5 items to detect poor drainage at solar power plants using drone surveying

At solar power plants, it is important not only to inspect the generating equipment itself but also to continuously monitor drainage conditions on the site. If drainage problems are left unaddressed, they can lead to slope erosion, scour around racking foundations, muddy maintenance roads, standing water around cables, and delays in mowing and inspection work, potentially affecting operation and maintenance across the entire plant. Water flow and topographic changes that are easily overlooked during ground patrols can be more readily confirmed in an area-wide view from above by using drone surveying. When flying drones, you must check relevant regulations such as aviation law, the facility manager’s rules, the surrounding environment, and weather conditions, and plan with safety as the top priority. This article explains five items that operational personnel should check to detect drainage failures at solar power plants using drone surveying.

Table of Contents

• The importance of detecting poor drainage at solar power plants

• Check the extent of standing water and how puddles persist after rain.

• Read the low-lying parts of the terrain and the flow paths where water tends to accumulate.

• Check for signs of erosion and scouring on slope faces and constructed surfaces.

• Suspect clogging around drains, catch basins, and culverts.

• Assess the impacts on racking foundations, access roads, and the areas around the cables.

• How to Leverage Drone Survey Results for Maintenance Management

• Summary

The Importance of Detecting Poor Drainage at Solar Power Plants

In managing solar power plants, attention tends to focus on power output, panel soiling, equipment abnormalities, and weed overgrowth, but the site's drainage condition is also an important inspection item for stable operation. In particular, at plants on reclaimed land, in mountainous areas, on slopes, or in valley terrain, rainwater flow can concentrate in certain areas more than anticipated, and over time this can affect the ground and management roads.

Poor drainage initially appears as small puddles and deposits of mud. However, if left unaddressed, topsoil can be washed away, slopes can be eroded, the area around the foundations of mounting structures can become unstable, and passage for inspection vehicles may be impeded. Furthermore, if drains are clogged and heavy rain occurs, water can overflow even in places where problems are not normally visible, causing sediment to be carried downstream.

Ground-based patrol inspections are indispensable, but solar power plants have continuous rows of panels that tend to block sightlines, making it difficult to grasp the overall flow of water across the entire site at once. Areas under the panels, behind the mounting racks, outside the maintenance roads, and near the toe of the slope are places where it is hard to get an overall picture even by walking inspections. This is where drone surveying is useful.

In drone surveying, the entire solar power plant can be photographed from above and, when necessary, organized into orthophotos, point clouds, and topographic data. This makes it easier to confirm across the site where water remains, which direction it is flowing, and over what extent terrain changes are occurring. Poor drainage should not be assessed by looking at a single point; it is important to examine the connectivity from upstream to downstream. In that sense, drone surveying is one of the methods well suited to drainage management at solar power plants.

However, photographing with a drone does not automatically reveal all drainage issues. The timing of the capture, where to look, combining it with ground verification, and comparing with past data are all important. In particular, because how water remains changes with time—immediately after rain, a few hours later, the next day—the inspection results can differ even for the same power plant. To detect drainage problems, drone surveying must be carried out not as mere aerial photography but with a perspective aimed at finding signs of drainage issues.

View the extent of standing water after rain and how puddles persist

The most straightforward check for detecting poor drainage is the extent of standing water after rainfall. It is not uncommon for water to pool immediately after rain, but if certain spots continue to hold water even as the surrounding area begins to dry, insufficient drainage slope, ground subsidence, blockage of drainage routes, or an overly compacted surface may be suspected.

Drone surveys make it easier to identify the location and extent of puddles because they provide an overhead view of the entire power plant. During ground patrols, you can confirm the puddles immediately in front of you, but it can be difficult to judge how large they are relative to the whole site, whether multiple puddles are occurring in the same row, or whether they continue downstream. From above, you can compare whether standing water is concentrated between panel rows, along access roads, at slope toes, or around catch basins.

What matters is not just whether puddles are present, but how they persist. For example, even if a large puddle temporarily forms in one corner of a power plant, it may not be a major problem if it disappears after a few hours. On the other hand, if even a small puddle remains for a long time, the ground may be slow to dry, which could affect workability and the conditions around equipment. Because water depth is difficult to determine accurately from aerial images alone, a practical approach is to use drones to narrow down the area and then confirm the necessary locations on the ground.

The timing of photography is also important. During or immediately after heavy rain, the entire site may be wet, making it difficult to distinguish abnormal areas from normal wetness. If you want to check drainage capacity, wait some time after the rain stops and compare places where water has naturally drained with places where it remains—this makes it easier to judge. Of course, since safety and flight conditions must be prioritized, avoid attempting flights that would be unsafe.

Also, appearances change with the seasons. In summer, evaporation is faster and puddles are less likely to remain, while weeds become denser and make the ground surface harder to see. In winter, drying is slower and muddy conditions can persist for longer. During the rainy season or after typhoons, drainage problems are more likely to surface, but at the same time it is necessary to check for signs of sediment runoff and slope deformation. It is important not to judge from a single shoot; keep records that reflect how things appear at different times of year.

When recording the locations of puddles, organize the information so it clearly shows which block within the power plant, which panel row, and which nearby maintenance road they are near. Simply writing "puddle on the north side" makes it difficult to pinpoint the location later for repairs or reinspection. Indicating the area on images created by drone surveys and correlating them with ground photos and inspection notes makes the information much more usable for operations and maintenance.

Reading Low Points in Terrain and Water-Collecting Flows

Poor drainage can sometimes be too late to address if you only deal with it after it becomes visible as puddles. By analyzing where water is coming from and where it flows, you can identify locations that are likely to cause problems in the future. A major advantage of using drone surveying is that it allows you to assess the terrain across the entire power plant, making it easier to find low spots and flow paths where water tends to collect.

In solar power plants, even when a drainage plan is laid out during site development, actual rainwater flow is affected by subtle undulations, compaction conditions, vegetation growth, sediment accumulation, and ruts in access roads. Water that on drawings is supposed to flow into drainage channels may on site run between rows of panels or collect in low spots on access roads. These field realities can be difficult to discern from ground-level viewpoints alone.

When you check terrain information obtained from drone surveying, it becomes easier to identify slight elevation differences and depressions. In particular, the center of the developed surface, the boundary between cut and fill, the upper parts of slopes, curves in maintenance roads, and areas just before connections to drainage channels require attention as places where water tends to accumulate. It is natural for water to gather in low-lying parts of the terrain, but if that water is not safely drained and remains around equipment, it can lead to problems.

When assessing water flow, always check the upstream and downstream together. If you look only at areas of standing water, it may seem that only that spot is the problem, but in reality the direction of the water can be altered by a blockage in an upstream drainage channel or by raised access roads. Within the power plant site, because the rows of panels are neatly aligned, one tends to assume the water will flow in the same direction, but a slight slope in the graded surface can cause it to flow diagonally.

Also, drainage problems may not be confined to the inside of the power plant. Rainwater flowing in from adjacent land, surface runoff from the mountainside, inflow from surrounding roads, or insufficient capacity of perimeter drainage can also have an impact. Conducting drone surveys that include the perimeter makes it easier to identify where water enters the site from off-site and where it flows out of the site. However, when photographing areas outside the site, it is important to limit the scope to what is necessary and to consider the flight area, land-rights issues, privacy, and safety management.

When reading terrain, be careful not to determine slope solely from the appearance of an image. Shadows, grass, soil color, and wetness can make areas look different from their actual elevation differences. Especially during times when panel shadows are strong, it can be difficult to discern surface undulations. If possible, check the same location on days with different conditions, and, if necessary, verify heights and drainage directions on the ground to improve the accuracy of your judgment.

Understanding the terrain is essential when considering drainage improvements. Simply filling in the places where water collects with soil can change the paths the water takes and cause pooling to move to other locations. Using drone surveys to understand how water accumulates, and formulating measures after examining the relationships with drainage channels, catch basins, slopes, and maintenance roads, is the key to reducing rework.

Check for signs of erosion and scour on slopes and cut-and-fill surfaces

Poor drainage can appear not only as standing water but also as movement of sediment. At solar power plants, when rainwater concentrates on graded surfaces or slopes, the topsoil can be scoured away and narrow rill-like erosion channels can form. In the early stages these may appear only as small streaks or differences in soil color, but with repeated rainfall the channels deepen and can affect slope stability and drainage performance.

Drone surveying allows inspection of the entire slope from above, making it easier to identify the continuity of erosion that is difficult to see from the ground. When inspecting from below and looking up at the slope, it can be hard to confirm subtle deterioration at the top or the lateral extent. From above, traces of rainwater flowing along the same channels, places where sediment has accumulated, and areas where vegetation has thinned are easier to find.

Erosion also requires attention around support foundations and drainage structures. When rainwater flows around foundations or along the edges of access roads, it can locally wash away soil. In particular, the downstream ends of drainage channels, areas around catch basins, the toes of slopes, and the outlets of cross drains are places where water velocity tends to concentrate and where scour often begins. If drone imagery shows exposed soil, narrow rills, accumulated sediment, or turbid water flow, those locations should be inspected in detail on the ground.

When inspecting erosion on engineered slopes, comparing with past images is effective. A single survey flight can make it difficult to determine whether a feature is part of the original terrain or a recently formed deformation. By conducting regular drone surveys and comparing the same area, you can confirm whether gullies are widening, sediment accumulation is increasing, or the extent of vegetation loss is changing. Areas where changes are progressing are more likely to be experiencing poor drainage or continued concentration of rainwater.

Also, the condition of vegetation on slopes provides clues. Compared with areas where grass grows uniformly, places where grass is thin in streaks or where soil is exposed may indicate that rainwater is concentrating and flowing. Conversely, in areas where wet conditions persist, the species and density of grass may appear different from the surrounding area. Rather than drawing conclusions from drone images alone, it is important to assess vegetation, sediment, topography, and traces of water together.

When erosion or scouring is found, immediate large-scale repairs are not always required. However, if you locate the problem while the deformation is still minor, you can consider cleaning drainage channels, protecting the downstream outlet, repairing the surface, and dispersing stormwater before soil loss spreads. At solar power plants, large areas are often managed by a small team, so if abnormalities are noticed only after they have become extensive, responding can take time. Early detection through drone surveying also helps reduce maintenance costs and the labor burden.

Suspect clogging around drainage channels, catch basins, and culverts

A common cause of poor drainage is clogging of drains and catch basins. At solar power plants, grass blown by the wind, mowed grass, fallen leaves, sediment, small stones, and similar debris can enter drainage pathways and gradually impede flow. In particular, after mowing, after strong winds, and after heavy rain, debris tends to accumulate at the inlets and bends of drainage equipment.

With drone surveying, it becomes easy to follow the entire length of a drainage channel from above, making it simple to identify which sections have standing water and where sediment has accumulated. In ground inspections, some parts of the drainage channel can be overlooked, and it can be difficult to reach collection points located behind rows of panels. By checking the whole system from the air, you can narrow down spots where the channel changes color, where it is obscured by vegetation, and where water appears to be flowing back.

The area around a catch basin is a particularly important inspection point. If sediment and grass accumulate at the inlet of the catch basin, water can overflow into the surrounding area and standing water can spread across access roads and between rows of panels. Depending on whether there is a cover and on its construction, you may not be able to see the interior from above, but by observing how the surrounding area is wet, the buildup of sediment, the way vegetation has been flattened, and how the water has spread, you can judge the likelihood of a blockage.

Culverts and underground drains are facilities that are difficult to inspect directly from above. However, abnormalities can be suspected from the areas around culvert inlets or outlets, the wetness of the ground surface, linear bands of residual water, or localized subsidence. For example, if water is not flowing out of a culvert outlet but ponding remains upstream, there may be a blockage or damage somewhere along the line. Conversely, if only the area around the outlet is heavily scoured, the outfall protection may be inadequate.

When inspecting drainage facilities, it is important not only to determine whether they are clogged but also to record conditions that make clogging likely. Check whether grass clippings tend to accumulate nearby, whether the slope allows soil and sediment to flow in, whether the location is difficult to inspect, and whether it is distant from maintenance roads and hard to clean. Even if a drainage facility is cleaned once, it will clog again if the same conditions remain. If drone surveys repeatedly reveal anomalies in the same locations, consider reviewing not only cleaning but also the structure and maintenance methods.

Also, insufficient capacity of the drainage channels may be suspected. Even if there is no problem during normal rain, locations that only overflow after heavy rainfall may have drainage routes that are inadequate for the volume of water collecting from the surrounding area. However, it is dangerous to conclude from images alone whether the issue is insufficient capacity or a blockage. It is necessary to identify abnormal locations with drone surveying and then make a determination after confirming on site the presence of deposits, flow conditions, and the condition of the drainage outlet.

Assess impacts on mounting structure foundations, maintenance roads, and areas around cables

The purpose of detecting poor drainage is not just to find puddles. What’s important is determining how that water affects the power plant’s equipment and maintenance work. In particular, racking foundations, access roads, and areas around cables are places where the effects of poor drainage are likely to appear.

Around the mounting foundation, concentrated rainwater can wash away soil and create depressions around the foundation. This does not necessarily lead immediately to structural problems, but if erosion progresses the area around the foundation may appear unstable and the bearing conditions of the ground surface may change. With drone surveys, you can view whole rows of panels and identify locations where the ground surface color or shape differs for particular rows. If you find areas of concern, inspect on the ground the condition of the soil around the foundation, any settlement, cracks, and the drainage direction.

Management roads are important routes used by inspection vehicles and workers. When drainage is poor, muddy conditions, ruts, shoulder collapse, and gravel washout can occur, hindering inspections, grass cutting, and emergency response. In particular, on management roads that run through low-lying areas, roads along slopes, and roads parallel to drainage channels, water can flow over the road and erode the surface. From above, it is easier to confirm how water remains along ruts, soil washout from shoulders, and deposits alongside the road.

Attention should also be paid to areas around cables. At solar power plants there are various electrical installations such as underground conduits, exposed conduits, cable racks, and junction boxes. If poor drainage causes the surrounding area to remain constantly wet, it not only makes working conditions during inspections worse but is also undesirable as an environment around the equipment. Of course, electrical abnormalities cannot be determined from drone images alone, but checking whether there is standing water or sediment accumulation around cable routes can help decide the priority of maintenance inspections.

Poor drainage also affects weed management. In areas that tend to stay moist, grasses grow more easily, and grass clippings can flow into drainage channels, making them more likely to clog. If access roads become muddy, mowers and inspection vehicles have difficulty getting in, which can result in increased weed proliferation. By overlaying locations of standing water with areas of dense weeds from drone surveys, the relationship between drainage and vegetation management becomes clearer.

When assessing impacts on equipment, it's practical to evaluate hazards in stages. Sort and organize areas where access or inspections are immediately obstructed, areas likely to worsen in the next heavy rain, and areas that can be left under observation. Trying to fix everything at once makes prioritization unclear, but drone surveying that provides an overview of the entire power plant makes it easier to determine which areas to address first.

How to Leverage Drone Survey Results for Maintenance Management

When signs of poor drainage are detected in drone surveys, it is important to incorporate those findings into inspection records and repair plans. Simply capturing images and saving them may not be sufficient for subsequent inspections or for sharing with stakeholders. In practice, it is essential to organize the workflow as a continuous sequence from capture, verification, and documentation to on-site response and reinspection.

First, decide the area you want to check before shooting. Even when regularly photographing the entire power plant, designating areas prone to poor drainage as priority inspection zones can reduce oversights. For example: perimeter drainage, slopes, low sections of access roads, areas around sumps/collection pits, and places that have experienced standing water in the past. To enable comparison from the same viewpoint each time, it is also effective to keep shooting altitude, coverage, and timing as consistent as possible.

In the shooting plan, checking flight safety is also essential. At solar power plants, there are elements to watch for during flight such as reflections from panel surfaces, overhead lines, trees, slopes, and workers or vehicles on access roads. When inspecting after rain, ground and road surface conditions tend to worsen, so confirming in advance the placement of the pilot and assistant, takeoff and landing locations, and emergency response procedures will make it easier to proceed safely.

Next, review the captured images and extract candidate anomalies. At this stage, it is not necessary to determine the cause from the images alone. Note areas where water remains, where sediment is flowing, where drains are obscured by grass, and where slope surfaces show streak-like changes. It is safer to identify suspected locations broadly and narrow them down during on-site verification.

During on-site inspections, we verify the locations shown in drone images against the actual conditions. Water depth, the amount of mud, clogged drains, sediment accumulation, the passability of access roads, and the condition around equipment are things that sometimes can only be determined on the ground. Drone surveying does not replace on-site verification; it is more useful when regarded as a means to efficiently identify where to carry out inspections within a large power plant.

How you keep records is also important. For abnormal areas, recording the location on the image, the date found, the weather, the elapsed time since rainfall, what was checked, and the response plan will make later comparisons easier. Because poor drainage is affected by weather conditions, recording not only the date the photo was taken but also the rainfall situation immediately beforehand makes judgment easier. The priority of responses will change depending on whether water is present this time only in places that previously had none, or whether it appears in the same places every time.

After repairs or cleaning, re-inspecting with a drone makes the effects easier to see. By cleaning drainage channels, you can confirm whether puddles have been eliminated, whether the flow has shifted to another location, or whether slope erosion has stopped. If you have before-and-after images of the measures, it also makes it easier to explain the situation to the power plant owner, the management company, and the contractors.

Also, the results of drone surveys can be used not only for one-off inspections but also for long-term maintenance. Because solar power plants have long operating periods, areas that had no problems immediately after construction can develop drainage issues years later due to settlement or sediment accumulation. By regularly recording the same locations, you can understand trends in those changes and take action before problems become serious.

What matters for practitioners is to incorporate drone surveying into routine inspections and post-rain checks, rather than using it just once as a special survey. By using it with clear objectives—such as getting an overall view after heavy rain, checking drainage conditions before and after mowing, or confirming changes after repairs—it becomes valuable material for on-site decision-making.

Summary

Poor drainage at solar power plants tends to be a lower inspection priority because it is not an abnormality of the power generation equipment itself. However, leaving drainage problems unaddressed can lead to ponding, muddiness, soil runoff, slope erosion, deterioration of access roads, scour around racking foundations, and other issues that may affect overall operation and maintenance. To operate the plant stably, it is important to understand water flow early and address problems while they are still small.

Items to check with drone surveying include the extent of ponded water after rainfall, low-lying terrain and water flow, erosion of slopes and developed surfaces, blockages in drainage channels and catch basins, and impacts on racking foundations, access roads, and around cables. By checking these from above on an area-wide basis, you can more easily identify locations that are likely to be missed during ground inspections alone.

However, drone surveying is not infallible. It is important not to determine causes from images alone, but to extract suspicious locations and combine them with on-the-ground verification. In particular, drainage problems can appear differently depending on the amount of rain, the timing of the survey, the season, the condition of vegetation, and past repair history. By conducting regular imaging and keeping records, and comparing them with past data, it becomes easier to identify the weaknesses of each power plant.

In the maintenance and management of solar power plants, you need to inspect large sites efficiently and set priorities with limited personnel. By utilizing drone surveying, you can detect signs of poor drainage early and more easily decide on cleaning, repairs, and re-inspections. Rather than relying solely on specific equipment or service names, it is important to organize the imaging objectives, required accuracy, flight conditions, and on-site inspection framework, and then choose the drone utilization method that fits your company’s power plant management.