The standard EN 12975, which is specifying test methods for solar thermal collectors, was originally developed with the focus on water-based flat-plate collectors. Other collector designs have been researched in the past, but except for vacuum tube collectors there was no viable market for them in Europe. This has changed in recent years. The overall market has grown to more than 4 million m2 of collector area per year and alternative collector designs are more and more showing up in the market.

In various cases, test methods described in EN 12975 are not fully applicable to mid- temperature collectors and to collectors with new design using largely polymeric materials, and a Solar Keymark cannot be issued. This creates additional hurdles for these products, as authorities in charge of solar thermal support programmes do not immediately recognise non-Keymark’ed products. Amongst the products suffering from this disadvantage are:

• tracking and/or concentrating collectors (medium-temperature collectors)
• new collector designs using largely polymeric materials

New products of these types have entered the market already, and especially medium-temperature collectors are expected to strongly gain market shares in the coming years.

This work aims at providing the basis for a wider scope of EN 12975 by including appropriate test methods also for these collector types. This would allow them to receive the Solar Keymark, and to immediately benefit from support schemes in many EU Member States.

Even for the more traditional flat-plate and vacuum-tube collectors, the standard or its interpretation need to be further developed. Different interpretations of EN 12975 could lead to different test results by different test laboratories, which could lead to a “shopping-around” of the manufacturer for the “best” test laboratory. It could also result in loss of credibility of methods and institutes from the industry’s point of view and in the worst case even the value of the Solar Keymark might be at stake. It will be developed concrete proposals to specify more clearly the applicable tests and to thus avoid a degradation of the EN 12975 standard and the Solar Keymark.

The work will be accomplished through intensive exchange with the European Solar Thermal Industry Federation (ESTIF), with WG1 of CEN TC312 and with the national standardization committees of the project participants. It will consist of definition of appropriate requirements and test methods needed to evaluate and present performance and to assure quality and safe implementation of recent and upcoming developments in solar thermal collector technology. Validation of proposed methods through inter-laboratory comparisons will also form part of the work. These inter-comparisons need not be compared to the round robin tests as they are for new technologies, more informal and with a lower number of participants. This work will create optimum conditions for a quick update of the European standards to the state of the art level by delivering supporting documents; guides, drafts and scientific papers to the work group in CEN.

The work will be coordinated with activities related to solar thermal collectors in IEA-SHC, CEN, ISO, ASHRAE and AS/NZS. For a better manageability these activities will be carried out within the project.

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Test Method for mid-temperature collectors

Both, the ESTTP and the IEA-SHC Task 33 have identified a huge potential for solar thermal applications in the temperature range of 80°C up to 250°C, and new collectors are just starting to show up in the market. The huge potential of solar heat for industrial applications can not be neglected because it can be a great contribution for the 20% RES at 2020 goal, as stated in a new EU directive (COM 2008 19 final).

There is a growing interest in industrial solar heat applications and new developments are based on completely different technical approaches from the ones used for low temperature solar thermal applications like DHW, These emerging concepts include new collector components like sun-tracking systems, concentrating devices and heat collecting elements. Providing higher temperatures due to low thermal losses, these collectors could provide the thermal energy to drive commercial and industrial applications as well as improve the efficiency of solar cooling systems.

Nowadays mid-temperature collector manufacturers find serious problems to get an independent product characterisation of their products because there is no standard testing procedure that fits for their products. Improvements in energy performance and/or durability can hardly be evaluated.

Also producers of components used as part of a mid-temperature solar thermal collector (like aluminium/mirror based reflector materials or new receiver/ absorber elements) are pushing independent laboratories for testing performance and durability of their products in order to get technical information to be used in marketing and competition.

The current EN 12975 was not developed with such collectors in mind. Parts of the test – originally foreseen for flat plate collectors – therefore cannot be used unless they are modified. This work could pave the way for an inclusion of these mid-temperature collectors in the EN standard(s) and thus help them enter the market more broadly.

The focus will be on commercially available collectors technologies applied for industrial solar heat applications as well as district heating, but not for solar thermal power plant applications for electricity production.

The main work deals wth definition of test conditions for a collector efficiency test procedure based on the quasi-dynamic test of EN 12975. The work will focus on “minor” adjustments of the existing method but avoid research oriented and (presumably) time consuming method development work.   

A performance testing procedure for mid-temperature solar thermal collectors, including definition of additional efficiency parameters (if relevant).

A concrete proposal for the revision of EN 12975 with respect to tracking/ concentrating collectors will be presented to CEN. Once the extended Standard is in place, the Solar Keymark scheme rules will be adapted to allow also the Keymarking of medium-temperature collectors, thus removing an important hurdle for these products.

Durability Assessment

Due to the cost structure in all solar energy investments, long lifetime expectancy is a major prerequisite for a strong expansion of the market

QAiST will therefore contribute to enhanced quality assurance and improved durability of solar thermal collectors by addressing several shortcomings of the present EN 12975, related to durability assessment and testing.  

Performance Calculation Tool 

The current EN 12975 includes test procedures to assess the performance of the collector. However, the performance is described in a power curve and does not easily allow calculation of the annual energy output.  

In Germany, one of the requirements in the federal incentive programme, MAP (Market Stimulation Programme), has been a minimum annual performance of 525 kWh/m2*a. The assessment was carried out by the test institutes based on the EN 12975 performance test. Other support programmes in Europe are also moving towards supporting Kilowatt-hours produced, not square meters installed.  

However, no generally agreed method exists so far and the tools developed so far are not suitable for e.g. tracking or unglazed collectors.  

In general, all tasks of this WP will be managed in close collaboration with CEN TC 312/ WG 1-Solar collectors. Additionally, the ongoing work in IEA-SHC Task 39 (Polymer materials for solar thermal applications) will provide an up to date and thorough input to this work.     

The tool developed within Solar Keymark-II will be further developed in order to manage also the output of tracking and unglazed collectors. As presentation of “precise” energy output figures will often lead to discussions, a calculation of uncertainty for the presented energy output must also be developed and included in the tool. After validation the tool is planned to be implemented in the Solar Keymark scheme rules and later possibly in the standard itself.  

The resulting method and tool will allow European testing laboratories to easily convert parameters from collector tests to a common format for energy output.

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1. Concrete proposals for revision of the present EN 12975 with respect to tracking/ concentrating and mid temperature collectors including ETC: the present standard is in principle applicable for performance testing of this type of collectors. However, the application will be reviewed in the light of recent experience and further clarified in the guideline. Furthermore, the durability and reliability tests in the standard are designed for stationary and mainly non concentrating designs. New requirements and methods will therefore be proposed to CEN in order to widen the scope of the standard.   
                                         
2. A report on durability and reliability requirements and testing methods for all collectors and its components (incl. new designs), including proposal for changes or complements to current EN12975  
                               
3. A guideline to the EN 12975 allowing uniform interpretation of requirements, harmonized application of the standard and presentation of results will be developed. It will thus strengthen the quality assurance within testing and certification and facilitate the introduction of new laboratories to solar collector testing.      
                                               
4. The calculation of annual energy output of solar thermal collectors based on short term test results for tracking and unglazed designs will be integrated in the performance calculation tool. The tool will be further validated and thus made ready for inclusion in the Solar Keymark scheme rules and in the EN Standard for collectors.

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