NOVELTY - The method for hardening a coating of a solar collector element including a conductive material or a conductive layer by induction heating, is claimed. A portion of the coating is selectively heated by an induction coil (B) surrounding the portion of the coating. The induction coil is capable of moving along the coating to progressively harden the coating. A temperature of the portion of the coating heated by the coil is determined by a velocity of movement of the coil and/or a current flowing through the coil. The coating is directly deposited on a tubular substrate of the element.    USE - The method is useful for hardening a coating of a tubular element in a solar collector (all claimed).    ADVANTAGE - The method is capable of rapidly, uniformly and economically hardening the coating with good level of reproducibility to produce the coating with high quality, homogeneous color and good appearance.    DETAILED DESCRIPTION - The method for hardening a coating of a solar collector element including a conductive material or a conductive layer by induction heating, is claimed. A portion of the coating is selectively heated by an induction coil (B) surrounding the portion of the coating. The induction coil is capable of moving along the coating to progressively harden the coating. A temperature of the portion of the coating heated by the coil is determined by a velocity of movement of the coil and/or a current flowing through the coil. The coating is directly deposited on a tubular substrate of the element or another coating. A coating thickness enables observation of interference phenomena from natural light. The coating is obtained by a chemical process such as sol-gel methods or spray pyrolysis and deposited by a deposition method or dip coating-spray reprinting. The method is carried out using dust in a rarefied atmosphere, where oxygen concentration of dust is controlled. INDEPENDENT CLAIMS are included for:    (1) a solar collector; and    (2) a method for producing a solar collector element.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic perspective view of an apparatus for producing a solar cell element.    Linear screw rail (3)    Carriage (5)    Mobile tank (9)    Heating device (15)    Induction coil. (B)