The stroke of a pen in Utah set off a solar chain reaction across the United States. Last March, the Western state legalized plug-in photovoltaic: solar panels small enough they can plug into a typical household outlet, helping power the house. Dozens of states followed suit shortly thereafter. Balcony solar, as the tech has become known since it could be deployed on the balcony of an apartment building, is now legal in states such as Colorado and Virginia. By July 2026, balcony solar bills had passed one or both houses of the legislatures states including New York, New Jersey, and California.

The U.S. embrace of this technology happened so fast that legalization has raced ahead of regulations needed to make sure it works safely. No panels meet newly created certification standards that are still in flux. The country still must solve a suite of legal and technical problems, said Craig Morris, the CEO of the German plug-in solar trade association Bundesverband Steckersolar. “If you get the law,” he said, “then your work begins.”

Morris knows the growing pains because Germany is where balcony solar came of age. In the 2010s, tinkerers realized they could use newly available microinverters, from large solar arrays, to send AC power from a single, affordable panel to a household plug. Balcony solar took off in popularity there as a clean and affordable energy solution after the 2022 Russian invasion of Ukraine sent natural gas prices soaring. Now, Germans can buy plug-in panels at Aldi or IKEA, and the country has more than 2 gigawatts of balcony solar deployed.

In December 2025, Germany finalized a regulatory standard to ensure these devices could safely send electricity back into a home power outlet and even the grid, though . Germany’s balcony solar law forbids net metering, in which grid operators pay customers who return electricity to the grid, because it creates so much uncertainty for grid managers. Morris’s organization got German firefighters to agree the technology isn’t dangerous. German law also protects renters whose landlords don’t want them to mount solar panels for aesthetic reasons. Property owners need a legitimate reason to oppose a resident’s request, such as necessary repairs to the balcony.

Coming to America

Ken Boyce watched all this from afar. Boyce is vice president of principal engineering at UL Solutions, the firm that creates testing and certification standards for a wide variety of electrical technologies, which now includes balcony solar. The speed of U.S. adoption of balcony solar caught him by surprise. “That Utah legislation passed and we said, “Oh, how about that?” Soon after, Boyce and a cadre of engineers got to work. By the end of 2025 UL Systems had developed a basic framework for UL 3700, their attempt at a U.S. testing and certification standard for balcony solar.

The standard addresses numerous concerns about the safety of plug-in PV. The simplest problem is that household wiring simply wasn’t designed to handle power flowing into the outlet from a plug. Unlike ordinary appliances, a solar panel’s plug can be electrically conductive when the device unplugged, which may surprise unwary customers. Plug-in panels inject power into the home electrical system downstream of circuit breakers and other overcurrent protections, making those safeguards blind to the extra load. Electricity flowing backward through the GFCI (Ground Fault Circuit Interrupter), the electrical safety device built into power outlets, could cause GFCIs to fail. “There’s this kind of insidious aspect to it,” Boyce said, “and now you’ve bypassed that protection that’s required to protect consumers from electric shock hazards.”

All of these factors make a plug-in solar panel much different from household appliances, such as a toaster or refrigerator, says Nadav Enbar, a program manager at the nonprofit Electric Power Research Institute (EPRI). Nevertheless, he says it’s crucial that regulators treat balcony solar panels like an appliance. Their ability to plug in and just work—without the owner needing agreement from a utility, permits, or an electrical upgrade—is central to the technology’s mass appeal and its ability to get solar into so many more homes.

Making balcony solar safe to plug and play

So, UL3700 addresses those dangers. In addition to specific requirements such as the thickness of insulation, it also requires manufacturers to account for other known risks–for example, by using wiring methodologies that lend additional overcurrent protection or by using GFCIs built to withstand bidirectional current. Plug-in solar also must also power down in the case of a local blackout. This addresses one of the chief concerns cited by power utilities: that plug-in PV, were it to send power onto the grid during an outage, poses a danger to linemen.

How plug-in PV manufacturers satisfy those rules is up to them. But because UL3700 and balcony solar panels are so new, no panels have achieved the standard so far. Enbar notes that the UL standard is a high bar to clear, and, in fact, some of its requirements may not be solvable at this moment. For example, the bidirectional GFCI disconnect is not yet commercially available.

Balcony solar is momentarily caught in limbo: The systems now available, and going online in states like Utah, are either not certified or cite some other electrical certification that wasn’t written for plug-in PV, according to EPRI.

The last piece of the puzzle is transparency. David Eisenhauer, a representative of the power utility SoCal Edison, told IEEE Spectrum that while Edison supports their customers gaining access to plug-in solar, “It’s really important that customers notify us before they start to think about or install plugin or balcony solar. That’s going to help us ensure that they’re installing certified equipment, help us track connections so that we can balance and operate the grid.”

This may be easier said than done: EPRI’s research shows that even in industry leader Germany, unregistered balcony solar panels outnumber registered two to one. Some customers simply don’t want to do extra homework to register a purchase, while others, Morris says, might not want to publicize their plug-in PV or let landlords know about it. Given the likely rise of unregistered “guerilla” solar, plug-in PV just has to work safely, every time, no matter how many people set up a solar panel on their balcony or in their backyard.