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WO2012120015A2 - Beam down mirror, system with the beam down mirror and use of the system - Google Patents

Beam down mirror, system with the beam down mirror and use of the system Download PDF

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Publication number
WO2012120015A2
WO2012120015A2 PCT/EP2012/053837 EP2012053837W WO2012120015A2 WO 2012120015 A2 WO2012120015 A2 WO 2012120015A2 EP 2012053837 W EP2012053837 W EP 2012053837W WO 2012120015 A2 WO2012120015 A2 WO 2012120015A2
Authority
WO
WIPO (PCT)
Prior art keywords
mirror
beam down
front surface
cooling
down mirror
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/EP2012/053837
Other languages
French (fr)
Other versions
WO2012120015A3 (en
Inventor
Dan Sagie
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Siemens Concentrated Solar Power Ltd
Siemens Corp
Original Assignee
Siemens AG
Siemens Concentrated Solar Power Ltd
Siemens Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG, Siemens Concentrated Solar Power Ltd, Siemens Corp filed Critical Siemens AG
Publication of WO2012120015A2 publication Critical patent/WO2012120015A2/en
Publication of WO2012120015A3 publication Critical patent/WO2012120015A3/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/70—Arrangements for concentrating solar-rays for solar heat collectors with reflectors
    • F24S23/82—Arrangements for concentrating solar-rays for solar heat collectors with reflectors characterised by the material or the construction of the reflector
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/70—Arrangements for concentrating solar-rays for solar heat collectors with reflectors
    • F24S23/72—Arrangements for concentrating solar-rays for solar heat collectors with reflectors with hemispherical reflective surfaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/70—Arrangements for concentrating solar-rays for solar heat collectors with reflectors
    • F24S23/79—Arrangements for concentrating solar-rays for solar heat collectors with reflectors with spaced and opposed interacting reflective surfaces
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/40—Solar thermal energy, e.g. solar towers

Definitions

  • the invention is in the field of the solar power concentration and relates to the tower technique, particularly its beam-down variation.
  • the invention can be applied in particular in for solar power generation.
  • Concentrated solar power systems use optics, for example lenses or mirrors, to concentrate a large area of sunlight, or solar thermal energy, onto a small area.
  • the beam-down arrangement of optics was proposed in Ari Rabl, Tower Reflector for solar plant, Solar energy 1976; 18: 269-271.
  • electrical power can be generated by concentrating sun rays with a heliostat or reflector field and directing them towards a beam-down reflector held by a tower and then towards a solar energy receiver, which may be positioned in a focus of the beam-down mirror and on the ground level.
  • the concentrated light may be converted to heat which can drive a heat engine, typically a steam turbine, connected to an electrical power generator.
  • a heat engine typically a steam turbine
  • the beam-down scheme may be considered as a variation of the ordinary tower scheme in which the tower holds not the reflector, but the receiver.
  • the receiver assembly and a power block e.g. the heat engine with the electrical power generator, can be readily installed and maintained on the ground level.
  • a suitable beam-down reflector or mirror has to be provided for the beam-down scheme.
  • a portion of solar energy is lost due to the beam-down mirror, in particular imperfect reflection and optical deviations.
  • the present invention provides a novel system and method for solar power concentration. This technique can further be adapted for solar power generation.
  • the main idea of the invention is to use as a beam down mirror a front surface mirror. Further, the beam down mirror can be associated with cooling. It can be recalled that in the theoretically most efficient beam-down mirror geometry, the beam-down mirror has a shape of a hyperboloid surface. The reflector's virtual focus is then situated above the mirror and the real focus below it. Sun rays propagating from a heliostat envelop a cone with a locus in the virtual focus of the mirror.
  • the mirror can have smaller dimensions if it is situated closer to its virtual focus.
  • the mirror is to receive the whole solar field, i.e. the solar energy from the whole heliostat field.
  • the mirror structure has to withstand higher energy flux density.
  • beam-down power plants are not yet built on a commercial scale.
  • the typical mirror is back surface silver coated.
  • the mirror heating then allows only large beam-down mirrors, but mirrors of large size are expensive. Also, it is difficult to accurately and securely position large mirrors: heights of above 120 m may be needed.
  • the front surface mirror may have a glass substrate.
  • this substrate may be under the reflective coating, i.e. on the back side of the mirror. Some light, for example, up to 4%, may get transmitted through the reflective coating. The glass substrate may then absorb as little as a fraction of percent of the radiation transmitted through the coating .
  • the front surface mirror may include an aluminum alloy substrate. Such substrate can absorb most of the light transferred through the reflective coating, but it can provide the mirror structure with rigidity and allow efficient cooling.
  • a front surface mirror configured for the use in a beam-down solar concentration arrangement.
  • the mirror can be of a substantially hyperboloid shape.
  • the mirror may reflect more than 98% of radiation in the solar spectrum.
  • the mirror may have a glass substrate.
  • the mirror may have an aluminum substrate.
  • the mirror may have an aluminum alloy substrate.
  • the front reflective layer may cover the glass substrate which may cover the alloy substrate.
  • the mirror has ribs bonded to the glass substrate.
  • the ribs may be oriented parallel to the mirror or towards the mirror.
  • the mirror has ribs the mirror has ribs bonded to the aluminum alloy substrate .
  • the ribs may be oriented parallel to the mirror or towards the mirror.
  • the front surface reflective layer of the mirror may be covered with a thin protective layer of a transparent material, in particular glass.
  • the system can include at least one air blower.
  • the blower may be positioned and oriented to create an air flow along the front surface of the mirror. Also, the blower may be positioned and oriented to create an air flow along the back surface of the mirror .
  • the system can include a heat pipe configured to cool the mirror.
  • the system can include a water cooling system configured to cool the mirror.
  • the system can include a tower that holds the mirror.
  • the tower can also hold the heat pipe if it is present.
  • the tower can also hold the water cooling system if it is present.
  • a beam down mirror for a beam down power plant is provided, wherein the beam down mirror is a front surface mirror. Additionally a system with the beam down mirror is provided as well as a use of the system in a beam down power plant.
  • the front surface mirror comprises a glass substrate and/or a metal substrate with at least one metal. Just one metal is possible. Mixtures of different metals are possible, too, resulting in alloys.
  • the metal is aluminum.
  • the metal substrate can be a aluminum substrate as well as a substrate with an aluminum alloy.
  • This protective layer is thin with a thickness of some microns .
  • the front surface mirror comprises ribs. These ribs can be attached to the glass substrate as well as to the metal substrate. These ribs have the function of cooling the front surface mirror.
  • the system comprises a cooling system for cooling the beam down mirror.
  • the cooling system comprises a water cooling system for cooling the front surface mirror.
  • the cooling system comprises a heat pipe for cooling the front surface mirror.
  • Figure 1 shows a heliostat field.
  • Figure 2 shows a system including a solar radiation receiver.
  • the system can include a heliostat field. Such system is illustrated by Fig. 1.
  • Table 1 presents the dependence of the mirror area required for 1000 m diameter solar heliostat field on the average flux that mirror is able to withstand: lA3 ⁇ 4uimiions
  • the system can include a solar radiation receiver. Further, the system can include a power block, e.g. the heat engine with the electrical power generator. Such system is schematically shown in Fig . 2.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Optical Elements Other Than Lenses (AREA)
  • Photovoltaic Devices (AREA)
  • Lasers (AREA)
  • Mounting And Adjusting Of Optical Elements (AREA)

Abstract

A beam down mirror for a beam down power plant is provided, wherein the beam down mirror is a front surface mirror. Preferably the front surface mirror is cooled. Additionally a system with the beam down mirror is provided as well as a use of the system in a beam down power plant.

Description

Description
BEAM DOWN MIRROR, SYSTEM WITH THE BEAM DOWN MIRROR AND USE OF THE SYSTEM
BACKGROUND OF THE INVENTION
1. Field of the invention
The invention is in the field of the solar power concentration and relates to the tower technique, particularly its beam-down variation. The invention can be applied in particular in for solar power generation.
2. Description of the related art
Concentrated solar power systems use optics, for example lenses or mirrors, to concentrate a large area of sunlight, or solar thermal energy, onto a small area. The beam-down arrangement of optics was proposed in Ari Rabl, Tower Reflector for solar plant, Solar energy 1976; 18: 269-271. Within the beam-down concept, electrical power can be generated by concentrating sun rays with a heliostat or reflector field and directing them towards a beam-down reflector held by a tower and then towards a solar energy receiver, which may be positioned in a focus of the beam-down mirror and on the ground level.
From the solar energy electric power may be generated. For example, the concentrated light may be converted to heat which can drive a heat engine, typically a steam turbine, connected to an electrical power generator.
The beam-down scheme may be considered as a variation of the ordinary tower scheme in which the tower holds not the reflector, but the receiver. In fact, the receiver assembly and a power block, e.g. the heat engine with the electrical power generator, can be readily installed and maintained on the ground level. However, a suitable beam-down reflector or mirror has to be provided for the beam-down scheme. Also, a portion of solar energy is lost due to the beam-down mirror, in particular imperfect reflection and optical deviations.
SUMMARY OF THE INVENTION There is a need in the art for efficient solar power concentration and generation. As well, there is a need in the art for a convenient in installation and use beam down mirror.
The present invention provides a novel system and method for solar power concentration. This technique can further be adapted for solar power generation. The main idea of the invention is to use as a beam down mirror a front surface mirror. Further, the beam down mirror can be associated with cooling. It can be recalled that in the theoretically most efficient beam-down mirror geometry, the beam-down mirror has a shape of a hyperboloid surface. The reflector's virtual focus is then situated above the mirror and the real focus below it. Sun rays propagating from a heliostat envelop a cone with a locus in the virtual focus of the mirror.
Hence, the mirror can have smaller dimensions if it is situated closer to its virtual focus. However, the mirror is to receive the whole solar field, i.e. the solar energy from the whole heliostat field. With a smaller mirror, the mirror structure has to withstand higher energy flux density.
Indeed, beam-down power plants are not yet built on a commercial scale. At present, the typical mirror is back surface silver coated. The mirror heating then allows only large beam-down mirrors, but mirrors of large size are expensive. Also, it is difficult to accurately and securely position large mirrors: heights of above 120 m may be needed.
The front surface mirror, that is to be used as the beam-down mirror in accordance with the invention, may have a glass substrate. In particular, this substrate may be under the reflective coating, i.e. on the back side of the mirror. Some light, for example, up to 4%, may get transmitted through the reflective coating. The glass substrate may then absorb as little as a fraction of percent of the radiation transmitted through the coating . Also, the front surface mirror may include an aluminum alloy substrate. Such substrate can absorb most of the light transferred through the reflective coating, but it can provide the mirror structure with rigidity and allow efficient cooling. Hence, in one broad aspect of the invention there is provided a front surface mirror configured for the use in a beam-down solar concentration arrangement.
The mirror can be of a substantially hyperboloid shape.
The mirror may reflect more than 98% of radiation in the solar spectrum.
The mirror may have a glass substrate.
The mirror may have an aluminum substrate.
The mirror may have an aluminum alloy substrate.
The front reflective layer may cover the glass substrate which may cover the alloy substrate. In some embodiments the mirror has ribs bonded to the glass substrate. The ribs may be oriented parallel to the mirror or towards the mirror. In some embodiments the mirror has ribs the mirror has ribs bonded to the aluminum alloy substrate . The ribs may be oriented parallel to the mirror or towards the mirror.
The front surface reflective layer of the mirror may be covered with a thin protective layer of a transparent material, in particular glass.
In another broad aspect of the invention there is provided a system for the solar power concentration.
The system can include at least one air blower. The blower may be positioned and oriented to create an air flow along the front surface of the mirror. Also, the blower may be positioned and oriented to create an air flow along the back surface of the mirror .
The system can include a heat pipe configured to cool the mirror.
The system can include a water cooling system configured to cool the mirror.
The system can include a tower that holds the mirror. The tower can also hold the heat pipe if it is present. The tower can also hold the water cooling system if it is present. Summarizing the invention includes following:
A beam down mirror for a beam down power plant is provided, wherein the beam down mirror is a front surface mirror. Additionally a system with the beam down mirror is provided as well as a use of the system in a beam down power plant.
Preferably the front surface mirror comprises a glass substrate and/or a metal substrate with at least one metal. Just one metal is possible. Mixtures of different metals are possible, too, resulting in alloys.
Various metals are possible. Preferably the metal is aluminum. So, the metal substrate can be a aluminum substrate as well as a substrate with an aluminum alloy.
In order to protect a reflective layer of the front surface mirror the front surface mirror is covered by a transparent protective layer. This protective layer is thin with a thickness of some microns .
In one embodiment the front surface mirror comprises ribs. These ribs can be attached to the glass substrate as well as to the metal substrate. These ribs have the function of cooling the front surface mirror.
Additionally or alternatively, the system comprises a cooling system for cooling the beam down mirror. The cooling system comprises a water cooling system for cooling the front surface mirror. Alternatively or additionally the cooling system comprises a heat pipe for cooling the front surface mirror.
BIEF DESCRIPTION OF THE DRAWING
Further features and advantages of the invention are produced from the description of an exemplary embodiment with reference to the drawing. The drawings are schematic. Figure 1 shows a heliostat field.
Figure 2 shows a system including a solar radiation receiver. DETAILED DESCRIPTION OF THE INVENTION
The system can include a heliostat field. Such system is illustrated by Fig. 1.
Table 1 presents the dependence of the mirror area required for 1000 m diameter solar heliostat field on the average flux that mirror is able to withstand: lA¾uimiions
D Solarfleld m 1000 EffKiencr
A Solarfleld m2 785398
Efle rve reflective area m1 3O0OOD 30.2%
Nominal flux k fm2 1
Cross power BH¥ft 300
Net power ■NH* 240 ao.0%
iReflertwe beam-down mirror
Figure imgf000008_0001
The system can include a solar radiation receiver. Further, the system can include a power block, e.g. the heat engine with the electrical power generator. Such system is schematically shown in Fig . 2.
Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention described herein without departing from its scope.

Claims

Patent claims
1. Beam down mirror for a beam down power plant, wherein the beam down mirror is a front surface mirror.
2. Beam down mirror according to claim 1, wherein the front surface mirror comprises a glass substrate.
3. Beam down mirror according to claim 1 or 2, wherein the front surface mirror comprises a metal substrate with at least one metal .
4. Beam down mirror according to claim 3, wherein the metal is aluminum.
5. Beam down mirror according to one of the claims 1 to 4, wherein the front surface mirror is covered by a transparent protective layer .
6. Beam down mirror according to one of the claims 1 to 5, wherein the front surface mirror comprises ribs.
7. System with a beam down mirror according to one of the claims 1 to 6.
8. System according to claim 7, wherein a cooling system for cooling the beam down mirror exists.
9. System according to claim 8, wherein the cooling system comprises a water cooling system for cooling the front surface mirror .
10. System according to claim 9, wherein the cooling system comprises a heat pipe for cooling the front surface mirror.
11. Use of the system according to one of the claims 7 to 10 in a beam down power plant.
PCT/EP2012/053837 2011-03-07 2012-03-07 Beam down mirror, system with the beam down mirror and use of the system Ceased WO2012120015A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201161449765P 2011-03-07 2011-03-07
US61/449,765 2011-03-07

Publications (2)

Publication Number Publication Date
WO2012120015A2 true WO2012120015A2 (en) 2012-09-13
WO2012120015A3 WO2012120015A3 (en) 2012-11-08

Family

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CN (1) CN102679574A (en)
WO (1) WO2012120015A2 (en)

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6708687B2 (en) * 2001-06-12 2004-03-23 James B. Blackmon, Jr. Thermally controlled solar reflector facet with heat recovery
US8359861B2 (en) * 2004-08-31 2013-01-29 Tokyo Institute Of Technology Solar heat collector, sunlight collecting reflector, sunlight collecting system and solar energy utilization system
US20070223121A1 (en) * 2006-03-23 2007-09-27 Centre Luxembourgeois De Recherches Pour Le Verre Et La Ceramique S.A. (C.R.V.C.) Method of making reflector for solar collector or the like and corresponding product
US20080142000A1 (en) * 2006-12-15 2008-06-19 Sol Focus, Inc. Optic spacing nubs
US8266908B2 (en) * 2008-06-30 2012-09-18 Ormat Technologies, Inc. Multi-heat source power plant
US20100027144A1 (en) * 2008-07-31 2010-02-04 Guardian Industries Corp. Articles with protective coating

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
ARI RABL, TOWER REFLECTOR FOR SOLAR PLANT, SOLAR ENERGY, vol. 18, 1976, pages 269 - 271

Also Published As

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WO2012120015A3 (en) 2012-11-08
CN102679574A (en) 2012-09-19

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