Solar panels and type AC RCBO's what's the situation?

[ericmark]

I have not got the latest edition of BS 7671, since not retrospective it did not really matter, however my RCBO's all have this logo showing them as being type AC, but the boxes they came in clearly showed as being type B which I thought at the time was very good, didn't know you could get single width RCBO's as type B, clearly they were really curve B type AC but that was not what it said on the box.

I was not really worried, had I realised at the time I would have paid extra for type A, but type A are only good to 6 mA so unless one has a RDC rather pointless anyway.

However now having solar panels fitted, with a battery, and the UPS option, so what needs to change, will I need an earth rod for the UPS option, and will I need type A RCBO's? My copy of BS 7671 is 2008, so not really any help, I have no idea how the system disconnects with a power cut from the DNO supply, and if an earth rod is required, and since during a power cut it will all be supplied from the inverter if the RCBO's all need changing.

Would be nice to know before it is installed, so I can ensure it all complies.

 

[JohnD]

In the event of a power cut, the inverter shuts down immediately.

The Electricity act requires that generators must not feed into the network when dead. This protects engineers working on a fault.

Some recent inverters have an "off grid" socket so you can use it as emergency supply, such as lighting or to run a gas boiler. I guess this is your UPS? Otherwise the main supply would need to be isolated.

My inverter is connected to the CU into a spare way, so could have its own RCBO

 

[Murdochcat]

Is RCD protection actually required?

I’ve not got any on my PV system

 

[bernardgreen]

In the event of a power cut, the inverter shuts down immediately

How does the inverter decide that there has been a power cut if there are other solar powered inverters feeding into the network ?

Can the inverter tell the difference between power from a power station and power from a neighbours invertor. ?

 

[JohnW2]

Is RCD protection actually required? I’ve not got any on my PV system

RCD protection of what?

Anything in the installation which requires RCD protection obviously needs that protection regardless of where the electricity is coming from.

 

[JohnD]

How does the inverter decide that there has been a power cut if there are other solar powered inverters feeding into the network ?

Can the inverter tell the difference between power from a power station and power from a neighbours invertor. ?

In some circumstances, solar "islands" occur, where the solar power is a near match to load.

I hear it happens in some US towns in sunny areas, and is discovered when the sun goes down.

 

[JohnW2]

How does the inverter decide that there has been a power cut if there are other solar powered inverters feeding into the network ?

Interesting question - and I imagine that it would be next-to-impossible if the solar generation in the part of the network concerned was able to fully service all the loads in that part of the network.

If, in the absence of 'power from the grid' the solar generation alone cannot fully service the loads, voltage will presumably fall, quite possibly to the extent that all the inverters switch off.

Kind Regards, John

 

[ericmark]

How does the inverter decide that there has been a power cut if there are other solar powered inverters feeding into the network ?

Can the inverter tell the difference between power from a power station and power from a neighbours invertor. ?

I was told if the frequency or voltage goes out of limits it disconnects. But that is not the same as closing down.

In some circumstances, solar "islands" occur, where the solar power is a near match to load.

I hear it happens in some US towns in sunny areas, and is discovered when the sun goes down.

Surprised if in this country the voltage remains in the 207 to 254 volt range at 50 Hz for long if the supply fails, but over and under volt causes a shut down, however on the over voltage unlikely all solar systems disconnect at the same time so likely it will hold for some time before every panel disconnects.

In the event of a power cut, the inverter shuts down immediately.

The Electricity act requires that generators must not feed into the network when dead. This protects engineers working on a fault.

Some recent inverters have an "off grid" socket so you can use it as emergency supply, such as lighting or to run a gas boiler. I guess this is your UPS? Otherwise the main supply would need to be isolated.

This was what I thought also, but I am told it is now all automated, clearly it does need to disconnect from the network for safety reasons, and once running on battery there will be a limit as to what I can use, but not sure exactly how this works, hence trying to get some more info before it is fitted.

RCD protection of what?

Anything in the installation which requires RCD protection obviously needs that protection regardless of where the electricity is coming from.

Also my thoughts, so in the event of a power failure I will have no earth, all will be bonded of course, but without the PEN there will be no reference point, also if the PEN is disconnected one there needs to be some to keep the bonding linked to earth, and of course the supply interruption could be due to loss of PEN.

My wife said yes, the scaffolding has gone up, but I as yet have no idea how the system will work. The UPS part is costing an extra £500, which is worth it to ensure freezers don't fail, also my central heating will still work, but looking at three independent circuits, not even in the same abode although they are in same property.

I was worried that if I export without a smart meter I will be charged for what I export, I am assured this is not the case, but spent that much time asking about that, forgot to ask how the safety systems work.

But main point is if it needs an earth rod, then I want to know before it goes in, so I can ensure it is fitted, same goes for type AC RCBO's and any loss of PEN protection. I have a SPD but it is hardly going to protect against loss of PEN.

 

[Murdochcat]

RCD protection of what?

Anything in the installation which requires RCD protection obviously needs that protection regardless of where the electricity is coming from.

The cable

 

[Murdochcat]

In the event of a power cut here, our inverter shuts down after a few seconds

This is why pv systems shouldn’t feed into a circuit on a shared RCD

 

[flameport]

However now having solar panels fitted, with a battery, and the UPS option, so what needs to change

Most inverters have DC fault protection built in, so you don't need an external Type B.

Inverters in general should not be supplied from RCD protected circuits, as the vast majority of RCDs / RCBOs available for consumer units are not bidirectional, and therefore are not suitable for solar or battery installations.

 

[flameport]

Can the inverter tell the difference between power from a power station and power from a neighbours invertor. ?

Yes it can.
Grid connected inverters do not output a sinewave.

 

[bernardgreen]

Grid connected inverters do not output a sinewave.

What waveform do they produce ? If the waveform of the invertor does not match the waveform of the network then the power transfer will not be smooth.

 

[JohnD]

...the vast majority of RCDs / RCBOs available for consumer units are not bidirectional...

If the RCD is comparing the current passing through two poles, how does it "know" which way the electrons in an AC circuit are "flowing"

 

[flameport]

What waveform do they produce ?

It depends on the inverter, output current and various other factors, but it's typically part or all of a sinewave but with parts missing or modified such as the top of the wave flattened off.

then the power transfer will not be smooth.

It often isn't, harmonics and other distortions are commonplace. PWM drivers are often used to vary the output power and although there is some filtering on the output, it's inevitable that the output will not be a perfect sinewave. It's also inevitable that the grid supply it's connected to won't be a perfect sinewave either.