Drone Surveying Techniques for Weed and Drainage Inspection at Solar Power Plants

At solar power plants, it is important not only to inspect the generation equipment itself but also to continuously monitor the condition of the entire site. In particular, weed overgrowth and poor drainage are on-site issues that can potentially affect power generation, equipment maintenance, worker safety, and operation and maintenance costs. Relying solely on ground patrols can lead to overlooking changes across the site, and inspection results may be influenced by the experience of the person in charge. A practical option is drone surveying and aerial photography, which allow wide areas to be inspected from above. This article explains, from a practical perspective, the concepts for using drone surveying to check weeds and drainage at solar power plants, pre-flight preparations, points to check, how to record findings, and how to translate those findings into on-site improvements.

Table of Contents

• Why weed and drainage inspections are important at solar power plants

• Weed management points that can be confirmed by drone surveying

• Signs of poor drainage that can be detected by drone surveying

• Site information to organize before shooting

• Flight planning considerations suitable for weed inspection

• Appropriate shooting timing for drainage inspection

• Procedures for using drone surveying data in site management

• Methods to improve accuracy by combining with ground inspections

• Points easily overlooked in weed and drainage inspections

• How to compile records and reports usable for ongoing management

• Summary

Why Weed and Drainage Inspections Are Important at Solar Power Plants

In the operation and maintenance of solar power plants, attention tends to focus on electrical equipment such as panels, mounting structures, power conditioners, junction boxes, and cables. However, to sustain stable operation it is also important to understand the condition of the site. Especially for ground-mounted solar power plants, the way weeds grow and the way rainwater flows affect power generation efficiency, equipment maintenance, and the safety of inspection work.

If weeds grow tall, they can cast shadows on the front of the panels and between rows. When shading affects part of a panel, it can lead to reduced power generation or decreased output at the string level. In addition, weeds that get tangled around fences or cables make it harder to check the condition of equipment during inspections. There is also a risk of damaging cables and piping during mowing, so it is important not to treat this as merely an aesthetic issue.

Poor drainage is also a problem that cannot be overlooked. Solar power plants are installed on land with various conditions, such as former forest land, developed sites, land converted from agricultural use, sloping terrain, and reclaimed land. Even if problems are not apparent immediately after development, repeated rainfall can cause topsoil erosion, muddy ground, puddles, clogged drainage channels, and slope erosion. In poorly drained areas, the ground around mounting foundations can be scoured, maintenance access paths can become difficult to use, and the efficiency of mowing and inspections may be reduced.

In traditional patrol inspections, personnel walk through the power plant and visually inspect the presence of weeds and the condition of drainage. While this method makes it easy to check details, it can be time-consuming at large plants and inspection coverage may be uneven. At sites with many panel rows in particular, inter-row spaces at the back, areas along fences, drainage channels, and the lower parts of slopes tend to be left until later. By using drone surveying, the entire site can be viewed from above, making it easier to grasp the areal extent of weed growth and to identify locations suspected of poor drainage.

The value of drone surveying is not merely taking aerial photographs. It lies in regularly photographing the same location so changes over time can be compared. By accumulating data on where grass tends to grow from spring to summer, where water is likely to collect after rain, and which drains are prone to clogging, you can move from ad-hoc responses to planned maintenance.

Weed management points that can be confirmed by drone surveying

In weed management at solar power plants, simply checking whether grass is present is not sufficient. In practice, you need to determine where it is growing, how much it has grown, and which equipment it is likely to affect. Drone surveying and aerial photography are well suited to capturing the overall view needed for these assessments.

First, check for weeds that could cast shadows on the front of the panels. From the ground you may only be able to see some rows, but aerial photography makes it easier to compare how far the vegetation is growing in front of the panel rows and the differences between rows. This is especially true at power plants with low-mounted racks, where grass height can cause shading. While reviewing the images, focus on areas near the lower edge of the panels, the front access aisle, and spots between rows where vegetation height is high.

Next, weeds along fences and property boundaries are also important. Areas around fences are prone to seed influx from outside, sunlight exposure, and wind, making them places where weeds readily grow. When vegetation becomes entangled in fences, it can impair inspections, lead to encroachment onto neighboring properties, and result in inadequate perimeter management. Combining angled (oblique) shots as needed makes it easier to assess the extent of growth along the fence across a wider area.

Also, weeds under the panels are easy to overlook. Because photography taken directly overhead makes it difficult to see beneath the panels, combining oblique-angle photos with ground-level checks makes it easier to assess the density of grass between rows and under the panels. If grass is dense beneath the panels, it can make checking footing during inspections difficult and may interfere with confirming cables and supporting members. When deciding whether to carry out mowing, it is important to consider not only the impact on power generation but also the safety of maintenance work.

With drone surveying, weed extents can be recorded as areas, making it easier to give instructions on mowing areas. When instructions are conveyed verbally on site, questions like "how far should we cut?" and "which rows should be prioritized?" tend to become ambiguous, but indicating the areas on aerial images makes it easier for workers to share the same understanding. Keeping before-and-after images of the mowing can also be used to verify that the work has been completed.

Also, by photographing from the same angle and area each time, you can compare seasonal growth. If you can identify locations that tend to become overgrown at the same time each year, you can move up mowing times, designate priority management areas, and consider the need for weed-prevention measures, leading to preventive management. Because weed management is not a one-time task, accumulating records from drone surveys is highly valuable.

Signs of Poor Drainage Detectable by Drone Surveying

In drainage inspections, it is important not only to check for puddles but also to understand where water flow is stopping and where sediment is accumulating. Using drone surveying makes it easier to detect terrain connectivity and abnormalities in drainage routes that are difficult to discern from the ground.

Clear signs are puddles and mud. After rain, aerial photographs can reveal places where water remains: maintenance access paths, between panel rows, around racking foundations, and near drainage channels. If puddles form in the same places every time, there may be problems with the surrounding slope, the drainage outlet, soil compaction, or the capacity or clogging of the drains. What may look like a localized problem from the ground can, when seen from above, show water from a wide area gathering in a single spot.

Next, attention should be paid to traces left by sediment flow. In places where rainwater flows strongly, narrow gully-like erosion, changes in soil color, uneven distribution of gravel, and sediment accumulation in drainage channels may be observed. When photographed from above, the water’s pathways from the upper to the lower parts of the slope can appear as linear features. If left unaddressed, this can lead to slope collapse, scouring around mounting structures, and the formation of step-like drops in pathways.

The areas around drainage channels and catch basins are also important points to check. If drainage channels are becoming clogged with weeds or sediment, rainwater may not flow along its intended course and can overflow onto the property. Viewed from above with a drone, it's easier to identify places where vegetation is densely aligned along the channels, where sediment has accumulated and changed color, and where the ground appears wetter than surrounding areas. However, aerial footage alone cannot reveal fine blockages or the condition inside covered drains, so a practical approach is to use drone imaging to pick out suspicious spots for on-the-ground inspection.

Poor drainage requires attention not only around power generation equipment but also in relation to areas outside the power plant. If water from the site flows onto neighboring properties or roads, it can lead to disputes with neighbors or management issues. Conversely, water can also flow from surrounding land into the power plant. Drone surveying provides an overhead view of the fence perimeter, the roadside, the toe of slopes, and the directions of drainage outlets, making it easier to confirm the connections of water inside and outside the site.

When checking drainage, the important thing is not to judge based only on sunny conditions. Even if problems aren’t visible on a clear day, puddles and flow channels can appear immediately after rain. In addition to photographing during regular inspections, scheduling photo opportunities after substantial rainfall makes it easier to grasp the actual extent of drainage problems.

On-site information to organize before shooting

To use drone surveying effectively, pre-flight preparation is important. Simply taking aerial photos without a clear purpose can leave you unsure when you review the images later. By organizing site information before flying and clarifying what you are trying to check, you can produce data that can be used for weed and drainage management.

The first thing to sort out is the power plant’s boundaries and equipment layout. Identify the panel rows, maintenance access paths, fences, entrances and exits, drainage ditches, catch basins, slopes, regulating ponds, and the locations of electrical equipment. If there are plant drawings or past inspection records, compare them with the planned photography coverage and decide which locations should be checked intensively. Also, incorporating the on-site personnel’s knowledge about elevation changes or areas that are difficult to access or hard to interpret from the drawings will make it easier to develop the photography plan.

Next, check locations where problems have occurred in the past. Identify in advance places where mowing was delayed, rows suspected of being affected by shadows, areas where water remained after rain, places where soil or sediment washed away, and clogged drains. Drone imaging can record wide areas, but being aware of priority spots makes it easier to secure the necessary angles and resolution.

You also need to consider the imaging objectives separately. Depending on whether you want to assess the extent of weed growth, confirm completion after mowing, check drainage routes, or record puddles after rain, flight altitude, camera angle, and timing will change.

For example, when checking the overall distribution of weeds, it is important to photograph the entire site under consistent conditions. On the other hand, if you want to check for clogged drains or slope erosion, oblique shots and additional low-altitude shots can be helpful.

Safety checks are also essential. Within a power plant there are elements to be aware of during flight, such as overhead lines, utility poles, fences, trees, slopes, work vehicles, and workers. Also, if there are residences, roads, farmland, or construction sites nearby, you need to consider the flight area and shooting direction. Drone surveying is convenient, but it is important to conduct it on the premise of complying with aviation law and other relevant regulations, obtaining permission from facility managers, taking into account the surrounding environment, and securing safe takeoff and landing locations.

Additionally, decide in advance how the images will be used after shooting. Determine who will review the images, in what format they will be saved, how they will be attached to inspection reports, and how they will be shared with mowing contractors and repair personnel; doing so makes it easier for the captured data to lead to on-site improvements. It is important not to stop at taking the photos, but to organize them in a way that can be used for decisions and instructions.

Considerations for Flight Planning Suitable for Weed Inspection

In drone surveys for weed inspection, it is effective to combine imagery that captures the entire site with detailed imaging of problem areas. At large power plants, trying to shoot closely at low altitude from the start takes a lot of time. A practical workflow is to first take an overview of the whole site, extract the ranges where growth is conspicuous, and then focus detailed checks on the locations that need them.

For the overall inspection, capture the panel rows, walkways, areas along fences, slopes, and vacant spaces so they are recognizable as a single continuous frame. Set the capture altitude to prioritize understanding the overall area rather than the fine details of the grass. Ensuring overlap between images makes it easier to confirm positional relationships later. If the power plant’s shape is complex or there are elevation differences, divide the survey area into sections to avoid any gaps.

If you want to see the height and density of weeds, angled shots are effective. Images taken directly overhead can make it difficult to judge how much the weeds are standing up. Shooting from an oblique angle makes it easier to check the positional relationship with the lower edge of the panel, the condition of weeds tangled on the fence, and the visibility between rows. However, because oblique shooting changes appearance depending on the shooting direction, it is important to set conditions that make comparison easy, such as shooting from the same direction each time.

Pay attention to the time of day when shooting. When the sun’s elevation is low, shadows lengthen and shadows cast by weeds can overlap with those from panels and racking, making them difficult to distinguish. Conversely, if you want to check how shadows appear, deliberately shooting at times when shadows are more pronounced can be useful. Separating the objective—whether it is to understand weed distribution or to assess shadow impact—makes it easier to decide on the shooting time.

When comparing before-and-after images of mowing, it is important to keep the imaging conditions consistent. If flight altitude, shooting direction, coverage area, or time of day differ significantly, it becomes difficult to compare the effects of mowing. By photographing the same plot under similar conditions, you can confirm to what extent the areas that were overgrown before the work have improved. These records are useful for work instructions, completion reports, and planning the next operation.

Also, when checking for weeds, it is important to separate locations that may cause a reduction in power generation from those that pose safety issues for work. Weeds close to the panels should be inspected with priority given to their impact on power generation. On the other hand, weeds along access paths and fence lines affect worker movement, the ease of patrolling, and the ease of equipment inspection. Organizing the site by section so you can determine from drone images which areas should be addressed first makes the process more practical for operations.

Optimal times to photograph for drainage inspection

In drainage inspections, the timing of photography greatly affects the results. If photos are taken after a prolonged period of fine weather, signs of poor drainage may be barely visible. Conversely, photographing immediately after rain makes puddles, wet soil, flow paths, and sediment accumulation more apparent. It is important to vary the timing of photography according to the purpose.

First, shooting after a substantial rainfall is effective. If not much time has passed since the rain stopped, you can identify places where water tends to remain. It becomes easier to spot locations where water remains on maintenance access paths, areas where mud has formed between panel rows, traces of water overflowing from drains, and places where sediment has accumulated at the bottom of slopes. However, flying during rainfall, strong winds, or low visibility poses safety issues, so operations should be conducted only after the weather has calmed.

Photographing some time after rainfall is also helpful. Even if water remains immediately after rain, areas with proper drainage will dry over time. In contrast, areas with poor drainage will remain damp or retain puddles even after other areas have dried. Waiting before taking photos makes it easier to determine whether the water is a temporary puddle or a chronic drainage problem.

Drone surveying is also effective for post-construction and post-repair inspections. After installing a new drainage ditch, repairing a pathway, or reshaping a slope, it is necessary to check after rainfall whether water is flowing as intended. Viewed from above, how water accumulates and the direction of flow are easy to see, making it useful for confirming the effectiveness of repairs. Even if ground-level checks make an area appear free of local problems, drone images can reveal issues when the overall drainage route is compromised.

It's important to be aware of seasonal differences. Poor drainage tends to become apparent during the rainy season and typhoon season, while in winter, with less vegetation, it can be easier to check the condition of the ground surface. From spring through summer, weeds can make drains and waterways difficult to see, so inspecting weeds and checking drainage at the same time is efficient. Keeping records while changing the purpose of photography by season makes it easier to develop a year‑round maintenance plan.

For drainage inspections, in addition to photographing from directly overhead, taking oblique shots of slopes and drainage channels is also effective. While overhead images make it easy to confirm the extent of puddles, they can make it difficult to see steps, scouring, the thickness of sediment, and the condition of slope faces. If you find a suspicious spot, take additional photos from different angles and use them to prioritize on‑the‑ground inspection.

Steps to Use Drone Survey Data for Site Management

Images and survey data obtained from drone surveying become more valuable when organized and used. Even if large amounts of captured data remain, if you don't know which image corresponds to which location, it becomes difficult to use for site management. In practice, it is important to establish a workflow of capture, organization, assessment, sharing, response, and reconfirmation.

The first thing to do is organize the captured shooting data. Record the shooting date, weather, purpose of the shoot, target coverage, elapsed time since rain, and whether it was before or after mowing, among other details. Even for the same power plant, a general inspection on a clear day, a drainage check after rain, and a completion check after mowing have different meanings. Including the date and purpose in file and folder names makes it easier to compare them later.

Next, extract the problem areas on the images. For weeds, check areas with tall vegetation, areas close to the front of the panels, areas entangled with fences or drainage channels, and areas blocking walkways. For drainage, check for puddles, wet areas, sediment accumulation, signs of runoff, and locations where blockage of drainage channels is suspected. Assign numbers or section names to the problem areas to make them easy to identify on site.

In assessments, separate locations that require immediate action from those that can be monitored over time. For weeds, prioritize areas likely to cast shadows on panels and places that obstruct inspection routes. For drainage, prioritize scour around equipment foundations, obstructions to passage on walkways, slope erosion, and spots likely to lead to external outflow. Trying to address everything at once increases workload, so it is important to organize tasks by impact and urgency.

When creating shared documents, ensure that site personnel, managers, and workers have the same understanding. Indicating the target area on aerial images and including the section name, required actions, priority, and verification date makes the information easier to grasp. Rather than writing only "there is a lot of grass on the north side," showing the area on the image reduces misunderstandings. In cases of poor drainage, it is also important to use expressions that make the location clear, such as "a puddle in the walkway on the east side of row 3."

After measures are taken, we will photograph again to confirm the state of improvement. For grass cutting, you can compare before and after the work. For drainage repairs, check how water remains after the next rainfall. By performing this re-check, you can determine whether the measures were effective. Drone surveying can be used not only to detect problems but also to verify the effectiveness of measures.

How to Improve Accuracy by Combining with Ground Verification

Drone surveying is excellent for gaining an overview of large areas, but not everything can be determined from aerial imagery alone. The actual height of weeds, blockages inside drainage ditches, the softness of the ground, minor scouring around mounting foundations, and the condition around cables all require ground inspections. By combining drone surveying with ground inspections, you can improve verification accuracy.

An effective approach is to first capture the entire site with a drone and narrow down locations where problems are suspected. Then limit the areas for ground inspection. Rather than walking the entire large power plant, it’s more efficient to concentrate inspections on the locations identified by aerial footage. Narrowing the patrol area is especially helpful for safety during the summer months when vegetation is thick or after rain when footing is poor.

During on-site inspection, verify how much impact the issues seen in aerial images actually have. For weeds, check whether vegetation height is close to the bottom edge of the panels, whether there are times when shadows fall on them, and whether they are entangled with cables or racking. For drainage, check the water depth, extent of muddy areas, discharge destination, thickness of sediment accumulation, and the passability of access routes. Because the impression from aerial images can differ from on-site reality, it is important to examine both and make a judgment.

Record the results of on-site verification by linking them to the aerial images. If you only keep on-site photos, you may not know where each photo was taken. Number the aerial images and organize the on-site photos and notes using the same numbers; this makes them easy to understand when reviewed later. This linkage is especially important at power plants managed by multiple people.

We will also reflect insights gained on-site in the next drone flight plan. For example, if a drainage ditch was hard to discern in the aerial photos, next time we will shoot that area from an oblique angle. If the grass under the panels was difficult to see, we will change the shooting angle or time of day. In this way, by repeatedly improving drone surveying and ground verification, an inspection method tailored to the site is created.

Drones do not completely replace human inspections; if they are seen as tools to make inspections more efficient and to provide more information for decision-making, they become easier to adopt in practice. View the entire site from the air and verify the details on the ground. This division of roles is effective for weed and drainage management at solar power plants.

Points Easily Overlooked When Checking Weeds and Drainage

When using drones for surveying, you need to pay attention not only to the convenience but also to aspects that are easy to overlook. Aerial images are excellent for grasping the overall picture, but depending on shooting conditions and how they are interpreted, they can lead to incorrect judgments.

When inspecting for weeds, be careful not to judge grass height from overhead images alone. An overhead view can show the area the grass covers on the ground, but it can be difficult to accurately determine height. Even if the density is high, the impact may be small if the grass is short, and conversely, even a small area of tall grass in front of the panels may require priority action. It is important to combine angled shots with on-the-ground inspections.

Also, attention should be paid to how shadows appear. Depending on the time of day the photo is taken, the shadows cast by panels, mounting racks, fences, and nearby trees will change. You need to confirm whether dark areas in the image are shadows from weeds, shadows from equipment, or simply differences in exposure. When judging the impact on power generation, being aware of the time the photo was taken and the position of the sun can reduce misunderstandings.

When checking drainage, it is difficult to make a judgment unless the amount and timing of rain are recorded. Just because there are no puddles after a light rain does not necessarily mean there are no drainage problems. Conversely, water may remain only temporarily immediately after heavy rain. Recording not only the date the photos were taken but also the rainfall conditions, the time until the photos were taken, and how dry the site was will make ongoing comparisons easier.

Be careful not to focus only on puddles. Signs of poor drainage can appear even when no water remains. Check for sediment buildup, topsoil erosion, uneven gravel distribution, changes in vegetation, ruts in pathways, and streak-like marks on slopes. Especially in clear weather, make a point of looking for traces left after the water has disappeared.

Consideration must also be given to the resolution of drone images. Capturing images from a high altitude allows efficient inspection of a wide area, but small drain blockages and fine erosion become hard to see. Conversely, capturing at a low altitude reveals details but makes it difficult to grasp the overall picture. Depending on the purpose, it is practical to separate overall inspections and detailed inspections.

Additionally, careful management of captured data is necessary. As the number of images grows, it takes time to find the data you need. Organize them by date, section, and purpose, and add comments to important locations so they can be easily used during the next inspection or in reports. Drone surveying is not just about taking photos; it only proves effective when the data are organized into a usable state afterward.

How to Compile Records and Reports for Use in Continuity Management

For weed and drainage inspections at solar power plants, it is important not only to rely on a single inspection result but to track continuous changes. The condition of a plant varies with seasons, rainfall, mowing, site development status, and the surrounding environment. By accumulating records from drone surveys, you can identify locations and times when problems are likely to occur and reflect that in maintenance planning.

In the records, the capture date, purpose of capture, weather, capture area, inspection results, and actions taken are kept together. For weed inspections, record the extent of growth, equipment suspected to be affected, the area requiring mowing, and the timing of the next inspection. For drainage inspections, record the location of puddles, traces of sediment outflow, the condition of drainage ditches, whether ground-level verification is necessary, and the need for repairs. Combining these with aerial images makes the report easier for stakeholders to understand.

In reports, it's important to describe not only whether a problem exists but also the reason for your judgment. Simply stating "weeds present" does not indicate the priority for response. If you write something like "Vegetation is dense close to the front of the panels and may affect shading and inspection access, so prioritize it at the next mowing," it will facilitate management decisions. For drainage as well, writing "After rain, water remains in the center of the accessway and dries more slowly than the surrounding area, so an on‑site check of the slope and drainage outlet is necessary" makes the next actions clear.

In ongoing management, comparative images taken from the same position are useful. Lining up before-and-after photos of mowing, before and after rain, before and after repairs, and seasonal changes makes it easier to see the effectiveness of improvements and patterns of recurrence. In particular, if you can identify trends—such as grass growing in the same spot at the same time every year, or water remaining on the same path under similar rainfall conditions—it becomes easier to develop preventive measures.

Drone images are also effective for work instructions. If you indicate the mowing area on the image, you can reduce misunderstandings about the scope of work. Even for drainage repairs, indicating on images where soil removal, channel cleaning, pathway repairs, and slope inspections are required can shorten on-site briefing time. The fact that the power plant manager, on-site personnel, and contractors can discuss while looking at the same image is a major practical advantage.

Also, in the long term, it is effective to review drone survey records together with power generation data and inspection records. By checking whether periods when weeds grew coincide with drops in power generation, and whether equipment failures occurred where drainage problems took place, you can improve the accuracy of maintenance. However, because fluctuations in power generation involve multiple factors such as solar irradiance, temperature, equipment condition, and grid-side constraints, you should not conclude that weeds or drainage alone are the cause and must make a comprehensive judgment.

Summary

Using drone surveying for weed and drainage inspections at solar power plants lets you view large sites from above and makes it easier to identify locations prone to problems. For weed management, you can comprehensively assess conditions across areas such as in front of panels, between rows, along fences, around drainage channels, and on maintenance access paths. For drainage management, it becomes easier to check for puddles, muddy patches, sediment runoff, blockages in drainage routes, and changes to slopes and pathways.

The important thing is to use drones not merely as aerial photography tools but as materials for maintenance decision-making. Clarify the purpose before shooting, vary shooting timing and angles for weed checks and drainage checks, and link problem areas to on-the-ground inspections to improve the accuracy and efficiency of inspections. Furthermore, if you organize captured data together with the date, weather, plot, and actions taken, you can use it for mowing plans, drainage repairs, work reports, and recurrence prevention.

Solar power plants continue to experience changes in site conditions even after they begin operation. Weed growth varies with the seasons, and drainage problems become apparent depending on rainfall patterns and site development conditions. That is why it is important to combine regular drone surveys with on-the-ground inspections to visualize changes at the site. If you want to streamline weed and drainage checks, do not rely solely on drone imaging; managing and linking drone footage with site records, inspection results, and repair histories leads to improved maintenance accuracy.