Absorber tube and method for the reversible loading and unloading of a getter material

1. An absorber tube for solar collectors in solar thermal power plants, comprising:

a collector mirror that reflects solar irradiation and directs the reflected solar irradiation onto the absorber tube;

a metal tube that conducts and heats a heat transfer medium;

a sheath tube surrounding the metal tube, the sheath tube forming an annular space that can be evacuated;

a wall running between the sheath tube and the metal tube to seal the annular space;

a getter material configured to bind free hydrogen that is present in the annular space;

a membrane in the wall that is permeable to the free hydrogen, and purges free hydrogen from the annular space; and

a temperature changing device that changes a temperature of the getter material, the wall, and the membrane.

2. The absorber tube according to claim 1 , wherein the wall comprises a transition element and an outer ring, the membrane being disposed in or on the transition element and/or the outer ring.

3. The absorber tube according to claim 1 , further comprising an expansion bellows that equilibrates expansion differences between the sheath tube and the metal tube.

4. The absorber tube according to claim 1 , wherein the membrane comprises a material selected from the group consisting of iron, palladium, and niobium.

5. The absorber tube according to claim 3 , wherein the expansion bellows and/or the wall comprise(s) a doped region that increases permeability for the free hydrogen.

6. The absorber tube according to claim 2 , wherein the getter material is in a container that is fastened to the outer ring and/or to the transition element.

7. The absorber tube according to claim 6 , wherein the container comprises a fabric sock.

8. The absorber tube according to claim 2 , wherein the outer ring has an opening that points towards the getter material and that is sealed by the membrane.

9. The absorber tube according to claim 2 , wherein the outer ring and/or the transition element has a section that at least partially encloses the getter material.

10. The absorber tube according to claim 9 , wherein the membrane is disposed in the section.

11. The absorber tube according to claim 9 , wherein the temperature changing device is adjacent to the section.

12. The absorber tube according to claim 3 , wherein the temperature changing device runs at least partially in folds of the expansion bellows.

13. The absorber tube according to claim 1 , wherein the temperature changing device comprises a heating device.

14. The absorber tube according to claim 13 , wherein the heating device comprises a heating filament.

15. A method for changing the temperature of a membrane of an absorber tube, the absorber tube comprising:

a collector mirror that reflects solar irradiation and directs the reflected solar irradiation onto the absorber tube;

a metal tube that conducts and heats a heat transfer medium;

a sheath tube surrounding the metal tube, the sheath tube forming an annular space that can be evacuated;

a wall running between the sheath tube and the metal tube to seal the annular space;

a getter material configured to bind free hydrogen that is present in the annular space;

a membrane in the wall that is permeable to the free hydrogen, and purges free hydrogen from the annular space; and

a temperature changing device that changes a temperature of the getter material, the wall, and the membrane,

the method comprising the steps of:

reflecting solar irradiation and directing the reflected solar irradiation onto the absorber tube with a collector mirror;

changing the temperature of a getter material by a temperature changing device; and

changing the temperature of the membrane by the getter material.

16. A method for the reversible loading and unloading of a getter material with free hydrogen in an absorber tube, comprising the following steps:

reflecting solar irradiation and directing the reflected solar irradiation onto the absorber tube with a collector mirror;

loading the getter material at a first temperature (T 1 );

changing the temperature of the getter material to a second temperature (T 2 );

unloading the getter material at the second temperature (T 2 ); and

changing the temperature of getter material to the first temperature (T 1 ).

17. A device for discharging free hydrogen from an annular space of an absorber tube, comprising:

a collector mirror that reflects solar irradiation and directs the reflected solar irradiation onto the absorber tube;

a metal tube that conducts and heats a heat transfer medium;

a sheath tube surrounding the metal tube, the sheath tube forming an annular space that can be evacuated;

a wall running between the sheath tube and the metal tube to seal the annular space;

a getter material configured to bind free hydrogen that is present in the annular space;

a membrane in the wall that is permeable to the free hydrogen, and purges free hydrogen from the annular space; and

a temperature changing device that changes a temperature of the getter material, the wall, and the membrane;

a temperature measuring unit that determines a temperature value of the sheath tube; and

a comparison unit that compares the temperature value of the sheath tube to a selectable critical temperature value.

18. A method for discharging free hydrogen from an annular space of an absorber tube, comprising the following steps:

reflecting solar irradiation and directing the reflected solar irradiation onto the absorber tube with a collector mirror;

determining a temperature value of a sheath tube of the absorber tube by a temperature measuring unit;

comparing the temperature value with a selectable critical temperature value by a comparison unit; and

changing the temperature of a getter material, a wall, and/or a membrane of the absorber tube with a temperature changing device so that hydrogen that is bound to the getter material is released and is discharged from the annular space.