Power and efficiency ratings are key for both buyers and sellers and PV modules, in demonstrating the quality and performance of the product. However, as solar power makes its way both into more regions of the world, and more specific applications, it is becoming apparent that the performance of the same module can vary greatly depending on the local climate and other factors, something which is not accounted for in power ratings measured under standard test conditions, even though it can potentially have severe effects on project economics further down the line.
This issue is examined in detail in a new report published by the International Energy Agency’s Photovoltaic Power Systems Program (IEA PVPS) – an international working group that aims to improve quality and reliability in the PV industry.
The report, Climatic Rating of Photovoltaic Modules: Different Technologies for Various Operating Conditions, outlines the need for modules to be assessed on a realistic estimate of performance in different climatic conditions. Providing a ‘climate-specific energy rating’, rather than the standard power rating, say the authors, would allow buyers to compare the performance of different products and make a better decision based on the parameters of their specific project.
“The criteria for the selection of a PV module should shift from a power-based rating to a more accurate and climate-specific rating on the expected lifetime yield e.g. an energy-based rating…,” state the report’s authors. “Deeper knowledge in energy rating can have multiple benefits.”
They explain that for manufacturers, the energy rating demonstrates performance in varying climates. Project developers would be able to make more accurate yield assessments early on in a project, and policymakers could more accurately calculate requirements for product lifetime, quality and ecodesign.
The report notes encouraging developments already on this shift, with standards body the IEC introducing a simple methodology to obtain performance estimates for different climates. But for ‘energy ratings’ to become an accurate industry standard, much more work is needed – to take into account different degradation mechanisms, and to adapt to technological developments such as the recent growth of bifacial modules.
“Climate classification presents a multifaceted problem, in which solutions have to balance specificity, accuracy, simplicity, and applicability,” the report concludes. “Efforts have been made, but still the correlation with field-observed degradation modes are needed.”
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