5 Preparations for Conducting Pre-Renovation Surveys of Solar Power Plants Using Drone Surveying

In refurbishing a solar power plant, whether the on-site conditions are correctly understood greatly affects subsequent design, estimating, construction planning, and schedule management. In particular, issues such as settlement of reclaimed land, poor drainage, deformation around mounting racks, deterioration of access roads, and obstructions caused by weeds or accumulated deposits are often not fully discernible from drawings alone. One effective method is drone surveying, which can verify large areas from the air. However, simply flying a drone does not immediately produce materials that can be used for refurbishment decision-making. To utilize it in pre-refurbishment investigations, it is necessary to organize in advance the purpose, scope, accuracy, site conditions, safety management, and intended use of the deliverables.

Table of Contents

• Organize the renovation objectives and the scope of the survey first.

• Compare existing documents with on-site conditions.

• Finalize flight plans and safety management in advance

• Establish criteria for surveying accuracy and verification items

• Align the intended use of deliverables with the renovation plan.

• Summary

First, organize the renovation objectives and the scope of investigation

When conducting drone surveying as a pre-renovation investigation of a solar power plant, the first thing to clarify is "what are you measuring for?" Whether you want to understand overall degradation trends across the plant, check for problems in drainage routes, consider changes to racking or panel layouts, or determine the repair scope for access roads and slopes will change the required survey coverage and the information that needs to be confirmed. If you plan flights while the purpose remains vague, you are likely to face rework after shooting, such as "the necessary locations weren't captured," "height information is insufficient," or "the data is too coarse to use for renovation design."

In pre-refurbishment surveys, the purpose is not simply to take clean photographs of the plant. As material for decision-making before construction, it is important to clarify where problems exist and what scope should be subject to refurbishment. For example, if a plant is suspected of poor drainage, you need to check not only the condition of the panel rows but also the drainage channels, collection sumps, slope toes, sedimentation areas, and the connection points for drainage leaving the site. If settling or tilting of the mounting structures is an issue, it is important to examine the grading of the prepared surface, height differences between rows, deformations of the surrounding ground, and the directions in which rainwater tends to flow.

When deciding the survey scope, consider separately whether to measure the entire site uniformly or to focus on candidate areas for renovation. A comprehensive survey is suited to updating management records and grasping degradation trends because it allows an overview of the power plant’s overall topography and equipment layout. Conversely, surveying focused areas makes it easier to obtain the detailed information useful for renovation design and for estimating construction quantities. While one of the strengths of drone surveying is that it can capture a wide area in a short time, when using it to inform renovation decisions it is necessary to balance broad coverage with detailed inspection.

Also, at solar power plants the items to be checked are wide-ranging, including panel rows, mounting racks, areas around power conditioners, areas around cubicles, management roads, drainage facilities, slopes, fences, and entrances/exits. Depending on the scope of the renovation, it may be better to separate and organize checks of the electrical equipment itself from civil engineering terrain inspections. Drone surveying is effective for understanding the terrain and layout, but it cannot substitute for assessing the internal condition of electrical equipment or for detailed equipment diagnostics. It is realistic to define the scope drone surveying will cover on the assumption that it will be combined with on-site visual inspections, inspection records, and electrical measurement results.

When setting the scope of an inspection, it is important not to overlook the areas surrounding the renovation target. For example, even if you only check the drainage channels, you may misidentify the cause if you do not look for sediments flowing in from upstream or rainwater entering from nearby slopes. In repairing management roads, checking not only cracks in the road surface but also shoulder collapse, poor drainage, vehicle circulation, and material delivery spaces makes it easier to reflect these issues in the construction plan. In pre-renovation surveys, you need a perspective that reads not only the visible defect but also the background circumstances that led to it.

Before commissioning or conducting drone surveying, organizing the survey objectives in writing reduces misunderstandings among stakeholders. For example, clarify the intended use in forms such as "overall understanding of the power plant's current condition", "identification of areas with poor drainage", "inspection of ground deformation around mounting racks", "reviewing the scope of renovation work", and "creation of baseline data for pre- and post-construction comparisons". If there are multiple objectives, it is also important to set priorities. Trying to satisfy everything in a single flight can complicate shooting conditions and deliverable specifications, making the resulting materials harder to use on site.

Furthermore, it is essential to be mindful of recording the conditions at the time of the survey. A solar power plant can appear differently depending on the season, weather, vegetation growth, puddles after rain, and sunlight conditions. To enable later comparison of pre-refurbishment survey results, it is helpful to record the survey date, weather, rainfall up to the previous day, whether mowing was carried out, and the areas that were accessible. Because looking only at drone survey results can make it difficult to determine why things appeared as they did, records of site conditions should be regarded as part of the survey deliverables.

Reconcile existing documentation with on-site conditions

Before using drone surveying for pre-renovation investigations, gather as many existing documents as possible and identify the points that need to be checked on site. Solar power plants may have as-built drawings, site layout plans, grading/land development plans, drainage plans, racking layout drawings, access/maintenance road maps, boundary documents, past inspection records, repair history, patrol reports, photo ledgers, and so on. By reviewing these materials in advance, it becomes clear what should be verified with drone surveying.

When reviewing existing documentation, be aware that the drawings may not match the current conditions on site. Drainage installations may have been added after completion, access roads may have been repaired, and the positions of fences or the use of entrances and exits may have changed. In addition, changes made during construction may not have been fully reflected in the drawings. In pre-renovation surveys, it is important not to treat existing documentation as the definitive answer, but to use it as a clue to identify differences from the actual site.

In drone surveying, you can obtain aerial images and topographic data that cover the entire power plant. By overlaying existing drawings on these, it becomes easier to identify layout discrepancies, undocumented equipment, changes in drainage routes, and deformations of roads and slopes. However, if the coordinate conditions, scale, or creation date of the existing drawings are unclear, it is dangerous to make accurate judgments based solely on a simple overlay. You should confirm the drawing reference, on‑site control points, coordinate system, and the accuracy of the surveying results, and, if necessary, verify reference points on site.

At solar power plants, panels and mounting structures are arranged in regular patterns, so aerial photos can sometimes make the site appear orderly. However, for pre-refurbishment surveys it is important to detect small changes within that regular appearance. For example, changes such as only some rows having narrower aisle widths, the ground around mounting structures having subsided, sediment having flowed along slopes, drainage channels being obscured by grass or sediment, or the edges of service roads having sunk can be difficult to grasp from ground level alone. Comparing existing records with drone survey results makes it easier to identify these changes.

During site-condition checks, confirm not only the area where the drone will be flown but also the takeoff and landing sites, the operator’s standing position, the placement of assistants, vehicle parking locations, and the movement routes of personnel. Even on large solar power plant sites, rows of panels, fences, electrical equipment, slopes, mud, and weeds can limit the areas where work can actually be carried out safely. During the pre-renovation survey stage, it is helpful to record site access conditions with future construction and material deliveries in mind.

Vegetation growth also affects the accuracy and visibility of drone surveys. When grass is tall, it becomes difficult to see the ground surface, drainage channels, slope toes, and road shoulders. If you want to check topography and drainage conditions in a pre-rehabilitation survey, you need to consider whether to measure before or after mowing. The condition before mowing is useful for identifying maintenance issues, but after mowing may be more suitable for confirming ground elevations and drainage structures. Depending on the objective, it is important to decide the timing of imaging and the schedule of on-site preparation.

When reconciling existing documentation with on-site conditions, it is important not to proceed with surveying while leaving uncertainties unresolved. For example, if you decide the flight area while the power plant’s boundaries are unclear, you may inadvertently include adjacent land in the area to be photographed. If drainage outlets connect outside the site, failing to confirm the relationship with off-site areas can lead to overlooking the scope of adjustments required in renovation plans. It is essential to clarify the survey targets by organizing the site’s accessible areas, permissions from stakeholders, and positional relationships with neighboring facilities.

Firm up flight planning and safety management in advance

When conducting drone surveys at solar power plants, you need to finalize flight plans and safety protocols in advance. Because these plants are outdoors and cover large areas, they may at first glance seem easy to fly in. In reality, however, there are many hazards to be aware of during flights, such as power lines, transmission equipment, mounting racks, fences, trees, slopes, access roads, work vehicles, and inspection personnel. In particular, pre-renovation surveys may require approaching areas suspected of deterioration or damage, so more cautious planning than for standard photography is required.

In a flight plan, first decide the order in which to capture the entire survey area. Trying to photograph the whole power plant at once makes you more susceptible to factors such as battery changes, the pilot’s line of sight, communication conditions, and changes in weather. Dividing the site into multiple sections and establishing takeoff/landing locations and checkpoints makes it easier to prevent missed coverage. Organize the imaging objectives for each section and assign roles—such as overview, detailed inspection, and supplementary imaging—so the deliverables are easier to use in subsequent processes.

An important part of safety management is checking for obstacles and access control before flight. Solar power plants may have thin power lines and guy wires, monitoring equipment, weather instruments, and communications equipment that are difficult to see from above. It is necessary to conduct a ground-based preliminary inspection and identify anything that could interfere with the drone’s flight path. When conducting detailed low-altitude photography in particular, plan to leave sufficient distance from panel rows and the tops of mounting racks, and avoid sudden maneuvers or unnecessary close approaches.

Depending on the flight location and method, it may be necessary to check relevant laws and regulations such as the Aviation Law, rules of local governments and facility managers, coordination with nearby facilities, and any required permits or approvals. In pre-renovation surveys, even within the power plant premises, it is necessary to consider surrounding roads, adjacent land, power transmission equipment, and the presence of third-party access. Before carrying out operations, confirm whether flight is permitted, access control, and how to inform relevant parties, and ensure the plan complies with laws and on-site rules.

During pre-refurbishment surveys, other inspections or on-site checks may be carried out simultaneously at the same site. Therefore, it is necessary to inform relevant personnel so that people do not inadvertently enter the filming area or takeoff and landing zones during flight. Sharing the flight time, flight area, areas to avoid entering, and emergency contact procedures in advance can reduce confusion on site. At large power plants it can be difficult for the pilot alone to monitor the entire site, so assistants should be assigned as needed to share responsibility for surrounding safety checks.

Checking the weather is also essential. In drone surveying, wind, rain, fog, strong sunlight, and sudden weather changes can affect the quality of results and safety. Solar power plants are sometimes installed in mountainous areas, along coastlines, on hilly terrain, or on developed sites, and site-specific winds may occur. Even if the wind feels weak at ground level, it can change at altitude or near slopes. Checking not only the weather on the day of the flight but also mud from rain up to the previous day and drainage conditions can improve the safety of on-site work.

We include shooting conditions in the flight plan. Solar panels readily reflect light, and depending on the sun’s angle images can become difficult to see. During times of strong reflection or when shadows are long, it can be hard to discern the condition of panel surfaces, walkways, and drainage equipment. For pre-renovation surveys, it is more important to obtain images that make inspection targets easy to assess than to prioritize aesthetic appearance. Adjust shooting times as needed and plan to minimize the effects of shadows and reflections.

When planning a flight route, consider the overlap and shooting direction required for the deliverables. To capture the overall topography and layout, it is necessary to shoot at a consistent altitude with sufficient overlap. Conversely, supplemental oblique photography can be effective for inspecting drainage ditches, slopes, road edges, and deformations around support structures. Because the information needed for pre-renovation surveys is not limited to planar positions, combining overhead shots with oblique inspections makes it easier to understand site conditions.

Also decide in advance how to respond to any contingencies. Share beforehand the criteria for aborting or pausing flights in cases such as unstable communications, the onset of strong winds, workers or vehicles entering the flight area, or battery levels dropping faster than expected. Pre-renovation surveys are preparatory work for construction planning, and there is no need to force a flight. It is important to reliably measure what can be safely obtained and plan to supplement any missing data at a later date.

Establish Standards for Surveying Accuracy and Verification Items

It is important to decide in advance what level of accuracy is required when using drone surveying for pre-refurbishment surveys. The accuracy required and the way deliverables are produced differ between gaining an overall understanding of a power plant and calculating quantities for refurbishment design. If the goal is only to grasp overall deterioration trends, wide-area imagery and approximate terrain information may be sufficient. On the other hand, when using drone surveying to reassess drainage slopes, repair embankment surfaces, refurbish maintenance roads, or check ground deformation around racking foundations, you need to define the accuracy requirements more carefully.

When considering surveying accuracy, be aware of the units required for refurbishment decisions. For example, when checking for poor drainage, slight differences in elevation can affect water flow. If the data will be used for renovating graded surfaces or drainage facilities, handling elevation information—not just images—becomes important. Conversely, if the purpose is to confirm equipment layout or the positions of obstructions, prioritizing a clear organization of planar positional relationships may be more important. Demanding accuracy that does not match the purpose leads to excessive work, while insufficient accuracy makes the refurbishment plan difficult to use.

Handling reference points and control points is also important. When overlaying drone survey outputs onto drawings and design materials, you must align the positional relationship between the site’s reference points and the survey data. Even if existing survey results are available, verify whether those reference points are still usable, whether their positions can be confirmed, and whether they sufficiently cover the area targeted for renovation. If deliverables are produced while the reference points are ambiguous, this can later cause the drawings and the site not to match and leave uncertainty in judging the construction scope and quantities.

The criteria for inspection items should also be determined before surveying. In pre-renovation surveys of solar power plants, items to be checked include clogged drainage systems, sediment accumulation, traces of puddles, ground subsidence, slope erosion, damage to maintenance roads, scouring around mounting structures, deformations along fences, impaired visibility due to weeds, and obstructions to vehicle traffic routes. However, if what is regarded as abnormal varies from person to person, there will be inconsistencies in organizing the survey results. It is important to align in advance the priority viewpoints to be checked, such as low-lying areas where water tends to pool, locations where sediment flows in, and places where heavy machinery and vehicles will pass during renovation.

Deliverables obtained from drone surveying include aerial photographs, orthophotos, three-dimensional terrain data, point clouds, and cross-section verification data. Which deliverables to use depends on the specifics of the renovation. For overall explanations and sharing with stakeholders, images taken from above can be easier to understand. Data that include elevation information are useful for checking terrain changes and drainage gradients. When considering estimates of the construction extent and earthwork volumes, organizing the data so that cross-sections and areas can be checked makes them more usable.

At the same time, it is important not to place too much confidence in the results of drone surveys. Aerial imagery can make it difficult to confirm conditions beneath panels, ground hidden by vegetation, the interior of drainage ditches, or small details of equipment. Strong reflections or shadows, vegetation, wet ground, and narrow passages can also affect appearance and measurement results. For that reason, locations where important decisions must be made should be combined with ground verification and additional surveying. Drone surveying is an effective means of efficiently understanding large areas, but it does not replace all on-site inspections.

In pre-renovation surveys, it is important not only to ensure the accuracy of deliverables but also to be able to trace the rationale behind decisions. If stakeholders check later and it is unclear what area was measured and when, under what conditions images were taken, or which points were used as the basis for organization, the reliability of renovation decisions decreases. Recording the survey date, flight coverage, imaging conditions, reference points used, the site conditions confirmed, and whether supplemental photography was performed, and keeping these records with the deliverables, makes it easier to explain matters among designers, contractors, management companies, and clients.

Also, when planning to compare conditions before and after renovation, it is useful to prepare so that re-surveying can be carried out under the same conditions. Aligning flight altitude, shooting area, reference points, output formats, and inspection items makes it easier to compare changes before and after construction. A pre-renovation survey not only identifies issues at that time but also serves as baseline data for verifying the effects after renovation. Considering future comparisons in advance can increase the value of drone surveying.

Align the Use of Deliverables with the Renovation Plan

Drone surveying deliverables are not finished simply by acquisition; it is important to organize them with consideration for how they will be used in renovation planning. In the renovation of solar power plants, multiple stakeholders are involved, including management companies, designers, construction teams, equipment inspection personnel, and clients. Each requires slightly different information. Management companies often want to grasp overall trends in defect locations, designers want to confirm terrain, dimensions, and the scope of construction, and construction teams prioritize access routes for heavy machinery and vehicles, material storage areas, and ease of work. Deliverables need to be organized to suit these intended uses.

First, for materials used to share with stakeholders, it is important that they can intuitively understand where the problems are. By indicating the survey area and points to check on aerial images, even people who are not familiar with the site can grasp the situation more easily. Organizing issues such as poor drainage, sediment accumulation, road damage, and slope deformation by area makes it easier to discuss repair priorities. However, if you cram too much information into images they become hard to read, so it is necessary to present them according to their purpose—for example, by separating overview maps and detailed maps.

When used for design and quantity estimation, data that allows you to verify elevations and cross-sections, not just plan information, becomes important. When reviewing drainage routes, you must identify which areas are high and which are low. For maintenance of management roads, it is necessary to check pavement settlement, shoulder collapse, and the relationship with drainage destinations. For slope repairs, the extent of deterioration, the gradient, and the distance to nearby facilities serve as criteria for judgment. For these uses, converting survey results into drawings and organizing candidate repair areas and inspection cross-sections makes them easier to use in design reviews.

When used for construction planning, documents that convey how easily work can be carried out are required. At solar power plants, panel rows may be closely spaced, equipment may be installed on slopes, and access roads may be limited. For refurbishment work, it is necessary to consider in advance material delivery, heavy machinery access, temporary storage, worker movement, and separation from existing equipment. Drone surveying results allow verification of vehicle routes and work spaces from above, making it easier to identify constraints that are easily overlooked by on-site surveys alone.

Additionally, the results of pre-renovation surveys are also useful as explanatory materials for clients and stakeholders. Simply describing on-site defects in writing can make it difficult to convey the severity and extent of the situation. By using aerial imagery and terrain data, you can visually share which areas are experiencing which issues. This is especially helpful at large power plants, where it can be hard to tell where specific defects are located within the whole site, so materials that combine an overall map with enlarged views are useful.

When organizing deliverables, file names and management methods should not be overlooked. In pre-refurbishment surveys, the same power plant may undergo multiple surveys, additional photography, on-site verifications, and design changes. If files accumulate whose survey date, scope, purpose, or revision number are unknown, there is a risk of mistakenly using outdated materials. Deliverables should be clearly labeled with the power plant name, survey date, area covered, purpose, revision number, etc., so that stakeholders can refer to the same materials. This may seem like a small task, but it has a large effect on preventing rework in refurbishment planning.

Additionally, you need to decide in advance what format you will receive the deliverables in. Whether just images for viewing are sufficient, whether you need data that can be overlaid onto drawings, or whether you need data that can be reviewed in three dimensions will affect the shooting and processing methods. If you request a format change later, additional work or reprocessing may be required. It is efficient to clarify where the deliverables will be used—renovation design, internal reporting, construction planning, or maintenance records—and decide on the required deliverables from the outset.

In pre-renovation surveys, it is important not only to identify problems but also to prioritize them. By separating locations that require immediate action, those that can be monitored until the next regular inspection, and those that can be repaired during construction, it becomes easier to plan renovation costs and schedules. Using drone survey results allows multiple defect locations to be compared from the same perspective, making it easier to explain the renovation scope and build consensus. However, final decisions should also be based on on-site verification and specialist inspection results.

Summary

Using drone surveying for pre-renovation investigations of solar power plants makes it efficient to grasp the current conditions of large sites and helps organize issues such as poor drainage, ground deformation, deterioration of maintenance roads, changes to slopes, and obstructions around equipment. In particular, an aerial perspective is a great aid when considering the scope of renovation and explaining plans to stakeholders. On the other hand, drone surveying does not automatically produce usable deliverables just by flying; by preparing in advance the renovation objectives, survey scope, existing documentation, site conditions, safety management, accuracy requirements, and the intended use of the deliverables, you are much more likely to obtain materials that can be applied to the renovation plan.

The most important thing in preparation is to clarify the objective. Whether you want to inspect drainage, examine ground conditions, determine the construction scope, or compare before-and-after renovation will change the required imaging methods and deliverables. If the objective is vague, even capturing a wide area may not provide sufficient information for decision-making. Sharing the checklist items with stakeholders in advance and deciding what will be recorded as the deliverables improves the quality of the survey.

Cross-checking with existing documentation is also indispensable. As-built drawings, drainage plans, and past inspection records provide clues for interpreting on-site conditions. However, because drawings do not always match the actual site, it is necessary to use the results of drone surveys to verify differences. Site conditions, vegetation growth, weather, takeoff and landing locations, and accessible areas also affect survey results. Recording not only the deliverables but also the conditions during the survey makes later assessments easier.

From a safety perspective, it is important to carefully carry out flight planning, notify relevant parties, assign assistants, check for obstacles, and assess the weather. While solar power plants are extensive, they are sites with many points of concern—electrical equipment, racking, fences, embankments, and power lines. Furthermore, depending on the flight location and method, you must confirm applicable laws and regulations, the facility manager’s rules, and whether any permits or approvals are required. By avoiding unsafe flights and excessive proximity and planning to reliably capture only the necessary scope, it becomes easier to balance safety and the quality of the results.

Consider surveying accuracy based on how it will be used in the renovation plan. The information required differs for overall understanding, detailed design, quantity estimation, construction planning, and explanations to stakeholders. Clarify which decisions will use the images and terrain data obtained from drone surveys, and realistically combine them with ground verification or additional surveying as needed. In pre-renovation investigations, it is important not to over-rely on them and to leverage the advantage of broad-area coverage.

To succeed in pre-renovation surveys, it is important to position drone surveying not as mere photography but as the entry point for the renovation plan. By clarifying survey objectives, cross-referencing the site with documentation, flying safely, determining accuracy requirements, and organizing deliverables for ease of use, it becomes easier to make decisions before construction. If you want to efficiently grasp the condition of a solar power plant and prepare materials that can inform the renovation plan, it is important to consider the scope of drone surveying with a view from on-site surveys through to the utilization of the results.