Specification of solar radiation sensors

Pyranometers are classified according to the ISO 9060 standard: "Solar energy - Specification and classification of instruments for measuring hemispherical solar and direct solar radiation". The standard is officially approved by the World Meteorological Organization (WMO). The standard specifies three classes:

Secondary Standard: Scientific quality and highest accuracy
Applications: Meteorology (BSRN Network); Testing in PV, CPV and CSP

First Class: Good quality
Applications: Measurements for hydrology networks and greenhouse climate control

Second Class: Medium quality
Applications: Economic solution for routine measurements in weather stations and field testing

ISO 9060 PYRANOMETER SPECIFICATIONS	SECONDARY STANDARD	FIRST CLASS	SECOND CLASS
Response time: time to reach 95% responds	< 15 s	< 30 s	< 60 s
Zero-offset
Offset-A: response to 200 W/m² net thermal radiation, ventilated	+ 7 W/m²	+ 7 W/m²	+ 7 W/m²
Offset-B: response to 5 K/h change in ambient temperatur	± 2 W/m²	± 2 W/m²	± 2 W/m²
Non-stability: % change in responsivity per year	± 0.8%	± 1.5%	± 3%
Non-linearity: % deviation from responsivity at 500 W/m² due to change in irradiance from 100 ... 1000 W/m²	± 0.5%	± 1%	± 3%
Directional response (for beam irradiance): the range of errors caused by assuming that the normal incidence responsivity is valid for all directions when measuring from any direction, a beam radiation whose normal incidence irradiance is 1000 W/m²	± 10 W/m²	± 20 W/m²	± 20 W/m²
Spectral selectivity: % deviation of the product of spectral absorbance and transmittance from the corresponding mean, from 0.35 ... 1.5 μm	± 3%	± 5%	± 10%
Temperature response: % deviation due to change in ambient within an interval of 50 K, (e.g. -10 ... +40°C typical)	2%	4%	8%
Tilt response: % deviation in responsivity relative to 0 ... 90° tilt at 1000 W/m² beam irradiance	± 0.5%	± 2%	± 5%
Achievable uncertainty (95% confidence level)
Hourly totals	3%	8%	20%
Daily totals	2%	5%	10%