A guide to solar panel batteries

by Holly Jackson a year ago 8 min read

Solar energy continues to provide a reliable and environmentally friendly way of powering homes all over the world. But while modern solar arrays do an amazing job on their own when generating electricity, it’s always smart to have a reserve in place.

Solar batteries are a handy, efficient, and cost-effective way to make sure every kilowatt of electricity you generate with your panels is put to good use. Serving as the perfect addition to your overall solar setup, they work to save you thousands in the long run.

In this useful guide we’re going to explore everything you need to know about solar panel batteries. From understanding the different options available, to the most important factors to consider when buying one, here’s everything you need to know about solar storage options.

What is solar panel battery storage?

First and foremost, it’s important to understand exactly what a solar panel battery unit is. In essence, these devices are attachable and chargeable additions to your overall solar panel system.

They bank any solar energy which is produced and not used throughout the day, with the intent of providing a household with a guaranteed supply of energy after sundown, during periods of peak energy demand, or in the event of a power outage.

The addition of a battery to a solar array allows you to make the most use of the electricity your panels have generated meaning fewer units of electricity you need to import from the grid at a hefty price. You can also sell stored energy you don’t use back to the grid.

Since the end of the Feed in Tariff in March 2019, a new export programme has commenced - the Smart Export Guarantee.

Generally the rates paid by energy suppliers to export electricity to the grid is very low, on average £0.055/kWh while the rate paid to import is much higher, £0.34/kWh on average. Therefore, in the UK in particular, it makes a lot of sense for consumers to invest in a battery storage system to go alongside their solar PV system.

Here is a league table provided by Solar Energy UK of Smart Export Guarantee rates offered by energy suppliers:

	Supplier	Tariff Name	Tariff Type	Tariff Length	Tariff Rate (p/kWh)	Payment Cycle	Includes Battery Storage	Must be on supplier import tariff
1	Octopus Energy	Outgoing Fixed	Fixed	12-month fixed term	15p	Monthly	Yes	Yes
2	Tesla	Tesla Energy Plan¹	Fixed	Unknown	12.0p	Unknown	Yes (must be Tesla Powerwall)	Yes (Octopus Energy)
3	Tesla	Tesla Energy Plan²	Fixed	Unknown	10.0p	Unknown	Yes (must be Tesla Powerwall)	Yes (Octopus Energy)
4	British Gas	Export & Earn Flex	Currently Fixed	No fixed end date	6.4p	3 months	Yes	No
5	Bulb Energy	Export Payments	Fixed	No fixed end date	5.57p	3 months	Yes	Yes
6	E.ON Energy	Next Export Exclusive	Fixed	12-month fixed term	5.5p	Unknown	Unknown	Yes
7	ScottishPower	Smart Export Variable Tariff	Fixed	No fixed end date	5.5p	6 months	Unknown	No
8	OVO Energy	OVO SEG Tariff	Currently Fixed	12-month fixed term	4.0p	3 months	Dependent on Installation	No
9	SSE	Smart Export Tariff	Fixed	No fixed end date	3.5p	12 months	Unknown	Yes
10	Shell Energy	SEG V1Tariff	Currently Fixed	No fixed end date	3.5p	12 months	Unknown	Yes
11	E.ON Energy	Next Export	Fixed	12-month fixed term	3.0p	Unknown	Unknown	No
12	EDF Energy	Export+Earn	Fixed	12-month fixed term	3.0p	Unknown	Unknown	Unknown
13	Utility Warehouse	UW Smart Export Guarantee	Fixed	No fixed end date	2.0p	Unknown	Unknown	Unknown

Source

It’s important to note, however, that having a battery storage unit does not mean you will be completely cut off from the grid altogether. While this is an option, it greatly increases the strain on and cost of your storage unit; the marginal cost of ensuring constant back up power is very expensive but possible to achieve if your system is large enough.

How does solar panel battery storage work?

At its core, a solar panel battery works in a three-step process to generate, store, and then utilise power for a home.

Solar panels produce power as they conventionally would, but send any excess energy they don’t use to a battery storage unit
The power sits in the battery waiting to be repurposed
When the sun goes down your house can draw upon the electricity stored in the battery to decrease the amount you will need to import from the grid

While the basics of taking energy and storing it for later use are the same for all kinds of units, the exact nature of battery storage technology will vary depending on the type of coupled storage inverter being used.

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Different types of solar batteries

Just as inverter units differ, so too do the batteries themselves. There are four different types of batteries to choose between, with each having their own pros and cons. Let’s take a closer look at the different options.

Lithium ion batteries. Emerging as the modern face of solar panel batteries, lithium ion units are incredibly efficient, long lasting and require little to no maintenance. They also maximise the amount of energy being stored before needing to be recharged. They tend to cost a little more than older models, but the benefits easily outweigh the small additional costs.
Lead acid batteries. These deep cycle batteries were the most common option for solar panels since their inception. Like the batteries in your combustion engine vehicle, they are affordable and recyclable. They do, however, need occasional maintenance. The efficiency of lead acid batteries is considerably less than lithium ion batteries.
Nickel-based batteries. While not commonly used, these types of batteries are durable – which is why they’re generally used in more industrial projects than on a home. However, the cadmium included as part of their design is impossible to recycle, which means they’re actually banned in some countries.
Flow batteries. This emerging technology used a water-based electrolyte liquid to create a chemical reaction, which in turn causes electricity to be discharged and stored. They’re long-lasting and resistant to quite a lot, but their relatively new presence on the market means they tend to cost more than other options. They also have low charge and discharge rates in relation to their size – which is considerably large. Therefore these battery systems will not be suitable for residences in the near future.

The benefits of using solar battery storage

As you can imagine, there are a host of benefits to utilising a battery storage unit as part of your solar array. Some of the most relevant for the average household include things like:

Maximising power efficiency. Running a solar array which doesn’t store electricity means if your setup fails to create enough when you actually need it, you’ll have to draw on the grid during periods of lowered or no production (night). This can be costly. What’s more, on days when you overproduce, you’ll be able to store more for when you actually need it.
A sense of energy security. It’s always nice to know you don’t have to rely on anyone else to successfully power your home. Having a battery storage unit could mean you could power your home, regardless of what’s happening around you.
Lower noise pollution. Unlike traditional backup generators, solar panel batteries emit almost no noise, reducing the disturbance to both your neighbours and yourself.
Reduce energy bills. The more self-sufficient you are when generating and storing your own energy, the lower you can expect to pay when it comes to your overall energy bills.
Prepare your home for the next generation of smart energy. Virtual power plants are developing in the UK and will allow consumers with batteries to equalise charge (controlling your battery so it doesn’t over-charge) across the grid, giving them a chance to profit from this benefit in the future.
Use your battery for energy arbitrage. If you have access to a cheaper night time rate of electricity you may be able to benefit by drawing from the grid at night on a cheap rate, to use during the times when electricity rates are more expensive. However this requires sophisticated manipulation of your inverter and battery. What’s more, if your daytime rates are comparably higher you’ll need to factor this in when considering the additional investment.

What to consider when choosing a solar panel battery

Understandably, you’ll want to weigh up all your options when deciding on the right kind of battery unit to include as part of your system. Here are some of the key considerations to keep in mind as part of your choice.

Lifespan. When it comes to longevity, you’ll want to get as many years or cycles out of your battery as possible. The key is to look not only for batteries which promise a long lifespan, but that come with a warranty covering the majority of that period.
Capacity. This will be measured in kilowatt hours (kWh). Most batteries will show both their total and usable capacity. The number you’ll want to pay more attention to is the latter. To optimise a solar PV system you should consider the size of your system to determine what the maximum output potential is and what your actual consumption habits are during a day – as well as what your household actually spends daily. A battery makes its return on investment when it is utilised not when it is storing electricity.
Power rating. This rating determines how much energy can be delivered to your home at once. It’s measured in kilowatts (kW), and will give you an idea of how many and which appliances can be run at the same time. There will be two ratings, and both are important:
Continuous power rating – which means how much power it can provide constantly to the appliances in your home as a base level
Peak power rating – which refers to how much power it can emit during short bursts when required
Safety. Just as with most things in life, safety is always of paramount importance. While the chances of an electrical fire are incredibly low with solar batteries, it’s still a factor which needs to be kept in mind. Be sure to check guidance on the battery unit in order to maintain them properly. The most important safety consideration is during the installation process, so make sure your installer has experience in battery installation.
Cost. An average solar panel battery will cost £5000. That doesn’t mean you should expect to pay that much. The total cost will vary depending on your battery capacity, location in the country, and ease of installation.

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Frequently asked questions

If you’re interested in learning more about solar panel batteries, make sure to check out this handy list of frequently asked questions. If you can’t find the answer you’re looking for, reach out directly to a member of the Otovo team for further help. We’re happy to help you find an appropriately sized battery.

How safe are solar batteries?

Owing to a lack of moving parts, solar batteries tend to be very safe. The only time there’s any chance of an issue or fault is after immense periods of degradation, or if they haven’t been installed properly. For that reason, it’s vitally important you use an installer you know you can totally trust and rely on.

What is the average lifespan of a solar battery?

While most solar panel systems can last for in excess of 25 years, a battery is more likely to start degrading around the year 10-15 mark. As technology continues to improve, expect to see both of these figures rise.

What can damage the condition of the battery?

Temperature is the primary cause of damage and wear to a solar battery. It’s important to keep your battery in a location where it’ll stay cool. That also means regularly maintaining and checking on it. Temperature moderation is a feature of most modern batteries, so be sure to check this is included with your chosen model.

How long will a battery be able to power my home for?

One of the most important factors to consider when choosing a battery is its capacity to power your home when it’s needed most. This will largely depend on the total and usable capacity of the battery. Make sure to understand both of these figures before committing to a storage unit.