Test success for robot inspector


From pv magazine 12/23-01/24

Grid-scale solar segment growth and increasing labor costs are driving solar site managers to find new ways to expand inspection capabilities while reducing overheads. Solar sites require extensive preventative maintenance to keep equipment running optimally. The detailed visual inspections currently being conducted by field technicians can be laborious and time-consuming.

“Most maintenance contracts include service-level guarantees requiring responsiveness and insight into system performance, and the demand for these insights is increasing each year,” said Scott Canada, from McCarthy Building Companies’ renewable energy team. “Current examples of monitoring systems and methods used include stationary monitoring systems or aerial drones but these methods often have inadequate capabilities and practical limitations.”

Researchers at robotics startup OnSight Technology have developed the Bulldog robot to help bridge the gap and provide an alternative monitoring system. After incorporating enhanced technology that increases battery life and offers wireless charging, thermal camera resolution, outdoor-rated components, and advancements in machine vision training techniques, the latest ground-inspection robots were ready to be field tested.

“By automating the process, inspections can be systematically completed with a higher level of accuracy and efficiency by the robot, reducing human error and maintaining a consistent level of high-quality checks,” said Graham Ryland, chief product officer with OnSight. “Not only does automation increase operational efficiency, it frees up human resources to focus on more complex tasks, thereby optimizing overall workflow.”

Field testing

McCarthy partnered with OnSight on several solar projects and use cases. The robot maker built out barcode-scanning capabilities for a 195 MW project in Arizona that included geo-location as a contractual requirement to ensure ease of operation and warranty fulfillment. A head-to-head comparison was conducted using human labor versus the latest technology in ground-based robotic inspection.

“Through a three-phased approach, OnSight made improvements to barcode scanning on-site that increased the scanning speed from two modules per minute to 18 modules per minute, rivaling the human field technician’s rate of 21 modules per minute,” Ryland said. “This was achieved by adapting the technology on-site to optimally perform inspections.”

The OnSight robot was equipped with a 4k color camera, 33x optical zoom and high-precision GPS. It operated on battery power for eight hours daily and recharged using solar generator charging stations.

The robot was managed remotely by a human operator using manual and autonomous modes to undertake the scanning process, instead of eight-hour shifts and two-and-a-half-hour roundtrip commutes by field technicians to the site.

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Human module scanning is quicker than robot scanning but only when skilled and reliable personnel are available on site. With human scanners coping with extreme weather conditions, their overall time scanning throughout the day was significantly less than that of the robot, ensuring the per-day performance of modules scanning by a human and robot were similar.

Where the robot excelled was in the accuracy and reliability of scanning mission results. This was due to the robot’s use of an auto-stop functionality, serial number integrity verification, and constant mission recording, which combined to prevent the robot from missing a barcode while scanning a row. This level of precision is important because the robot’s scanning results aligned exactly with the project’s as-built drawings and made locating a faulty module much easier.

Test results

Production rateCurrent
Quantity of robots or crews1
Total modules470,892
Module scanning start dateAug. 2, 2023
Financial close date (due to owner)Aug. 15, 2023
Modules per work-minute1821
Modules per hour810945
Total modules per day6,4806,615
Total modules – 20-day period129,600132,300
Months to complete44
Estimated completion dateMay 20, 2023May 18, 2023
Based on this analysis, the robot cost was one third the cost of humans performing the same task


Access to a high-power, radiometric thermal camera enabled the robot to perform back-of-module hotspot and MC4-connector infrared inspections and barcode scanning missions at the same time. This occurred without negatively affecting barcode scan rate unless an issue was discovered and needed to be documented.

Lessons learned

The McCarthy and OnSight collaboration illustrated that time-consuming, repetitive, and detail-oriented tasks, particularly focused on data collection and identification, are better completed with technical solutions, especially when it involves the rapid deployment of multiple automated robots. The potential benefits of ground-based robots include: cost savings on quality inspections by eliminating the need for quality engineers and manual inspections; efficient remedial work by having all issues identified with geotags; less rework for quality inspections; and higher revenues, thanks to higher DC availability.

“Rather than replacing humans in the construction and commissioning of these projects, we anticipate these tools can be used to free up specialized workers and technicians to do higher-value work,” OnSight’s Ryland said. “With labor shortages and [solar] demand only expected to increase, ground-based robots make sense to incorporate on projects.”

About the author: Zachary Nichols is director of operations and maintenance (O&M) for McCarthy Building Companies renewables group. He provides strategic guidance for operations and maintenance of solar projects. With more than 15 years' experience in commissioning, O&M, and warranty programs, he works to deliver value to project owners and shareholders through innovation and client-service program strategies.

The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.

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