IEC 60904-7:2019

Overview

IEC 60904-7:2019 - "Photovoltaic devices - Part 7: Computation of the spectral mismatch correction for measurements of photovoltaic devices" - defines the procedure to correct spectral mismatch errors that arise when the test light spectrum and the reference spectrum (for example AM1.5) differ, and/or when the spectral responsivities of the reference device and the device under test differ. The procedure reduces systematic uncertainty for single-junction PV devices (principle extendable to multi-junction devices). This is the 4th edition (2019), replacing the 2008 edition.

Key topics and requirements

• Spectral mismatch factor SMM: The standard introduces the spectral mismatch factor SMM (renamed from MM) to distinguish it from angular mismatch factors (AMM, SAMM). SMM quantifies the correction needed so measured irradiance from a reference detector produces the same short-circuit current as the reference spectrum.
• Correction relationship: The effective reference irradiance is obtained by applying the spectral mismatch factor to the measured irradiance (document shows G_eff = SMM × G_meas).
• Determination of spectral responsivity: Measurement of device spectral responsivity follows IEC 60904-8; SMM computation requires accurate SR data for both reference and test devices.
• Test spectrum determination: For compatibility and reduced redundancy, the clause on determination of the test spectrum refers to IEC 60904-9 (solar simulator performance requirements).
• Simplified formulae: The standard includes formulae for derivation and application of SMM and provides a simplified expression for thermopile (pyranometer) type detectors.
• Applicability and limits: Applies to PV devices linear in spectral responsivity (see IEC 60904-10). The calculated SMM is valid only for the specific combination of test and reference devices measured with the particular test spectrum.
• Reporting and uncertainty: Guidance is given on reporting and on including spectral mismatch uncertainty in total measurement uncertainty.

Practical applications

• Correcting measured short-circuit current and performance data for PV cells and modules when using reference cells or thermopile radiometers.
• Calibrating and operating solar simulators to achieve reference-condition irradiance (e.g., STC 1 000 W/m²) accounting for spectral differences.
• Reducing systematic bias in lab and field PV performance testing, certification, and R&D comparisons.
• Providing a repeatable method for converting measured outputs under a known test spectrum to outputs under a defined reference spectrum (AM1.5 or other).

Who should use this standard

• PV test laboratories and accreditation bodies
• Reference-cell calibration laboratories
• PV module and cell manufacturers
• Solar simulator operators and test engineers
• Researchers and certification agencies concerned with accurate, traceable PV performance measurements

Related standards

• IEC 60904 series: -1, -2, -3, -8, -9, -10
• IEC 60891, IEC 61215, IEC 61646, IEC TS 61836

Keywords: IEC 60904-7, spectral mismatch, spectral responsivity, SMM, photovoltaic devices, AM1.5, solar simulator, reference cell, pyranometer.