Plate heat exchanger (1,1') for solar heating comprising a plurality of channels (4) extending between an inlet (5) and an outlet (6) for conducting a heat transferring fluid. The plurality of channels (4) are defined between a first plate (2) and a second plate (3), the first and second plates (2, 3) being formed by stainless steel. Each of the plurality of channels (4) has a single-curved extension between the inlet (5) and the outlet (6) as seen in a plane A corresponding to the major surface extension of the first and second plates (2, 3). Each of the plurality of channels (4) has along at least a portion of its longitudinal extension a triangular or a chamfered triangular cross-section or a parallelogram or a chamfered parallelogram cross-section. The side walls (10) of two adjacent channels (4) define an angle α corresponding to, or smaller than, 100 degrees and more preferred smaller than 90 degrees.