4 Methods to Identify Puddle Locations at Solar Power Plants Using Drone Surveys

At solar power plants, leaving puddles that remain after rain can lead to difficulties in inspection, muddy conditions around the mounting racks, delays in weeding operations, deterioration of conditions around drainage facilities, and the overlooking of ground subsidence and scour. Especially at large plants, simply walking the site makes it hard to grasp the extent and patterns of puddle formation, and it can be difficult to determine whether the same locations are repeatedly affected or the pooling is only temporary.

Drone surveying of solar power plants is an effective method for broadly identifying such puddle locations from above and organizing them together with positional and terrain information. However, simply conducting aerial photography makes it difficult to sort out the causes and priorities, even if you can visually confirm where water appears in the photos. By combining the timing of post-rain photography, organization of positions using orthophotos, verification of elevation differences, and cross-checking with drainage routes, you can produce information that is easy to use for site management.

Table of Contents

• The importance of identifying puddle locations at solar power plants

• Method 1: Check for puddles from above shortly after it rains.

• Method 2 Record the location and extent of puddles in orthomosaic images

• Method 3: Reading terrain where water tends to accumulate from elevation difference data

• Method 4: Narrow down the cause by cross-referencing the drainage route with on-site conditions

• Precautions when managing puddle locations in drone surveying

• Summary

The Importance of Identifying Puddle Locations at Solar Power Plants

Solar power plants are installed on various types of land, such as former forest land, developed sites, fallow fields, landfill sites, and sloping terrain. Because the generation equipment itself is widely distributed on the ground, the ground and drainage conditions within the site greatly affect the ease of daily maintenance. Puddles may seem like a minor problem at first glance, but if they occur repeatedly in the same place, multiple factors may be involved, such as depressions in the terrain, insufficient drainage gradient, clogged side ditches, uneven embankment/fill, ruts from vehicle traffic, and dense vegetation growth.

In areas where puddles remain for long periods, it can become difficult for inspectors to walk. At solar power plants, there are occasions when personnel walk between rows of panels to perform visual inspections, mowing, cleaning, and minor repairs. When the ground is muddy, not only does work efficiency decline, but slips and soiling from mud sticking to shoe soles also become more likely. If puddles form on maintenance access roads used by vehicles, wheel ruts can deepen, creating conditions that make water collect even more easily.

Also, locations where water tends to collect can provide clues to changes in the ground. If puddles repeatedly form around the foundations of mounting structures, around cable racks, near drainage channels, or at the bases of slopes, the surface water flow may be different from what was assumed. You don't need to immediately conclude a serious fault, but it's worth monitoring continuously.

In traditional ground inspections, personnel walked the site to check puddles, take photos, and record locations. This method is suitable for checking details, but it takes time to grasp the distribution across a large site. Especially after rain, footing can be poor, making it difficult to walk and inspect every row and drainage channel. By utilizing drone surveys of solar power plants, you can view the entire site from above and more easily map and organize where puddles occur.

What is important is not to use drone surveying merely as record photography, but to prepare it in a form that can be used for on-site decision-making. By cross-referencing the locations and areas of puddles with the surrounding terrain, their relationship to drainage facilities, and past occurrences, it becomes easier to identify areas that should be prioritized for countermeasures. In the maintenance and management of solar power plants, because it is necessary to inspect wide areas within limited time, aerial overview information from drone surveying is a great help to operations personnel.

Method 1 Check for puddles from the air shortly after rain

The most important thing when identifying puddle locations is the timing of the photography. If you fly a drone after a stretch of sunny weather and no water remains, you cannot directly confirm where water tends to collect. If you want to identify puddles at a solar power plant, the basic approach is to carry out imaging after substantial rainfall, during the period when water remains on the ground.

It does not mean that any time immediately after the rain has stopped is acceptable. You should not attempt to fly during heavy rain, strong winds, or poor visibility. Prioritize the aircraft’s safety, the operator’s visibility, and consideration for the surroundings, and conduct filming only after the weather has recovered to conditions suitable for flight. Because shallow puddles disappear if too much time passes after the rain stops, it is important to set an early date to check the standing water conditions according to the objectives at the site.

When capturing images, fly with awareness of places where water tends to collect—not only to view the entire solar power plant at once but also between panel rows, along maintenance aisles, alongside drainage channels, at the bases of slopes, at the ends of racking, and around entrances and exits. From above, chains of small puddles that are hard to notice on the ground, standing water along walkways, and wet areas that are difficult to see in the shadow of panel rows may become easier to identify.

In solar power plants, reflections on panel surfaces and shadows can cause water surfaces and dark shadows to be mistaken for one another. In particular, during periods of low solar elevation, the shadows of panels and mounting racks extend long and can overlap the outlines of puddles. Therefore, it is necessary not to make an immediate judgment based solely on captured images, but to assess brightness, reflections, the surrounding terrain, and the locations of drainage facilities together. If possible, checking the same location from different angles and altitudes makes it easier to reduce misidentification due to reflections.

Shooting altitude is also an important operational factor. If it is too high, you can check a wide area at once, but small puddles or water in ruts become difficult to distinguish. If it is too low, details are easier to see, but it becomes harder to grasp the overall flow and distribution across the site. For this reason, it is effective to separate shots for overall assessment from shots that examine areas of concern in detail. First, overview the entire site to confirm the distribution of puddles, then photograph key areas at a slightly lower altitude so that both their locations and conditions are easier to record.

Also, when photographing after rain, pay attention not only to the puddles themselves but also to the traces left by flowing water. Linear grooves where soil has been eroded, areas of flattened grass, places where mud has accumulated, and signs that turbid water flowed toward drains can all be used to infer the direction of water flow. Even after the water has receded, if these traces remain, you can identify locations that are prone to forming puddles.

Post-rain drone surveys are more valuable when conducted multiple times rather than as a single event. Recording under different conditions—after heavy rain, after light rain, and after seasonal rainfall—makes it easier to compare whether water consistently remains in the same locations or whether it occurs under specific rainfall amounts or grass-height conditions. In solar power plant management, comparing past records with current conditions makes it easier to prioritize improvements.

Method 2 Record the location and extent of puddles using orthophotos

When a puddle is only observed from above, it can be difficult to accurately share its location afterward. Even if on-site personnel describe it as “at the back of that row” or “near the bend in the service aisle,” it can be hard for other staff or contractors to understand. What helps is recording the puddle’s position and extent using an orthophoto created by drone surveying.

An orthoimage is an image produced by correcting and stitching together multiple photographs taken from the air into a form that is easy to use as a map. In ordinary oblique photos, spatial relationships can appear distorted at the edges of the frame or because of the shooting angle, but when an orthoimage is properly created it becomes easier to grasp the overall layout of the plant, rows of panels, pathways, drainage channels, fences, embankments, and other relationships. When managing puddles at a solar power plant, recording the extent of the puddles on the orthoimage makes it easier to check later and to issue instructions for countermeasures.

When recording the extent of puddles, do not simply outline only the places where the water surface is visible; also check the surrounding wet ground and the spread of mud. As time passes after rain, the water surface will shrink, but muddy or damp areas may remain. What actually affects workability in walkways and between rows is not just the water surface but also the poor footing around it. Therefore, if you can record the water-surface extent and the affected area separately in images, you can manage things in a way that is more practical for operations.

When organizing location information, it is important to align it with the names used on site, such as power plant section names, panel row numbers, aisle names, and drainage ditch numbers. Position information shown only on images obtained from drone surveys may not allow field workers to immediately understand the location. For example, matching it with expressions used on site—such as north aisle, along the east fence, near the central substation equipment, or below the southwest slope—makes it easier to give inspection and repair instructions.

The advantage of using an orthophoto is that the distribution of puddles can be viewed like a single site plan. With only ground photographs you can understand the condition of individual puddles, but it is difficult to grasp whether they are concentrated in a particular direction across the whole site, whether they are more common away from drainage channels, or whether they are continuous along low walkways. Overlaying the puddles on an orthophoto makes it easier to see where they tend to occur.

Orthophotos are also effective for assessing the area of puddles. However, the area derived from images is influenced by capture conditions, processing accuracy, and how the ground surface appears. If the outline of the water surface is obscured by shadows or vegetation, it may differ from the actual extent. Therefore, it is realistic to use the measured area not as an exact design quantity but as a comparative indicator for maintenance and management. They are suitable for confirming whether a puddle has expanded since the previous observation, remains in the same location, or has newly appeared elsewhere.

When keeping records, it is useful to record the capture date, rainfall conditions, capture time, the extent of remaining puddles, and any on-site verification details together. Even the same puddle can appear different depending on the amount of rain and the elapsed time before shooting. If you only keep images, it becomes difficult to judge differences in conditions when reviewing them later. If you are using drone surveys of solar power plants for maintenance management, it is important to manage images together with on-site notes.

Recording puddles with orthoimages is a method that is easy to use in internal reports. Rather than explaining in text alone that "there are many puddles on the south side of the site," indicating the area on an image makes it easier for stakeholders to understand. Because multiple stakeholders—power plant owners, maintenance personnel, contractors, vegetation control teams, and those considering drainage improvements—can look at the same information while discussing it, it becomes easier to reduce misunderstandings about countermeasures.

Method 3 Reading terrain where water is likely to collect from elevation difference data

When considering why puddles form, elevation differences on the ground are an important clue. Water generally flows from higher areas to lower areas and tends to accumulate in depressions and places with gentle slopes. In drone surveys of solar power plants, captured imagery, positioning information, point clouds, and elevation models are used as appropriate, and by understanding the terrain’s undulations you can estimate where water is likely to collect.

If you look only at the appearance of puddles, you can tell where water remains after rain. However, it can be difficult to understand why water stays there. Checking elevation data makes it easier to examine the site-wide slope, depressions in pathways, bowl-shaped terrain at the base of slopes, transitions at the edge of fill, insufficient gradient toward the drainage outlet, and so on. This allows you not only to remove the water but also to investigate the causes that make recurrence likely.

In solar power plants, because rows of panels extend in long, narrow strips, slight differences in elevation can affect water flow. Even walkways that look flat may actually be slightly lower in the center, or vehicle ruts may act like channels. Gentle slopes that are hard to notice by walking on the ground become easier to understand when viewed across the area using drone surveying.

When using elevation difference data, it is important to view it overlaid with the locations of puddles. A low spot does not necessarily become a puddle. If a drain is nearby and flow is ensured, water may not remain for long. Conversely, even where elevation differences are small, water can stagnate in places where the outlet is blocked, vegetation is dense and obstructs flow, or sediment has accumulated. Therefore, terrain information should not be judged on its own but confirmed together with the on-site drainage conditions.

There are also limits to elevation data. In areas where grass is tall, the surface of the vegetation rather than the ground surface may be captured. Panels, mounting racks, materials, weeds, and shadows can also make interpreting the terrain difficult. To determine the causes of puddles in detail, on-site inspections and ground surveys should be combined as needed. Drone surveys are strong for grasping trends over wide areas, and it is realistic to use them for that while supplementing final detailed judgments on site.

When reading the terrain to determine where water is likely to accumulate, also pay attention to nearby inflow sources. If you only look at the locations where puddles are present, you may misidentify the cause. In reality, water may be flowing in from upstream slopes, collecting from adjacent pathways, or moving along between rows of panels toward lower areas. By surveying the entire site with a drone, you can more easily estimate not only the locations of puddles but also the upstream and downstream flows.

Confirming elevation differences is also helpful when considering priorities for drainage improvement. If only small puddles are scattered, you may decide to monitor them during routine patrols. On the other hand, if water from a wide area concentrates at a single point and affects maintenance access routes or areas around equipment, it becomes necessary to consider reviewing drainage paths, removing sediment, and repairing pavement. Using topographic data makes it easier to identify where repairs could change the flow of water.

Furthermore, if topographic data from before or immediately after construction remain, they can be compared with the current conditions. By comparing the planned slopes during development with the current surface conditions, it may be possible to identify locations where settlement, deposition, or deformation of pathways is suspected. In the operation and maintenance of solar power plants, it is important to assess changes relative to the as-built condition. Regular records from drone surveying serve not only to detect the occurrence of puddles but also as documentation to track changes across the entire site.

Method 4: Cross-check drainage routes with on-site conditions to narrow down the cause

After identifying the locations of puddles, it is necessary to narrow down why water remains there. To do that, compare images and terrain data obtained from drone surveys with drainage routes and on-site conditions. At solar power plants, multiple drainage elements are involved, such as side ditches, catch basins, drainage pipes, open channels, slope drainage, balancing ponds, and discharge points outside the site. Looking only at where puddles form can miss causes that originate upstream or downstream.

First, what you should check is whether there is a drainage outlet near the puddle. If there is a drain right next to the puddle yet water remains, possible causes include a clogged drain, accumulated sediment, overgrown vegetation, insufficient slope, or a step at the inlet. If the drainage outlet is far away, the route that conveys water may be inherently weak. Aerial surveys with a drone make it easier to grasp the positional relationship between the puddle and the drainage facilities.

Next, examine the continuity of drainage paths. If a water flow is interrupted, it spreads out and pools in low-lying areas. For example, sediment deposited partway along a passage may stop the flow, dense vegetation may block shallow channels, or ridges formed by vehicle traffic may act like small weirs. In aerial imagery, you may see bands of wetness or traces of mud flow, which can be used to infer the water’s pathway.

When verifying drainage routes, use the power plant’s design drawings and management drawings if they are available. However, the drainage plan shown on the drawings may not exactly match on-site conditions. Sediment accumulation after construction, weed overgrowth, small slope failures, ruts in access paths, and shape changes due to repairs can all alter water flow. Comparing current images obtained from drone surveys with the drainage routes on the drawings makes it easier to find discrepancies between the plan and the actual conditions.

On-site verification is also indispensable. Drone surveying excels at grasping conditions over wide areas, but it may not be sufficient to assess the insides of catch basins, the bottoms of gutters, blockages hidden by vegetation, the softness of the ground surface, or the depth of mud. Locations where puddles are identified in images should be checked on the ground as necessary to confirm drain blockages, sediment buildup, pavement settlement, and impacts on surrounding infrastructure. Using drones to narrow down candidate locations and then confirming causes on the ground improves inspection efficiency.

When narrowing down the cause, also consider the type of countermeasure. If puddles are caused by temporary blockages from fallen leaves or sediment, cleaning may improve the situation. If ruts or subsidence in a pathway are the cause, consider pavement repair or adding crushed stone. If the drainage route itself is insufficient, it may be necessary to improve channels or review the gradient. If vegetation is obstructing the flow of water, responding in conjunction with a weed-control plan is effective.

At solar power plants, equipment maintenance, civil engineering management, vegetation control, inspections, and management of risks around equipment tend to be handled separately. However, puddles are a cross-cutting problem. Poor drainage can hinder inspections and patrols, reduce the efficiency of mowing, increase sediment accumulation, and worsen the environment around equipment. By visualizing puddle locations with drone surveying and comparing them with drainage routes, stakeholders can consider countermeasures while viewing the same situation.

Drone surveying can also be used to verify the results after countermeasures. After cleaning or repairs, photographing under the same conditions after the next rainfall allows you to compare whether puddles have decreased or moved to different locations. Don’t just stop at implementing measures; recording their effectiveness makes future management decisions easier. Identifying puddle locations should not end with discovery — it’s important to treat the process as a continuous flow from confirming causes to taking measures and rechecking.

Points to note when managing puddle locations in drone surveying

When managing puddle locations during drone surveying of solar power plants, the first thing to be mindful of is safety. After rain, the site can be slippery and there may be mud where the pilot and assistants need to move. If takeoff and landing areas are unstable, the risk of the aircraft becoming soiled or tipping over increases. Before flight, choose a place where you can safely take off and land, and check for surrounding obstacles, overhead lines, fences, equipment, and worker movement paths.

Careful attention must also be paid to flight conditions. For puddle surveys, photographing after rain is effective, but you should not fly when the weather is unstable. If there is wind, fog, rain, lightning, or poor visibility, you should decide to postpone the flight. Solar power plants are often located in open areas, and some sites are particularly susceptible to wind. Prioritize conditions that allow safe flight, and as a rule do not force operations just to obtain records.

Before flying, confirm the applicable laws and regulations, flight rules, the power plant operator’s rules, and consideration for nearby residents. Depending on the power plant’s surrounding environment and the flight location, prior coordination, permits, or notifying relevant parties may be required. Do not omit safety checks or required procedures in a rush to check for puddles.

When interpreting images, it is important to avoid misidentification. What appears to be a puddle may actually be a panel shadow, wet pavement, a dark weed-control sheet, dense vegetation, or a difference in soil color. Conversely, puddles can be hard to see when hidden by grass. Aerial imagery is useful, but it cannot determine everything accurately. Critical locations need to be supplemented by ground confirmation and comparison with past images.

Also, it is important not to judge the condition of a site solely by the presence or absence of puddles. When rainfall is heavy, places where water temporarily remains will occur. The issue is how long the water remains, whether it repeats in the same location, whether it affects walkways or equipment, and whether the drainage paths are functioning. Rather than drawing major conclusions from a single recording, it is preferable to record under multiple conditions and observe the trends.

To make use of drone survey results in management, you need to decide how to organize the data. If file names and storage locations are inconsistent for each capture date, it will be difficult to compare them later. Organizing the power plant name, capture date, weather, survey purpose, target area, and puddle-check results makes past data easier to find. This is especially important when managing multiple power plants; keeping records according to the same rules is essential.

Plan how to share information with stakeholders as well to make it more practical for operational use. When sharing images taken by field personnel with maintenance managers, property management companies, contractors, and weed-control staff, you need to organize them so that it is immediately clear where the problem is. Simply sending a large number of photos will leave recipients unsure how to assess them. Mark puddle locations on an orthophoto, link them to site names or plot identifiers, and include a brief written note of the required actions to facilitate the next steps.

Furthermore, information obtained from drone surveys can also serve as supporting documentation for repairs and drainage improvements. Recording the extent of standing water, its frequency of occurrence, and its relationship to surrounding facilities makes it easier to explain and justify priorities. Aerial imagery and topographic data are useful materials when deciding where to take action first within limited budgets and work days. However, for final design and construction decisions, it is important to combine them with specialized on-site inspections and surveys as necessary.

Drone surveys of solar power plants are useful not only for detecting puddles but also for standardizing routine management. If you define the places to check after rain, the areas to photograph, the items to record, and the criteria for referring sites for ground inspection, it becomes easier to manage from the same perspective even when the person in charge changes. Building a system that enables decisions based on images and location data, rather than relying solely on individual experience, leads to stable operation and maintenance.

Summary

To identify puddle locations at solar power plants, it is effective to combine drone surveying with ground patrols to perform comprehensive, area-wide inspections. At the appropriate time after rain, inspect from the air, record locations and extents with orthophotos, read terrain prone to water accumulation using elevation data, and cross-check drainage routes and on-site conditions so the results are organized into information usable for management decisions rather than mere photographic records.

Puddles occur for various reasons, such as depressions on the site, insufficient drainage gradient, clogged side ditches, overgrown vegetation, ruts in access paths, and sediment accumulation. Rather than determining the cause from aerial imagery alone, it is important to make a judgment by combining topography, drainage infrastructure, on-site inspection, and historical records. In particular, when water repeatedly remains in the same location, or when impacts are observed on maintenance/access paths, around mounting racks, or along drainage channels, it is necessary to keep ongoing records and consider the prioritization of remedial measures.

Applying drone surveys of solar power plants to standing water management makes it easier to locate problem areas even on large sites, and facilitates sharing with stakeholders and comparing conditions after countermeasures. If used as documentation that connects routine inspections, vegetation control plans, drainage improvements, and repair decisions, it can streamline site management.

To avoid overlooking post-rain conditions and to map how water accumulates across the entire plant, it is important to standardize on-site recording methods and establish a system that enables continuous comparison. Consider using drone surveying as a means to efficiently identify water-pooling locations at solar power plants and to inform maintenance management.