Battery Storage Self Consumption Calculator
Estimate how a home battery may change solar self-consumption, grid imports, export value, annual bill saving and simple payback using your own tariff and battery assumptions.
Enter Solar, Battery And Tariff Details
Estimated Battery Impact
Enter your solar and tariff figures to estimate self-consumption.
Result Reading
Share this estimate with an installer or household decision-maker.
What Battery Self-Consumption Means
Solar self-consumption is the share of your solar generation that is used in the home rather than exported. A battery can raise that share by storing midday surplus and discharging it later, often during evening cooking, lighting, entertainment, heat-pump use or EV top-up. The financial gain is not the full import price for every stored kWh, because exported solar has a value and battery charging loses some energy.
This calculator compares a simple “solar without battery” case with a “solar plus battery” case. It estimates direct solar use, stored solar, export reduction, grid import reduction, export income change, tariff arbitrage from cheap charging and a simple payback. It is best used before a quotation meeting or after receiving a proposal, so you can challenge the assumptions rather than reading a single headline saving.
Calculation Method
Direct solar use = solar generation x direct-use percentage
Stored solar input = minimum(surplus solar, usable battery capacity x cycles x 365)
Useful stored energy = stored solar input x round-trip efficiency
Extra value = avoided import - lost export + cheap-tariff gain
The battery can only store solar that would otherwise be exported. It also cannot discharge more useful energy than the remaining household demand after direct solar use. The estimate therefore caps stored solar by surplus generation, battery throughput and remaining demand. Round-trip efficiency is then applied to show the useful kWh delivered back to the home.
Export value is included because a stored kWh may replace a sold kWh. If your import price is 24.67p/kWh and export tariff is 12p/kWh, the gross value of shifting one perfect kWh is 12.67p before battery losses. If export is very well paid, the saving from a battery may be smaller than expected.
Inputs To Check Before Buying
Half-Hourly Use
Smart meter data or an inverter app gives a better self-consumption estimate than an annual bill alone.
Export Contract
A high export tariff reduces the extra value of storing surplus solar. Use your actual SEG rate.
Usable Capacity
Nameplate battery size is not always the usable size. Reserve settings and warranty limits matter.
Ask installers for usable capacity, inverter charge and discharge limits, whether the battery can charge from the grid, expected warranty throughput, fire-safety positioning, monitoring app access and how export metering will work. If you have a heat pump or EV, check whether evening demand is large enough to use stored energy. If everyone is home in the day, direct solar use may already be high, reducing the battery’s additional gain.
Example Battery Scenarios
| Home Pattern | Battery Effect | Saving Risk | Useful Check |
|---|---|---|---|
| Empty home in daytime | Battery may capture more midday surplus for evening use. | Export tariff could already pay well. | Compare import price minus export price, not import price alone. |
| Work-from-home household | Direct solar use may already be high. | Battery has less surplus solar to store. | Check real midday import and export before sizing. |
| EV on driveway | Large flexible demand can soak up solar directly. | EV charging may compete with the home battery. | Model EV charging schedule separately. |
| Heat pump home | Evening demand can raise battery usefulness. | Winter solar surplus may be limited. | Look at monthly generation, not only annual kWh. |
| Time-of-use tariff | Cheap grid charging may add value. | Tariff terms, losses and standing charges still matter. | Use cheap import field and check supplier rules. |
Tariff And Price Notes
The default import rate is 24.67 p/kWh, matching Ofgem’s Great Britain direct debit average electricity unit rate for 1 April to 30 June 2026. Ofgem stresses that actual rates vary by region, payment method, meter type and tariff. Northern Ireland has a different energy market. Export tariffs are not set by the price cap, so enter the rate from your supplier or Smart Export Guarantee contract.
Standing charges are not included in the saving because a household usually pays them whether or not a battery is installed. If a battery lets you move to a different tariff, compare the whole annual bill, including day rate, night rate, export rate, standing charge and any EV or heat-pump add-ons.
Battery Payback Limits
Simple payback divides the installed cost by the annual saving. It is easy to read but incomplete. It does not include finance interest, maintenance, inverter replacement, battery degradation, warranty throughput, lost interest on cash, property value, resilience value, carbon goals or future tariff changes. A battery may still be worthwhile for outage backup, tariff flexibility or using more of your own solar, even where simple payback is long.
Ask for a year-by-year estimate if the purchase is large. A credible proposal should state solar generation assumptions, direct self-use, battery throughput, export tariff, import tariff, degradation and review date. If the sales quote claims very high self-consumption, request the half-hourly load profile used to support it.
FAQs
What is a good solar self-consumption rate?
It depends on the home. A household that is out during the day may use less solar directly, while a home with daytime appliance use, EV charging or heat-pump demand may use more. The best rate is one based on real import and export data, not a fixed national figure.
Does every stored kWh save the full import rate?
No. A stored solar kWh may replace exported electricity that would have earned an export tariff. Battery losses also reduce useful output. The extra value is closer to avoided import minus lost export, adjusted for round-trip efficiency.
Should I include cheap overnight charging?
Include it only if your battery, inverter and tariff allow grid charging and your supplier permits the use case. The saving is the difference between avoided day import and cheap import cost, after battery losses. It can be useful, but tariff rules can change.
What battery size should I choose?
This calculator does not prescribe a size. A useful size depends on surplus solar, evening demand, inverter limits, budget and warranty. Too small a battery may fill early; too large a battery may sit partly unused for much of the year.
Does a battery cut standing charges?
Usually no. Standing charges are daily fixed charges and are normally paid even when you import fewer kWh. This calculator focuses on unit-rate savings and export changes, so it does not treat standing charge as a battery saving.
Can the result be used for a finance decision?
Use it as an initial estimate only. For finance, compare quotes, warranty terms, interest, degradation, tariff risk and installer credentials. Ask for written assumptions and keep them with the contract.
Sources
- Ofgem. (2026). Energy Price Cap Unit Rates And Standing Charges. Ofgem. https://www.ofgem.gov.uk/information-consumers/energy-advice-households/energy-price-cap-unit-rates-and-standing-charges
- Energy Saving Trust. (2025). Solar Panel Battery Storage. Energy Saving Trust. https://energysavingtrust.org.uk/advice/solar-panel-battery-storage
- Microgeneration Certification Scheme. (2024). Battery Storage: Consumer Guide. MCS. https://mcscertified.com/technology/battery-storage/
- Ofgem. (n.d.). Smart Export Guarantee. Ofgem. https://www.ofgem.gov.uk/environmental-and-social-schemes/smart-export-guarantee-seg