Understanding Performance Ratio

Performance ratio (PR) is the factor through wchich you can assess the plant performance. If a plant has a performance ratio of 80%, it shows that 20% energy generated through the PV panels is lost in the system losses. Performance ratio is defined in the two parameters.

A. Energy Performance Ratio

B. Power Performance Ratio

The Energy Performance – Ratio shall be calculated as the ratio of Measured, Actual Energy Evacuate in the Grid (KWh) over one year of the at the evacuation point at a particular instant, and Calculated, Nominal Energy Output (KWh) over one year


                                                       Measured, Actual Energy Evacuate in the Grid (KWh)

Power Performance Ratio            =             __________________________

                                                         Calculated, Nominal Energy Output (KWh)

 The Nominal Energy output of the Plant is calculated as the integral of the Nominal over, Output of the plant over the one year period.


The power performance is calculated as follows:


                                                       Specific yield (KWh/kWp)

Power Performance Ratio            =             __________________________

                                                         Irradiation on a inclined plane (KWh/m2)


The following factors can have influence to the PR value: • Environmental factors

‒ Temperature of the PV module
‒ Solar irradiation and power dissipation
‒ The measuring gage  is in the shade or soiled
‒ PV module in the shade or soiled
• Other factors
‒ Recording period
‒ Conduction losses
‒ Efficiency factor of the PV modules
‒ Efficiency factor of the inverter
‒ Differences in solar cell technologies of the measuring gage (e.g. Sunny SensorBox) and of the PV modules
‒ Orientation of the measurement gage 

If  the total solar irradiation on a plant is 130 kWh/m2, and the total module area is 100 m2, and module efficiency is 15%,. The net electricity export to the frid is about 1600 MWh.

The performance ratio is estimated as follows:

PR= 1600/(130*100*0.15)=82%.


However if the net export to the grid reduces to 1300 MWh the performance ratio will be as follows:

PR=1300/ (130*100*0.15)=66%.

It means that one third of the total energy generated by the modules is lost in the plant systems. This loss can be accounted for the DC wiring loss, thermal loss, conduction losses, inverter ;losses, etc. Such reduction in generation will greatly affect the plant financial viability. Hence it is important to the plant owner to clearly understand that where all these losses are taking place. It require a detailed plant audit to be carried out at each component level.

A continuous monitoring of PR require the monitoring of energy flow at each string level. While many investors are reluctant in investing in string level monitoring systems. It becomes extremely difficult to identify real causes of the losses. These days automatic PR monitoring systems are available and one can track its plant PR on real time basis and take corrective action. 




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