What Size Solar Battery Do I Need? Sizing, Costs and Examples
As the morning sun shines over the neighborhoods of Manchester, more and more rooftops are being fitted with solar panels to power homes. In recent years, the adoption of solar panels in the UK has continued to rise. However, for families holding a quotation and preparing for installation, the excitement often comes with confusion: what size solar battery do I need? How should the battery capacity be matched to electricity demand? What should be noted during the installation process? And what is the typical price range for the initial investment? In the following sections, we will break down these key questions and provide a detailed analysis of solar battery sizing, installation, and costs
What Is a Solar Battery?
A solar battery is an energy storage system that captures and stores excess electricity generated by solar panels during the day for later use. It allows homeowners to power their homes at night, on cloudy days, or during outages, thereby reducing dependence on the grid. These batteries store the direct current (DC) generated by solar panels and then release it as alternating current (AC) to power household appliances and other electrical systems.
How Solar Power Works
Power Generation
During daylight hours, solar panels capture sunlight and convert it into direct current (DC) electricity. Modern panels are designed to be highly efficient, even on partly cloudy days, and use photovoltaic cells to transform solar energy into usable electrical power for your home.
Storage
If your household doesn’t use all the energy immediately, the excess electricity is stored in a solar battery. This allows you to save energy for later use, reducing reliance on the grid and helping cut electricity bills. Some systems even allow multiple batteries to be linked for larger storage capacity.
Usage
When sunlight is unavailable, such as at night or during extended cloudy periods, the solar battery releases the stored energy to power your home. This ensures uninterrupted electricity for essential appliances, lighting, and devices, giving homeowners energy independence and peace of mind.
Conversion
The DC electricity stored in the battery must be converted into alternating current (AC) before it can be used by standard household appliances. The battery inverter performs this conversion efficiently, maintaining stable voltage and frequency so devices run smoothly and safely, just like grid electricity.
Types of Solar Batteries
Solar systems require batteries to store electricity, and the lifespan varies significantly depending on the type.
Lithium-Ion Batteries
Lithium-ion batteries are the mainstream choice for residential solar systems due to their high energy density, efficiency, and long lifespan.
Among them, lithium iron phosphate (LFP) batteries are particularly popular. The lifepo4 battery life can reach 10–15 years, with some high-end models lasting up to 20 years under ideal conditions. They are heat-resistant, durable, and reliable.
For example, the EcoFlow portable power station uses LFP batteries.
The EcoFlow DELTA 2 Max Portable Power Station is equipped with an upgraded lithium iron phosphate battery, delivering outstanding durability and longevity. It supports up to 3,000 full cycles while maintaining over 80% of its original capacity. Even with daily use, it can provide nearly 10 years of stable power.
EcoFlow DELTA 2 Max Portable Power Station
Lead-Acid Batteries
Lead-acid batteries are based on older technology and come in two types: flooded and sealed. Flooded models generally last 3–5 years, while sealed options can last 5–10 years. They are less efficient and shorter-lived than lithium-ion batteries, and have largely been replaced in residential applications.
Flow Batteries
Flow batteries are less common for home use. They use liquid electrolytes, offering high efficiency and long-lasting performance. While they can last over 20 years, their large size and high cost make them less practical for residential setups.
UK Solar Battery Costs and Typical Price Ranges
In the UK, solar battery prices do not follow a fixed standard, as they vary depending on the battery’s capacity, brand positioning, technical specifications, and installation scenario. Special attention should be paid when adding a battery to an existing solar system, as this type of installation is often more expensive. This is because it not only requires additional labor costs but may also incur extra expenses for inverter upgrades due to system compatibility issues.
Below are the average costs for solar energy storage systems in the UK, including installation, with typical price ranges for different capacity systems:
Small Storage Systems (3–5kWh): Costs range from £2,500 to £5,000.
Medium Storage Systems (9–10kWh): Price range is £4,500 to £9,500.
Large Storage Systems (15kWh+): Suitable for high electricity demand or near off-grid lifestyles, typically costing over £7,000–£10,000.
From a per-unit perspective, the cost per kilowatt-hour of a solar storage system is relatively stable, generally ranging from £265 to £415 per kWh.
Key Reasons to Add a Solar Battery to Your Home
UK homeowners are increasingly installing battery storage to boost resilience and cut bills. Here are the main benefits:
Energy Independence
Store surplus daytime solar to use after dark or when the grid is constrained, reducing reliance on mains imports. That stored energy lets households run key loads at night or during peak-price windows, and it gives everyday freedom from being tied to grid schedules.
Cost Savings
Batteries let you shift consumption to cheaper self-generated power and avoid buying electricity at peak rates; paired with time-of-use or agile tariffs this can materially lower annual bills. Over time the repeated avoidance of high-price periods improves payback on the system, especially where export payments are low.
Backup Power
A home battery provides immediate, quiet backup during blackouts so essentials like the fridge, lights, comms and medical devices stay powered. Actual runtime depends on battery size and load, but even modest systems can keep critical circuits running through short outages without needing a petrol generator.
Grid Support
Household batteries can enrol in Virtual Power Plants (VPPs) or demand-response programs to supply capacity at peak times, helping stabilise the grid and accelerate renewables uptake. Participating homes may receive payments or bill credits, turning stored energy into both resilience and a small income stream.
What Size Solar Battery Do I Need in the UK?
The core value of a solar battery lies in its ability to store solar energy generated during the day for use at night. This means you can still benefit from solar power even if you’re not at home during the day. But how do I know what size solar battery I need? Choosing the wrong size battery can be costly:
If the battery is too large, you’ll pay for excess capacity you don’t actually use, while also sacrificing valuable space.
If it’s too small, you risk wasting hundreds—or even thousands—of pounds in potential savings.
Selecting the right size solar battery is therefore essential for maximizing your return on investment. The size of your solar battery should be based on your energy usage, household goals, and the output capacity of your solar panel system. Here are the most important factors to consider when deciding what size battery do I need for my solar system.
Calculate Daily Energy Consumption
Check your electricity bills to find your monthly energy usage. Divide this figure by the number of days in the month to determine your daily consumption (measured in kilowatt-hours, kWh).
As a reference, the average UK household consumes around 8–10 kWh per day.
Assess Backup Power Needs
List the essential appliances you would need to run during a power outage. Record each appliance’s wattage and daily operating hours.
Formula for calculating energy consumption: (Wattage × Hours) ÷ 1000 = Energy use (kWh)
Add up the consumption of all essential appliances to calculate your total backup energy requirement.
Match Battery Capacity to Actual Usage
So, what size solar battery storage do I need? Start by calculating your average daily energy consumption. Then, factor in local sunlight conditions and solar panel efficiency to estimate the wattage needed. Finally, apply an efficiency loss factor (usually around 70–80%) to get the actual storage requirement.
Also, consider the Depth of Discharge (DoD):
Lithium-ion batteries: 80%–90%
Lead-acid batteries: around 50%
Example: If you require 5 kWh of usable energy, you should select a battery with a total capacity of 6.25 kWh (calculated as 5 ÷ 0.8) based on 80% DoD.
Common Solar Battery Capacities and Size References
What size solar battery is needed to power a house? The physical dimensions of a solar battery are directly related to its storage capacity. Different capacities come with notable differences in height, width, and depth. Below are typical size references for commonly used solar batteries.
5 kWh Solar Battery
Dimensions
Height: approx. 575 mm
Width: approx. 480 mm
Depth: approx. 183 mm
(Data based on the average measurements of four 5kWh batteries from major UK manufacturers.)
Best For
Small homes or households with light energy needs.
10kWh Solar Battery
Dimensions
Height: approx. 909 mm
Width: approx. 600 mm
Depth: approx. 221 mm
(These figures are based on the average of four different 10kWh batteries produced by leading manufacturers.)
Best For
Sufficient to cover the average daily electricity consumption of a UK household.
15kWh+ Solar Battery
Dimensions
Batteries of this size are significantly larger, though no standard dimension data is currently available.
Best For
Large homes or households aiming for a near off-grid lifestyle.
Flexible Expansion Options Recommended
Some brands now offer flexible solar battery expansion solutions. For example, the EcoFlow DELTA 2 Portable Power Station features 1–3kWh expandable capacity, and you can add extra batteries up to 3040Wh for higher energy needs. By pairing it with portable solar panels, the DELTA 2 can recharge efficiently during daylight hours, making it ideal for families who want a greener energy solution without waiting long. Its smart MPPT system optimizes solar input, ensuring you get the most out of available sunlight. This combination makes it a highly practical choice for home backup needs.
EcoFlow DELTA 2 Portable Power Station
For lighter home use or outdoor trips, the EcoFlow RIVER 3 Portable Power Station offers a compact 245Wh capacity with 300W output. X-Boost mode supports appliances up to 600W, while solar charging lets you recharge quickly on the go. Using small foldable solar panels, the RIVER 3 can capture sunlight efficiently even in tight spaces, making it a versatile and portable solution for camping, emergencies, or occasional power outages.
EcoFlow RIVER 3 Portable Power Station
Conclusion
Equipping your home with a solar battery truly meets household energy needs. It not only helps reduce energy consumption but is also highly environmentally friendly. But what size solar battery do I need? This requires a comprehensive calculation of daily electricity usage, backup needs, and depth of discharge to determine the right capacity. For households planning to install a solar system in the UK, the information in this article will help you get fully prepared for solar battery installation in 2025.
FAQs
Is a 5kW or 10kW solar battery better?
The answer depends on your household’s energy usage, budget, and overall goals, such as reducing reliance on the grid or ensuring backup power during outages:
A 5kW battery is ideal for smaller, energy-efficient homes with moderate electricity consumption.
A 10kW battery is better suited for larger households with higher energy demands, such as those using electric heating or running multiple large appliances. It stores twice the energy of a 5kW system and can power more loads simultaneously.
Should I buy a larger capacity solar battery?
The right choice comes down to your needs and priorities.
If your goal is to cover only essential daily usage, a standard-sized battery may be sufficient.
If you want to maximize savings, a larger battery offers more advantages. It can store more solar energy to reduce electricity bills, take advantage of time-of-use rates to buy low and sell high, and deliver greater long-term value. A bigger battery also helps hedge against rising energy prices and prepares your home for future needs such as electric vehicles or heat pumps.
What should I consider when installing a solar battery?
Choose the best location that avoids shading, with the right orientation and tilt based on your region (south-facing in the Northern Hemisphere, north-facing in the Southern Hemisphere).
Ensure the mounting structure is stable, corrosion-resistant, and securely fixed. Pay attention to polarity during wiring to prevent short circuits or sparks.
Schedule installation during safe weather conditions (avoid rain or strong winds), and always have the system installed by qualified professionals with enough clearance for safe operation and maintenance.