Who from the IET is working with the government to allow <800W inverters to be 'plugged in'?

In respect of BSI committee work (BS 7671 is developed by a committee jointly managed by the IET and BSI, but that follows the BSI rules for developing standards) specific discussions in committees cannot be shared. Similarly, content of standards and draft standards can only be discussed when they are published, or made available as drafts for public comment.

Would those rules prevent someone confirming whether a committee (or indeed which sub committee) had been asked to consider a particular request or requirement?

The comments on RCD operation seem somewhat unclear to me. Mark started off taking about a certain type of RCD that the Germans had the foresight to drop many years ago (which I take to be AC types) - but the article says "But some older RCDs were never designed for electricity flowing back into the circuit" - but bi-directionality is a completely different feature - and not one universally found even in the latest RCDs. I suppose we should add in single pole switching RCDs (mostly RCBOs) where the local generation isn't separated from Earth when the RCD trips, so the shock hazard persists until inverter shutdown - again a problem that isn't mitigated by ensuring your installation is up to current standards.

   - Andy.

But it won't have one.

What it will do is shut off immediately if the mains supply is disconnected. Which means that a non-bidirectional RCD won't burn out.

The whole bidirectional RCD thing is trying to solve a problem that in practice doesn't actually exist.

the balcony system will need one in its output.

But without a N-PE link at the balcony system (which would be prohibited for parallel operation with the mains) - an RCD at that end would never "see" the imbalance - so never trip.

   - Andy.

Simon Barker said:

The whole bidirectional RCD thing is trying to solve a problem that in practice doesn't actually exist.

AJJewsbury said:

But without a N-PE link at the balcony system (which would be prohibited for parallel operation with the mains) - an RCD at that end would never "see" the imbalance - so never trip.

What about island mode arrangements, where the inverter is self-commutating and is re-energized once the grid has been disconnected by the island mode isolator (now termed switching device for islanding, SDFI) and a system referencing connection made by the system referencing switch (now called SRCSD or system referencing conductor switching device)? 

At present, there isn't a designated standard for the products, so we can't really develop a 'use case' in BS 7671 with any additional provisions that may be necessary.

I guess JPEL/64 might be in a good position to anticipate likely problems and so feed into a suitable BS for such systems? (i.e. look at the problem the other way around).

One thought - the issue of several inverters fooling each other into thinking the mains is still present might be addresses by the inverters monitoring they output current? In the case of 4-inverters plugged into a 4-way extension lead which is then unplugged from the wall the output currents must surely drop to practically zero - so the inverters could use that as an additional signal that something was amiss and shutdown (perhaps until voltage had disappeared and then reappeared). In other situation where some loads might still be connected on the inverter side of the break, the output currents wouldn't drop to zero but in almost all cases would alter from what would normally be expected - so possibly still detectable by the same means?

The case of RCDs being potentially compromised by new types of "appliances" isn't new of course - we've had that a few times over with AC vs A vs F vs B vs B-EV types - yet BS 7671 hasn't seeked to prohibit such devices - it's merely updated the regs for new work to better handle the situation. I guess we'll end up in a similar situation with this one.

   - Andy.

What about island mode arrangements

I don't think anyone's suggesting an 800W plug-in balcony system should be capable of island operation (at least not when feeding back into the main "plug" - it would need upstream isolation from the grid - which would defat the easy plug & play aspect).

   - Andy.

AJJewsbury said:

I don't think anyone's suggesting an 800W plug-in balcony system should be capable of island operation (at least not when feeding back into the main "plug" - it would need upstream isolation from the grid - which would defat the easy plug & play aspect).

If we are keeping this purely to even if there are no other inverters, and we are looking at the plug-in solar debate, the power to the final circuit might be disconnected by the operation of the RCD because of a faulty appliance on that circuit ... mains loss protection is not instantaneous, as in 'zero time'.

G98/G99 has time delays for under-voltage and under-frequency, that are at least 500 ms (longer ... nearly twice as long ... as the disconnection time of the RCD). RoCoF doesn't have a time delay, but would still need some time to detect the phenomenon (somewhere between 100 and 500 ms).


So, I believe it still leaves the unidirectional vs bidirectional to be considered; I'd be happy for testing to demonstrate to me it's not an issue.

I accept that, if the RCD disconnects the neutral, the shock risk isn't increased as the disconnection time of the RCD isn't increased.

BUT

Many RCBOs are single-pole with unswitched neutral, so the presence of plug-in PV has effectively increased the RCBO disconnection time from 40 ms to at least 140 ms.

So ... split-load boards may well be safer for plug-in PV than single-pole RCBO boards !

Below from G98 Issue 2 2025:

AJJewsbury said:

In the case of 4-inverters plugged into a 4-way extension lead which is then unplugged from the wall the output currents must surely drop to practically zero

Surely, the two without battery storage will be charging the batteries of the two that have battery storage.. (now that such things exist) .

The joys of globalisation. Man the barricades, the heathens with their two pin flat bladed plugs are coming.  (just saying)

AJJewsbury said:

One thought - the issue of several inverters fooling each other into thinking the mains is still present might be addresses by the inverters monitoring they output current?

I think that Mike has touched on that in another thread.

However, the idea of plugging in 4 systems is just fanciful. Where would you put them?

In Portsmouth, you would struggle to find many houses that can accommodate even one of them.

This surely  is the point - they are not aimed at the folk who have a large semi-detached with roof area and driveway - they can probably get a full size hard wired system, and have the ability to afford it. They are aimed at those renting a mid terrace with a flat roof on the bit at the back that used to be a coal-shed and outside loo, and is now an annex to an inadequate  kitchen,  So there will be a few square metres of panel at best, and perhaps some pretty ropy installation mechanics done by family and friends, or maybe some dodgy Dave and his  mate at the pub who also works as a builder's labourer. But that's fine, because its a sector of society that will otherwise never get reached by the current formal channels, and needs to be somehow, anyhow. 
Having lots of the thing plugged into the same house, or into lots of flats in the same block or many houses on the same phase (every third house) in a street, the mutual support and self power problem is the same, and it is solved.

Basically they all free-run slow, and correct against the grid. If there is no grid, then the group will slow down as they time off each other, and within a few cycles drop off due to an out of frequency fault. 

Actually one might take the experimental argument that if 960W (800 W plus max tolerance) is demonstrably OK, as per continental in practice experience,  on a 16A radial in 1,5mm2,  then maybe rather more power is OK on a 16 or 20A radial wired in 2.5mm2, and more still on a 32A ring final  or socket on a 32A 4mm2 radial or larger cooker supply.

About the only thing that could get sketchy with UK wiring practice would be tapping into the common 1mm2 (6A) lighting circuit, and with LED lights, even that is very lightly loaded nowadays , but a lot of older houses of a certain era still have no or only partial lighting CPC. As far as I know, most of the continent does not separate lights and power in that way, preferring one radial for lights and power in each  zone of the building. This lends itself in 3 phase areas to a couple of 16A radials per phase on a 32A supply.

Mike

mapj1 said:

So there will be a few square metres of panel at best

The system on special offer at Lidl is now sold out, but the two panels are almost exactly 2 m² each.

Interestingly, whilst the Quick Start Guide has the system plugged in on the Continent, it is hard-wired in UK (page 07).

mapj1 said:

So there will be a few square metres of panel at best

The system on special offer at Lidl is now sold out, but the two panels are almost exactly 2 m² each.

Interestingly, whilst the Quick Start Guide has the system plugged in on the Continent, it is hard-wired in UK (page 07).

The description on that webpage of the registration is also instructive, I cannot imagine an English  equivalent of Sie müssen aber, wie auch Solarspeicherbatterien, im Markenstammdatenregister der Bundesnetzagentur angemeldet werden.

You shall however, and also with Solar Storage Batteries,   in the Official Data Register of the Federal Network Operator be registered... 

Apparently registration and de-registration is a simple Internet operation,  the German rules do not apply to the whole EU, specifically note that users in the Czech republic may not export to their public grid at all see configuration instructions for how to do that.
Aldi may be leading, but the German technical  approach is clearly not the only one.

Mind you, I bet these will turn up in all sorts of places and not all will be registered.

regards

Mike