Making Rooftop Solar Safe
by Ankil Sanghvi and Chris Chappell
This article was originally published in pv magazine - June 2023 edition.
Commercial and industrial (C&I) solar rooftops are becoming widespread as businesses strive to reduce carbon footprints and electricity bills. The industry has suffered fires and faces other safety risks, however. Clean Energy Associates (CEA) has performed safety audits on more than 600 commercial PV rooftops and has found safety issues in 97% of them, report Ankil Sanghvi and Chris Chappell.
The good news is that many problems detected by CEA in C&I rooftops are related to installation and the balance of plant components: grounding, connectors, wiring, and terminations. Fixing these problems is typically more labor intensive than capital intensive. And safety risks are easily avoidable in the first place. A comprehensive specification covering equipment selection, design, and installation, coupled with appropriate on-site oversight can avoid virtually all risks. How can developers and end-users prevent the common causes before incidents occur?
Damaged modules
Damaged modules is a broad term that can encompass manufacturing defects and improper installation. It is difficult to identify manufacturing defects when an installer is on the roof – the right time to catch those is at the factory. The risk of manufacturing defects can be reduced by identifying quality module providers.
Improper installation and maintenance are a much more common cause of module damage and can be initiated by a variety of factors. In some cases, installers and maintenance workers are climbing and walking on modules. Doing so can easily break or crack the PV cells, which are very, very thin.
Mishandling of modules can damage the backsheet, which can lead to a safety issue. CEA’s experience shows that if a worker leaves connectors or cables dangling on the module while carrying it, the dangling cables that touch the backsheet while walking can damage cells. We have also seen damage from improper use of impact drivers and incorrect storage and staging of modules, as well as poor transportation and shipping practices.
Cracked or damaged cells may result in hotspots and operation of the cell at elevated temperatures, which can potentially lead to burning of the backsheet.
Cross-mated connectors
Miscommunication and misalignment of incentives between developers and on-site workers can also cause installation problems. In many cases, the developer hires an engineering, procurement, and construction (EPC) services company and the EPC hires a subcontractor, which may hire another subcontractor. Technicians on the roof may lack key information and training and often don’t have the same long-term system performance concerns that building owners have.
For example, many installers fail to realize that cross-mating or mismatching connectors from different manufacturers can lead to an arc and a fire. If they knew how dangerous cross-mating can be, they would stop it. It is a matter of training, clarifying this in the design, and communicating to be sure proper procedures are followed.
Another common fault involves installing wiring and connectors over a sharp edge. Thermal expansion and contraction cycles, through weather change, can wear through or damage cable insulation over time, potentially leading to shock hazards and safety incidents.
Incorrect racking
Many problems can be avoided by diligently following the manufacturer’s installation instructions; this also applies to racking. In 4% of CEA-inspected sites, we found installation issues associated with incorrect torquing, improper placement of ballast blocks, and incorrect anchoring of systems to roofs, as recommended by manufacturers.
One retailer experienced a module flying off the roof during high winds and landing in the store’s parking lot near the main entrance. They were lucky no one was injured. Other clients have had similar incidents.
While 4% of sites sounds like a relatively low number, the chances of a location being affected by wind events over time is much higher. That 4% of sites may very likely have a serious event like this occur eventually.
Proper training
These are just some of the common flaws we’ve found on many of the C&I solar rooftops in use today. The first step in avoiding many of them is a very clear and detailed set of specifications or work instructions for how these systems are designed and should be installed. Then, a mechanism should ensure that people follow the drawings.
One example is an interim step that we call the “golden row” (and which is also known by other names). The crew installs a row of modules which is then inspected before the job moves forward.
The golden row incorporates all of the terminations, wire management, connectors, and clipping or through-bolting required for the system.
Then that golden row is inspected by the developer with the prime contractor to ensure that it’s the way it should be, based on the design specs.
Any deviations are corrected, and then when everyone is in agreement, the crew moves forward by duplicating that row. As the crew continues with the installation, consistent oversight, training, and communication is required to maintain the quality demonstrated in the golden row.
If a detailed audit is performed as a follow up, before the system is energized – ideally while the construction crew is still on site and can fix problems before they demobilize – that combination can fix the vast majority of these problems.
Solar is safe if done right, but it takes careful planning, implementation, and auditing before you turn on the system to ensure that these all-too-common safety problems don’t arise at your site.
Ankil Sanghvi is an engineering manager at CEA. He is responsible for quality inspection and testing services, energy performance modeling, commissioning services, design reviews, and test data analysis. Sanghvi provides expertise on PV cell technology and has a broad scientific understanding of solar cell technology and its manufacturing processes.
Chris Chappell is a senior director of engineering services at CEA. As a North American Board of Certified Energy Practitioner (NABCEP) energy professional with a degree in industrial and mechanical engineering, Chappell has spent 35 years in the power industry. He began as a project engineer with Bechtel and became a power production engineer with Pacific Gas & Electric.
