MSE guide: plug-in solar panels

prowla

https://forums.moneysavingexpert.com/discussion/comment/82116872#Comment_82116872

That document says "Currently, only one plug-in solar panel system up to 800 W is permitted per household.", which appears to be correct, since the Final interim product specification states "NOTE: While this specification permits one device per final circuit, GB network connection requirements also apply. As of publication, current network requirements Engineering Recommendation G98 Issue 2 Amendment 1 2026 restrict this to one device per household, which applies unless and until that is amended.".

https://forums.moneysavingexpert.com/discussion/comment/82116479#Comment_82116479

Regarding the 890W option: the legislation states "a maximum rated alternating current output not exceeding 800 watts", so an 890W system would appear to exceed that.

ref. Plugs and Sockets etc. (Safety) Regulations 1994 and Electricity Safety, Quality and Continuity Regulations 2002 (Amendment) Regulations 2026 (SI 2026/848)

QrizB

Regarding the 890W option: the legislation states "a maximum rated alternating current output not exceeding 800 watts", so an 890W system would appear to exceed that.

That's an error in reading the regs and/or the specs.

The larger UKSOL kit has 890 watts of solar PV, but that's DC. They're connected to an 800 watt AC inverter.

This means they comply with the 800W AC limit in the Interim Product Specification, and the 2000W DC limit.

See section 4.1 here:

https://assets.publishing.service.gov.uk/media/6a60a03c47af652afa0c89f5/plug-in-solar-final-_interim-product-specification.pdf

Edit: if you're catching up with this thread, prowla keeps banging on about this until at least page 14.

prowla

https://forums.moneysavingexpert.com/discussion/comment/82118511#Comment_82118511

No error: they offering for sale an integrated UK-legal plug-in solar system as 890W

Product title:

UKSOL Pro Duo Plug In 890W Solar Kit Ground Mount

Product Description:

Expand your home generation with the UKSOL Pro Duo 890W Plug-In Solar Kit.
Perfect for patios, flat roofs, and garden spaces, this dual-panel kit uses advanced N-Type TOPCon technology with minimal light-induced degradation (LID) to provide reliable, long-term energy savings.

There is no such thing as an 890W UK-legal plug-in solar system.

If you expand it you then see the detail that its microinverter is indeed limited to 800W.

So, looking into that 890W; what doesn it really mean in this plugin system?

The current draw of a system is defined by the consumer of the current, which in this case is the inverter; therefore, even though oversizing the panels may make them capable of more, there will be no more current flowing than the inverter accepts and so they may never acttually produce that extra power; this is descrbed at https://solarenergyconcepts.co.uk/post/connecting-solar-panels/#add-to-the-existing-string-using-the-same-configuration-when-possible , which states "the inverter only draws the current it needs".

We see this in our general house usage, where the grid is capable of supplying typically 60 Amps to a house, which equates to approx 15kW, but my current (haha!) use is 365W; in other words the capacity of the generation system is an irrelevance.

Now, it could well be that the extra 90W covers any loss due to the DC-AC conversion process so it can genuinely output the maximum permitted 800W, but that still doesn't make it anything more than an 800W system.

Of course, savvy people will know that and also understand that over-spec'ing the panels (to be capable of up to 2kW) will help extend the yield to cover less sunny days, but that doesn't make such a system one diddleysquat more than 800W.

In other words, the capacity of any of the components is an irrelevance with regards to the maximum permitted output of 800W.

So why advertise an integrated UK-legal plug-in solar system as 890W when there is no such thing?

QrizB

No error: they offering for sale an integrated UK-legal plug-in solar system as 890W

If you're not misreading, you're misunderstanding what you've read.

What they're selling is an 800W inverter with 890W of solar panels. That's entirely legal.

they may never acttually produce that extra power;

Correct. The system will never supply more than 800 watts ofAC to the house.

In other words, the capacity of any of the components is an irrelevance with regards to the maximum permitted output of 800

The bit I've put in italics is not correct. The capacity of the PV panels is important, for reasons you yourself have identified:

Of course, savvy people will know that and also understand that over-spec'ing the panels (to be capable of up to 2kW) will help extend the yield to cover less sunny days,

So you clearly understand why you'd want 890 watts of panel with an 800 watt plug-in system. Your misunderstanding is simply how it's being described on the website?

So why advertise an integrated UK-legal plug-in solar system as 890W when there is no such thing?

Because that's how solar PV is always advertised, using the nominal panel output.

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/82118638#Comment_82118638

As long as there isn't a significant cost difference*, anyone getting a 800W system, with room for larger/more panels, should really go for 1,000Wp to 1,200Wp of panels. But 890Wp sounds fine. That way, there is more chance of getting close to the 800W grid (AC) limit, and will of course generate a bit more, even in poorer weather.

Assuming bi-directional batts get approved in the near future (maybe before Spring next year), then 2kWp to 3kWp of PV should work fine, with an 800W AC house feed, so long as the batts can buffer the excess to minimise clipping of generation on best days.

*In fact, the larger system may hopefully be proportionately cheaper (per Wp) than the smaller, as only the panels will cost more, the rest of the kit may remain the same.

Edit - BTW I have 6.725kWp of PV going through a 3.68kW capped inverter. I may be wrong, but I think my system would be described as 6.725kW not 3.68kW. I also have a 2kWp system running through a 2.2kW inverter, and that too, would I believe, be described as 2kW not 2.2kW. But I really don't mind.

Further edit that may help. The issue here is the regulations which relates to the 800W inverter output. That could/can be compared to my DNO export permission which is based on the sum of my inverters at 5.9kW, not the sum of the panels at 8.725kWp. In fact, in a friendly chat with the DNO, they basically told me that they really don't care how much PV I have, it's the theoretical max AC output (the inverters) that they need to know.

QrizB

In practice, most of the cheaper "800 watt" systems will use two rooftop panels. And cheap rooftop panels are almost all 450 watts or larger these days (500+ watts is becoming commonplace). So we'll see lots of systems at the cheaper end of the scale which are overpanelled like this.

Octopus are suggesting they'll have systems with physically smaller panels available next year. I'm expecting those to work out more expensive, simply because (a) 200 watt panels are a bit niche, and are made in smaller quantities than the larger ones and (b) extra panels means extra cables and connectors and more aluminium for the frames and more mounting hardware. But for people who can't work with panels that are roughly 2m x 1.2m, they'll be an option.

prowla

https://forums.moneysavingexpert.com/discussion/comment/82118647#Comment_82118647

No; (as you kindly point out) I understand what the system componentry is and how the parts fit together.
I'm pointing out that the system states 890W and it is not an 890W system.

The overpanelling does not make it an 890W system.

If your kitchen kettle is rated at 1.5kW, the fact that it runs off a 13A plug which is capable of 3.12kW doesn't make the kettle a 3.12kW item.

prowla

https://forums.moneysavingexpert.com/discussion/comment/82118815#Comment_82118815

Yes, you do indeed confirm that the capability of the panels does not define the rating of the system.

My solar system's certificate states:

Max AC Power Output:
5.00
Nominal Storage Capacity:
5.76

jimi_man

https://forums.moneysavingexpert.com/discussion/comment/82118638#Comment_82118638

I would have thought that was obvious - for marketing purposes. As has been said, 800w is the maximum AC output so none of the systems can exceed that, but the bigger systems collect more and therefore output (on average) closer to the 800w limit consistently.

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/82118932#Comment_82118932

Sorry but no. The rating of the system is the kWp of the panels, as described, in this case 890Wp. The rating of the inverter output for regulation purposes is 800W.

My example, was to show to you that one of my PV systems has a power rating of 6.725kWp, but for regulatory purposes, is capped at 3.68kW. But it's a 6.725kWp system, and will generate far more per year than a 3.68kWp PV system would (in the same location/setup), even if all generation over 3.68kW was clipped.

The 890Wp system will generate more than a 800Wp system, even via a 800W AC inverter. In fact, I'd suggest that clipping will be so small/negligible that the ratio of generation between two such systems would be pretty much 890:800.