What sizes do solar batteries come in, and how do I choose the right one?

Solar batteries in the UK come in a variety of sizes, typically measured in kilowatt-hours (kWh), which indicates how much electricity they can store. The right size battery depends on your household or small business energy consumption, your solar panel system capacity, and your goals for energy self-sufficiency.

Common Sizes of Solar Batteries

• Small batteries: Around 4-5 kWh — suitable for low energy users or homes with smaller solar panel systems.
• Medium batteries: About 8-10 kWh — typical for average UK homes, especially with moderately sized solar panels.
• Large batteries: 10 kWh and above — ideal for high energy consumers or larger businesses.

For example, most UK households with a typical three-bedroom home (average annual electricity use about 3,400 kWh as of 2024) tend to install around a 5 kWh battery because their solar panels provide electricity during the day, reducing the need for large storage at night. Larger homes or small businesses with higher electricity demands (5,000 to 10,000 kWh annually or more) usually require 9-10 kWh or higher capacity batteries[1][2][3].

How to Choose the Right Size for Your Needs

1. Understand Your Energy Consumption

Start by checking your Estimated Annual Consumption (EAC) or your recent electricity bills to see how much energy you use annually. Here is a general guideline:

• Up to 5,000 kWh per year → 4-5 kWh battery
• Between 5,000 and 10,000 kWh per year → 9-10 kWh battery
• Over 10,000 kWh per year → Batteries over 10 kWh

2. Consider Your Solar Panel Capacity

Solar battery size should match your solar generation capacity. For example, a 4 kWp solar panel system typically produces about 8 kWh per day under good sunlight. To store most of this energy, you'd consider a battery around 8 kWh capacity[2][4].

3. Decide Your Storage Goals

• Maximise self-consumption: Store excess solar power during the day to use at night, reducing reliance on the grid.
• Backup power: Some batteries can power your home during outages, requiring a larger capacity if you want significant backup.
• Export tariffs: If you’re on a smart export tariff (like Intelligent Octopus Flux), your battery might discharge to the grid during peak times, so you might need less battery size for nighttime use[1].

4. Think About Future Expansion

Stackable modular batteries allow you to start with a smaller size (e.g., 5 kWh) and add more capacity later as your energy needs grow, which is helpful for both homeowners and small businesses[1].

Practical Advice for UK Homeowners and Small Business Owners

• Most small businesses, similar to larger households, should consider batteries in the 8-12 kWh range unless their electricity use is very low or very high.
• A battery that's too small means you won’t capture enough solar energy and will rely more on the grid.
• Oversizing the battery can mean unnecessary upfront costs and underutilised capacity.
• Consult with a qualified UK solar installer who can analyse your specific energy usage and solar setup to recommend the optimal size.
• Consider battery warranties, lifespan, and safety features as well.

Key Pros and Cons of Different Battery Sizes

Battery Size	Pros	Cons
Small (4-5kWh)	Lower cost, fits modest households, easy to install	Might not store enough energy for large families or businesses
Medium (8-10kWh)	Good balance for average UK homes and small businesses	Higher upfront cost; may be too large if usage is low
Large (10+kWh)	Supports high consumption, useful for backup power	Expensive, needs more space, potential underuse if consumption drops

Common Mistakes to Avoid

• Choose a battery based on your daily and annual consumption rather than price alone.
• Consider the capacity of your solar panels in the sizing decision.
• Account for changes in household size or business operations that may increase electricity use.
• Factor in planned future expansion or additional solar panels.
• Take into account smart export tariffs and how they affect battery use and grid interaction.

In summary, most UK homeowners will find a battery in the 4-10 kWh range suits their needs, with 5 kWh being typical for average three-bedroom homes. Small businesses or homes with high electricity usage may need batteries of 10 kWh or more. Matching battery size to your solar panel output and consumption patterns ensures you optimise savings and energy independence without overpaying.