Performance Ratio

Posted · Add Comment

Performance ratio is a very important parameter of a solar PV plant. Performance ratio is the factor through which the plant performance is assessed. Let us suppose in a very simple way that the solar radiation received in an ideal case of 25 degrees C on the solar pane is 1000 W/m2. or 1 kW / m2. The solar panel has an efficiency of 10%, then the power from the panel becomes 0.1 kW. Then there are the further losses due to the cable loss, grid loss etc after which the power which reaches the grid is around 0.07 kW. The performance ratio (PR) calculated is :

PR = 0.07/0.1 = 70%

The Performance Ratio is calculated above is in a very simple assumption.

Performance ratio (PR) is calculated using the formula in the practical case as :

PR (Performance Ratio) =  Plant Yield /   Net PoA insolation x Plant Nominal DC capacity



Plant yield = Annual (Export energy of plant + Auxiliary energy) in kWh

Net POA insolation = Annual plane of array (POA) insolation in kWh/m2.

Plant nominal DC capacity = As per the project

100%  grid availability would be considered in this case.

If there is a grid outage, loss of generation due to grid outage is calculated on annual basis


Let us consider a sample case of a 2200 kWp plant set up :

Nominal DC capacity of the plant = 2200 kWp

If the plant yield is  27,00,000 kWh for a day and POA insolation on an annual basis is 1600 kWh/ Sq.m. The loss of POA insolation due to grid outage is 25 kWh/m2.

Then the net POA insolation is 1600 – 25 = 1575 kWh/m2.


PR = 27,00,000 / (1575 x 2200) = 77.92%


Loss of generation due to grid outage

Loss of generation due to grid outage  =        27,00,000 x 25 / 1575 = 42,857 kWh


Actual Plant Yield considering grid outage for the day =  27,00,000+42,857 = 27,42,857 kWh

Cumulative Actual Plant Yield considering grid outage for all the days of the year is equal to Actual Annual Plant Yield Considering Grid Outage.


Annual Plant Yield to meet the guaranteed PR of 82.5% in year 1:

PR = 82.50 = Annual expected yield /(1575 x 2200) = 28,58,625 kWh


As per contract, Guaranteed Annual Plant Yield is 28,58,625 kWh for the First year of operation. So the plant is under-performing than the guaranteed generation.

As the plant is underperforming than the guaranteed PR, the contractor is liable to pay loss of revenue calculated @ Rs. 7/kWh.

Penalty on the contractor due to loss of generation for underperformance = (28,58,625 – 27,42,857) x 7


Net penalty payable to the contractor = Rs. 8,10,376


Published by Kaushik Bhattacharya





Leave a Reply

Your email address will not be published. Required fields are marked *