# Step by step procedure for PR test calculation for a solar power plant

Solar power plants are an important source of renewable energy. These plants require regular maintenance and testing to ensure their optimal performance. One of the most important tests for solar power plants is the Performance Ratio (PR) test. In this article, we will discuss the step-by-step procedure for conducting the PR test for solar power plants.

Introduction: The PR test is a crucial test that determines the performance of a solar power plant. It measures the actual energy output of the plant against its theoretical energy output. The PR test is conducted to ensure that the plant is performing as per the contractual requirements.

Functional Guarantee Tests for Solar PV Plant: Functional Guarantee for Solar PV Plant comprises of two Guarantees. First is the Performance Ratio Guarantee test for operational acceptance, and second is the Annual Generation Guarantee up to a period of 10 years (O&M Period), starting from the date of Operational Acceptance.

Performance Ratio Guarantee Test: The PR test is conducted within 60 days of the commissioning of Plant Facilities to demonstrate that the plant has achieved the Guaranteed Performance Ratio as per the bidding document. The PR test period would be continuous measurement of 30 consecutive days. The test shall be conducted in accordance with the IEC-61724 as per the methodology described in Technical Specifications under section VII of the bidding document.

Pre-PR Test: Before conducting the PR test, the following pre-PR test is performed:

- Check the correct installation of monitoring equipment and data loggers.
- Verify the accuracy of measurement equipment and sensors.
- Check the accuracy of weather stations and pyranometers.
- Verify the calibration certificates of the measurement equipment.

PR Test Procedure: The PR test procedure involves the following steps:

Step 1: Calculate Plant Yield The first step in the PR test procedure is to calculate the Plant Yield. The Plant Yield is the sum of Export energy of plant + deemed generation due to reverse power relay/back feed energy reduction. It is calculated on an annual basis in kWh.

Step 2: Calculate Net POA Insolation The next step is to calculate the Net Plane of Array (POA) Insolation. The Net POA Insolation is the annual POA insolation in kWh/m2 after considering the loss of POA insolation due to grid outages.

Step 3: Calculate Performance Ratio (PR) The PR is calculated by dividing the Plant Yield by the Net POA Insolation and Plant nominal DC capacity. The formula for PR calculation is as follows:

PR = (Plant Yield) / (Net POA Insolation × Plant nominal DC capacity)

Step 4: Loss of Generation due to Grid Outage If there is a grid outage, the loss of generation due to grid outage is calculated on an annual basis. The loss of generation due to activation of reverse power relay in kWh shall be recorded based on the data recorded by reverse power relay in the data logger.

Step 5: Calculate Actual Plant Yield The Actual Plant Yield considering grid outage for the day is calculated by adding the loss of generation due to grid outage to the Plant Yield.

Step 6: Calculate Cumulative Actual Plant Yield The Cumulative Actual Plant Yield considering grid outage for all the days of the year is equal to Actual Annual Plant Yield Considering Grid Outage.

Step 7: Calculate PR for Year 1 The Annual Plant Yield to meet the guaranteed PR of ___% in year 1 is calculated using the formula:

PR= ___% = (Annual expected yield) / (Net POA Insolation × Plant nominal DC capacity)

Step 8: Check Performance If the actual PR is less than the guaranteed PR, the plant is underperforming. In this case, the contractor is liable to pay a penalty.

The PR formula can be calculated as follows:

PR = (Plant Yield)/(Net POA Insolation × Plant nominal DC capacity)

where, Plant Yield = Annual (Export energy of plant + deemed generation due to reverse power relay/backfeed energy reduction) in kWh Net POA Insolation = Annual plane of array (POA) insolation in kWh/m2. Plant nominal DC capacity = installed capacity of the plant in kWp.

To understand this calculation better, let’s take the example of a 1 MW solar power plant. The installed capacity of this plant is 1,000 kWp. The annual energy generation of the plant is 1,500,000 kWh, which includes energy exported to the grid and energy deemed to be generated due to reverse power relay/backfeed energy reduction. The annual plane of array insolation on the plant is 1,800 kWh/m2.

Using the formula above, we can calculate the PR of the plant as follows:

PR = (1,500,000 kWh) / (1,800 kWh/m2 x 1,000 kWp) = 0.8333 or 83.33%

This means that the plant is able to convert 83.33% of the sunlight it receives into electrical energy that can be exported to the grid. The remaining 16.67% is lost due to various factors such as thermal and conduction losses, and energy consumption for plant operation.

In conclusion, PR testing is an essential step in ensuring optimal performance of a solar power plant. The PR calculation helps to identify the efficiency of the plant in converting sunlight into electrical energy and can be used to identify areas for improvement to increase the PR of the plant. By conducting PR testing, plant owners can ensure that their plant is operating efficiently and generating maximum output, ultimately leading to higher profitability and sustainability.