Solar heat collector for heating a circulating fluid and process for manufacturing a solar heat collector

A solar heat collector for heating a circulating fluid with an inner glass tube having an open end and a closed end, and an outer glass tube having an open end and a closed end, wherein the inner glass tube and the outer glass tube are connected at the open ends of both glass tubes, and a space between the inner glass tube and the outer glass tube is evacuated, wherein the inner space of the inner glass tube is divided by an insert to define a first channel and a second channel within the inner glass tube, the first and second channels being connected at the closed end of the inner glass tube, wherein the inner glass tube and the outer glass tube have smooth inner and outer surfaces, and the insert is provided such that the first and second channels and a space between the end of the insert and the closed end of the inner glass tube define the same cross-section.