The breadth and coverage of analytical expertise in the IEA Technology Collaboration Programmes (TCPs) are unique assets that underpin IEA efforts to support innovation for energy security, economic growth and environmental protection. The 39 TCPs operating today involve about 6 000 experts from government, industry and research organisations in more than 50 countries1.

Concentrated Solar Power (SolarPACES TCP)


Standardising solar mirror tests reduces costs

The SolarPACES TCP aims to facilitate technology development, market deployment and collaborations for concentrating solar technologies. Identifying less expensive, lighter and more robust alternatives to glass mirrors will enable widespread development of solar concentrating technology. 

Illustration of sunlight reflection and scattering on a sun-tracking mirror (Almeria, Spain).*

Concentrated solar power (CSP) technologies use sun-tracking mirrors to collect and concentrate the sunlight and use it as a form of high-temperature heat for electricity generation and industrial processes. Despite the higher investment cost, operating costs for CSP plants are lower than fossil fuel alternatives, and there are no costs for the “fuel”. Identifying economical reflecting materials could further reduce investment costs.

Yet currently there is a lack of standard measurement procedures for these materials as well as a lack of commercially available instruments capable of measuring the reflectance (the ratio between the amount of energy of the reflected and naturally occurring sunlight) that is a fundamental measure of the performance of a reflector material.

Currently glass mirrors lined with silver are the most efficient material for CSP (95%), yet due to their high cost, weight, fragility and risk of corrosion from dust storms, CSP developers and operators are seeking alternatives.

For these reasons the SolarPACES TCP set out to establish guidelines for measuring and testing reflective materials for CSP collectors in collaboration with ISO and IEC. The project consisted of two elements: setting a standard procedure for materials measurements and testing the procedures under laboratory conditions.

Two parameters were defined to assess the quality of all types of solar reflector materials: reflectance and specularity (capacity to reflect all light into the direction of the solar receiver). Four commercially available materials (floating glass mirrors, metalised polymer films, polished aluminium and anodised aluminium) were tested. The best optical performance was achieved by glass mirrors lined with silver as they presented the highest solar reflectance and optimum specular behaviour.

Three recommendations emerged from the study. First, commercial products should specify the wavelength and angle of the measured reflectance in order to be comparable. Second, with highly specular materials (e.g. silvered-glass mirrors) the recommended procedure is to measure two types of reflectance (hemispheric and monochromatic) within acceptable ranges. Finally, innovative reflector materials (e.g. multi layer silvered polymer films or aluminium mirrors) require a deeper investigation of the specular properties (at several acceptance angles),** due to scattering of light rays. Further research is being conducted to update the guidelines for these new types of materials. 

These and further findings are available in the report, Parameters and Method to Evaluate the Solar Reflectance Properties of Reflector Materials of Concentrating Solar Power Technology.

* Photo courtesy of SolarPACES TCP

** The acceptance angle is the maximum angle at which incoming sunlight can be captured by a solar collector


  • Solar chemistry research
  • Solar energy and water processes and applications
  • Solar heat integration in industrial processes
  • Solar resource assessment and forecasting
  • Solar technologies and advanced applications
  • Solar thermal electric systems


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Contracting Parties  10 11 1
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