Glass tube with infrared light reflective coating, method for manufacturing the glass tube, heat receiver tube with the glass tube, parabolic trough collector with the heat receiver tube and use of the parabolic trough collector

Abstract

A glass tube with a glass tube wall is provided, wherein an inner surface of the glass tube wall comprises at least partially at least one infrared light reflective coating. Additionally a heat receiver tube for absorbing solar energy and for transferring absorbed solar energy to a heat transfer fluid, which can be located inside a core tube of the heat receiver tube, is provided. The core tube comprises a core tube surface with a solar energy absorptive coating for absorbing solar absorption radiation of the sunlight. The core tube surface and an encapsulation are arranged in a distance between the core tube surface and the inner surface of the encapsulation wall with the infrared reflective surface such, that the solar absorption radiation can penetrate the encapsulation with the infrared light reflective coating and can impinge the solar energy absorptive coating.

Claims

1. A heat receiver tube for absorbing solar energy and for transferring absorbed solar energy to a heat transfer fluid located inside a core tube of the heat receiver tube, wherein: the heat transfer fluid is a thermo-oil; the core tube comprises a core tube surface with a solar energy absorptive coating for absorbing solar absorption radiation of the sunlight; the core tube is enveloped by an encapsulation with a glass tube with a glass tube wall, wherein a space between the core tube and the encapsulation is evacuated; an inner surface of the glass tube wall comprises at least partially at least one infrared light reflective coating; the infrared light reflective coating includes a transparent conducting coating comprising indium tin oxide, wherein the transparent conducting coating is configured to permit solar absorption radiation to impinge the core tube, and wherein the transparent conducting coating is configured to capture infrared radiation radiating from the core tube and direct the infrared radiation back to the core tube; an intermediate layer of aluminum oxide arranged between the inner surface of the glass tube wall and the infrared light reflective coating; an additional layer of aluminum oxide or silicon oxide covering the infrared light reflective coating, wherein the additional layer is between the infrared light reflective coating and the solar energy absorptive coating such that the additional layer is adjacent to the infrared light reflective coating and the space; the core tube surface and the encapsulation are arranged in a distance between the core tube surface and the inner surface of the glass tube wall with the infrared reflective surface such, that the solar absorption radiation can penetrate the encapsulation with the infrared light reflective coating and can impinge the solar energy absorptive coating.

2. The heat receiver tube according to claim 1, wherein the infrared light reflective coating comprises a transmission for solar radiation with a wavelength below 1200 nm, which is selected from a range between 0.5 and 0.99.

3. The heat receiver tube according to claim 1, wherein the inner surface of the glass tube wall comprises the infrared light reflective coating on a part of its circumference.

4. The heat receiver tube according to claim 1, wherein the tin oxide is doped with aluminum or aluminum oxide.

5. A parabolic trough collector comprising at least one parabolic mirror having a sunlight reflecting surface for concentrating sunlight in a focal line of the sunlight reflecting surface; and at least one heat receiver tube according to claim 1, which is arranged in the focal line of the parabolic mirror.

6. A method for manufacturing a glass tube of a heat receiver tube according to claim 1, the method comprising following steps: a) providing a glass tube; and b) attaching the infrared light reflective coating onto an inner surface of the glass tube.

7. The method according to claim 6, wherein the attaching the infrared light reflective coating is carried out with the aid of at least one technology, which is selected fefrom the group consisting of dip coating, spray coating and atomic layer deposition.

8. The heat receiver tube according to claim 1, wherein the infrared light reflective coating comprises a transmission for solar radiation with a wavelength below 1200 nm, which is selected form a range between is 0.8 and 0.95.

9. The heat receiver tube according to claim 1, wherein the thickness of the additional layer is about 120 nm.

10. A heat receiver tube for absorbing solar energy and for transferring absorbed solar energy to a heat transfer fluid, which can be located inside a core tube of the heat receiver tube, wherein: the heat transfer fluid is a thermo-oil; the core tube comprises a core tube surface with a solar energy absorptive coating for absorbing solar absorption radiation of the sunlight; the core tube is enveloped by an encapsulation with a glass tube with a glass tube wall, wherein a space between the core tube and the encapsulation is evacuated; an inner surface of the glass tube wall comprises a first area configured to face sunlight reflecting off of a mirror surface, and a second area configured to face the sun; wherein the first area comprises a high transmission for complete sun radiation, and the second area has a high reflectivity for infrared light; at least one infrared light reflective coating defined by the second area, wherein the infrared light reflective coating includes a transparent conducting coating comprising indium tin oxide, wherein the transparent conducting coating is configured to permit solar absorption radiation to impinge the core tube, and wherein the transparent conducting coating is configured to capture infrared radiation radiating from the core tube and direct the infrared radiation back to the core tube; wherein between the surface of the glass tube wall and the infrared light reflective coating is an intermediate layer of aluminum oxide; the core tube surface and the encapsulation are arranged in a distance between the core tube surface and the inner surface of the glass tube wall with the infrared reflective surface such, that the solar absorption radiation can penetrate the encapsulation with the infrared light reflective coating and can impinge the solar energy absorptive coating.

11. The heat receiver tube according to claim 10, wherein the infrared light reflective coating is covered by an additional layer.

12. The heat receiver tube according to claim 11, wherein the additional layer comprises silicon oxide or aluminum oxide.

13. The heat receiver tube according to claim 12, wherein the thickness of the additional layer is about 120 nm.

14. A solar power plant for converting solar power plant into electrical energy comprising: a steam generator; a heat exchanger, for generating steam for the steam generator; and a heat receiver tube as set forth in claim 1, wherein said heat receiver tube heats the thermo-oil as a heat transfer fluid to thereby generate the steam in the heat exchanger.

15. The method of claim 6 for manufacturing a glass tube of a heat receiver according to claim 1, wherein the attaching the infrared light reflective coating onto an inner surface of the glass tube includes at least one of dip coating and spray coating a first area of the inner surface of the glass tube such that the first area comprises a high transmission for complete sun radiation, and a second area of the inner surface of the glass tube has a high reflectivity for infrared light.

16. The solar power plant of claim 14, wherein the inner surface of the glass tube of the heat receiver tube comprises a first area configured to face sunlight reflecting off of a mirror surface, and a second area configured to face the sun; wherein the first area comprises a high transmission for complete sun radiation, and the second area has a high reflectivity for infrared light.

Description

BRIEF DESCRIPTION

(1) Further features and advantages of the invention are produced from the description of an exemplary embodiment with reference to the drawings. The drawings are schematic.

(2) FIG. 1 shows a cross section of a glass tube from the side.

(3) FIG. 2 shows a cross section of a parabolic through collector with the heat receiver tube comprising an encapsulation with the glass tube.

DETAILED DESCRIPTION

(4) Given is a glass tube 1 with a glass tube wall 10. The inner surface 11 of the glass tube wall 10 comprises at least partially at least one infrared light reflective coating 12. The glass tube 1 is an encapsulation 20 of a heat receiver tube 2.

(5) The infrared light reflective coating 12 comprises indium tin oxide. The thickness of the infrared light reflective coating 12 is about 135 nm.

(6) The infrared light reflective coating 12 is covered by an additional layer 13. This additional layer 13 comprises silicon oxide. In an alternative example the additional layer 13 comprises aluminum oxide. The thickness of this additional layer 13 is about 120 nm.

(7) An alternatively following sequence is implemented: Inner side of glass tube/Al.sub.2O.sub.3 (30 nm)/TCO (150 nm)/Al.sub.2O.sub.3 (50 nm)/SiO.sub.x (120 nm-Dip coat).

(8) Between the infrared light reflective coating 12 and the inner surface 11 of the glass tube wall 10 there is an intermediate layer 14. This intermediate layer comprises aluminum oxide. The thickness of this intermediate layer is about 85 nm.

(9) The core tube 21 of the heat receiver tube 2, which is enveloped by the glass tube 1, is made of steel. Additionally the core tube surface of the core tube comprises an absorptive coating for absorbing sunlight (not shown).

EXAMPLE 1

(10) By using half coating of the inner surface of the glass tube (dip and spray coating), a (absorptivity for the sunlight) will be reduced only by small fraction (0.2%) due to reduction of glass transmissivity on the upper segment of the glass tube. Heat losses due to radiation will be reduced by 20%-10% (from 1000 Watt/tube to 800-900 Watt/tube).

EXAMPLE 2

(11) The complete inner surface 11 of the glass tube wall 10 is covered by the infrared light reflective coating 12. For the manufacturing an ALD process is carried out. By this a will be reduced by 1%-1.5% due to decrease in solar transmissivity thorough the glass tube. But on the other hand, heat losses due to radiation will be reduced by 40%-60% (from 1000 Watt/tube to 600-400 Watt/tube. The heat receiver tube 2 is part of a parabolic trough collector 1000. The parabolic trough collector 1000 comprises at least one parabolic mirror 3 with a sunlight reflective surface 31. By the reflective surface 31 sunlight is concentrated in the focal line 32 of the parabolic mirror 3. The concentrated sunlight is absorbed by the heat receiver tube 2.

(12) The parabolic trough collector (and the Fresnel mirror collector, respectively) is used in a solar power plant for converting solar energy into electrical energy. The heated heat transfer fluid is used to produce steam via a heat exchanger. The steam is driving a turbine, which is connected to a generator. The generator produces current.