ISO 9845-1:2022

Overview

ISO 9845-1:2022 - "Solar energy - Reference solar spectral irradiance at the ground at different receiving conditions - Part 1" defines standardized reference solar spectral irradiance distributions for air mass 1.5. The standard provides one direct normal spectrum (5.8° field-of-view centered on the sun), one hemispherical spectrum on an equator‑facing plane tilted 37°, and 171 subordinate hemispherical tilted spectra for varying atmospheric and tilt conditions. Spectral data (280 nm to 4 000 nm) are supplied as downloadable .xls files from ISO.

Download data: https://standards.iso.org/iso/9845/-1/ed-2/en/

Key topics

• Spectral range & resolution: 280 nm to 4 000 nm with improved wavelength sampling (high-resolution dataset covering UV through near‑IR).
• Air mass: Reference spectra are defined for AM 1.5, the common reference for terrestrial solar applications.
• Receiver geometry: Direct normal irradiance for a 5.8° FOV; hemispherical irradiance on an equator‑facing plane tilted 37° (albedo = light sandy soil).
• Subordinate spectra: 171 hemispherical tilted irradiance spectra covering multiple atmospheric conditions and tilt angles (useful for realistic sky/receiver scenarios).
• Modelling & validation: Reference spectra generated with the SMARTS radiative transfer model (versions 2.9.2 and 2.9.5). SMARTS performance has been validated against spectroradiometric data and compared to other models (differences typically small; up to ~5% in some UV comparisons).
• Spectral weighting & integration: The standard provides formulas and procedures for calculating spectrum‑weighted properties (e.g., absorptance, responsivity) and integrated irradiances from the tabulated spectral data.

Applications

ISO 9845-1:2022 is directly applicable to:

• Photovoltaic (PV) system testing and rating - determining relative spectral performance and spectral mismatch corrections.
• Solar thermal design and materials testing - evaluating wavelength‑dependent absorptance, transmittance and reflectance.
• Solar simulation and optical modelling - input spectra for ray‑tracing, sensor simulation, and radiative transfer studies.
• Laboratory accreditation and product comparison - standardized reference for performance comparisons under ideal clear‑sky AM 1.5 conditions.
• Research & development - spectral analyses for materials, coatings, and concentrator optics.

Who should use this standard

• PV and solar thermal engineers
• Test laboratories and certification bodies
• Materials scientists and optical engineers
• Solar resource analysts and modelers
• Manufacturers of solar components and solar simulators

Related standards

• ISO 9488 (solar energy vocabulary) and other ISO/IEC documents on solar measurements can be used alongside ISO 9845-1 for terminology and measurement practice.

ISO 9845-1:2022 provides comprehensive, high‑resolution reference spectra and subordinate cases critical for accurate, reproducible spectral analysis in solar energy engineering and testing.