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Comment by gorbypark | Hacker News Reader

I’ve been looking into doing this on my balcony in Spain. They sell “plug in” solar kits, but I’ve yet to determine if it’s actually legal here. I have a south facing balcony that’s about 1mx3m, so should be able to get about 400-600 watts of panels on the railing.

I actually came across this article in my research and it’s the only thing I’ve found saying it’s legal if it’s under 800w. From what I’m gather it’s just a few solar panels and an inverter that feeds electricity into a socket, more or less. My concern is what happens when there’s a power outage? I’d then be feeding power into a system that’s “denergized”. I know with real solar setups there’s an automatic cutoff when that happens to protect people working on the lines…all the kits i see here mention nothing about a cutoff system.

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I live in Berlin, I have some friends that bought some panels just because they could. I'm considering myself even though I don't get a lot of sunlight on my balcony. I only pay about 60 euro per month. But these kits only cost a few hundred euros. So why not? If it saves me 10 euro per month or so, it would earn itself back in 3-4 years under ideal circumstances. It's not a huge saving obviously.

> My concern is what happens when there’s a power outage? I’d then be feeding power into a system that’s “denergized”.

This is Germany, they would have studied that topic thoroughly. In short, the certified inverter that you must use for this would indeed shut down in case of a power loss. This is usually called "anti-islanding protection" and not an optional feature for this.

Ask yourself why you are interested in an investment that has only meager returns if everything works out well? Is it worth your time thinking about +/- €10 per month? If that's the case, you could probably achieve it just by using a little less electricity.

Or do both?

This is very much a fire and forget thing. Install takes 2 hours and then generates electricity for years.

Electricity is rather cheap anyway. If you don't heat/cool water or the house with it, electricity cost in Germany is less than 100 EUR per month for a family of 4.

Interestingly, owning even a small PV setup like these "balcony solar" devices, and monitoring its output, causes many people to think more about their grid power consumption, and to reduce it or adapt their usage pattern to solar energy availability to some extent. There is something like gamification going on.

In Berlin, you could get it for free through the SolarPLUS[1] subsidy program. My setup (2 panels, inverter and mounts) cost less than 500€ and was fully subsidized.

[1] https://www.ibb-business-team.de/en/solarplus/

> But these kits only cost a few hundred euros. So why not? If it saves me 10 euro per month or so, it would earn itself back in 3-4 years under ideal circumstances

I'm not saying this is an unreasonable position, but the net present value of an investment that pays 10 euros a month for 4 years is also a couple of hundred euros. So in the end it might be a wash (or might not beat out investing in higher yield projects)

https://www.calculatorsoup.com/calculators/financial/present...

Regarding legality: According to Commission Regulation EU 2016/631 systems under 800W don't qualify as any of the regulated types of power generating facilities, so any law that would limit their installation must be local.

In practice you need to have a two-way meter installed by the power company and you're good to go.

My understanding is that the inverter you get in the kit that you plug into the wall will shut itself off if the power goes out, the same as most larger non off-grid solar systems.

Not only as a safety feature but as an inherent part of their design: they are designed to produce AC that's in sync with the grid. Same frequency and peaks/valleys as the same time. In a blackout there is no grid to follow, so the inverter shuts off.

It is also interesting to read up how this plays into black start plans for the european power grid. You would think solar parks make black starts ... "easy" - just turn them on and have some power, but due to the inverter functions, that's not the case.

Instead, one of the plans I've read about has to start a few black start capable power-plants first to get some kind of phase into the grid. Then you can bring consumers and solar parks online until there is enough load on the grid to bring up larger power plants, while the quick-reacting solar parks are taken online and offline to balance the grid so it never has too much or too little load on it.

There's a link to a pdf manual for what appears to be a fairly common one here: https://github.com/tbnobody/OpenDTU/discussions/855

The inverter is designed to stop feeding power if the grid drops off.

I've an EcoFlow plug & play inverter, and it automatically shuts off if the grid comes down. That's a requirement for all these devices.

Those are grid tie inverters, they cannot/will not output if no grid is present.

At additional cost, one could install a fully manual physical transfer switch which disconnects the PV panels entirely from the gridtie inverter and your apartment's breaker panel, and connects it instead to a charge controller and battery system. Such as one of the nominal 50Ah or 100Ah "48V" Chinese LiFePo4 batteries which come in 2U to 4U rackmount size.

It would be an either/or configuration if done as cheaply as possible such as for a balcony storage system, not capable of both usages simultaneously.

You would then need to have a separate distribution of power from the battery system to your loads. Such as something like a 1000W true sine wave inverter to power essentials like laptop, phone chargers, basic lighting etc during a full power outage.

The small inverters used in these balcony setups aren't setup to provide power without a grid reference.

Yes but they are saying you could - in a power outage - use just the panels, disconnecting them from the grid tie inverter and instead plugging them into a regular off grid charge-controller+battery+inverter setup.

That would cost a bit, but would let you use the same panels for emergency power

The inverter connects directly to the panel and has short DC leads.

Look at the "Component proximity" bit here:

https://robinsun.es/en/products/robinsun-performance-basic-b...

There's probably other setups, but I bet this is how most of the small, cheap ones work.

I’ve not installed these balcony kits, but I’d be surprised if they used microinverters..

Either way, there is no issue using the panels in the kit you linked to in the way described; they are separate panels with standard MC4 connectors. Just unplug the inverter and plug in the grid forming one.

If you look in the menu, I've linked the setup that doesn't include any mounting hardware for the panels, but it's exactly the stuff that's used in the balcony kits.

We've move some distance away from toggling your transfer switch over to the battery charger. Just rewire all the panels, or put in relays at all the DC connections, or...

Huh, for some reason I assumed the balcony kits would be… “dumber”.

Either way, I’ve installed many panels with exactly these little boxes clipped to the back of them, and there is nice clean DC power to pull directly off the panel if you like by just disconnecting the inverter

What I was saying is you completely disconnect the inverter from the panels. The panels become an island, with the positive and negative from the strings instead going through something like a basic DIN mount DC circuit breaker and into the input feed side of a battery charge controller.

I'd be interested to find out what sort of anti-islanding techniques they employ. Most inverters are relatively slow to detect grid failure, and if you pull the plug out quickly you might get a shock.

Maybe check the inverter specs or look for one explicitly listed as compliant with EU safety standards

The way power is shunted into the grid is very simple.The inverter you have senses the line voltage, and by keeping its voltage a tiny bit higher, "knows" that the power will flow out. nothing to sense and push against and it will idle likely doing an on and off test routine till if finds something to push against. Vs an off grid inverter that is stand alone, and self referential. There are hybrid off/on grid inverters, but they will quickly stop sending current, without a reference voltage, and drop back to battery/solar. As to legalities....,if there is no regulation adressing it, its legal, beurocracys hate that, but there it is. Its not like they wouldn't pin an (unlikely) accident on you either way, so..... and with no batteries, there is more risk in dropping the panel or another mechanical failure than anything electrical

> As to legalities....,if there is no regulation adressing it, its legal, beurocracys hate that, but there it is.

This is not law works. Either way there absolutely is regulation in minute detail about backfeeding power into your home, in any jurisdiction in EU or USA I’m aware of

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