YOUR SOLAR. YOUR SAVINGS.
One panel.
A brighter outlook
for your energy bills.
See how a small solar system could add up over 10 years — including the cost of buying it.
Calculate your savingsAn estimate you can explore. Every assumption explained.
01 / MAKE IT YOURS
Start with your numbers.
Change the example below to match your quote and electricity bill.
YOUR 10-YEAR OUTLOOK
Historic average · 10.37%Estimated savings after your upfront cost
Calculating your example…
Watch the savings add up.
Cumulative savings after the upfront cost
The starting point is your upfront cost. The £0 line is where it has been recovered.
All three figures are savings after the same upfront cost. Historical increases are scenarios, not a forecast or guaranteed return. Standing charges are not saved.
02 / YEAR BY YEAR
Your 10-year breakdown.
Ten full operating years, starting when the system is installed.
Scroll across the table to see all figures
| Year | Solar kWh | Used at home kWh | Unit rate p/kWh | Bill saving £ | Export income £ | Running costs £ | Annual benefit £ | Net since purchase £, after upfront cost |
|---|
Figures are rounded for display; calculations use full precision. Annual benefit = bill saving + export income − running costs. Net since purchase deducts the upfront cost once.
03 / BEHIND THE ESTIMATE
Clear assumptions.
Useful answers.
A solar estimate should be easy to check. Here is what goes into this one.
Discuss your installationHow is the solar output estimated?
The default is 489 kWh in the first year, rounded from 488.72 kWh. It uses the European Commission’s PVGIS 5.3 hourly model for an illustrative Maidstone location (51.27° N, 0.52° E), with one 0.45 kWp crystalline-silicon panel facing south at 35° above horizontal.
We retain the original 2005–2023 weather data (PVGIS-SARAH3), ventilated mounting assumption, terrain horizon and 10% non-ageing system-loss assumption. For this one-panel version, we scale the original hourly power series to 0.45 kWp before applying the same 800 W output limit and averaging the weather years. Nearby trees and buildings are not included. Hourly weather data cannot capture every short power spike.
The unshaded weather-year outputs ranged from about 457 to 523 kWh in that model. Actual output can differ because of location, weather, shading, mounting and equipment. Changing the angle selects another calculation for the same example location; it does not assess your property.
A separate 0.5% annual reduction starts in Year 2. This is an editable modelling assumption, informed by a published review of panel degradation, not a warranty for your panels. PVGIS’s usual 14% loss default includes ageing, so that default is not used on top of this separate reduction.
PVGIS calculation methods ↗Reproduce the default PVGIS input ↗Panel degradation review ↗
Where does the annual price increase come from?
We use DESNZ’s QEP table 2.2.4, UK overall average variable electricity unit price, excluding standing charges. The latest five complete calendar years are 2021–2025; 2020 provides the baseline for five annual changes. These historical prices include VAT and the Energy Price Guarantee where applicable, but exclude fixed Energy Bills Support Scheme payments.
| Year | p/kWh | Annual change |
|---|
10.37% average annual change: add the five percentage changes and divide by five. This is the initial scenario, matching a simple average of annual increases and decreases.
8.44% compound annual average: (2025 price ÷ 2020 price)1/5 − 1. This reproduces the total increase across that five-year period. The two methods differ because the annual changes were uneven.
The period contains the 2022 price shock. Repeating either average for another decade is a scenario, not a prediction. A 0% growth comparison is included. The historical UK all-tariff series and the Ofgem GB default-tariff starting example cover different populations; enter your own actual unit rate.
DESNZ source and update history ↗QEP 2.2.4 workbook · 30 June 2026 ↗
Which starting tariff and equipment cost are used?
The example starts at 26.32p/kWh, Ofgem’s average electricity rate for Direct Debit default tariffs in Great Britain for 1 October–31 December 2026. Your region, supplier and tariff can differ.
Ofgem’s published rate reflects the temporary removal of electricity VAT from October 2026 to March 2027. This calculator uses the entered price as a Year 1 scenario value and does not separately model future tax-policy changes. Replace it with your actual or assumed first-year unit rate.
£650 is an illustrative total upfront budget, not a confirmed price for the specified single 450 W panel / 800 W inverter. Include equipment, delivery, any VAT and installation in your own total. The £650 example is retained from the original calculator so you can compare the two configurations on the same basis. Enter your actual all-in price for a one-panel system.
How are savings and payback calculated?
Only solar electricity used at home reduces your electricity purchases. The default assumes 70% self-consumption, no battery, no export payment and no annual running costs. These are example inputs, not measured household usage. The remaining generation is treated as export; payment is counted only if you enter an eligible export rate.
Generation in year n = Year 1 generation × (1 − shading loss) × (1 − annual output reduction)n−1
Unit price in year n = starting unit price × (1 + annual price change)n−1
Bill saving (£) = generation (kWh) × proportion used at home × unit price (p/kWh) ÷ 100
Net since purchase = cumulative bill savings + cumulative export income − cumulative running costs − total upfront cost
All money values are nominal, undiscounted pounds. Standing charges, financing, grants, carbon benefits and changes to general household consumption are not included. Export rates and running-cost allowances stay fixed. Equipment replacement is excluded unless you include an allowance.
Estimated payback interpolates within the first operating year in which cumulative benefits recover the upfront cost, assuming benefits accrue evenly in that year. Solar is seasonal, so this is an approximate time, not a promised calendar date. The chart and table show annual totals.
A SMALL SYSTEM. A PERSONAL ESTIMATE.
Find the right fit for your home.
Talk to us about your wall, your daytime electricity use and your equipment options.