Living in a village in rural South Derbyshire or towards the Derbyshire Dales is beautiful. But although power cuts might not be commonplace, homes supplied by overhead lines can be more exposed to wind, falling branches and other faults.
So, if the grid does go down, can you use your solar panels and battery to keep your home running?
Well, yes, but not automatically. Storing electricity isn’t the same as supplying backup power during an outage. Your overall system must be designed to do both.
At Electrical Innovations, we’re a family-run, MCS-certified solar installer serving homeowners across Derby and the Midlands. In this guide, we’ll explain how solar battery backup works, whether it can run your whole home, how long the stored energy could last and what to check when comparing systems.
Does a solar battery automatically work during a power cut?
Not always. Most home solar systems connect to the grid. When the grid goes down, a standard system shuts down. This prevents your home from sending electricity into the network while engineers may be repairing it. Your solar battery may shut down as well.
To keep supplying your home, the system needs a backup function, often called an Emergency Power Supply (EPS). In simple terms, the backup equipment detects the power cut, safely separates your home from the grid and allows the EPS to supply electricity from the battery.
Can a solar battery run the whole house during a power cut?
It can, provided the system is designed for whole-home backup. Your installer can set up your battery backup system to supply any of the following:
One dedicated backup socket
Selected circuits, such as your lights, fridge, internet router and heating controls
Most or all of your home
Even if you have a battery set up to power your whole home, there are still limits to what it can do. You don’t need to calculate these figures yourself. Your installer will do it for you. But these two ratings are important to know about:
Power, measured in kilowatts (kW): how much electricity the battery and inverter can supply at one time.
Capacity, measured in kilowatt-hours (kWh): how much energy the battery can store.
To put that into numbers, a standard 10kWh battery could support a steady 1,000-watt (1kW) load for about 10 hours. Increase the load to 2kW and the same supply would last about five hours.
In practice, those times will be slightly shorter. This is due to conversion losses (the small amount of energy lost as electricity moves through the system) plus the battery’s minimum charge level and changing household demand.
That’s why, for many homes, it’s usually more useful to use battery power to back up selected critical circuits, such as your central heating system, than trying to run everything.
Practical examples of what a 10 kWh battery can do
Ofgem estimates that a typical UK household uses around 6.8kWh of electricity a day. On paper, a fully charged battery with 10kWh of usable capacity therefore stores more than a typical local home uses in a day.
During a power cut, a fridge-freezer, router, television and laptop might create a relatively low combined load of around 500 watts. If that load remained constant, the battery could support it for up to 20 hours, in theory. Add a 2kW electric heater and the total load rises to 2.5kW, reducing the theoretical backup time to four hours.
An important factor here is the system’s continuous EPS output. This determines how much it can power at once. Many domestic systems with backup capability provide around 3kW to 6kW of continuous EPS output. For instance, a 3.68kW system could run your essentials and perhaps a 3kW kettle if little else were switched on, but it couldn’t support a 9kW electric shower. A power cut probably isn’t the time for a long shower anyway.
Will solar panels recharge the battery during a power cut?
Yes, provided the solar panels have been included in the backup design. In a compatible system, they can power your home during daylight and send any surplus electricity to the battery.
Naturally, solar output still depends on the time of day, season, weather and shading. If the battery fills while demand is low, the system may reduce or pause generation. It can’t send electricity to the grid during a power cut.
How can you make battery backup last longer?
Some systems let you reserve part of the battery’s charge for emergencies. A higher reserve gives you more backup energy but leaves less available for reducing your bills on normal days.
If the power goes off, use your monitoring app to check the remaining charge and see how much electricity your home is using. Avoid charging an electric vehicle or using an oven, tumble dryer or other high-demand appliance unless your system was designed for it. These appliances demand a lot of power, and just one can use the same energy as several essentials.
Equipment that must never lose power may need its own uninterruptible power supply, as a home battery doesn’t guarantee a seamless changeover.
What should you ask about solar battery backup?
You shouldn’t have to work this out from a product sheet. Before accepting a quote, ask:
Does the price include an EPS or other backup arrangement, or only battery storage?
Which sockets or circuits will it supply during a power cut?
What is its continuous output in backup mode, and can it handle brief startup surges?
Will the solar panels operate and recharge the battery while the grid is down?
How does the changeover work, and will you notice an interruption?
Can you set aside a backup reserve in the app?
If you have more questions about how a solar battery is set up to supply electricity during a power cut, get in touch with our team at Electrical Innovations. We’ll help you design a solar battery storage system around your electricity use and plans for a power cut. We’ll explain the specifications, show you what the system can and can’t run and check compatibility before installation.
Contact us today to discuss the level of backup that would suit your home.
