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Department for Business, Energy and Industrial Strategy

Solar Thermal Collectors

1.1    Scope

Solar thermal collectors are energy saving products that reduce the amount of energy consumed by conventional water or space heating equipment. They are built around a solar absorbers that uses radiation to increase the temperature of heating fluid flowing through the collector. This heat is then transferred to a storage vessel by means of a circulating fluid, or in some instances, the solar collector could be directly connected into the heating circuit.

To be eligible for inclusion on the Energy Technology List (ETL), products shall meet the requirements as set out below.

1.2    Definitions

Solar thermal collectors are products that are specifically designed to capture solar energy and convert it, with a broader solar system, to useful heat for water or space heating applications. 

1.3    Requirements 

1.3.1    Eligibility requirements  

To be eligible, products shall be collectors that comply with the requirements of BS ISO 9806:2017 “Solar energy. Solar thermal collectors. Test methods”. 

For models introduced to the market before 2017, compliance with BS EN 12975-2:2006 will be accepted.

1.3.2    Performance requirements 

The solar collector within the product shall pass the reliability tests detailed in the standards specified in Table 1.1 below: 

Table 1.1    Requirements for reliability tests

Year of Market Entry

Applicable Standard

Solar collectors introduced to the market in 2017 or later

BS EN ISO 9806:2017 “Solar energy. Solar thermal collectors. Test methods”.

Solar collectors introduced to the market before 2017

BS EN 12975-2:2006 “Solar energy. Solar thermal collectors. Test methods”.

Upon application, the supplier shall declare the following collector parameters:

  • Active Area (m2)
  • Zero-loss Efficiency (-)
  • First-order Efficiency Coefficient (W/m2K)
  • Second-order Efficiency Coefficient (W/m2K2)

1.4    Measurement and calculations

1.4.1    Test Requirements

All products shall be tested in accordance with the procedures and test conditions laid down in the standards specified in the performance criteria above.

1.5    Verification for ETL Listing 

Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:

  • In-house testing – Self-certified
  • In-house testing – Self-tested and verified or cross-checked by an independent body
  • Witnessed testing
  • Independent testing

Further information regarding the first three routes can be found in the ETL Testing Framework.

1.6    Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.

1.7    Review 

1.7.1    Indicative review date 

The next technical review is scheduled for 2023-24. 

1.7.2    Illustrative future direction of the requirements  

Future changes to the Specification may include:

  • Switching to new international standard metric
  • Re-introducing solar thermal systems
  • Creating a separate category for collectors designed specifically to act as heat sources for heat pumps