On order...

GivEnergy AC 3.0 Inverter

We just placed an order (through Cawoods who are local to us[1]) for a GivEnergy 9.5KWh solar battery and 3KW inverter - demand is high at present, so it may not be fitted for a while, but....

Essentially it gives us 9.5KWh of storage at a charge/discharge rate of 3KW, and it's (if we ever want to) expandable with more batteries and more inverters. As we are on the Octopus Go tariff for our car, we are getting 4 hours of very cheap (7.5p/KWh) electricity with which to charge both the car and the battery, which we can then use over the course of the rest of the day and top up from the solar panels. We can link it to the solar panels so it knows what's being generated, and also to the car charger infrastructure.  

GivEnergy 9.5 battery

I suspect it will take a little exploration and fine-tuning to optimise things so we use as little peak rate (35p!!!!) power as possible, but barring days when the office heat pump (more on THAT later, I guess) is on, we should be able to offset most of our power consumption to the cheap night rate. 

More info as and when it's installed, and hopefully periodic updates after that as we tune the settings. My initial back-of-envelope maths (and a big spreadsheet) suggest we could potentially save £1000 a year at current (exorbitant) energy prices, which represents a pretty decent ROI.

To answer the obvious question, yes the battery can be used as a backup during power outages. 

[1] For those wondering why we didn't use Hereward Solar Solutions, who fitted our panels. the simple answer is the company quietly folded without notifying their customers in 2017. Caveat emptor, I guess.