GB1569809A - Selective solar absorber - Google Patents

Selective solar absorber Download PDF

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Publication number
GB1569809A
GB1569809A GB3832/77A GB383277A GB1569809A GB 1569809 A GB1569809 A GB 1569809A GB 3832/77 A GB3832/77 A GB 3832/77A GB 383277 A GB383277 A GB 383277A GB 1569809 A GB1569809 A GB 1569809A
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GB
United Kingdom
Prior art keywords
solar
radiation
absorber
supporting layer
values
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.)
Expired
Application number
GB3832/77A
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Philips Electronics UK Ltd
Original Assignee
Philips Electronic and Associated Industries Ltd
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 Philips Electronic and Associated Industries Ltd filed Critical Philips Electronic and Associated Industries Ltd
Publication of GB1569809A publication Critical patent/GB1569809A/en
Expired legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/26—Deposition of carbon only
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S10/00—Solar heat collectors using working fluids
    • F24S10/40—Solar heat collectors using working fluids in absorbing elements surrounded by transparent enclosures, e.g. evacuated solar collectors
    • F24S10/45—Solar heat collectors using working fluids in absorbing elements surrounded by transparent enclosures, e.g. evacuated solar collectors the enclosure being cylindrical
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S70/00—Details of absorbing elements
    • F24S70/20—Details of absorbing elements characterised by absorbing coatings; characterised by surface treatment for increasing absorption
    • F24S70/225—Details of absorbing elements characterised by absorbing coatings; characterised by surface treatment for increasing absorption for spectrally selective absorption
    • 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
    • Y02E10/44—Heat exchange systems

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Thermal Sciences (AREA)
  • Sustainable Energy (AREA)
  • Sustainable Development (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Metallurgy (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Optical Filters (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Chemical Vapour Deposition (AREA)
  • Surface Treatment Of Glass (AREA)
  • Laminated Bodies (AREA)
  • Physical Vapour Deposition (AREA)

Description

(54) SELECTIVE SOLAR ABSORBER (71) We, PHILIPS ELECTRONIC AND ASSOCIATED INDUSTRIES LIMITED of Abacus House, 33 Gutter Lane, London, EC2V 8AH, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a solar absorber for selectively absorbing radiation from the solar spectrum. In particular the invention relates to a solar absorber of the kind for selectively absorbing solar radiation which comprises a radiation absorber, a U-shaped tube which contains a heat transport medium and a heat-insulating transparent glass casing.
When radiation from the sun is incident on a colder object a part of the energy is reflected and, consequently, lost; the remaining part of the radiation is either absorbed or passed on by means of transmission. The absorbed energy can be radiated back with a longer wavelength.
It is known that ' black bodies absorb more solar radiation and, consequently, become hotter than white bodies and that in general black bodies are efficient radiators for infrared radiation.
Black bodies absorb radiation of the visible spectral range and radiate a great part of this energy in the form of infrared radiation.
It is known to use as solar collectors socalled black mirrors or non-reflecting layers having a layer thickness ti of the wavelength of the radiation which is to be reflected only to a very slight extent (GB Patent Specification No. 1,060,788).
The prior art black layers proposed for the selective absorption of solar energy have certain disadvantages. For example, they are thermally unstable at temperatures > 200 C and they have a very short thermal long-term stability at temperatures exceeding 100"C. In addition, it is often necessary to perform several consecutive processing steps to achieve the desired layer properties such as adhesion to the supporting material, layer thickness or mechanical stabilisation of the surfaces of the layer. This applies, for example, to layers which have been produced by means of electrolysis.
For the sake of adhesion it is often necessary to apply several layers consecutively; as, however, black layers which are to be used as selective absorbers for solar energy only function satisfactorily.
within narrow layer thickness ranges, considerable difficulties occur in the production to stay within the narrow layer thickness tolerances. The expensive starting materials are an additional disadvantage.
One object of the present invention is to provide a solar absorber in which the above mentioned disadvantages are mitigated and the production of which requires simple processing steps only and furthermore, which operates very efficiently.
According to the present invention there is provided a solar absorber for selectively absorbing radiation from the solar spectrum comprising a solar radiation absorber, a Ushaped tube which contains a heat transport medium and a heat insulating transparent glass casing characterised in that the radiation absorber consists of a coating of X-ray amorphous carbon on a supporting layer having the metallic properties of good heat conductivity.
The carbon in the coating of amorphous carbon may have a particle size in the range from > 0.2 to < 0.5 Fum. An optimum absorption is accomplished with this particle size range as the particle size is in the wavelength range of the radiation to be absorbed.
Preferably the thickness of the carbon coating is in the range from > 0.1 to < 1.5 ,um. This furnishes the advantage that these coatings have both a sufficient absorption and also a sufficient transparency for infrared radiation.
The supporting layer for the absorbing coating is preferably a metal which may be a metal coating or a metal film coated for example, on a material having the metallic properties of good heat conductivity. When the metal is coated on a substrate such as glass the thickness of the coating may be less than 0.4 mm and the metal is preferably silver.
Suitable metals are aluminium, copper, gold or silver. When the supporting layer is in the form of a metal coating or a metal film, a thickness of > 0.4 m has the advantage that good reflection properties of the metal are obtained.
The invention is based on the recognition of the fact that a selective absorber must have a highest possible absorption for radiation of the solar spectrum (A = 0.3-2.3 yam) and a highest possible reflection in the range of the infrared radiation. This can be achieved by applying coatings of an amorphous carbon having a.
layer thickness < 1.5,um on a metallic supporting layer, as then a high absorption for radiation from the solar spectrum, a particularly high transmission for long wave infrared radiation and, on the metal of the supporting layer, a high reflection for the infrared radiation portion is obtained.
The advantages obtained with the present invention particularly consist in that the values for the absorption of solar radiation ct and for the emission of infrared radiation E of a coating of X-ray amorphous carbon can be adjusted for maximum effect by making a corresponding adjustment during production to give a considerably more favourable ratio of a/E than with the prior art absorbing layers. Further advantages are the very cheap starting materials, simple processing steps and a particularly favourable thermal long-term stability at temperatures > 100 C.
An embodiment of the invention will now be described in more detail with particular reference to the accompanying drawings in which: Fig. 1 shows a cross-section of a solar collector according to the invention.
Fig. 2a and 2b are graphic representations of the values for the emission of infrared radiation for coatings of X-ray amorphous carbon according to the invention at an operating temperature of 90"C.
Fig. I shows a cross-section of a solar collector having an absorbing layer of X-ray amorphous carbon (3) on a supporting layer (4) of, for example, aluminium, copper or iron, this collector being disposed in a heatinsulating glass casing (1). The amorphous carbon coating (3) was produced by means of vacuum deposition. To that end a vacuum chamber was first evacuated to a pressure of 1.33 . 10-5 to 1.33 . 10-6 mbar and thereafter filled with a non-reactive protective gas (for example nitrogen, argon or oxygen) to a pressure of 1.33 . 10-' mbar. This pressure was maintained during the entire vacuum coating process.A carbon-arc was used for the vacuum deposition of amorphous carbon onto a supporting layer in the form of an aluminium foil of a thickness of > 0.4 ym. It is understood for the purpose of the present invention that the gas selected for filling the chamber, for example, nitrogen, argon or oxygen, at the aforesaid pressure, is sufficiently non-reactive to the amorphous carbon to allow deposition of the amorphous carbon onto the supporting layer. Coatings of various thicknesses were produced by varying the vacuum deposition times in the range from 1 - 3 sec. the coating thicknesses having values of < 1.5 y.
Reference (5) indicates a tube through which a heat transporting medium flows.
References (6), (7) represent the inflow and outflow openings respectively of the heat transporting medium, for example water.
It is also possible to use, for example, a supporting layer in the form of a vacuumdeposited silver coating on a glass substrate.
The silver coating shall not be thicker than > 0.4 cm.
Fig. 2a and Fig. 2b show the reflection and emission spectra respectively for four coatings of X-ray amorphous carbon of varying thicknesses (the reflection is specified in % and the emission at an operating temperature of 90 C). The coatings were produced under the following conditions:
Pressure in Value for the Value for Deposition the vacuum absorption of the emission time chambers solar radiation of infrared Test No. (in s) (mbar) (a) (e) 50 1 1.3-3.10-1 0.85 0.05 17 51 2 1.33.10'' 0.93 0.15 6.2 53 3 1.33.10-1 0.87 0.09 9.67 55 2 1.06.10-3 0.92 0.11 8.36 Under these processing conditions values for the ratio absorption solar radiation/emission infrared radiation at 90"C (a/E) in the range from 6 - 17 were obtained.
Compared herewith, a prior art copper oxide coating which was used as a selective absorbing coating had values for the ratio /E in the range from 6 - 7.5.
The curves in Fig. 2a and Fig. 2b represent spectral curves which were obtained by means of measurements. The measured values for the reflection can be derived from these curves.
The values for the emission of infrared (heat) radiation (E) and for the absorption of solar radiation (a) as shown in the table have been calculated from the measured value for the reflection according to Fig. 1 and Fig. 2.
As the sum of reflection plus absorption is always 1, the absorption of solar radiation a can be calculated by means of weighting by multiplying values for the difference 1reflection at given wavelength by the values of the relative intensity of the solar spectrum.
As also the equation: emission plus reflection = I can be set up, the emission of heat radiation E can be calculated by means of weighting by multiplying the values for the difference l-reflection by the values of the relative intensity of the heat radiation.
WHAT WE CLAIM IS: 1. A solar absorber for selectively absorbing radiation from the solar spectrum comprising a solar radiation absorber, a Ushaped tube which contains a heat transport medium and a heat-insulating transparent glass casing, characterized in that the radiation absorber consists of a coating of X-ray amorphous carbon on a supporting layer having the metallic properties of good heat conductivity.
2. A solar absorber as claimed in Claim 1, characterized in that the carbon has a particle size in the range from > 0.2 to < 0.5 ,um.
3. A solar absorber as claimed in Claim 1, characterized in that the carbon coating has a thickness in the range from > 0.1 to < 21.5 ,am.
4. A solar absorber as claimed in Claim 1, characterized in that the supporting layer is a metal coating.
5. A solar absorber as claimed in Claim 1, characterized in that the supporting layer is a metal foil.
6. A solar absorber as claimed in Claim 4 or 5, characterized in that the supporting layer consists of aluminium.
7. A solar absorber as claimed in Claim 4 or 5, characterized in that the supporting layer consists of copper.
8. A solar absorber as claimed in Claim 4 or 5, characterized in that the supporting layer consists of gold.
9. A solar absorber as claimed in Claim 4 or 5, characterised in that the supporting layer consists of silver.
10. A solar absorber as claimed in Claim 1, characterized in that the solar radiation absorber and the U-shaped tube are built into the heat-insulating glass casing.
11. A method of manufacturing a solar absorber as claimed in Claim I, characterized in that the X-ray amorphous carbon layer is deposited by means of vacuum coating at a pressure in the range from 1. 10-1 to 1.10-l mbar in a non reactive, protective gas atmosphere.
12. A method as claimed in Claim 11, characterized in that argon, nitrogen or oxygen is used as the non-reactive protective gas atmosphere.
13. A method as claimed in Claim 1, characterized in that a metal coating or a metal film having a thickness of > 0.4 Mm is used as the supporting layer.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (15)

**WARNING** start of CLMS field may overlap end of DESC **. Pressure in Value for the Value for Deposition the vacuum absorption of the emission time chambers solar radiation of infrared Test No. (in s) (mbar) (a) (e) 50 1 1.3-3.10-1 0.85 0.05 17 51 2 1.33.10'' 0.93 0.15 6.2 53 3 1.33.10-1 0.87 0.09 9.67 55 2 1.06.10-3 0.92 0.11 8.36 Under these processing conditions values for the ratio absorption solar radiation/emission infrared radiation at 90"C (a/E) in the range from 6 - 17 were obtained. Compared herewith, a prior art copper oxide coating which was used as a selective absorbing coating had values for the ratio /E in the range from 6 - 7.5. The curves in Fig. 2a and Fig. 2b represent spectral curves which were obtained by means of measurements. The measured values for the reflection can be derived from these curves. The values for the emission of infrared (heat) radiation (E) and for the absorption of solar radiation (a) as shown in the table have been calculated from the measured value for the reflection according to Fig. 1 and Fig. 2. As the sum of reflection plus absorption is always 1, the absorption of solar radiation a can be calculated by means of weighting by multiplying values for the difference 1reflection at given wavelength by the values of the relative intensity of the solar spectrum. As also the equation: emission plus reflection = I can be set up, the emission of heat radiation E can be calculated by means of weighting by multiplying the values for the difference l-reflection by the values of the relative intensity of the heat radiation. WHAT WE CLAIM IS:
1. A solar absorber for selectively absorbing radiation from the solar spectrum comprising a solar radiation absorber, a Ushaped tube which contains a heat transport medium and a heat-insulating transparent glass casing, characterized in that the radiation absorber consists of a coating of X-ray amorphous carbon on a supporting layer having the metallic properties of good heat conductivity.
2. A solar absorber as claimed in Claim 1, characterized in that the carbon has a particle size in the range from > 0.2 to < 0.5 ,um.
3. A solar absorber as claimed in Claim 1, characterized in that the carbon coating has a thickness in the range from > 0.1 to < 21.5 ,am.
4. A solar absorber as claimed in Claim 1, characterized in that the supporting layer is a metal coating.
5. A solar absorber as claimed in Claim 1, characterized in that the supporting layer is a metal foil.
6. A solar absorber as claimed in Claim 4 or 5, characterized in that the supporting layer consists of aluminium.
7. A solar absorber as claimed in Claim 4 or 5, characterized in that the supporting layer consists of copper.
8. A solar absorber as claimed in Claim 4 or 5, characterized in that the supporting layer consists of gold.
9. A solar absorber as claimed in Claim 4 or 5, characterised in that the supporting layer consists of silver.
10. A solar absorber as claimed in Claim 1, characterized in that the solar radiation absorber and the U-shaped tube are built into the heat-insulating glass casing.
11. A method of manufacturing a solar absorber as claimed in Claim I, characterized in that the X-ray amorphous carbon layer is deposited by means of vacuum coating at a pressure in the range from 1. 10-1 to 1.10-l mbar in a non reactive, protective gas atmosphere.
12. A method as claimed in Claim 11, characterized in that argon, nitrogen or oxygen is used as the non-reactive protective gas atmosphere.
13. A method as claimed in Claim 1, characterized in that a metal coating or a metal film having a thickness of > 0.4 Mm is used as the supporting layer.
14. A method of manufacturing a solar
absorber substantially as hereinbefore described with reference to Figures 1, 2a and 2b of the accompanying drawings.
15. A solar absorber substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.
GB3832/77A 1976-02-03 1977-01-31 Selective solar absorber Expired GB1569809A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE2604019A DE2604019A1 (en) 1976-02-03 1976-02-03 SELECTIVE ABSORBER FOR RADIATION FROM THE AREA OF THE SOLAR SPECTRUM

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GB1569809A true GB1569809A (en) 1980-06-18

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JP (1) JPS5295340A (en)
DE (1) DE2604019A1 (en)
FR (1) FR2340516A1 (en)
GB (1) GB1569809A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002062714A2 (en) * 2000-10-27 2002-08-15 Honeywell, Inc. Wavelength specific coating for mirrored optics and method for reducing reflection of white light

Families Citing this family (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH631540A5 (en) * 1977-09-24 1982-08-13 Emil Baechli SOLAR PANEL.
FR2422117A1 (en) * 1978-04-04 1979-11-02 Lampes Sa ELEMENT SELECTIVELY ABSORBING RADIED ENERGY AND SENSOR OF SOLAR ENERGY CONTAINING SUCH ELEMENT
FR2429392A1 (en) * 1978-06-21 1980-01-18 Ratton Paulette Solar energy collector of great efficiency - is of porous or spheroidal graphite above aluminium reflector
FR2444238A1 (en) * 1978-12-12 1980-07-11 Lampes Sa Heat transfer element for solar heating panel - has S=shaped metal inside vacuum double-walled tube to hold two heat conducting fluid pipes
GB2047877A (en) * 1979-03-26 1980-12-03 Secr Defence Solar heating panels
JPS5819018B2 (en) * 1980-03-31 1983-04-15 大阪府 Method of manufacturing solar heat absorber
EP0044273A1 (en) * 1980-07-01 1982-01-20 Aroka Holding AG Absorbing layer
EP0044811A1 (en) * 1980-07-22 1982-01-27 Aroka Holding AG Covering element for transporting a heat-exchanger liquid, and process for its manufacture
DE3029636A1 (en) * 1980-08-05 1982-03-04 Gerätebau Schwarting KG, 7991 Eriskirch Solar heat collector panel for drying hay - uses absorber plates with granular coating and optional slots for heating air
JPS57202449A (en) * 1981-06-04 1982-12-11 Toshiba Corp Manufacture of heat collecting body
FR2524618B1 (en) * 1982-03-31 1987-11-20 Commissariat Energie Atomique COATING FOR PHOTOTHERMAL CONVERSION
FR2524620A1 (en) * 1982-04-02 1983-10-07 Vironneau Pierre Selectively coating substrate with carbon layer - by carbon mon:oxide decomposition, esp. for solar collector mfr.
JPS61223453A (en) * 1985-03-22 1986-10-04 Sharp Corp Member converting light into heat and manufacture thereof
US4834066A (en) * 1985-12-23 1989-05-30 The University Of Sydney Evacuated solar collector tube
DE3630418C1 (en) * 1986-09-06 1987-12-17 Kernforschungsanlage Juelich Process for coating workpieces with amorphous, hydrogen-containing carbon
JPS63269103A (en) * 1987-04-28 1988-11-07 Toshiba Electric Equip Corp Reflector

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES247631A1 (en) * 1959-02-13 1959-06-01 Amat Bargues Miguel Solar heater
US3227153A (en) * 1963-09-04 1966-01-04 American Mach & Foundry Solar collector

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002062714A2 (en) * 2000-10-27 2002-08-15 Honeywell, Inc. Wavelength specific coating for mirrored optics and method for reducing reflection of white light
WO2002062714A3 (en) * 2000-10-27 2002-10-17 Honeywell Inc Wavelength specific coating for mirrored optics and method for reducing reflection of white light
US6822788B2 (en) 2000-10-27 2004-11-23 Honeywell International Inc. Wavelength specific coating for mirrored optics and method for reducing reflection of white light

Also Published As

Publication number Publication date
JPS5295340A (en) 1977-08-10
DE2604019A1 (en) 1977-08-11
FR2340516A1 (en) 1977-09-02

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