Matt Tinkler/13th March 2023

Battery storage: everything you need to know

Everyone is talking about battery storage and all the information can seem a little overwhelming so we thought we’d put together a little guide with everything you need to know.

What is solar battery storage?

Let’s start with the basics. A storage battery stores your solar power and in many ways is similar to a rechargeable mobile phone battery. It is much larger though, commonly storing enough solar power to charge your mobile phone 2000 times.

What does a solar battery do?

When your solar panels are generating more power than you are currently using, the battery stores that spare electricity. 

Later on, whenever your house needs more electricity than your panels are producing, the battery will supply that extra power to your house.

solar battery storage in house

How does battery storage work with solar panels?

The solar panels and battery system plug into an inverter, which controls the whole system. The inverter will tell the battery to discharge power if it detects that your house is about to import electricity from the grid. And, the inverter will tell the battery to charge if it detects that your house is producing too much solar electricity and about to export electricity to the grid.

battery inverter solar panel

Why would I want battery storage?

Adding battery storage to your solar PV system saves excess solar electricity so you can use it when your panels aren’t producing solar power.

Most residential solar installations produce more power than you can use at certain times of the day. Solar power generation tends to be fairly steady, whereas household energy needs go up and down. Without battery storage, the excess solar power flows back to the grid. It is not wasted, but you do not get to benefit from it yourself.

For an average home solar PV installation in the UK, you might use 65% - 70% of the solar power your panels generate, with the rest flowing back to the grid.

If you add a battery, you might use 85% - 90% of the solar electricity.

A typical day of solar energy production and consumption 

Solar panels generate nice steady power throughout the day. Even for people who are at home during the day, most households use more electricity in the mornings and evenings, when electricity-hungry appliances such as kettles, ovens, and showers are used.

Your battery stores the excess solar energy produced from the middle of the day so you can use it later on.

Household energy consumption tends to peak and trough a lot when you are home. When you take a shower or switch on the kettle, your house might suddenly be using triple the amount of electricity just for those few minutes.

A battery will discharge energy to help supply the shower or kettle (if needed) just for those few minutes, then will start recharging immediately afterward.

Solar panels with sunset

How many batteries do I need to power my home?

The average three-bedroom household needs an 8 kWh solar battery. If you live in a house with one or two bedrooms, a 2-4 kWh battery will probably be enough, but if your property has four or five bedrooms, you’ll most likely need 9.5 kWh solar batteries.

- How big are solar batteries?

They tend to be about the size and shape of a desktop PC tower. Usually, we recommend placing it in your loft right next to the inverter.

- What types of solar batteries are there?

4 main types of battery technology are used with solar PV.

Lead-acid batteries

Lithium-ion batteries

Nickel-based batteries

Flow batteries

Lithium-ion batteries are the most popular battery storage technology in the UK due to their longevity.

battery storage solar

What does a solar battery cost?

Buying a 5kWh solar storage battery (the most common size) would add between £3,600 - £7,000 to the cost of your solar system.

Are solar batteries expensive?

A solar storage battery system is one of the more expensive parts of a solar electricity system. This extra cost is made up of three main parts:

The cost of the battery itself

A hybrid inverter (roughly £1,000 - £1,200 more than a standard "string inverter" (that only connects solar panels to your home electrical supply).

Solar power installers will charge for labour such as mounting, wiring, etc.

How long before I need to replace the battery?

The average life expectancy of solar batteries is between 7-10 years, so you will need to factor in battery replacement costs when working out the return on investment (ROI)of your solar PV system.

The good news is that replacing a battery is much cheaper than the initial installation because you don’t need to replace the expensive hybrid inverter, wiring, or mounting.

How long is the warranty for a solar battery?

All of our batteries come with a 10-year warranty.

Can I get a grant for battery storage?

No. But if you buy your battery storage with solar panels, the VAT is cut to 0%. Also, there are some green home improvement loans with low or zero interest rates. For example, Last week Nationwide launched a new product to encourage their 5000 existing mortgage holders to borrow an additional £5-15.000 interest-free over 2 or 5 years for energy-efficient measures including solar battery storage.

Should I get a solar storage battery?

There isn’t a straightforward answer here as it depends on your system and energy usage. We can gladly do a quote for you both with and without battery storage so you can compare the numbers for yourself.

battery solar storage on wall

How much power can a solar storage battery hold?

The most common storage battery size for a house in the UK is 5kWh. To put this in daily context, 5kWh could boil an average kettle for 2.5 hours.

Can a battery store a full day's solar power for use in the evening?

Generally no, but it would depend on the size of your solar PV system, battery, and time of year.

An average 3-bed house might be able to generate 20+ kWh of electricity during a long summer's day, and a standard battery could store 25% of this. Your house will have been using a lot of that power during the daylight hours anyway.

During a dark December day that same solar system might generate less power and the battery would store it all.

solar power diverter

Is there an alternative to a solar battery?

Yes. If you want to use as much of your solar electricity as possible, then we recommend also considering the following alternatives: 

Hot water diverter

This technology sends excess electricity to an immersion heater in your hot water tank. Once your tank is hot, the excess electricity is sent to the grid.

EV charger

Certain types of EV chargers can be connected to your solar PV system (for example some Hypervolt EV chargers). The electricity your solar panels produces firstly powers your home, then excess electricity charges your car. When your car is fully charged, the excess electricity is exported to the grid.

Electric car batteries are usually large, so often can use up a few days of excess electricity even when daylight hours are long. If you have an EV and are at home most of the time, this can be a great use of excess electricity.

What is a cycle in a battery?

If you can imagine your phone battery going from 100% fully charged to 0%, then charging back up to 100%. This is classed as one "cycle".

hypervolt ev charger

What is a battery management system (BMS)?

A BMS is a "Battery Management System" and is a crucial element in batteries. It monitors the battery's voltage, current, and temperature. It protects the battery in the event of a fault.

- What is battery backup?

A backup battery is different from a solar storage battery.

Most hybrid inverters can provide a backup supply of electricity to dedicated circuits that are not connected to the grid in the event of a grid failure. Battery backup is used more for industry rather than in homes.

- Are solar batteries dangerous?

Much the same as the batteries in your mobile phone, solar batteries are safe and have built-in functionality to prevent any issues. 

As you have read this article, you now know that battery is an important part of the solar system. We have a team of solar panel installers in Peterborough, Newark, and other nearby locations who can help you during installation.  If you have any more queries, please do contact us and we’d be delighted to help.