Methodology
Calculator Methodology
This page explains how the Solar Savings Calculator UK creates its estimates, what assumptions it uses, and why the results should be treated as a starting point rather than a formal solar quote.
Last updated: May 2026
Important summary
The calculator is designed to give a quick planning estimate for UK homeowners. It estimates system size, generation, installation cost range, annual benefit, payback period, battery benefit, EV charging relevance, and CO2 savings.
It does not replace a proper installer survey. Final quotes, system design, suitability, savings, and payback depend on your actual property and chosen products.
Main calculator assumptions
Electricity bill to annual usage
The calculator estimates annual electricity usage by converting your monthly electricity bill into yearly spend, then dividing by an assumed electricity unit rate.
System size estimate
The calculator estimates a rough solar system size based on annual usage and typical UK generation assumptions, then adjusts the size based on bedroom count.
Regional generation
The calculator uses different generation assumptions for South England, Midlands/Wales, North England, and Scotland/Northern regions.
Roof direction
South-facing roofs are treated as strongest. South-east and south-west are slightly reduced, east/west is reduced further, and north-facing roofs are reduced significantly.
Shading
No shading uses the full estimate. Light, moderate, and heavy shading reduce estimated generation.
Self-consumption
The calculator estimates how much solar electricity is used at home based on daytime usage, battery interest, and EV ownership.
Export income
Unused estimated solar generation is treated as exported electricity and valued using a simple assumed export rate.
Payback period
Estimated payback is calculated by dividing the estimated installation cost range by the estimated annual benefit.
How the estimate is calculated
Estimate annual electricity usage
Monthly electricity bill is converted into estimated yearly electricity spend, then divided by an assumed electricity unit rate.
Estimate solar system size
The calculator estimates a rough system size based on annual usage, then keeps the result within a typical range for the selected property size.
Estimate annual generation
Estimated system size is multiplied by a regional generation assumption, then adjusted for roof direction and shading.
Estimate self-consumption and export
The calculator estimates how much solar electricity is used at home and how much may be exported to the grid.
Estimate annual benefit and payback
Estimated bill savings and export income are added together, then compared with the estimated installation cost range.
What the calculator includes
- • Estimated annual electricity usage
- • Estimated system size
- • Estimated generation
- • Estimated installation cost range
- • Estimated annual benefit
- • Estimated payback range
- • Estimated CO2 saving
- • Battery and EV relevance
What the calculator does not include
- • It does not inspect your actual roof
- • It does not check planning, structural, or electrical suitability
- • It does not use live electricity tariffs
- • It does not guarantee Smart Export Guarantee rates
- • It does not include all possible installation complications
- • It does not replace an MCS installer quote or survey
- • It does not guarantee savings, payback, or performance
Why your real quote may be different
Solar installations are property-specific. Two homes with the same electricity bill can still need different system designs and receive different quotes.
Roof direction, pitch, size, condition, and shading
Location and local solar generation conditions
Household electricity usage and when electricity is used
Electricity import tariff and export tariff
Solar panel, inverter, battery, and EV charger choice
Installer pricing, warranty, scaffolding, and installation complexity
Future electricity prices and export rates
How to use the results properly
Use the calculator as an early planning tool. It can help you understand whether solar may be worth exploring, what size system may be relevant, and whether battery storage or EV charging could change the result.
Before making a decision, compare real installer quotes and check roof suitability, warranties, product choice, export rates, electrical requirements, and final installation cost.
Next step
Start with the calculator estimate, then compare quotes if the result looks promising.