In roof system (GSE?) and MCS -012 certification..I'm new to this and it is seems to be a minefield

[jimseng]

Hello. I am getting on with my self build house and was getting quotes for a 24 panel GSE in roof system when suddenly my supplier threw up the MCS 012 certification and the supply of solar panels approved for an installation. I was planning on doing the install myself, it doesn't seem that complicated, and I am only concentrating on the infrastructure for now. It makes sense to spend what funds I have on putting the solar on the roof at the build stage. Then this spanner has been thrown in the works. I have had a quote for JA solar and AIKO panels but I don't think I can install them as they don't meet the new requirements. So I joined this forum hoping someone can guide me through this. What are people's thoughts? For instance, does it make more sense to put a conventional roof on and not go with in roof? I don't want to because of the aesthetics but I need to look at all options given I don't have all the money in the world and I need to get building regs sign off. My goal is to cram as much solar on the roof as I can and I'm not  interested in exporting to the grid, only running the house, if that is an important detail. 

?

[JohnMo]

MCS isn't applicable if you do it yourself.

 

But only Octopus will pay for export, after going through a few hoops and paying then £250.

 

30 minutes ago, jimseng said:

does it make more sense to put a conventional roof on and not go with in roof?

No - the panels are cheaper than tiles or slates. If you are paying more than £70 per panel get other quotes, look at City Plumbing.

 

Cram lots on roof, but to make use of it you need a battery really, otherwise most will be exported for free. In summer you will struggle to use 3kWp let alone loads more.

[jimseng]

 

Quote

MCS isn't applicable if you do it yourself.

Really? So I can get building regs sign off with GSE and a panel of my choice? I haven't seen that written anywhere but I am floundering around trying to get accurate information. If that is the case then I guess it makes it much easier. I certainly intend as much battery as I can afford. I was planning on not exporting to the grid but I think that means G99 application for a decent inverter, but I guess that is for another thread.

Edited Monday at 12:20 by jimseng

[Nick Laslett]

GSE trays comply with MCS 012 certification. 
 

I used Midsummer for my supply. 
 

Trina panels comply with MCS 012. 
 

My electrician is MCS qualified, so he signed off the install. 

[JohnMo]

27 minutes ago, jimseng said:

 

Really? So I can get building regs sign off with GSE and a panel of my choice? I haven't seen that written anywhere but I am floundering around trying to get accurate information. If that is the case then I guess it makes it much easier. I certainly intend as much battery as I can afford. I was planning on not exporting to the grid but I think that means G99 application for a decent inverter, but I guess that is for another thread.

Introspective of how installed you still need G98 up the 3.2kW allowable export and G99 above that. Regardless of any plans to export or not. G98 can be completed after install, G99 has to be done prior to install.

 

You need a decent grid tied inverter anyway. Something like a Sunsynk hybrid inverter of any size will allow you to export limit to 3.2kW which I think (?) makes ok for G98. Battery & inverter needs some thinking about, depends if you need full house power backup in event of a power outage. Hybrid inverter will give very limited output during a power cut, grid tied AC systems will give whole house backup during an outage.

[jimseng]

I think I am going to have to go for G99 as I can't see 3.6k being enough.

As for MCS 012 I'm still confused. My understanding is that GSE is MCS 012 compliant, many solar panels are MCS 012 compliant but NOT necessarily together, which is where I am at right now. But then if it is a DIY install MCS doesn't apply? Or does it?

[JohnMo]

You don't have to use GSE there are other systems.

 

If not an MCS install, MCS rules don't apply. 

[garrymartin]

5 minutes ago, jimseng said:

I can't see 3.6k being enough.

Are you single-phase or three-phase?

[jimseng]

I'm having an 18kva single phase supply. 

[Dillsue]

For G98 compliance the inverter must be factory limited to 3.68kw and manufacturer certified as such. If it can do more but you limit it to 3.68kw then it's not G98 compliant. It then needs a G99 application plus a G100 supplement to cover the set up of the export limitation.

 

My very limited experience of G99 is that it's straight forward and worth the effort to get consent for the max your local grid will support. Imagine export payments being £1 a unit and your neighbours had grabbed all the spare export capacity:)

[jimseng]

Quote

My very limited experience of G99 is that it's straight forward

That is exactly what I am thinking. 

Quote

You don't have to use GSE there are other systems

I have seen Solfit and made inquiries but what else can I consider?

[Dave Jones]

6 hours ago, JohnMo said:

 

 

But only Octopus will pay for export, after going through a few hoops and paying then £250.

 

 

 

interesting! Tell more.

 

We installed our own and I asked octopus about paying for export and they refused without a MCS cert.

[garrymartin]

9 minutes ago, Dave Jones said:

interesting! Tell more.

 

[sharpener]

21 hours ago, Dillsue said:

For G98 compliance the inverter must be factory limited to 3.68kw and manufacturer certified as such. If it can do more but you limit it to 3.68kw then it's not G98 compliant. It then needs a G99 application plus a G100 supplement to cover the set up of the export limitation.

 

My very limited experience of G99 is that it's straight forward and worth the effort to get consent for the max your local grid will support. Imagine export payments being £1 a unit and your neighbours had grabbed all the spare export capacity:)

 

If you have the roof space IMO definitely worth putting up more panels than the old default 3.68 kW limit. At 15p/unit from Octopus it is a sound economic proposition.

 

Need all I can get (for the new heat pump) so I had a further 3.24 kW installed under MCS, connected them to my battery system via a DC-DC converter, completed the G99 and G100 paperwork as a self-install and after a certain amount of fuss got approval from NG (formerly WPD) for unlimited exports. 

 

Because they are not connected at AC the new panels can't export directly, so no need to involve Good Energy who are my FIT provider, or Octopus either.

 

Also this means that I can use all 6.9 kW of PV for the house/EV/HP or export it all, using the one 4.4 kW hybrid inverter.

As @Dillsue says, best to reserve the capacity while you can. There are going to be limits imposed I am sure, as the Spanish are discovering with their lack of grid stability.

 

Edited Tuesday at 11:37 by sharpener

[Dillsue]

1 hour ago, sharpener said:

 got approval from NG (formerly WPD) for unlimited exports. 

 

Because they are not connected at AC the new panels can't export directly, so no need to involve Good Energy who are my FIT provider, or Octopus either.

Unlimited export?? Are you sure it's unlimited?

 

Why wouldn't you need to involve your FIT provider if you've increased your TIC?

[sharpener]

50 minutes ago, Dillsue said:

Unlimited export?? Are you sure it's unlimited?

 

Yes, after I put in the G99 application they completely removed the 3.7 kW battery inverter power limit and the 3.68kW export limit, and did not replace them with anything higher. (I am though limited to 80A export by their company fuse.)

 

In passing I am surprised @jimseng the OP is only getting an 80A/18kW supply. But I think I read somewhere that DNOs are now reverting to that from 100A which was the previous standard for new installations. I had to (self-) declare a limit of 80A as I did not want to upgrade the meter tails, which go through a thick stone wall. With batteries, an HP and an EV this required some fairly heroic assumptions about time diversity.

 

50 minutes ago, Dillsue said:

Why wouldn't you need to involve your FIT provider if you've increased your TIC?

 

I haven't. The FIT provider is only interested in the TIC connected to their 230V a.c. Total Generation Meter which is the basis of their payments.

 

The second array is connected to a DC-DC charge controller which converts the output to 48V d.c. which goes straight into the battery. Any subsequent transformation of this into AC for export is subject to any limits set by the DNO (i.e. none) but nothing to do with the FIT provider. Exports are measured by Octopus using their smart meter, as I have now opted out of the "deemed export" regime at 50% of what is measured by the TGM.

[jimseng]

Quote

In passing I am surprised @jimseng the OP is only getting an 80A/18kW supply. Shop

I live in the sticks and there will be two dwellings on the single run from the transformer. 1 is already connected and has a 6kw PV array so I don't know if the limit is due to the single cable running from the pole. I'm toying with the idea of limiting my inverter to g98 and having a second one dedicated to an off grid supply in the house. But I will see what a G99 application comes back with as that is the simplest solution. (if I can work out how to fill it in)

[Dillsue]

1 hour ago, sharpener said:

The FIT provider is only interested in the TIC connected to their 230V a.c. Total Generation Meter which is the basis of their payments.

 

The second array is connected to a DC-DC charge controller which converts the output to 48V d.c. which goes straight into the battery. Any subsequent transformation of this into AC for export is subject to any limits set by the DNO (i.e. none) but nothing to do with the FIT provider. 

?? You said you can export all your PV through one hybrid inverter so its AC output likely powers the house/grid and would have your FIT generation meter in the output?? Maybe you've got a FIT system inverter feeding the hybrid inverter via the FIT generation meter??? I seem to remember you've got a complex system??

[Dillsue]

1 hour ago, jimseng said:

I live in the sticks and there will be two dwellings on the single run from the transformer. 1 is already connected and has a 6kw PV array so I don't know if the limit is due to the single cable running from the pole. I'm toying with the idea of limiting my inverter to g98 and having a second one dedicated to an off grid supply in the house. But I will see what a G99 application comes back with as that is the simplest solution. (if I can work out how to fill it in)

If you go for a larger than 3.68kw system but export limit it, you can draw what you want but just not export it. Save peeing around with a second off grid system and the headaches that could come with 2 differing systems.

[jimseng]

Quote

If you go for a larger than 3.68kw system but export limit it

This is something I haven't been able to establish. I don't currently care about exporting to the grid, I am only interested in keeping all the energy for my self. Are you saying there is a way of installing a > 3.6kw inverter but limiting its export to < 3.6kw and only having to submit a G98 and not go through the hoops of G99? If so how is the limit achieved and verified by National grid?

[Dillsue]

22 minutes ago, jimseng said:

This is something I haven't been able to establish. I don't currently care about exporting to the grid, I am only interested in keeping all the energy for my self. Are you saying there is a way of installing a > 3.6kw inverter but limiting its export to < 3.6kw and only having to submit a G98 and not go through the hoops of G99? If so how is the limit achieved and verified by National grid?

 

On 14/07/2025 at 14:57, Dillsue said:

For G98 compliance the inverter must be factory limited to 3.68kw and manufacturer certified as such. If it can do more but you limit it to 3.68kw then it's not G98 compliant. It then needs a G99 application plus a G100 supplement to cover the set up of the export limitation.

G98 is factory limited to <3.68kw. Anything >3.68kw is G99. Anything >3.68kw that can be installer/user export adjusted is G99+G100

 

3.68kw is a fair bit of power and there's lots of G98 inverters that can have much more PV connected than 3.68. Solaredge allow 100% oversizing so their 3.68kw inverter can have 7.4kw of panels connected, and much more if the panels are facing differing directions. We have 8.5kw hooked up to one of our 3.68kw inverters but the panels are facing 3 differing compass points so the peak is reduced but generation is for much longer

Edited Tuesday at 18:07 by Dillsue

[JohnMo]

It called overclocking. Big array and smaller inverter. In full sun PV production is great, but 95% of the time we don't have that. So in 5% your panels produce loads but the inverter clips output to only output 3.6kW max. The rest of the time you are still limited to the inverter capacity of 3.6kW but you are more likely to actually produce that.

 

Not all inverter like overclocking. Quite a few hybrid inverters do.

[jimseng]

OK. So I am still G99 then. I'm hoping to cram 11kw on the roof and 3.6k isn't going to be enough for me.

[JohnMo]

48 minutes ago, jimseng said:

OK. So I am still G99 then. I'm hoping to cram 11kw on the roof and 3.6k isn't going to be enough for me.

Your missing the point. You will have a battery - all your available DC power can go direct to battery charging. The battery inverter is basically pegged at 3.6kW.  So can give 3.6kW to the house or the grid if battery is full. If you want a bigger inverter get a G99 etc.

 

With 11kW on the roof, you are going to be exporting or wasting a bucket loads of energy in the summer. You will.not know to put the energy after lunch most days

[-rick-]

2 hours ago, jimseng said:

OK. So I am still G99 then. I'm hoping to cram 11kw on the roof and 3.6k isn't going to be enough for me.

 

Unless you have (or can easily get) 3-phase. With that you are allowed 3.6kw per phase = 10.8kw.