Adding a second 9.5 battery to an existing set up

Hello all, tired to search and read relevant posts and am still a bit confused... my system is working really well - a couple of months this year over 1000kWh generation. I have 7.3kWh panels with a dedicated 6Kw Solis inverter and then an AC GE Inverter to a 9.5 battery. Given the excellent payback on the installation and the ability to charge batteries with low rate night time tariffs I'd like to add a second 9.5 battery.

I'm not very technical but from what I've read two batteries can cause issues as the system can't see both, there are more errors (?) with two battery set ups, only GE qualified engineers can fit a second battery, I'd be limited by the 6Kw Solis inverter and then the 3.6Kw battery inverter. There is some discussion of having the two strings split on to an inverter each but I don't think that applies to a AC set up?

So my questions are - is there a way to have a second 9.5 fitted which wont compromise my set up (been trouble free once I'd sorted a dongle issue) for nearly a year now. Will the GivEnergy app see both on one account and do I need /would it work better to have another dedicated AC Inverter with the new battery?

Sorry for the basic questions 🙂

I have 2 x 9.5 KW batteries attached to the AC inverter
The original installer just installed the second mounting bracket and linked the second battery to the first battery with the link cable

The installer then contacted the Givenergy commissioning desk who reconfigured my site for 2 batteries
My App also shows 2 batteries

My understanding is you need the installer to do this and the customer cannot DIY

The negative for the setup is the inverter can only provide the maximum 3kw charge through the inverter so to charge both batteries fully it will be slower than if you added a second inverter with single batteries

Thanks @robertneal I will enquire with my installer!

Pitva there’s no issues with multiple batteries on one inverter, the inverter just sees them as one large battery

The issues you have seen are multiple inverter setups each with their own batteries. The inverters don’t know about each other

I have a very similar setup. 7.6kW panels, AC3.0 inverter and on installation one 9.5kW GE battery.
I had a second 9.5 added to the AC3.0 inverter.

The extra flexability to play the smart tariffs has been great and has worked well.

Remember the 2nd battery will not be VAT free unless it is part of a new solar panel installation. It might be worth adding 1-2 panels and a small inverter if space and direction allowed.

Overall I am much happier with 18kW batteries than I was with 9.5

Thanks both, sounds like just another battery will work well and I would have couple more panels if it wasn't for the scaffolding costs - I have room for at least another 3. I'll have a chat with the installer.

Pitva Just remember that you pay VAT on the battery & installation unless solar panels are included in the install You may find that also having the extra panels makes very little difference as it then becomes 0% rated, worth pushing the installer.

Things might change but I'm not holding my breath
https://committees.parliament.uk/committee/62/environmental-audit-committee/news/195426/vat-rules-could-change-on-battery-storage-when-installed-after-solar-panels/

Pitva Nothing to stop you having the extra panels on a stand in the garden, or on a shed roof.
And if it is easy to access maybe your installer will fit without scaffolding. My 16 FIT panels were all installed off ladders

geoffreycoan My panels on my house roof has been installed without scaffolding so for me companies putting scaffolding for solar panels instalation literally scam customers for extra money as they can do this without it. It would cost me extra £1k to put scaffolding so I chose company who do not set it up.
About 0 vat in current situation. If I have solar system already to qualify for 0%vat on new battery do you need have battery, solar panels and inverter to be installed or battery and solar panels would be enough?

HipHopAst You need to ask the installer, they understand the VAT rules better than us.

The idea of a single panel in the garden + a small inverter might be workable. Nothing says the panel have to stay in use. I wish I had thought of that when I had my 2nd 9.5 installed.

I like the idea of a single panel in the garden that could become a spare - I think the scaffold last time was a fixed cost of £495 from a separate scaffold company so don't think the installers were profiting much from it. Shame the support rails for the panels were cut as I guess fixing those requires scaffold for most installers - I have a fairly steep pitch... thanks again all.

I recently wrote to my MP and this is her reply. The first para is standard MP testicles but the second is more relevant.

Thank you for contacting me about VAT on solar panels and battery storage.

I welcome the Government's decision to reduce VAT on the installation of energy-saving products such as solar panels and some battery products from 20 per cent to zero until March 2027. This change means that a typical family having rooftop solar panels installed will save more than £1,000 in total on installation, and then £300 annually on their energy bills. This is a significant step that will help households reduce their energy bills and their carbon footprint.

Any decision to modify our tax regime is a matter for the Treasury and careful consideration will be given to any proposed amendments to current VAT rates. It should be stressed that the Government keeps all taxes under review, including VAT. I shall be following the developments on this issue closely, and I will ensure my colleagues at the Treasury are aware of the strength of feeling on this issue and the specific issue you have raised with me.

I hope Givenergy and other manufacturers are pushing for this.

Rogerbu imho, you don't need a small inverter, just buy exactly what you have as a spare and same goes for solar panel, and keep them as spare because the inverter has a fixed lifespan and will need to be replaced sooner than the batteries and you may not get 20% VAT off at that time (scheme only until 2027). 0% VAT is on the bill and not on install !!

Pitva How much do you consume on a daily basis to justify the second 9.5kWh battery? At the moment we're averaging 6.7kWh during the Intelligent Octopus peak period, but I'm struggling to decide if a single 9.5kWh is cutting it a bit close.

deepanshus Do you need to be VAT registered to get 0% Vat on eligible Renewables purchases? Or just be an ordinary purchaser rather than trade?

billG any purchase through a trade installer gets billed at zero VAT.

billG Essentially you need to be VAT registered to reclaim any VAT you have been charged. Therefore VAT is liable all the way down to the end user Customer, however, the VAT % rate can vary on the final invoice to an end user as is the case with a solar system installation (currently must include panel(s)) where it is VAT 0% rated. In this case the installer effectively charges HMRC the VAT amount they have actually paid out for the materials, (panels, battery, inverter etc) via their VAT in/out returns.
Therefore being 'Trade' doesn't matter, it is whether the trader is VAT registered.

SilverArt So basically end customers will get absolutely f**k all as installers will get all benefits from 0vat.

The don't charge VAT on a solar installation, so the customer should benefit.

HipHopAst No... in exactly the same way as normal, the end user Customer gets their quotes and goes with the one that best meets their need. Those installers who really take the mickey won't get the business... that's their choice.

The installers could actually argue that having 0% VAT is an absolute PITA as it means HMRC are more likely to be extremely thorough if they are audited as HMRC are worried that VAT returns in a split VAT could be 'fiddled'.

I am in a similar position - have a Gen1 5.0 hybrid inverter and a 9.5 kWh battery plus 14 solar panels.

I am charging it to 100 % most nights at the moment using Octopus Intelligent Go so we get 6 hrs @ 7 pence per kWh.
But since the panels are generating very little at this time of year , and our house sadly uses a fair bit of electricity - the battery is pretty much empty by mid afternoon ...
So considering a second battery... questions...

• can both be charged at the same time ? Or will one fill first then the other ? If the latter , at 2.6kW per hour and 6 hours , I will only actually be able charge 15.6kWh worth during my cheap period ...

• can both discharge at the same time up to the 5 kW limit of the inverter during heavy usage ?

skinnerneil If you have a single inverter and connect a second battery to it, then the inverter sees it as one giant battery. You don't manage them individually, they both will charge together.

On a gen 1 hybrid you are limited to 2.6kW charging and 2.6kW discharging unfortunately regardless of the number of batteries, its an inverter limit not a battery limit. The 5.0 refers to max potential inverter throughput from the battery and solar. So if its a really sunny day you can convert up to 5kw from the panels, but only 2.6 still into the battery.

I have the same inverters and find I don't always get the full 2.6 either, 2.6 discharging but often only 2.4 charging.

If you had two inverters or a later gen 2 or gen 3 you could improve your charging & discharging rates

geoffreycoan much appreciated

Looks like gen 2 and gen 3 have 3.3/3.6kW for charge discharge so I might need to budget for the inverter upgrading too …

I wish I had known all this during install - I would have pushed for the gen 2 …

HipHopAst Frankly it all depends on how much the installer cares about the safety of their staff.