Is a home battery worth it?

Two ways a battery makes you money — and one of them is rarely modelled in the quotes you'll receive.

The two value streams

Most installers will tell you a battery makes solar more valuable by storing daytime generation for evening use. That's true, but it's only half the picture in 2026.

Stream 1 — Solar self-consumption uplift

Without a battery, around 40% of your solar output is consumed in the home. The rest exports to the grid at the SEG rate, which is currently 4–16p depending on supplier. With a battery, daytime generation that would have exported instead charges the battery and discharges to power your evening usage.

Each kWh you self-consume instead of exporting saves you the difference between your import rate and your SEG rate. At 24.5p import and 7p SEG, that's 17.5p per kWh shifted. A 10 kWh battery typically shifts an extra 800–1,200 kWh per year of solar — worth £140–£210 a year in uplift.

Stream 2 — Time-of-use arbitrage

Tariffs like Octopus Go offer overnight electricity at around 8.5p/kWh (versus 24.5p peak). Charge a 10 kWh battery overnight at 8.5p, discharge during peak hours, and you save 16p on every kWh shifted — even before you've added any solar to the picture.

A 10 kWh battery cycling 280 times a year (90% efficient) shifts roughly 2,500 kWh of usage from peak to off-peak, saving ~£400 a year. And this works for households with no solar at all.

Putting the numbers together

Let's take a concrete example: average household, 3,500 kWh annual usage, 4 kW south-facing solar generating 3,400 kWh, 10 kWh battery, Octopus Go tariff.

• Battery cost: ~£5,500 installed (post-0% VAT)
• Solar uplift: ~£175/year
• TOU arbitrage: ~£320/year (some overlap with solar means cycles drop slightly)
• Combined annual saving: ~£495/year
• Simple payback: ~11 years

Same setup on a flat 24.5p tariff:

• Solar uplift: ~£195/year (slightly higher because of larger export-vs-import gap)
• TOU arbitrage: £0/year
• Combined annual saving: ~£195/year
• Simple payback: ~28 years

That's the difference. Choose your tariff first; the battery business case follows from it.

When a battery doesn't make sense

Low overall electricity usage

If you use only 1,800 kWh per year, you can't shift much usage from peak to off-peak — there isn't much peak usage to shift. TOU arbitrage drops to ~£150/year. Combined with low self-consumption uplift, payback can stretch beyond the 12-year warranty.

You can't access TOU tariffs

If you're with a smaller supplier, on a fixed deal you can't break, or in a niche situation (some prepayment customers), TOU tariffs may be off the table. Without them, batteries pair with solar only — and the payback maths is much weaker.

Your usage is mostly daytime

Households at home all day (retired, working from home full-time, young family) already self-consume more solar without a battery — perhaps 60% rather than 40%. The battery's solar uplift drops accordingly. Conversely, an empty-during-the-day household sees the biggest battery benefit.

You're moving in 4 years

Batteries do add some value at resale (perhaps £1,000–£2,500 depending on age and capacity) but nothing close to the install cost. If you're moving soon, the maths almost never works.

The hidden cost: degradation

Battery capacity drops roughly 1% per year under normal cycling. By year 12 (typical warranty end), a 10 kWh battery delivers about 8.8 kWh — a 12% reduction in storage and savings. Most calculators ignore this.

Some manufacturers warrant a minimum end-of-warranty capacity (often 70% or 80%). Check yours. Tesla Powerwall, GivEnergy, EcoFlow PowerOcean, and Sigenergy all provide capacity warranties; cheaper imported brands often don't.

Sizing: bigger isn't always better

Battery payback flattens above a certain size for most households. The first 5 kWh captures most of the achievable solar uplift and shifts most of your peak usage; each kWh after that earns less.

Rough sizing rule for an average household with solar: battery size in kWh ≈ daily evening consumption. For a 3,500 kWh/year household with ~60% evening usage, that's roughly 5–6 kWh of evening load. A 10 kWh battery covers that easily and leaves headroom for TOU arbitrage. A 15+ kWh battery starts to struggle to fully cycle except in winter.

Things to ask your installer

• What's the round-trip efficiency? 90%+ is good; below 85% is poor.
• What's the warranty period and capacity guarantee? 10 years minimum; ideally 12.
• Is the inverter hybrid or AC-coupled? Hybrid is more efficient if installed alongside solar; AC-coupled is more flexible for retrofits.
• Does it support time-of-use scheduling out of the box? Octopus Go customers will want native integration with the supplier's smart-charging APIs.
• Can it provide backup during a power cut? Most batteries don't by default — true off-grid backup needs specific configuration and adds cost.

Power cuts and backup: the non-financial case

The UK grid is generally reliable, with the average household experiencing about 0.4 unplanned outages per year, lasting around 38 minutes each. But averages hide a lot. Rural areas — particularly in North Scotland, South Wales, South West England, and Northern Ireland — experience significantly more frequent and longer outages. Overhead power lines running through exposed countryside are vulnerable to storms, fallen trees, and equipment failures in ways that urban underground cables aren't.

A home battery with backup capability can keep your essentials running during a power cut. The critical word is "essentials" — you're not running the oven and the tumble dryer. But lights, fridge, broadband router, phone charging, and a couple of devices can run comfortably on roughly 1–1.3 kWh per hour. That means:

• 5 kWh battery: ~4–6 hours of essential backup
• 10 kWh battery: ~8–11 hours — covers a typical overnight outage
• 15 kWh battery: ~12–17 hours — covers most UK power cuts comfortably
• 20+ kWh battery: full-day backup, with solar recharging during daylight hours you could potentially ride out multi-day outages

Important: not all battery systems support backup. Some grid-tied inverters shut down entirely during a power cut (by design, for safety — they prevent feeding electricity back into a line that engineers are working on). If backup is important to you, specifically ask your installer for a hybrid inverter with EPS (Emergency Power Supply) or backup gateway capability. This is a question of hardware design, not battery size.

For rural homeowners who've experienced multi-hour outages, especially in winter, the backup value of a battery can outweigh the financial payback argument entirely. It's peace of mind that doesn't show up in a calculator.

Our honest take

For a household with solar and a willingness to switch to a TOU tariff, a 5–10 kWh battery is one of the better home-energy investments available in 2026 — payback in 5–8 years and ~£400–£600/year of savings after that.

For a household on a flat tariff with solar, it's marginal. Wait for tariff flexibility before adding a battery.

For a household with no solar, a battery on Octopus Go is worth running the numbers on — TOU arbitrage alone can pay back in 8–12 years on a properly-sized system, and you don't need a roof to do it.

Run your own numbers with our battery payback calculator.

Updated 28 April 2026. Tariff rates and SEG rates change frequently — confirm before committing.