Do you need whole-home backup power?
Lots of people assume that a home battery system will continue to power your home during a power cut. However, most systems won't, at least not without paying significantly more for that capability.
This article looks at the data on UK power cuts, explains why backup power isn't standard on most battery systems, and helps you decide whether whole-home backup is worth the premium price.
How reliable is the UK grid?
Before deciding whether you need backup power, it's worth understanding how often you're likely to need it.
The UK has one of the most reliable electricity grids in the world, and it's been getting better. According to Ofgem, less than half of UK households experience a power cut in a year. When outages do occur, they typically last less than 95 minutes.
Most outages are weather-related - storms, lightning strikes, snow, and ice account for the majority of unplanned interruptions. Major blackouts affecting large areas, like the August 2019 event that cut power to over a million customers, are extremely rare. The government's National Risk Register estimates just a 1-5% chance of a significant regional or national grid failure over any five-year period.
For most UK households, power cuts are infrequent and brief. You might lose power for an hour or two once every few years. Whether that's a minor inconvenience or a serious concern depends entirely on your circumstances.
Why don't all battery systems provide backup?
This is where things get a bit technical - but it explains why whole-home backup capability costs extra and isn't included as standard.
The safety requirement: grid-tied systems must disconnect
Any battery system connected to the grid must, by law, disconnect when the grid fails. This isn't a flaw, it's a critical safety feature.
When there's a power cut, utility workers are sent out to repair the fault. They work on the assumption that the power lines they're touching are dead. If your battery system were feeding electricity back into the grid during an outage, it could electrocute someone trying to restore your power. The technical term for this is "anti-islanding protection," and it's mandatory for all grid-connected systems in the UK.
So without additional hardware, your battery will sit there during an outage, unable to power your home, waiting for the grid to return before it can operate again.
What's needed for whole-home backup capability
To provide power during an outage, a battery system needs several additional components:
First, a transfer switch or gateway. This device monitors the grid connection and, when it detects an outage, automatically isolates your home's electrical system from the grid. This isolation is what makes it safe for your battery to power your home, because you're no longer connected to the external power system.
Second, islanding capability. Your inverter needs to be able to create its own stable electrical supply, independent of the grid's frequency and voltage. During normal operation, grid-tied inverters synchronise with the grid. During an outage, a backup-capable inverter must generate its own reference signal to keep your home's electricity stable.
Third, sufficient inverter capacity. Your inverter needs to handle whatever loads you might run simultaneously. If you switch on a kettle (3kW), an oven (2-3kW), and a few other appliances at once, a small inverter will simply trip out. Whole-home backup systems typically need inverters rated between 5 and 11kW continuous output.
Finally, intelligent battery management. The system needs to manage the transition smoothly, monitor remaining battery capacity, and potentially limit non-essential loads to preserve power for critical circuits.
Why this adds significant cost
These components aren’t cheap. A transfer switch or gateway adds £500-1,500 to the system cost. A higher-capacity inverter with islanding capability costs more than a grid-tied model. Installation is more complex, requiring additional wiring and potentially a new consumer unit configuration. And the whole system needs Distribution Network Operator (DNO) approval and more extensive testing and commissioning.
In total, backup capability typically adds £2,000-6,000 or more to a battery system's cost. That's why many systems designed primarily for energy storage and management don't include backup as standard. The manufacturers have made a deliberate choice: keep the core product affordable and let customers who specifically need backup pay for that capability.
Whole-home backup: what does it cost?
Let's look at what you'd pay for a system with full backup capability.
The Tesla Powerwall 3 is probably the best-known example of a backup-capable home battery. Fully installed in the UK, it typically costs around £8,500. For that, you get 13.5 kWh of storage capacity, an integrated hybrid inverter, and the Tesla Gateway, which provides automatic whole-home backup with seamless switchover during outages. When the grid fails, the Powerwall detects it, isolates your home, and keeps everything running. You might not even notice the lights flicker.
It's an impressive piece of technology. But it's also comes with a premium price compared to a battery system designed purely for energy arbitrage.
For comparison, the EquiVolt 15kWh system costs £2,999 with standard installation. It's designed to do one job extremely well: charge up on cheap electricity and discharge during expensive peak hours, saving you money every single day. But it won't power your whole house during an outage, because that's not what it's built for.
So the question becomes: is whole-home backup worth £5,500 extra?
Here's one way to think about it. If your system lasts 10 years, that's £550 per year for backup capability. The average UK household loses about 30 minutes of power per year. That works out to roughly £1100 per hour.
Is an hour without power once every couple of years worth more than £1000 to avoid? For some people, absolutely. For others, that money would deliver far more value invested elsewhere.
The middle ground: limited backup options
Whole-home backup isn't the only option. Some systems offer partial backup at a fraction of the cost - enough to keep essentials running without the complexity and expense of powering your entire house.
EquiVolt offers an optional Emergency Power Supply (EPS) socket for an additional £300. This is a single 13A socket hardwired directly to the inverter, which remains powered even when the grid is down. It won't run your oven or keep every light in the house on, but it will let you charge charge devices or boil a kettle for a cup of tea while you wait for the power to return.
For most UK households experiencing a 90-minute outage once every few years, an EPS socket covers the practical essentials. You can stay connected, make a hot drink, and wait out the outage. This approach makes sense if you want basic resilience without the premium price tag. It doesn't make sense if you have specific needs that require continuous full power: medical equipment, for example, or a home business where any downtime might cost you money.
System costs (£)
Beyond the numbers
Not every decision comes down to financial return. Some people choose to pay more for backup capability simply because they prefer to have it - and that's a reasonable choice.
Before deciding, it's worth asking yourself:
How does a 90-minute power cut affect your household?
Would the £5000+ cost difference deliver more value spent elsewhere?
Is the peace-of-mind that a backup provides worth it regardless?
There's no right or wrong answer. What matters is making the decision based on your situation and how much difference a full backup system would make to your quality of life.
What happens during an outage?
It might help to understand what each scenario looks like in practice.
Without any backup capability:
The grid fails. Your battery system detects the loss of grid voltage and immediately disconnects - this happens within milliseconds, as required for safety. Your home loses power just like your neighbours'. Your battery sits idle, waiting. When the grid returns (typically within an hour or two), your system reconnects, verifies the grid is stable, and resumes normal operation. Your battery starts working again as if nothing happened.
With whole-home backup:
The grid fails. Your system's transfer switch detects the outage and isolates your home from the grid within milliseconds. Your battery seamlessly takes over, and you might not even notice. Your home continues to run normally, powered entirely by stored energy. The system monitors battery levels and may intelligently limit non-essential loads if the outage continues for a long time. When the grid returns, the transfer switch reconnects your home to mains power, and the battery resumes its normal charging and discharging behaviour.
With an EPS socket only:
The grid fails. Your household loses power like your neighbours'. But the single EPS socket, hardwired to your inverter, remains powered from the battery. You can plug in your phone charger, keep your router running, or boil a kettle. The rest of the house stays dark until the grid returns. For most outages, this covers what actually matters - staying connected and comfortable - without the complexity or cost of whole-home backup.
Who needs whole-home backup?
Based on everything above, here's our assessment of who genuinely benefits from whole-home backup versus who probably doesn't.
Whole-home backup makes sense if:
You depend on powered medical or mobility equipment, such as a stair lift, that doesn’t have a backup supply of it’s own.
You live in a remote location with a historically unreliable grid connection, where outages happen more frequently and last longer than the national average.
You run a home business where any power interruption has significant financial consequences. For example, lost billable hours, missed deadlines, or damaged client relationships.
You have specific critical loads that absolutely must stay powered, whether that's a security system, a fish tank with expensive tropical fish, or server equipment.
Whole-home backup probably isn't necessary if:
You live in an urban or suburban area with a reliable grid connection and experience outages rarely.
A brief power cut would be inconvenient but not harmful - you'd light some candles, read a book, and wait it out.
You're primarily interested in saving money through energy management and would rather invest your budget where it delivers the clearest return.
You're on a tighter budget and would prefer to put the £5,500 difference toward other priorities.
The middle ground:
If you want basic continuity during outages - charging devices or making hot drinks - but don't need whole-home backup, a system with an EPS socket option gives you that at minimal extra cost.
Making your decision
The UK grid is reliable. Most households don't need whole-home backup - statistically, you're protecting against roughly 30 minutes of inconvenience per year. But some people will genuinely benefit from that protection, and others will value the peace of mind enough to justify the premium.
Neither choice is wrong. What matters is making the decision based on your actual circumstances and what features are valuable to you.
At EquiVolt, we've designed our systems primarily for energy arbitrage because that's where the clearest, most consistent financial benefit lies for most UK homes. We offer an optional EPS socket for those who want basic backup at minimal extra cost. For those who genuinely need whole-home backup capability, products like the Tesla Powerwall exist - and we'd much rather point you toward them than oversell you features you don't need.