Plug-in solar / Balcony solar / DIY solar

[lovelyhead]

Plug in solar is only putting a few amps into the local circuit. The circuit breaker will be looking for many tens of amps to trip on a fault condition, which a short circuit will produce pretty much instantly whether solar plugged in or not. I think it's a red herring.

What happens if you plug in a tumble dryer to the same circuit as your plug in solar and then turn on the kettle?

Sparks minimum wage, about 350 an hour…


The problems are probably because of all the different possibilities of regulations houses will have been wired too and type of earth the house has is also a factor. I’d also imagine a lot comes to interpretation of the regs and peoples opinions. The latest Bi-RCBO might required for 32 amp charger, but not for a 3 amp solar system etc.

I’d imagine back feeding 3amps in at least some situations isn’t a problem at all, but I am well behind on the latest regulations and what’s important is you have a safe and stable installation that is signed off by a qualified electrician.

It seems to me that the only safe way to implement plug in solar is to have your house electrics tested before hand. As you say that would cost probably around the same amount of money as the plug in solar kit itself doubling the payback time. I find it hard to believe that you would just be able to go into Lidl and pick one up if you need to have had a safety check first but then again you can buy 5 electric fan heaters and plug them all into an extension cord and nobody stops you so who knows. Will you have to declare that you have plug in solar to your insurance company? Will landlords let you use them?

 

[Bluecube]

99.9% of the population have no idea what a bi-directional circuit breaker is. I have done research on the subject I don't know if the circuit I would be potentially planning to plug solar into has a bi-directional breaker. The RCD's in my consumer unit have no markings other than their amperage.

Mine do which is how I know they’re bidirectional. This is in a 26 year old house. I did have to look them up to check what they were though

 

[jigger]

What happens if you plug in a tumble dryer to the same circuit as your plug in solar and then turn on the kettle?


It seems to me that the only safe way to implement plug in solar is to have your house electrics tested before hand. As you say that would cost probably around the same amount of money as the plug in solar kit itself doubling the payback time. I find it hard to believe that you would just be able to go into Lidl and pick one up if you need to have had a safety check first but then again you can buy 5 electric fan heaters and plug them all into an extension cord and nobody stops you so who knows. Will you have to declare that you have plug in solar to your insurance company? Will landlords let you use them?

Yeah, it’s all going to come to individual case. I’d imagine a lot of properties don’t have an RCBO at all, so not a problem? You might have a main panel without a RCBO and sub panel fitted later with. I’d imagine you could also bypass the house panel entirely or possibly even install the required switch gear up stream on a ring main.

The only time directionality should matter is if you intend to also charge a battery from the grid with the system. But as you say, that same ring main could also have numerous electric heaters pulling significantly more power than a battery charger will.

I think the best advice would be to talk to a reputable electrician and get a quote for any work before buying anything.

 

[danlightbulb]

What happens if you plug in a tumble dryer to the same circuit as your plug in solar and then turn on the kettle?

It will pull a few amps from the grid at the same time as using some of the solar power. The amps from the grid will pass through the MCB/RCD as normal in the standard direction and be balanced across live and neutral as normal.

 

[Bluecube]

I think the best advice would be to talk to a reputable electrician and get a quote for any work before buying anything.

That’s the point being made - these things are supposed to be plug and play. Something that your average, can-barely-use-Windows person in the street can use without involving any electricians. I’m sure if our European friends manage with these systems then we will too.

 

[danlightbulb]

That’s the point being made - these things are supposed to be plug and play. Something that your average, can-barely-use-Windows person in the street can use without involving any electricians. I’m sure if our European friends manage with these systems then we will too.

It will most likely be fine for almost everyone.

If you have existing dodgy electrics then you might have an issue. Cross that bridge if you come to it is my view. This is a few hundred watts of power, not several kw. It will be fine in 99% of cases is my guess.

 

[lovelyhead]

Cross that bridge if you come to it is my view.

After the house fire?

 

[jigger]

That’s the point being made - these things are supposed to be plug and play. Something that your average, can-barely-use-Windows person in the street can use without involving any electricians. I’m sure if our European friends manage with these systems then we will too.

I wouldn’t use an IEC plug, but yeah fused spur fitted by a competent person.

 

[danlightbulb]

After the house fire?

Plug in solar won't cause a house fire on its own. If your electrics are bad the risk of this is already there.

Want to expand on how a few hundred watts of solar feed in can cause a fire if one hasn't already happened when running multiple kW loads of washing machines, kettles etc?

 

[lovelyhead]

Plug in solar won't cause a house fire on its own. If your electrics are bad the risk of this is already there.

Want to expand on how a few hundred watts of solar feed in can cause a fire if one hasn't already happened when running multiple kW loads of washing machines, kettles etc?

I'm not an electrician obviously but I have read that if a circuit is close to it's limit with appliances drawing power, plug in solar could push it past the limit in a way that the RCD would not detect causing things to overheat. Hopefully someone who knows what they are talking about will understand what I mean.

 

[danlightbulb]

I'm not an electrician obviously but I have read that if a circuit is close to it's limit with appliances drawing power, plug in solar could push it past the limit in a way that the RCD would not detect causing things to overheat. Hopefully someone who knows what they are talking about will understand what I mean.

I see.
Yes, if your circuit is dodgy somewhere and you increase the current in the circuit by a few amps, it could push it over the edge.
But the same thing can happen if someone plugs in an extra hairdryer or whatever.

Its not the solar that caused this, and nothing much to do with RCD either here.

Even with solar plug in, a large fault current to earth or a gap between live and neutral current will still trip the breakers/RCDs.

The solar issue is pretty niche and only to do with neutral earth faults really. In which case the issue wouldn't be a fire but nuisance tripping.

Fires are caused by poor connections which arc generating high heat (which also needs high current to produce) or running circuits over their capacity melting cables etc. A few amps of solar won't cause that on its own.

I could see a fire being blamed on solar though, even though the solar wasn't really the cause.


Imagine a 32A ring main circuit which trips the breaker at 50A after 5 minutes (breakers are current & time dependant devices, they trip faster the higher the current. Running 50A on a 32A breaker might not trip it at all).

Firstly running 50A on a ring main is not normal. You'd need all sorts plugged in at the same time, already way over typical use. Eg multiple electric fires or something.

But lets say you did have 50A being drawn on a ring main by the appliances and you added in 4 Amps of solar.

You'd still have 50A on the circuit, not 54 amps. Why? Because the appliances are still drawing 50A, its just now you have 4A of that from the solar and 46A coming from the grid. No change in total current on the circuit.

 

[jigger]

I'm not an electrician obviously but I have read that if a circuit is close to it's limit with appliances drawing power, plug in solar could push it past the limit in a way that the RCD would not detect causing things to overheat. Hopefully someone who knows what they are talking about will understand what I mean.

It would actually help to reduce the load.

 

[Armageus]

I'm not an electrician obviously but I have read that if a circuit is close to it's limit with appliances drawing power, plug in solar could push it past the limit in a way that the RCD would not detect causing things to overheat. Hopefully someone who knows what they are talking about will understand what I mean.

I'm also not an electrician but I don't see how.

If you plug in 800w of panels = that's at best case ~3.5 Amps, but then that's 3.5 Amps less you pull from the mains. There is no more current than there would be pulling it entirely from the mains - the only difference is where it comes from.

 

[Mercenary Keyboard Warrior]

I think you guys are misinterpreting the issue, at least my understanding of the issue from what I have seen sparks arguing about (and why many consider this plug in unsafe unless on a specific circuit)

The risk is that you can have current on a circuit that the RCD/RCBO cannot see.
So its not in effect as quick to react as if the whole current was flowing directly through it.
Plus your relying on the speed of the inverter to cut off and stop supplying current if the RCD/RCBO itself trips and the inverter cannot see grid.

The current itself isn't going to fry you if your fit and healthy but its probably going to be a more significant shock than you would get right now from a similar incident.
If your unhealthy then I don't know could potentially be life threatening.

 

[lovelyhead]

I think you guys are misinterpreting the issue, at least my understanding of the issue from what I have seen sparks arguing about (and why many consider this plug in unsafe unless on a specific circuit)

The risk is that you can have current on a circuit that the RCD/RCBO cannot see.
So its not in effect as quick to react as if the whole current was flowing directly through it.
Plus your relying on the speed of the inverter to cut off and stop supplying current if the RCD/RCBO itself trips and the inverter cannot see grid.

The current itself isn't going to fry you if your fit and healthy but its probably going to be a more significant shock than you would get right now from a similar incident.
If your unhealthy then I don't know could potentially be life threatening.

I have found the warning I read about here:

https://www.theiet.org/media/press-releases/press-releases-2026/press-releases-2026-january-march/24-march-2026-iet-urges-households-to-check-electrical-safety-before-using-plug-in-solar-products

• Risk of overload or back feed: Plug-in solar can create scenarios where parts of a circuit carry more current than intended, even if the circuit breaker appears to operate normally.

 

[Bluecube]

Clearly UK houses aren't going to be be able to handle these plug in systems. What's the difference between UK house wiring and European house wiring?

 

[Uther]

That’s the point being made - these things are supposed to be plug and play. Something that your average, can-barely-use-Windows person in the street can use without involving any electricians. I’m sure if our European friends manage with these systems then we will too.

Exactly. People will expect to just pop on to Amazon or down to Aldi, buy the kit, stick the plug in the socket, flick the switch and get 'free' solar power.
Paying an electrician £lol isn't what these kits are about is it?

 

[Armageus]

I have found the warning I read about here:

https://www.theiet.org/media/press-releases/press-releases-2026/press-releases-2026-january-march/24-march-2026-iet-urges-households-to-check-electrical-safety-before-using-plug-in-solar-products

• Risk of overload or back feed: Plug-in solar can create scenarios where parts of a circuit carry more current than intended, even if the circuit breaker appears to operate normally.

Which means what exactly?

Unless you can draw a diagram showing how you can get more amps on a circuit than you otherwise would, I don't see how its possible.

If devices are consuming the solar electric you aren't going to have any more current, and if devices aren't consuming it, then you aren't drawing from the mains anyway

 

[danlightbulb]

I can understand the edge case RCD risk.

Very limited set of circumstances where say 30mA of fault current (say you touch a faulty appliance when standing on carpet in your house - high impedance, therefore low current shock), would have normally tripped the RCD but now it doesn't because some of that is hidden from it by the solar.

Before RCDs we didn't have this protection at all. I guess a good way to describe it is we've gone from no RCDs (100% risk) to full RCDs (1% risk) and with plug in solar we might regress ever so slightly to 2% risk due to the edge cases. Obviously not real numbers just to illustrate the point.

I think that article is probably intentionally misleading - the risk of plug in solar causing direct overheating of cabling is not the concern at all.

The edge case RCD risk, yes I can understand that one.


Edit - just to add, a 'bidirectional' RCD doesn't resolve this issue either. That just means it works when the solar is pushing current back through to the grid. It doesn't change the risk of failure to trip due to sharing of fault current.

Edit 2- just to add as well to demonstrate how edge case this is - there are probably still many thousands of houses (maybe even hundreds of thousands) in the UK that don't have RCDs at all. My parents house still has fuses! This RCD issue on plug in solar makes absolutely no difference if you don't have RCDs in the first place.

 

[Journey]

Are half the people in here lobbyists for foreign energy generation companies?

800w of plug in solar across a circuit designed for much higher power draw is not going to impact safety in any meaningful way. Even the edge cases in the consumer unit RCD/RCBO are so slim that if you are worrying about your house burning down you should probably not own a toaster/oven/hairdryer/air fryer etc. And if you've got a wood burning stove you may as well just set your own house on fire right now!