Battery Systems - size is everything

Yes indeed @BPLightlog, in order to qualify for FiT payments ten years ago, you’re perfectly correct: we had to get an MCS approved installation, which included a G83 approved inverter for connection to the Grid, apply for approval from our DNO for the system, and obtain a satisfactory EPC for the house. In ten years, our Fronius inverter has generated 23,500 kWh, of which nearly 18,500 kWh have been exported back to the grid! 
 

The more recent mini-system add-on, on the other hand, cannot be allowed to export to the grid, so, without enlarging my existing approved system into an integrated and approved design such as might mirror those systems described in this thread, there are only a limited number of options. These might include an off-grid system which isolates the household from the grid whilst in use, or a system which undertakes not to export to the grid whilst in use. 
 

You’re also absolutely correct when you say one cannot have enough battery storage! Our ten year old system is nominally 3.2 kWh split array, but given our location is probably more like 2.2kWh maximum.  I can hardly wait to obtain more battery storage (the luxury of being able to turn on the oven at a moment’s notice!!) but there will always be the overhead of re-charging the batteries.  I’m very interested in the discussion about using low-cost nighttime tariffs, (9p a kWh for 4 hours a night!).  Amazing, I guess that’s the way to go, and I’m sure we’ll see ever more and more smart tariffs for the responsive householder who has the capacity.  But in the meantime, for small levels of consumption (we’re talking winter, of course:  in the summer there’s absolutely no problem with even a small PV array such as my own effortlessly charging quite extensive battery storage for 7 or possibly even 8 months of the UK year) in a small household I’ve been very impressed with my small add-on supplementary battery system. 
 

Of course, the householder must seek expert advice on matters such as approvals and safety. 

And with a change in vat policy now announced to start in Feb 2024, more might start to look to add batteries to their solar PV systems 

https://www.renewableenergymagazine.com/pv_solar/solar-energy-uk-celebrates-the-success-of-20231213