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When it comes to demonstrating the performance of photovoltaic (PV) plants to potential buyers or lenders, capacity and performance ratio tests play a crucial role in reducing the risks associated with their acquisition. One widely recognized test is ASTM E2848-13, "Standard Test Method for Reporting Photovoltaic Non-Concentrator System Performance." The purpose of this test is to compare the modeled system's performance against its actual operational output, ensuring that the system performs as expected within a defined uncertainty range. Using standardized tests like ASTM E2848 ensures consistency in methodology and sets clear expectations for minimum quality.
This type of testing is particularly significant for both owners and financiers because failed tests or delays in completing the test can lead to penalties such as liquidated damages (LDs). These penalties often occur at the conclusion of the development and construction phase when the test is carried out.
The process of conducting this test might appear simple at first glance, but the calculations involved are intricate and prone to errors. Here's a breakdown of how the test is typically performed:
**Step 1: Gather Inputs**
To ensure smooth execution of the test, it's essential to gather all necessary inputs beforehand. Key prerequisites include:
- A validated PVSYST model.
- Experience in regression modeling and access to a functional test sheet.
- A fully operational system with well-maintained equipment and accurately calibrated weather stations.
- At least five to seven days of continuous system operation, contingent on favorable weather conditions.
**Step 2: Export Data**
Once the inputs are secured, the next step involves preparing the data for analysis:
- Extract annual raw data from the PVSYST model. This data should encompass Global Horizontal Irradiance (GHI), ambient temperature, wind speed, correction factors for calculating Plane of Array (POA) irradiance, along with timestamps for each dataset.
- Retrieve climate and performance data from your data acquisition system. This information should include timestamps, production meter readings, temperature, wind speed, and POA irradiance.
- Review the system's mechanical and electrical blueprints to identify any unique challenges like shading or excessive inverter clipping that might affect modeling accuracy.
**Step 3: Filter Data for Quality**
Sorting through the data to eliminate low-quality or incorrect entries is arguably the most challenging part of the test. The filtering process ensures that the data meets the following minimum requirements:
- A minimum of 50 fifteen-minute data points or 750 minutes of total data.
- Exclude data points below 400W/m² and those exceeding 98% of the inverter's nameplate capacity.
- Ensure reporting conditions for POA are within ±20%.
- Although there are no specific restrictions for temperature or wind, excluding non-correlated data can enhance reliability.
**Step 4: Perform Regression Analysis**
Run the regression model to determine the power capacity and standard error of the regression measurements. A successful test results when the ratio of measured power to modeled power exceeds 95%, and all regression errors remain under 5%.
If these criteria aren't met, common issues include:
- Collecting sufficient valid data points may take up to a month depending on system design and seasonal variations.
- The PVSYST model must provide hourly data; merely relying on the summary PDF isn't sufficient.
- Improper regression setups often occur during initial attempts due to the absence of dedicated tools for analysis.
- Inaccurate sensor calibration significantly impacts test outcomes, emphasizing the need for precise calibration before data collection.
**Who Conducts This Complex Test?**
Pure Power boasts an experienced Owner’s Engineering division specializing in ASTM E2848 and other performance evaluations. As an independent third-party consultant, Pure Power ensures unbiased analysis adhering strictly to industry standards.