Calculator
Battery Storage Calculator
Right-size your home battery to maximize savings and backup protection
Home battery storage lets you keep the lights on during outages and maximise the value of your solar investment — but sizing it wrong means either overspending or running out of power when you need it most. This calculator determines the optimal battery capacity for your UK home based on your electricity usage, critical load requirements, and whether you have solar panels. It factors in current UK battery pricing, 0% VAT relief on energy-saving materials, SEG export rates, and regional Ofgem standing charges to give you a complete cost picture.
0% VAT on energy-saving materials expires 31 March 2027. SEG export rates vary by supplier — check your tariff. Read the policy details
Enter Your Details
Fill in the form and click Calculate to see results.
Policy status
UK solar and battery incentive policy status
UK incentive assumptions depend on the project year and your eligibility. RenewableCalc applies 0% VAT on energy-saving materials (until 31 March 2027) and Smart Export Guarantee (SEG) export rates. ECO4, Boiler Upgrade Scheme (BUS), and Home Energy Scotland grants are available for eligible households — verify current eligibility on gov.uk before treating any estimate as final.
Policy last reviewed: 2026-06-09 · Source: Ofgem SEG guidance, HMRC Energy Saving Materials Relief, and MCS installer standards.
Next best actions
Battery economics depend heavily on your utility's export credit and time-of-use rates.
Overview
Home battery storage lets you keep the lights on during outages and maximise the value of your solar investment — but sizing it wrong means either overspending or running out of power when you need it most. This calculator determines the optimal battery capacity for your UK home based on your electricity usage, critical load requirements, and whether you have solar panels. It factors in current UK battery pricing, 0% VAT relief on energy-saving materials, SEG export rates, and regional Ofgem standing charges to give you a complete cost picture.
Use this result
Use the calculator inputs first, then compare the result against local rates, incentives, roof conditions, and utility export rules.
Method, assumptions, and sourcesOpen this section when you want to audit the calculation behind the estimate.ShowHide
Calculation Method
Battery capacity is sized using: Required Capacity (kWh) = Daily Energy Consumption × Backup Duration (days) ÷ Depth of Discharge (DoD). We assume a standard DoD of 90% for lithium iron phosphate (LFP) batteries, which dominate the current residential market per SEIA 2024 data. Critical load calculation sums essential circuits: refrigerator (1.5 kWh/day), lighting (0.5 kWh/day), internet/communication (0.1 kWh/day), medical equipment if applicable, and HVAC allowance. The calculator cross-references against leading battery models (Tesla Powerwall 3: 13.5 kWh, Enphase IQ 5P: 5 kWh modules, LG RESU 16H: 16 kWh) and labels federal battery incentive assumptions as project-year dependent, with state-specific incentives referenced through the DSIRE database.
Key Assumptions
- Backup sizing should separate whole-home loads from critical loads such as refrigeration, lighting, internet, and medical equipment.
- Usable capacity is lower than nameplate capacity because depth of discharge and reserve settings matter.
- Bill-savings payback depends on solar export credits, time-of-use rates, and household load timing.
- Backup and resilience value should be reviewed separately from pure utility bill savings.
Data Sources
Electricity rates
Ofgem
Uses the Ofgem price cap for England, Scotland and Wales. Updated quarterly. Current cap: 24.5p/kWh (April–June 2026).
Battery specifications
MCS Product Database
Battery models and specifications sourced from MCS-certified product listings. Typical UK installations use Tesla Powerwall 3 (13.5 kWh), GivEnergy (9.5 kWh), or Fox ESS.
Installation costs
MCS Installer Database
UK battery installation costs typically £3,000–£7,000 before VAT relief. 0% VAT applies to battery storage installed alongside solar panels until March 2027.
Export rates
Smart Export Guarantee (SEG)
SEG export rates (1–27p/kWh) affect whether storing solar in a battery beats exporting it. Higher SEG rates reduce the financial case for batteries.
Assumptions Data Sources Related Links
How to Use This Calculator
Enter your average daily electricity consumption in kWh (use our Energy Consumption Calculator if unsure). A typical UK home uses 7–10 kWh per day (electricity-only, gas-heated); adjust based on your smart meter readings. Select whether you have solar panels — this affects whether you're storing excess solar or just using the grid. Choose your backup priority: full home backup (all circuits), partial backup (essential loads only), or solar self-consumption (no backup focus). The calculator recommends battery capacity in kWh, shows compatible battery models, estimated total cost after 0% VAT and SEG incentives, and payback period based on your Ofgem electricity rate and Economy 7/Time-of-Use savings potential.
Formula & Methodology
Battery capacity is sized using: Required Capacity (kWh) = Daily Energy Consumption × Backup Duration (days) ÷ Depth of Discharge (DoD). We assume a standard DoD of 90% for lithium iron phosphate (LFP) batteries, which dominate the current residential market per SEIA 2024 data. Critical load calculation sums essential circuits: refrigerator (1.5 kWh/day), lighting (0.5 kWh/day), internet/communication (0.1 kWh/day), medical equipment if applicable, and HVAC allowance. The calculator cross-references against leading battery models (Tesla Powerwall 3: 13.5 kWh, Enphase IQ 5P: 5 kWh modules, LG RESU 16H: 16 kWh) and labels federal battery incentive assumptions as project-year dependent, with state-specific incentives referenced through the DSIRE database.