ISO 9806 is the single global test standard for solar thermal collectors, defining thermal performance measurement plus durability and safety tests for glazed, unglazed, air and PVT collectors. One accredited ISO 9806 test campaign generates the data behind both Solar Keymark certification in Europe and SRCC certification in North America — one test, many markets. The current edition is ISO 9806:2017.
What does ISO 9806 cover?
ISO 9806, titled "Solar energy — Solar thermal collectors — Test methods", is the standard every serious collector on the market has passed. The 2017 edition replaced the 2013 version, which had already absorbed what was previously Europe's separate test standard, EN 12975-2; in Europe it is adopted verbatim as EN ISO 9806. Its scope is deliberately universal: glazed and unglazed liquid-heating collectors, air-heating collectors, and PVT hybrid collectors all run through the same procedures, which is what makes their published performance figures comparable.
The standard has two halves: thermal performance measurement — in steady-state or quasi-dynamic outdoor conditions — and a battery of durability, reliability and safety tests that simulate years of rooftop stress in a laboratory campaign.
What performance parameters does ISO 9806 produce?
The headline outputs are the three coefficients of the collector efficiency curve: optical efficiency η0 and the heat loss coefficients a1 and a2. Typical certified flat-plate values run η0 = 0.75–0.82 and a1 = 3–4 W/m²K. The test also delivers the incidence angle modifier, the collector time constant, effective thermal capacity and power output at standard temperature differences — the exact numbers simulation tools and subsidy calculators consume. Because every laboratory measures to the same procedure, a planner can compare a collector tested in Germany with one tested in Australia coefficient by coefficient.
Which durability tests must a collector survive?
| ISO 9806 test | What it proves |
|---|---|
| Internal pressure | Absorber circuit integrity at working pressure |
| High-temperature resistance | Survival at dry stagnation, typically 160–200 °C for flat plates |
| Exposure | 30+ days of real outdoor weathering without degradation |
| External / internal thermal shock | Sudden rain on a hot collector; cold fluid into a hot absorber |
| Rain penetration | Casing keeps water out |
| Mechanical load | Positive and negative loads for snow and wind uplift |
| Impact resistance | Hail strikes on the glazing |
| Freeze resistance | For collectors claimed freeze-tolerant |
The high-temperature test matters most in practice: every collector spends part of its life at stagnation temperature when pumps stop, and ISO 9806 proves it survives.
How does ISO 9806 relate to Solar Keymark and SRCC?
ISO 9806 is a test method, not a certificate — certification schemes wrap quality assurance around its data. In Europe, Solar Keymark combines EN 12975 requirements with EN ISO 9806 test results, five-year certificates and annual factory inspection. In North America, SRCC OG-100 builds its collector ratings on the same test data. That is the "one test, many markets" principle documented by the IEA Solar Heating & Cooling Programme: one accredited laboratory campaign can support certification on several continents. For a manufacturer exporting widely — Solimpeks ships collectors from Konya to 96+ countries — this single shared standard is what keeps multi-market certification affordable.
Does ISO 9806 apply to PVT collectors?
Yes. Since the 2013 revision the standard explicitly covers PVT collectors: the thermal side is tested like any collector (usually with the PV side both in open circuit and at maximum power point), while electrical safety and performance remain the territory of the IEC photovoltaic standards. This dual coverage is what allows PVT products to obtain Solar Keymark like purely thermal collectors. The global fleet measured on this basis is substantial — IEA SHC counts 544 GWth of solar thermal capacity worldwide delivering 443 TWh of heat in 2024 — and effectively all of it is rated on ISO 9806-derived data.
Frequently asked questions
What is the difference between ISO 9806 and EN 12975?
EN 12975 is the European collector requirements standard; its former test-methods part, EN 12975-2, was replaced by EN ISO 9806. Today EN 12975 defines what a collector must fulfil and EN ISO 9806 defines how it is tested — together they form the technical basis of Solar Keymark.
Who performs ISO 9806 tests?
Independent laboratories accredited to ISO/IEC 17025 for the standard's methods. Certification schemes such as Solar Keymark and SRCC only accept results from accredited labs, which is what gives the published coefficients their credibility.
Is ISO 9806 testing legally mandatory?
The standard itself is voluntary. It becomes unavoidable in practice because certification schemes and subsidy programs — Solar Keymark in Europe, SRCC in North America — are built on it, and without those certificates most markets and funding schemes are closed.
Does ISO 9806 predict how long a collector lasts?
It stress-tests the failure mechanisms — stagnation heat, thermal shock, hail, wind and snow loads — rather than stating a lifetime. Field experience supplies the answer: well-built flat-plate collectors routinely exceed 20–25 years.