Performance ratio (PR) is the most important parameter of a solar PV plant. Every investor’s primary focus is about PR and EPC contract provides the guarantee of PR of the plant. Although no of software are available in the market which are able to calculate the performance ratio of the plant but from an investor and EPC contractor eye, it is worth to understand the performance ratio and right way to calculate it. Here, in this article, I have used PVSYST, well known and widely used software for the designing and analysis solar PV plant and cross check the manually calculated values with the PVSYST results.

Performance ratio (PR) is the factor through which you can assess the plant performance, how the plant is behaving. 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.

There are two basic parameters to calculate the performance ratio Y _{f} (Final PV system yield) and Yr (Reference yield). PR is the Ratio of Y _{f} and Y_{r} .

**Performance ratio = Y _{f}/Y_{r}**

Y _{f} = E/P_{0}

E= Net energy Output in KWh

P_{0}= Installed PV array in KW

Yr= H/G

H= Total plane irradiance in KWh/m^{2}

G= PV reference irradiance in KW/m^{2}

**Case Study**

Take a 1 MW PV plant for calculating the performance ratio. E is taken from PVSYST generated report and P_{0} is 1 MW. H is taken from the PVSYST table and G is the value at STC which is 1000 W/m^{2}.

Manual calculation result to 74.9% and software is also showing the same value.

Posted by: Er. Gaurav Sharma , gsharma@firstgreenconsulting.in

The above figures show a very good representation of % of losses due to different factors like ohmic losses, PV losses due to temperature & irradiance. Can u please eloborate on how u have arrived at those figures. I am specially curious about how the PV losses due to temperature (which is significantly large=15.9%) are calculated.

The figure shown in the article was Snapshot taken from the PVSYST report and all the value are automatically calculated by the software, however, we can calculate these values. Your main concern is a calculation method of PV losses due to temperature.

If you look at the manufacturer data sheet, you will see term called ‘Temperature coefficient P max’ in %/Deg C. In Jaipur, Rajasthan, for which I have done the PR analysis, operating temp of the Solar PV plant goes around 65˚ C to 70˚ C , which means it is around 40˚C to 45˚C higher than the STC (Standard test condition: 25˚C). I had used Canadian Solar CS5P-240P modal for my PR analysis and temperature coefficient for this particular module is -0.43%. So, for every degree C increase in temp from the STC generation will reduce by 0.43%.

Every solar plant owner wishes for more sunshine for the more generation, however, it will also increase panel temperature and this will lead to increase in losses. For typical solar PV Plant this increase in temperature from STC may reduce solar PV plant output by 10% to 25% depending upon location to location.

Thank you Mr sharma for the information. I look forward to gain more information from you in the time to come. Can you tell me when & why do we apply the temperature correction factor to the PR & what is its effect on PR – increases or decreases the effective PR?