What Size Solar Battery Do I Need in the UK? A Practical Homeowner’s Guide

More homes across the UK are benefiting from solar energy and installing solar batteries alongside their solar systems. Solar batteries allow you to store excess solar energy, ideal for using during high demand and increasing your energy independence. 

But what size solar battery will you need? The optimum size will depend on your solar usage, generation and lifestyle. Rollings Renewables installs solar batteries and solar panels across the Midlands, and this guide will help homeowners choose the right solar battery size without overspending or under-sizing. 

How Solar Batteries Work 

A solar battery is integrated with a home or business’s solar network and allows excess solar energy to be used at a later date. For example, energy generated during the day can be stored and used at night. But it’s not as simple as going for the biggest battery size; it’s finding the perfect balance between efficiency and savings. It’s important to choose a solar battery that supports your solar system, average energy consumption and need for extra capacity.

What To Consider When Choosing Your Solar Battery Size

1. Your Household Electricity Usage 

The average UK home will use around 3,400kWh of electricity per year, which is about 9.3kWh per day. This of course will vary based on home size and what powered systems you have. For example, homes with EVs, heat pumps and high usage applications will on average use more energy per year and per day. 

It’s important to consider your daily electricity usage over your average yearly amount. For example, two households may both use 4,000kWh per year, but one could consume most of its electricity during the day, while the other uses the majority in the evening. The second household would generally benefit more from battery storage because it can store surplus solar generation during daylight hours and use it after sunset. 

By understanding your daily electricity usage rather than relying solely on annual figures, you can choose a solar battery that matches your actual energy habits and delivers better value from your solar investment. 

2. Your Solar Panel System Size and Output 

The size of your solar panel system directly affects how much surplus electricity is available to charge a battery. Larger systems typically generate more excess energy, especially during sunny periods. However, solar output varies significantly throughout the year in the UK, with much higher generation in the summer than winter. 

It’s also important to remember that batteries do not generate electricity themselves, as they simply store unused solar energy for later use. 

3. When You Use Electricity 

Your daily energy usage pattern plays a major role in determining the ideal solar battery size. Homes that consume most of their electricity in the evening often benefit most from battery storage, as stored solar energy can be used after sunset. Working from home, shift work or other non-traditional schedules can also affect when electricity is needed and how much stored energy is required throughout the day. 

4. Seasonal Energy Differences in the UK 

Solar generation in the UK varies considerably between seasons. During summer, solar panels will often produce more electricity than a household can use, creating surplus energy for either battery storage or selling back to the grid. 

In winter, shorter days and lower sunlight levels often result in reduced generation and greater reliance on grid electricity. For this reason, batteries are rarely sized to provide complete winter independence. Instead, they are designed to maximise self-consumption and deliver savings throughout the year. 

Understanding Battery Capacity (kWh Explained Simply)

It’s very important to understand solar battery capacity when choosing the right size. Solar battery capacity is measured in kWh (kilowatt-hours) and represents the total amount of energy it can store. 

You may think that choosing the largest capacity is best, but this is not the case. This is due to depth of discharge (DoD), which is the total capacity of the battery you can use before risk of damage. The DoD will be represented as a percentage, with many reaching highs of 90%. For example, an 8kWh solar battery with 90% DoD will discharge 7kWh of stored energy before needing to recharge. 

Understanding this difference helps ensure you compare battery systems accurately and choose a size that meets your household’s energy needs. 

How to Calculate the Right Battery Size 

A Step By Step Guide

Step 1: Check daily electricity usage

Remember, daily usage is more important than annual usage. A good way to check is to use previous annual energy bills and divide it by 365 to find your average daily usage.

For example, a household using 3,650kWh per year consumes an average of around 10kWh per day. While this won’t account for seasonal fluctuations, it provides a useful baseline for battery sizing. If you have a smart meter, you can get a more accurate picture by reviewing your daily and hourly consumption data. Pay particular attention to how much electricity you use during the evening and overnight, as this is typically when a battery delivers the greatest benefit. 

Step 2: Estimate solar surplus

The next step is to estimate how much of your solar generation is left over after meeting your daytime electricity needs. This surplus energy is what charges your battery. For example, if your solar panels generate 15kWh on a typical day and your household uses 7kWh during daylight hours, you could have around 8kWh available for storage. 

Step 3: Decide how much of your evening and night usage you want covered

Consider how much electricity you typically use after the sun goes down. Common evening loads include lighting, televisions, kitchen appliances and charging devices. Some homeowners aim to cover only their peak evening demand, while others have enough stored energy to power the home throughout the night. Your goal will influence the battery size that makes the most sense for your household. 

Step 4: Match your usable battery capacity

Once you know your daily consumption, estimated surplus and overnight energy requirements, you can compare these figures with a battery’s usable capacity. Focus on the usable kWh rating rather than the total capacity, as this reflects the amount of stored energy you can actually access. As a general rule, choosing a battery that closely matches your typical surplus generation and evening demand will usually provide the best balance of performance and value. 

General Rule Of Thumb 

Here’s an approximate guide on the battery size UK homes should choose based on their average daily electricity consumption:

Small home:

• Average daily electricity consumption = 7.5kWh
• Battery size = 7-8kWh

• Average daily electricity consumption = 9kWh
• Battery size = 9-10kWh

Larger homes (with EVs, heat pumps, etc)

• Average daily electricity consumption = 10-15+kWh
• Battery size = 18-19kWh

Common Mistakes When Choosing a Solar Battery 

Don’t make these common mistakes when choosing a solar battery:

• Oversizing – Choosing a battery that’s larger than your solar surplus or energy needs can result in paying for storage capacity that is rarely used. 
• Undersizing – A battery that’s too small may run out of stored energy before the end of the evening, reducing the benefits of your solar system. 
• Ignoring solar panel output – Even a large battery cannot store energy that your solar panels aren’t generating, so battery size should always be matched to solar production. 
• Not considering seasonal variation – Sizing a battery based solely on summer generation can lead to unrealistic expectations during the darker winter months. 
• Forgetting future needs – Upcoming additions such as an electric vehicle charger, heat pump, home extension or growing family could increase your future electricity demand. 

How to Get The Most Out Of Your Battery Size and Savings 

Match Battery Size to Solar Production 

For the best return on investment, your battery should be sized to match the amount of excess energy your solar panels typically generate. An oversized battery may never fully charge, while an undersized system could leave valuable solar energy unused. Although some battery systems can be charged from the grid on off-peak tariffs, relying too heavily on grid charging can reduce the overall benefits of your solar system. 

Shift Energy Use to Daytime Where Possible 

One of the simplest ways to improve the performance of your solar and battery system is to use more electricity during daylight hours when your panels are generating more power. Running appliances such as washing machines, dishwashers and tumble dryers during peak solar production hours can reduce the amount of electricity imported from the grid. Smart timers can help automate this process and maximise self-consumption. 

Consider Future Energy Needs 

When choosing a battery size, it’s worth thinking beyond your current electricity usage. Future additions such as an electric vehicle charger, heat pump, home extension or changes in household occupancy can significantly increase energy demand. Factoring in potential future requirements can help ensure your battery system remains suitable for years to come without needing costly upgrades. 

Choosing the right solar battery size in the UK is about finding the best balance between your household’s electricity usage, solar panel output and daily energy habits. By understanding how much electricity you use, when you use it and how much surplus solar energy is available, you can select a battery that delivers meaningful savings without paying for unnecessary capacity. 

While larger batteries may seem attractive, the most effective solution is usually one that closely matches your actual energy requirements and solar generation. For more details, check out our other article on whether solar panel batteries are worth it.
For the most accurate recommendation, speak to our team at Rollings Renewables for a professional assessment and a free quotation. Call us on 01905 621777, email sales@rollingsrenewables.co.uk or send your details using our contact form, and we’ll be happy to advise and install the ideal solar battery.