Plate heat exchanger (1, 1') for solar heating comprising an inlet and an outlet, and a plurality of channels extending between the inlet and the outlet for conducting a heat transferring fluid between the inlet and the outlet, wherein the plurality of channels are defined between a first plate and a second plate, each of the plurality of channels along at least a portion of its longitudinal extension has a triangular or a chamfered triangular cross-section or a parallelogram or a chamfered parallelogram cross-section, wherein the side walls of two adjacent channels define an angle α corresponding to, or smaller than, 100 degrees and more preferred smaller than 90 degrees, wherein the channels of the first and/or the second plates (2, 3) are formed by deep drawing a flat sheet billet, and wherein the deep drawing is made to such extent that a surface enlargement as measured across an area delimited by the outermost boundary lines of the outermost channels on opposing sides of a symmetry line extending between the inlet and the outlet is at least 120% as compared to a non-pressed flat sheet billet, characterized in that: the first and second plates (2, 3) are formed by stainless steel, wherein each of the plurality of channels has a single-curved extension between the inlet and the outlet as seen in a plane A corresponding to the major surface extension of the first and second plates (2, 3), and wherein each of the plurality of channels along its longitudinal extension between the inlet and the outlet further has a single curved extension as seen in a direction transverse the plane corresponding to the major surface extension of the first and second plates (2, 3) and as seen in parallel with an imaginary line extending between the centers of the inlet and the outlet, and wherein each channel has a maximum depth (y) halfway its longitudinal extension. the plurality of channels are defined between a first plate and a second plate, each of the plurality of channels along at least a portion of its longitudinal extension has a triangular or a chamfered triangular cross-section or a parallelogram or a chamfered parallelogram cross-section, wherein the side walls of two adjacent channels define an angle α corresponding to, or smaller than, 100 degrees and more preferred smaller than 90 degrees, wherein the channels of the first and/or the second plates (2, 3) are formed by deep drawing a flat sheet billet, and wherein the deep drawing is made to such extent that a surface enlargement as measured across an area delimited by the outermost boundary lines of the outermost channels on opposing sides of a symmetry line extending between the inlet and the outlet is at least 120% as compared to a non-pressed flat sheet billet, characterized in that: the first and second plates (2, 3) are formed by stainless steel, wherein each of the plurality of channels has a single-curved extension between the inlet and the outlet as seen in a plane A corresponding to the major surface extension of the first and second plates (2, 3), and wherein each of the plurality of channels along its longitudinal extension between the inlet and the outlet further has a single curved extension as seen in a direction transverse the plane corresponding to the major surface extension of the first and second plates (2, 3) and as seen in parallel with an imaginary line extending between the centers of the inlet and the outlet, and wherein each channel has a maximum depth (y) halfway its longitudinal extension. the first and second plates (2, 3) are formed by stainless steel, wherein each of the plurality of channels has a single-curved extension between the inlet and the outlet as seen in a plane A corresponding to the major surface extension of the first and second plates (2, 3), and wherein each of the plurality of channels along its longitudinal extension between the inlet and the outlet further has a single curved extension as seen in a direction transverse the plane corresponding to the major surface extension of the first and second plates (2, 3) and as seen in parallel with an imaginary line extending between the centers of the inlet and the outlet, and wherein each channel has a maximum depth (y) halfway its longitudinal extension.