Oversizing and FIT Payments

[bontwoody]

I have recently bought a house with an existing solar installation of 14x190W panels and a 3kW Fronius inverter. Its rated output is 2.66kW and it has a FIT payment at the highest rate.

I know I want to increase the solar output and I’ve been looking at ways in which I can do this in a cost effective manner.

The idea I had last night, which I would like to get opinions on, is the following:

• Remove the existing solar panels and replace them with modern high output ones (say 400W) giving an output of 14x400=5.6kW, but using the existing roof mounted supports.
• Replace the existing 3kW inverter with either a 3kW or 4kW hybrid inverter.
• Add DC coupled batteries to the system at some point

If I understand things correctly, then this should have the following advantages:

• No costs in providing addition roof or ground mounted supports
• The current inverter is about 11 years old and will probably need replacement soon anyway
• Minimised inverter costs for the smaller size, while still making use of the clipped output by charging the batteries
• A higher overall output from the array throughout the year
• No need to seek approval from the DNO

The potential issue is, I think, with the FIT payments. As I understand it Ofgem are happy for people to increase a solar array size, so long as they notify them. The generation figures are then pro-rataed down to take account of the increased production.

The change I am contemplating will produce an increased output when compared to a non-oversized system with the same inverter size but less than a system that has an inverter matched to its panel output. I’m not trying to pull the wool over Ofgem’s eyes but equally I wouldn’t want the FIT assigned output of the system to be below its current output.

Does anyone know how Ofgem would view this? Would they take the Panel size as the rated size, or the inverter size? Or something in between?

 

Thanks in advance

[Dillsue]

You need to speak to your FIT payment provider as OFGEM dont get involved with customers. I asked OFGEM a similar question a few years back and thats the response I got back.

 

From what I understand you can only change things on a like for like basis if something has failed.  Upgrading the size of the array is unlikely to fall into the definition of like for like. Only exception would be if a 190watt panel failed and a direct replacement wasnt available then I think youd be justified in going to the next larger available size,  but thats unlikely to be 400 watt and it wouldnt be all the panels either. 

 

If you ask and get approval definitely post back as theres likely 1000's of peeps that would love to up their FIT payments,  me included.

 

Even if you could fo this swap one of the savings you mentioned was no change to the mounts but I think youll find 400 watt panels are considerably larger than your 190s

[bontwoody]

Hi Dillsue

 

Im fairly confident you can increase the capacity of your system, as Ive seen mention of it on various websites, also this https://www.ofgem.gov.uk/sites/default/files/2021-12/Feed in Tariffs_Consultation on the treatment of replacement generating equipment_Decision_13122021.pdf

 

"From 15 January 2016, any extensions to an accredited installation’s TIC are not eligible to
receive FIT payments. The generator must notify Ofgem and their FIT licensee if they do so
and, if generation and export meters are shared, payments will be prorated accordingly"

 

Im not actually trying to increase the FIT payments, just not to lose those I already have. The bonus for me is gaining the battery storage and power. I havent checked the physical size of the panels yet, but Im sure i could increase the output considerably by upgrading them to newer models. Im also fairly tight for roof space, so that would be the best way for me to go if possible.

[Dillsue]

TIC is total installed capacity, so that statement says that if you increase TIC you wont get paid for it. Lets say you doubled your capacity then youll only get paid for half what you subsequently generate, so you are still only getting paid for generation off the originally installed and registered TIC.

 

Im fairly sure you need to have the extra capacity installed by an MCS installer so youll pay through the nose for the extension, yet get no premium return by way of extra FITs. 

 

Maybe Im reading what you are saying wrongly, but thats my understanding based on enquiries I made a few years back, post 2016 but before covid.

 

[bontwoody]

No, you are reading it correctly, you get no FIT payments on the extra installed capacity, but they prorate the reading so you dont lose out either, so if you doubled your capacity they would halve the meter reading and you would essentially get the same level of FIT payments.

 

Im interested in the extra capacity purely for charging batteries (and running daytime appliances via the batteries) and am hoping that the installation fees will be lower because I already have the panel support system. I could even change the panels myself as its a bungalow and just get an MCS installer to change over the inverter.

[Dillsue]

Probably best to ask an MCS installer if theyll sign off work youve done and kit that you may have supplied.

 

400watt panels are likely 1100mm+ wide versus under a metre for the 190s so assuming a 2x7 array youve got at least 700mm of extra rail width. The panel height will likely be 100mm different so you may need to move the top and bottom rails if youre unlucky. Maybe worth checking the panel mounting so your clear whats needed?? MCS guys are not known for lashing things up so you want to be clear that you can extend/relocate mounts 

[bontwoody]

Yes, that is an issue, I will have a good look when im on the roof. Even if I could only get the total to 4kW, that would be something. No point in trying to ask one now though as they are all too busy.

 

Im still on a cheap fixed energy tariff at the moment so there is no rush at the moment, but I would like to use something like Octopus Go or Agile once that ends, hence the battery system. Thanks

[TonyT]

I can only imagine that you would loose your FIT payments. These organisations don’t like change..

to get them back,  I bet it will be a lot of hassle.

Edited July 29, 2022 by TonyT

[Dillsue]

14 hours ago, bontwoody said:

Yes, that is an issue, I will have a good look when im on the roof. Even if I could only get the total to 4kW, that would be something. No point in trying to ask one now though as they are all too busy.

 That document you linked to is very interesting. If you look at the top of page 9 it refers to non accreditted extensions not affecting FIT payments from the original accreditted system. I read that as meaning you dont need an MCS installed extension to continue receiving FIT from the original accreditted installation, so DIY extensions are ok??

 

If you are limited on space for an extension that might not help you too much. Theres also a link at the bottom of the last page to a similar document covering battery storage install. I didnt read it in depth but it seems to be quite favourable towards batteries so your batteries could be ok. I seem to recall someone posted that they had added batteries to a FIT system, so likely its doable legitimately.

[bontwoody]

3 hours ago, Dillsue said:

 That document you linked to is very interesting. If you look at the top of page 9 it refers to non accreditted extensions not affecting FIT payments from the original accreditted system.

I hadnt really studied it in detail, but that is interesting, as is the battery info, so Ill take some time to do so thanks.

 

17 hours ago, TonyT said:

I can only imagine that you would loose your FIT payments.

It doesnt look like that is so Tony, but ill certainly make all the checks I can before changing anything

[bontwoody]

So Ive had a couple of realisations on reading the documents. If I want to keep my FIT payments and use off peak charging for the batteries then I will have use an AC coupled system so I dont confuse the generation meter readings. In that case there isnt really any advantage to oversizing the panels since the clipped output would be wasted. I cant actually see either how the TIC would be calculated if the inverter size was smaller than the panel size. My guess is that they would use the panel size which would disadvantage me.

 

I think my choices will be:

1. leave the panels and inverter untouched and just add an AC coupled battery system

2. upgrade the panels and current inverter up to 4kW and add an AC coupled battery system

 

probably sensible to do 1. first and then complete 2. once the current inverter fails.

 

 

[bontwoody]

Addendum. I was wrong about the installation having to be AC coupled if I want to keep my FIT payments. It can be DC coupled if a bi-directional meter is used.

 

 

[Dillsue]

I cant speak for other manufacturers but Solaredge allow significant oversizing of the array for a given size of inverter...an SE3680H is rated at the G98 limit of 3.68kw but can have up to 5.7kw of panels connected. Youll see some some clipping on clear sunny days for a few weeks of the summer but most of the year youll be able to use everything off the array. 

We installed an SE3680H with 5.1kw of panels at my daughters house earlier this year and her hubby was fretting about clipping when it was sunny but has got his head round the fact that its only gonna be short lived in the peak of the summer

[Ferdinand]

59 minutes ago, Dillsue said:

I cant speak for other manufacturers but Solaredge allow significant oversizing of the array for a given size of inverter...an SE3680H is rated at the G98 limit of 3.68kw but can have up to 5.7kw of panels connected.

 

They didn't when I put mine in 🤔. Or someone didn't.

 

9.98 kWp of panels and 2 x 5.3 kW max inverters.

 

Ironically I blagged 2 spare panels and 2 spare Solaredge panel-optimisation-wotsits from the supplier as spares, so I could take it up to 10.48 kWp out of stock.

[Dillsue]

11 hours ago, Ferdinand said:

 

They didn't when I put mine in 🤔. Or someone didn't.

 

9.98 kWp of panels and 2 x 5.3 kW max inverters.

 

An SE5000H can have up to 7.750kw of DC input and an SE6000H can have up to 9.3kw so just shy of your total array. If the array is split over different orientations, so panels arent all generating at peak at the same time, then you can have more PV than the stated max input.

I think yours was an installer limit, not an SE one as even a now obsolete SE4000-16 could have 5.4kw attached

[Dillsue]

11 hours ago, Ferdinand said:

Ironically I blagged 2 spare panels and 2 spare Solaredge panel-optimisation-wotsits from the supplier as spares, so I could take it up to 10.48 kWp out of stock.

If you check your inverter specs, you could well be able to add those now👍

[Ferdinand]

2 hours ago, Dillsue said:

An SE5000H can have up to 7.750kw of DC input and an SE6000H can have up to 9.3kw so just shy of your total array. If the array is split over different orientations, so panels arent all generating at peak at the same time, then you can have more PV than the stated max input.

I think yours was an installer limit, not an SE one as even a now obsolete SE4000-16 could have 5.4kw attached

 

Mine were also installed in December 2015, so the rules may have changed. It is East / West, with plans in my head to move some of it to a South facing veranda roof.

 

It was not that early as an install, but still some time ago.

 

[Dillsue]

4 minutes ago, Ferdinand said:

 

Mine were also installed in December 2015, so the rules may have changed. It is East / West, with plans in my head to move some of it to a South facing veranda roof.

 

It was not that early as an install, but still some time ago.

 

Exact same time as our first system.  It may have been a FIT banding limit that the installer worked to which is what limits ours to 4kwp of PV with a 4kw inverter that can take 5.4kwp of PV input.

[bontwoody]

14 hours ago, Dillsue said:

I cant speak for other manufacturers but Solaredge allow significant oversizing of the array for a given size of inverter...an SE3680H is rated at the G98 limit of 3.68kw but can have up to 5.7kw of panels connected. Youll see some some clipping on clear sunny days for a few weeks of the summer but most of the year youll be able to use everything off the array. 

 

Yes I saw that as I was looking at some specs. My roof doesnt have any shading issues so Im not sure it would be worth the expense of going down the optimiser route. I also saw some negative reviews on trustpilot for solar edge https://uk.trustpilot.com/review/www.solaredge.com

Have you had any call to use their support department?

[Dillsue]

Not suggesting you use SE but just showing that you can have an array thats far bigger than the inverters rating. Check your preferred manufacturers spec to see if they are the same as it may save you changing your inverter??

 

We had an optimiser fail a few years ago and SE did remote diagnosis and sent a replacement straight away. I looked at the trust pilot reveiws and many are frustrations with installers and many are from the US posting on a UK web site. Not really a true reflection on SE, in my view and experience.

 

Everyone gets shading as it includes segull s**t, saharan dust, algae, passing cloud shadows, snow, faulty module etc. With a conventionally wired system, the entire string output is reduced when any of the above happen to one or more panels. Youve also got individual panel monitoring with optimisers (or micro inverters) so you can see at a glance if youve got a problem. With conventionally wired panels it could take months or years to spot a problem, if ever!

[bontwoody]

3 hours ago, Dillsue said:

 

We had an optimiser fail a few years ago and SE did remote diagnosis and sent a replacement straight away. I looked at the trust pilot reveiws and many are frustrations with installers and many are from the US posting on a UK web site. Not really a true reflection on SE, in my view and experience.

Thats good to hear thanks 🙂