No special equipment required: PVsyst-compatible high-precision smartphone surveying made possible by LRTK

In designing solar power plants, detailed on-site survey data is indispensable for accurately understanding the site's topography and solar exposure conditions caused by surrounding obstructions. However, conventionally, high-precision surveys have required specialized surveying equipment such as total stations, RTK-GPS units, and drone surveys, along with expert skills, and in small-scale projects sufficient surveying was sometimes omitted due to cost concerns. If high-precision surveying with a single smartphone were possible, on-site data could be easily obtained and reflected in designs, leading to optimized PV system layouts and improved accuracy of power generation forecasts. This article explains how to acquire and utilize high-precision survey data compatible with simulations in PVsyst, using a smartphone-mounted device leveraging real-time kinematic positioning technology, the “LRTK”. From on-site constraints and the challenges of conventional methods, we provide a detailed overview of the potential offered by smartphone-only surveying: the principles and characteristics of LRTK technology, concrete smartphone-based surveying workflows, applications of the resulting point cloud data for shading analysis, and the impacts on the design process.

Challenges of Traditional Surveying Methods and On-site Constraints

During the planning stage of a solar power plant, it is important to assess in advance the effects of the site's terrain and surrounding buildings and trees. However, conventional surveying methods present the following challenges.

• Specialized equipment and personnel required: High-precision surveying required equipment such as total stations, high-performance GNSS receivers, and drones, and skilled survey technicians were indispensable for operation. On extensive sites, securing survey points required multiple people, and preparation and setup were time-consuming.

• Cost and schedule burden: Procuring surveying equipment or hiring external contractors incurs costs, and scheduling surveying dates is also necessary. Especially for mountainous or remote sites, the cost of transporting equipment and dispatching personnel is high, which has been one reason small-scale projects have foregone adequate surveying.

• Variability in data accuracy: If one relies on convenient alternatives such as topographic maps, satellite imagery, or common smartphone GPS, position and elevation errors can reach several meters (several ft). As a result, there is a risk of reduced simulation accuracy due to inconsistencies between actual terrain and design or underestimation of shadows caused by overlooked obstacles.

• Site constraints and safety: In sloped terrain or densely wooded areas, surveying with conventional equipment can itself be difficult. Limited space for setting up tripods or needing to enter hazardous areas to secure lines of sight can create site constraints that affect surveying accuracy.

Because of these challenges, solar power generation projects often cannot obtain sufficient survey data in the initial stages, and are frequently forced later to correct terrain gradients and revise power generation forecasts. A simpler and more flexible surveying method was needed.

Principles and Characteristics of LRTK Technology

What has changed this situation is a smartphone-compatible RTK positioning technology called 'LRTK' that has emerged in recent years. RTK (real-time kinematic) is a method in satellite positioning that, by using simultaneous observation data in real time to correct positioning errors between a base station (reference station) and a rover (mobile station), determines positions with centimeter-level accuracy (half-inch accuracy). While ordinary smartphone GPS has errors of several meters (several ft), RTK can improve accuracy to a few centimeters (a few in).

LRTK (Eruārutīkē) is a solution consisting of a dedicated GNSS receiver and a smartphone app that brings RTK positioning to palm size. For example, the "LRTK Phone" is an ultra-compact RTK-GNSS module that can be attached to the back of a smartphone (iPhone/Android), and simply launching the dedicated app instantly enables high-precision positioning from satellites. Unlike conventional stationary GNSS equipment, there is no need for complicated antenna setup or external power; just attach the device with a built-in battery and antenna to your smartphone and the smartphone itself transforms into a surveying instrument.

The main features of LRTK technology can be summarized as follows:

• Centimeter-level positioning accuracy: Using an RTK method that utilizes the phase difference of satellite signals, planar positions can be determined within a few cm (a few in), and heights can also be measured with an accuracy of about a few cm (a few in). By using the averaging function, stable positioning results on the order of millimeters (inches) can also be obtained.

• Real-time and immediate sharing: Positioning results can be checked on a smartphone in real time, allowing on-site verification of accuracy. Acquired data can be uploaded to the cloud immediately and shared instantly with design staff in the office.

• Simple one-person surveying: A compact device weighing only about 150 grams allows easy, one-person portable surveying. Recording survey points is completed with button operations on the smartphone screen only, eliminating the traditional need for multiple people to measure angles or take notes.

• Low cost and high ease of adoption: It is overwhelmingly less expensive than conventional equipment, and minimal additional hardware is required as long as you have a smartphone. The user-friendly design enables intuitive operation even by field staff without special training.

• Positioning in global coordinate systems: The LRTK app automatically converts acquired latitude, longitude, and height into map coordinate systems such as the Japan Geodetic Datum 2011 (JGD2011) and the World Geodetic System 1984 (WGS84). Survey points can also be output in coordinate systems convenient for design, such as plane rectangular coordinates, making it easy to import survey data directly into CAD or simulation software.

• Out-of-coverage support via CLAS: When using LRTK in Japan, it supports the centimeter-level augmentation service (CLAS) provided by the Quasi-Zenith Satellite “Michibiki,” allowing high-precision positioning to be maintained via augmentation signals from satellites even in areas with unstable Internet connectivity, such as mountainous regions.

• Versatile applications (photos, AR, point-cloud measurement): Photos taken with a smartphone camera can be tagged with high-precision coordinates and saved to the cloud, and positions can be laid out on site using AR display based on acquired coordinates, expanding uses beyond surveying. It also includes a function to acquire 3D point-cloud data with high-precision coordinates by combining with a smartphone LiDAR scanner.

In this way, LRTK makes RTK surveying, which previously required specialized equipment, easy for anyone to carry out, turning "one smartphone per person" surveying into a reality.

High-Precision Surveying Workflow Using a Smartphone + LRTK

Now, let's look at the specific steps for surveying land for a solar power plant by combining a smartphone with LRTK. Below is an example of a smartphone-only surveying workflow.

• Preliminary Preparation and Planning: Attach the LRTK device to the smartphone and launch the dedicated app. Set the positioning mode to RTK and confirm receipt of correction information (reference station data via the network or CLAS signals). Plan in advance the extent of the survey area and the measurement items (such as terrain elevation differences, locations and heights of obstacles).

• Measurement of Control Points and Boundaries: Upon arrival on site, first survey the site boundaries and any known control points. Obtain the coordinates of the start point, then along the site boundary record survey points by pressing the button on the smartphone screen at important corner points and vertices. Each survey point automatically saves coordinate values (latitude, longitude, elevation) and a timestamp, and you can add notes if needed.

• Collection of Terrain Data: Walk around the site while collecting point clouds to capture elevation differences. The LRTK app also has a continuous positioning mode, which can automatically record coordinates at regular intervals along your walking route. This yields a large amount of point cloud data representing surface undulations. In areas with steep slopes or large steps, take points densely to gather material for a detailed terrain model.

• Measurement of Obstacle Positions and Heights: If there are surrounding obstacles that could cast shadows on the solar panels (for example tall trees, utility poles, adjacent buildings, etc.), measure their positions and heights as well. For position, approach the base of the object and take a GPS position; for height, you can measure relative height using the smartphone's LiDAR or AR functions. For example, you can measure a tree's height with the smartphone's AR surveying function, or obtain a point cloud of a standing tree with a LiDAR scan and calculate the height later. Because LRTK ties each dataset to geographic coordinates, the exact positional relationships can be reproduced when inputting the data into PVsyst as described below.

• 3D Scanning with Smartphone LiDAR (If Needed): In addition to terrain capture by survey points, if a more detailed on-site 3D model is required, obtain point cloud data on site using the smartphone's built-in LiDAR sensor or camera-based photogrammetry. With LRTK, the smartphone's self-position is continuously and highly accurately corrected during scanning, so the entire acquired point cloud is given global coordinates, and even with a wide scan area there is no need to worry about point cloud distortion or scale errors. The resulting colored point clouds and 3D models are useful later for checking in design software or measuring required dimensions.

• Data Saving and Sharing: Upload recorded survey point data and point cloud data from the LRTK app to the cloud while still on site. In the office, simply access the cloud via a web browser to instantly check the latest data obtained on site. For example, survey points are plotted on a map in the cloud, and you can view each point's coordinate values and notes. Also, since survey point data can be downloaded in CSV format, designers can import it into PVsyst or similar software on their office PCs and begin analysis.

As shown above, by utilizing LRTK you can complete everything from on-site surveying to data organization almost entirely with just a smartphone. The obtained geotagged photos and point clouds are also useful as materials for subsequent processes, and they can streamline the traditionally time-consuming processes of creating topographic maps and preparing reports.

Data Integration with PVsyst and Application to Shading Analysis

High-precision data acquired with a smartphone + LRTK can be imported into the photovoltaic simulation software PVsyst, enabling more realistic power generation forecasts and layout planning. PVsyst has a mechanism to treat shadows from nearby obstructions (buildings or trees near the array) and from distant obstructions on the horizon (such as mountain ranges) separately. By utilizing the acquired data in the following ways, you can improve the accuracy of shading analysis.

• Reflecting terrain data: Using elevation data measured within the site by LRTK, reproduce the site’s terrain model in PVsyst. For example, create contour lines or a mesh from the measured points and use PVsyst’s terrain import function to reflect elevation differences in the 3D scene. This allows panel row heights and tilts to be set according to the actual terrain even on sloped land, making irradiance and shading calculations more accurate.

• 3D modeling of nearby obstructions: Use coordinate information obtained from surveying to place nearby buildings and trees in PVsyst’s 3D shading scene. For example, if you know the base coordinates and height data of trees on the south side of the site, you can place objects of corresponding height (cylindrical or rectangular models, etc.) at the same positions in PVsyst to faithfully reproduce their spatial relationship with the panel array. This enables simulation of the actual shadows cast on panels by season and time of day, allowing quantitative evaluation of generation losses due to shading.

• Setting distant horizon shading: At solar power plants, surrounding ridgelines or forests can block low-angle morning and evening sunlight. If you measure the horizon altitude for each distant direction on site using LRTK (for example, by pointing a smartphone toward surrounding mountain ridgelines and recording the elevation angle), you can set that data as the horizon profile in PVsyst. In PVsyst, by entering horizon altitude angles by azimuth, you can reflect solar cuts due to distant shading in the calculations. If the high-precision coordinates obtained with a smartphone allow you to derive positions and elevations of distant obstructions, you can also virtually determine the horizon from the height difference to the horizontal plane.

• Detailed shadow analysis using point cloud data: Colored point clouds and 3D models obtained with LRTK and smartphone LiDAR cannot be directly imported into PVsyst, but they are a very useful information source for designers. Visualizing the point cloud lets you understand exactly how far tree branches and foliage spread and the fine undulations of the terrain. Based on this information, you can tune obstruction models in PVsyst down to the details or decide which trees, if any, should be pruned or removed. You can also take the acquired point cloud itself into external 3D software to perform solar radiation simulations and develop advanced analyses by comparing and validating results with PVsyst.

As described above, by incorporating smartphone survey data into PVsyst, a precise simulation that integrates the effects of shading can be achieved. Because shading assessments that previously relied on approximations and rules of thumb can now be performed based on measured data, the reliability of power generation forecasts is dramatically improved.

The Impact of High-Precision Surveying Data on Solar Design

By utilizing high-precision surveying information obtained with a smartphone + LRTK in design, various positive effects are brought to the planning process of solar power plants.

• Improved power generation forecasting accuracy: By faithfully modeling actual terrain variations and shading elements, you can narrow the gap between simulated predicted generation and actual output. In particular, correctly estimating solar irradiance losses in the mornings, evenings, and winter can reduce risks in business planning.

• Layout optimization and reduced design revisions: Based on a detailed site model, you can optimize PV array placement, tilt angles, and row spacing. For example, arrays can be sited to avoid locally shaded areas, and advance decisions on tree removal that would cause shading can be made as needed. Using high-accuracy data in the early stages also reduces rework from repeated design changes later.

• Incorporation into civil engineering and construction planning: High-precision topographic data is useful for earthwork planning. Cut-and-fill volumes can be calculated from acquired point clouds to develop optimal grading plans. Grasping the current terrain helps racking designs suited to slopes and drainage planning, improving the accuracy of civil-engineering considerations at the design stage.

• Faster decision-making and increased efficiency: Because necessary surveying can be completed with a single smartphone, initial on-site investigations can be conducted quickly. This enables faster decisions on land acquisition and layout. Where designs previously waited for survey results, immediate on-site data acquisition and analysis shortens the overall schedule and improves efficiency.

• Precise design possible even for small-scale projects: With reduced surveying costs, designs based on accurate site data become feasible for small-scale solar projects and distributed installations. Detailed surveys, which were often omitted for cost-effectiveness, can be easily performed using LRTK, allowing pursuit of optimal designs regardless of project size.

Thus, leveraging high-precision surveying data further enhances the accuracy and efficiency of solar power plant design, increasing the likelihood of project success.

Summary: The Potential of Smartphone-Only Surveying and the Future Opened by LRTK

High-precision surveying that can be completed using only a smartphone, without relying on special equipment, is revolutionizing the design and development process of solar power plants. With flexible surveying that is less constrained by site limitations and accurate data integration, designers can conduct layout evaluations and power generation simulations that more closely reflect reality. At the center of this is the LRTK technology introduced in this article. By using LRTK to turn a smartphone into a surveying instrument with cm level accuracy (half-inch accuracy), anyone can obtain on-site data whenever needed, enabling agile design that is not bound by conventional common sense.

Now, there is no need to wait for specialized surveying teams or expensive equipment. With the realization of an end-to-end workflow to measure, record, and share with a single smartphone, the solar power sector is poised for major change. Smartphone-based simplified surveying using LRTK can be applied widely, from small sites to large-scale developments, and its accuracy and ease of use make it a trump card for on-site DX (digital transformation). To make the design of solar power plants even smarter and more reliable, why not consider this new surveying approach?

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