PPA Mechanics

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.

FAQs

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.