Arrangement, system and method for producing hot water from solar energy

A method for heating water with solar energy using an elongated solar collector device, wherein the elongated solar collector device comprises a first end and an opposite second end, the elongate solar collector device having at least one first opening arranged at the first end and/or the second end for receiving water into a plurality of elongate cavities extending longitudinally between the first end and second end, and at least one second opening for tapping off water, arranged at a middle part of the elongate solar collector device, the middle part being arranged at approximately the same distance from the first end as from the second end;

• and
• at least one valve adapted to be arranged in a respective one of the at least one second opening, the valve being openable and closable in order to be able to tap off any water housed in the cavities, wherein the method comprises the steps:
• arranging the elongated solar collector device on at least a first support adjacent to the first end and second support adjacent to the second end such that the middle part of the elongated solar collector device bends between the supports placing the valve horizontally below the first and second ends, and
• filling, through the at least one first opening, the elongated solar collector device with water up to a level where, after filling, the cavities will contain water up to the filling level and air above the filling level.