A new report from HelioVolta, an independent solar and energy storage software and technical advisory services company, details critical safety issues linked to the use of module-level solar rapid shutdown devices (RSDs).
Such devices, which are mounted under each module in a solar array, are commonly used by U.S. solar installers to comply with rules in the National Electrical Code (NEC) that require rapid shutdown of PV systems installed on buildings.
The report, entitled “Unintended Consequences: Rapid Shutdown Devices And Safety In Commercial Rooftop Solar Systems,” covers 74 high-risk safety incidents in installations that use RSDs, occurring between 2021 and early 2026, and sourced from HelioVolta’s field inspections of commercial rooftop PV systems, information reported to HelioVolta by third parties and legal filings.
The report’s authors assert that while RSDs were developed and deployed with the best of intentions, they add multiple points of failure to systems, which can have the opposite of the intended safety effect.
They point out that while no firefighter deaths associated with PV system fires have been documented in the US to date, systems with RSDs and other module-level power electronics (MLPEs) have 66% higher rates of critical safety issues than installations that do not employ these devices, actually leading to more — not less — fire risk.
“Faulty RSDs are operating on buildings across the U.S., unintentionally putting people at risk. As these devices age, worst-case scenario failures are more likely to occur,” said James Nagel, CTO of HelioVolta. “No one wants to acknowledge safety risks hidden in solar portfolios, but we can only eliminate the dangers of RSDs with transparent, informed technical discussions.”
The data gathered by the company include 40 incidents of RSDs melting or overheating, 13 incidents in which there was evidence of a contained fire that damaged one or more RSDs and 21 rooftop fires.
While the number of incidents involved does not represent a large proportion of the total number of solar installations that use RSDs, the report asserts that the details of PV thermal events are usually protected by non-disclosure agreements, and points out that there is no national database for the root causes of solar installation fires.
“Since publishing this report, we’ve heard from developers in the UK and Latin America who recently began installing RSDs as a proactive safety measure.” said David Penalva, CEO of HelioVolta in comments to pv magazine USA. “Instead of exporting best practices globally, we’ve exported problems. All because vital data is locked inside of NDAs.”
A full version of the report is available for download from the HelioVolta website.
Alternatives to RSDs
The report includes several recommendations to improve outcomes, urging system designers to avoid using RSDs in new construction projects, or to exercise caution in sourcing connector hardware and specifying requirements for proper mounting.
For existing systems, the authors recommend system owners implement careful, proactive operations and maintenance checks that include regular visual and thermal inspections and voltage checks.
“Many US asset owners with large-scale C&I fleets now prohibit RSDs in new construction. Some have even retrofitted portfolios to remove RSDs at great expense,” Penalva told pv magazine USA. “Our goal is not to promote a single technology pathway for PV systems,” he added. “It is to help the industry build safer, more reliable systems that benefit everyone.”
One alternative to module-level RSDs that is compliant with the NEC is the installation of a PV hazard control system, as defined by the UL 3741 standard.
These systems allow designers to use a list of approved components to meet the NEC rapid shutdown requirements using more robust string rapid shutdown devices that reduce complexity and the number of connectors necessary to complete a compliant system.
Derek Mast, a solar technician and content creator who runs a website dedicated to information about PV hazard control, celebrated the release of the HelioVolta report.
“This white-paper makes it clear that rapid shutdown, in its current form, must be reassessed from the ground up,” Mast told pv magazine USA. “Those of us who have lived this reality on the ground for years are feeling extremely vindicated by finally seeing this data. There’s a reason that the rest of the world doesn’t use rapid shutdown – it’s unreliable, dangerous, and makes solar worse.”
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