Solar & Battery Quote Checker
Received a solar quote? Check the generation, savings and payback against independent location-specific modelling before you sign. Add a second installer quote to compare them on the same assumptions.
What this checker does differently
It checks the installer claim
Most solar calculators start with a generic system. This tool starts with the system you have actually been offered, independently models location-specific annual and monthly generation and then compares that result with the generation, savings and payback claimed in the quote.
It compares battery size, not just battery/no battery
The result tests smaller and larger usable battery capacities against the same monthly production and household demand assumptions. The purpose is to expose diminishing returns where a larger battery captures little additional solar.
Data and calculation methodology
- Location: your Great Britain postcode is resolved to latitude and longitude using Postcodes.io. Northern Ireland BT postcodes are not accepted in this version. The installer name, price and claimed savings are not sent with that request.
- Solar production: our Cloudflare API calls the European Commission Joint Research Centre PVGIS 5.3 grid-connected PV model using the system kWp, roof pitch, orientation and loss assumption you enter.
- Household matching: monthly generation is compared with estimated monthly household demand. Daytime occupancy changes the proportion of load that can directly use solar. Winter-heavy usage can be selected for homes with substantial electric heating.
- Battery: a daily-average storage model limits charging by solar surplus, usable battery capacity, remaining household demand and round-trip efficiency. A variability factor is applied because monthly averages cannot represent every cloudy/sunny day.
- Value: self-used solar is valued at your avoided import rate and exported solar at your export rate. Standing charges are excluded because installing solar normally does not remove them.
Current tariff reference
The calculator defaults to 26.11p/kWh, the Ofgem average electricity unit rate for a Direct Debit customer on the GB price cap from 1 July to 30 September 2026. Ofgem announced 26.32p/kWh for 1 October to 31 December 2026. Your actual tariff can be different, so the editable rate from your bill is the right input.
Frequently asked questions
Does a green result mean the installer is recommended?
No. It means only that the numerical claims entered are broadly aligned with the modelling assumptions. Installer quality, MCS status, warranties, workmanship, equipment choice, roof condition and contract terms still need separate checks.
Why might your generation differ from the installer?
Differences can come from shading, horizon assumptions, exact array layout, inverter clipping, panel model, system losses and the weather dataset or model used. A modest difference is not automatically a problem; a large unexplained difference is a reason to ask the installer how their figure was produced.
Is the battery model exact?
No. Without half-hourly smart-meter data, no calculator knows exactly when your household uses electricity. This tool therefore reports a central estimate plus a conservative-to-higher-use range and labels the assumptions rather than presenting false precision.
Primary sources
“Independent” describes the calculation method: the installer name entered does not alter the formula or result. The site may display advertising, which does not affect calculator outputs.