Summary: Very happy. Very worth while
I have had 4kw PV for about 8 years, with solar diverter for hot water I added 8.2kWh GivEnergy storage a year ago. Originally on Octopus Agile, now on Octopus Go Faster 5. I have been really happy witht he solution. Even in December / January my average £/kWh if < £0.08. In the summer I did get down to effectively being off grid. My direct debit to octopus for both gas and electric is £25
The GivEnergy system is modular. I would suggest using that to get detailed evidence of your usage prior to investing too much. Start small but leave open ptins to expand later. There is a "goldilocks" configuration for your use case, but your will be different to mine, which will be differ to another persons.
Octotopus Go was orginally targetted at both EV and storage customers. The rules have now changed and storage only customers can not access the reduced tariffs. Really mad economics currently have resulted in my buying MG ZS EV to retain cheeper tariffs. My economonic case to make the switch previously was borderline. Now factoring in domestic energy savings and taxbreaks its a no brainer. I was going to do it anyway, but this brought it forward by a year.
Having had the system for a long time I have gone through the emotional cycle and heart and head battles. I did actually order a second battery by have cancelled that having redone the maths. I had not factoredi just how much load shifting I have mananged to do ( which is the zeroinvestment way to save energy costs e.g. washing machines, driers etc overnight)
If your energy supplier provided peak and offpeak cost breaksdown or you can download your usage it straight forward to work out where your goldilcks zone is. Look how much energy is consumed on average at peak each day.
As I have had the GE system for so long I can also see my power usage graphs during the day so can see its very rare during peak I exceed 2.5kw. A single inverter can satisfy that, the question is then whether the occassional ability to supply >2.5kW is worth the considerable investment for an additional inveter .
Capacity can be increased again due to the modular design. a single inverter can ony charge at 2.5kWh so depending on the off peak period you have that will limit ideal capacity eg.g. mine is 5 hours so 2.5 * 5 = 12.5kWh. PV can top that up further so 16.4kWh would be the most I would consider, accepting that I ony get the benefit of 4kWh for part ofthe year when PV is assisting
There is no simple answer to the question if storage is beneficial and how much. Sorry to say there is a bit if work getting your own data and anlaysing in spreadsheets etc to to prodictions and "what if" scenariois.
Comment above re payback. The wider the gap between offpeak and peak rats gets the quicker the payback. mine was 7 years on the 8p difference. Now the difference is up to 23p that period comes down to 3 or 4 years.
Also think total energy and cost footprint i.e. Car, House, heating, Hot water. Historically they are seperate in peoples minds. Now they overlap significantly. Costs in one area may well be offset by savings in another.
my expected use of battery and Ev is as follows:
1) charge car + battery off peak overnight
2) supply house from PV
3) if spare PV charge battery
4) if spare PV and battery full heat water
5) if spare pv, battery full, hot water hot and PV >1kw, charge car for 30 mins at 3kW ( if I can )
The battery removes the need for expensive PV intergrated chargers, just use short burst charging
Does anyone know if MG have API to invoke charging? I can do via charge point but would be nice to just use MG as I want to automate heating too based on shift patterns and weather
I chose to buy the MG ZS EV instead of another battery. I was looking at v2l in the future to effectively suppliment the GE system but CCS bidirectional chargers are not mainstream yet.