Solar-and-Battery Payback in the UK (2026): What a Battery Actually Adds

Adding a battery to solar is one of the most over-sold decisions in home energy. Sometimes it genuinely pays for itself; often it adds thousands to your bill for a marginal gain. The difference almost always comes down to one thing — your electricity tariff — and that's exactly the number a salesperson has no reason to scrutinise. We do. Here's how the maths actually works as at October 2026.

Solar alone: self-consumption is where the value sits

A typical UK array yields around 850 kWh per kWp per year (roughly 900–1,000 in south England, 750–800 in Scotland). The biggest single saving is self-consumption — electricity you generate and use yourself, which offsets grid power at around 24.67 p/kWh under the current Ofgem cap. For a typical household, solar self-consumption saves somewhere in the region of £400–£700 a year.

Anything you don't use is exported. Under the Smart Export Guarantee (SEG) you're paid for it — but rates are retailer-set and range widely, roughly 4 to 16.5 p/kWh. Octopus Outgoing's flat rate sits around 12 p/kWh; a standalone SEG rate can be as low as 4.1 p/kWh. So exported power is worth far less than power you use yourself. That gap is the whole reason a battery can help.

What a battery actually adds

A home battery has three possible jobs:

• Store your own solar — soak up midday surplus and use it in the evening instead of exporting it cheaply and buying it back dear. The value is the gap between your import rate and your SEG rate.
• Arbitrage on a smart tariff — charge the battery overnight on a cheap window (e.g. Intelligent Octopus Go's roughly 7 p/kWh overnight rate — verify current) and run the house on it during peak hours. This works even without solar.
• Unlock a premium export tariff — some of the highest-paying export tariffs, such as Intelligent Octopus Flux (time-of-use, peak 4–7pm), require a battery to qualify.

Indicatively, a 5 kWh battery installs for around £3,500–£5,000 and a 10 kWh unit for £6,500–£9,000. There's 0% VAT on home batteries — including standalone retrofit — until 31 March 2027. Typical battery payback lands around 7–12 years. Crucially, there is no grant or subsidy for a general household battery: the case rests entirely on your tariff.

When a battery doesn't pay

Be honest with yourself about these cases — they're common:

• You're on a flat, single-rate tariff and won't switch. No cheap overnight window means no arbitrage, and the only benefit is storing surplus solar instead of exporting it — often not enough to justify the kit within its warranty life.
• Your solar is already highly self-consumed. If you're home during the day, or already run a hot-water diverter into the cylinder, there may be little surplus left for a battery to capture.
• You're export-limited or have a small array. Single-phase systems above 3.68 kW/phase need a G99 application and may be export-capped at 3.68 kW. A small array simply won't fill a large battery.
• The battery is oversized. A 10 kWh battery you only ever cycle 4 kWh through is money sleeping on a wall. Size to your actual evening load, not the biggest unit offered.

A cheap hot-water diverter — sending surplus PV to your immersion cylinder — captures a chunk of the same benefit for a fraction of the cost. For many households that's the better first move.

A worked way to think about it

Scenario	What drives the saving	Battery likely to pay?
Solar + smart tariff with cheap overnight window + evening-heavy usage	Arbitrage + self-consumption + possible premium export	Strongest case
Solar, but home all day, flat tariff, no EV	Only stored surplus vs SEG gap	Weak — check diverter first
No solar, smart tariff, willing to shift load	Pure overnight-to-peak arbitrage	Possible, but thin margins

Note: the SEG and smart-tariff rates above are illustrative ranges. Export tariffs can change with 30 days' notice and the Ofgem price cap resets quarterly, so the exact numbers that decide your payback must be confirmed against live rates — we flag the current figures rather than quoting a brochure.

Northern Ireland runs a separate electricity market, so the SEG and smart-tariff landscape there differs — treat the figures above as Great Britain only.

Getting the decision right

The honest order of operations is: maximise self-consumption first (behaviour, timers, a diverter), get the right import and export tariffs — which can be from different suppliers — and only then size a battery against what's genuinely left on the table. Any MCS-certified install plus a SMETS2 smart meter is the baseline for SEG and premium tariffs.

We don't sell batteries, solar, or anything else — and no installer pays us a referral fee. Even the "free" comparison sites get paid by whoever they send you to. We charge one fixed fee to model your actual tariff and usage, and we'll tell you plainly if a battery won't pay for you. Sometimes the right answer is a £300 diverter, not a £7,000 battery.

Figures in this guide are current at the date of publication and indicative only — SEG/export rates change with 30 days' notice, the Ofgem price cap resets quarterly, and grant terms change. Confirm the current numbers for your situation before you commit. This is general information, not personal financial advice.