Solar PPA Escalators: Fixed, RPI or CPI?
An escalator is the annual % uplift baked into your PPA tariff. Get the escalator wrong and a 25-year contract that looks cheap in year 1 ends up costing more than buying outright.
Year-1 vs lifetime cost: the four escalator types
| Escalator type | Year 1 tariff | Year 25 tariff | 25-yr cumulative cost (250kWp, 237,500 kWh/yr) |
|---|---|---|---|
| 0% (fixed) | 13.5 p/kWh | 13.5 p/kWh | £801,000 |
| RPI-linked (assume 3% avg) | 12.5 p/kWh | 26.2 p/kWh | £1,099,000 |
| CPI-linked (assume 2.5% avg) | 12.8 p/kWh | 23.7 p/kWh | £1,032,000 |
| Fixed 2.5% | 13.0 p/kWh | 24.1 p/kWh | £1,051,000 |
Illustrative only — assumes constant generation and constant tariff bands; real models include performance degradation (~0.5%/yr) and discounted cashflow.
Why escalators exist
Solar generation degrades — panels lose ~0.5% per year. So a 100kWp system that delivers 95,000 kWh in year 1 delivers ~83,000 kWh in year 25. The provider's IRR maths needs to compensate. The escalator does that.
But escalators also reflect the provider's funding model. A fund with an inflation-linked LP base will offer an RPI-linked PPA. A fund with fixed-rate debt will prefer a fixed escalator.
How to negotiate the escalator
- Ask for the year-25 number, not just year-1.
- Model cumulative cost under both 0% and RPI scenarios.
- Push for an RPI-capped-at-3% structure if the provider insists on inflation linkage.
- If you're investment-grade, push for fixed 0% — your covenant gives the provider the security to accept.
Frequently asked questions
Which escalator should I pick?
Fixed 0% if your grid forecast is stable; RPI-linked if you expect grid prices to keep rising and want to hedge. Generally the lowest 25-year cumulative cost wins — model both.
Can I cap the escalator?
Yes — RPI-capped-at-3% is common in 2026 contracts. The cap protects you against runaway inflation while giving the provider some uplift.
What if RPI drops below the escalator?
Most contracts include a floor of 0%. If RPI goes negative, your tariff stays flat that year.
Run your site through our calculator
Model fixed vs RPI escalators with your actual kWh and tariff assumptions in 30 seconds.
Open calculatorFor a worked 20-year example comparing a flat, a fixed-2% and a CPI-linked escalator on the same opening tariff, with every assumption shown, see the companion post.
An escalator only makes sense read alongside the rest of the tariff: the starting price, the structure and the charges a contract can add on top.
Find out what tariff your site would be offered
Solar PPA Escalators: Fixed, RPI or CPI? — tell us about your site and we'll return an indicative p/kWh tariff for it. Reply by email within one working day.