An honest answer before you spend a penny
The Green Calculator helps UK homeowners compare energy options, calculate what they would save and decide what to do, without a sales pitch attached. We do the maths in the open and cite the source behind every figure.
Why we built it
Most home energy "calculators" are lead forms wearing a tool costume: enter your details, get a vague number, then field a week of cold calls. The honest part, what you would actually generate, save or pay, is the part they hide. We wanted the opposite. A place that does the real maths, shows its working, and lets you reach your own conclusion first.
It started as a single solar calculator. It is growing into the resource a UK homeowner can check before any energy decision: solar, batteries, heat pumps, EV charging, insulation, tariffs, grants and suppliers, in one place.
What we stand for
🔍 Transparent
Every figure shows the assumptions behind it and a cited source. No black boxes.
🤝 Independent
Estimates are not tuned to sell a bigger system. Rankings are not paid placements.
🔒 Privacy-first
We ask only for what the maths needs and explain how it is handled in our Privacy Policy.
📚 Evidence-based
Assumptions come from public, authoritative datasets, updated as those change.
Where our data comes from
- PVGIS (European Commission JRC) for satellite-derived solar irradiance, used to model location-specific generation.
- Ofgem for price-cap unit rates and Smart Export Guarantee benchmarks.
- GOV.UK and MCS for median installation and battery costs.
- DESNZ for carbon conversion factors and typical consumption values.
- GOV.UK EPC register for property energy data.
How we make money
When you ask to be matched with installers, we may earn a referral fee from the installer if you go ahead. That fee never changes the estimate you see, and you are never required to request quotes to use any calculator. We take no payment from energy suppliers to be listed or ranked. If any of that changes, it will be stated plainly on the page it affects.
Who is behind it
The Green Calculator began as a personal project to answer one frustrating question honestly, and is being developed in the open into a proper tool for UK households. It is currently in beta, improving regularly.