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Home Battery Savings Calculator

Estimate UK home battery savings and payback from installed cost, usable capacity, daily cycles, import versus export rates and round-trip efficiency.

Home battery · solar battery · UK payback

Calculator workspace

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£

Total installed price after any discount.

kWh
p/kWh

What you pay for grid electricity — the cost avoided when using stored power.

p/kWh

SEG or export tariff — what you would earn without storing surplus solar.

Advanced options
%

Most lithium batteries do not use 100% of nominal capacity to preserve life.

cycles

How often the battery fully charges and discharges on a typical day.

%

Energy lost charging and discharging — typically 85–95%.

Quick facts
  • Home battery savings come from using stored electricity instead of buying from the grid at a higher import rate.
  • The gap between import price and export rate (tariff spread) drives value — storing solar you would otherwise export is the common case.
  • Round-trip efficiency accounts for energy lost when charging and discharging.
  • Real savings depend on solar generation, load profile, tariff type and battery control — this is a simplified model.
Quick answer

How is home battery payback estimated?

Annual savings = usable capacity × daily cycles × 365 × round-trip efficiency × (import rate − export rate). Payback = installed cost ÷ annual savings. A 5 kWh battery at £4,500 with a 9.5p/kWh spread might save around £112/year in this model — payback roughly 40 years unless cycles or spread improve.

Real-world economics improve with time-of-use tariffs, high evening consumption, EV charging and more solar surplus than this baseline assumes.

Solar export vs self-use

Why replacing export with self-use creates value

Solar panels often generate more than you use at midday. Without a battery, surplus goes to the grid at your SEG export rate — often 4–20p/kWh. Using that energy yourself avoids buying at your import rate — often 22–27p/kWh.

The battery captures that spread. Higher import prices and lower export rates both widen the gap and improve savings per kWh stored.

When batteries make sense

EV, heat pump, time-of-use and high evening use

Batteries make most sense when there is a regular surplus to store or a tariff to arbitrage. Common UK scenarios: solar PV with high export, time-of-use electricity tariffs, EV charging overnight from stored solar, and homes with heat pumps that run in the evening.

If you have little solar surplus and flat-rate electricity, savings may not justify upfront cost — treat this calculator as a starting point before installer quotes.

FAQ

Frequently asked questions

How much can a home battery save in the UK?

Savings depend on how often the battery cycles, the spread between your import rate and export rate, and round-trip efficiency. A 5 kWh battery cycling 0.8 times a day with a 9.5p/kWh spread might save around £100–£120 a year in this simplified model. Homes with time-of-use tariffs, high evening use or lots of surplus solar can do better.

How long does a solar battery take to pay back?

Payback = installed cost ÷ annual savings. At £4,500 installed cost and £112 annual savings, payback is roughly 40 years in this simplified model — which is why battery economics usually improve with higher self-consumption, better tariffs or falling install prices. Run your own figures above rather than relying on generic payback claims.

Does a battery improve solar panel payback?

It can, by shifting solar generation to evening use instead of exporting at a lower SEG rate. Whether the combined system pays back faster depends on battery cost, how much surplus you currently export, and your import tariff. Use this calculator alongside the solar panel payback calculator to compare scenarios.

What is round-trip efficiency?

Round-trip efficiency is the percentage of energy you get back when discharging compared to what you put in when charging. A 90% round-trip efficiency means 10% is lost as heat in the inverter and battery. Typical home lithium systems achieve 85–95%.

Is a battery worth it without solar?

Without solar, a battery only saves money on a time-of-use or dynamic tariff where off-peak import is cheap and peak use is expensive. You charge cheap and discharge during expensive periods. If import and export rates are similar and you have no tariff arbitrage, savings are minimal — which is why most UK battery installs pair with solar PV.

Why does export rate affect savings?

When you have solar, stored energy replaces electricity you would otherwise export at the SEG rate. The value of storage is roughly the difference between what you pay to import (e.g. 24.5p/kWh) and what you earn exporting (e.g. 15p/kWh). A wider spread means each stored kWh is worth more.