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A guide to batteries for solar panels

A solar battery is a storage device for excess solar electricity

A solar-plus-storage system saves the average 3-bed house £582 per year

You’ll typically cut your carbon footprint by 7% with a solar battery

The cost of solar panels is coming down, but it’s still too high to waste half of the energy they generate, as the average household does.

A solar battery can store this electricity for you to use later on. This will help you be more energy independent, cut your carbon footprint by 7% on average, and save 30% more on your energy bills than you would with solar panels alone.

Here’s everything you need to do if you’re considering increasing your savings by adding a solar battery to your system.

To find out how much a new solar-plus-storage will cost you, simply fill in this free form, and our qualified installers will be in touch.

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What is a solar battery?

A solar battery is a device that allows you to store the excess electricity your solar panels generate, so you can use or sell this energy at a later time.

Unless you or the people you live with are at home and using electricity every minute of every day, you’ll have solar power that goes unused.

Typically, you’ll lose 50% of the electricity produced by your solar panels this way – but not when you have a solar battery.

a person in a dark jacket crossing their arms and smiling in front of a solar battery system

How does a solar battery work?

A solar battery works as an overflow storage unit.

When sunlight hits solar panels, they turn this natural resource into direct current (DC) electricity, before converting it into alternating current (AC) electricity that powers your home.

And when your home is fully powered, any excess solar energy will be rerouted to charge your battery, in much the same way you charge your phone.

a graphic showing the solar battery charging up from sunlight during the day, then powering the house by night

You can either get a lead acid battery or a lithium-ion model, which offers faster charging and a higher capacity.

After the sun goes down and your panels stop producing energy, it’ll be time for your solar battery to shine, by providing you with all the energy it’s gathered.

This will happen automatically, with your panels and battery seamlessly passing the baton between them, so you won’t need to worry about monitoring the system.

The sun’s time in the sky and the times you use energy at home don’t line up perfectly, and a battery solves this problem.

Bear in mind that you’ll need to make sure your system includes a solar charge controller to prevent overcharging and the current from flowing backwards.

How much does a solar battery cost?

An 8 kWh solar battery typically costs £4,500 for a three-bedroom house, though the exact amount depends on the model, the brand, and the materials it’s made from.

Batteries also require little to no maintenance, so your initial outlay will probably be the last time you have to spend money on them.

You’ll usually pay 10% to 20% more for a solar battery that can take you completely off-grid, which typically works out to around £5,000.

For more information on how much you can expect to pay, read our guide to solar battery costs.

And take a look at our comparison article to see the best solar batteries available this year.

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How much money do you save with a solar battery?

The average three-bedroom household will save £582 per year with a solar battery.

This is 30% more money than the same household would save with solar panels alone.

However, the initial cost of a solar battery – £4,500, on average – means you’ll end up saving less than you would if you just bought solar panels.

For more information, please read our guide, Are Solar Batteries Worth It in the UK?

Want to get a better idea of what it’s like to own a set of solar panels? Check out our case study with Shirley Ward – a 73-year-old retired office worker, based in North Yorkshire. 

Shirley has a 2.4 kW solar array and a Solax battery, and managed to break even on the system in 10 years. Despite electricity prices increasing around the world, Shirley’s panels have brought her energy bills down to £15 a month, instead of £50. 

Check out the full interview with Shirley to learn more about solar panels.

What size solar battery do you need?

The average three-bedroom household needs an 8 kWh solar battery.

If you live in a house with one or two bedrooms, you’ll likely need a battery with 2-4 kWh of capacity.

And if your household has four or five bedrooms, start by looking at 9.5 kWh solar batteries.

For more information, check out our guide, What Size Solar Battery Do You Need?

How long does a solar battery last?

Solar batteries usually last for 15 years and come with a 10-year warranty – though their capacity might decline in their later years.

They have to perform repetitive, daily charging and draining cycles, and just like your phone’s battery, this eventually wears them out.

If you buy a top-quality model, the chances are higher that it’ll last beyond its 10-year warranty.

What is ‘Depth of Discharge?’

Depth of Discharge (DoD) is a measure of the maximum amount of a battery’s capacity you should ideally use.

For example, if you own a battery with total capacity of 10 kWh and a maximum DoD of 85%, you should only use a maximum of 8.5 kWh. Although you may be able to use more, if you repeatedly do so it’ll wear away the battery much more quickly.

Thankfully, technological advances are continually increasing the lifespan and performance of solar batteries, which means they’ll only improve.

Solar battery cost calculator

The pros and cons of a solar battery

It allows you to save £592 per yearIt costs £4,500 on average
You’ll reduce your carbon footprint by an extra 15%You’ll have to set some space aside for it
You can be more energy independent, so energy price hikes will affect you less
You may have your own energy supply in a power cut happens

What type of solar battery should I buy?

Once you’ve decided to buy a solar battery, you need to decide on its chemical composition and electricity current.

It’s wise to speak to multiple professional installers about this before you make a decision, but we’ve explained the basics below.

Lead acid or lithium-ion?

Lead acid batteries come in two varieties: flooded or sealed.

The typical lifespan of a flooded lead acid battery is a bit longer than a sealed lead acid battery (5-7 years vs 3-5 years), but it also requires more maintenance.

If you’re looking for the cheapest type of solar energy storage system, the flooded lead acid battery is best.

Lithium-ion batteries are the most expensive type of solar battery, but they’re very compact (about half the size of a lead acid battery), and have a typical lifespan of more than 10 years.

Furthermore, lithium-ion batteries have a higher efficiency, a faster charging ability, and much more capacity. You’ll definitely get value for money from one of these.

AC or DC?

While the Aussie rock band went for a bit of both, you have to choose one or the other. If you’re installing a solar battery at the same time as solar panels, it’s best to opt for a DC (direct current) battery, which connects directly to the panels and doesn’t require an additional inverter.

However, if you already have solar panels, you’ll need an AC (alternating current) battery. This is much easier to retrofit to an existing system, as it’s connected via the electricity meter, but it also requires an additional inverter.

You should always seek professional help when choosing and installing a solar battery storage system. Make sure your installer is signed up to the Renewable Energy Consumer Code (RECC) as this ensures that they’re signed up to a high standard of conduct, and covers you should you need to make a complaint or claim.

What’s the best solar battery on the market?

The Powervault 3 is the best solar battery on the market at the moment.

The 4 kWh model costs just £3,229, comes with a 10-year warranty, and is the smallest top-tier battery available right now – so it won’t take up much space.

You can also monitor how your battery is doing online. All in all, British company Powervault has knocked it for six with this machine.

If you want to see the other best models according to our in-depth analysis, check out our guide to the best solar batteries.

Retrofitting a solar battery to an existing solar PV system

If you already own solar panels at home, that’s not a problem; you can easily retrofit a solar battery to an existing solar PV system.

When the solar battery is installed, it must be either AC-coupled or DC-coupled, and this depends on the type of inverter that your solar panels are using.

If your PV system has a microinverter, then the solar battery will have to be AC-coupled. This is the cheaper of the two options (as you won’t need to replace the inverter), and the installation process is fairly quick.

However, this solution does lead to additional energy loss over time, because it involves converting the solar-generated electricity twice.

On the other hand, if you don’t have a microinverter, then you’ll need to replace your existing inverter with one that can work with your solar battery.

This is more expensive up front (your whole system will need to be rewired), but it only involves converting the solar-generated electricity once, so there is less energy loss in the long term.

To find out how much it will cost you to retrofit a solar battery to your solar PV system, simply fill in this quick form, and our professional installers will be in touch.

They can help you work out exactly what size battery you need and whether it needs to be AC-coupled or DC-coupled.

Next steps

The next step is to find a solar-plus-storage network that suits your home perfectly – especially considering 65% of people told our latest National Home Energy Survey that they’d buy a house with solar panels.

We’re entering a new, green era, and you can reap all the rewards.

Just complete this short form, and you can get free quotes from qualified installers. You’ll be taking advantage of everything solar batteries have to offer in no time.

Frequently asked questions

Lithium-ion batteries are the best choice for a home with solar panels.

They’re more efficient, faster at charging up, and come with more capacity than lead acid batteries, as well as lasting for 10-15 years – about twice as long.

They’re also more expensive, but they’re worth it.

It’s usually not worth adding a battery to your solar panel system.

A solar battery will typically save you an extra 30% on your energy bills, but you’ll need two batteries over the course of your panels’ lifespan.

That adds up to £9,000 to the costs for the average three-bedroom house – and the great majority of homes won’t save enough to break even on this amount.

A 5 kWh battery will typically last between 10 and 15 years.

Your battery’s exact lifespan will depend on how many cycles it can endure and its cycle duration.

Most will be able to go through 5,000 cycles before they start significantly deteriorating – which puts them squarely in the range of 10-15 years.

A 10 kWh battery can power your house for 30 hours, on average.

A typical three-bedroom household uses 7.9 kWh per day, meaning you’ll be covered for a day and six hours if the grid fails – or even longer, if you’re careful.

Make sure the engineer who sets up your battery installs it so you can use it during a power cut, and you’ll be set.

Written by:
josh jackman
Josh has written about eco-friendly home improvements and climate change for the past four years. His work has been displayed on the front page of the Financial Times, he's been interviewed by BBC One's Rip-Off Britain, and he regularly features in The Telegraph and on BBC Radio.
Reviewed by:
Tamara Birch, senior writer, The Eco Experts
Tamara has written about environmental topics for more than four years. This includes advising small business owners on cost-effective ways, like solar panels and energy-efficient products to help them become more sustainable. 
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