Solar PPA calculator: estimate your UK saving (2026)
This solar PPA calculator estimates what a power purchase agreement would save your business: enter your system size, grid rate and the PPA tariff you have been offered, and it returns year-one and whole-term figures. Every default is sourced or labelled as an assumption in the tables below.
Quick answer: what this calculator does
Enter your array size, your delivered grid rate and the year-one PPA tariff you have been offered. The calculator applies your self-consumption share, export terms, escalator, panel degradation and any grid-price change year by year, and returns your year-one saving and the total over the term. With its defaults — a 250 kWp roof on a 13 p/kWh tariff against 24.1 p/kWh grid power — it shows £18,731 in year one. No email required.
Solar PPA savings calculator
Year-one saving and the total over your contract term. Every input is adjustable; the defaults are explained below the calculator.
Year one, then the whole term
Indicative arithmetic on your inputs, not a quotation. Totals are simple sums with no discounting. For a binding tariff, providers need your half-hourly data — send it through the quote form.
How the solar PPA calculator works
The solar PPA calculator runs the same five steps for every year of your contract, then adds the years up:
- Generation = system size × yield, reduced by the degradation rate for each year the panels have been in service.
- Units used on site = generation × your self-consumption share. The rest is exported.
- Grid cost avoided = units used on site × your grid rate, adjusted by any grid-price change you enter.
- PPA cost = the same units × the PPA tariff, raised by the escalator each year.
- Net saving = grid cost avoided − PPA cost, plus export income only if your contract assigns it to you.
Two design choices keep the result honest. Export income is excluded by default, because the provider owns the array and export revenue is only yours if the contract assigns it to you — switch it on only if yours does. And the totals are plain sums rather than a discounted net present value, so a finance team can apply its own discount rate to the year-by-year figures.
The default inputs, and where they come from
A calculator is only as good as its defaults. Each one is either sourced or labelled as an assumption you should replace with your own data:
| Figure on this page | Value | Source | Verified |
|---|---|---|---|
| Grid import rate | 24.1 p/kWh (24.14 p/kWh all-band average, including CCL) | DESNZ Quarterly Energy Prices, table 3.4.2 (non-domestic, including CCL, excluding VAT), Q1 2026, last updated 30 June 2026 | 26 Sep 2026 |
| Yield | 900 kWh/kWp a year — a conservative planning assumption | Assumption, checked against PVGIS v5.3 (EU Joint Research Centre) — PVGIS-SARAH3 radiation data, 1 kWp crystalline silicon, 14% system loss (table below) | 26 Sep 2026 |
| PPA tariff | 13 p/kWh year one | Assumption inside this site's indicative 8–22 p/kWh on-site band | — |
| Self-consumption | 75% | Assumption. We are not aware of an official UK statistic for commercial self-consumption — use your half-hourly data | — |
| Export rate | 6 p/kWh | Assumption. Ofgem — Smart Export Guarantee: suppliers set their own rates, which must be above zero; solar PV installations up to 5 MW in Great Britain are eligible | 26 Sep 2026 |
| Escalator | 2.5% a year | Assumption. Inflation target 2%: Bank of England | 26 Sep 2026 |
| Degradation | 0.5% a year (median of 1,920 reported rates) | Jordan & Kurtz, Photovoltaic Degradation Rates — An Analytical Review, Progress in Photovoltaics, 2013 (NREL) | 26 Sep 2026 |
| Contract term | 20 years | Contract convention, not a published statistic | — |
UK solar yield by city (PVGIS)
Yield is the input that varies most by location. These are PVGIS results for 1 kWp of crystalline silicon at a 14% system loss, for an array at its optimum pitch and for a low 10° array facing due south — closer to what many flat commercial roofs carry. Use the figure nearest your site, or run PVGIS for your own postcode.
| City | Optimum pitch (kWh/kWp/yr) | 10° flat roof, due south (kWh/kWp/yr) |
|---|---|---|
| Southampton | 1,066 | 964 |
| Cardiff | 1,044 | 946 |
| London | 1,023 | 920 |
| Birmingham | 971 | 875 |
| Newcastle | 954 | 844 |
| Leeds | 951 | 851 |
| Belfast | 922 | 828 |
| Aberdeen | 900 | 791 |
| Manchester | 888 | 807 |
| Glasgow | 855 | 772 |
PVGIS v5.3 (EU Joint Research Centre) — PVGIS-SARAH3 radiation data, 1 kWp crystalline silicon, 14% system loss; optimum pitch = PVGIS optimised slope and azimuth (39–43°), free-standing mounting. Queried 26 Sep 2026.
Worked example: a 250 kWp warehouse roof
This example is modelled, not observed — it is the calculator's own arithmetic at its default inputs, and describes no real site or customer. A 250 kWp array at 900 kWh per kWp generates 225,000 kWh in year one. At 75% self-consumption, 168,750 kWh are used on site and 56,250 kWh are exported.
| Line | Modelled figure |
|---|---|
| Grid cost avoided (168,750 kWh × 24.1 p) | £40,668.75 |
| PPA cost (168,750 kWh × 13 p) | £21,937.50 |
| Net saving, year one (export kept by the provider) | £18,731.25 |
| Add export income if the contract assigns it to you (56,250 kWh × 6 p) | £3,375.00 |
| Total over 20 years, 2.5% escalator, flat grid price | £243,514 |
| Same, with the grid price rising 2% a year | £407,125 |
| Same, with a fixed tariff (0% escalator) and a flat grid price | £357,353 |
The table shows why the escalator matters more than the starting tariff. With grid prices held flat, a 2.5% escalator lifts the tariff to 20.78 p/kWh by year 20 and shrinks that year's saving to about £5,090. Whether that is a good trade depends entirely on what you expect grid prices to do — which is why the calculator lets you set both. Remember too that a fixed tariff is normally offered at a higher starting price than an escalating one, so compare real offers rather than the same tariff with the escalator switched off.
How big a solar system do you need for your consumption?
Divide the annual kWh you want solar to cover by your site's yield. Covering 24,000 kWh a year at 900 kWh per kWp needs about 26.7 kWp — roughly 59 modules at 450 W each (module ratings vary, so treat the module count as illustrative). On a commercial site that is rarely the right target, though. Solar output is heavily seasonal — in London about two-thirds of an optimally tilted array's annual output arrives between April and September — so an array sized to your whole annual demand exports much of its summer output at an export rate, often to the provider rather than to you. Sizing to your daytime base load keeps self-consumption high, and self-consumed units are the ones worth your full grid rate.
London monthly split from PVGIS v5.3 (EU Joint Research Centre) — PVGIS-SARAH3 radiation data, 1 kWp crystalline silicon, 14% system loss, optimised angle: April–September 66.3% of 1,022.9 kWh/kWp. Sizing arithmetic is modelled. Queried 26 Sep 2026.
What is the average price of a solar PPA in the UK?
There is no official average — tariffs are negotiated privately. This site's indicative bands put 2026 on-site tariffs at 8–22 p/kWh in year one, falling with system size and covenant strength, and utility-scale corporate strikes at £55–£75/MWh. Our guide to the PPA tariff explains how each band is built and what else a contract can charge for, and the solar PPA rates page breaks the bands down by system size.
Solar PPA calculator FAQs
How accurate is the solar PPA calculator?
It is arithmetic on your inputs, so it is as accurate as they are. It models generation, degradation, self-consumption, export and escalation year by year, but not half-hourly load matching, performance guarantees, buy-out terms or the time value of money. For a binding figure, providers need your half-hourly data — send it through the quote form.
What yield should I use for my site?
Use PVGIS for your postcode. At PVGIS v5.3 with an optimised angle, 1 kWp produces about 1,023 kWh a year in London, 971 in Birmingham and 855 in Glasgow; a low 10° array produces less — 920, 875 and 772 respectively. The 900 default is a conservative planning assumption.
Why does self-consumption matter so much?
Each unit used on site displaces a grid unit at your full delivered rate, while an exported unit earns only an export rate — and often not for you. We are not aware of an official UK statistic for commercial self-consumption, so replace the 75% default with a figure from your half-hourly meter data.
Should I model a fixed tariff or an escalator?
Run both. At the calculator's defaults, a 13 p/kWh tariff rising 2.5% a year saves about £243,500 over 20 years against a flat grid price, while the same tariff held flat saves about £357,400 — but fixed tariffs usually start higher, so compare real offers side by side. See our escalator comparison.
Who gets the export income under a PPA?
Whoever the contract says. The provider owns the array, so unless the contract assigns export revenue to you, assume it stays with the provider — the calculator excludes it by default. If your contract assigns export to you, change that setting and enter your supplier's rate: SEG rates are set by each supplier and must be above zero, for solar installations up to 5 MW in Great Britain.
What is the average price of a solar PPA in the UK?
There is no official average. This site's indicative bands put 2026 on-site solar PPA tariffs at 8–22 p/kWh in year one, depending on system size and structure, and utility-scale corporate strikes at £55–£75/MWh. The PPA tariff guide breaks both down.
How big a solar system do I need for my consumption?
Divide the annual kWh you want to cover by your site's yield: 24,000 kWh a year at 900 kWh per kWp needs about 26.7 kWp. On a commercial site, size to your daytime base load instead, because generation you cannot use on site is exported at a much lower value.
What this calculator doesn't model
The calculator now models degradation and grid-price change, but it still leaves out:
- Half-hourly matching of generation to your load — the self-consumption share stands in for it
- Performance-ratio guarantees and make-good payments
- Buy-out, extension or removal at the end of the term
- Discounting — the totals are simple sums, not a net present value
- Site costs such as roof refurbishment or a DNO connection upgrade
- Standing, capacity and network charges that a PPA does not change
For a full DCF model run by your finance team, see our 25-year DCF comparison. Or send us your site data and we'll model in real provider scenarios via the quote form.
Run real provider numbers
A 60-second form gives us enough to match you to PPA providers and return real binding tariff ranges.
Get an indicative PPA tariffThe single input that moves the twenty-year total more than any other is the PPA escalator, so set it deliberately rather than accepting a default.
Above a certain annual demand the pricing logic changes entirely and corporate PPA volumes are negotiated against covenant strength rather than roof size.
This model assumes power delivered to your meter; virtual PPA pricing works from a strike price and a settlement difference instead.
Self-consumption is the number the result is most sensitive to, and on-site generation explains why the profile of your working day matters more than your annual total.
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Ask us what a PPA would cost at your site
Solar PPA calculator: estimate your UK saving (2026) — tell us about your site and we'll return an indicative p/kWh tariff for it. Reply by email within one working day.