A Guide to Solar Batteries 2019

A solar battery will help you use up to 30% more of the energy your solar panels generate.

Check out the best solar batteries on the market, rated in terms of capacity, lifespan, power, and more.

To receive quotes for solar batteries, fill in the short form above and our professional installers will be in touch.


DISCLAIMER: Our partners no longer take appointments for homeowners looking to benefit from the Feed-in Tariff, which concluded on 31st March 2019



What happens to all the solar power that doesn’t get used?

Solar panels are genius pieces of technology, but you’re not getting the best out of them until you’ve united them with a solar battery. Solar batteries store up the electricity that your solar panels generate throughout the day, so it’s there for you to use when you get home.

Solar companies all over the world have realised the importance of “solar-plus-storage” systems, and every man and his dog is recommending that homeowners get their hands on one.

On this page, we’ll tell you everything you need to know about solar battery storage, including the best solar batteries on the market in 2019, and their typical costs.

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



cartoon solar battery with solar panel

What's in this guide to solar batteries?

Jump straight to a section by clicking on the links.



What is a solar battery?

A solar battery is an energy storage system that homeowners can connect to their solar panels. It is usually made from lead acid or lithium-ion, and can store up the electricity that your solar panels generate while you’re out during the day. Lithium-ion batteries are the best on the market, offering fast charging and high capacity.




How do they work?


When solar panels operate on their own, the majority of their efforts sadly go to waste. This is because solar energy can be used only as and when it is available.

93% of homeowners we surveyed think that solar batteries are a good investment*

*Based on a survey we conducted in January 2018 of 310 UK homeowners with a solar battery storage system.

The peak time for solar power generation is in the middle of the day, when the sun is at its highest point – but that’s also when you’re not at home. You’re unable to use it, and the electricity just goes into the grid. Then, once you’re back home in the evening, your panels have clocked off for the day; the sun’s down, and you have to pay for the power you use.

Fortunately, teamwork makes the dream work. Enter: the solar battery. Chuck one of these bad boys into the mix, and you’ll be getting way more out of your solar panels. All the unused electricity that’s produced throughout the day goes into your solar battery for safekeeping, ready for you to use whenever you need it. When there’s little or no daylight (or there’s a power cut), you can turn to your solar battery for assistance.

Most solar batteries aren’t designed to make you entirely independent from the National Grid, but they can make a huge difference to your energy bills – not to mention your carbon footprint. However, some models – such as Tesla’s 13.5 kWh Powerwall 2.0 – are big enough to keep you off-grid entirely, if you so wish.


Already own a solar PV system? No worries. You can easily retrofit a solar battery to an existing set of solar panels. Simply fill out this form to start receiving solar-battery-only quotes today.


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How much does a solar battery cost?

The cost of a solar battery generally ranges from £2,000 to £6,000, depending on variables such as the battery’s capacity, material, lifespan, and installation process. Obviously, the more electricity a solar battery can store, the more it’s likely to cost.

A Which? survey found that 25% of members paid under £3,000 for their solar battery storage system, while 41% of members paid between £4,000 and £7,000.

You’ll normally find better deals if you buy a solar battery and a solar panel system at the same time, but that doesn’t mean you can’t find a good value solar battery as a solo purchase.


Are they a good investment?

Solar batteries can seriously increase the money-saving potential of your solar panels. For example, according to E.ON, with a 9.6kWh solar battery (and 12 x 315W panels) in central England, you could use up to 30% more of the energy your solar panels generate, and decrease your annual energy bill by up to £560.

So long as you buy a reliable solar battery (or batteries) with a decent lifespan (like the models listed above), your solar-plus-storage system will do a lot more with the sunshine than lone solar panels.

To receive free, tailored quotes for solar panels and solar batteries, simply fill in this short form and our professional installers will get right back to you.


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Pros and cons of solar energy storage

Pros

More solar power. With a solar battery in place, you’ll use more of the electricity that your solar panels create. This means you’ll be using less of the National Grid’s power supply, and reducing your carbon footprint even further

Energy bill savings. Increased solar power usage also means lower energy bills - Increased solar power usage also means lower energy bills - just take a look at the example from E.ON in the ‘Are they a good investment?’ section above. In a survey of 119 solar battery owners by Which? from May 2019, almost 75% of people said that their battery was helping them save money on electricity ‘to a great extent’ or ‘to some extent’.

Backup power supply. When a power cut strikes, your smug little box of energy will suddenly become very useful. Some batteries are programmed to switch off when there’s a power cut (due to risk of electrocution), but certain models (such as the Tesla Powerwall 2.0) are built to operate independently of whatever nonsense the grid gets up to.

Increased independence. Energy companies are always hiking up their prices and getting more money out of their customers. Buy a solar battery, and that’s one big step towards off-grid self-sufficiency.



solar panels on a tree-covered hill

Cons

Expensive. With most solar batteries costing somewhere between £2,000 and £6,000, it’s not a cheap purchase – but for most people, the benefits outweigh the initial expense.

Demands on your space. Some high-capacity solar batteries are about the size of a small kitchen fridge, so be ready to give over some room for one of these things – especially if the model can only be located indoors.


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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.


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 for you.

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, they 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.

If, on the other hand, you already have solar panels, you’ll need an AC (alternating current) battery. These are much easier to retrofit to an existing system, as it is 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.


Did you know? The outermost atmospheric layer of the sun is known as the ‘corona’, just like the Mexican beer.Simply fill out this form to start receiving free solar battery quotes today.


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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.


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The best solar batteries in 2019

We put our research caps on and investigated the solar battery market, creating a list of the six best solar batteries for your home. Check out the table below for our top picks (note: all of these batteries are lithium-ion, as lead acid is on the way out). But firstly, what was our criteria?

Capacity

The size of a battery is obviously a big factor. It’s measured in kilowatt hours (kWh), and the market standard generally ranges from 1 to 13 kWh. However, a battery’s ‘total capacity’ can be misleading, as you can only ever use a certain percentage of a battery’s energy before having to recharge, otherwise you’ll damage it. That’s why ‘useable capacity’ is just as important, and another factor we’ve considered.

Power

Although commonly confused with ‘capacity’, ‘power’ is a different thing entirely. ‘Power’ tells you how much energy a battery can provide at any given moment, and it’s measured in kilowatts (kW). The higher a battery’s power rating, the more appliances it can power simultaneously.

However, if you purchase a high-capacity battery with a low power rating, your battery will have a lot of juice, but it won’t be able to use much of it in one go. A standard solar battery’s power rating typically ranges from 2-5kW.



engineer on solar panel roof

Depth of discharge

As previously mentioned, if you continually use a battery’s full capacity before recharging it then you’ll gradually damage its insides. A battery’s ‘depth of discharge’ (DoD) dictates how much of the battery’s capacity should be used before recharging it.

For example, if you have a 10kWh solar battery with an 80% DoD, you should only use it for 8kWh of energy before allowing it to recharge. Most modern lithium-ion batteries come with a DoD of 90-95%.

Warranty

Naturally, you want your solar battery to be with you for the longest haul possible. Every battery comes with a guaranteed number of ‘cycles’, with one ‘cycle’ being one complete discharge and one complete recharge.

Not that you’ll ever use your battery in that way - instead, you’re likely to use about 50% and then charge it back up to 100%, which would count as half a cycle. Every solar battery also comes with a product warranty, which is usually 10 years.

Bearing these factors in mind, here are the eight top-performing solar batteries for residential solar PV systems. To find out their typical prices, head to the section below, where we go into a bit more detail.


Model

Storage capacity

Useable storage capacity

Product warranty

Cycles warrantied

Weight

Max power output

Powervault 3
4.1-20.5kWh
4.1-20.5kWh
10 years
>6,000
129-329kg
3.5-5.5kW
Duracell Energy Bank
3.3kWh
3kWh
10 years
n/a
96kg
2kW
Tesla Powerwall 2.0
14kWh
13.5kWh
10 years
Unlimited
125kg
5kW
Sonnen Batterie eco 9.43
5-15kWh
4.5-13.5kWh
10 years
10,000
108-200kg
2.5-3.3kW
LG Chem RESU10
3.3-10kWh
2.9-8.8kWh
10 years
Unlimited
31-75kg
3-5kW
SolaX Power
3.3-6.5kWh
3.1-6.2kWh
10 years
3,000
26-44kg
Up to 2.5kW
Moixa Smart Battery
2-3kWh
1.6-2.4kWh
10 years
10,000
40-49kg
Up to 0.46kW
Enphase AC Battery
1.2kWh
1.2kWh
10 years
7,300
25kg
0.26kW


Information updated in July 2019.


We've selected a specific size of battery from each of the seven brands and taken a closer look…

Powervault 3

One of the best for capacity

Founded by an entrepreneurial bunch in 2012, the London-based Powervault has seriously mastered the design of high-performance, high-capacity solar batteries. Its ‘Powervault 3’ battery comes in five different capacities (starting from 4.1kWh), reaching up to the dizzying heights of 20.5kWh. If you want to get yourself off-grid forever, Powervault will sort you out.

The Powervault 3 also comes with two DC-inputs, enabling you to connect it directly to your solar panels. This means that, if and when your existing inverter fails, you won’t need to buy a replacement. That’s basically saving you about £1,000.

What’s more, you can now buy a new Powervault 3 8.2kWh alongside EDF Energy and get up to £2,060 off the cost when you sign up with EDF Energy's Grid Services. If you buy the 4.1kWh model with EDF Energy, you’ll receive a £1,560 discount.

Typical price: £4,999

Dimensions: 1,270mm x 1,000mm x 250mm

Weight: 179kg

Storage capacity: 8.2kWh

Useable capacity: 8.2kWh

Depth of discharge: 100%

Max power output: 5.5kW

Installation: Standing, indoor only

Limited warranty: 10 years, or at least 6,000 cycles


Tesla Powerwall 2.0

One of the best for capacity

The impressively named ‘Powerwall’ is Tesla’s answer to solar power storage. Quite fabulously, the Powerwall is a futuristic-looking white box that operates almost entirely without noise. It can be installed quickly, requires little to no maintenance, and operates with liquid thermal control.

What’s more, if you get hooked on solar power storage, you can stack up to 10 Tesla Powerwalls on top of each other. Unlike most solar batteries on the market, the Powerwall also comes with emergency backup capabilities (useful in the event of a power cut).

Typical price: £7,450

Dimensions: 1,150mm x 755mm x 147mm

Weight: 114kg

Storage capacity: 14kWh

Useable capacity: 13.5kWh

Depth of discharge: 95%

Max power output: 5.0kW

Installation: Standing or wall-mounted, indoor or outdoor

Limited warranty: 10 years, or unlimited cycles


Sonnen Batterie eco 9.43

One of the best for capacity

Another behemoth of the solar battery market, the Sonnen Batterie eco is a sleek, German-made storage solution of the highest quality. It comes with 11.25kWh of useable capacity, and - similar to the Powerwall - it has backup capabilities to keep you ticking along during a power cut.

Sonnen has completed over 40,000 installations to date, and its eco model is very easy to plug in to a residential solar panel. The eco also arrives “smart-home-ready” with intelligent accessories.

Typical price: £8,060

Dimensions: 1,186mm x 670mm x 230mm

Weight: 177kg

Storage capacity: 12.5kWh

Useable capacity: 11.25kWh

Depth of discharge: 90%

Max power output: 3.3kW

Installation: Wall-mounted, indoor only

Limited warranty: 10 years, or 10,000 cycles


Did you know? You can add a solar battery to an existing solar PV system. Simply fill out this form to start receiving free solar battery quotes today.


LG Chem RESU

One of the best mid-range batteries

LG is a big name in the home electronics and solar industries, and its Chem RESU10 solar battery is a fine bit of kit. If you’re after something that’s mid-range in terms of price, and offers sufficient capability in all categories, the Chem RESU10 is ideal.

Plus, the battery itself is splendidly shiny and metallic, meaning you can store your electricity and be stylish at the same time.

Typical price: £6,100

Dimensions: 452mm x 483mm x 227mm

Weight: 75kg

Storage capacity: 9.8kWh

Useable capacity: 8.8kWh

Depth of discharge: 95%

Max power output: 5.0kW

Installation: Standing or wall-mounted, indoor or outdoor

Limited warranty: 10 years, or unlimited cycles


SolaX Power

One of the best mid-range batteries

SolaX’s Power solar battery is another strong candidate if you’re looking for a reliable jack-of-all-trades. It comes with 6.2kWh of useable capacity, a 6,000-cycle guarantee, and a nice and manageable weight of 44kg. It ultimately offers a bit less than LG’s Chem RESU10 in every sense, but it also comes with a slightly smaller price tag, so you get what you pay for.

The SolaX Power also comes with a very easy ‘plug and play’ installation process, which is a big time-saver (and money-saver) when it comes to installing the battery.

Typical price: £5,706

Dimensions: 586.6mm x 445mm x 110mm

Weight: 44kg

Storage capacity: 6.5kWh

Useable capacity: 6.2kWh

Depth of discharge: 95%

Max power output: 2.0kW

Installation: Standing, indoor only

Limited warranty: 10 years, or 6,000 cycles


Moixa Smart Battery

The best for 24-hour charging

The Moixa Smart Battery is aptly named, capable of charging day and night. Once the sun goes down, the Smart Battery will start to charge from the grid (when rates are cheaper), ensuring that it’s almost always topped up.

Moixa also has a scheme called GridShare, which gives Smart Battery users a free extended warranty (and three £50 payments in the first three years) in exchange for any unused electricity. Moixa then trades this electricity with the National Grid, in support of a low-carbon future. Along with the 2kWh and 3kWh batteries, a 4.8kWh model will soon be available.

Typical price: £3,450

Dimensions: 505mm x 345mm x 245mm

Weight: 48.7kg

Storage capacity: 3kWh

Useable capacity: 2.4kWh

Depth of discharge: 80%

Max power output: 0.46kW

Installation: Wall-mounted, indoor only

Limited warranty: 10 years, or 4,500 cycles


Duracell Energy Bank

The best for small homes and low energy requirements (1/2)

Duracell has long been a household name thanks to its triple-A batteries, but the American manufacturer has recently branched into solar energy storage. Its Energy Bank solar battery is a superb option if you’re looking to power a small household, offering 3.3kWh of capacity, and easy installation. Plus, if your household starts to grow, you can easily add another Energy Bank and scale it up to 6kWh.

Duracell’s Energy Bank has been developed in conjunction with a bright young company called Social Energy, whose ‘solar energy trading platform’ is breaking new ground. Social Energy will connect your Energy Bank to everyone else’s, and then use artificial intelligence to automatically trade, swap and sell your solar-generated electricity with other battery owners. As Social Energy puts it, it’s basically “a power plant in the sky”.

You can get your hands on the Energy Bank through Project Solar, who also offer an impressive pair of high-efficiency solar panel models.

Typical price: £4,499

Dimensions: 680mm x 256mm x 610mm

Weight: 96kg

Storage capacity: 3.3kWh

Useable capacity: 3kWh

Depth of discharge: 90%

Max power output: 2kW

Installation: Wall-mounted or standing, indoor only

Limited warranty: 10 years


Enphase AC Battery

The best for small homes and low energy requirements (2/2)

California-based Enphase knows all about sunny weather. Its AC Battery is an ultra-lightweight solar power storage option, weighing just a feathery 25kg. With 1.2kWh of capacity, this battery isn’t going to take you off the grid, but it will be good for short-term power supply in the evenings.

The AC Battery also has a 100% depth of discharge, which means you can use all 1.2kWh of its capacity before recharging it (some solar batteries aren’t as generous). Plus, if you ever need more, you can stack up to 13 of these little guys.

Typical price: £2,726

Dimensions: 390mm x 325mm x 220mm

Weight: 25kg

Storage capacity: 1.2kWh

Useable capacity: 1.24kWh

Depth of discharge: 100%

Max power output: 0.26kW

Installation: Wall-mounted, indoor only

Limited warranty: 10 years, or 7,300 cycles


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How big is a solar battery?

There’s no one-size-fits-all answer. Solar battery dimensions vary depending on their capacity; a 2kWh battery is about the size of a microwave and is capable of being mounted on a wall, while most fridge-sized 13kWh batteries need to be stood on the floor.


What size solar battery is needed to power a house?

You can calculate the amount of battery storage you need based on your energy usage, which is measured in kilowatt hours (kWh) over a certain period of time, e.g. kWh per day. According to Smarter Business, the average UK household uses between 8.5 and 10 kWh per day, or 3,100 kWh per year.

Generally speaking, a three-bedroom house will need a 3-4 kilowatt peak (kWp) solar panel system, which consists of around 12-16 panels and produces approximately 2,500 kWh of electricity per year. To go with this, a three-bedroom house would need a solar battery with around 3-6kWh of capacity. However, if you’re wanting to go completely off-grid, you’d need at least a 10kWh-capacity battery.

As a rule, it’s much better to have multiple batteries in your solar storage system and use around 40-50% of their capacity before recharging them. If you just have one battery and repeatedly use 100% of its capacity, you’ll degrade its power and efficiency much more quickly. You can learn more about a solar battery’s ‘depth of discharge’ further down the page.


Did you know? According to Which?, a 4kWh solar battery can store enough electricity to boil a kettle 37 times.Simply fill out this form to start receiving free solar battery quotes today.


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How much electricity can a solar battery hold?

The ‘capacity’ of a solar battery refers to how much electricity it can hold, measured in kilowatt hours (kWh). A ‘kilowatt hour’ is equivalent to one kilowatt of power sustained for one hour.

Most solar batteries on the market today generally have a capacity of 3-7kWh, although you can also find smaller and larger models to suit your needs.

You should also consider a solar battery’s ‘power rating’, which is how much electricity a battery can deliver at any one time (measured in kilowatts, or kW). If a solar battery has a high capacity but a low power rating, it will be able to hold a lot of electricity, but you won’t be able to power many things at once.

Fortunately, most models of solar battery are stackable, so if one isn't enough, you can just pile more on top. For example, up to 10 Tesla Powerwalls can be stacked on top of each other before things get too dangerous/silly.


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How long do they last?

A solar battery lives a trying life of repeated charging and draining ‘cycles’, which gradually wears it away - similar to the way your mobile phone battery gets steadily worse.

As shown in the table near the top of the page, the typical warranty of a solar battery is 10 years. This doesn’t mean that a battery will stop working after 10 years, but it will usually start to operate at a reduced level (e.g. around 70% of its original capacity). After about 15 years, you will probably need to replace the solar battery.

As your solar battery goes through cycles, it will slowly experience a decrease in its ‘depth of discharge’ (DoD), which refers to how much of a battery’s capacity is actually useable. For example, if you own a 10kWh-capacity battery with an 85% DoD, you should only use a maximum of 8.5kWh at any one time. If you repeatedly use 100% of the battery’s energy, it will wear away the battery much more quickly.

Fortunately, you yourself can have an impact; proper maintenance, along with protecting your battery from significantly low or high temperatures, will keep it ticking along nicely. What’s more, technological advances are continually increasing the lifespan and performance of solar batteries, so things are only going to get better.


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Finding a professional installer

The next step is finding a solar battery that’s right for you. To start collecting quotes from qualified installers, simply answer the question below, fill in the form, and our suppliers will get back to you. You’ll be stockpiling solar energy in no time.


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