What Size Solar Battery Do I Need? UK Guide 2025

Understanding solar battery storage

How solar batteries work with your home energy system

A solar battery stores the electricity your panels produce during the day so you can use it later when generation drops.

This means you rely less on grid power and make the most of your renewable energy.

Why battery size matters for efficiency and savings

The right battery capacity ensures you store enough energy to cover your needs without paying for unused space.

Undersized systems may discharge too early, while oversized ones increase upfront cost and extend payback time.

Typical solar battery sizes in the UK

Average capacity ranges for homes (3-15 kWh)

Across the UK, most domestic solar batteries range from 3 kWh to 15 kWh.

How to estimate the right size for your usage

Check your electricity bill to find your average daily use in kWh.

A good rule of thumb is to store enough power to run your evening and overnight needs when your panels aren’t generating.

Example: how much energy a 5 kWh or 10 kWh battery can store

A 5 kWh battery can supply several hours of lighting and appliances for a small home.

A 10 kWh battery can typically power a 3-bed home overnight, including essentials such as the fridge and washing machine.

Factors that affect what battery size you need

Your home’s daily electricity use

According to Ofgem, the average UK household uses 8-10 kWh per day.

Homes with higher consumption or electric heating usually benefit from a larger 10-15 kWh battery.

Solar panel output and generation

A 4 kW solar array generates roughly 16 kWh on a sunny summer day and 6-8 kWh in winter.

Matching battery capacity to your system’s output ensures you can store most of what you produce.

Battery efficiency and depth of discharge

Higher-quality lithium-ion batteries allow deeper discharges.

This means you can use more of their total capacity each cycle. Look for models with 90% or higher efficiency for better value.

Battery lifespan and warranty

Modern lithium-ion batteries usually last 10-15 years and include 10-year manufacturer warranties.

iHeat only installs systems that meet recognised UK standards and carry strong warranty protection.

Future upgrades or electric vehicle charging

If you plan to buy an EV or expand your solar system later, choosing a slightly larger battery gives flexibility for extra energy use.

common UK solar battery sizes and performance

Figures represent typical UK averages in 2025 and vary by brand, setup, and installer.

Is a larger battery always better?

When a smaller battery can be more efficient

If your panels produce limited energy or you have low evening demand, a smaller battery provides better cycling and quicker returns.

When investing in a bigger system makes sense

Homes with higher usage or EV charging benefit from larger batteries.

They offer longer backup times and higher energy independence, though with higher initial cost.

How to calculate your ideal solar battery size

Step-by-step method using usage data and panel output

1. Check your average daily energy use (in kWh) from your bill.

2. Multiply your system’s solar output (kW) by expected sunlight hours.

3. Decide how much of that energy you want to store for use after sunset.

4. Choose a battery that stores roughly 70-100% of that usable energy.
   

Example calculation for an average UK home

A 4 kW solar system producing 16 kWh per day in summer and 7 kWh in winter would pair well with a 6-8 kWh battery, covering evening use and storing surplus power for the morning.

Installer tip: Most homeowners use only 60-70% of their solar generation directly.

A well-sized battery captures the rest, improving savings and system payback.

iHeat and solar battery storage

Expert guidance and installation support

iHeat installs both solar panels and battery storage nationwide, available either together or separately. 

As a Which? Trusted Trader with thousands of verified reviews, iHeat helps homeowners choose the ideal setup based on energy use, budget, and long-term goals.

Finance and integration with solar panel systems

With 0% APR finance available, iHeat makes it easier to install solar batteries without a large upfront payment. 

All systems are installed by qualified engineers and include full product warranties for peace of mind.

Choosing the right solar battery for your home in 2025

The ideal solar battery balances cost, capacity, and usage.

For most homes, 5-10 kWh offers the best mix of savings and independence. 

Larger batteries suit high-consumption properties or homes planning for EV charging.

Battery technology continues to improve, and prices are becoming more competitive. 

With expert installation and finance options from iHeat, UK homeowners can enjoy efficient, long-lasting storage that maximises solar power throughout the year.