Solar panel for water-heater of the type comprising a heat exchanger made of moulded synthetic material, having a plurality of passages 7 in which a heat-exchanging fluid can circulate and a translucent cover sheet 17 attached to the exchanger with a clearance, characterized in that the heat exchanger constitutes the brace supporting the panel and consists of two identical half-shells 1a, 1b furnished with parallel longitudinal central projecting ribs 2a, 2b and one projecting edging rib 4a, 4b of greater dimension than a central rib, the two half-shells being bonded or heat sealed so that the central ribs define the abovementioned passages 7 and that the respective edging ribs 4a, 4b define a sealed hollow edging frame full of insulating air confined on the periphery of the exchanger.