What is PR (Performance Ratio) and why is it so important?

The Performance Ratio (PR) is the relationship between the actual/effective yield of the system and the theoretical/ideal yield it could achieve if it operated under standard conditions (STC).

It includes in a single numerical value all losses and inefficiencies: soiling, nearby shading, IAM, degradation, mismatch, wiring losses, inverter efficiency, batteries, etc.

Furthermore, it allows you to determine and compare the quality of different systems, as it is independent of the meteorological database and module orientation (normalized based on the incident insolation on the plane).

To calculate it during the design phase of a project, the formula in the image is used, where:

• $PR$ represents the performance ratio.
• $E_{AC}$ is the energy supplied by the photovoltaic system.
• $P_0$ is the total nominal power of the modules.
• $H$ is the annual plane-of-array insolation.
• $G_{STC}$ is the reference irradiance (under standard conditions).

Although reaching a PR of 100 % is impossible, it is important to get as close as possible, and it is common to find values above 80 %, which decrease year after year due to module degradation.