Posted by: @batpred

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i would have thought they would only put out ac current after they sense one that matches g99. 
When the grid goes off, if there are two on the same phase, i cannot see how they know it is off unless the other inverter (be it battery or solar fed) happens to go off…
It would be useful to examine the test condition and the result for one of those “reputable manufacturers“…

They've been extensively tested by folks like the German and Swiss test labs, people who don't mess about or take backhanders.

They will not put out AC current if they don't detect a suitable grid voltage and waveform. If they do detect one then they follow it and the try and perturb it a microscopic amount now and then.

If you are backfeeding with only another grid following inverter then a) the whole waveform will collapse in a mess anyway in moments, and b) the disturbance will ensure it happens and is seen, whereas poking the grid won't.

Now if you build yourself a suicide cable to a generator and have a strong enough grid forming generator they will be fooled. This is actually used (without the suicide cable) by Sunsynk/Deye and later Tesla kit to back microinverters when the grid proper is down. In those cases the inverter grid forms on the microinverter port and the microinverter power goes into the batteries and they are either managed by feeding them 52Hz when you want to shut them up or just disconnecting them like a generator when the battery can no longer reliably take the power they are supplying.

It’s been a while since we updated this thread, and quite a lot has happened since we first started discussing whether genuine plug-in solar would ever be allowed in the UK. Most importantly, we now appear to have reached the point where this stops being a hypothetical discussion.

The new rules are due to come into force this Thursday, 27 August 2026, allowing compliant plug-in solar systems to connect to a normal UK socket. When we started talking about this, I was fairly sceptical that Britain would adopt anything approaching the simplicity of the German balcony-solar model, so this is a pretty significant change.

The basic concept is exactly what we’ve been discussing throughout this thread: solar panels connected to a microinverter, supplied as a compliant product with a factory-fitted UK plug, which can then feed electricity into the household circuit through a normal socket. The interim specification limits AC output to 800VA and 3.5A, although up to 2,000W of PV modules can be connected on the DC side.

There has, however, been an important change to what was originally being proposed. DESNZ had developed its framework around the possibility of allowing one plug-in solar system per final circuit. In a typical house that could potentially have meant two or more systems operating on different circuits. That raised some fairly obvious questions because the safety testing commissioned by DESNZ had assessed individual plug-in systems, rather than multiple systems operating simultaneously within the same domestic installation. The IET was particularly unhappy about this and raised concerns around RCD behaviour, loss of mains protection and the consequences of having several inverter-based devices feeding an installation at the same time.

That particular argument now appears to have been settled. On 11 August 2026, Ofgem approved the amendment to G98 and decided that plug-in microgeneration will be limited to one system per customer installation, which for normal domestic purposes means (at the way I understand it) one system per household. So the position going into 27 August is much simpler than some of the earlier proposals: one compliant plug-in solar system per home, with a maximum AC output of 800VA.

I actually think that’s a sensible place to start. I’m strongly in favour of plug-in solar because I don’t think someone should necessarily need scaffolding, a conventional solar installation and several thousand pounds simply to generate a few hundred watts of electricity during the day. An 800W system isn’t going to make anyone energy independent, but that rather misses the point IMO. A couple of panels producing several hundred watts through the middle of the day could cover a useful proportion of the background consumption from fridges, routers, computers, pumps and all the other things consuming electricity around the house. More importantly, it opens solar up to people who previously couldn’t realistically participate at all.

Where I remain uneasy is the assumption that making the product plug-and-play automatically makes the installation it is being plugged into suitable. The IET has argued that the existing electrical installation should be assessed by a competent electrician before one of these systems is connected. The issue isn’t necessarily whether a properly engineered 800W plug-in solar product can be safe, because clearly it can. The bigger unknown is what that product gets plugged into. Britain has an enormous mixture of domestic electrical installations, ranging from relatively modern systems with contemporary protection through to homes with old consumer units, ageing wiring and protection arrangements that the homeowner probably knows very little about.

The government has stopped short of requiring a mandatory electrical inspection before one of these systems is connected, instead relying heavily on the product specification, instructions and consumer guidance. There is a contradiction in that for me. We’ve decided that allowing several plug-in solar systems in one house introduces enough uncertainty that limiting everyone to one is the somehow prudent approach, yet that one system can potentially be plugged into an electrical installation that hasn’t been professionally inspected for many years. I suspect this is going to remain one of the more contentious parts of the whole scheme once these products start appearing in significant numbers.

There are considerably more safeguards in the framework than there appeared to be when we first started discussing this, though. The complete plug-in solar product has to comply with the relevant UK specification, including requirements around anti-islanding, contact protection and the plug arrangement. Extension leads, multi-way adaptors and travel adaptors aren’t permitted, and products need to carry the appropriate instructions and warnings, including the one-system-per-household restriction and the requirements around DNO notification. In other words, 27 August does not suddenly mean that somebody can buy any random microinverter online or at Aldi with your veg, stick a 13A plug on the end and declare that they have a legal UK plug-in solar system.

So my position remains very much in favour of this. Make plug-in solar inexpensive, accessible and genuinely simple, but make the safety requirements equally straightforward and impossible to misunderstand. We’re about to find out whether Britain can actually achieve that balance because.

My thought is simple.  Bring it on and bring on plug in batteries asap as well.  

I think that the g98 position may mean that you can still have 1 plug in per circuit, but it will require a G99 application.  Happy to be corrected.

Safety concerns are well overstated, even the IET accepts that the RCD 'issues' do not justify a mass updating of older solar installations and the probability of the RCD blowing in the 30ms or so it takes for the reverse power to be cut off must be tiny given that the coil is designed to be energised for up to 30ms anyway as thats the 'normal' cut out time (note that this super fast cut off is a requirement because its plug in and does not apply to permanently wired which can take seconds to disconnect).  Nothing in life is risk free, we kill 3000 people per year on the roads but we tolerate it because of the upsides, I am happy to bet £10 that not a single person will die in the UK in the next 10 years because of a compliant plug in solar device.

I wouldn't like to predict rate of take up.  Flats with balconies are an obvious opportunity (it's not called Balkonkraftwerk in Germany for nothing) but anyone with a flat roof could well be interested.  I'm thinking of adding 3 panels, 1.5kWp on top of my existing installation using plug in (will need G99 I know and I want batteries as well, so will sadly have to wait).  Spare garden space, a car port etc all lend themselves to installations that simply wouldn't be economic done professionally but make a very sensible DiY project.

This is IMHO long overdue and finally brings solar to less well off people.  If Germany can do it why can't we?