction.

Also, drainage problems may not be confined to the site. If rainwater is flowing in from outside the power plant or water from within the plant is flowing out of the site, inspecting the boundary areas is important. Use drone surveys to assess conditions along fences, neighboring property boundaries, the roadside, the forested side, and the farmland side, and verify traces of inflow and outflow on site. When determining the scope of corrective work, consider whether repairs within the site will be sufficient or whether measures at the boundaries are necessary.

When checking drainage routes, it is important to separate and organize causes and effects. The puddles themselves are the effect, and possible causes include ground subsidence, insufficient drainage slope, clogged equipment, increased inflow, and sediment accumulation. Drone surveying provides an overall dataset to help isolate each of these. By overlaying puddles found on site onto a map and checking them against surrounding elevation differences and the locations of drainage facilities, it becomes easier to determine the direction of corrective work.

As Item 3, check slopes and the edges of the development for deformation

Before remedial work at a solar power plant, it is also important to check slopes and the edges of developed areas for deformation. At plants installed on developed land, deformations can appear on fill and cut slopes, at development edges, at drainage junctions, and along fences. Even small erosion or soil runoff, if left unaddressed, can expand in extent and potentially affect maintenance access routes, racking, and drainage facilities. Using drone surveying makes it possible to inspect the condition of entire slopes from above and makes it easier to identify areas of concern and prioritize responses.

When inspecting slopes, check for collapses, cracks, scouring, denudation of the ground, uneven vegetation, sediment accumulation, and concentrated drainage. When confirming conditions from the ground, you may not be able to safely approach the top or bottom of the slope. In areas with poor footing, forcing an approach can create a risk of falling or sliding. Using drones makes it easier to inspect conditions from above or at oblique angles even in areas that are difficult to access. However, fine cracks and the condition of the ground surface should be checked on the ground as needed, in combination with drone inspections.

At the edges of earthworks, check whether the ground near the boundary has subsided, whether rainwater is concentrating, and whether soil is flowing toward neighboring properties. Solar power plants may be installed in mountainous areas, hilly terrain, land-development sites, or idle land, and there can be significant elevation differences between the site and its surroundings. If there are abnormalities at the edges of the earthworks, they may affect not only the equipment on the site but also the surrounding environment and relations with neighboring properties. Recording the condition before corrective work makes it easier to use as explanatory material for stakeholders.

When inspecting slopes with drone surveys, images taken from oblique angles as well as from directly above are effective. Images taken directly above make it easy to understand positional relationships, but they can make it difficult to discern the slope’s inclination and three-dimensional deformations. Combining oblique images makes it easier to grasp features such as the slope crest, slope toe, steps, depth of erosion, and the flow of sediments. When creating survey deliverables such as point clouds or 3D models, it is also necessary to plan the photography so that slope areas are not omitted.

When inspecting slope deformation, always check its relationship with drainage. Even if it appears that only part of the slope has collapsed, the cause may be rainwater flowing in from above. If the drainage ditch near the slope crest is clogged, if water from a pathway is flowing onto the slope, or if rainwater from rows of panels is being concentrated in one direction, surface repairs alone may allow recurrence unless upstream conditions are checked. In drone surveys, it is important to confirm not only the slope but also the upstream topography and drainage routes.

The condition of vegetation can also provide clues for slope inspections. Areas with very little grass, exposed soil, locations where the color differs from the surroundings, or where plants are flattened may indicate rainwater flow or sediment movement. Such surface differences can sometimes be easier to detect in images taken from above. However, because vegetation color and density also change with the seasons, do not judge based on this alone; field confirmation and comparison with past images are more practical.

When inspecting slopes before remedial work, it is important to distinguish between locations that require immediate repair and those that can be monitored over time. Trying to fix everything at once can make the scope of work too large. Conversely, overlooking changes that warrant attention can become a major problem later. Using drone surveying to capture the overall picture and to organize the locations and extents of changes, the distances to nearby facilities, and their relation to drainage makes it easier to determine priorities.

As Item 4, check for changes around the mounting structures, foundations, and access paths

During remedial work at a solar power plant, it is also important to check the conditions around the racking, foundations, and maintenance access routes. If ground movement or poor drainage occurs close to the power generation equipment itself, it can affect maintainability and safety. Because drone surveys can inspect the layout of panel rows, the positions of access paths, and the surface conditions around foundations over a wide area, they make it easier to understand both localized defects and overall trends.

Around the mounting racks, check for exposed foundations, scouring at the feet, ground subsidence, accumulation of sediment, and traces of water flow. When inspecting from the ground, visibility beneath the panels is poor, and it takes time to inspect every row under the same conditions. Aerial images can also have areas that are hard to see because of panel shadows and angles, but they provide clues to changes in the surface by row and trends in water flow. If necessary, combining oblique drone photography with ground photos makes assessment easier.

Changes around the foundation should be checked carefully because they affect the long-term stability of the power plant. For example, if soil is eroding only around the foundation, rainwater may be concentrating in that area. Conditions such as the foundation appearing to float, there being a step or unevenness around it, or sediment flowing in one direction are signs that the cause should be investigated during corrective work. However, avoid making a definitive judgment about the foundation’s integrity based solely on drone surveys; it is important to carry out specialist inspections and on-site measurements as needed.

Maintenance access routes directly affect the constructability of corrective works. Mud, ruts, uneven surfaces, subsidence, and poor drainage on the routes can hinder the passage of construction vehicles and the delivery of materials. Vehicles entering the site to perform corrective work can further damage the routes. Conducting a drone survey in advance to assess the overall condition of the access routes and to identify problem areas makes it easier to develop delivery and temporary-works plans.

In areas around pathways, pay attention to places where rainwater crosses the path. The path may be blocking the flow of water, or conversely the path may be acting like a channel. In such locations, you may need to consider not only repairing the path but also cross drainage or slope adjustments. Using drone surveys to understand elevation differences and water flow, and verifying these together with on-site mud and erosion traces, makes it easier to specify corrective measures.

Also, at solar power plants, attention must be paid to the ground conditions around cable routes and electrical equipment. In locations where cables are buried, where conduits are likely to become exposed, and around junction boxes and electrical equipment, soil runoff and water ponding can become operation and maintenance issues. Using drone surveys to clarify overall spatial relationships and supplementing details with on-site inspections can reduce oversights. Decisions related to electrical equipment should always be made in coordination with the appropriate personnel.

When inspecting around mounting frames, foundations, and walkways, it is important not only to view defects near equipment as "points" but to look at the extent of occurrence as "areas." Organizing whether scouring is observed at multiple locations in the same row, whether settlement is occurring only along specific walkways, or whether sediment is accumulating on the downstream side of drainage routes makes it easier to infer the cause. By compiling this information before corrective work, you can more easily prevent countermeasures from being overly focused on localized repairs.

Item 5: Confirm the construction scope and delivery routes

During pre-correction drone surveys, confirming the work area and the access routes for vehicles and materials is also important. Even if the location of a defect is known, unless it is confirmed where vehicles and materials will enter, which areas will be used temporarily, and whether the work will affect power generation equipment or existing structures, it cannot be incorporated into the actual construction plan. Because equipment at solar power plants is distributed over a wide area, securing access to the correction site and sufficient workspace tends to be a challenge on site.

By using drone surveying to view the site from above, you can comprehensively identify entry and exit points, maintenance walkways, spacing of panel rows, fence locations, existing drainage facilities, adjacent roads, and areas that could be used for temporary material storage. Even on large sites that would take a long time to inspect on foot, aerial images make it easier for stakeholders to consider delivery routes and work areas on the same drawings. For meetings about corrective works, simply having this kind of overall map makes it easier to reduce misunderstandings.

When checking access routes for deliveries, inspect the width that vehicles can pass through, locations where turning is possible, areas with steep slopes, places prone to becoming muddy, and spots with level differences. Because drone surveys alone cannot fully determine pavement strength or fine-level differences, they should be combined with on-site inspections; nevertheless, they are effective for narrowing down candidate routes in advance. In particular, when bringing in heavy machinery or materials, confirm the condition of the passage beforehand and, if necessary, consider temporary protection or rerouting.

When confirming the scope of work, we look not only at the corrective target location but also at the areas around it that may be affected. When improving drainage, if upstream and downstream are not considered, water may concentrate in another location. For slope repair, it is necessary to check the work space, temporary storage of excavated soil, diversion of drainage, and the distance to nearby equipment. For pathway repairs, detour routes during construction and impacts on maintenance and inspections must also be considered. Visualizing the work area using drone survey results makes it easier to carry out these assessments.

In addition, corrective work may require coordination with the operation of power generation equipment. If the work area is close to panel rows or if work is carried out around electrical equipment, safety management and confirming the scope of shutdown are necessary. Organizing the positional relationships of equipment through drone surveying and indicating the construction area and caution zones on a diagram makes it easier to use for pre-work meetings. Allowing on-site personnel to check the same materials together helps prevent accidents and avoid rework.

Do not forget to check fences and access points. Even if there is a location close to the correction area, you may not be able to bring materials in from there. Confirm the width of the access points, connections to surrounding roads, the position of existing fences, whether they can be opened or closed, and the boundaries with neighboring properties. If there is a possibility of affecting roads outside the site or the surrounding environment, it is important to make the necessary adjustments early. Drone survey images are easy-to-use materials for explaining these surrounding conditions.

Organizing the work area and delivery routes makes it easier to improve the accuracy of estimates and scheduling for corrective work. If estimates are prepared while site conditions remain unclear, additional work is likely to occur during construction. By using drone surveying in advance to grasp current conditions and clarifying the work area, travel routes, temporary storage locations, and points of caution, stakeholders can align conditions and more easily create plans. Surveying before corrective work is not only a site check but also an activity to enhance the quality of construction preparation.

How to Organize Drone Survey Results for Use in Remedial Construction

To leverage drone survey results for remedial construction, it is necessary to be conscious of how deliverables are presented and used. Even if you produce high-resolution images and point clouds, they will be difficult to use in construction planning if stakeholders do not know where to look. For materials prepared before remedial construction, it is important to organize them so that the problem locations, estimated causes, scope of response, priorities, and methods for post-construction verification are clear.

First, include information that specifies the location in the survey results. Indicate which part of the power plant it is, which row of panels it is near, which walkway it is along, and which drainage facility it relates to. A single photograph alone can make it difficult for someone unfamiliar with the site to grasp the location. Combining an overall map, an enlarged map, and on-site photographs makes it easier for the client and the construction personnel to understand the situation.

Next, classify the pre-remediation conditions. Organize them by type of defect—such as ground subsidence, poor drainage, slope erosion, pathway damage, scouring around foundations, and sediment accumulation—so that it becomes easier to consider corrective measures. If multiple problems exist at the same location, explain causes and effects separately. For example, rather than looking only at a muddy section of pathway, organize information to include upstream rainwater inflow, the pathway gradient, and the condition of the drainage outlet.

Organizing urgency and priority is also important. If you separate locations into those that require immediate safety measures, those to be addressed before the next heavy rainfall, and those suitable for monitoring, it becomes easier to schedule corrective works. Prioritization should be judged not only by the extent of deterioration but also by proximity to equipment, frequency of worker passage, impact on the surroundings, likelihood of recurrence, and so on. Results from drone surveying can be used as supporting evidence to explain and justify these decisions.

It's also important to organize the surveying conditions on the premise that comparisons will be made after construction. To compare pre- and post-correction, you should match the survey extent, imaging conditions, control points, and the format of deliverables as closely as possible. Even if you cannot make the conditions exactly the same, recording the assumptions for comparison will make later verification easier. By retaining the pre-correction data, it becomes easier to explain how the terrain changed after construction and whether the drainage routes were improved.

For materials intended for stakeholders, it is also important not to rely too heavily on overly technical wording. Expressions that surveyors understand can be difficult for clients or managers to grasp. While using the necessary technical terms, provide explanations that make clear what is happening on site and what the corrective works will fix. Drone surveying of solar power plants is not an end in itself; it is a means to share site issues and connect them to appropriate remedial works.

Summary

The items to check with drone surveying before corrective work at a solar power plant can be organized into five: current topography and elevation differences, drainage routes and ponding locations, deformation of slopes and edges of created ground, changes around racking, foundations, and accessways, and the work area and delivery routes. By confirming these in advance, it becomes easier to grasp not only the problem locations but also their causes and the impacts on surrounding areas.

On remedial work, if decisions are made by looking at only part of the site, countermeasures can become localized and leave causes for recurrence. By utilizing drone surveying, you can take an overhead view of a large site and organize the relationships among topography, drainage, facilities, access routes, and boundary areas into a single document. This helps with building consensus on the scope of work, organizing estimate conditions, construction planning, safety management, and post-construction comparison and verification.

However, it is not appropriate to try to make all assessments based solely on drone surveying. Fine ground-surface conditions, blockages in drainage facilities, details around foundations, and checks related to electrical equipment need to be combined with on-site inspections and verification by specialists. The important thing is to grasp the overall picture with drone surveying, supplement the details with on-the-ground verification, and organize the information in a form that can be used for corrective (remedial) work.

To smoothly carry out corrective work at a solar power plant, it is important to assess the current conditions before construction. Recording the site’s condition from the air and ensuring stakeholders can make decisions while looking at the same materials makes it easier to reduce rework and misunderstandings. To proceed consistently from pre-correction surveys and organizing the scope of work through to post-construction comparative checks, it is important to combine drone surveying with on-site inspections and review of existing drawings, and to apply it in a way that fits the site conditions.