System specification
Tesla Powerwall 3 (13.5 kWh, LiFePO4) with whole-home backup mode. Zappi v2 7 kW tethered EV charger (Octopus Intelligent Go compatible). Existing 4 kWp Jinko solar array kept on Solis hybrid inverter (battery coupled AC-side via Powerwall 3 internal inverter). Octopus Outgoing Fixed SEG tariff (export). Octopus Intelligent Go tariff (import) for 7p overnight EV charging.
Property
4-bed detached 2008-build, integrated garage, existing 4 kWp roof PV from 2022
The Sunderland property had a 2022-vintage 4 kWp solar array but no battery. The owner was importing electricity at peak rates (27p) during evenings while exporting solar at the lower SEG rate during peak generation — losing 12p per kWh of misaligned demand. Battery retrofit was the obvious answer.
We specified the Tesla Powerwall 3 for the whole-home backup capability (Andy works from home in a rural-edge SR3 postcode that gets occasional power cuts) and for Tesla's best-in-class app integration. AC-coupling to the existing Solis hybrid inverter avoided any rework of the original solar install — clean retrofit, single new outdoor enclosure.
The Zappi was added at the same time. Andy bought a Kia EV6 in early 2026 and was previously charging at a 3-pin granny lead in the garage at 22p/kWh. The Zappi gives him 7p overnight via Octopus Intelligent Go (the API integration lets Octopus manage the charge timing for grid-cheap windows) plus solar-only Eco+ mode for shoulder-season days when there's surplus solar.
Install completed in a single day — Tesla Powerwall 3 wall-mounted in the garage, Zappi mounted on the garage external wall, electrical commissioning, app handover. Northern Powergrid G99 was approved 12 days earlier so no install-day delays.
After 4 months of operation the system is delivering 92% self-consumption (vs ~30% before the battery). The Kia EV6 charges almost entirely from Octopus Intelligent Go at 7p/kWh, saving Andy approximately £1,580/year vs equivalent petrol mileage. Powerwall provided whole-home backup during a 4-hour grid outage in March (downed line in nearby Houghton-le-Spring) — Andy reported the house "didn't notice" the outage until his neighbour mentioned it.
