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How the rate finder works

Two free Ofgem publications, neither usable as published. This page says exactly what we do with them, so that if a number here is wrong you have enough to prove it.

The sources

The tariff table

Ofgem publishes the CPI-adjusted tariff table as a spreadsheet, most recently on 23 March 2026, covering the tariff year from 1 April 2026 to 31 March 2027. It has a sheet per eligibility-date band and 943 rate rows in total. Rates were adjusted by CPI of 3.4 per cent, taken from the ONS series for December 2025.

We parse every sheet and keep every column that changes a rate: technology, installation type, capacity band, energy efficiency band, and the tariff period within the year. The lookup then matches on all of them.

The installation register

The Feed-in Tariff installation report for 2025-12-31 is published as three spreadsheets totalling about 108MB, one row per accredited installation. We count 869,807 of them holding 6,489.2 MW, which matches the figures Ofgem quotes in its own annual report.

The check this has to pass

Ofgem's spreadsheet contains a worked example: a 4kW solar system with an eligibility date of 12 July 2013, on the higher tariff, is paid 24.46p per kWh.

That example is built into our data pipeline as an assertion. If a future tariff table changes shape and our parser silently mis-reads it, the build fails rather than publishing a wrong number. It is a small check and it already caught a real bug: two column headings in the Ofgem file differ from the rest by a double space and a trailing word, and an exact-match parser dropped both. The fields it dropped were the two that tell a 15.07p tariff from a 35.56p one.

What the lookup does, in order

1. Takes your eligibility date and finds the rate rows whose tariff period contains it.
2. Narrows to your technology.
3. Narrows to the capacity band your system size falls in.
4. For solar from April 2012, narrows to your installation type and energy efficiency band.
5. If exactly one rate remains, shows it. If more than one remains, shows them all rather than picking one, and says what distinguishes them.

That last point is the important one. It would be easy to always return a single confident number. On this data that would frequently be the wrong number, and it concerns money people are owed.

The judgement calls

• The five-installation threshold. Area pages are built where at least five installations share a postcode district. Ofgem publishes the register at installation level, but a district with two systems in it starts to identify houses, so we publish aggregates and stop at five.
• Counts, not rates of uptake. We publish how many installations are in an area, not what share of households that is. Converting one to the other needs a household count we have not sourced, and an unsourced denominator is how misleading league tables get made.
• Majority assignment. A postcode district can straddle constituencies. Where it does, we attribute it to the constituency holding most of its installations and say so rather than splitting it.

What this cannot tell you

• What you will actually be paid. We show the rate Ofgem publishes for your tariff. Your payment depends on how much you generate, your meter readings, and your FIT licensee. We have no access to any of that.
• Your eligibility date. It is on your FIT statement. We cannot look it up, and guessing it from a commissioning date is exactly the kind of near-miss that produces a wrong rate.
• Anything about individual installations. The register is anonymised to postcode district. There is no address-level data here and there will not be.
• Smart Export Guarantee rates. Those are set by each supplier and change constantly. We explain how export payments work rather than publishing a table that goes stale.

Corrections and licence

If a rate here does not match your FIT statement, tell us at editor@ownergy.co.uk with your eligibility date, technology and capacity. We will check it against the Ofgem table and, if we are wrong, fix it and say what changed.

Both sources are Crown copyright, published under the Open Government Licence v3.0. The compiled tables and CSVs here are offered on the same terms.