Solar Performance Ratio Calculator

Calculate the performance ratio of a solar installation against its theoretical output.

About Solar Performance Ratio Calculator

The performance ratio separates system quality from site quality, because irradiation is already in the denominator. A well-designed system achieves 80 to 85 per cent regardless of location. Performance ratio is the right metric for diagnosing faults, since a low value cannot be blamed on poor weather.

Formula

Solar Performance Ratio

PR = actual generation ÷ (installed kW × irradiation in the array plane)

performance ratio: Measures system quality independently of the solar resource

Worked example

With the default values below, Solar Performance Ratio Calculator returns Performance Ratio of 91.852%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Actual generationminimum 0 kWh: 6,200 kWh
System sizeminimum 0.001 kW: 5 kW
Annual irradiation in the plane of the arrayminimum 1 kWh/m2: 1,350 kWh/m2

Results

Performance Ratio: 91.852%
Theoretical Generation: 6,750.0 kWh
Generation Lost to System Losses: 550.0 kWh
Specific Yield: 1,240.0 kWh/kW
Rating: Excellent — a well performing system

Step by step

1Values used
2Solar Performance Ratio
3Performance Ratio= 91.852
4Theoretical Generation= 6,750.0 kWh
5Generation Lost to System Losses= 550.0 kWh
6Specific Yield= 1,240.0 kWh/kW
7Rating= Excellent — a well performing system

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Solar Performance Ratio calculated?

PR = actual generation ÷ (installed kW × irradiation in the array plane) The performance ratio separates system quality from site quality, because irradiation is already in the denominator. A well-designed system achieves 80 to 85 per cent regardless of location.

Why does Solar Performance Ratio matter?

Performance ratio is the right metric for diagnosing faults, since a low value cannot be blamed on poor weather.

What values do I need to enter?

This calculator takes 3 inputs: Actual generation, System size, Annual irradiation in the plane of the array. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.