Solar battery cost & sizing
A battery only earns its money if it’s the right size. Tell us your system size and when you use electricity, and we’ll recommend a capacity — then price it at 2026 UK install rates.
Figures checked October 2026 Estimate
Sized so roughly a third or more of your daily use can be shifted from daytime solar into the evening, capped by what your panels actually export. Costs assume ~£650–£850 per kWh installed (estimate).
How big a battery do you actually need?
The sizing mistake most people make is buying storage for energy they never generate. A battery can only store what your panels export, so the right size is the smaller of two numbers: how much you use after the sun goes down, and how much surplus your system produces on an average day. For a typical 4kWp system and a household that’s out during the day, that maths lands on 5kWh — which is why it’s the most common UK battery size. Our recommendation works on the same principle: shifting around 35% of your daily use from generated to stored power.
Price-wise, a 5kWh battery installed costs an estimated £3,000–£4,500 in 2026, with larger units getting cheaper per kWh (a 10kWh unit is typically £5,500–£8,000, not double the 5kWh price). Most modern batteries are lithium iron phosphate (LFP), warrantied for around 10 years or a set number of cycles, and usable to about 90% of their nameplate capacity — a “5kWh” battery gives you roughly 4.5kWh of working storage.
When a battery pays — and when it doesn’t
A battery earns money two ways: storing solar you’d otherwise export for a few pence (worth 26.32p/kWh avoided at the October 2026 cap, minus the 3–6p export payment you give up), and — on smart tariffs — charging cheaply overnight. If you’re home all day using power as it’s generated, self-consumption is already high and a battery adds little. If you’re out all day, it can lift self-consumption from ~40% to ~70% and is often the difference between an 11-year and an 8-year payback. Check the combined numbers in the payback calculator before committing.
Battery questions
Can I add a battery later?
Usually, yes — either as an AC-coupled unit that works with any inverter, or by swapping to a hybrid inverter. Adding it during the original install is normally cheaper, and both fall under the 0% VAT rate until 31 March 2027 when installed as part of an energy-saving installation.
Will a battery power my home in a power cut?
Only if it’s wired for backup (EPS) — many standard installs go dark with the grid for safety reasons. If blackout protection matters, ask for it specifically; it can add cost.
How long do solar batteries last?
Expect around 10 years of warranty coverage and 4,000–6,000 cycles (estimate). Capacity fades gradually rather than failing outright — most warranties guarantee ~70% remaining capacity at the end of the term.
Ready for real prices?
Calculators give you the ballpark. Get free, no-obligation quotes from MCS-certified UK installers and compare them against these numbers.