UL Solutions has published new technical guidance and a proposed certification pathway for plug-in balcony solar systems, outlining safety risks and design requirements as several US states move to legalise the technology.

From pv magazine USA

UL Solutions has released new design guidance and a proposed certification framework for balcony solar, also known as plug-in PV (PIPV), as US policymakers and manufacturers begin to explore consumer-installed solar systems that connect directly to wall outlets.

In a white paper titled “Interactions of Plug-In PV (PIPV) with Protection of Existing Power Systems,” UL outlines safety considerations for products that allow consumers to plug solar modules into existing residential circuits. The document identifies three primary risk categories: overcurrent protection, touch safety and ground-fault protection.

UL moved quickly to develop a new certification pathway, UL 3700, an Outline of Investigation for Interactive Plug-In PV Equipment and Systems, following the passage of Utah’s balcony solar legislation. Similar bills are now under consideration in other states, including California’s Senate Bill 868.

According to UL, overcurrent protection presents a key challenge because PIPV systems can inject power into branch circuits without being detected by standard circuit breakers. In some scenarios, combined household loads and injected solar power could exceed a circuit’s design limits without triggering protective devices, increasing the risk of overheating conductors and associated components.

UL said potential mitigation measures include dedicated circuits for PIPV systems, solar-specific receptacles, or connection to circuits with oversized conductors.

Touch safety is another concern, as PIPV systems are handled directly by consumers rather than trained electricians. While standard household plugs are well understood as loads, UL notes they have not been evaluated as power sources. The organization also flagged challenges related to inverter behaviour, particularly anti-islanding and grid-response functions that may not be designed for frequent plug-in and unplugging events.

Ground-fault protection was identified as the third major risk area. Because PIPV systems are typically installed outdoors and exposed to weather, UL said interactions with ground-fault circuit interrupters require careful design. Current electrical code requires outdoor receptacles to be on dedicated branch circuits, which may necessitate new outlet designs or dedicated connections for PIPV systems.

Ken Boyce, vice president of principal engineering at UL Solutions, said the organisation’s role is to evaluate safety outcomes rather than commercial viability. As of mid-January, he said UL was not aware of any PIPV products that had completed certification under UL 3700, noting that the outline was only released in mid-December.

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