ISO 9060:2018 Classification Guide for Pyranometers
ISO 9060:2018 classification is the international standard that defines how pyranometers are graded for accuracy, stability, and response quality. Every solar monitoring project, from utility-scale PV to national meteorological stations, references this standard when specifying equipment. Understanding what ISO 9060:2018 classification actually requires helps procurement teams, engineers, and researchers select the right sensor for the job. This guide walks through what the standard defines, what changed in the 2018 revision, and how the classification maps to real project requirements.
What Is ISO 9060:2018 Classification?
ISO 9060 is the international standard for classifying pyranometers and pyrheliometers used in solar radiation measurement. Published by ISO Technical Committee 180 (Solar Energy), the standard sets performance thresholds against 12 measurable criteria. It applies to thermopile-based and photodiode-based sensors alike. Manufacturers who claim a specific class under ISO 9060:2018 classification must demonstrate that every sensor meets or beats every threshold for that class.
The original ISO 9060 dates from 1990. The 2018 revision brought the standard in line with modern sensor technology and current PV industry needs.
What Changed in the 2018 Revision
The 2018 update to ISO 9060 classification made four significant changes to the system.
Renamed classes. The 1990 names (“Secondary Standard,” “First Class,” “Second Class”) confused non-specialists. ISO renamed them Class A, Class B, and Class C. Class A now corresponds to the old “Secondary Standard” tier.
New sub-categories. ISO 9060:2018 added two optional labels a manufacturer can apply to a sensor: “spectrally flat” for sensors with uniform spectral response, and “fast response” for sensors with response times under 0.5 seconds.
Explicit inclusion of photodiode sensors. The 1990 standard treated silicon-cell pyranometers ambiguously. The 2018 update makes clear that photodiode-based sensors can meet Class B or Class C thresholds, provided the manufacturer properly documents the spectral response.
Updated response time definition. The 2018 revision defines response time as the 95% response, replacing the earlier 63% definition used in some literature. Older datasheet response times may therefore look different from current ones for the same physical sensor.
The 12 Performance Criteria Behind ISO 9060 Classification
ISO 9060 classification is based on 12 performance parameters. The most influential include:
- Response time — how quickly the sensor reaches 95% of a step change in irradiance
- Zero offset A (thermal radiation) — the sensor reading under a clear night sky with no shortwave radiation present
- Zero offset B (temperature change) — the sensor reading when ambient temperature changes at 5 K/hour
- Non-stability — the change in sensor sensitivity over one year
- Non-linearity — the largest deviation from a linear response between 100 and 1000 W/m²
- Directional error — the maximum error attributable to sun angle
- Spectral selectivity — the largest spectral response deviation across the solar spectrum
- Temperature response — total variation in sensitivity across a 50 K ambient temperature range
- Tilt response — the change in sensitivity between 0° and 90° tilt at 1000 W/m²
Each criterion has three threshold values, one per class. A sensor claiming Class A under ISO 9060:2018 classification must meet or beat every Class A threshold, not just some.
How the ISO 9060 Classification Thresholds Compare
The differences between classes appear starkest in the physical error thresholds:
- Zero offset A: Class A ≤ 7 W/m², Class B ≤ 15 W/m², Class C ≤ 30 W/m²
- Non-stability per year: Class A ≤ 0.8%, Class B ≤ 1.5%, Class C ≤ 3.0%
- Directional error: Class A ≤ 10 W/m², Class B ≤ 20 W/m², Class C ≤ 30 W/m²
- Temperature response: Class A ≤ 1%, Class B ≤ 2%, Class C ≤ 4%
- Tilt response: Class A ≤ 0.5%, Class B ≤ 2%, Class C ≤ 5%
Over a 12-month monitoring campaign, these differences add up. A Class A sensor may hold total measurement uncertainty below 2%, while a Class C sensor typically operates around 4 to 6%.
Sub-Categories: Spectrally Flat and Fast Response
Spectrally flat. A spectrally flat pyranometer maintains uniform response across the 285 to 2800 nm solar spectrum. This matters most when the incident spectrum shifts — for example, at low sun angles, under clouds, or when the solar spectral distribution differs from clear-sky conditions. Non-spectrally-flat sensors underreport or overreport during these events.
Fast response. A fast-response sensor reaches 95% of a step change within 0.5 seconds. This label matters for cloud transition studies, short-term forecasting, and inverter-clipping analysis on utility PV plants. Standard thermopile pyranometers typically respond in 5 to 30 seconds, which is why fast-response units are essential for high-frequency data campaigns.
Why ISO 9060:2018 Classification Matters for Your Project
ISO 9060:2018 classification affects four practical decisions:
- Regulatory alignment. IEC 61724-1 requires Class A pyranometers for utility-scale PV performance monitoring. Choosing a lower class means non-compliance.
- Procurement clarity. RFPs, tenders, and grant applications specify the required class under ISO 9060 classification. Meeting the spec is a threshold requirement, not a preference.
- Bankability. Investors and lenders reviewing a solar project financing model require Class A irradiance data for energy yield forecasts.
- Cross-manufacturer comparison. ISO 9060 classification is manufacturer-neutral. It lets a buyer compare an EKO MS-80 against a competitor’s Class A sensor on the same physical criteria.
How EKO Pyranometers Meet ISO 9060:2018 Classification
EKO manufactures pyranometers in every ISO 9060:2018 class. Every unit undergoes independent testing against the standard’s 12 criteria before shipping. Every EKO pyranometer leaves an ISO/IEC 17025 accredited calibration laboratory with traceability to the World Radiometric Reference (WRR) in Davos, Switzerland.
The EKO pyranometer lineup by ISO 9060:2018 class:
- Class A, spectrally flat, fast response: MS-80SH, MS-80S, MS-80
- Class B: MS-60S, MS-60
- Class C: MS-40S, MS-40, ML-01
Ready to select a pyranometer that meets your ISO 9060:2018 classification requirement? Contact our team for assistance or to request a quote.
