One concern is a phenomenon called breaker masking. Within a home, a single circuit can provide power to several outlets. Each circuit is equipped with a circuit breaker, a safety device within the electrical panel that shuts off power if that circuit is overloaded, which happens when too many appliances try to draw too much electricity at the same time. That prevents overheating or a fire. When a balcony solar device sends power into a circuit while other appliances are drawing power from the circuit, the breaker can’t detect that added power supply. If the circuit becomes overloaded — imagine turning on your TV while a space heater is running and you’re charging your laptop, all in the same room — the circuit breaker might fail to activate.
This was a concern in Germany, so it developed standards that limit balcony solar units to just 800 watts, about half the amount used by a hairdryer. That threshold is considered low enough that even in the country’s oldest homes, the wiring can withstand the heating that occurs in even the worst of worst-case scenarios, said Sebastian Müller, chair of the German Balcony Solar Association, a consumer education and advocacy group. As a result, Ofenheusle said there haven’t been any cases of breaker masking causing harm. In fact, with millions of the devices installed nationwide, Germany has yet to see any safety issues beyond a few cases where someone tampered with the devices to add a car battery or other unsuitable hardware, he said.
Another issue in the U.S. 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 hairdryer falls into a sink. Yet there are no certified GFCI outlets in the U.S. 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 U.S. standard will likely need to formalize that requirement.
The lack of an Underwriters Laboratories, or 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 U.S. 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 U.S. 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 said.
One major sticking point is that any standard must comply with the National Electrical Code, a set of guidelines for electrical wiring in buildings that does not allow for the installation of plug-in energy systems like balcony solar. The rules are issued by the National Fire Protection Association, a nonprofit trade association, and adopted on a state-by-state basis.
The code is updated every three years, with the next iteration due later this year for the 2026 edition. Ginsberg-Klemmt and his working group submitted recommendations for amending the code to allow plug-in solar — and every one of them was rejected in October.
Jeff Sargent, the National Fire Protection Association’s staff liaison to the National Electrical Code committee, said that this is the first time the organization had received public comments about plug-in solar systems. For now, it cannot consider amendments to allow their use until a compatible ground fault circuit interrupter exists, he said. Once that’s available, he said, the association can ensure that outdoor outlets can be safely used for balcony solar.
Electrical standards are constantly evolving, and it often takes more than one cycle of code changes to allow for new products, said Sargent. Ginsberg-Klemmt said his group will continue to pursue other avenues to amend the codes.
Until that happens, a UL standard for plug-in solar is unlikely to go anywhere. But interest in plug-in energy solutions isn’t going away, and decision-makers will have to adjust to that reality eventually, Ward said. It happened in Germany, where people across the political spectrum have embraced the technology. Ward believes the same thing will happen here. The way he sees it, “It’s just a good thing if you set up a system so people have a way to take care of as much of their own problems as they can.”
