The constant need for ever cheaper collectors is exemplified in the ongoing shift from copper to aluminum and the even more radical material change related to the introduction of polymeric materials in solar collectors [1]. Many process heat and solar cooling applications demand medium temperature collectors providing reasonable efficiencies up to 250 °C [2]. Even higher temperatures occur in concentrating solar power applications [3], while the combination of solar thermal systems with heat pumps extends the operating temperatures well below 0°C [4].
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