What is Performance Ratio in Solar PV Power Plant

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Hi Guys, welcome to Minutes 2 Energy. We are a team of Solar professionals with more than 10 years of experience in technology and business fields and today we are going to share our knowledge and experience with you. Please see the video till the end for useful resources.


Today’s topic is Solar Plant Performance Ratio or in short PR. PR is a very important tool or factor that being used globally by companies and professionals to assess the healthiness of Solar PV system. So let’s know how this PR is calculated and how it is so important for Solar PV System.

The Definition

So what is Performance ratio or the PR for Solar PV Power Systems?

PR is the Ratio of Effective Produced Energy to Ideal Energy Yield at STC Condition.

  • As it’s a Ratio it is Unit less and globally it is being denoted as a Percentage value.
  • Here the term Effective Energy is the available Useable Energy delivered to the Grid or to the End User.
  • While calculating the PR all the losses like Optical losses PV array Losses DC to AC conversion losses and the other System losses are taken into Account. Please follow our other videos for detail info on Different types of system losses.
  • Simple Annual PR measured on the basis of Actual Annual useable energy and the Annual Solar Irradiance

Now let’s see the Formula of PR

So PR is equals to E_Grid divided by the product of GII and P_NomPV.  Here E_Grid is the Useable energy available at the User End. Unit of E_grid is kWh/year. GII refers to the Global Inclined Irradiation received by the Solar PV array at a certain tilt angle. Next is PnomPV. This is Solar PV array’s installed DC capacity and denotes as kWp.

Next is the types of PR which are there for their own significance and applicability. So let’s know more about them.


First is STC Equivalent PR. It is determined by adjusting the power at each recording interval to compensate for difference between the actual PV module temperature and the STC reference temperature.

This method normally used when the System PR is to be measured at a short duration of day time.

Annual Temperature corrected PR is similar to the previous one. Here PR is calculated by adjusting the reporting period with respect to power to compensate for the difference between the actual PV module Temperature and the expected annual average module temperature.

Annual Temperature correction is significant when the Annual PR is required to be Validated for within 15 to 20 days of operation.

Now let’s look at an example of how to calculate simple annual PR with available plant operational data.


For any given year and location say from a 1000kWp Solar PV On-Grid installation, the annual Global Irradiance received at the PV plane (GII) is 1875 kWh/m2/year, and the useable energy fed to grid is 1540 MWh in entire year.

Now here the E_grid is 1540 MWh or 1540*1000 kWh per year. GII is  1875 kWh/m2/year, and the PnomPV is 1000kWp.
Then the yearly PR Should be calculated as 1540000/(1875*1000)
Which is 0.82 or 82%.

So hope you now understand how to calculate Annual Performance ratio of solar Plant. Please check out our Free Premimum Tool to Calculate PR in MS Excel for more detailed understanding.

The Solar Plant Performance Ratio PR is defined in the norm IEC EN 61724. Please follow the latest edition that is IEC 61724-1 (2017 edition).

Now let’s talk about Few Points you should keep in mind while assessing the Solar Plant Performance Ratio.

First PR always represented as Percentage. Second PR is a Ratio of actual energy generated to the ideal energy Yield for a given period. And the third one is that it is independent of location’s specific Irradiance level.

So What is the Significance of Plant Performance Ratio? Well The PR is an important metric in the PV industry it is often used as a contractual condition / contract warranty when commissioning a PV system Irrespective Of System Size Or System Type whether be it ground-mount or rooftop based Grid-connected or Off-grid be it a small rooftop system or even an Ultra Megawatt utility scale solar plant.

Also we professionals always check PR for the HEALTHINESS of the plant and to VERIFY the annual energy yield.

So this is all about Solar Plant Performance Ratio. To know more about the PR please see these videos. Please let us know how did you find this article helpful in the comment section. We read all of your comments.

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