What Happens in a Power Cut?
What equipment do you need for power during a blackout? This guide is a high-level overview to help you understand your options and have informed conversations with your installer.
Important Safety Notice — Always have a qualified electrician review and implement any work associated with running a system in island / off-grid mode.
Why Doesn't My Solar Just Keep Running?
In the UK, grid-connected inverters are specifically designed to shut down when there is no grid power. This is a deliberate safety mechanism to protect the grid infrastructure and the engineers working on the lines during an outage.
This means your system cannot simply 'take over' from the grid automatically in a standard installation. For your system to continue supplying power during an outage, it needs to be configured to operate in Island Mode — completely isolated from the grid so that no power can flow back into the street network.
How Does the Switchover Work?
There are two main approaches. Both disconnect your home from the grid and power your appliances from your batteries:
| Manual Changeover | Automatic Changeover (UPS) | |
|---|---|---|
| How it works | You manually flip a switch to disconnect the grid and enable battery supply | System detects the outage and switches automatically — usually with no noticeable interruption |
| Trade-off | Causes a brief power interruption while switching | Often called an Uninterruptible Power Supply (UPS) |
Key Design Requirements
Regardless of which option you choose, any island-mode setup must address three areas:
- Earthing — your entire system needs a correctly designed earth when operating off-grid. This is a critical safety requirement.
- Inverter power — your inverter must have enough capacity to handle the peak load of all appliances you intend to run at the same time.
- Battery capacity — your batteries must be able to sustain supply for the expected duration of the outage.
Your Options
Option 1 — Single Emergency Socket (EPS)
The simplest and most affordable route. Many modern inverters include built-in Emergency Power Supply (EPS) functionality. A qualified electrician can wire up a dedicated socket that remains live from your batteries when the grid goes down.
During an outage you can plug an extension lead into this socket and run essentials — phone chargers, router, a lamp, a small fridge.
Good for: Easy to implement if your inverter supports EPS. Low cost. Gives you a controlled, low-drain emergency supply that you remain in full control of.
Option 2 — Selected Household Circuits
An extension of the EPS approach — this powers a defined set of circuits within your home. Some households colour-code these sockets (e.g. red outlets) so it is clear which remain energised during an outage.
This requires changes to your main household wiring and a more detailed earthing design. Battery drain will be higher, so careful planning of which circuits to include is important.
To consider: More complex and costly than a single socket. Requires careful earthing design and modifications to your consumer unit wiring.
Option 3 — Whole House Failover
A changeover switch (manual or automatic) disconnects the entire house from the grid and energises it from your inverter and batteries. This gives you full backup power — but at significantly higher cost and complexity.
A whole-house setup demands a higher-rated inverter, substantial battery storage, and comprehensive earthing design. Automatic failover also carries the risk of powering an unplanned load (e.g. a tumble dryer left switched on) and rapidly draining your batteries.
Author's preference: Manual cutover of selected circuits or a single emergency socket. This keeps you in control of what runs during an outage, making your battery last considerably longer.
Option 4 — EV Vehicle-to-Load (V2L)
Don't overlook the EV on your driveway. A growing number of electric vehicles support Vehicle-to-Load (V2L) capability, effectively turning the car into a large mobile battery that can power appliances directly.
If the grid goes down, this may already give you a ready-made emergency power source — with no additional installation required.
Solar Generation During an Outage
This guide focuses on batteries supplying power when the grid is down. It is worth noting that grid-connected solar inverters behave the same way — they also shut down during a grid outage by default.
If you want your solar panels to continue generating and charging your batteries during a power cut (rather than just running down what is already stored), that capability also needs to be specifically designed and configured as part of your island-mode setup. Raise this with your installer at the same time.
Summary Comparison
| Option | What It Covers | Cost | Complexity |
|---|---|---|---|
| Single EPS Socket | One dedicated emergency socket — plug appliances in | Low | Low |
| Selected Circuits | Defined ring of sockets stays live during outage | Medium | Medium |
| Whole House Failover | Full home supply from inverter & batteries | High | High |
| EV Vehicle-to-Load | EV battery powers appliances directly (if V2L supported) | None* | None* |
* Assuming you already own a V2L-capable electric vehicle.
Always consult a qualified electrician. Island-mode operation involves safety-critical earthing design and wiring changes. This guide is intended to help you understand your options and discuss them with an installer — never attempt to implement any of these changes without a qualified professional.
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