Pyranometers are precision instruments used to measure solar irradiance, a critical parameter in photovoltaic (PV) system performance analysis. Depending on their operating principle, pyranometers are generally categorized into two types: thermopile pyranometers and photovoltaic pyranometers (also known as photovoltaic cell pyranometers, irradiance sensors, or reference cells).
Each type of pyranometer adheres to specific international standards and metrological references that govern their construction, calibration, and application in solar energy monitoring. Understanding these standards is essential for selecting the right sensor technology based on accuracy, response time, and compatibility with your PV system monitoring requirements.
When evaluating this specific type of pyranometer, it is essential to distinguish between the standards in place up to 2009 and those introduced thereafter. This differentiation reflects significant advancements in photovoltaic measurement technology and standardization.
Until the early 2000s, photovoltaic pyranometer cells available on the market often delivered inaccurate readings. This inaccuracy was primarily due to two major issues: sensitivity to cell temperature and degradation over time (aging). However, modern high-precision solar irradiance sensors have long since overcome these limitations, offering stable and reliable performance.
A key milestone in improving measurement accuracy came in 2008 with the development of the IEC 60904 standard series, established by leading photovoltaic research institutions. This family of standards governs the design, traceability, and calibration of reference solar cells used in irradiance measurements:
IEC 60904-2 specifies the procedures for the manufacturing and calibration of reference cells.
IEC 60904-3 defines the measurement principles and the reference solar spectrum.
These international standards ensure consistency, accuracy, and reliability in solar irradiance measurements—critical for the performance analysis and optimization of photovoltaic systems.
Thermopile pyranometers have been widely used since the early 20th century, which led to the development of standardized specifications as early as the 1990s. The primary reference during that period was ISO 9060:1990, which defined the specifications and classification criteria for solar radiation sensors.
In 2018, the standard was updated and replaced by ISO 9060:2018. This revision introduced additional sensor technologies and redefined pyranometer classifications into three accuracy classes: Class A (High Accuracy), Class B (Medium Accuracy), and Class C (Basic Accuracy). These classes are based on parameters such as measurement precision and response time, providing a more comprehensive framework for comparing sensor performance.
For calibration procedures, the relevant standard is ISO 9847, which specifies the methods for calibrating pyranometers against a reference instrument under natural sunlight conditions.
These international standards ensure consistent performance, traceability, and reliability—making thermopile pyranometers a trusted solution in both research and commercial solar energy applications.
In addition to the previously mentioned standards, large-scale photovoltaic system operators and integrators often refer to IEC 61724-1. This standard outlines the terminology, equipment, methodologies, and measurement procedures used for performance monitoring and analysis of photovoltaic (PV) systems.
Now in its third edition, IEC 61724-1 has evolved to emphasize improved measurement accuracy. It places a preference on thermopile pyranometers for performance monitoring due to their stability and low temperature sensitivity. However, despite these advantages, thermopile pyranometers may be slightly less accurate in determining Performance Ratio (PR) compared to photovoltaic pyranometers, which more closely replicate the behavior of actual PV modules under standard operating conditions.
At Soluzione Solare, we ensure full compliance with all relevant international standards across both thermopile and photovoltaic pyranometer technologies. Our products and services are supported by a robust ISO 9001:2015-certified quality management system, ensuring consistent performance, traceability, and reliability in solar energy monitoring.
