Performance Ratio Guarantees in Solar PPAs
Performance ratio (PR) is the metric that defines whether a PPA system is generating as promised. What good PR guarantees look like in 2026.
Performance ratio explained
Performance ratio (PR) is the ratio of actual energy output to the theoretical maximum the system could have produced. It captures real-world losses — inverter efficiency, soiling, cable losses, temperature derating, downtime — in one number.
What good looks like in 2026
| PR band | Quality assessment |
|---|---|
| 82%+ | Excellent — well-designed, well-maintained |
| 78-82% | Good — typical UK target |
| 74-78% | Marginal — investigate |
| Below 74% | Material problem — design, install or maintenance issues |
How PR guarantees work
Most providers offer a PR guarantee of 78-82% averaged over 12 rolling months. Below target = make-good payment. Above target = no extra payment to you (asymmetric).
Watch-outs in the contract
- How PR is calculated — IPMVP Option B is gold standard
- Reference irradiance source — local pyranometer vs satellite vs default
- Force majeure exclusions — too broad and you have no protection
- Dispute resolution mechanism
- Independent assessor right (with cost cap)
Make-good payment options
- Tariff reduction next quarter
- Direct cash payment (rare)
- System remediation (provider must fix the issue)
- Combined remediation + tariff reduction
See what tariff your site qualifies for
A 60-second form gives us enough to match your site to providers and return an indicative tariff range within one working day.
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