What Happens During a Power Cut & How Backup Power Works
Backup power from solar battery systems is not always guaranteed during a power cut.
Many homeowners assume that solar panels and battery storage automatically provide backup power, but this depends entirely on system design and installed equipment.
In this guide, we explain how backup power works, why most solar systems shut down, and what is needed to keep your home running during a blackout.
Learn more about our solar PV panels and battery storage systems.
One of the most common questions we receive from homeowners considering battery storage is:
“If there’s a power cut, will my solar panels and battery keep my house running?”
Why Solar Systems Do Not Provide Backup Power During a Power Cut
Standard grid-connected solar systems are designed to shut down automatically when the electricity network fails. This is called anti-islanding protection.
This safety requirement exists to protect engineers working on the grid and is mandated under UK standards G98 and G99.
Key takeaway:
Even if your solar panels are generating power and your battery is full, your system will shut down without backup equipment.
- Sunlight does NOT guarantee power during outages
- Batteries alone do NOT guarantee backup
- Grid-tied systems are designed to shut down for safety
What Is a Solar Battery Backup System?
A solar battery backup system allows your home to continue running during a power cut by disconnecting from the grid and using stored energy.
This creates a self-sufficient system known as:
- Emergency Power Supply (EPS)
- Island Mode
- Backup Mode
- Off-Grid Mode
In simple terms:
Your home temporarily becomes independent from the grid during a power outage.
What Equipment Is Needed for Backup Power?
A battery alone is not enough. A proper backup system requires multiple components working together.
Hybrid / Backup-Capable Inverter
- Supports EPS (Emergency Power Supply)
- Enables island mode operation
- Manages solar + battery switching
Gateway / Automatic Transfer Switch (ATS)
- Detects grid failure
- Disconnects home from grid
- Prevents back-feeding electricity
Independent Earthing System (UK Critical Requirement)
- Earth rod (earth electrode)
- Earthing changeover system
- Maintains safety in island mode
Important UK safety note:
When the grid disconnects, the property loses its utility earth connection and must switch to a local earth rod system.
Essential Loads Consumer Unit (Optional)
- Lighting circuits
- Fridge/freezer
- Internet router
- Heating controls
Cost-saving tip:
Most homeowners choose essential loads backup instead of full house backup to maximise battery duration.
How Grid Isolation Works
The gateway continuously monitors the grid supply. When a power cut is detected, it disconnects your home and allows the battery to take over safely.- Prevents electricity feeding back into the grid
- Enables safe island mode operation
- Keeps essential circuits running
Solar systems must comply with UK grid connection standards set out under G98 and G99 regulations, which ensure safe disconnection during a power cut.
How Fast Does Backup Power Switch Over?
When the grid fails, the system automatically switches to battery power.
Typical switch times range from 20 milliseconds to 2 seconds.
- Most appliances continue running normally
- Some sensitive devices may briefly reboot
Sensitive devices include:
- Broadband routers
- Desktop computers
- CCTV systems
- Home servers
UPS vs Solar Battery Backup: What’s the Difference?
Many homeowners confuse a solar battery backup system with an Uninterruptible Power Supply (UPS). While both provide backup power, they serve completely different purposes.
| Feature | Solar Battery Backup (EPS) | Dedicated UPS |
|---|---|---|
| Primary Purpose | Powers household circuits during outages | Keeps individual devices running |
| Typical Runtime | Hours or even days | Minutes to a few hours |
| Switch Time | 20ms to 2 seconds | Near-instant (0ms–10ms) |
| Power Source | Solar panels and battery storage | Internal battery |
| Best For | Lighting, refrigeration, heating controls | Routers, computers, servers |
| Long-Term Backup | Excellent | Limited |
Many homeowners choose to use both technologies together. The solar battery provides long-duration backup power for the home, while a small dedicated UPS protects sensitive electronics from brief interruptions during switch-over.
What Happens to the Battery Overnight?
Your battery gradually discharges overnight to power your home.
Most systems allow you to reserve a percentage for backup protection in case of outages.
- Smart tariff charging during off-peak hours
- Automatic energy management
- Backup reserve settings (10–30%)
Full House vs Essential Loads Backup
Essential Loads
Only key circuits are powered, improving battery duration and cost efficiency.
Full House Backup
Powers almost the entire home for maximum convenience during outages.
And the final Question: Is Battery Backup Worth It?
Backup systems add cost but significantly increase energy resilience and independence. For many homeowners, the main value is simple: peace of mind during a power cut.