What is solar panel battery storage and how does it work? – UK Times

If you’re considering installing solar panels at home, you’ve likely come across solar batteries, which are large lithium-ion packs that store excess power for when the sun isn’t shining. Using the same technology found in electric vehicles, these batteries let you use stored solar energy at night, charge from the grid during off-peak hours, and even provide backup power during outages.

Adding a battery can significantly improve efficiency and long-term savings, especially when paired with the best solar panels. However, the extra investment means you’ll need to factor in the cost of solar panels and installation to see whether the upgrade is worthwhile. For help weighing up your return on investment, see our guide on are solar panels worth it, or check current solar panel grants that can help reduce the upfront expense.

Get a quote for solar panels on your home

Use our comparison tool to get free quotes from leading solar panel installers across the UK.

How much do solar batteries cost?

Solar batteries typically cost between £2,500 and £6,000, depending on size and brand, with installation adding around £3,000 more if fitted separately. For most homeowners, combining installation with new panels is the most cost-effective option..

Lloyd Greenfield, founder of Glow Green, a solar panel fitter, said: “Batteries are definitely suited to people who typically use their energy in the evening. So if you’re a high daytime consumer, it might be a faster payback, actually, without the battery.”

Here, we make use of our connections in the solar power market to answer key questions and do the maths on whether batteries are a good choice for you.

How do solar batteries work?

Like a typical battery, solar batteries can be charged and discharged. In your home, they can be charged by solar energy, effectively for free, or from cheap overnight electricity if your tariff allows this. An inverter then converts the lower voltage of the battery to the 230v your home ring main uses.

You can get a huge range of capacities, but they typically range from about 5 kilowatt hour (kwh) to about 14kwh. You can also add capacity and use two or more at once.

How long does a solar battery last?

They are typically guaranteed for 10 years but can last for much longer.

Is solar panel battery storage worth it?

Here is the tricky bit. It would be very useful to be able to work out how much it costs to store energy in the battery.

Just like any rechargeable battery, a solar battery has a finite life, largely down to how many times you can charge and discharge it.

So in theory, you can work out how many pence it costs to store and then use a kilowatt hour (kwh) of energy.

Once you have that, you’ll be able to see if it is worth it compared with power from your energy company, which from April will cost 27 pence under the price cap. For instance, if you could store a kwh of power for less than 20 pence, then storing sun power would make sense since power from the grid costs 7 pence more.

If you could store it for even less, then buying super-cheap overnight electricity on some tariffs for as little as 7.5 pence could make sense too, so long as the storage price plus 7.5 pence is less than the grid price.

But as we are about to see, this figure is not simple to arrive at, and even if it were, there are other things to think about.

To make things more difficult, batteries don’t just stop working after a certain number of cycles; instead they lose more and more of their ability to store energy.

Let’s do the maths anyway

With all of this in mind, let’s take a real-world example to get a figure, even if it isn’t set in stone, since it will give a rough indication of whether a battery is worth it.

Duracell’s Dura5 storage system is guaranteed for 10 years and 10,000 cycles. If we assume we can discharge the 5.12kwh battery by 90 per cent, that gives us 4.608kwh of useable charge per cycle. The unit can be bought for £2,280 including VAT but not including fitting.

For 10,000 cycles of 4.608kwh, a total of 46,080kwh of power charged and drained through its guaranteed life. If we take the price and divide it by this lifetime storage figure, we get a price of five pence per stored kilowatt hour.

This is a good price, because it means stored sunlight – which is free to generate – only costs 5 pence per kilowatt hour, less than a quarter of the current grid price. If you can buy power overnight cheaply – some tariffs offer prices as low as 7.5 pence – then buying and storing the power would cost just 12.5 pence per unit, way below daytime grid prices.

Cons of solar battery storage

Wait! There are quite a few caveats. If the battery lasts longer than 10,000 cycles, the price per use is even lower. But towards the end of the life of the battery, it will keep less charge, meaning the price will creep up.

The price also doesn’t include fitting, which could double the cost, and bring about a final figure of about 10 pence.

Then, there is yet another thing to think about – with most batteries the guarantee is in years, not cycles. So, will you use it enough in 10 years to keep the price per kilowatt down?

Less usage should make the battery last longer, in theory, but with no guarantee after 10 years, that might prove cold comfort.

In real life, batteries may last longer than their warranties, just like any consumer product. It’s just that you aren’t financially protected if they don’t.

Mr Greenfield said: “We think batteries would last, typically, circa 15 years, maybe 20, depending on quality.”

The average home uses about 2,700kwh of energy per year, and so 27,000kwh in 10 years. That’s just under half the 46,080kwh in our example, pushing up the price per stored kwh if the battery dies on its 10th birthday.

If, however, you use a heat pump for central heating, your usage will be a lot higher, and it could make the battery viable again.

And then, of course, there’s yet another complication. How much can you get for selling the solar energy you generate back to the grid? You can get up to 15 pence from many companies, which could make storing it less attractive.

If you can sell the energy for 15 pence and buy it back when you need it for 27 pence – April’s energy cap charge – then you may not deem the difference as worth it.

If all this is making your head spin, and you’d be getting the device to try and save money, then a solar battery might not be for you.

But if you found all that maths a fun exercise and you’ve found a deal where you can store cheap sunlight and use it at night at a lower price than you buy from a utility company, then it could be a good option.

What size solar battery do I need?

The right solar battery size depends on how much electricity your household uses and how much excess energy your solar panels generate. Most UK homes use between 8–10kWh of electricity per day, so a battery with a usable capacity of 4–10kWh is often sufficient to store daytime energy for evening use.

If you have a larger home, EV charger, or high nighttime consumption (for example, running heating or appliances overnight), a 10–15kWh system may be more suitable. Smaller homes or those on lower budgets might opt for a 3–5kWh battery to cover key appliances and lighting.

Remember that bigger isn’t always better. A battery that’s too large may never fully charge, reducing efficiency and increasing payback time. The ideal system balances capacity, cost, and daily consumption, so you store enough power to cover your needs without overspending on unused storage.

How are they installed?

Solar batteries are typically bolted to a wall inside or outside your home. They need to be kept cool and accessible in an emergency.

How to find the right solar battery installer

Choosing a qualified installer is essential to ensure your solar battery system performs safely and efficiently. Look for MCS-certified installers (Microgeneration Certification Scheme) — this accreditation guarantees that both the installation and equipment meet UK industry standards.

It’s also worth checking whether your installer is a member of the Renewable Energy Consumer Code (RECC) or the Home Insulation & Energy Systems Quality Assured Contractors Scheme (HIES). These organisations offer extra consumer protection, including dispute resolution and deposit insurance.

Before signing a contract, compare at least three quotes. Reputable installers will:

Finally, read customer reviews on Trustpilot or Checkatrade, and ask about post-installation support. A trustworthy installer will be transparent about performance monitoring and aftercare, helping you get the most from your investment.

Should I invest in a solar battery?

If you don’t mind taking a bit of a gamble that the battery will outlast its guarantee, and you use a lot of electricity, perhaps through a heat pump or electric car, or both, and you have a large solar array to feed it, then a battery could be for you.

This is because you will make the most of it in the guarantee period, charging and discharging it a lot, and getting a cheap price per stored unit of energy.

Mr Greenfield, of Glow Green, said: “If you’re a working, busy professional, and you’re out the house all day, and then you when you get in the evening, that’s when you have a high consumption, whether it’s plugging in an EV car or running lots of electrical appliances or lots of washing and tumble dryers, and high consumption appliances going in the evening, you’d definitely be suited for a battery.”

If you have lower usage or a smaller solar array, you may want to be more cautious.

Either way, you will need to ensure the battery is properly set up to soak up cheap sunshine during the day, and maybe cheap grid power at night, to avoid costlier energy.