How do solar batteries work and store energy?

How Do Solar Batteries Work and Store Energy?

Here we explain what a solar battery does, how it stores your energy, and whether it's the right upgrade for your home. If you're still weighing up whether solar panels are right for your home, it's a good place to start.

Solar panels are a great way to cut your energy bills and your carbon footprint. Add a battery, and you can go even further. A solar battery stores the extra energy your panels produce, so you're not stuck relying on the grid the moment the sun goes in.

What Is a Solar Battery?

A solar battery stores the excess energy your solar panels generate, so you can use it later, at night, or on a cloudy day, instead of drawing power from the grid.

Most solar batteries store this energy as electricity. How they do it depends on the type of battery in your system, which we'll get into below.

How Does a Solar Battery Work With Your Solar Panels?

Before we look at the different battery types, it helps to understand how a battery fits into your wider solar setup.

Your solar panels convert sunlight into DC (direct current) electricity. What happens next depends on whether your system is AC-coupled or DC-coupled.

AC-Coupled Systems

DC electricity flows from your panels to an inverter, which converts it to AC (alternating current) electricity. This can power your home directly, or go to a battery inverter that converts it back to DC for storage. When you need that stored energy, it's converted back to AC.

DC-Coupled Systems

DC electricity flows straight from your panels into the battery. When you need it, the battery sends it to the inverter, which converts it to AC for use in your home.

Where you place your panels and how many you install both affect how much energy reaches your battery in the first place. Our guides on roof placement and how many panels you need can help you get the setup right.

Types of Solar Battery

A few battery technologies can pair with solar panels, but two dominate the UK home market: lead-acid and lithium-ion.

Lead-Acid Batteries

Lead-acid batteries are the older technology, and cheaper upfront than lithium-ion. They come in two main types: flooded, which need regular maintenance, and sealed, which don't.

They're now much less common in modern UK solar installations. They have a lower depth of discharge (DoD), meaning you can use less of their stored energy before it affects the battery's lifespan, and they typically last 3 to 7 years.

Why some people still choose them: lower cost and reliable performance, if you're happy to maintain them.

Lithium-Ion Batteries

Lithium-ion batteries are now the standard choice for UK homes. They offer a higher DoD, greater energy density, faster charging, and a longer lifespan than lead-acid batteries, typically 10 to 15 years, and up to 20 years for lithium iron phosphate (LFP) batteries specifically.

Why most people choose them: they last longer, need less maintenance, and get more use out of every charge.

We fit batteries from Duracell, Fox ESS, and Tesla, with capacities from around 5kWh, and 0% finance available on selected products. You can explore our battery options to see what would suit your home.

Benefits of Solar Battery Storage

Whichever battery you choose, adding one to your solar panels can help you:

• Lower your energy bills: store excess solar energy instead of exporting it for a lower rate, and draw less from the grid. If your battery does run low, you can top it up from the grid during cheaper, off-peak periods
• Use solar energy after dark: once it's stored, you can use it at night or on a day when your panels produce less energy than usual
• Keep the lights on in a power cut: depending on your battery's size, it can back up your home for hours, or longer
• Cut your carbon footprint further: producing and storing your own solar energy means relying less on fossil fuels
• Add value to your property: a complete solar and battery setup can make your home more appealing, whether that's for the backup power or the lower running costs

Get the Most Out of Your Solar Power With So Energy

If you'd like to know more about solar batteries, get a quote and our team will help you find the right setup for your home.

FAQs

How Does a Solar Battery Charge?

Your solar panels convert sunlight into electricity, which charges the battery as DC electricity. It's then stored for use as DC or AC electricity later, depending on your system.

How Long Does a Solar Battery Last?

This depends on what you mean by "last".

If you mean how long a full charge holds before it drains on its own, lead-acid batteries typically lose 4% to 8% of their charge a month when not in use. Lithium-ion batteries lose much less, usually under 2% a month.

If you mean how many years before you need a new one, that depends on the battery type. Lead-acid batteries usually last 3 to 7 years. Lithium-ion batteries typically last 10 to 15 years, with LFP batteries lasting up to 20 years. For comparison, solar panels themselves last much longer, so you may need to replace your battery once or twice over the life of your panels.

What Size Battery Do I Need?

It depends on your goals. If you want to go off-grid completely, you'll need a bigger battery than someone who just wants backup for cloudy days (which, despite the myth, your panels will still work through) or the odd power cut (or solar eclipse).

Your energy use matters too. A one-person home and a four-person home won't need the same size battery. Our team can help you find the right fit based on how you use energy at home.

What Happens When the Battery Is Full?

This depends on whether your system is off-grid or connected to the grid.

If you're off-grid, your panels reduce how much electricity they produce, so the battery doesn't overcharge. Any energy you're not using or storing goes to waste.

If you're connected to the grid and have the right meter, your excess electricity goes back to the grid, and you're paid for it through the Smart Export Guarantee (SEG). SEG replaced the older Feed-in Tariff (FiT) scheme, which closed to new applicants in March 2019. If you signed up to FiT before then, you'll keep receiving those payments under your original terms.

Are There Any Drawbacks to Solar Batteries?

The main one is cost. Before adding a battery, it's worth factoring in:

• the cost of the battery itself
• installation costs
• ongoing maintenance, and eventual replacement

Our 0% finance options can help spread the cost if that makes the decision easier.

‍