PV Pros: Evaluate PV Plant Real Performance – Performance Ratio (PR)
PR (Performance Ratio) is a core indicator for PV plant operation, project acceptance and bidding decisions. Defined in IEC 61724-1:2021, it serves as a unified benchmark for PV systems, directly reflecting efficiency, losses and O&M quality, and represents the golden standard for performance compliance. Using real project cases, we break down PR to help you quickly assess actual plant performance!
I. Core Concept: What Exactly Is PR?
PR (Performance Ratio) = Actual Power Output ÷ Theoretical Ideal Power Output
In simple terms: total solar irradiation represents the “full theoretical score”, actual generation is the “achieved output”, and their ratio is PR. The closer PR is to 100%, the higher the efficiency, the lower the losses, and the better the operation and maintenance.
II. Key Note: PR Is Not a Single Value,But a Professional Evaluation System
Many evaluators rely only on raw PR. In fact, the national standard defines four categories of PR for different scenarios and precise assessment requirements:
1. Basic PR (Raw Value) – Quick overview of daily performance
2. 25°C Temperature-Corrected PR – Eliminates temperature influence for fair comparison
3. Annual Equivalent Temperature-Corrected PR – Stable and acceptable for long-term evaluation
4. Bifacial System-Specific PR – Includes rear-side gain for more accurate assessment
III. Practical Case: Calculate All 4 PR Types for a 100kWp PV System
1. Using actual daily data from a 100kWp PV plant, we calculate the full set of PR step by step:
l Front-side irradiation: 5.0 kWh/m²
l Actual AC output: 340 kWh
l Module temperature: 45℃
l Power temperature coefficient: -0.38%/℃
l Bifaciality: 0.85
l Measured rear-side irradiation: 0.45 kWh/m²
✅ Conclusion: The PV system only achieved 68% of its theoretical performance on the day, indicating relatively high power losses.
2. 25°C Temperature-Corrected PR (Objective & Fair Value)Temperature directly affects module performance. According to the national standard, all values shall be corrected to the 25°C standard condition to eliminate interference from seasonal and weather temperature variations.
Temperature correction factor = 1 + (-0.0038) × (45 - 25) = 0.924
Corrected theoretical hours = 5 × 0.924 = 4.62 h
Temperature-corrected PR = 3.4 ÷ 4.62 ≈ 73.6%
✅ Conclusion: After excluding high-temperature effects, the actual system efficiency is 73.6%, providing a more objective evaluation.
3. Annual Equivalent Temperature-Corrected PR (For Acceptance & Warranty) Corrected to the annual average module temperature, data is free from seasonal fluctuations, enabling year-over-year comparison, contract acceptance and annual assessment.
Annual average module temperature: 35℃
Annual correction factor: 0.962
Annual equivalent PR = 3.4 ÷ (5 × 0.962) ≈ 70.7%
✅ Conclusion: Suitable for long-term evaluation, serving as the key basis for project acceptance and warranty verification.
4. Bifacial System-Specific PR (Essential for Bifacial PV Plants) Bifacial modules generate power from the rear side; conventional PR underestimates theoretical generation. Rear-side gain must be included to avoid data distortion.
Total theoretical generation hours = 5.0 + 0.45 × 0.85 = 5.38 h
Bifacial system PR = 3.4 ÷ 5.38 ≈ 63.2%
✅ Conclusion: Accurately reflects the real performance of bifacial power stations and eliminates evaluation bias.
IV. Core Summary: 4 Key Points for Professional PV Plant Evaluation
1. PR is the unified evaluation yardstick for PV plants; no PR means no reliable way to judge plant performance.
2. Raw PR is only for preliminary reference — temperature-corrected PR enables fair comparison.
3. Bifacial plants must use bifacial-specific PR, otherwise data will be distorted.
4. Accurate assessment requires collecting: backsheet temperature, front-side + rear-side irradiation of the array.
GB/T 20513.12025 provides the industry with a unified, fair and comparable evaluation standard.For future plant inspections, reports and acceptance, do not report only raw PR.Presenting temperaturecorrected PR, annual equivalent PR and bifacial PR is the standard practice for PV professionals.
