Another issue in the US is the lack of a compatible safety device called a ground fault circuit interrupter, or a GFCI. They are typically built into outlets installed near water sources, like a sink, washing machine, or bathtub. They’re designed to minimize the risk of electric shock by cutting off power when, for example, a hair dryer falls into a sink. Yet there are no certified GFCI outlets in the US designed for use with devices that consume power, like a blender, and those that generate it, like a balcony solar setup. Germany’s equivalent of a GFCI, called a residual current device, can detect bidirectional power flows, said Andreas Schmitz, a mechanical engineer and YouTuber in Germany who makes videos about balcony solar.
Some people have raised concerns about the shock risk of touching the metal prongs of a plug after unplugging a balcony solar device. German regulators accounted for that by requiring the microinverter—which converts currents from the panel into electricity fed into the home—shut down immediately in an outage or when it is suddenly unplugged. Most of them already have this feature, but any US standard will likely need to formalize that requirement.
The lack of an Underwriters Laboratories (UL) standard is perhaps the biggest obstacle to the adoption of balcony solar. The company certifies the safety of thousands of household electrical products; according to Iowa State University, “every light bulb, lamp, or outlet purchased in the US usually has a UL symbol and says UL Listed.” This assures customers that the product follows nationally recognized guidelines and can be used without the risk of a fire or shock.
While some companies have sold plug-in solar devices in the US without a UL listing, the company’s seal of approval typically is a prerequisite for selling products on the wider market. Consumers might be wary of using something that lacks its approval. Utah’s new balcony solar policy, for example, specifies that the law applies only to UL-listed products.
Achim Ginsberg-Klemmt, vice president of engineering at the plug-in solar startup GismoPower, has been working on creating such a standard for more than a year and a half. In 2023, the Department of Energy awarded his company a grant to work with UL to develop a standard.
GismoPower sells a mobile carport with a roof of solar panels and an integrated electric vehicle charger. Unlike rooftop solar, the system doesn’t need to be mounted in place but can be rolled onto a driveway and plugged in, generating electricity for the car, house, and the grid. “We’re basically taking rooftop solar to the next level” by making it portable and accessible for renters, Ginsberg-Klemmt said. The product is in use at pilot sites nationwide, though a lack of standardized rules for plug-in solar has forced the company to negotiate interconnection agreements with local utilities—a time-consuming and sometimes costly process.
GismoPower’s product avoids one of the biggest technical challenges with balcony solar by plugging into a dedicated 240-volt outlet, the kind typically used for dryers. Such an outlet serves a single appliance and uses a dedicated circuit, sidestepping the risk of overloading. But it runs headlong into the same obstacle of lacking a compatible UL standard. Ginsberg-Klemmt is working with researchers at the Lawrence Berkeley National Laboratory, other entrepreneurs, and engineers at Underwriters Laboratories to develop such a standard, but it hasn’t been easy. “We have found so many roadblocks,” he told Grist.
