Will a battery keep my power on during a power cut?
Short answer
Only if it is installed with backup equipment. Standard solar switches off in a power cut. Backup needs an islanding device such as a gateway, and on most homes an earth rod so the house stays safe when disconnected. Switchover can cause a brief interruption, and runtime depends on the reserve you keep.
Last checked 24 September 2026 · 2 sources
In more detail
- IET CoP EESS: island-mode TN-S with consumer earth electrode (<=200 ohm) and interlocked N-E bond relay; BS 7671 551.4.3.2.1.
- Powerwall 3 supported islanding device: Backup Gateway 2.
The facts, dated
- 01Maximum acceptable consumer earth electrode resistance for island-mode TN-S (IET CoP EESS) — 200 ohm
standard · UK · checked 24 September 2026 · IET
- 02Powerwall 3 supported islanding device — Backup Gateway 2
manufacturer · UK · checked 24 September 2026 · energylibrary.tesla.com
What we saw in the field
[QA review 2026-09-24] C2-8/C2-9 AGREE; C2-10 Wall Connector opinion UNVERIFIABLE; C2-11 AGREES (partly). | Earlier notes: Agrees and adds: customer 1 said the gateway switched cleanly (early unit hummed); customer 2 lost power ~45 minutes overnight in a 24-hour cut with a 20% reserve, and devices rebooted at switchover. Consistent with backup being limited by reserve setting and non-UPS transfer. Customer 2's 'Wall Connector weakest part' and 'wire chargers upstream of battery' are installer design points, not verified.
Sources
- IET — electrical.theiet.org/wiring-matters/years/2021/84-march-2021/island-mode-earthi…
- energylibrary.tesla.com — energylibrary.tesla.com/docs/Public/EnergyStorage/Powerwall/3/Datasheet/en-uk/Po…
Last checked: 24 September 2026