Keyur Rakholiya P75 is the annual energy yield a solar plant is expected to exceed with 75% probability, taken from the uncertainty distribution in an energy yield assessment. Assuming a normal distribution, P75 equals P50 minus about 0.674 times the combined standard uncertainty. It sits between the median P50 and the lender-focused P90 estimate.
Quick Facts
| Field | Detail |
|---|---|
| Term | P75, 75th Percentile Energy Yield |
| Category | Engineering Math / Bankability |
| Sits Between | P50 (median) and P90 (lender-conservative) |
| Formula | P75 = P50 − 0.67 × σ |
| Typical Use | Commercial PPA hedge structures, IPP risk modeling |
| Software Used | PVsyst, SAM |
What Is P75?
Formal definition
The P75 annual energy yield is the value Q where the cumulative probability function P(annual energy ≥ Q) = 0.75, in plain terms, a 75% chance the plant produces at least P75 in any given year.
Engineering definition
P75 is computed the same way as P50 and P90: start from the mean simulated annual energy (P50), then subtract a multiple of the combined uncertainty σ (inter-annual weather variability plus PVsyst/SAM modeling uncertainty). For P75, that multiple is 0.67, smaller than P90’s 1.28, so the resulting number sits closer to the median than P90 does.
Industry definition
P75 doesn’t have the near-universal role that P50 (equity) and P90 (debt) play. It shows up mainly as an intermediate confidence band in commercial PPA hedge structures and IPP-side risk modeling, where a party wants more conservatism than the median forecast but doesn’t need the full 90% confidence buffer lenders require.
Worked Example
Using the same simplified statistics as a typical Energy Yield Assessment:
- Mean simulated annual yield (P50), μ = 250 GWh/yr.
- Combined uncertainty, σ = 6% of mean = 15 GWh.
- P75 = μ − 0.67 × σ = 250 − (0.67 × 15) = 250 − 10.05 ≈ 240 GWh.
For comparison, the same plant’s P90 (μ − 1.28 × σ) would be about 231 GWh, a bigger haircut off the mean because P90 demands a higher confidence level.
P75 vs. Other Confidence Levels
| Metric | Confidence | Typical Use |
|---|---|---|
| P50 | 50% | Equity IRR, expected revenue |
| P75 | 75% | Commercial PPA hedges, IPP risk modeling |
| P90 | 90% | Senior debt sizing (most common) |
| P99 | 99% | Stress test / worst-case scenarios |
Key Takeaways
- P75 = 75th-percentile annual energy yield.
- Between P50 (median) and P90 (lender-conservative).
- Used in some commercial PPA hedge structures.
- Formula: P75 = P50 − 0.67 × σ.
- Less common in finance than P50 and P90.
Related Reading
P75 rarely appears on its own, it’s one line in a broader Energy Yield Assessment that also reports P50 and P90, and understanding how those numbers get built (and reviewed by lenders) makes the P75 figure easier to place in context. For a lender’s-eye walkthrough of how these confidence bands are derived and challenged during due diligence, see P50, P90, P99 in Solar Yield Reports.
If you’re commissioning the underlying yield study rather than just reading one, Bankable PVsyst Reports, The Complete 2026 Guide covers the methodology and common errors that make a P50/P75/P90 report hold up (or fall apart) during financial close.
Frequently Asked Questions
3 commonly searched questions about P75.
When is P75 used in solar projects?
Is P75 more or less conservative than P90?
How is P75 calculated?
Need engineering-backed solar designs?
Heaven Designs prepares solar drawings, structural calculations, electrical engineering documents, and project-specific permit plan sets.