Solar collector device which operates according to the thermosiphon principle, with a fluid circuit comprising: • a solar collector with a throughflow duct which has an entry opening and an exit opening which is situated geodetically higher than the entry opening, • a fluid storage unit with an extraction point and an infeed point which is arranged geodetically higher than the extraction point, wherein the fluid storage unit is arranged at least partially geodetically above the solar collector, • a return line which hydraulically connects the entry opening of the throughflow duct to the extraction point of the fluid storage unit, • a supply line which hydraulically connects the exit opening of the throughflow duct to the infeed point of the fluid storage unit, and • a valve, wherein the inlet opening of the valve faces the flow direction of the extraction point and the outlet opening of the valve faces the flow direction of the infeed point, characterized in that the valve is provided with a casing which narrows from an inlet opening to an outlet opening in the longitudinal direction, wherein the casing has an elastic material, so that the outlet opening is able to be deformed elastically, wherein inside said casing, a first flow space which extends beyond the inlet opening in the longitudinal direction is formed, and outside said casing, a second flow space which extends beyond the outlet opening in the longitudinal direction is formed, wherein the first flow space and the second flow space are able to be flow-connected via the outlet opening and at least one first bypass with a first bypass valve, wherein the first bypass valve is temperature-controlled. • a solar collector with a throughflow duct which has an entry opening and an exit opening which is situated geodetically higher than the entry opening, • a fluid storage unit with an extraction point and an infeed point which is arranged geodetically higher than the extraction point, wherein the fluid storage unit is arranged at least partially geodetically above the solar collector, • a return line which hydraulically connects the entry opening of the throughflow duct to the extraction point of the fluid storage unit, • a supply line which hydraulically connects the exit opening of the throughflow duct to the infeed point of the fluid storage unit, and • a valve, wherein the inlet opening of the valve faces the flow direction of the extraction point and the outlet opening of the valve faces the flow direction of the infeed point, characterized in that the valve is provided with a casing which narrows from an inlet opening to an outlet opening in the longitudinal direction, wherein the casing has an elastic material, so that the outlet opening is able to be deformed elastically, wherein inside said casing, a first flow space which extends beyond the inlet opening in the longitudinal direction is formed, and outside said casing, a second flow space which extends beyond the outlet opening in the longitudinal direction is formed, wherein the first flow space and the second flow space are able to be flow-connected via the outlet opening and at least one first bypass with a first bypass valve, wherein the first bypass valve is temperature-controlled.