Selecting the Right NABL-Accredited Calibration Laboratory for Pyranometers and Temperature Sensors
Introduction
The accuracy of solar plant performance evaluation depends on the reliability of measurement instruments such as pyranometers and temperature sensors. To ensure data integrity, these instruments must be calibrated in a NABL-accredited laboratory. Accreditation provides traceability to international standards, including the World Radiometric Reference (WRR), and guarantees that calibration results are reliable, repeatable, and globally accepted.
In this blog, we explore why calibration is necessary, the risks of neglecting it, the applicable standards, the methods of calibration (ISO 9847 and ISO 9846), and the best practices to consider when selecting a laboratory.
Why Calibration is Required
Calibration is essential because sensor accuracy naturally degrades over time due to environmental exposure, dust accumulation, and electronic aging. Without calibration, even minor drifts can lead to major consequences. For example, a pyranometer deviation of just 2β3% can artificially lower the calculated performance ratio (PR), misrepresenting the efficiency of the plant. Temperature sensor errors can distort module thermal loss evaluations, leading to incorrect O&M strategies. Inaccuracies of this nature undermine investor confidence, regulatory compliance, and long-term plant performance.
Consequences of Non-Calibration
Uncalibrated sensors introduce systematic errors into plant monitoring systems. These errors can result in miscalculated energy yield, overstated or understated PR values, and misguided operational decisions. Financially, this can translate into reduced revenue, disputed settlements, or investor mistrust. Therefore, ensuring calibration through a NABL-accredited laboratory is not just a compliance requirement, but an operational safeguard.
Standards Governing Calibration
Calibration processes are defined by globally recognized standards. ISO 9847 specifies laboratory-based calibration using artificial light sources, while ISO 9846 outlines open-air calibration under natural sunlight. Complementing these, IEC 61724 recommends recalibration of pyranometers and temperature sensors once every two years. A qualified laboratory must adhere to these standards while maintaining NABL accreditation to ensure the validity of its results.
Laboratory Calibration β ISO 9847
Laboratory calibration is performed in controlled indoor environments. At the SuryaLogix Pune calibration setup, a Sun Simulator (small flash tester machine) is used. This equipment directs focused irradiation from a calibrated lamp onto the sensor in a darkroom environment, eliminating ambient influences. A certified reference sensor, previously calibrated, is used as the standard for comparison. Sensors are tested across four to five irradiance set points to confirm linear response, and both shaded and unshaded conditions are assessed. The result is a highly accurate calibration process with full traceability to WRR standards.
Open-Air Calibration β ISO 9846
Open-air calibration is carried out under natural sunlight, where the test sensor is placed alongside a reference calibrated sensor. Their outputs are measured simultaneously and compared to detect deviations. This method reflects real-world operating conditions but requires strict procedural controls to minimize environmental variability such as cloud movement, wind, or temperature fluctuations. A competent laboratory must demonstrate rigorous protocols to ensure reliable results from open-air calibration.
Best Practices for Selecting Calibration Laboratories
When choosing a calibration centre, stakeholders should prioritize NABL accreditation and evaluate additional best practices. Reliable labs provide alternate sensors during calibration to prevent data loss at plant sites. They reduce human error by employing automated calibration systems and ensure that every certificate includes uncertainty values, accreditation references, and traceability details. Facilities that combine both laboratory (ISO 9847) and open-air (ISO 9846) calibration capabilities provide maximum flexibility for clients.
Recommended Timeline
Both IEC 61724 and ISO standards recommend calibrating pyranometers and temperature sensors once every two years. Following this schedule ensures that measurement data remains precise, regulatory-compliant, and financially reliable for stakeholders across the solar value chain.
Conclusion
Selecting the right calibration laboratory is critical for the accuracy and credibility of solar plant performance data. A NABL-accredited facility that adheres to ISO 9847, ISO 9846, and IEC 61724 provides the assurance that results are precise, transparent, and internationally recognized.
At SuryaLogixβs Pune calibration facility, these standards are embedded in every process. With advanced equipment, NABL-accredited procedures, and best practices such as alternate sensor availability and reduced human intervention, SuryaLogix ensures that solar stakeholders receive calibration services that uphold global benchmarks of quality and reliability.
