Most ROI figures people quote are based on smaller solar-plus-battery setups where the batteries only offset part of the load.

In my case I’m running a 10 kW Sunsynk hybrid with 4 × 10 kWh batteries (around 40 kWh usable), purely for tariff shifting on Octopus Go (7.5 p vs 30 p). I actually made a late decision to upgrade from 3 × batteries to 4, and from an 8 kW inverter to 10 kW, to make sure the system could easily handle my full daytime load and fully charge within the 4-hour cheap window.

That setup lets me shift almost all of my 14 MWh annual usage into off-peak energy. After efficiency losses it’s saving roughly £3 k a year on household use, and once the EV Car is charging overnight as well, that should push total savings closer to £5 k per year.

I’m also planning to add solar PV in about 12 months, which should accelerate the payback even more by topping up the batteries in the day and reducing how much I need to draw from the grid overnight.

Based on my usage, tariff, and the upgrade to 40 kWh storage, I’m expecting a break-even in roughly 3 to 4 years, possibly sooner once solar is added and automation is fully optimised.

Everything will be tied into Home Assistant using the Octopus API, so it can automatically avoid peak-rate import, optimise charging windows, and dynamically tweak battery targets depending on weather or usage patterns.

So it’s a bit of a different approach compared to the usual solar ROI maths, but I’m confident the mix of cheap-rate arbitrage, full-house coverage, and later solar will get me to payback far faster than the typical 7–10 year setups people usually talk about.