Performance Ratio (PR) Definition
The performance ratio (PR) indicates the
overall effect of losses on the array's rated output due to array temperature,
incomplete utilization of the irradiation, and system component inefficiencies
or failures.
Specifically, the performance ratio is the
ratio of the actual and theoretically possible energy outputs.
Calculation of PR:
Further, PR can be calculated in 2 major method - One is yearly basis calculation and the Other one - Daily or Monthly basis calculation where temperature correction must be incorporated while calculating.
These TWO methods shall be discussed in 2 parts, the yearly calculation method explained in this blog and the temperature corrected method shall be discussed in "Performance Ratio For Solar PV Plants - Part 2"
Calculation of yearly PR:
Actual energy generated in a year in kWh
(which is YA here in this case) divided by the Ideal energy
generation of the plant in that year in kWh, let us call it YI.
As per IEC-61724:1998 edition, PR calculation formula can be described as :
The
summations are over a defined period of time (Here, it’s years)
PR = performance ratio (unit less)
ENAC = measured AC electrical generation (kW)
PSTC = summation of installed modules’ power rating from
flash test data (kW)
GPOA = measured plane of array (POA) irradiance (kW/m^2)
i
= a given point in time
GSTC = irradiance at standard test conditions (STC) (1,000
W/m^2)
Now, coming to actual day-to-day practice in the industry, we follow the below formula to evaluate yearly Performance Ratio or PR of a Solar PV Power Plant:
Net Energy Produced = Total Energy Produced (kWh) - Auxiliary Consumption (kWh)
Irradiance at STC (GSTC ) = 1kW/m^2
Irradiation on inclined Plane = GII (kWh/m^2)
Let's see an example of Yearly PR calculation in a spreadsheet. The link to example spreadsheet is here.
Step-1: Collect Yearly Generated Energy of the Plant and sum all the periodic interval values. Here, I've tabled monthly Solar Energy Generation for a given year, for a given location.
Step-2: Assign values to EAac, Gstc, GII & ENac.
Step-3: Put formula as discussed above in your spreadsheet and determine the ANNUAL PLANT PR!!
Here, in this example, the Annual PR is 79.3%. Please note that, the Annual auxiliary consumption determined @0.4% of total energy Generation. This basis will be discussed on a separate post.
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