WO2014053249A1

WO2014053249A1 - Glass body with infrared light reflective coating with graphene, method for manufacturing the glass body, heat receiver tube with the glass body, parabolic trough collector with the heat receiver tube and use of the parabolic trough collector

Info

Publication number: WO2014053249A1
Application number: PCT/EP2013/054457
Authority: WO
Inventors: Yuval Ofir
Original assignee: Siemens Aktiengesellschaft; Siemens Concentrated Solar Power Ltd.
Priority date: 2012-10-02
Filing date: 2013-03-06
Publication date: 2014-04-10

Abstract

A glass body with a glass body surface is provided, wherein at least one infrared light reflective coating is attached to the glass body surface and the infrared light reflective coating comprises at least one graphene material. The method for manufacturing the glass body comprises following steps: a) Providing a glass body and b) Attaching the infrared light reflective coating onto a glass body surface of the glass body. For instance, the glass body is a glass tube with a glass tube wall. 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 is enveloped by an encapsulation with the glass body. A parabolic trough collector is provided with at least one heat receiver tube, which is arranged in a focal line of a parabolic mirror, too. The parabolic trough collector is used in a solar power plant for converting solar energy into electrical energy.

Description

GLASS BODY WITH INFRARED LIGHT REFLECTIVE COATING WITH GRAPHENE, METHOD FOR MANUFACTURING THE GLASS BODY, HEAT

RECEIVER TUBE WITH THE GLASS BODY, PARABOLIC TROUGH COLLECTOR WITH THE HEAT RECEIVER TUBE AND USE OF THE PARABOLIC TROUGH COLLECTOR

BACKGROUND OF THE INVENTION

1. Field of the invention

This invention relates to a glass body and a method for manu^¬ facturing the glass body. Moreover, a heat receiver tube with the glass body, a parabolic trough collector with the heat receiver tube and a use of the parabolic through collector are provided.

2. Description of the related art

A sun energy collecting unit of a sun field power plant based on the concentrated solar power technique is for instance a parabolic trough collector with parabolic mirrors and a heat receiver tube. The heat receiver tube is arranged in a focal line of the mirrors. By sunlight reflecting surfaces of the mirrors the sunlight is focused to the heat receiver tube, which is filled with a heat transfer fluid, e.g. a thermo-oil or molten salt. With the aid of a solar radiation absorptive coating of a core tube (inner tube) the heat receiver tube absorbs energy from the sun. Energy from the sun is efficiently coupled into the heat transfer fluid. Solar energy is converted to thermal energy.

In order to minimize a loss of thermal energy, the heat re- ceiver tube comprises an encapsulating outer glass body

(glass tube) . The glass tube, which is transparent for the sunlight, is arranged coaxially around an inner, central stainless tube of the heat receiver tube. The space between the inner tube and the glass tube is evacuated, to minimize convection .

SUMMARY OF THE INVENTION

It is an object of the invention to provide an additional re^¬ duction of thermal loss of a glass tube, which can be used as an encapsulation of a heat receiver tube. It is another object of the invention to provide a method for manufacturing such a glass tube.

Further objects of the invention are the providing of a para^¬ bolic trough collector with the heat receiver tube comprising an encapsulation with such a glass tube and the providing of a use of the parabolic trough collector.

These objects are achieved by the invention specified in the claims .

A glass body with a glass body surface is provided, wherein at least one infrared light reflective coating is attached to the glass body surface and the infrared light reflective coating comprises at least one graphene material.

Preferably the glass body is a glass tube with a glass tube wall and the glass tube wall comprises the glass body sur^¬ face. Preferably an inner surface of the glass tube wall com^¬ prises the glass body surface.

The inner surface of the glass tube wall comprises at least partially at least one infrared light reflective coating and the infrared light reflective coating comprises at least one graphene material.

The infrared light reflective coating comprises a transmis^¬ sion for solar radiation with a wavelength between 300-2500 nm, which is selected from the range between 0.5 and 0.99 and preferably selected form the range between is 0.8 and 0.95. The infrared light reflective coating is more or less trans^¬ parent for the sunlight radiation in this wavelength area. Preferably the infrared light reflective coating comprises at least one graphene material film. The inner surface of the glass tube wall comprises the infrared light reflective coat^¬ ing on a part of its circumference. A method for manufacturing the glass body is provided, too. The method comprises following steps: a) providing a glass body and b) attaching the infrared light reflective coating onto an glass body surface of the glass body. 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 ab- sorbing solar absorption radiation of the sunlight. The core tube is enveloped by an encapsulation with the glass body (glass tube) with the infrared light reflective coating. The core tube surface and the encapsulation are arranged in a distance between the core tube surface and the inner surface of the encapsulation wall with the infrared reflective sur^¬ face such, that the solar absorption radiation can penetrate the encapsulation with the infrared light reflective coating and can impinge the solar energy absorptive coating. Moreover a parabolic trough collector is provided 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, which is arranged in the focal line of the parabolic mirror. Alternatively, a solar collector with linear Fresnel technology can be realized. So, a linear Fresnel mirror col^¬ lector with at least one Fresnel mirror having a sunlight re^¬ flecting surface for concentrating sunlight in a focal line of the sunlight reflecting surface and at least one heat re^¬ ceiver tube, which is arranged in the focal line of the Fres^¬ nel mirror.

The glass body is preferably a glass tube with a glass tube wall and the glass tube wall comprises the glass body sur^¬ face. Preferably an inner surface of the glass tube wall com^¬ prises the glass body surface.

The glass body, for instance the glass tube with the glass tube wall, is transparent for a wide wavelength range of the rays of the sun. Preferably the glass tube wall of the glass tube comprises glass (SiO_x) . Other transparent materials are possible, too. The infrared light reflective coating, which is attached to the inner and/or outer surface of the glass tube, acts as a mirror for infrared light. By this, infrared light, which is radiated by the core tube of a heat receiver tube, is reflected back to the core tube. The overall thermal loss of the heat receiver tube by infrared light radiation of the core tube of the heat receiver tube is reduced.

The glass tube surface can comprise the infrared reflective coating on its complete circumference. But it is also possi^¬ ble, that the inner surface of the glass tube wall comprises the infrared light reflective coating is just on a part the circumference of the inner glass tube surface. For instance the inner surface of the glass tube is half covered by the infrared reflective coating. Using trough technology, the heat receiver tube is arranged in a focal line of parabolic mirrors. Since the sun incident to the trough parabola downwards, rays of the sunlight are collimated onto a lower half of the core tube circumference. An upper half of the core tube circumference is directly hit by rays of the sun (estimated to be about 1.2% from total in^¬ cident rays) and stray rays, which come from mirror distor^¬ tion and statistical aberration (estimated to be about 0%-2% (This depends on the two segmental coatings) of the total in- cident rays) . So, it is preferable to divide the inner sur^¬ face of the glass tube wall into two areas. One area, which is located face to face to the sunlight reflecting surface of the mirror, has got a high transmission for the complete sunlight radiation. In contrast to that, the area, which is face to face to the sun and which is averted to the sunlight reflecting surface of the mirror, has got a high reflectivity for infrared light. There is a minor loss concerning the di^¬ rect infrared radiation coming from the sun. But the reduc^¬ tion of thermal loss via infrared radiation emission of the core tube multiply compensates the minor loss.

In a preferred embodiment the graphene material comprises at least on material which is selected from the group consisting of graphene, graphene oxide (GO) , reduced graphene oxide (rGO) , graphene quantum dots, ID (one-dimensional) graphene nanoribbons (GNR) , graphene nanomeshes, few layer graphene (FLG) and chemically functionalized graphene (CFG) . The chemically functionalized graphene comprises at least one chemical functional group.

The infrared light reflective coating can comprise additional materials. In a further preferred embodiment the infrared light reflective coating comprises at least one nanomaterial . Preferably the nanomaterial is selected from the group con- sisting of nanoparticles , nanorods and nanowires. Mixtures of these materials are possible.

The nanomaterial can comprise a lot of different components. In a preferred embodiment the nanoparticles comprise at least one nanomaterial which is selected from the group consisting of Au, Ag, Cu, Ni, Pd, Ir, Si0₂, Ti0₂, A1₂0₃, ZnO, ITO (Indium (doped) tin oxide) , ATO (Antimony (doped) tin oxide) , AZO (Aluminum (doped) zinc oxide, Sn0₂, Mn0₂, C0₃O₄, Fe₂C>3, NiO, Cu₂0, Ru0₂, CdS, CdSe, CdTe, InP, III-V semiconductors and

II-VI semiconductors. III-V semiconductors comprise elements of the main groups III and V of the periodic table, e.g. Ar- sen (AS) and Gallium (Ga) and II-VI semiconductors comprise elements of the main groups II and VI of the periodic table.

The infrared light reflective layer can be attached directly onto the glass body surface of the glass body. But in a pre^¬ ferred embodiment an intermediate layer with intermediate ma^¬ terial is arranged between the glass body surface of the glass body and the infrared light reflective coating. For in^¬ stance, the intermediate layer improves the adherence of the infrared reflective coating onto the glass body surface of the glass body or make the manufacturing easy. To assist the coating process and/or to enhance the adhesion of the various graphene materials to the surface of the glass body, various materials can be coated before or after the deposition of the graphene (sheets) . For example, deposition of a functional self assembled monolayer (SAM) on the inner surface of the glass tube that can chemically bind to the graphene. The SAM can incorporate a functional group that will react with the graphene sheet and adhere it to the glass. Examples include functional groups as carboxyl, hy- droxyl, p-phenyl-S03H, epoxy, amine, azide, isocyanate, car^¬ bamate, amides and diazonium salts.

The graphene materials can be further incorporated into opti- cally transparent polymers or optical adhesives and then coated on the tube to form the transparent conducting and IR reflecting film.

The Graphene-based film can be further coated with an anti- reflective layer to reduce energy losses due to reflection from the glass body (glass tube) .

Preferably the chemically functionalized graphene and/or the intermediate layer material comprise at least one functional organic group which is selected from the group consisting of carboxyl group, hydroxyl group, epoxy group, amine group, azide group, isocyanate group, carbamate group, amide group and diazonium group. The diazonium group form a diazonium salt .

These functional organic groups lead to modified graphene ma^¬ terial to which covalently or non-covalently additionyl mate^¬ rial can be fixed such as polymers like Poly vinyl alcohol (PVA) , poly (methyl methacrylate) (PMMA) , Polycaprolactone (PCL) , polyurethane (PU) , Polyvinylbutyral (PVB) , Polystyrene (PS), Polyaniline (PANi) , Polyacrylonitrile (PAN), Poly (3,4- ethylenedioxythiophene) and Poly (styrenesulfonate) (PEDOT- PSS) . The graphene material can be additionally modified. In a pre^¬ ferred embodiment the graphene material comprises on dopant which is selected from the group consisting fluorine, chlo^¬ rine, bromine, nitrogen, potassium, iron chloride (Fe2<0₃) and boron . In a preferred embodiment of the method for manufacturing the glass tube following additional steps are carried out: c) At^¬ taching a precursor layer of the infrared light reflecting layer and b) Converting the precursor layer into the infrared light reflecting layer.

For the attaching the infrared light reflective coating or for the attaching the precursor layer at least one technology is carried out, which is selected form the group consisting of dip coating, spray coating, bar coating, ultrasonic coating, electrospray coating and inkjet printing. These are so^¬ lution-based techniques. Alternative methods like transfere printing are possible, too.

Especially for the method with the precursor layer a transfer printing method is possible. For instance, graphene can be produced by thermal reduction of PMMA/PAN and other carbon sources on a catalytic metal surface or CVD based methods can be transfer-printed onto the glass tube.

Finally a use of the parabolic trough collector in a power plant for converting solar energy into electrical energy is disclosed .

Summing up, following main advantage result from the invention concerning a glass tube: The addition of the IR reflect^¬ ing film inside the glass tube on a sectional circumference (150 degrees) with a transparency of 90% and IR reflection of 80% will reduce the heat loss of the tube sitting at 430C by approximately 10-20%. A full coating of graphene on the cir^¬ cumference of the glass tube with a transparency of 90% and IR reflection of 80% will reduce the heat loss of the tube sitting at 430C by >30%. BIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention are produced from the description of an exemplary embodiment with refer- ence to the drawings. The drawings are schematic.

Figure 1 shows a cross section of a glass tube from the side.

Figure 2 shows a cross section of a parabolic through collec- tor with the heat receiver tube comprising an encapsulation with the glass tube.

DETAILED DESCRIPTION OF THE INVENTION Given is a glass body in form of a glass tube 1 with a glass tube wall 10. The glass body surface is the inner surface 11 of the glass tube. 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.

The infrared light reflective coating 12 comprises at least one graphene film with graphene sheets. The thickness of the infrared light reflective coating 12 is about 135 nm.

The infrared light reflective coating 12 is covered by an ad^¬ ditional layer 13. This additional layer 13 is an antireflec- tive layer. Between the infrared light reflective coating 12 and the in^¬ ner surface 11 of the glass tube wall 10 there is an interme^¬ diate layer 14. This intermediate layer comprises organic functional groups like carboxyl groups. The core tube 21 of the heat receiver tube 2 which is envel^¬ oped 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) .

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 reduc^¬ tion of glass transmissivity on the upper segment of the glass tube. Heat losses due to radiation will be reduced by 20% -10% (from 100 OWatt/tube to 800-900Watt/tube)

The heat receiver tube 2 is part of a parabolic trough col^¬ lector 1000. The parabolic trough collector 1000 comprises at least one parabolic mirror 3 with a sunlight reflective sur^¬ face 31. By the reflective surface 31 sunlight is concen^¬ trated in the focal line 32 of the parabolic mirror 3. The concentrated sunlight is absorbed by the heat receiver tube 2.

The parabolic trough collector (and the Fresnel mirror col^¬ lector, 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 gen^¬ erator. The generator produces current.

Claims

Patent claims

1. Glass body with a glass body surface, wherein at least one infrared light reflective coating is attached to the glass body surface and the infrared light reflective coating com^¬ prises a at least one graphene material.

2. Glass body according to claim 1, wherein the glass body is a glass tube with a glass tube wall and the glass tube wall comprises the glass body surface.

3. Glass body according to claim 2,

wherein an inner surface of the glass tube wall comprises the glass body surface.

4. Glass body according to one of the claims 1 to 3, wherein the infrared light reflective coating comprises at least one graphene material film.

5. Glass body according to one of the claims 1 to 4, wherein the graphene material comprises at least one material which is selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, graphene quantum dots, ID gra^¬ phene nanoribbons, graphene nanomeshes, few layer graphene and chemically functionalized graphene.

6. Glass body according to one of the claims 1 to 5, wherein the infrared light reflective coating comprises at least one nanomaterial .

7. Glass body according to claim 6, wherein the nanomaterial is selected from the group consisting of nanoparticles, nano- rods and nanowires.

8. Glass body according to claim 6 of claim 7, wherein the nanoparticles comprise at least one nanomaterial which is se^¬ lected from the group consisting of Au, Ag, Cu, Ni, Pd, Ir, Si0₂, Ti0₂, A1₂0₃, ZnO, ITO, ATO, AZO, Sn0₂, Mn0₂, Co₃0₄, Fe₂0₃, NiO, Cu₂0, Ru0₂, CdS, CdSe, CdTe, InP, III-V semiconductors and II-VI semiconductors.

9. Glass body according to one of the claims 1 to 8, wherein an intermediate layer with intermediate material is arranged between the glass body surface of the glass body and the in^¬ frared light reflective coating.

10. Glass body according to one of the claims 5 to 9, wherein the chemically functionalized graphene and/or the intermedi- ate layer material comprise at least one organic functional group which is selected from the group consisting of carboxyl group, hydroxyl group, epoxy group, amine group, azide group, isocyanate group, carbamate group, amide group and diazonium group .

11. Glass body according to one of the claims 1 to 10, wherein the graphene material comprises on dopant which is selected from the group consisting fluorine, chlorine, bro^¬ mine, nitrogen, potassium, iron chloride and boron.

12. Glass body a according to one of the claims 1 to 11, wherein the infrared light reflective coating comprises a transmission for solar radiation with a wavelength below 1200 nm, which is selected from the range between 0.5 and 0.99 and preferably selected form the range between is 0.8 and 0.95.

13. Heat receiver tube (2) for absorbing solar energy and for transferring absorbed solar energy to a heat transfer fluid, which can be located inside a core tube (21) of the heat re^¬ ceiver tube (2), wherein

- the core tube comprises a core tube surface with a solar energy absorptive coating for absorbing solar absorption ra- diation of the sunlight;

- the core tube is enveloped by an encapsulation with a glass body according to one of the claims 2 to 13, and

- the core tube surface and the encapsulation are arranged in a distance between the core tube surface and the inner sur- face 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.

14. Parabolic trough collector (1000) comprising

- at least one parabolic mirror (3) having a sunlight re^¬ flecting surface (31) for concentrating sunlight in a focal line (32) of the sunlight reflecting surface (31); and

- at least one heat receiver tube (2) according to claim 11, which is arranged in the focal line (32) of the parabolic mirror (3) .

15. Method for manufacturing a glass body according to one of the claims 1 to 12, the method comprising following steps: a) Providing a glass body; and

b) Attaching the infrared light reflective coating onto an glass body surface of the glass body.

16. Method according to claim 15, wherein the attaching the infrared light reflecting layer comprises following addi^¬ tional steps:

c) Attaching a precursor layer of the infrared light reflect^¬ ing layer and b) Converting the precursor layer into the infrared light re^¬ flecting layer.

17. Method according to claim 13 and/or claim 14, wherein the attaching the infrared light reflective coating is carried out with the aid of at least one technology, which is se^¬ lected form the group consisting of dip coating, spray coat^¬ ing, bar coating, ultrasonic coating, electrospray coating and inkjet printing.