What Size Solar Battery Do I Need? UK Expert Guide

Last Updated on May 29, 2025

Solar batteries are becoming a vital part of residential and commercial solar systems in the UK. If you’re investing in solar panels or already have them installed, it’s natural to ask: what size solar battery do I need?

In this guide, we’ll walk you through everything you need to consider when choosing the right solar battery size for your home or building, from daily energy usage and solar generation to battery capacity, scalability, and return on investment.

What Size Solar Battery Should I Choose?

Choosing the right size solar battery is not just about picking the biggest or most expensive unit available,  it’s about matching the battery’s storage capacity to your property’s energy profile. A battery that’s too small won’t store enough power to make a real difference, while an oversized one may cost more than necessary and deliver diminishing returns.

A well-sized battery strikes the right balance between maximising solar usage, reducing grid reliance, and staying within budget. Below are the key factors to help determine the ideal battery size for your home or commercial property:

If you’re still unsure whether investing in a solar battery is the right decision for your home or business, check out our detailed guide on are solar batteries worth it? to explore the benefits, costs, and long-term savings.

Average Daily Electricity Consumption (in kWh)

Understanding how much electricity your household or building uses each day is the foundation of proper battery sizing. For example:

• A typical 3-bedroom UK home might use 10–13 kWh/day
  
• A small commercial unit may use 20+ kWh/day

The more energy you consume, the larger your battery needs to be if you want to store enough solar energy to cover that usage,  especially during peak evening hours.

Solar Panel Output

Battery size should complement your solar panel system’s generation capacity to maximise energy storage and savings. For example, a typical 4kW solar panel system in the UK generates roughly 10–11 kWh per day under average conditions.

If your household consumes around 6 kWh during daylight hours, this leaves approximately 4–5 kWh of excess solar energy that can be stored for use later in the evening or overnight. To store this surplus effectively, you’ll need a battery with a usable capacity of at least 4 to 5 kWh.

• For instance, a 5 kWh battery (with about 4.5 kWh usable capacity) would be well-suited to store the excess energy from a 4kW system in this scenario.
  
• If you want to store more energy or cover a larger portion of your daily consumption, consider sizing up to a 7–10 kWh battery, which is ideal for homes with higher evening usage or larger solar systems (e.g., 5kW+).

Matching your battery size to your solar system’s excess generation means you make the most of your solar investment by maximising self-consumption and reducing energy fed back to the grid, where financial returns are lower.

Usage Patterns & Time-of-Use Shifting

How and when you use electricity plays a huge role in choosing the perfect solar battery size. Many UK households experience peak energy use during the evening hours, when solar panels aren’t generating power and electricity tariffs tend to be higher. 

This makes time-of-use shifting, using stored solar energy during these expensive peak times a key way to maximise your savings.

To do this effectively, it’s best to size your battery to cover around 80–100% of your typical evening electricity consumption. For example, if you use 5 kWh on average between 6 pm and 11 pm, a battery with at least 4 to 5 kWh usable capacity will allow you to shift most of your energy usage away from the grid during those hours.

However, not all households have the same energy usage patterns:

• If you or your tenants are home during the daytime (such as remote workers, retirees, or people who run home businesses), you’ll naturally consume more solar energy as it’s produced. This reduces the amount you need to store, so a smaller battery might be sufficient.
  
• Conversely, if your household primarily consumes electricity in the evening or overnight , when solar panels aren’t producing energy, a larger battery will be necessary to store enough power during the day for use later.

Understanding your lifestyle and daily energy habits is crucial to avoid undersizing (which means running out of stored power early) or oversizing (which can lead to unnecessary expense).

Backup Requirements (e.g. Power Cuts)

Some batteries come with backup power functionality, allowing you to run essential appliances during a power cut. If energy security is a concern (e.g. you rely on medical devices or work from home), you may want a larger battery that can store enough energy to power key circuits for several hours.

This often means sizing beyond your daily usage to ensure you have spare reserve capacity in case of emergency.

Grid Independence vs Backup

If you’re aiming for total grid independence, you may need a battery bank plus hybrid inverter. If you’re just looking to store daytime solar for use at night, a mid-size battery suffices.

Budget and Future-Proofing

Solar batteries range in cost depending on brand, technology, and capacity. It’s important to balance your current energy needs with what you can afford — but also think ahead.

Many UK homeowners opt for modular or expandable battery systems, allowing them to start with a smaller capacity and add more later. This approach keeps upfront costs manageable while allowing flexibility as your energy demands change (e.g. adding an EV charger, heat pump, or home office).

Scalability

Some battery systems (like Tesla Powerwall or GivEnergy) allow modular expansion, letting you start small and scale up.

Typical Solar Battery Sizes and What They’re Suited For

Here’s a simplified overview to help you understand which solar battery capacity might suit different types of UK properties. All values below assume typical usage patterns in the UK and solar systems between 3kW and 6kW in size.

Note: These are guidelines. Actual needs depend on your unique circumstances. Request a quote to receive a tailored recommendation.

Sizing Strategy for Different Goals

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