Capacity and performance ratio tests are used to demonstrate the performance of PV plants to buyers or lenders and de-risk their acquisition.
One popular test is ASTM 2848-13 “Standard Test Method for Reporting Photovoltaic Non-Concentrator System Performance”. The goal of this test is to compare the ratio of a modeled system vs the actual system performance, and the system should perform the same as the model, minus some uncertainty. By using a test like ASTM E2848 where the test criteria is well defined and controlled by a standards committee, it insures a consistency of methods and expectations for minimum quality.
Why is this important for owners and financiers?
Failed tests or delays in testing progress could impact liquidated damages (LDs), since this test occurs at the end of the development and build process.
How is the test conducted?
This test may seem straightforward in nature, but the calculations are actually very detailed, complex, and prone to errors.
Step 1 – Gather inputs
To avoid delays in conducting your test, be sure you prepare the proper items for a test. The following are the prerequisites for conducting this test:
Step 2 – Export data
Take the inputs and prepare the data for analysis:
Step 3 – Filter the data for quality
The most complicated aspect of the test is in the sorting of the data to exclude low quality or erroneous points. The data shall be filtered such that the minimum data requirements for site data are:
Step 4 – Run the regression
The regression model is run to find the power capacity and the standard error of the regression measurements. If the ratio of power measured / power modeled is greater than 95%, and all regression errors are less than 5%, you have a valid test with a passing result!
If you are not getting satisfactory results, the most common pitfalls are:
Who conducts this complicated test?
Pure Power has an Owners Engineering department that specializes in the ASTM E2848 and other performance tests. As a third party, Pure Power is an impartial engineer that will run the analysis by the book