How to calculate performance ratio of solar power plant

Performance Ratio Formula

The Performance Ratio (PR) is calculated using the following formula:

PR = (Y_f / Y_r) × 100%

Where:

• Y_f (Actual Yield) = Total energy output (E_out) / System rated power (P₀)
• Y_r (Reference Yield) = Total solar irradiation (H_i) / Reference irradiance (G_i,ref = 1 kW/m²)

Step-by-Step Calculation

1. Determine Actual Yield (Y_f)

• E_out: Measure the plant’s total energy output over a specific period (e.g., annual energy production in kWh).
• P₀: Sum the rated power of all solar modules under Standard Test Conditions (STC, 1 kW/m² irradiance, 25°C cell temperature).
• Y_f = E_out (kWh) / P₀ (kW) → Units: Hours (h).

2. Calculate Reference Yield (Y_r)

• H_i: Measure the total in-plane solar irradiation received by the panels during the same period (in kWh/m²). Use pyranometers or sensors like Sunny SensorBox.
• G_i,ref: Use the reference irradiance (1 kW/m²).
• Y_r = H_i (kWh/m²) / 1 kW/m² → Units: Hours (h).

3. Compute PR

PR = (Y_f / Y_r) × 100% → Expressed as a percentage.

Example

Assume a 1 MW (1,000 kW) plant generates 1,500,000 kWh annually and receives 1,800 kWh/m² irradiation:

• Y_f = 1,500,000 kWh / 1,000 kW = 1,500 h
• Y_r = 1,800 kWh/m² / 1 kW/m² = 1,800 h
• PR = (1,500 / 1,800) × 100% ≈ 83.3%

Key Notes

• Purpose: PR isolates system efficiency from location-specific factors (e.g., solar resource) to compare performance across different plants or time periods.
• Losses Included: Factors like temperature derating, wiring losses, inverter inefficiency, shading, and dust accumulation are inherently reflected in PR.
• Timeframe: Typically calculated annually but can adapt to shorter periods (monthly/daily) with context-aware interpretation.

For accurate results, ensure precise measurements of irradiation (H_i) and energy output (E_out).