If you fitted solar before 2023, you almost certainly don't have battery storage. Adding one now is one of the best returns going on home upgrades — but only in the right circumstances.
The case for adding battery
Without battery, your home self-consumes about 30% of the solar it generates. The other 70% gets exported to grid for 5p–15p/kWh, then you buy electricity back at 25p–36p/kWh in the evening. The economics are bad.
A 13 kWh battery flips this: self-consumption rises to 80–90%. On a 4 kW system in the Midlands, that's an extra £400–£600/year saved.
When battery payback makes sense
Battery makes sense if: - You generate 3,000+ kWh/year of solar - You use 2,500+ kWh/year of electricity (excluding solar) - You can switch to a battery-friendly tariff (Octopus Flux) - You'll be in the property 7+ years
Battery payback is typically 6–9 years on a £6,800 EcoFlow 5 kWh, or 8–11 years on a £8,400 Powerwall 3.
When it doesn't
Battery doesn't make sense if: - Your home is small and uses < 1,500 kWh/year - You're moving in 2-3 years - Your existing inverter is failing (replace inverter first, then battery later) - Your roof has a tiny system (sub-2 kW)
AC-coupled vs DC-coupled retrofit
99% of retrofits are AC-coupled — the battery has its own inverter and connects to your home AC supply. Compatible with any existing solar system.
DC-coupled retrofits require swapping the solar inverter for a hybrid. More efficient (single conversion) but more expensive (£1,400–£1,800 extra for the inverter).
For most homes, AC coupling is fine. The 3-5% efficiency loss is dwarfed by avoiding a hybrid inverter swap.