Thermosiphonkollektor and process for its preparation

The invention relates to a Thermosiphonkollektor comprising at least a liquid reservoir for a liquid heat transfer medium and at least one solar absorber with at least the solar absorber is formed of a double-walled extruded sheet having at least two channels, wherein at least a first channel with a lower portion of the liquid reservoir in fluid communication, and at least a second channel to an upper portion of the liquid reservoir is in fluid communication and at least a first channel with at least a second channel at the end facing away from the liquid reservoir of the solar absorber is in fluid communication.