FWIW I have been investigating battery recently (for about the 4th time - basically I struggle to make the business case work) and my judgement of the market is that, even now, whole house backup with off-grid PV support is not ready for mainstream.  It is possible, but either you have to spend a lot of money for a high end system or you have to put something together more or less yourself using Chinese components.

So you were mis-sold, but probably couldn't actually have done much better at the time unless you had spent a lot more.

I may have some thoughts later on how you could get it working as you intended but it will probably depend on a replacement inverter (if you can find one that will work with your existing batteries) plus some switchgear.  As to whether anyone would be prepared to fit it, thats a whole other question!  Others may well comment before I do.

Posted by: @little-lights

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... before being told by the installer "We're busy doing commercial work not residential."

I hope Saint Homobonus is looking after the "commercial work" victims.

Sounds like you have had a rough ride, and I'm thinking you might be flogging the proverbial dead horse on this imstall. I would tend to agree with your prognosis on equipment "value". The resale value is no more than what someone  is prepared to bid and what you are prepared to accept. However, the panels and battery should be transferrable into a revamped setup.

Everyone's ciircumstance varies and I do not presume to know yours.  Have you done your own cost/ benefit analysis and perhaps  consider preparing your own business case: viz. the cost of achieving the Spec you want, from reputable installers ( they do exist!) and borrowing over a period you can afford to repay. There are "high street" lenders who give preferential rates for projects like this.

I hope you find a positive way ahead.

Thank you so much for that - the prospect of possible further thoughts is tantalising. I just re-read an email I got from Pure Drive in May 2025, and frankly it's triggered tech PTSD (it's all basically a bit beyond me), so you are probably right about it not being 'mainstream'... though I thought GivEnergy and Sig did something like this now?

Without going into the technical detail (which is mostly about the particularities of our system install and the 'workaround' installed by the second installer) Pure Drive were saying that ...

• There was a way to do it if the Solis AC inverter was on our back up circuit, however, that's against recommendation (they said: "After looking at Solis PV inverter data sheet, this requires 14A (amps) of power. Critical circuits can support up to 11A so it would power the inverter for a little while but not for a prolonged period of time").
• They also said that in order to use a hybrid inverter we would need a new battery (which isn't an option), however at different times they also said that we could install a hybrid inverter with our current battery, but it wouldn't do anything additional without a back up circuit (which our second installer did in an 'unofficial' kind of way, to create the system that works off grid but can't recharge from solar).

In the end I think I was just blinded with science, and the installers I spoke to at the time hit a wall, so I knocked it on the head and decided to live with what we have at the moment.

I'm aware however that the technology is changing and updating quite quickly, so wondered if anyone here had any further thoughts.

As above - thanks again - I really do appreciate any insight even if it's just 'bad luck' and 'dream on'...!

@colinc I think if I had a clear way to achieve what we wanted, I might consider something like that... probably a bit after I've blown all my savings on my extension/renovation(!). I'm more of a saver than borrower by instinct, but my lender does zero rates on secured loans for certain green 'upgrades' (not sure if this would qualify, but you're right it's worth looking into). It's partly more than just cost/benefit - I have meds that we need to keep cool in the fridge, and we did originally invest in this for the (intended) resilience. Hard to weigh that kind of thing. First things first - is it even possible. I wonder how compatible different battery systems are... as we have Pure Drive, I presume it won't integrate into any one else's system (understandably).

Posted by: @little-lights

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Is there any way - any at all - that I can affordably (I'm thinking £2k-ish...?) get this system to work as I originally wanted it to: panels and battery, optimising home usage, and in the event of a power cut to have the ability to charge up the battery from the panels and run the (low-power) essentials of the house from the battery, off grid.

Posted by: @jamespa

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FWIW I have been investigating battery recently (for about the 4th time - basically I struggle to make the business case work) and my judgement of the market is that, even now, whole house backup with off-grid PV support is not ready for mainstream.  It is possible, but either you have to spend a lot of money for a high end system or you have to put something together more or less yourself using Chinese components.

OK so here are my thoughts.

Your panels and battery fundamentally dont in principle need changing, they are not where the 'smarts' are.  The issue is with your inverter which is what connects them and the house and contains (or doesnt contain) all the functionality to do the whole house backup/off grid PV.   Inverters are 1-2K, the cost is in the panels and battery (and installation)

(1) Its possible that your existing inverter can be coaxed to do the job with some (possibly manual) switchgear.  The main issues are that the PV will require a grid like frequency before it will operate, and the 'backup' port of your inverter probably wont accept a PV input.  However some Solis inverters have a generator port and if you connect the PV to that it may well work (@batpred knows quite a lot about this).  With manual switchover and a bit of judicious requiring and restricting what circuits you use when off grid this may well worm

(2) If the existing inverter cant do the job then others can, but its a complex subject.  To get an idea have a look at this 15 page thread  I am making the assumption here that the inverters in question are compatible with your batteries, thats likely (particularly given that your current inverter is a Solis one)  but not absolutely certain.  If you can find someone to re-jig your setup and fit an alternative inverter then that will be your best option if (1) cant be got to work.  

(3) If you cant find anyone to do the above then it will be don to replacing both inverter and battery.  Thats going to be expensive, 6-8K, so probably you will deem it not worthwhile.

I think your main problem is finding someone who will (a) work out a solution and (b) do what is a non standard job ((1) or (2))  The guy who did the conversion you have already had done might be your best bet, otherwise you may find its down to working out a solution and then finding an electrician.  The regular grant harvesters probably wont touch it because they dont do off the wall things.

One thing I would think about is what load you actually need in 'backup' mode (including the ASHP).  My fuse is 80A (18kW) but my actual consumption never goes above 10kW even including the EV (albeit on a 2.4kW granny charger not a 7kW 'proper' charger) and it rarely goes above 5kW and then only if I specifically try (eg when electricity is negative price).  So in practice 5kW backup would be more than adequate.  The problem is that most installers cant get their mind round anything between a 'few sockets' (what you have) and the 'full monty'.  Thats a pain because it makes the problem near impossible without spending lots of money.  However maybe the uy who did your backup could.

In summary what you want to achieve is possible for sure, but whether you can find anyone to it is another matter.  @batpred and @transparent both of whom have done a lot of work on this sort of thing may wish to comment.

@jamespa OK - I'll need to digest that I think. I got a taste of how complicated inverters can get in 2025, and haven't quite recovered yet (!).

I feel like I'll need to set a bit of time aside for a bit of reading around switchgear in the first instance, as I've got a better chance of working out if that's feasible. The back up circuit is already restricted in terms of what is included on it, and we're aware we need to be careful what we use in a power cut. At the moment the switch to back up in a power cut is automatic, which seems a bit of a risk to me (we've been told not to overload the back up, but don't actually know when a power cut will occur so can't really plan for that!).

Thanks again!  

Posted by: @little-lights

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@jamespa OK - I'll need to digest that I think. I got a taste of how complicated inverters can get in 2025, and haven't quite recovered yet (!).

I feel like I'll need to set a bit of time aside for a bit of reading around switchgear in the first instance, as I've got a better chance of working out if that's feasible. The back up circuit is already restricted in terms of what is included on it, and we're aware we need to be careful what we use in a power cut. At the moment the switch to back up in a power cut is automatic, which seems a bit of a risk to me (we've been told not to overload the back up, but don't actually know when a power cut will occur so can't really plan for that!).

Thanks again!  

Its definitely quite complicated and as I say whole house backup with PV off grid is very much not yet mainstream.  I havent gone ahead with a battery because I simply cant make the business case work (and there isnt a convincing environmental case).  However we rarely get power cuts so I cant assign much value to backup capability and, unlike you, I don't already have a 10kWh battery!

Based on what I found, if whole house backup with PV off grid is important, to you, I would pursue it given where you are, but definitely assign a fair amount of time to understanding it and there is no guarantee you can find someone to do it.  The principal issue is not understanding it in principle (although there is some of that to do), its understanding what half baked compromises the current products have made!

I would definitely think of this as a separate project of its own.  Hopefully someone who has actually done this will chip in.

@jamespa Thanks - I'm OK with having part of the house, not the whole house - I've def made my peace with that. In an outage, if we could keep the heating / hot water, lights, and a judicious use of sockets I'd be a-OK (esp if it was able to recharge from solar). So I've figured out: the Solis inverter we have doesn't have a generator port.

PureDrive suggested Victron, but then slightly back-tracked.

I'm tired enough (and non-technical enough) to ask ChatGPT. It suggested Victron MultiPlus-II (5kVA) ... (?) as an addition to our current Solis (S6-GR1P3K) alongside the Pure Drive II AC coupled battery. 

As ever with this topic (which I think you're right to say is a stand alone project!)... I start looking into it and get that horrible 'can't take your eyes off the horror' feeling as I (for instance) start scanning through technical compatibility sheets from inverter companies. I stopped looking into this in May 2025, and I'm starting to remember why. But if the Victron MultiPlus-II is a go-er, maybe I can start the ring around for willing installers. I'll wait to see whether there's additional input

As above - thank you again - I feel more hopeful, though I know it still might not be possible for various reasons (as you say installer reluctance being maybe the main one). 

Posted by: @jamespa

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whole house backup with off-grid PV support is not ready for mainstream

Most of the times whole house backup can't work without a large generator, simply because while a realistic PV installation can easily produce enough to power the whole house some days (ideally most days) it can't do it every day.

If there's a blackout, it's likely to coincide with terrible weather: storm, snow, etc, therefore low PV production. In this case all the stuff idling in the house will still draw power, then the heating or the water heater turns on, and the battery gets drained pretty fast.

On the other hand, if the backup circuit only powers essential loads (a few lights and the freezer) then they can keep running even if the weather is bad.

Back to OP's problem:

You have a grid tied inverter, which is specifically designed to only work when connected to the grid, and to shut down when there is no power, in order to not zap the guy from the utility who is trying to fix the wires. This is mandated by law.

You also have an unspecified AC coupled battery, so there's an reversible inverter in it. It seems to do backup, so there's probably an auto transfer switch in it too.

To charge the battery offgrid via AC coupling, you need:

- PV inverter connected to battery's AC backup port

- The battery's internal inverter must be grid-forming, ie it can pretend to be the grid well enough that the inverter believes it's on grid and connects

- The battery's internal inverter and the Solis inverter must talk to each other so the Solis inverter can limit its power injection when the battery is near full charge, otherwise it will all shut down. This is usually done by frequency shifting. This requires both machines to be compatible with each other. Fronius and Victron do it, I have no idea if your kit can do it. AC coupling is pretty annoying.

Posted by: @little-lights

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- Most mornings the battery trips out when the sun comes up, and we have to flip it back on at it's fuse board. No idea why. If we miss that, it's just out until we notice.

Needs info on the battery, the breaker, and the wires between the two.

Posted by: @little-lights

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- Intermittently but at multiple occasions in the day the Solis inverter presents a 'NO GRID' error, mostly when it's sunny.

Open manual

Section 6.4.1 "Show 100 latest alarm messages"

See page 36 for what the messages mean.

Maybe you can find an error before the "NO GRID" message which gives info on the cause.

Posted by: @little-lights

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It also turns out that the Solis inverter wasn't installed with remote monitoring, and my original installer agreed to install the required piece of kit so that it could be remotely monitored, and then didn't.

If you want remote monitoring, you can get the wifi stick, it's rather cheap. By the way, if you registered the inverter with Solis using the serial number on the label, you can also open support tickets and ask questions, they respond pretty quickly and have competent service.

@little-lights If I understand you correctly your system is AC coupled, (ie you have 2 inverters).  Its the battery inverter you need to concentrate on which is why I mention battery compatibility above.

FWIW here is where I got to when I was trying to work out what I could do.  This would, I believe, work with either a sunsynck or a solis 'hybrid' inverter, possibly others.  Incidentally several inverters have some sort of 'gateway' module for whole house backup which sits between the grid feed and the inverter/CU.  These tend to be obscure in function, in my diagram I interpose manual switchgear to ensure (I think) that things can never be connected that shouldn't be connected.

My idea is not to separate backup circuits but just rely on the fact that my load rarely exceeds 5kW which is commonly available from BU ports, inverters can stand overcurrent for a short while and then self protect by shutting down, and I can self-censor circuits when its in backup mode if I have manual changeover.  The rationale for this is that I don't want to have to decide in advance which circuits to run on battery, because this will be different from winter to summer!

My proposed circuit is AC coupled because I need to keep the solar separate, due to the fact I have 10years of FiT (generation) tarrif still to collect at the best part of 30p/kWh (this is in  addition to the 12p/kWh I get from export).  In your case you may be able to use a single inverter and feed the solar panels directly to the MPPT ports of a single 'hybrid' inverter.

Hopefully this gives you some further food for thought.

Oh woe!

1: I've just read the Solis Inverter specs and Installation Manual for a S6-GR1P3K. I think you have a typo because I can't find a S6-GR13PK.
So I now understand that this is a solar string-inverter with an AC output which synchonises to the 50Hz grid frequency.

If the grid goes down then the inverter must stop working under the G98 regulations.

When the grid becomes available again then your inverter must wait a randomised period of time before reconnecting.
Those are the rules.

2: We've previously discussed Pure Drive storage batteries here on the Forum.

Did you find this and read it?

3: In a dispute like this you are protected by the Consumer Rights Act, which covers both goods and services such as installation.

That is administered by the Citizens Advice Bureau. You don't need legal advice. They offer routes via Mediation and Arbitration.

4:

Posted by: @little-lights

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I'm tired enough (and non-technical enough) to ask ChatGPT. It suggested Victron MultiPlus-II (5kVA)

That's a very 'safe' response. Victron is the Rolls Royce manufacturer amongst those who supply components for solar and battery storage options.

ChatGPT is basically telling you to throw money at a problem which it hasn't understood.

5: You might think that you've bought "a system". But functionally neither the Solis inverter nor the inverter in the Pure Drive battery 'know' about each other.

Each inverter connects to the grid via your Consumer Unit.
Neither has an "always on" port which provides power independently of the grid.

I don't know how your Second Installer has managed to provide you with a few live sockets which operate during a power cut.
Nor can I tell if that workaround is within the Pure Drive warranty, or 'safe'.

We really need a sketch of what you've got if we were going to take this discussion further.

It doesn't need to be as good as the one James has just posted.
Hand-drawn on the back of an envelope will do, then take a photo with your smartphone.