Solar Panels Can I add solar panels to an existing system without losing my fits

Sparkyrob · Apr 12, 2023

Can I add solar panels to an existing system without jeopardising my feed in tariff?
I have a 3.8kw system but was thinking of adding a few more. Could I have 6kw of solar but limit the inverter to 3.8kw so it will help in the winter when I need it the most.
Or would I need a second meter to keep it separate?
Thanks

LeeH · Apr 13, 2023

There is no limit on the size of the actual array, but not sure of the implications of certification if you modify the existing installation.

But if you don’t tell them, I promise I won’t so who’s going to know?

Also have you done the maths for the ROI? It may not be worth it as you already know solar is a bit pants in the darker months and low sun.

littlespark · Apr 13, 2023

When I fill in my FIT meter reading with Scottish gas, I need to tick a box to say there’s been no changes to my equipment.

That’ll be their get out clause.

If it’s found by them that you haven’t declared, it’ll be looked at as a breach of contract and they’ll stop paying.

LeeH · Apr 13, 2023

littlespark said:
When I fill in my FIT meter reading with Scottish gas, I need to tick a box to say there’s been no changes to my equipment.

That’ll be their get out clause.

If it’s found by them that you haven’t declared, it’ll be looked at as a breach of contract and they’ll stop paying.

I'm with SSE for FITS, I tick no such box. Maybe a change is due for the OP if so.

I doubt the solar police will be knocking at his door, the ROI is the thing I would be worried about.

Max105 · Apr 14, 2023

See here:
https://www.ofgem.gov.uk/sites/defa...nt generating equipment_Decision_13122021.pdf

and here:
Oversizing and FIT Payments - https://forum.buildhub.org.uk/topic/28280-oversizing-and-fit-payments/

If they want to pro-rata FIT payments by size of panels only, that seems very unfair, but it's not made at all clear in the guidance.

Given that most decently specified systems installed these days will have more panel capacity than inverter capacity, quite rightly IMO to cater for all the months, probably 8-10 months out of 12 in the UK, where matched panels will come nowhere near the output capacity of the inverter, then I think it's only fair that an older system should be able to be upgraded in this way i.e. uprating panels, so long as the output capacity of the inverter is unchanged (and that the inverter can take it of course).

If you want to be totally in the clear, the guidance does imply that any material changes to the system need to be OK'd your FIT provider. It's not something I'd like to test without clearance, given that the possible penalty would be to forfeit all FIT payments, past and future. Having said that, is there anyone on here who has ever had their FIT installation audited?

I'd like to think that any fair minded and rational inspector would not object to any system or inflict a penalty where the inverter output power was unchanged, but since when did "fair and rational" apply to anything "official" or "Gov" related these days?

Sparkyrob · Apr 14, 2023

Max105 said:
See here:
https://www.ofgem.gov.uk/sites/defa...nt generating equipment_Decision_13122021.pdf

and here:
Oversizing and FIT Payments - https://forum.buildhub.org.uk/topic/28280-oversizing-and-fit-payments/

If they want to pro-rata FIT payments by size of panels only, that seems very unfair, but it's not made at all clear in the guidance.

Given that most decently specified systems installed these days will have more panel capacity than inverter capacity, quite rightly IMO to cater for all the months, probably 8-10 months out of 12 in the UK, where matched panels will come nowhere near the output capacity of the inverter, then I think it's only fair that an older system should be able to be upgraded in this way i.e. uprating panels, so long as the output capacity of the inverter is unchanged (and that the inverter can take it of course).

If you want to be totally in the clear, the guidance does imply that any material changes to the system need to be OK'd your FIT provider. It's not something I'd like to test without clearance, given that the possible penalty would be to forfeit all FIT payments, past and future. Having said that, is there anyone on here who has ever had their FIT installation audited?

I'd like to think that any fair minded and rational inspector would not object to any system or inflict a penalty where the inverter output power was unchanged, but since when did "fair and rational" apply to anything "official" or "Gov" related these days?

Thanks for the link. I agree that the ofgem guidance is out of date regarding upgrading old systems as I’d like to put a bigger solar system on same size inverter so I can fill the battery up quicker and will help in the spring and Autumn. Make sense to use the inverter as the max capacity and not the system capacity.

adamneve · Apr 14, 2023

Hi All

I am a great believer in keeping things simple.
Simple being why didnt Ofgem recomend that as long as the generation limit of 3.68kw (G83) was not exceeded then you can have as many panels as you can afford.
After all is the general ideology being to generate carbon neutral energy?

People are investing their hard earned cash and these nitwits cant make it simple.

I have an existing FIT system with 3.84kw shown as 'declared net capacity' on the mcs certificate.

Is 'declared net capacity' = total installed capacity (TIC) as mentioned in the Ofgem cryptic message ?

I have 16x240w panels and by maths deduced this as the 'declared net capacity' but the fronius inverter is indeed limited to a maximum power output of 3.68kw.

This in itself is the limit where by you have to get permission from the DNO to generate more than 3.68kw (G83) so theres already a brake in place to stop over generating.

This is where we need clear and precise guidance.

Most generators want to add or uprade their solar panels while retaining the limit of 3.68kw

As Max105 asked earlier it would be good to know if anyone has been audited or indeed had their FIT payment TERMINATED for whatever reason.

Maybe a separate thread on this subject?

Max105 · Apr 15, 2023

adamneve said:
.......why didnt Ofgem recomend that as long as the generation limit of 3.68kw (G83) was not exceeded then you can have as many panels as you can afford. After all is the general ideology being to generate carbon neutral energy?
I have an existing FIT system with 3.84kw shown as 'declared net capacity' on the mcs certificate.
Is 'declared net capacity' = total installed capacity (TIC) as mentioned in the Ofgem cryptic message ?
I have 16x240w panels and by maths deduced this as the 'declared net capacity' but the fronius inverter is indeed limited to a maximum power output of 3.68kw.
This in itself is the limit where by you have to get permission from the DNO to generate more than 3.68kw (G83) so theres already a brake in place to stop over generating.
This is where we need clear and precise guidance.

I could not agree more. Nobody is trying to do OFGEM down. I can't see what the issue is and why they cannot be more clear on the matter. I have 285W panels x42 = 11,970W, and two SamilPower 6kW inverters, nominal input 6kW, max output 5,750W and on my MCS cert. the Declared Net Capacity is 11.50 kW i.e. the limit set by the inverter output power. As far as I can see the original intention is simply not to exceed the 11.50kW limit but within that I would assume improving the system efficiency is perfectly acceptable and indeed to be encouraged. If I want to add more panels (or in my case replace with better spec panels) to improve the generation efficiency especially in the winter months, then surely that's beneficial to the power network. Basically the grid gets potentially more dirt cheap generation from me and I am never exceeding my "Declared Net Capacity" as specified when the installation was declared for FIT payments. As I mentioned, this seems normal accepted practice now anyway i.e. say 5kW of panels into 3.68kW inverter, and most newer inverters are designed with higher acceptable string voltages for exactly that reason.

Why OFGEM would want to penalise/prosecute a small scale producer for simply improving the efficiency of their system while staying within the FIT agreement power output would be totally beyond me, and I think they could easily clarify this. However, it would not surprise me if the pen-pushers who set these rules don't actually have the faintest idea about what we are proposing here, because they had the perfect chance to make it crystal clear in the PDF I linked, and yet they clearly did not and chose to leave it as a grey area. I wonder if this was intentional "buck passing" on the part of the writer. Nobody in authority seems to be able to take responsibility these days for fear of some sort of repercussion.

I'd certainly like to upgrade at least some of my panels to improve winter output and in fact after 10 years, my system seems to have dropped in efficiency anyway, so I never see anywhere near my 11.50kW of output even in peak summer and never really have done. I also lose about 3% anyway due to long cable from array, so more/better panels would compensate for this also to some degree, perhaps by also installing more modern inverters and all without exceeding my 11.50kW net output at the grid insertion point.

I don't think this needs another thread. I think the OP title says it all. Does anyone with perhaps close links to OFGEM have a definitive answer? Maybe with luck someone "in the know" at OFGEM might get to view this thread?

Sparkyrob · Apr 15, 2023

Max105 said:
I could not agree more. Nobody is trying to do OFGEM down. I can't see what the issue is and why they cannot be more clear on the matter. I have 285W panels x42 = 11,970W, and two SamilPower 6kW inverters, nominal input 6kW, max output 5,750W and on my MCS cert. the Declared Net Capacity is 11.50 kW i.e. the limit set by the inverter output power. As far as I can see the original intention is simply not to exceed the 11.50kW limit but within that I would assume improving the system efficiency is perfectly acceptable and indeed to be encouraged. If I want to add more panels (or in my case replace with better spec panels) to improve the generation efficiency especially in the winter months, then surely that's beneficial to the power network. Basically the grid gets potentially more dirt cheap generation from me and I am never exceeding my "Declared Net Capacity" as specified when the installation was declared for FIT payments. As I mentioned, this seems normal accepted practice now anyway i.e. say 5kW of panels into 3.68kW inverter, and most newer inverters are designed with higher acceptable string voltages for exactly that reason.

Why OFGEM would want to penalise/prosecute a small scale producer for simply improving the efficiency of their system while staying within the FIT agreement power output would be totally beyond me, and I think they could easily clarify this. However, it would not surprise me if the pen-pushers who set these rules don't actually have the faintest idea about what we are proposing here, because they had the perfect chance to make it crystal clear in the PDF I linked, and yet they clearly did not and chose to leave it as a grey area. I wonder if this was intentional "buck passing" on the part of the writer. Nobody in authority seems to be able to take responsibility these days for fear of some sort of repercussion.

I'd certainly like to upgrade at least some of my panels to improve winter output and in fact after 10 years, my system seems to have dropped in efficiency anyway, so I never see anywhere near my 11.50kW of output even in peak summer and never really have done. I also lose about 3% anyway due to long cable from array, so more/better panels would compensate for this also to some degree, perhaps by also installing more modern inverters and all without exceeding my 11.50kW net output at the grid insertion point.

I don't think this needs another thread. I think the OP title says it all. Does anyone with perhaps close links to OFGEM have a definitive answer? Maybe with luck someone "in the know" at OFGEM might get to view this thread?

With a lot of systems coming up to 10 years old that is a 10%decrease in output(1% loss per year) I think a lot of people would love to upgrade their systems. I have space for 6 kw and my 3.68kw system can barely do 3kw on a sunny day. Nobody with a good fits tariff is going to give it up for a modern efficient system.
If I do upgrade without telling ofgem then surely it would flare up an inspection because my generation meter will be higher than most people in the country with a 3.68kw domestic system. Or would it????
Now that is the million dollar question.

Max105 · Sep 6, 2023

Sparkyrob said:
I have space for 6 kw and my 3.68kw system can barely do 3kw on a sunny day. Nobody with a good fits tariff is going to give it up for a modern efficient system. If I do upgrade without telling ofgem then surely it would flare up an inspection because my generation meter will be higher than most people in the country with a 3.68kw domestic system. Or would it???? Now that is the million dollar question.

OK, sorry for delay but I've been meaning to refresh this post for a couple of months now. Just to update, after quite an uphill struggle getting through to the right people, I have now had quite a bit of correspondence with both my FIT Licensee (payment provider) and also direct with OFGEM. They are totally clear cut on this issue. Basically they are adamant that TIC ALWAYS means the combined total output power of the panels, and the inverter sizing has nothing to do with it at all. They are also totally clear (and this is laid out in the current OFGEM guidance on this issue) that ANY addition to the panel capacity has to be reported to the FIT Licensee and, assuming they approve the extension (and absurdly they say they will not "pre-approve" the extension, so you have to do it, submit it and hope for the best) then your FIT payments from that point will be "pro-rata", so if you take panels up to 6kW, even though your inverted is 3.68kW, they will pro-rata your actual FIT generation figures by that ratio i.e. you will get 3.68/6.00 of whatever figure you generate. So clearly in this instance it only makes sense to make sure the inverter is upgraded to the panel capacity to extract maximum FIT payment.

Of course this only applies to anyone who has a current FIT agreement. For anyone on SEG then the more you export the more you get paid, end of story as far as I know.

So sadly that's the official word on it for anyone wanting to upgrade their FIT-claiming PV array. So no, adding panels to an already installed FIT system so that extra capacity goes through the original generation meter is probably not worth it. You might as well attach your new panels to a separate inverter and either make sure all the extra cannot reach the grid by setting a hardware export limit or get an uplift to the DNO authorisation to allow higher export and claim SEG. How that works claiming SEG alongside FIT I'm not sure. My guess is all the export would need to be via SEG (from smart meter reading) and the generation meter readings from the FIT system would be claimed separately as the FIT generation element of the FIT agreement in the same way as previously. You would need to work out if the combined SEG export payments would be likely to be a better deal than the FIT "deemed export" part of your FIT. And yes, apparently an sudden rise in the generation figures from a FIT system can in theory trigger an inspection. Whether it ever has done, who knows, but I for one would not take the risk as the FIT is too valuable to lose. I've still got over 10 years to run on mine and it's been a game changer for my energy bills.

So just to summarise, in "OFGEM World", TIC is always the combined total power output of the panels (which FIT payments are based on), and Declared Net Capacity is the power output at point of grid injection i.e. maximum inverter output less any other losses (long cables etc). So of course it's the Declared Net Capacity that needs clearing in the DNO authorisation. DNO could not care less what the TIC is.

Hope it helps.