What size solar battery do I need?

Do you have solar panels, or are you thinking about getting them? A solar battery can help you make the most of your solar electricity. Instead of sending your excess energy back to the grid, a battery lets you store it for later, cutting your electricity bills and giving you more control over your power.

But with so many options, it’s easy to wonder: ‘What size solar battery do I need?’

Go too small, and you won’t have enough stored energy for when you need it. Go too big, and you could end up with a battery storage system that costs more than it saves.

Let’s break it down and find the right solar battery capacity for your home.

Key takeaways

• How to decide on the right solar battery size
• How to calculate the right battery size
• Understanding solar battery capacity and performance
• How to match battery size to your energy needs and budget
• Other factors to consider when choosing a solar battery

How to decide on the right solar battery size

A well-sized battery depends on three key things:

• How much electricity you use per day
• How much solar power you generate
• How you plan to use your stored energy

The best place to start is your energy usage. Most UK homes use between 6 kWh and 10 kWh of electricity per day. Still, your daily electricity consumption depends on things like heating, cooking, and whether you have high-energy appliances like an air conditioner or heat pumps.

Got a smart meter? Then, it’s even easier to track your electricity usage. You can see how much solar electricity you use during daylight hours (while your solar panels are generating power) and how much you need at night. That’s super important for working out what battery storage capacity is right for you.

How to calculate the right battery size

An easy way to calculate the right kWh battery size is:

• Look at your daily electricity usage (from your smart meter or energy bill).
• Check how much excess electricity your solar system produces on a sunny day.
• Match the two to find a storage battery capacity that covers your evening and nighttime electricity demand.

For example, if you use 8 kWh of electricity per day and your solar panels generate 5 kWh of excess energy, a 5 kWh battery could be a good fit.

Already have a solar system? Use our solar battery calculator to find the best storage option. Try it now!

Understanding solar battery capacity and performance

Not all solar batteries are the same. Factors like usable capacity, the types of battery, and storage capacity can affect how well they work for your home. Here’s what you need to know before choosing the right one.

Usable vs. maximum capacity

A battery storage system isn’t just about size – it’s about usable capacity. Some batteries store more energy than you can actually use. For example, a 10 kWh battery might only have 9 kWh of usable capacity because a portion is reserved to extend battery life.

Lithium-ion vs lead-acid batteries

Most home solar batteries are lithium-ion, which last longer and charge more efficiently than lead-acid batteries. They also have a higher storage capacity in a smaller physical size. While lead-acid options are cheaper, they take up more space and have a shorter battery life.

How to match battery size to your energy needs and budget

Here are some important things to keep in mind when matching the size of your solar battery to your needs and budget:

Battery for backup vs. going off-grid

If you’re staying connected to grid electricity, a smaller solar battery storage system (4–8 kWh) could be enough to cut your energy bills without spending too much upfront. To be completely off-grid, you’ll need a much bigger battery storage capacity to get through the darker winter months. You’ll also need a system with an Emergency Power Supply (EPS) switch that can operate in Island Mode. Without this, your solar system won’t work during a power cut.

Storing energy for peak times

Electricity is more expensive at peak times. A solar battery lets you avoid using grid electricity when rates are high. If your energy provider charges different rates throughout the day, a well-sized battery can help you store cheap solar power and use it when prices go up.

Will a solar battery save me money?

A solar battery helps you use more of your own solar energy, lowering your energy costs.

But the savings depend on:

• The price of grid electricity
• How much excess energy you generate
• The cost of the battery installation

A battery storage system that matches your energy needs will give you the best return on investment.

Bigger isn’t always better

Oversized batteries cost more and may not always be worth it. If your solar array doesn’t generate enough excess electricity to charge a large battery, you won’t see the full benefit. On the other hand, the minimum battery capacity might not be enough to power your home at night, so you’ll still rely on grid electricity.

Other factors to consider when choosing a solar battery

Beyond capacity, practical factors like installation space and lifespan affect whether a battery is right for your home.

• Physical size and installation space – A storage battery takes up space, so think about where you’ll put it. Lithium batteries are more compact, while lead-acid batteries need more room and ventilation.
• Battery life and performance over time – Most lithium-ion batteries last 10–15 years, while lead-acid batteries need replacing sooner. Check the battery performance guarantee before you buy.

Get expert advice from our UK solar panel installers

The right solar battery capacity helps you cut electricity bills and use more of your own solar power. Not sure what size battery you need? Our UK solar panel installers can help you choose the best system to cut your energy bills and make the most of your solar power. Get in touch today.