I’m a little wary of plug-in solar in the US. Some of the bills propose allowing 1200 watt panels which can overload wiring depending on what else is on the circuit and how in the wall wiring is run. Limiting plug-in panel wattage to, say, 400 watts might be necessary
I love the idea. Scares the shit out of me.
I’m not as concerned with these things starting house fires, but I want to explain that away first. I’m a little weak on the science, but my understanding of how these work is that they attune to the grid frequency and voltage to deliver power at a slightly lower frequency than what is provided by your wall plug. This allows them to augment your home power use without refeeding power into the local grid. IIRC, if there’s no wall power, they only offer power through outlets on the devices themselves, vs through the wall plugs.
And, I think that the above safety feature will prevent over-amperage situations for in-house wiring loops, since the device cannot exceed the power delivery of the circuit it’s plugged into, when operating normally.These things scare the shit out of me because the U.S. power grid is badly under-engineered. Before actual electrical engineers hunt me down and kill me, think of building a bridge. You can do that by just pouring a billion tons of concrete into a ravine. But building something that is material and budget conscious while being safe enough to avoid lawsuits is not what I’m getting at. (Think of the phrase “Anyone can build a bridge, but not anyone can build a bridge that barely stands.”)
It’s a feature, not a bug. Otherwise, power lines would be I-Beams and we’d have some sort of insane switching technology to isolate and shut off every single segment of the grid.
But we don’t! Homes are never disconnected from the grid unless specialized hardware is installed at the meter to disconnect them. (Which happens for distributed/co-generation scenarios.)The existence of always connected power generation or storage sources as a potential threat vector is well known. In 2023, it caused a minor kerfluffle as several brands of EV chargers were shown to be easily hackable and as few as 300 of them could be used to take down a regional power grid. Not everyone can afford an EV, and usually those users are a tad more tech savvy. They generally are not buying third party chargers, anyway.
But the rate of adoption for these devices could be significantly higher. The law of averages being what it is, I think these pose a much higher threat to the grid from hacking. Everyone loves apps. No one thinks about security. They could easily exploited, rooted, and have their safety features disabled. Who needs 300 EV’s when you have 300,000 balcony chargers?Funnily enough, these would be in high demand if the U.S. grid got fried. It would take years to undo the damage.
You are vastly overestimating how much power actually gets generated by these panels.
Also, basically every assumption made in the first paragraph is incorrect.
Any wiring can handle 10 amps. I don’t understand why you think that’s too much. We have really old wiring and it wouldn’t be a problem.
Thanks for posting, this is awesome. Now do small wind too.
Small wind is horrible, the efficiency of wind is entirely based on the swept area of the blades. At scale it’s great, but at household sizes it’s just not worth the cost. Turbines and windmills are a ‘Go big, or go home’ situation as far as being cost effective. Solar, even with batteries, is more cost effective for household or mobile sizes.
They said “small wind is horrible”, not “I’d really like to spend money on small wind turbines that can’t deliver what they promise, I wish I knew where to find some”.
It’s important to note that Europe has 220/240v by default so most household wiring is robust to higher wattages at lower amps.
See my other comment in reply to OP as to why this might be a bad idea.
In Washington state, a labor union representing electrical workers and the Association of Washington Business, a regional business group, testified against the state’s plug-in solar bill. Neither responded to questions about their position.
Spokeswomen for Puget Sound Energy and Avista Corporation, two Washington State utilities that testified against the bill, said their companies had safety concerns about plug-in solar technology and were waiting to see how the issues are addressed.
Yeah I called PSE and asked about plug in solar. They said it was illegal to use on “their network”. And they gave that same spiel. Safety. They should partner with someone to make safe balcony solar kits for Washington state homes and apartments.
No vision.
Could be an issue for older homes with 14g branch circuits, but honestly i dont see 1200 watts being much of an issue on 20A circuits with 12g wire. Code required pretty much all branch circuits to be GFCI or AFCI protected now as well. Obviously that doesn’t mean anything for older homes that haven’t been updated yet, but AFCIs will catch the problems. Almost too aggressively.
1200 watts is only 10 amps, and branch circuits are laid out much more sensibly now than in previous decades.
Idk, as long as the home isnt like a double-wide from the 70s it should be fine.
There are a lot of older homes with really messed up wiring.
I mean, yes. That’s how I make my living, im an electrician. But once again, supplying 10 amps is really not a risk in the majority of cases imo
My big concern is that somebody plugs a panel in plus two high-amp appliances, like a space heater and a microwave, in a sequence that means they don’t trip a breaker.
Microwave on a dedicated circuit above counter in kitchens and gfci protected per code
You’re not putting a space heater on your kitchen counter
And once again youre supplying up to 1200w, not drawing 1200w. Any power supply system will just be matching the load being drawn
I really dont think this is the degree of a problem you think it is
I’m on board. It doesn’t have to be perfectly idiotproof to be rolled out–nothing is ever going to be perfectly idiotproof and we’re already being compelled to beta test things like Tesla’s poorly-designed self-driving software for its ability to handle human drivers and AI companies’ chatbots. Balcony solar has been in wide use in Europe, where many homes are much, much older than ours, for more than a decade now. We can look at their ideas, products, and safety standards and import and adapt them to meet our own needs pretty easily.
Fire safety is, of course, going to be critical. The way homeowners make decisions when they upgrade is like the Wild West out here, and not every system is going to work for every home. We can only do the best we can in the arena of safety, you know? We make a good faith effort to protect everybody as much as we can, but at some point, the homeowner needs to take responsibility for knowing what their wiring/electric situation is before trying to make big changes to it without an electrician. We lose a few houses every single year from people using turkey fryers improperly despite them having all the information they need not to do that.
One thing the article doesn’t mention is the computerized station that comes with a lot of these balcony solar systems to ensure proper loading, prevent pulling too much power, and to make sure you’re not feeding the grid when you need the power or pulling power from the grid when you don’t need it. Kind of weird that they skipped over that important piece of fire safety and risk management. There’s also a device called Ting you can get that plugs into your wall and notifies you of fire hazards and electrical problems. (It’s completely separate from balcony solar; I got mine through my homeowner’s insurance and they can be bought online.) Another thing that passing this legislation will help is developing a solid set of safety standards. Without the legislation, there won’t be enough social or political pressure to do it and could slow future adoption down by years.
Given the strain power utilities are under with the AI bubble, it seems irresponsible that they’re not pushing harder for this.
What happens when electricians need to do work but the lines are energized by these? This is a genuine question. It seems like a really difficult problem to solve
In Germany, where these “balcony solar” devices have been approved for years and seem to be the most popular out of any country, the panels have all kinds of safety mechanisms. One of them is a mechanism that shuts of the power coming from the panel if it detects that line power has been lost. It seems that this is what would prevent it from shocking electricians working on lines that they think are unpowered. This article goes into details about the various safety mechanisms on these: https://balkon.solar/news/2025/03/17/how-does-plug-in-pv-in-germany-work/
The plug in systems aren’t meant to provide power on their own, they’re meant to supplement grid power and reduce energy costs for the purchaser. They don’t provide electricity unless some is already detected on the line, for the exact reason you ask
I assume unplug the solar? If the whole point is that it plugs into an outlet
My backyard faces west. If I could, I’d fill up half of it with solar panels.
I am not an electrical engineer, but based on OP’s description, it sounds like a solar panel that connects to an outlet in an existing circuit. Say you have a solar panel plugged into the first outlet on a 15-Amp circuit, with solar producing 1200 Watts of available power. Then you have a 10-Amp load plugged into the next outlet in the circuit, and another 10-Amp load plugged in further down the circuit. That 15-Amp circuit has wiring rated for 15 Amps. You have 20 amps of load, but the solar panel is providing half of that downstream from the circuit breaker. The breaker sees only 10 amps of load and doesn’t trip, though you have wiring downstream from the solar panel that’s carrying 20 Amps. This will start a fire.
I’m not sure why all the downvotes, but overloading is true, see here how to avoid it:
https://balkon.solar/news/2025/03/17/how-does-plug-in-pv-in-germany-work/Preventing Circuit Overload (Source + Load on One Circuit)
The key safety concern is that a plug-in solar inverter feeds into a final sub-circuit “downstream” of the main breaker. Normally, a circuit breaker senses all current on its circuit and trips if the load is too high. But with a PV source injecting current at a wall socket, part of the load is supplied locally. The breaker only “sees” the net current from the grid – not the portion supplied by the solar module . This means the wiring could carry more amps than the breaker’s rating without tripping. For example, on a 16 A circuit a 600 W micro-inverter (≈2.6 A) plus a 16 A appliance could theoretically pull ~18.6 A through the wires while the breaker sees only ~16 A . Over time, such an unseen overload can overheat cables, especially in old or unfavorable installations.
The 800 W limit (specified as 800 VA) was chosen as a conservative safe value so that typical 1.5 mm² house wiring can handle the extra current margin. Even under full sun, a 800 W unit rarely sustains peak output (often max ~500–550 W ≈ 2.4 A), and most circuits can tolerate that small extra current. The limit is rising to 800 W (≈3.5 A) as EU regulations consider <800 W “not significant” generation. At 800 W, German guidance still deems the slight increase manageable, but extra safety margins are advised. For example, in older homes with uncertain wiring, it’s recommended to replace the 16 A breaker with a 13 A one. A 13 A MCB will trip sooner, ensuring that the sum of grid + solar current can’t overheat the cables (13 A from grid + ~3 A PV ≈ 16 A total). Another strategy is having an electrician connect the balcony PV on a dedicated circuit with its own breaker, so it doesn’t combine with heavy appliance loads on the same line. Then even larger system would be possible.
In practice, users are advised to avoid overloading scenarios proactively: connect the mini-PV to a circuit that isn’t already near capacity, and never daisy-chain multiple PV units or plug them into extension strips . Only one unit per outlet/circuit is allowed, which prevents additive overcurrent from two inverters. By following these limits and using the existing circuit protection, Germany keeps wiring stress “within tolerance” . Notably, tests have shown that issues (excessive heating) would only start to appear above roughly 700 W sustained feed-in combined with a fully loaded 16 A circuit in worst conditions.
I think you need to learn how electric circuits work.
I’ve had more than a few classes on circuits throughout my schooling, from high school physics to my mechanical engineering college coursework. Please enlighten me as to where my logic is flawed.
Two sources wired in parallel can supply more current than either individual source can supply on its own. The wiring on each parallel branch will have identical voltage, and the converged branch will carry the sum of the currents. Total load of 20 amps exceeds the capacity of the wiring, breaker doesn’t see the full load and doesn’t trip.
In Germany, it’s limited to more like 800 watts (and I think some other safety regulations). As I understand it, it’s generally worked without this being much of an issue despite millions of plug in solar installs (primarily for balcony solar)
The solar panel would be providing some of that electricity though. You’re not accounting for that.
I am accounting for that, that’s the whole point I’m making. Breaker is supplying 10 of its available 15 Amps, solar provides another 10 Amps, load downstream is drawing 20. Wiring between solar and load is carrying 20 Amps, but potentially rated for only 15.
