What is the performance ratio?

The performance ratio (PR) is one of the most important variables to evaluate the efficiency of a PV module or PV string.

The performance ratio is a measure of the quality of a PV system often described as a a quality factor. The performance ratio is stated as percent and describes the relationship between the actual and theoretical energy outputs of the PV system. It thus shows the proportion of the energy that is actually available for export to the grid after deduction of energy loss (e.g. due to thermal losses and conduction losses ) and of energy consumption for operation.
The closer the PR value determined for a PV system approaches 100%, the more efficient the respective PV system is operating.

The performance ratio is the ratio of the actual and theoretically possible energy outputs.

How to measure PR?

You need different variables to be able to calculate the performance ratio of your PV plant. On the one hand, the incident solar irradiation at your PV plant. On the other hand, you need the factor of the modular area of your PV plant and the relative efficiency of your PV modules which can be obtained from the data sheet.

The PR is then calculated:

$PR=100\% \cdot \frac{\text{actual energy [kWh]}}{\eta \cdot A \cdot G}$

$$\eta: \text{Efficiency}[\%]$$

$$A:\text{Area of PV-system }[m^2]$$

$$G:\text{In-plane irradiance}[\frac{kW}{m^2}]$$

AC or DC Performance Ratio?

The definition of PR treats a PV system as a black box. Only the AC-power that will flow into the grid is being analyzed compared to the amount of sunlight the system receives. For many research applications focus is not only on the generated AC power but on the power at the DC side (before the inverter) as well. This way the influence of the inverter efficiency and (long) cables can be eliminated.

Use PV-Blocks to obtain the PR of your PV system

PV-Blocks is the ultimate tool to monitor the Performance Ratio continuously. The basic configuration should at least measure the following two quantities:

1. The in-plane irradiance on the PV-system ($P_{in}$)
2. The electrical output of the PV-system ($P_{out}$)

The modular PV-Blocks system can measure these quantities in several ways. In order to show the modularity and possibilities of PV-Blocks for PR analysis we will configure 2 example systems. The following 2 use cases explain how to configure PV-Blocks to determine the PR.