Response time is a critical performance metric that directly influences how irradiance sensors are classified under the ISO 9060:2018 standard. Whether Class A, B, or C pyranometers, ensuring each device meets the required response time thresholds is essential for compliance and data integrity across your photovoltaic (PV) sites.

In the sections that follow, we’ll explore how response time factors into ISO 9060:2018 classifications, what the specific response time benchmarks are for each class.

What is ISO 9060:2018?

ISO 9060:2018 is the internationally recognized standard published by the International Organization for Standardization (ISO) that defines the classification and performance specifications for instruments measuring solar radiation.

This standard establishes the class ranking of pyranometers used across photovoltaic (PV) sites, dividing them into three tiers: Class A, Class B, and Class C. To learn more about the three class rankings and the ISO 9060 industry standards, be sure to read the Kipp & Zonen whitepaper “Solar Energy International Standards“.

One of the key measurement parameters ISO 9060 used to determine a pyranometer’s classification is its response time.

To qualify as a Class A pyranometer, a sensor must demonstrate a response time of less than 5 seconds to reach 95% of its final output value following a sudden change in irradiance. Called a step change, this step change serves as a standardized reference for evaluating how quickly and accurately a sensor stabilizes after a shift in brightness.

ISO 9060:2018 uses two benchmarks to assess response time:

63% of final value (one time constant)
95% of final value (full stabilization threshold)

These metrics help ensure that pyranometers deliver reliable, real-time data under dynamic environmental conditions.

For example, Class A pyranometers, such as the Kipp & Zonen SMP12, meet the highest performance criteria by reaching 95% of their final value in under five seconds, making these sensors also “fast response” and ideal for advanced PV analytics.

Response Time vs. Fast Response Time

Fast response is a specialized designation that goes beyond the standard ISO 9060 classifications of Class A, B, and C pyranometers. While a pyranometer with a response time under 10 seconds may qualify as Class A, it does not automatically meet the criteria for fast response.

To earn that label, a sensor must respond in under one second. The Kipp & Zonen SMP12 pyranometer, with a response time of 0.5 seconds, qualifies as both Class A and fast response.

Fast-response sensors are particularly valuable in environments with rapidly changing irradiance conditions and where real-time data accuracy is essential. Common use cases include:

Solar irradiance monitoring on PV sites
Real-time reporting from solar weather stations
Solar tracking systems that follow the sun’s path
Site performance analysis and forecast modeling

Fast Response Data Considerations

Fast-response pyranometers offer enhanced precision under dynamic solar conditions, but to benefit from fast-response capabilities, your data acquisition system must record at matching intervals. If your pyranometer responds in seconds, your logger should capture data in seconds.

If your system captures irradiance changes in real time, investing in fast-response sensors can significantly improve performance analysis and forecasting accuracy. But, if your system aggregates response time data into longer intervals you lose the value of fast response data and will miss short-term irradiance fluctuations.

ISO 9060:2018 Response Time Specifications
The table below summarizes and compares response time benchmarks for ISO 9060 Class A, B, and C pyranometers, including distinctions for fast-response and high-performance Class A irradiance sensors.

ISO 9060:2018 Class Type: Response Time Specification

CLASS A: < 15 seconds
CLASS B: < 30 seconds
CLASS C: < 60 seconds
CLASS A & FAST RESPONSE: < 0.5 seconds

Solar PV: Irradiance Sensor Response Time

Contact supplier

Stay in the loop!