Pipe and receiver insulation of smaller parabolic solar collectors are more difficult than bigger ones, because the conductive thermal loss basically depends only on the length of the pipe, but not on its diameter. As smaller collectors will inevitably lead to longer and smaller pipes, the conductive thermal loss may grow inverse proportionally with the width of the collectors, and the thermal insulation becomes much more difficult.
The solution is four fold: one should increase the thickness of the insulation layer, partially evacuate the insulation layer, fill the insulation layer with an inert gas of low conductivity, and fill the insulation layer of the pipe with insulating materials such as glass wool. See my article for details.
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