Battery Storage Sizes Explained: Which Capacity Do You Need?
Battery storage comes in sizes from 5kWh to 20kWh+. Choosing the right capacity for your home and solar system is the difference between optimal savings and over-engineering.
In This Article
- 1. Why Battery Size Matters More Than You Might Think
- 2. The 5kWh Battery: Who Is It Right For?
- 3. The 10kWh Battery: The Most Common Choice
- 4. The 13.5kWh–20kWh Range: When Is More Better?
- 5. Getting Battery Sizing Right for Your Home
Why Battery Size Matters More Than You Might Think
Battery storage is the component of a solar energy system that most homeowners get wrong — either under-specifying (leaving significant savings on the table) or over-specifying (paying for capacity they never use). Getting battery sizing right depends on three factors: your household's daily electricity consumption profile, the size of your solar panel system, and your energy tariff structure. The good news: the maths is straightforward, and our engineers model this precisely for every customer during the free survey.
The fundamental question is: how much surplus solar electricity does your system generate each day, and how much of that could you use in the evening if you stored it? A 4kW solar system on a sunny summer day in Yorkshire generates approximately 20–24 kWh. A typical three-bedroom home uses 8–12 kWh per day. The maths suggests 8–12 kWh of surplus per day in summer — and a battery that captures that surplus needs to be at least 8–10 kWh to be worthwhile.
The 5kWh Battery: Who Is It Right For?
A 5kWh battery (one module of a Tesla Powerwall 3, or a single Fox ESS EVO unit) is appropriate for smaller homes — one to two bedrooms — with lower electricity consumption. If your daily usage is 5–7 kWh and your solar system is 3kW or smaller, a 5kWh battery captures most of your daily surplus and covers most of your evening consumption. The cost saving versus a larger battery makes this a sensible entry point.
The limitation: on winter days when solar generation is lower, a 5kWh battery fills more slowly and may be empty by 9pm for households with evening-heavy usage. If you are considering an Octopus Intelligent or similar time-of-use tariff — where you charge cheaply overnight to discharge during peak evening rates — a 5kWh battery limits the volume of cheap overnight electricity you can store. Most households with a smart tariff strategy benefit from 10kWh+.
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The 10kWh Battery: The Most Common Choice
A 10kWh battery is the most popular choice for UK three-bedroom homes with 4–5kW solar systems. This pairing captures virtually all surplus summer generation (a 4kW system in Yorkshire generates 15–22 kWh on a good summer day, but most of that surplus occurs in a 6–8 hour window around midday, and filling a 10kWh battery from say 3kWh morning charge takes the whole afternoon generation window). In winter, a 10kWh battery can be filled overnight on a cheap tariff to provide evening and morning coverage.
Products in the 10kWh range include the Tesla Powerwall 3 (13.5kWh usable — slightly over), the SigenStor SigenEnergy 10kWh, the Fox ESS EVO 10kWh, and the Hanchu Hybrid 10kWh series. At approximately £4,500–£6,500 installed for a 10kWh unit, this tier offers the best balance of cost per kWh of usable storage against practical household benefit. See our battery storage guide for a full product comparison.
The 13.5kWh–20kWh Range: When Is More Better?
Larger batteries — the Tesla Powerwall 3 at 13.5kWh, the SigenStor at up to 20kWh, or stacked Fox ESS units — make sense in three scenarios: households with high electricity consumption (4,500+ kWh/year), homes with large solar systems (6kW+) generating substantial surpluses, and households on time-of-use tariffs who want to store large quantities of cheap overnight electricity for both self-consumption and EV charging.
The EV interaction is the strongest argument for larger batteries. If you have a 60kWh EV and want to charge from solar and cheap overnight tariff electricity rather than grid peak rates, you need the battery capacity to buffer between solar generation, cheap-rate charging windows, and your home consumption. A household with 6kW solar, a 15kWh battery, and an EV could theoretically run their home and charge their car on a combination of free solar and 7p/kWh overnight electricity for most of the year. This is the highest-ROI configuration available in 2026 for energy-conscious households.
Getting Battery Sizing Right for Your Home
The practical recommendation: discuss your electricity bills, daily usage pattern, and any planned EV purchase with our engineer during the free survey. We model your specific generation profile against your consumption data to identify the optimum battery size — not the one that maximises our revenue, but the one that maximises your savings and delivers the best payback period.
Our product range covers all sizes: Fox ESS EVO (5kWh, 8.2kWh, 10.24kWh), Tesla Powerwall 3 (13.5kWh), SigenStor SigenEnergy (10–20kWh scalable), and Hanchu Hybrid series. All come with the lifetime inverter and battery warranties that are a hallmark of our installation package. Call 01302 203 755 for a free survey, or see our costs guide for detailed pricing across our full battery range.
Get Expert Advice from ElectriFusion Solutions
At ElectriFusion Solutions, we are MCS-certified, NAPIT-registered, and TrustMark-endorsed specialists in solar panel installation, battery storage, and EV charger installation across South Yorkshire and Northern England. Our team has completed over 200+ installations and maintains a 4.7/5 rating on Trustpilot from 31+ verified reviews.
Whether you are considering solar panels for the first time or looking to add battery storage to an existing system, we offer free, no-obligation site surveys with transparent pricing and no pushy sales tactics. Every installation comes with our industry-leading warranty package, including 15 years workmanship, lifetime inverter, and lifetime battery warranties.
Contact our team today on 01302 203 755 or request a free survey online. We cover Doncaster, Sheffield, Rotherham, Barnsley, and the wider South Yorkshire region.