Why Balcony Solar Rules Are Different in Every State (And What That Means for You)

Yesterday, Bright Saver co-founder Rupert Mayer sat down (virtually, from California, at an early hour) with Todd and Henry Swayze at Greenzine, the weekly environmental news show on WFDR-LP, South Royalton Community Radio in Vermont. The conversation covers the questions we hear from almost every state: why balcony solar is legal but hard, what UL 3700 actually requires, and how a $29-a-year membership pays for a nationwide fight to make plug-in solar simple everywhere.

A quick note if you're reading this from Vermont: as Rupert explains below, Vermont is currently one of only three states where Bright Saver cannot ship a kit. Vermont's law requires full UL 3700 system certification, and that certification doesn't exist yet for any manufacturer. We ship to nearly every other state today. If you're in Vermont, consider becoming a Bright Saver member anyway — it locks in your discount for the day we can ship, and it funds the exact advocacy work this interview describes. If you're anywhere else, you can order a kit right now.

Listen to the full show here: royaltonradio.dreamhosters.com/podcasts/VermontGreenZine/stream.mp3

The short version

• Plug-in ("balcony") solar isn't illegal in any state. It's just treated like a rooftop construction project in states without a plug-in friendly law, which makes it slow and expensive.

• About ten states, starting with Utah, have passed laws that treat small plug-in systems like an appliance instead of a construction project.

• Vermont is one of only two states so far that wrote a specific safety standard, UL 3700, directly into its law. That standard is still in draft form, and no product on the market is fully certified against it yet. It requires a proprietary plug and outlet on a dedicated circuit for plug-in systems of any size.

• A 400-watt carve-out, equivalent to the established safety standards in most of Europe, is the fix many other states are using to allow true plug-and-play for small systems.

• Bright Saver sells kits at cost. The $29/year membership is what funds the organization and the advocacy work, not the hardware markup.

Why balcony solar exists in the first place

Rooftop solar in the U.S. costs about three times what it costs in Australia. Most of that gap comes from permitting: multiple site visits, inspections, and interconnection paperwork before a single panel goes up.

Germany took a different path. Millions of renters, without roofs of their own, started hanging small solar panels on balcony railings, plugging them into a normal outlet, and cutting their electric bill directly. No permit, no inspection, no utility sign-off. Rupert's co-founder Kevin Chou saw this on a trip to Germany and asked why the U.S. didn't have it. That question became Bright Saver, two years ago.

Is it legal in your state?

Plug-in solar was never illegal anywhere in the U.S. The problem is that most states have no specific rule for it, so it defaults to being treated like any other electrical construction project: permits, inspections, and an interconnection agreement, even for a panel the size of a window screen.

Utah was the first state to fix this, more than a year ago, by writing a law that treats small plug-in systems like an appliance instead of a construction project. About ten states have followed. Bright Saver ships kits to nearly all of them today. If you want to check your specific state, visit our legislation tracker.

What UL 3700 actually requires, and why Vermont is an exception

Vermont's and Maine's laws are the only ones so far that names a specific certification, UL 3700, directly in the statute. UL 3700 is a new standard covering an entire plug-in system, not just one component. It's still in draft form (an "outline of investigation," in UL's language), and it requires a proprietary connector setup that most existing hardware doesn't have.

The traditional safety standard for solar inverters, UL 1741, already requires rapid shutdown: if the grid goes down or a breaker flips, the inverter stops producing power immediately, so nobody gets shocked unplugging it. That's a built-in feature of every plug-in system, not something UL 3700 adds. What UL 3700 adds on top is stricter, and until a manufacturer's full system clears it, Bright Saver can't legally ship into Vermont.

Naother piece that many states have put in their law that's missing in Vermont is a 400-watt exemption. Europe settled on the equivalent of 400 watts (800 watts on their 230-volt circuits) as the level any household circuit can safely absorb without any special wiring. Many U.S. states with plug-in solar laws exempt systems under that threshold from the stricter certification requirements. Vermont's law doesn't currently have that carve-out, which is why, as of this interview, plug-in solar isn't yet workable there even though the underlying law allows it in principle.

Batteries and timing

A balcony solar panel produces the most power in the middle of the day, often when nobody's home to use it. Two things help: a constant daytime load (electric vehicle charging, a second fridge, air conditioning) or a small balcony battery, roughly the size of a stereo speaker, that stores the day's output and releases it in the evening when people come home and turn everything on.

Why membership, not just a product

Bright Saver sells its panels at cost. The organization doesn't profit on the hardware. The $29/year membership is what keeps the organization running and what funds the legislative work described above in state after state. Members also get access to the discounted panel pricing once a kit is available in their state.

As one of the hosts put it during the interview: it's solar with a socialist smile, or as Rupert has described it elsewhere, the Costco of clean energy, or the AARP for people who want cheaper power. Join for $29/year or, if a kit ships to your state already, order a Balcony Solar Kit starting under $300.

Full transcript: Bright Saver segment, Greenzine, WFDR-LP South Royalton

Lightly edited for readability: filler words, false starts, and a handful of mis-transcriptions have been corrected. Timestamps have been removed. Speaker labels reflect our best read of who is speaking; the interview alternates between hosts Todd and Henry Swayze and guest Rupert Mayer.

Hosts: Welcome to Greenzine.

Rupert Mayer: Hello. Thank you for having me.

Hosts: Good morning, Rupert. Glad to have you on the air. So we've given people a little bit of a rundown about plug-and-play solar and your involvement, but I wonder how you decided to throw yourself into the work of this project called Bright Saver.

Rupert Mayer: Great question to start with. I had been a software entrepreneur for most of my career, some in Europe, Austria, Germany, and then here in California. A little over five years ago, I decided to pivot and do something completely new, something more impactful. I decided to throw myself into the fight against climate change: climate action, climate solutions. Then I started gravitating, through my own lived experience, toward home electrification, heat pumps, batteries, all very mature technologies and very low-hanging fruit for rapid electrification, and of course EV's as well. A few years in, my now co-founder Kevin Chou pitched me on this idea of plug-in balcony solar. He said, "Hey, you're from Europe, it's all over the place there." He'd just traveled to Germany and saw solar panels hanging from every balcony, and asked why we don't have that in the U.S. and how we could make it happen. That's how we started, two years ago.

Hosts: You've done a lot in that time. I know Utah led the charge, made it legal to do plug-and-play solar with no permitting, no fuss, no muss, just buy it and play.

Rupert Mayer: I like to push back a little on the word "legal," because plug-in solar was never illegal, and it isn't illegal anywhere. It just comes with too onerous requirements. In every state without a plug-in-specific law, a simple, small plug-in panel is treated like a construction project on your roof, with permits and interconnection agreements. That makes it prohibitive. It's not illegal, it's just onerous. What these laws do, starting with Utah more than a year ago, is make it as simple as it should be: treating these small solar systems like an appliance rather than a construction project.

Hosts: Why do you think those regulations, developed probably over many decades, are in place? Was it a safety factor, or just bureaucracy?

Rupert Mayer: Probably a bit of a mix. These interconnection requirements exist for a real reason. If everyone put generation in or around their house, whether solar, a wind turbine, or a generator, and pushed power back to the grid, it would make planning difficult for the companies that operate it: how big the transformer needs to be, how much load is on the block. The whole grid was designed to be one-directional and centralized, power flowing from large plants through transmission lines to substations and down to homes. It wasn't designed for power to flow back, so there's a real point to wanting some control. But in Germany, millions of these small systems have gone up, and it hasn't been a problem for that grid or for household wiring. I listened to a podcast recently with one of the pioneers of German plug-in solar, back in 2012, when it was unheard of. People said it was dangerous, that people would electrocute themselves or burn down their houses, that the grid would collapse. Almost 15 years later, we're having the same discussions in the U.S. that Germany had at the start, except we can move faster here because we already have that precedent.

Hosts: Vermont has a law on the books, signed by the governor, remarkable since our governor frequently vetoes things that cost money. But it requires each component to carry an Underwriters Laboratories certification. I believe we're the only state with that requirement. Is that right?

Rupert Mayer: That's true. Quick note on the governor: what I love about this technology is that it's bipartisan. You can support this no matter where you stand politically, whether you think renewable energy is a leftist cause or not. The first state to pass this kind of law was Utah, a deeply red state. There's something in it for everyone: clean energy and social justice, but also citizens' rights, deregulation, and doing what you want in your own backyard without government or utility interference. And of course, everyone likes saving money. Now, back to your question: yes, the Vermont law is the only one so far, as far as I'm aware, that codifies this very specific UL 3700 standard into law. Most other states took a more generic route, requiring a nationally recognized testing lab rather than naming one specific standard.

Hosts: What does that standard actually require? There's already a UL standard that says solar can't feed power to the grid during an outage, an anti-islanding clause, so a lineman doesn't get shocked working on downed wires.

Rupert Mayer: Let's take a small step back, since we're getting technical. UL standards exist for most electric appliances. There's probably a UL certification sticker on the back of your dishwasher, TV, and washing machine. There are also UL standards for individual solar components: one for panels, so you don't shock yourself touching one or start a fire if it's hit by hail, and one for inverters, the box of electronics that converts direct current from the panels into the alternating current a home uses. The traditional inverter standard, UL 1741, already requires that rapid shutdown for grid and lineman safety. For a plug-in system, that's an inherent safety feature: these are "grid-following" inverters, meaning they only produce power when they detect a grid signal. The moment the grid goes down or a breaker or GFCI trips, the inverter stops instantly, so you don't shock yourself unplugging it. So the alignment-safety concern you hear cited a lot is really misguided. I'd call it opposition propaganda from people or entities who don't want this to happen.

Hosts: Can I ask something specific to this station? We've installed a Tesla Powerwall as backup at our transmitter, no solar yet. If we added balcony solar, would that feed into the Powerwall, or straight into the regular line, without needing a separate inverter since one's already built in?

Rupert Mayer: It would do both. You plug it into any outdoor outlet, and the electrons flow through that circuit back to your breaker panel, then out through the other breakers to whatever loads are running in the building. If your equipment and lights are running, those loads absorb the power directly and your grid usage drops accordingly. If the panel produces more than the building is using, the excess flows back toward the grid, only while the grid is up; if the grid goes down, the system stops immediately. Your Powerwall sits in between: since it's also connected to the breaker panel, it would likely absorb any surplus before it reaches the grid. Whether it actually does depends on the Powerwall's own software logic for when to charge. In principle, the two systems are independent but should work together fine.

Hosts: Very valuable information. You mentioned constant load: that's great when you have something running all day, like AC or electric heat, or an EV charging, or multiple fridges, absorbing that power while it's generated.

Rupert Mayer: Exactly. If nobody's home during the day and the only load is the fridge, a bigger balcony system will send some of its output back to the grid for no credit under net metering rules. That's where batteries come in. Beyond something like a Powerwall, there are dedicated balcony battery products, roughly the size of a stereo speaker. The panels connect to the battery, the battery plugs into the wall, and it acts as a buffer: it soaks up power during the day when the house isn't using much, then dispenses it in the evening when people come home and turn on the lights, the TV, and appliances. It's time-shifted to when the power is actually useful.

Hosts: Let's go back to UL 3700. My understanding is UL tends to be extremely cautious and never wants to be in a position of being wrong. It's an independent body that generates income by issuing certifications, so it has an incentive toward more paperwork, not less.

Rupert Mayer: UL 3700 in its current draft form doesn't distinguish between system sizes. We wish it had a lower, looser threshold for smaller systems, because in Europe, with millions of systems installed, 800 watts (on their 230-volt circuits) has been established as the safe limit for any circuit. On U.S. 120-volt circuits, the equivalent safe number is 400 watts: plug in below that, and you don't have to think about it. We were hoping UL 3700 would set that same lower bar and only apply its more rigid requirements above 400 watts. Unfortunately, the draft standard applies those rigid requirements starting from zero.

To back up: each component (panel, inverter, connector) has traditionally had its own UL sticker. UL 3700 is new because it certifies the entire assembled system together, and it's still in draft, called an "outline of investigation," a preliminary standard. It essentially says that even if every individual component is already UL certified, connecting them together and plugging the whole system into a wall triggers additional requirements, including a proprietary connector setup. That's the piece most manufacturers don't have yet, and it's why any plug-in system, regardless of size, currently needs that proprietary hardware to be considered compliant in Vermont.

Hosts: So how will this play out? Will systems eventually get UL 3700 certified?

Rupert Mayer: It's important to remember we're very early. One reason the standard got written directly into Vermont's law is that Vermont was the second state, right after Utah, to act, before there'd been much technical scrutiny of the standard itself in other states. As more states adopt a 400-watt exemption, similar to the European standard, Vermont's law may eventually get revised to match. At the moment, without that exemption, the law reads as requiring full UL 3700 compliance across all systems regardless of size, which means no plug-and-play solar in Vermont for the time being. We believe there will be forces pushing UL toward a 400-watt carve-out in the standard itself, and pushing Vermont legislators to add that carve-out to the law.

Hosts: So you're working on the UL side and also planning to go back to Vermont legislators about amending the carve-out?

Rupert Mayer: We don't have a seat at the table with UL directly. It's a bit of an opaue organization, part nonprofit, part for-profit, and it acts as both a certification lab and a standard-setting body, which creates some inherent conflicts of interest. They haven't engaged directly with us, but I expect the major manufacturers, especially those building larger battery-backed systems and actively pursuing certification, have more of a seat at that table and are pushing the standard to evolve.

Hosts: One more question, back to that proprietary outlet. It clearly adds expense: hiring a certified electrician, possibly a new breaker. If a homeowner or business went through that process anyway, would that unlock more than 400 watts under Vermont's current law?

Rupert Mayer: Yes. Vermont's law allows 1,200 watts once you've had an electrician confirm a dedicated circuit and install that special outlet. You can go even higher on the solar side if you add a battery, since the battery can buffer the output, up to roughly 2,000 watts of generation feeding a battery that itself feeds no more than 1,200 watts into the circuit. You can put a decently sized system on a porch or balcony that way.

Hosts: We'll take that up with our electrician off-air. Any closing comments?

Rupert Mayer: Just to note, if you go to brightsaver.org, you'll see we're supplying systems to most states, but Vermont isn't one of them yet, because the full system certification isn't in place. We're working on it, though it's hard to estimate exactly when: there's still a lot of interpretation involved in how testing labs will apply the standard. We're hoping for something in the next few months. In the meantime, we ship to almost every other state. Our balcony panels are lightweight, you can literally hang them on a balcony rail, porch, or deck railing with zip ties, and they start under $300. I'll also pitch our membership: we're a membership organization, we sell these panels at cost, we don't make money on the hardware. What sustains us as an organization, and builds the constituency to pass more plug-in-solar-friendly laws, is the membership itself.

If you go to brightsaver.org, even if you can't order a panel in your state yet, you can become a member for $29 a year, which unlocks the discount on panels once you're able to order.

Hosts: Solar with a socialist smile. The Costco of clean energy.

Rupert Mayer: [laughs] Or REI meets Sierra Club, or the AARP of solar.

Hosts: I'll definitely take out a membership myself. Even if it's not currently useful for me directly, I know it's helping the conversion to sustainable energy across the country. Thanks for joining us on Greenzine, Rupert, it's been a great pleasure.

Rupert Mayer: Thank you, I appreciate it very much. Have a great rest of your day, and thanks to everyone who tuned in.

Full audio of this Greenzine episode, WFDR-LP South Royalton Community Radio, is available at royaltonradio.dreamhosters.com/podcasts/VermontGreenZine/stream.mp3. The Bright Saver segment begins roughly 20 minutes in.

Ready to cut your power bill? Check if Bright Saver ships to your state and order a Balcony Solar Kit, or join for $29/year to lock in your discount and support the legislative work that's making plug-in solar simple everywhere, Vermont included.