Performance Ratio Calculation by Trackso
The performance ratio is a measure of the quality and performance of a PV plant which is independent of location thus often considered as a quality factor. The performance ratio (PR) is stated as percent and describes the relationship between the actual and theoretical energy outputs of the PV plant. It thus shows the proportion of the energy that is actually available after deduction of energy loss (e.g. due to thermal losses and conduction losses ).
How we calculate the PR ?
At Trackso, we have implemented the following formulas for calculating PR for sites with single orientation & tilt :
Type 1: Based on Output Active Power (as mentioned in SECI Guidelines)
It uses the value of irradiation from the Irradiation sensor (Pyranometer) and summation of Output Active Power of all the Inverters to calculate the PR of the plant.
We use the below mentioned formula* to calculate the performance ratio:
Instantaneous PR(%) = . 
Our system calculates the summary of the plant every half an hour.The algorithm picks the last value of the output active power from the inverters and last logged value of solar irradiation from the sensor and calculates the PR using the above-mentioned formula. These values are aggregated over the day and the Daily PR is calculated.
Instantaneous PR = Calculated every 30 mins using above formula
Daily PR = Avg of all the Instantaneous PR calculated in a Day
For the calculation of PR, its important that the exposure to radiation should be same for pyranometer and the PV panel. Thus, to cater the same Trackso suggests its clients to place the Pyranometer in the vicinity of the PV module, with the same angle of inclination as that of PV.
*Source : As mentioned in the SECI guidelines : https://solarrooftop.gov.in/notification/Notification05052016-2.pdf
Type 2: Energy Based PR
Performance Ration= Specific Yield * 100/ Solar Insolation
Type 3: Temperature Corrected PR
Seasonal variation of the traditional PR is removed by calculating a temperature-corrected performance ratio:
PR’ STC = (Eout / Ck P0) / (Hi / Gi,ref )
with
Ck = 1 + γ × (Tmod,k – Treference)
Using 25 °C as Tref gives PR’STC.
This term Ck corrects for the difference between the actual temperature and STC temperature used for power rating. The value of γ is usually negative and of the order of -0.3%/K.
Module temperature is correlated with irradiance, so in case the performance is modelled; you must use a weighted average. PV panels may rise up to 20 °C above ambient temperature.
Cell temperatures are typically 1 °C to 3 °C higher than the temperature measured on the module’s rear surface, depending on the module construction. The temperature difference may best be estimated as a function of irradiance, using the thermal conductivity of the module materials. Suggestions for this can be found in IEC 61724-2 Annex A.