Exanding PV and adding more storage

I currently have 4kW feeding a 5kW hybrid invertor and 8.2kWh. storage. I have had the PV a long time so its on FIT. With deemed export, thats a golden goose so I really do not wish to loose.

I am thinking of potentially expanding my PV capacity and storage capacity. I am finding it confusing about what can and cant be done.

I have 2 potential use cases:

1) Oversize PV for exisiting inverter
Just upgrade my existing system to say 6kW so that I get more power for longer each day and throughout the year.
Can I do that? The panels will be different to the 8 year old ones, is that a problem?

I think FIT is based on the inverter output not the PV panels, so if that doesnt change is this ok?

If I can produce more PV then the case for more storage is quite compelling. Maximise use in sunny periodds and have more capacity grid charged over the winter

2) Add new panels and inverter
Add new panels and a new inverter. I think thats just a new system thats total seperate to existing one. So the original stays on FIT and the new one is SEG. I would just need seperate meters? Is this correct? How do that work in practice?

I dont really need higher peak power output, but this solution would provide that. I would expect to pair this with a new battery, so all the complications of 'plant' management arise

Has anyone done anything like this so has experience of it?

We recently did something similar earlier this year.

Option 2 is the most viable option, but you will need to switch from deemed export for the 1st system, to SEG for all, but keep FIT on the 1st system.

If you add to the 1st system, the FIT payments will be worked out proportionately, so you would get paid 2/3rds of your total output from that system.

You will need to get DNO approval if going above 4kWp.

We have 4kWp PV on our west facing roof (installed in 2015) & 6kWp PV on our east facing roof (installed in 2021) + a 3kW inverter & 2x8.2kWh batteries.

At the moment, using all the PV output directly or to charge the batteries, but may apply for SEG, if we find we can't use more than 50% of what we generate.

Woodlands Thanks for the reply. I am sorry, I dont understand your first comment. "switch from deemed export for 1st, but keep FIT on first system". Are they not mutually exclusive? Do you mean switch from deemed to metered?

Does the proportionality for the additional panels for option 1 still apply if the inverter capacity doesnt change from 4kW? and as no more than 4kW can be produced does the DNO need to be informed. There is no way for more power to be sent into the grid if the inverter isnt changed

Its all very confusing, with the devil in the detail. Thats why I deferred these thoughts when I first considered them in the summer. If you, or anyone, knows of worked examples on the web please attach a link

Seye Does the proportionality for the additional panels for option 1 still apply if the inverter capacity doesnt change from 4kW? and as no more than 4kW can be produced does the DNO need to be informed. There is no way for more power to be sent into the grid if the inverter isnt changed

For the first part, yes the proportionality would apply, as existing FIT is based on the size of the array, not the inverter size.

However, if you did not have more than a 4kW inverter (3.68kW according to the regs) you would not need to seek DNO approval. Although I assume you already got DNO approval when you added the battery system, as the total output could already be above 3.68Kw.

Regarding the "deemed" & "metered" if you want SEG payments, you need to switch to metered for all output, but you can keep FIT payments on the original system.

I'm interested in this too. I currently have a 4kW inverter and a split of 2kW of panels east and 2kW panels west. If I added more panels to the west side I still wouldn't ever produce more than 4kW so not sure if I would need any sort of permission or not. I get FiT payments and I'm not sure if the proportionality applies to the inverter capacity or the panels theoretical total capacity.

judgepd you would need DNO approval as they would say you can generate more than 4kw despite the East/West split if you add more panels. At least that's my understanding of the G99 process, it's not based on how the array is arranged just it's total kwp as a whole system.

Don't forget the battery can add up to 3kw depending on your configuration that the DNO also factor in.

yandards This conversation opens up a whole new thread. I never got anything via my installer re DNO for battery. I have now read up on that following your post, so that should not have been the case and I should have had certifactes etc to say its ok.
They messed up installing the EPS too as they didnt ensure seperate earthing rod. How are we as customers suppsed to know this, we rely on expertise of installers.

I sense a lot of pain now as I progress this with them :-(

I've never had anything DNO related from my original solar install or the battery installation. Staring to wonder if the battery installer even sorted it out.

DNO stuff is a bloody nightmare, they elected to complete a safety cut outs inspection on my install.

I ended up digging into the DNOs documentation for G98/99 stuff and a lot of it still refers to the previous G stuff, G59 IIRC which changed over in May 19.

If you have had your install for a while you might not need the G99 approval and it's often just a case of your installer applying for it in the background, getting approval and you seeing nothing of the process.

The reason a lot of people have 4kw arrays historically as it meant the DNO was always going to approve the install with little effort required for installers. That didn't take into account any battery export potential under the older regulations as I understand it.

I have a 5kw cap from the DNO despite a 6kw PV array, the inverter won't be able to export more than 5kw to the grid hence the cap - although I could still be charging the battery at another 1kw due to DC coupled charging.

What I don't know is how that all works for those on legacy approvals who want to add more PV or a battery - my read is it needs applying for with a view of the complete install, G98/99/100 approval now including any potential battery output too.

Type equipment approval is yet another source of amusement, the GE stuff has not long had its full UK G99 approval, Sep this year for the HY5.0 array. Another faff with my DNO site visit was the firmware I was running was a higher revision state than the one listed on the G type approval certificate register - the inspector didn't know if that was ok or not (apparently it's fine).

It's the same with EV chargers, they should be applied for with the DNO, although you retro apply if your diversity calculation on the household consumption is below 60A - another bloody minefield!

I understand it's still the very early stages of mass adoption for a lot of people but we are all very dependent on installers to understand all of this on our behalf. I suspect most of us know we need MCS certs but the electrical safety test certs and DNO approval if required are probably not something that will come up.

I have 3.86 kW of existing PV and a 3kW Givenergy ac coupled inverter with a couple of 8.2kWh batteries, however when pushed my DNO have agreed for me to install an additional 5kW of PV as long as I limit the export from this additional installation to 1kW. I have to install an inverter with grid limitation that adheres to G100 specification. They will visit after the install and witness the grid limitation in action. Western power were really helpful and charge nothing for this. The only fly in the ointment is I have to give them a two week notice period to visit and it has to be a sunny day!! Wish me luck on that one.

that sounds promising.

Are both arrays feeding the same inverter? I read you comment as it is a new one. Is that a replacement for your current one or an additional one?
If its additional how can you limit export for just the second? Presumably that can provide more than 1kW to feed your local load and charge the battery, but if it can do that how do you restict export to the grid as the energy flows to the consumer unit that then flows to the grid if there is surplus.

Is there another box required to provide that limit to the system as a whole?

Asuming you are using a single inverter I think the GE hybrids can do this as they have the G100 certification you describe. Is that what you are implmenting?
https://midsummerwholesale.co.uk/pdfs/giv-g100-declaration.pdf
That would limit max to 5kW for %kW hybrid, so if you have 8.86kW you will plateau in the summer and be capped. I dont mind that as I would get more power consistently throughout the rest of the year

Can multiple inverters combine and work as one plant yet to meet this standard?

Would something like the Goodwe Gw2500-BP or similar if GE would make one be an idea?
it sits on the PV string side and feeds additional battery power into the PV strings which would increase capacity in both battery storage and discharge rates for existing inverter.
Been mulling one of these over for a while.

Only downside is you can't charge from AC (although you may be able to rig a changeover up to a small charger for overnight)

Hi Seye I'm leaving the existing the existing 3.86kW system as is. I am adding an additional Solis 5kW inverter and panels. The export is just limited on the additional inverter, this is achieved is by installing a hard wired C.T. to the meter tails. When the export exceeds my DNO ordained 1kW limit the inverter will reduce the output from the panels to accommodate this, it will only limit the export not the self consumption or local load. Yes I believe the Givenergy G100 compliance certificate will satisfy your local DNO however they do need some arm twisting and might try to put you off!