Securing 0% VAT on battery install

Boffinboy24

Hi All, I have existing solar and am looking at having a storage battery installed. With the new 0% VAT for renewables it may be more cost effective to also add an additional solar installation with 1-3 panels (as small and cost effective as possible). I have a flat roof - admittedly shaded in the afternoon - where this could be done facing East or South East without scaffold.

I am trying to figure out the cheapest and best way of doing this - either a small inverter for the new panels and an AC coupled battery system, or a hybrid inverter (avoiding the need for a separate inverter for the new panels, but having 3 inverters total). What I am unsure about is whether I can use a hybrid inverter for the battery storage and the new extra couple of panels, as well as still store from the AC side of the existing inverter? I am guessing I don’t want to combine all on to one hybrid inverter because the new panels will drag down the other much larger array (two strings) due to the poor location. 

QrizB

If your existing solar PV qualified for FIT payments, it will be much simpler for the new system to stand alone.

Exiled_Tyke

I've written about my experiences on this matter a few times on these boards.  I found the most cost effective and least dangerous to my FIT payments was to go with a couple of panels connected to one 600w micro inverter.  The battery then has it's own battery only inverter.   There are arguments for different set ups but this is the one that the installer and I decided was most appropriate for my circumstances. 

Boffinboy24

Existing system doesn’t qualify for FiT sadly, it’s nearly brand new (I should have just gone for a battery upfront, but that ship has sailed!). Given the shading on potential new panels I was thinking there are 2 options, but I am not sure if option 2 is viable:
1) New system on a new very s inverter, existing system on existing inverter, AC battery - disadvantage may be cost as need an extra inverter?
2) New system and battery on hybrid inverter, old system on current inverter - but I am unclear then if the old system charge the battery since it’s AC side?

I’m essentially trying to get a new small PV system for “free” / almost free since the VAT on battery would go from 20% to 0, which should comfortably cover a 2-4 panels. 

Boffinboy24

sorry, typo there… “very s inverter” should be “very small inverter”

Exiled_Tyke

Well what I did was essentially your option one. But the installer suggested that one microinverter which could cope with both of the new panels would be cheaper than a traditional wall mounted inverter.  This has it's own generation meter which I use to keep track of performance.  The only downside is that I don't have a monitoring portal for this set up but in the scheme of things it really doesn't matter. It's usually far more important for me to be looking at the battery performance rather than generation of just two panels.   If the new panels are subject to similar shading I'd probably go with this. Otherwise you'd need to find a very small inverter which will handle two separate strings. I don't know whether these exist.    

Personally I think option 2 has many issues (including having a large an inverter for the small production capacity which is inefficient as well as the issue you raise)   so making  it impractical but others may know better.  

ispookie666

I would probably get a system which would fill the whole roof safely provided you won't have to sell a kidney  .
I have enphase micro inverters and they are not the only game in town. 

gefnew

You could use Tigos as they can be fitted to the panels that have the shading and work with any inverter because they are just a bypass module.

Exiled_Tyke

gefnew said:

You could use Tigos as they can be fitted to the panels that have the shading and work with any inverter because they are just a bypass module.

Doesn't that though only deal with half the problem, an inverter is still needed?

Boffinboy24

gefnew said:

You could use Tigos as they can be fitted to the panels that have the shading and work with any inverter because they are just a bypass module.

Good suggestion! My assumption is this may not count as a system for VAT rules. My current inverter is also extremely undersized and right at available capacity, which the installer assured me would lose minimal production based on their modelling of generation whilst saving the G99 processand larger inverter cost, but having seen the clipping I am getting already I am not sure that was right…. Still, their estimate for annual production is only 10% less than PVGIS so maybe they are right *shrug*. I think I’d probably have preferred the larger inverter and a battery with hindsight, but hey ho!

Exiled_Tyke

Boffinboy24 said:

gefnew said:

You could use Tigos as they can be fitted to the panels that have the shading and work with any inverter because they are just a bypass module.

Good suggestion! My assumption is this may not count as a system for VAT rules. My current inverter is also extremely undersized and right at available capacity, which the installer assured me would lose minimal production based on their modelling of generation whilst saving the G99 processand larger inverter cost, but having seen the clipping I am getting already I am not sure that was right…. Still, their estimate for annual production is only 10% less than PVGIS so maybe they are right *shrug*. I think I’d probably have preferred the larger inverter and a battery with hindsight, but hey ho!

In which case I would definitely ask the installer whether you get away without buying an inverter.