Solar Performance Ratio Calculator

Enter actual energy produced, installed capacity, and irradiation — get your system's PR percentage, loss breakdown, and comparison to regional benchmarks.

System parameters

Actual energy produced?

kWh

Installed capacity?

kWp

Reference irradiation?

kWh/m²

Time period?

Total module area?

m²

Regional benchmark?

Performance Ratio

81.7% — Excellent

Reference yield130.0 kWh/kWp

Final yield (specific)106.3 kWh/kWp

Total system losses18.3%

Regional benchmark (82%)-0.3% vs benchmark

Estimated loss breakdown

Temperature losses (~35%)6.4%

Inverter losses (~18%)3.3%

Shading losses (~20%)3.7%

Soiling losses (~15%)2.7%

Wiring losses (~12%)2.2%

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How to Use This Calculator

Gather your actual output data

Read the actual energy produced from your inverter monitoring app or display. Most inverters show monthly and yearly totals. Use a consistent period — either a full calendar month or a full year. Partial periods introduce errors because irradiation data must match the same window.

Enter reference irradiation for the period

Irradiation is the solar energy that landed on your panels, measured in kWh/m². Monthly values range from about 60 kWh/m² in January at northern latitudes to 180+ kWh/m² in peak summer months. Annual values range from 900 kWh/m² in the UK to 2,200+ kWh/m² in the Australian outback. Use PVGIS (free, EU), NASA SSE, or your monitoring platform's irradiation data if available.

Read the Performance Ratio

PR above 80% is excellent for a real-world system. Values of 70-80% are good and typical. Below 70% means meaningful losses — investigate soiling, shading, wiring faults, or inverter issues. Below 60% indicates a serious problem requiring immediate attention.

The Formula

PR (%) = Actual Energy (kWh) ÷ (Installed Capacity (kWp) × Reference Irradiation (kWh/m²)) × 100 Final Yield (kWh/kWp) = Actual Energy ÷ Installed Capacity Reference Yield (kWh/kWp) = Reference Irradiation (kWh/m²) System Losses (%) = 100 − PR Loss Breakdown (empirical distribution of total losses): Temperature: ~35% of total losses Inverter: ~18% of total losses Shading: ~20% of total losses Soiling: ~15% of total losses Wiring: ~12% of total losses

Performance Ratio removes the effect of varying sunlight so you can compare system efficiency across locations and seasons. A PR of 80% means your system converts 80% of the available solar energy into usable AC electricity — the other 20% is lost to heat, wiring resistance, inverter conversion, soiling, and shading. The IEC 61724 standard defines PR as the ratio of final yield to reference yield.

Example

James — Annual review of 10 kWp system in Denver, CO

James installed a 10 kWp system in Denver. His monitoring app shows 13,200 kWh produced last year. Denver received 1,650 kWh/m² of irradiation. He wants to know if the system is performing well.

Actual energy13,200 kWh/year

Installed capacity10 kWp

Reference irradiation1,650 kWh/m²/year

Result

Performance Ratio80.0% — Excellent

Final yield1,320 kWh/kWp

Total losses20%

vs US Southwest benchmark−2% (benchmark: 82%)

At 80%, James's system is performing well — within 2% of the regional benchmark and solidly in the "Excellent" band. The 20% total losses are split across temperature, inverter conversion, minor soiling, and wiring. No action required; a cleaning in spring should maintain or slightly improve the figure.

FAQ

What is a good Performance Ratio for solar panels? ▼

Modern well-maintained residential systems typically achieve 75-85% PR. Values above 80% are considered excellent. Commercial and utility-scale systems can exceed 85% with optimal conditions. Values below 70% indicate significant losses — either from soiling, shading, inverter issues, or wiring faults — and warrant investigation. New systems in the first year often show the highest PR because panels have not yet degraded and are usually clean.

How does temperature affect Performance Ratio? ▼

Temperature is typically the largest single loss in a solar system. Silicon solar cells lose approximately 0.35-0.45% efficiency per °C above 25°C (the standard test condition). On a summer day with panels at 60°C, temperature alone can cause 12-15% output reduction. This is why desert climates with very high irradiation sometimes show lower PR than temperate climates despite producing far more energy — high temperatures offset the gains from abundant sunlight.

Where do I find reference irradiation data for my location? ▼

The best free sources are: PVGIS (pvgis.ec.europa.eu) — covers Europe, Africa, Asia; NASA SSE (power.larc.nasa.gov) — global coverage; NREL NSRDB — best for North America; SolarAnywhere — US-focused with high spatial resolution. Many inverter manufacturers also include irradiation data in their monitoring portals. Monthly GHI (Global Horizontal Irradiance) in kWh/m² is the correct input for this calculator.

What causes a sudden drop in Performance Ratio? ▼

Common causes of sudden PR drops: (1) Soiling or bird droppings on one or more panels — check visually. (2) Inverter fault — check for error codes on the display. (3) New shading source — a grown tree branch, new structure, or debris on the roof. (4) Failed string or module — one failed panel in a string drops the whole string's output. (5) Loose wiring connection — introduces resistance and reduces output. If PR drops more than 5% suddenly, a site inspection is warranted.

Can Performance Ratio exceed 100%? ▼

In theory, a PR above 100% means the system produced more than the reference calculation predicts — which can happen briefly when cold temperatures boost panel efficiency above Standard Test Conditions (25°C). However, a PR consistently above 100% usually indicates a data error — incorrect irradiation values, wrong installed capacity, or metering errors. Real-world best-in-class systems under optimal conditions typically peak around 85-90% PR on a yearly basis.

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