6 Drone Survey Checks for Land Assessment of Solar Power Plants

In planning a solar power plant, it is important not only to consider solar irradiation and grid interconnection but also to know how accurately the land itself can be understood. Simply walking the site makes it difficult to organize at once the overall elevation differences across the site, drainage directions, anticipated earthworks volumes, relationships with adjacent properties, and the ease of maintenance access. Drone surveying is useful for this purpose, as it records the site broadly from above and allows terrain and current conditions to be verified as data.

Table of Contents

• Organize the objectives for using drone surveying in land valuation

• Check 1: Confirm the overall undulations and elevation differences of the entire site

• Check 2: Confirm the amount of earthworks and the outlook for cut-and-fill

• Check 3: Confirm the drainage direction and areas where rainwater tends to collect

• Check 4: Confirm the relationship with boundaries, adjacent land, and existing structures

• Check 5: Confirm the permissible installation area and maintenance access routes

• Check 6: Organize into a format that is easy to explain as land valuation materials

• Precautions when using drone surveying for land valuation

• Summary: Sort out the land's hard-to-see risks at an early stage.

Organizing the purposes of using drone surveying for land evaluation

In land assessments for solar power plants, it is not sufficient to simply check whether the area is large enough. Even land that appears adequate on a plan can hide problems such as steep slopes, hollows where water tends to collect, elevation differences with neighboring properties, difficulty in securing access roads for deliveries, and a tendency for maintenance burdens to increase after site development. These issues can be understood to some extent through on-site inspections, but when the site is large or heavily vegetated it becomes difficult to uniformly observe changes across the ground surface.

The purpose of using drone surveying is not simply to preserve aerial photos of a site's condition. Based on the captured images, orthophotos, point cloud data, digital elevation models, cross-section verification documents, and other outputs are created to present the land's features in a form that is easy to compare. This makes it easier to consolidate multiple decision-making inputs—such as power plant layout studies, site development/earthworks policies, drainage planning, explanations for adjacent landowners, before-and-after construction comparisons, and maintenance planning—into a single foundational reference.

At the land-evaluation stage, the important thing is not to directly predict the power generation after completion, but to confirm whether the site can accommodate the power plant without undue difficulty and whether it is unlikely to incur unexpected burdens during construction or maintenance. Drone surveying provides a means to verify that judgment using geotagged images and terrain data, rather than relying solely on intuition.

However, the results obtained from drone surveying are not foolproof. Ground covered by trees and grass is difficult to see, and image processing alone cannot determine subsurface conditions or the strength of the ground. Surveying accuracy varies depending on flight planning, the placement of control points, imaging conditions, and analysis methods. When using it for land evaluation, it is important to first decide what you want to check and then carry out imaging and processing that match that purpose.

Check 1: Confirm the site's overall undulations and elevation differences

The first thing to check when evaluating land is the overall undulation and elevation differences of the entire site. Because solar power plants use large areas, a site may appear flat in parts but, when viewed as a whole, gently slope, have a low-lying center, or drop off steeply only at the edges. Even changes that are hard to discern from the ground become easier to grasp if recorded from above with drone surveys and organized as elevation data, allowing you to take a bird’s-eye view of the land’s shape.

Understanding terrain variations affects not only panel layout but also the height of mounting structures, foundation design, extent of site development, drainage planning, and the routing of construction vehicles. For example, even on land with the same area, the approach to pre-installation grading differs between land that is nearly flat and land that is undulating. On gentle slopes, configurations that utilize the terrain can be considered, but where there are many local steep inclines or level changes, constructability and maintainability must be carefully assessed.

In drone surveying, the site is photographed from above with a consistent overlap, and the images are stitched together to create three-dimensional terrain information. This makes it easier to identify high and low areas on the site, locations where slopes change, valley and ridge-like landforms, and traces of existing embankments or cuttings. In the early stages of land assessment, it is important to grasp the overall trends of the terrain before determining detailed design values.

When assessing topography, don’t just look at the raw elevation difference numbers; identify where on the site there are areas suitable for use as a power plant. Even if part of the site is flat, if the access routes to it are steep, material delivery and maintenance inspections may be impeded. Conversely, even if the whole site is sloped, if the slope runs continuously in the same direction it can make layout planning easier.

Also, in land evaluation, elevation differences between the site and surrounding areas cannot be overlooked. Differences in height relative to adjacent roads, waterways, farmland, and residential lots affect drainage, sediment runoff, and safety measures at boundaries. Recording the site and its surroundings together with a drone survey makes it easier to evaluate the land including the surrounding environment, rather than evaluating the land in isolation.

Check 2: Confirm earthwork volumes and cut-and-fill outlook

In land evaluations for solar power plants, it is important to grasp early on how much site preparation will be required. If the scale of site preparation becomes large, it will affect construction planning, permits and approvals, drainage planning, disposal of excavated soil, communication with neighbors, and schedule management. If expectations for site preparation are underestimated in the early stages of land acquisition or project evaluation, a revision of the overall plan may become necessary later.

Using drone surveying makes it easier to understand the current topography across the site and to assess which areas are likely to require cutting or filling. Of course, formal development design requires detailed surveys, geotechnical investigations, and clarification of design conditions, but at the land evaluation stage it is already very meaningful to be able to distinguish areas that will likely need relatively little earthwork from those that will require more extensive intervention.

For example, if a candidate site contains many depressions, the plan will vary depending on whether those depressions are filled in or avoided in the layout. If there are ridge-like rises, it is necessary to consider whether to cut them and level the ground or to arrange the layout following the terrain. By checking cross sections based on drone survey results, it becomes easier to explain terrain changes that are not apparent from plan views alone to stakeholders.

When forecasting earthwork volumes, it is important not to assume the entire site will be uniformly flattened; instead, consider separately the installation area for power generation equipment, access roads, drainage facilities, fences, and entrances. The approach to grading required for locations suitable for equipment layout differs from that for areas used for drainage and maintenance. Using terrain data obtained from drone surveys makes it easier to determine which parts of the land to preserve and which to adjust.

Also, you should check not only the volume of earthworks but also how they will affect the surrounding area. Cutting high ground will create slopes, and filling low ground will require consideration of embankment stability and drainage. When there are large elevation differences at the site edges, attention is needed to prevent soil erosion and rainwater runoff into adjacent properties. If you record the pre-development topography using drone survey results, it will be easier to use that information as supporting evidence when plans change or when explaining to stakeholders.

In land assessment, it is more important to make an early determination of whether a site carries a high earthworks risk than to precisely establish the volume of earthworks. Drone surveying provides an effective means to verify that judgment based not only on on-site impressions but on topographic data.

Check 3: Confirm the drainage direction and areas where rainwater tends to accumulate

A commonly overlooked factor when evaluating land for a solar power plant is the flow of rainwater. Even if an on-site inspection in fine weather appears problem-free, rainfall can reveal areas where water tends to collect, spots that become muddy, or places where soil and sediment are likely to move. Because a power plant will be operated outdoors for a long period, it is important to identify drainage issues at an early stage.

Drone surveying allows you to check elevation differences and terrain slopes across an entire site. This makes it easier to identify which way rainwater is likely to flow, where low spots are, and how they connect to existing water channels and side ditches. When you only inspect by walking the ground, you have to mentally piece together the site's overall water flow, but aerial imagery and terrain data make it easier for all parties involved to share the same understanding.

When assessing drainage direction, it is important not to limit the evaluation to the site itself but to check its relationship with the surrounding topography. Whether the land receives water flowing in from upstream or whether water on the site flows toward downstream neighboring properties will change the measures required. Pay particular attention to how rainwater accumulates on land in mountain valleys, large developed tracts, and properties that include former agricultural land or valley terrain.

Orthoimages produced by drone surveys help confirm the locations of existing waterways, roadside ditches, slopes, ruts, bare ground, and areas prone to moisture. Combined with elevation information, they also make it easier to identify low-lying areas where rainwater tends to collect and sloped areas where flow velocity is likely to increase. At the land assessment stage, it is not necessary to decide the detailed design of drainage facilities, but it is important to organize potential drainage concern points as candidates.

The flow of rainwater can lead to sediment runoff and slope erosion. Problems such as scouring of the ground beneath panels, muddy maintenance access roads, sediment accumulation near fences, and increased clogging of drainage channels affect the burden of maintenance after completion. If these risks can be predicted at the land evaluation stage, they can be more easily reflected in layout and site development plans.

When using drone survey results for drainage verification, it's effective to check not only the terrain data collected in clear weather but also traces of flow paths and signs of sediment accumulation observed on site. Aerial images can capture differences in color, vegetation patterns, and the roughness of the ground surface. By overlaying these with terrain information, it becomes easier to infer changes that are likely to occur during rainy conditions.

Check 4: Confirm the relationship with boundaries, adjacent land, and existing structures

During land evaluations for solar power plants, it is essential to check not only the on-site conditions but also the relationship with boundaries and adjacent properties. Power generation equipment, fences, service roads for maintenance, drainage facilities, and access points should be located with consideration for their distances from site boundaries and surrounding facilities. If planning proceeds without adequate checks near the boundaries, it can lead to encroachment onto neighboring properties, drainage runoff, insufficient working space during construction, and access problems during maintenance.

Orthoimages created by drone surveying are well suited for confirming the current conditions near boundaries across a wide area. Because existing markers such as stakes, walls, fences, roads, waterways, field ridges, and tree lines can be observed from above, it becomes easier to grasp the relationship between a site and its surroundings. However, lines visible in the images do not necessarily coincide with legal boundaries. When using them for land appraisal, it is important to handle them on the premise that they will be cross-checked against registration information, boundary documents, on-site inspections, and the required survey results.

Elevation differences are also a major point to check in relation to adjacent properties. If the site is higher than neighboring land, be aware of potential runoff of rainwater and sediment. If the site is lower than neighboring land, it may be land where water from the surroundings easily intrudes. Confirming elevation differences around the boundaries with drone surveying provides useful information for considering site layout and drainage planning.

Checking existing installations is also important. Within and around candidate sites there may be utility poles, guy wires, existing roads, waterways, conduits, structures, trees, agricultural facilities, vacant buildings, and so on. These may need to be removed or relocated, or they may become constraints that should be avoided in planning. Small structures that are easy to miss during ground inspections, or traces of paths hidden by grass, become easier to understand in terms of their spatial relationships when viewed in aerial imagery.

Additionally, for solar power plants, factors such as how they appear from neighboring areas, reflections, fence locations, and the safety of entrances and exits must also be considered. Recording the conditions of surrounding roads and adjacent land with drone surveying makes it easy to use as shared documentation among designers, contractors, landowners, and clients. Especially when there are multiple candidate sites, being able to compare boundaries and surrounding conditions using the same criteria makes evaluation easier.

In boundary verification, it is important not to make a final decision based solely on the results of drone surveys. Drone surveying is excellent for understanding current conditions, but it does not substitute for the legal determination of boundaries or the confirmation of rights. In land appraisal, it should be used as material that clearly visualizes the current situation, and one should be prepared to combine it with professional boundary verification and surveying as necessary.

Check 5: Confirm the installable area and maintenance access routes

When evaluating land for a solar power plant, you should not judge solely by the site area; you need to determine the actual extent where equipment can be installed. Even if the area shown on the plans appears sufficient, the effectively usable area can be smaller than expected once you exclude steep slopes, low-lying areas where water tends to collect, areas around existing structures, locations near boundaries, places where extra clearance is desired for safety, and access routes used for delivery and maintenance.

Using the results of drone surveying makes it easier to organize which locations across the entire site are easy to install on and which should be avoided. By overlaying terrain information on orthophotos, you can identify relatively flat areas, steeply sloped areas, areas with dense vegetation or existing structures, and areas that could be used as access paths. This allows you to confirm discrepancies between desk-based layout plans and actual field conditions early.

When considering the area available for installation, evaluate not only the locations for arranging panels but also potential service roads, inspection walkways, drainage systems, power collection equipment, fences, access points, and material storage areas. If you cram the power generation equipment in as densely as possible, post-completion maintenance inspections, vegetation control, and repairs can become difficult to perform. For long-term operation, it is important to consider maintenance access routes from the land-assessment stage.

For maintenance access routes, check where vehicles can enter, where people can walk safely, areas prone to becoming muddy after rain, and steep slopes. If drone surveying is used to grasp elevation differences and ground surface conditions, it becomes easier to compare multiple candidate routes. For example, the shortest path is not necessarily the optimal one. Even if it is somewhat longer, a route with a gentler gradient, fewer drainage problems, and less interference with adjacent properties may be easier to handle in practice.

Also, the area available for installation is viewed differently during construction and operation. During construction, workspace is required for heavy machinery and material delivery, while during operation, access is needed for inspections, weed control, and equipment replacement. If drone survey results are retained at the land assessment stage, construction and maintenance teams can review the same site condition data, making it easier to reduce planning oversights.

When checking the area available for installation, it is also important to get a rough sense of shadow effects from trees and surrounding terrain. Drone surveying itself does not determine power generation estimates, but by identifying nearby tall trees, slopes or embankments, buildings, and terrain rises, you can pinpoint locations where shadow impacts should be examined in detail. In land assessment, it is important to organize the elements of on-site conditions that require attention before conducting detailed power generation simulations.

Check 6: Organize into a format that is easy to explain as land evaluation materials

The value of drone surveying lies not only in photographing the site but in organizing that footage into materials that are easy to explain as inputs for land evaluation decisions. In evaluating candidate sites for solar power plants, people from multiple perspectives—landowners, clients, designers, contractors, maintenance personnel, and relevant agencies—review the information. Terrain and surrounding conditions that are difficult to convey in text-only reports can be more easily brought to a common understanding using images and topographic data.

When organizing land evaluation materials, an orthoimage showing the current conditions is effective as a first step. Because it allows you to view the entire site from above like a single map, it makes it easy to identify roads, waterways, areas near boundaries, existing structures, vegetation, bare ground, and signs of past earthworks. In addition, preparing materials that show elevation differences and cross-sectional profiles enables you to explain undulations and slopes that cannot be understood from plan view alone.

What's important when preparing materials is not increasing the number of deliverables, but organizing the necessary information according to the evaluation objectives. For land assessments, it is important to clearly summarize the site's overall topography, points of concern for site formation, points of concern for drainage, items to check near boundaries, areas available for installation, and candidate maintenance access routes. Simply handing over specialized data as-is can make it difficult to use for decision-making. The items to be checked should be presented in an easily readable format so that the person responsible can proceed to the next stage of review.

Also, in land evaluation documents it is important to separate confirmed matters from unconfirmed items. If you mix the current conditions confirmed by drone surveys with boundaries, ground conditions, regulatory restrictions, drainage outlets, property rights, and other matters that require separate confirmation, misunderstandings can arise in later stages. For example, even if something appears to be a waterway in an image, if its manager or function has not been confirmed, it is safer to organize it as a "subject to confirmation" rather than assert it definitively.

Additionally, it is helpful to keep land assessment materials in a form that allows later comparison. When comparing candidate sites, photographing from the same viewpoints and documenting them in similar formats reduces variability in decision-making. If kept as a record of site conditions before construction, they are also easy to use for comparison after development or after disasters. When the materials created during the land assessment phase are handed on to subsequent design, construction, and maintenance, the benefits of drone surveying are further enhanced.

To make materials easier to explain, attention must be paid to how technical terms are used. Even when using terms such as point clouds and elevation models, provide supplementary explanations so readers understand what they can assess from the materials. What is needed for land evaluation is not only to indicate the level of detail of the data, but to clarify what can be learned from that data and what additional checks should be made.

Considerations when applying drone surveying to land valuation

Drone surveying provides a great deal of information for land assessment of solar power plants, but misuse can lead to overconfidence. The first thing to be aware of is that how results appear changes depending on shooting conditions. Strong winds, abrupt contrasts between light and dark, overgrown vegetation, surface reflections, and mud after rainfall can affect image quality and the interpretation of the ground surface. When using it for land assessment, it is important to choose, as far as possible, seasons and weather that make the ground surface easy to inspect, and to photograph the entire required area without omissions.

Next, you need to clarify your approach to positional accuracy. The preparations required will vary depending on whether the data will be used for a rough land assessment or whether accuracy approaching baseline data for design studies is required. If you do not decide in advance whether to establish control points or verification points, how to handle the coordinate system, and how to reconcile with existing drawings, the ways the results can be used may be limited later. In particular, for decisions concerning boundaries or earthwork quantities, it is essential to confirm that the required accuracy is being met.

Also, drone surveying may not be able to fully capture the ground surface beneath trees and grasses. Point clouds produced by photogrammetry are essentially created from visible surfaces, so on land with abundant vegetation the elevation of the ground surface and the height of vegetation can become mixed. If you want to examine the shape of the ground for land assessment, you should take vegetation conditions into account and, if necessary, combine the data with ground surveying or on-site field inspection.

Checking legal regulations and flight safety is also essential. Depending on the location and conditions where the drone will be flown, prior procedures, explanations to stakeholders, safety management, deployment of assistants, and consideration for the surrounding area may be necessary. Even when surveying for land evaluation, cautious operation is required when flying above third parties, near roads, near power lines, or around residential neighborhoods. In practice, quality includes not only the survey results but also the safety of the data acquisition process.

Careful data management is also necessary. Drone surveying generates a large number of images and analysis datasets. If you do not organize the capture date, weather, flight area, coordinate information used, analysis conditions, and types of deliverables, you may not know later which data is the most recent. Land evaluation does not end with a single assessment; it can continue through site comparisons, design changes, pre-construction checks, and post-development checks. Deciding on a method for organizing data from the initial stage makes it easier to utilize in later stages.

Finally, the results of drone surveying are supplementary materials to aid judgment and do not replace all aspects of land evaluation. Ground strength, legal restrictions, rights relationships, grid-connection conditions, coordination with neighboring residents, and long-term maintenance conditions must be confirmed separately. In practice, drone surveying is best used as a means to clearly organize the current situation and quickly identify areas that require attention before proceeding with these investigations.

Summary: Organize the less-visible risks of land at an early stage

Early identification of risks that are not apparent from size or location alone is crucial in land assessment for solar power plants. The site's overall topography, projected earthwork volume, drainage direction, relationship with boundaries and adjacent properties, usable installation area, and maintenance access routes all affect project feasibility, constructability, and post-completion operations and maintenance. If these factors are judged solely by on-site impressions, plan changes or additional checks may become necessary later.

Using drone surveying, you can broadly record the current conditions of candidate sites from the air and organize terrain and positional relationships as data. By utilizing orthophotos, point clouds, elevation information, and cross-sectional verification materials, it becomes easier to share the characteristics of the land among stakeholders. In particular, when comparing multiple candidate sites or explaining the basis for a land evaluation to a client, visually easy-to-understand materials are helpful.

At the same time, you cannot determine everything about land from drone surveying alone. Boundaries, ground conditions, statutory regulations, drainage outlets, and rights and interests need to be combined with other investigations or verifications as necessary. The important thing is not to treat drone surveying as an all-purpose decision-making tool, but to use it as a practical means to identify issues in the early stages of land assessment and to organize the matters that should be checked next.

In planning a solar power plant, the burden of making changes grows larger the further you progress into later stages. For that reason, it is effective to use drone surveying during the land assessment phase to check terrain, drainage, earthworks, boundaries, and access routes early on. If you clearly document on-site conditions and enable stakeholders to make decisions while looking at the same materials, it becomes easier to improve the accuracy of the plan.

When you want to carry out everything from land evaluation to surveying, recording current conditions, pre- and post-construction comparisons, and maintenance management in an integrated manner, it is important to establish surveying methods that are easy to handle on site and a system for organizing data. When incorporating drone surveying for solar power plants into practical work, consider imaging plans, accuracy control, and methods for organizing deliverables that match your objectives, keeping in mind the entire workflow from site reconnaissance to final deliverable organization.