What is a performance ratio (PR)?

A system's Performance Ratio (PR) is a relative indicator its energy efficiency. It expresses the percentage of possible energy that is converted into actual output. The higher the PR, the more energy efficient your system is. Unfortunately it can never reach 100%, due to things like thermal losses, inverter efficiency and resistive cable losses.

Autarco’s calculations of PR take into account various factors. We expect your system to have a fairly constant PR over its entire lifetime.

• The measured insolation and temperature on your roof. Typically based on satellite data for small systems.
• The direction and tilt of your solar panels to convert the horizontal satellite measurements to a “plane-of-array” measurement which is the sunlight directly hitting the face of your solar panels.
• The shade of your system at every month/hour of the day.
• The age of your system (module degradation)
• The exact components used in your system and how they were installed (system stringing).

If your PR drops, it indicates module soiling, new shade (tree growth) or perhaps some product defect.