WO2016083648A1 - Mirror for solar energy applications and method for the manufacture thereof - Google Patents

Mirror for solar energy applications and method for the manufacture thereof Download PDF

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Publication number
WO2016083648A1
WO2016083648A1 PCT/ES2015/070852 ES2015070852W WO2016083648A1 WO 2016083648 A1 WO2016083648 A1 WO 2016083648A1 ES 2015070852 W ES2015070852 W ES 2015070852W WO 2016083648 A1 WO2016083648 A1 WO 2016083648A1
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WIPO (PCT)
Prior art keywords
layer
aperiodic structure
layers
metal layer
mirror
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PCT/ES2015/070852
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Spanish (es)
French (fr)
Inventor
Keith Boyle
Carlos ALCAÑIZ GARCIA
Mercedes ALCON CAMAS
Juan Pablo NUÑEZ BOOTELLO
Hernán Ruy Miguez Garcia
Mauricio Ernesto Calvo Roggiani
Alberto Jimenez Solano
Miguel ANAYA MARTIN
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Abengoa Solar New Technologies, S.A.
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Publication of WO2016083648A1 publication Critical patent/WO2016083648A1/en

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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
    • C03C17/34—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions
    • C03C17/36—Surface treatment of glass, not in the form of fibres or filaments, by coating with at least two coatings having different compositions at least one coating being a metal
    • 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
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • 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 present invention belongs to the field of solar energy technologies. More specifically, the invention relates to mirrors for solar thermal applications.
  • thermosolar in which the sunlight is concentrated on a predetermined objective, by means of sets of mirrors located properly around of that objective.
  • sets of mirrors are commonly known as heliostats.
  • heliostat technologies to obtain optimum performance it is necessary to keep the reflective surfaces of the mirrors perpendicular to the bisector of the angle between the direction of the sun and the lens, from the point of view of the mirror.
  • Heliostat costs represent approximately half of the capital cost of a tower solar power plant. Therefore, it is of interest to design less expensive heliostats for large-scale manufacturing, so that solar power plants can produce electricity at more competitive costs than the costs of conventional power plants (based on other sources, such as coal).
  • reflectivity throughout the entire range of the solar spectrum commonly referred to in the art as "solar reflectivity (RS) or solar energy reflection factor, or in English” solar spectrum weighted integrated reflectance "( SWIR)
  • RS solar reflectivity
  • SWIR solar spectrum weighted integrated reflectance
  • a conventional design for the heliostat comprises second-sided mirrors, the structure of which generally consists of: (i) a protective layer, (ii) a reflective silver layer and (iii) a thick glass top protective layer.
  • the invention described herein refers to alternative reflectors, the design of which allows the use of less expensive materials than silver, thus decreasing the dependence of this precious metal technology, whose market prices show large fluctuations. Any reflective material used must, in all In this case, reflect the incident solar energy with minimal loss, and its performance should not be affected by its interaction with humidity, ultraviolet radiation, dust, temperature and other environmental parameters.
  • silver is the preferred choice as a material for the reflective layer, due to the solid technological base established in the mirror industry, and because its reflectance is generally in the range between 0.95 and 0.97, for surfaces deposited by well established mirror manufacturing procedures.
  • the strong angular dependence of the reflectance spectrum prevents its use in technologies in which sunlight reaches the mirror with various angles of incidence.
  • the problem of covering a greater spectral range can be solved by multilayer designs based on the coupling of structures with different periodicities (see international application with reference WO2013 / 059228) but, even in this case, the number of layers needed to cover the entire Solar spectrum is so large that it is not a viable option.
  • Approaches related to this concept although based on random distribution of layers rather than aperiodic designs, have also been proposed to construct reflectors in shorter wavelength ranges (see WO2009 / 043374), but could not be extended to reflect the entire solar spectrum.
  • the present invention proposes novel mirror configurations and their corresponding manufacturing methods that can provide improved yields in terms of their wavelength sensitivity, their angular reflection properties and their dependence on high cost materials.
  • the present invention solves the technical problems mentioned above by proposing the use of mirrors based on a reflective layer made of a metal of free choice, which is coupled adjacent to an aperiodic sequence of layers of different composition, thicknesses and refractive indices.
  • the main technical advantage of these mirrors which arises as The consequence of this particular design is that they have a high optical reflectance for the entire solar spectrum (350 nm ⁇ ⁇ 2500 nm).
  • the mirrors of the invention can be optimized to achieve maximum reflectivity for a given angle of incidence of sunlight.
  • the ability to use free choice metals which may also be based on low-cost materials, makes the invention very competitive with conventional silver mirrors in terms of performance.
  • the present invention proposes a solution to the problem of achieving a high optical reflectance viable for the generation of electricity from solar energy without the need for structures with a large number of layers, matching the specific reflectance drops of the aperiodic layer structure, inherent in structures with fewer layers, with atmospheric absorption bands in the solar solar spectrum.
  • an objective of the invention is a mirror for solar energy applications comprising: a metal layer that exhibits reflection of at least a first range of wavelengths within the solar irradiance and absorption spectrum of at least a second range of wavelengths comprised in said spectrum; and a multi-layer aperiodic structure adjacent to the metal layer, comprising a plurality of layers of different refractive indices and thicknesses, which has reflection within the second range of wavelengths in which the adjacent metal layer exhibits absorption; the distribution of layers in the multilayer aperiodic structure being arranged so that the wavelength ranges with minimal reflection in said multilayer aperiodic structure correspond to wavelength ranges with maximum absorption in the terrestrial solar spectrum.
  • the multi-layer aperiodic structure of the invention is configured to reflect the light in the wavelength ranges absorbed by the adjacent metal layer, making the wavelength ranges of low reflectivity (due to, for example, the interference between the layers) coincide with the ranges of wavelengths in which the solar spectrum has occasional drops in irradiance (corresponding to those wavelengths included in the atmospheric absorption bands), so that the multilayer structure reflects the lengths wave with higher values of the radius within the solar spectrum.
  • the reflection / absorption properties of the metal layer it should be noted that this layer may have both reflection and absorption properties in the same wavelength range (i.e. the so-called first wavelength ranges and second included within the spectrum of solar radiation can be overlapping ranges, or even matching).
  • the mirror further comprises a substrate layer and / or a protective layer applied to the metal layer.
  • the thickness of the layers that form the multi-layer aperiodic structure is comprised between 1 nm and 1 ⁇ . More preferably, the thickness of the layers that form the multi-layer aperiodic structure is between 10 nm and 400 nm.
  • the number of layers in the multi-layer aperiodic structure is between 2 and 1 000. More preferably, the number of layers in the multi-layer aperiodic structure is between 4 and 200.
  • the multi-layer aperiodic structure is formed by an alternating sequence of two materials of different refractive index. More preferably, the multi-layer aperiodic structure is formed by alternating layers of silicon oxide and titanium oxide or any compound derived therefrom.
  • the metal layer comprises one or more of the following materials: copper, aluminum, chromium, iron, titanium, nickel, cobalt, palladium, rhodium, silver, gold, platinum, or any alloy of the same.
  • the multi-layer aperiodic structure and the metal layer are arranged to form a first or second-sided mirror.
  • the layers with the lowest refractive index within the multi-layer aperiodic structure have a porosity between 10% and 95% and the layers with the highest refractive index have a porosity between 0% and 10%.
  • a further objective of the invention relates to a method for manufacturing a mirror for solar energy applications, which preferably comprises the steps of:
  • a metal layer which may reflect a range of wavelengths comprised within the spectrum of the sunburst, adjacent to a plurality of layers of different refractive index and thickness, which form a multi-layer aperiodic structure that has reflection bands at wavelength ranges in which the adjacent metal layer absorbs;
  • the weakest reflection bands of the multi-layer aperiodic structure correspond to wavelength ranges coinciding with the most intense absorption bands in the terrestrial solar spectrum.
  • the multi-layer aperiodic structure or the metal layer is deposited on a substrate (for example, a glass substrate).
  • the method of the invention may comprise the step of depositing a protective layer on the metal layer.
  • the technique used to deposit the layers that form the multi-layer aperiodic structure or the metal layer comprises one or more of the following list: spin deposition, dip coating (dip -coating), Langmuir-Blodgett, chemical vapor deposition techniques or physical vapor deposition techniques such as thermal evaporation or sputtering.
  • the invention is highly competitive, in terms of performance, compared to conventional silver mirrors.
  • the mirror structure based on the combination of a metal layer of free choice and a pre-designed multilayer aperiodic structure, allows high reflection outside the absorption bands of the terrestrial solar spectrum (that is, the aperiodic structure strongly reflects wavelengths incidents that the metal absorbs), and presents both stable and constant SWIR values with respect to the direction of incidence of the light.
  • Figure 1 shows two embodiments of the multilayer distribution of a second-sided mirror ( Figure 1 a) and a first-sided mirror ( Figure 1 b) according to the present invention.
  • Figure 2 shows a graphic distribution of the terrestrial solar spectrum according to ASTM G173-03 in which the spectral regions of lower intensity of solar radiation are highlighted vertically.
  • Figure 3 shows a flow chart that includes the main stages of an optimization process used for the design of the multi-layer aperiodic structure for a mirror according to the present invention.
  • Figure 4 shows the real (n) and imaginary (k) parts of the refractive index of the materials used to construct a multilayer structure according to the invention, comprising T1O2 (upper figures) and S1O2 (lower figures).
  • Figure 5 shows the theoretically calculated reflectance of a first-sided mirror according to the invention, whose layer compositions and layer thicknesses are described in Table 1 of this document. The air mass spectrum (AM) of 1.5 is included as well as the SWIR value obtained.
  • Figure 6 shows values obtained at different angles of incidence for the multilayer composition described in Table 1 of this document.
  • AM air mass spectrum
  • Figure 7 shows the real (n) and imaginary part (k) of the refractive index of the materials used to construct a multilayer stacking structure according to the invention, comprising T1O2 (upper figures) and porous S1O2 (lower figures).
  • Figure 8 shows the theoretically calculated reflectance of a first-sided mirror whose layer composition and layer thicknesses are described in Table 3 of this document. An AM spectrum of 1.5 is included as well as the SWIR value obtained.
  • Figure 9 shows SWIR values obtained at different angles of incidence for the system according to the invention described in Table 3 of this document.
  • Figure 10 shows cross-sectional images obtained through field emission scanning electron microscopy (FESEM) of a 20 layer system of SIO2 / TIO2 with a copper layer on top. On the left and right side of the figure, an image of secondary electrons and an image of backscattered electrons are shown respectively.
  • the scale bar shown in the figure is 2 micrometers.
  • Figure 1 1 shows reflectance spectra of a theoretically calculated (intense line) and experimental multilayer SIO2 / TIO2 film constructed according to the invention, using the thickness values described in Table 5 of this document. SWIR values are also included.
  • Figure 12 shows SWIR values obtained at different angles of incidence for the system according to the invention described in Table 5 of this document.
  • Figure 13 shows reflectance spectra of a multi-layer SIO2 / TIO2 film calculated theoretically (intense line) and experimental (dim line) constructed according to the invention, using the thicknesses described in Table 7 of this document. SWIR values are also included.
  • Figure 14 shows SWIR values obtained at different angles of incidence for the system according to the invention described in Table 7 of this document. DETAILED DESCRIPTION OF THE INVENTION
  • an embodiment of the invention relates to a second-sided mirror that combines: - a multi-layer aperiodic structure (1) made of pre-designed layers of thicknesses and refractive indices, which can reflect sunlight in an efficient manner, in which the bands with the lowest reflectivity of said multi-layer aperiodic structure (1) are matched with the atmospheric absorption bands in the terrestrial solar spectrum, thereby reflecting intensely in the high energy bands of the solar solar spectrum.
  • the aperiodic multi-layer structure (1) is deposited on a layer of flat transparent substrate glass (2);
  • a layer of a metal (3) of choice deposited on such a multi-layer aperiodic structure (1) which can efficiently reflect a certain spectral region of sunlight;
  • a protective coating layer (4) such as enamel paint, whose function is to prevent the degradation of the entire multi-layer aperiodic structure (1).
  • This design is oriented towards the incident light from the side that ends in the glass layer (2).
  • the design of the multi-layer aperiodic structure (1) is such that it efficiently reflects the spectral region in which the metal absorbs, having the effect of giving rise to a high-reflection broadband mirror that covers the entire solar spectrum for all a cone of directions of incidence of the incident light.
  • the protective coating layer (4) of enamel paint serves to protect the back face of the metal layer (3) against corrosion or other environmental threats.
  • Another embodiment of the invention relates to a first-face mirror with a design that combines a layer of a metal (3) of free choice, which can efficiently reflect a certain spectral region, which is deposited on a substrate layer ( 2).
  • the mirror also comprises a multi-layer aperiodic structure (1) made of pre-designed layers of thicknesses and refractive indices, which can efficiently reflect the spectral region in which the metal absorbs. This effect is obtained by forcing the lower reflectivity bands of the structure to coincide with the atmospheric absorption bands in the terrestrial solar spectrum and by high reflection in the high energy bands of the terrestrial solar spectrum (see Figure 2 of this document, in which a graphic distribution of low energy bands in the direct and circumsolar spectrum is shown).
  • the mirror is designed so that the light strikes it from the end that ends in the multi-layer aperiodic structure (1).
  • This design results in a high-reflection mirror in a wide spectral range that covers the high-energy bands of the Earth's solar spectrum for a wide and adjustable cone of light incidence angles.
  • a further objective of the present invention relates to a method for manufacturing a second-sided mirror comprising the following steps:
  • a multi-layer aperiodic structure (1) in which the layers of high and low refractive index materials of different thickness alternate in an aperiodic manner (ie, not periodically but not chaotically).
  • This multi-layer aperiodic structure (1) is formed on the lower surface of a glass layer (2) that acts as the upper protective layer (4) of the complete mirror structure. It is the result of the alternating deposition of layers of controlled thickness of different materials to be chosen so that an aperiodic spatial modulation of the refractive index is achieved through the multi-layer aperiodic structure (1).
  • This modulation is responsible for the reflection properties of the multilayer and is designed to provide the maximum solar reflectivity (RS also called SWIR in English) possible in the wavelength range of 350-2500 nm for the entire mirror structure, having take into account the specific optical losses caused by the absorption of the materials that constitute it, particularly the metal layer (3), and the substrate (2) and protective layers (4).
  • the deposition of these layers can be achieved by any type of thin film coating technique such as rotation deposition (spin-coating), dip deposition (dip-coating), Langmuir-Blodgett, chemical vapor deposition or a method physical vapor deposition, such as evaporation or sputtering, and from a wide range of precursors.
  • each of the layers that form the multilayer is between 1 nm and 1 micrometer.
  • the number of layers in the multilayers can vary between 2 and 1000.
  • the structure of this multi-layer mirror that leads to a high solar reflectivity (RS or SWIR) that is maximum for an angle of incidence to choose, and that is so constant As possible for a wide range of incidence addresses around that, it is the key to the innovation proposed in this invention.
  • step (b) Deposition of a metal layer (3) of free choice composition on the multi-layer aperiodic structure (1) described in step (a).
  • the deposition of this metal layer (3) can be achieved by any type of thin film coating technique such as rotation deposition (spin-coating), dip deposition (dip-coating), Langmuir-Blodgett, chemical vapor deposition or a physical vapor deposition technique, such as evaporation or sputtering, and from a wide range of precursors.
  • the process is aimed at manufacturing a first surface mirror comprising the following steps: (a) Deposition of a metal layer (3) of free choice composition on the substrate (2) of glass.
  • the deposition of this metallic layer (3) can be carried out by any type of thin film coating technique such as rotation deposition (spin-coating), dip deposition (dip-coating), Langmuir-Blodgett, chemical deposition in vapor phase or physical deposition in vapor phase, such as evaporation or sputtering, and from a wide range of precursors.
  • step (b) Preparation of a multi-layer aperiodic structure (1) in which layers of high and low refractive index materials of different thickness alternate in an aperiodic manner (ie, not periodically but not chaotically).
  • the multi-layer aperiodic structure (1) according to this particular embodiment of the invention is preferably formed on the free surface of the metal layer (3) deposited in step (a).
  • the aperiodic multilayer structure (1) may be composed of any sequence of layers of materials of different refractive index and thicknesses, without any limitation imposed as to the number and type of compositions of material to be used, its microstructure or nanostructure, or its porosity.
  • the mirrors described herein can be used for any suitable purpose, including but not limited to heliostats and any type of optical element to be implemented in a thermal, photovoltaic, or combined solar thermal and photovoltaic solar power plant.
  • the solar reflectivity or solar energy reflection factor is defined, in English "solar spectrum weighted integrated reflectance" (SWIR or RS) as the result of integrating, between the selected wavelength range, the product of any target solar spectrum (which can be a standard spectrum such as AMO, AM1, 0, AM1, 5 ... or any other) and the reflectance spectrum f (X) (that is, the intensity of reflected light divided by the intensity of incident light for each wavelength), normalized by the integrated solar spectrum.
  • SWIR solar spectrum weighted integrated reflectance
  • RS or SWIR value is used as a merit factor to find an optimized design.
  • the optimization method is based on a genetic algorithm that samples an initial population, for example a population of 150 individuals (mirror designs), and retains, from each generation to the next, only a percentage (for example 10%) that It shows a better value of RS or SWIR. This process is iterated as much as necessary to reach a stable maximum value, which normally takes place after evaluating 45,000 individuals (300 generations) when the RS or SWIR is optimized for a specific incidence angle.
  • the number of generations required to achieve an optimized configuration is close to 1000.
  • the maximum number of generations under test is 5000, although such value was never reached in the calculations made for Find the designs described in this document.
  • the refractive indexes of the layers from which it is made are considered fixed input values, while the thickness can vary freely. In general, a maximum of 30 dielectric layers are considered for the multi-layer aperiodic structure (1), apart from the metal layer (3) and the substrate (2).
  • sol-Gel Among the various liquid processing routes, the sol-gel method provides a versatile and low-cost option for preparing metal oxides with different microstructures and aggregation states. In addition, sol-gel methods can be combined with liquid deposition techniques to obtain films with stable and crack-free structures.
  • the multi-layer aperiodic structure (1) was prepared using S1O2 and T1O2 layer dispersions obtained by sol-gel technique. A dispersion of S1O2 was obtained by mixing silicon tetraethoxide in an ethanolic solution of hydrochloric acid, while a dispersion of T1O2 was prepared from a solution of nitric acid in isopropanol, to which titanium tetraisopropoxide was slowly added.
  • Both dispersions were deposited on a glass substrate layer (2) using a rotation coating device (Laurell WS-400E-6NPP), in which both the acceleration ramp and the final rotation speed can be precisely determined. Samples were centrifuged for 1 minute and then treated at a temperature between 300 S C and 550 S C on a heating plate for a range of 10 to 300 seconds. After cooling in a metal layer (3), the coating procedure is repeated as many times as necessary to obtain the desired multi-layer aperiodic structure (1). The same process was carried out by immersion coating (ND-RDC, Nadetech Innovation) by submerging the substrates in the same metal oxide dispersions. Both processes result in a dense multi-layer aperiodic structure (1).
  • ND-RDC Nadetech Innovation
  • This method involves the deposition of the metal layer (3) and the metal oxide sheets for the multi-layer aperiodic structure (1).
  • the metal is deposited by a thermal evaporation technique or by sputtering. Both deposition methods involve a high vacuum chamber (Leica EM SCD500) equipped with a quartz scale (Leica EM QSG100) that monitors the deposited thickness.
  • the metal formed as wire was evaporated through a tungsten resistance polarized at 4 V and with an applied current of 30 mA.
  • Metal sputtering was performed using a specific target polarized at high voltage at an argon pressure between 5x10 -3 and 1 x1 0 -2 mbar.
  • Optical reflectance measurements Normal incidence specular reflectance spectra were obtained using a visible UV scan spectrophotometer (SHIMADZU UV-2101 PC) attached to an integration sphere and a Fourier transform spectrophotometer (BRUKER) coupled to a microscope which works in the wavelength range of 450 nm-2500 nm
  • EXAMPLE 1 In a first embodiment of the invention described herein, an optimized design of a first-face or first-surface mirror that maximizes the RS or SWIR is presented in this case for a wide range of angles of incidence of the light simultaneously, in this case assuming standard refractive index values of the dense phases of the materials used (S1O2 and T1O2). The spectral dependence of the refractive index and the assumed absorption coefficient for these calculations are presented in Figure 4. Such a mirror is made of a sequence of layers whose composition and thickness are listed in Table 1 of this document. This calculated design was achieved in the 1001 generation. Figure 5 visualizes its reflectance calculated at normal incidence.
  • Figure 7 Such a mirror is made of a sequence of layers whose composition and thickness are listed in Table 3 of this document. This calculated design was achieved in the 1001 generation.
  • Figure 8 visualizes its reflectance calculated at normal incidence.
  • the RS or SWIR values for different angles of incidence are listed in Table 4 and plotted in Figure 9, in which the optimized reflectance can be observed at an incident angle of incident light at 25 s , as well as the RS o SWIR almost constant between angles of incidence of 0 s and 40 s , which is one of the most relevant novel properties of the multilayer structures described herein.
  • EXAMPLE 3 In a third embodiment of the invention it is described how to prepare a mirror of second face of high solar reflectivity using the sol-gel method to deposit a multi-layer aperiodic structure (1) combined with an evaporation process to deposit a metal layer (3) of copper.
  • the design followed, obtained from the optimization calculations described in previous paragraphs, is provided in Table 5 of this document, and was achieved after 162 generations. Two different precursor suspensions were used to create thin films of silicon oxide and titanium oxide by rotational deposition.
  • silicon tetraethoxide (0.50 M), hydrochloric acid (10 -3 M), water (2.37 M) and ethanol (14.44 M) were used, while for the latter, tetraisopropoxide was used of titanium (0.30 M), nitric acid (5.60-10 " 3 M), water (0.1 6 M) and isopropanol (1,178 M).
  • Such a mirror is made of a sequence of layers whose composition and thickness are listed in Table 5 of this document.
  • the copper layer (3) is seen as a thicker shiny layer at the top.
  • Figure 1 the reflectance of the mirror for the target wavelength range is displayed for both the calculated and experimental multilayer realization, which show a very good concordance throughout the spectral range.
  • the angular dependence of the RS or SWIR is presented in Figure 12 and the corresponding data is displayed in Table 6.
  • EXAMPLE 4 In a fourth embodiment of the invention, it is described how to prepare a first-face mirror of high solar reflectivity using only a physical deposition method to construct a multi-layer aperiodic structure (1). Such a mirror is made of a sequence of layers whose composition and thickness are listed in Table 7 of this document. This calculated design was achieved in the 1001 generation. A layer (3) of copper was deposited on top of the substrate by sputtering. Two different targets were used to create thin films of silicon oxide and titanium oxide by sputtering. In Figure 13, the reflectance of the mirror for the target wavelength range is displayed for both the calculated and experimental multilayer realization, which show a very good concordance throughout the spectral range.

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Abstract

The invention relates to mirrors for thermosolar applications, the mirrors preferably comprising: a metal layer (3) which can reflect a range of wavelengths within the solar irradiance spectrum; and a multilayer aperiodic structure (1) adjacent the metal layer (3) and comprising a plurality of layers having different refraction indices and thicknesses, with reflection bands having wavelength ranges in which the adjacent metal layer (3) is absorbent. The mirror structure allows a high level of reflection outside the terrestrial solar spectrum absorption bands and has S.R. or SWIR values which are both stable and constant with respect to the light incidence direction.

Description

DESCRIPCIÓN  DESCRIPTION
ESPEJO PARA APLICACIONES DE ENERGIA SOLAR Y METODO DE FABRICACION DELMIRROR FOR SOLAR ENERGY APPLICATIONS AND MANUFACTURING METHOD OF
MISMO SAME
CAMPO DE LA INVENCION FIELD OF THE INVENTION
La presente invención pertenece al campo de las tecnologías de energía solar. Más específicamente, la invención se refiere a espejos para aplicaciones termosolares. The present invention belongs to the field of solar energy technologies. More specifically, the invention relates to mirrors for solar thermal applications.
ANTECEDENTES DE LA INVENCIÓN BACKGROUND OF THE INVENTION
La investigación en nuevos espejos para mejorar la eficiencia de tecnologías de energía solar es extensa, tanto en diseños como en materiales. Una de las tecnologías de este tipo que más demanda, en términos de la eficiencia de los espejos reflectores, es la conocida como termosolar, en la que la luz del sol se concentra en un objetivo predeterminado, mediante conjuntos de espejos ubicados de manera adecuada alrededor de dicho objetivo. Tales conjuntos de espejos se conocen comúnmente como heliostatos. En las tecnologías de heliostatos, para obtener un rendimiento óptimo es necesario mantener las superficies reflectoras de los espejos perpendiculares al bisector del ángulo entre la dirección del sol y el objetivo, desde el punto de vista del espejo. Research in new mirrors to improve the efficiency of solar energy technologies is extensive, both in designs and materials. One of the technologies of this type that is most in demand, in terms of the efficiency of the reflector mirrors, is known as thermosolar, in which the sunlight is concentrated on a predetermined objective, by means of sets of mirrors located properly around of that objective. Such sets of mirrors are commonly known as heliostats. In heliostat technologies, to obtain optimum performance it is necessary to keep the reflective surfaces of the mirrors perpendicular to the bisector of the angle between the direction of the sun and the lens, from the point of view of the mirror.
Los costes del heliostato representan aproximadamente la mitad del coste de capital de una central de energía solar de torre. Por tanto, resulta de interés diseñar heliostatos menos costosos para su fabricación a gran escala, de modo que las centrales de energía solar puedan producir electricidad a costes más competitivos que los costes de centrales eléctricas convencionales (basadas en otras fuentes, tales como carbón). Además de los costes, la reflectividad a lo largo de todo el rango del espectro solar (denominado comúnmente en la técnica como "reflectividad solar (R.S) o factor de reflexión de la energía solar, o en inglés "solar spectrum weighted integrated reflectance" (SWIR)) y la durabilidad frente al entorno son factores que deberán considerarse a la hora de comparar los diseños de los heliostatos. Heliostat costs represent approximately half of the capital cost of a tower solar power plant. Therefore, it is of interest to design less expensive heliostats for large-scale manufacturing, so that solar power plants can produce electricity at more competitive costs than the costs of conventional power plants (based on other sources, such as coal). In addition to costs, reflectivity throughout the entire range of the solar spectrum (commonly referred to in the art as "solar reflectivity (RS) or solar energy reflection factor, or in English" solar spectrum weighted integrated reflectance "( SWIR)) and durability against the environment are factors that should be considered when comparing heliostat designs.
Los intentos de reducir los costes de heliostatos se basan, principalmente, en la sustitución del diseño del heliostato convencional por uno que use materiales menos costosos. Un diseño convencional para el heliostato comprende espejos de segunda cara, cuya estructura consiste generalmente en: (i) una capa protectora, (ii) una capa de plata reflectora y (iii) una capa protectora superior de vidrio grueso. La invención descrita en el presente documento se refiere a reflectores alternativos, cuyo diseño permite el uso de materiales menos costosos que la plata, disminuyendo por tanto la dependencia de esta tecnología de metales preciosos, cuyos precios de mercado presentan grandes fluctuaciones. Cualquier material reflectante utilizado debe, en todo caso, reflejar la energía solar Incidente con una mínima pérdida, y su rendimiento no debe verse afectado por su interacción con la humedad, la radiación ultravioleta, el polvo, la temperatura y otros parámetros ambientales. En general, la plata es la elección preferida como material para la capa reflectora, debido a la sólida base tecnológica establecida en la industria de los espejos, y porque su reflectancia se encuentra generalmente en el intervalo entre 0,95 y 0,97, para superficies depositadas mediante procedimientos de fabricación de espejos bien establecidos. Attempts to reduce heliostat costs are based primarily on replacing the conventional heliostat design with one that uses less expensive materials. A conventional design for the heliostat comprises second-sided mirrors, the structure of which generally consists of: (i) a protective layer, (ii) a reflective silver layer and (iii) a thick glass top protective layer. The invention described herein refers to alternative reflectors, the design of which allows the use of less expensive materials than silver, thus decreasing the dependence of this precious metal technology, whose market prices show large fluctuations. Any reflective material used must, in all In this case, reflect the incident solar energy with minimal loss, and its performance should not be affected by its interaction with humidity, ultraviolet radiation, dust, temperature and other environmental parameters. In general, silver is the preferred choice as a material for the reflective layer, due to the solid technological base established in the mirror industry, and because its reflectance is generally in the range between 0.95 and 0.97, for surfaces deposited by well established mirror manufacturing procedures.
El uso de otros metales más rentables se ha evitado hasta ahora por la presencia de bandas de fuerte absorción que disminuirían en gran medida la reflectividad del espejo. Por otro lado, los enfoques basados en espejos dieléctricos (también conocidos como reflectores de Bragg, espejos dicroicos, espejos de interferencia, reflectores de Bragg distribuidos o, en una terminología más moderna, cristales fotónicos unidimensionales) presentan algunos inconvenientes graves. En primer lugar, la mayoría de los diseños se basan en una distribución periódica de capas de índices de refracción altos y bajos, lo que proporciona un fuerte pico de reflexión en un rango espectral que es mucho más estrecho que el espectro solar completo que se tiene como objetivo para aplicaciones de energía renovable (véanse, por ejemplo, las solicitudes de patente estadounidenses con las referencias US 2912/0263885 y US 2013/0342900). Además, la fuerte dependencia angular del espectro de reflectancia impide su uso en tecnologías en las que la luz del sol alcanza el espejo con diversos ángulos de incidencia. El problema de cubrir un rango espectral mayor puede solucionarse mediante diseños multicapa basados en el acoplamiento de estructuras con diferentes periodicidades (véase la solicitud internacional con la referencia WO2013/059228) pero, incluso en tal caso, el número de capas necesarias para cubrir todo el espectro solar es tan grande que no resulta una opción viable. Los enfoques relacionados con este concepto, aunque se basan en la distribución aleatoria de capas más que en diseños aperiódicos, también se han propuesto para construir reflectores en rangos de longitudes de onda más cortos (véase el documento WO2009/043374), pero no podrían extenderse para reflejar todo el espectro solar. The use of other more profitable metals has been avoided so far by the presence of bands of strong absorption that would greatly reduce the reflectivity of the mirror. On the other hand, approaches based on dielectric mirrors (also known as Bragg reflectors, dichroic mirrors, interference mirrors, distributed Bragg reflectors or, in more modern terminology, one-dimensional photonic crystals) have some serious drawbacks. First, most designs are based on a periodic distribution of layers of high and low refractive indices, which provides a strong reflection peak in a spectral range that is much narrower than the full solar spectrum as a target for renewable energy applications (see, for example, US patent applications with references US 2912/0263885 and US 2013/0342900). In addition, the strong angular dependence of the reflectance spectrum prevents its use in technologies in which sunlight reaches the mirror with various angles of incidence. The problem of covering a greater spectral range can be solved by multilayer designs based on the coupling of structures with different periodicities (see international application with reference WO2013 / 059228) but, even in this case, the number of layers needed to cover the entire Solar spectrum is so large that it is not a viable option. Approaches related to this concept, although based on random distribution of layers rather than aperiodic designs, have also been proposed to construct reflectors in shorter wavelength ranges (see WO2009 / 043374), but could not be extended to reflect the entire solar spectrum.
Debido a las limitaciones y los problemas técnicos mencionados anteriormente, la presente invención propone configuraciones de espejo novedosas y sus correspondientes métodos de fabricación que pueden proporcionar rendimientos mejorados en términos de su sensibilidad a la longitud de onda, sus propiedades de reflexión angular y su dependencia de materiales de alto coste. BREVE DESCRIPCIÓN DE LA INVENCIÓN Due to the limitations and technical problems mentioned above, the present invention proposes novel mirror configurations and their corresponding manufacturing methods that can provide improved yields in terms of their wavelength sensitivity, their angular reflection properties and their dependence on high cost materials. BRIEF DESCRIPTION OF THE INVENTION
La presente invención soluciona los problemas técnicos mencionados anteriormente proponiendo el uso de espejos basados en una capa reflectora hecha de un metal de libre elección, que se acopla de manera adyacente a una secuencia aperiódica de capas de diferente composición, espesores e índices de refracción. La principal ventaja técnica de estos espejos, que surge como consecuencia de este particular diseño, es que presentan una alta reflectancia óptica para todo el espectro solar (350 nm < λ < 2500 nm). Además, los espejos de la invención pueden optimizarse para conseguir una reflectividad máxima para un ángulo de incidencia de la luz solar dado. Además de estas características, la capacidad de usar metales de libre elección, que también pueden estar basados en materiales de bajo coste, hace que la invención sea muy competitiva con los espejos de plata convencionales en términos de rendimiento. The present invention solves the technical problems mentioned above by proposing the use of mirrors based on a reflective layer made of a metal of free choice, which is coupled adjacent to an aperiodic sequence of layers of different composition, thicknesses and refractive indices. The main technical advantage of these mirrors, which arises as The consequence of this particular design is that they have a high optical reflectance for the entire solar spectrum (350 nm <λ <2500 nm). In addition, the mirrors of the invention can be optimized to achieve maximum reflectivity for a given angle of incidence of sunlight. In addition to these characteristics, the ability to use free choice metals, which may also be based on low-cost materials, makes the invention very competitive with conventional silver mirrors in terms of performance.
Con relación a los costes relacionados a las estructuras multicapa, se ven afectados significativamente por la complejidad y los costes de deposición de sus capas. Por tanto, reducir significativamente el número de capas de una estructura multicapa mejora de manera significativa sus costes de producción. Por otro lado, reducir el número de capas de una estructura de reflector multicapa introduce caídas puntuales en el espectro de reflectividad (también conocidas como bandas de baja reflectividad). La presente invención tiene en cuenta el efecto de las caídas puntuales de reflectividad dentro de la estructura aperiódica, forzándolas a que coincidan con las bandas de absorción en el espectro solar terrestre, permitiendo por tanto una alta reflectancia óptica con un número de capas reducido en gran medida. En este sentido, la presente invención propone una solución al problema de conseguir una alta reflectancia óptica viable para la generación de electricidad a partir de energía solar sin la necesidad de estructuras con un gran número de capas, haciendo coincidir las caídas puntuales de reflectancia de la estructura de capas aperiódica, inherente a las estructuras con un menor número de capas, con las bandas de absorción atmosféricas en el espectro solar terrestre. In relation to the costs related to multilayer structures, they are significantly affected by the complexity and deposition costs of their layers. Therefore, significantly reducing the number of layers of a multilayer structure significantly improves its production costs. On the other hand, reducing the number of layers of a multilayer reflector structure introduces point drops in the reflectivity spectrum (also known as low reflectivity bands). The present invention takes into account the effect of specific reflectivity drops within the aperiodic structure, forcing them to match the absorption bands in the solar solar spectrum, thus allowing a high optical reflectance with a large number of layers reduced measure. In this sense, the present invention proposes a solution to the problem of achieving a high optical reflectance viable for the generation of electricity from solar energy without the need for structures with a large number of layers, matching the specific reflectance drops of the aperiodic layer structure, inherent in structures with fewer layers, with atmospheric absorption bands in the solar solar spectrum.
Por tanto, según las consideraciones anteriores, un objetivo de la invención es un espejo para aplicaciones de energía solar que comprende: una capa de metal que presenta reflexión de al menos un primer rango de longitudes de onda comprendidas dentro del espectro de irradiancia solar y absorción de al menos un segundo rango de longitudes de onda comprendidas en dicho espectro; y una estructura aperiódica multicapa adyacente a la capa de metal, que comprende una pluralidad de capas de diferentes índices de refracción y espesores, que presenta reflexión dentro del segundo rango de longitudes de onda en el que la capa de metal adyacente presenta absorción ; estando dispuesta la distribución de capas en la estructura aperiódica multicapa de manera que los rangos de longitud de onda con reflexión mínima en dicha estructura aperiódica multicapa corresponden a rangos de longitud de onda con una absorción máxima en el espectro solar terrestre. Por tanto, la estructura aperiódica multicapa de la invención está configurada para reflejar la luz en los rangos de longitudes de onda que absorbe la capa de metal adyacente, haciendo que los rangos de longitudes de onda de baja reflectividad (debido a, por ejemplo, la interferencia entre las capas) coincidan con los rangos de longitudes de onda en los que el espectro solar tiene caídas puntuales de irradiancia (correspondientes a aquellas longitudes de onda comprendidas en las bandas de absorción de la atmósfera), de modo que la estructura multicapa refleja las longitudes de onda con valores de ¡rradlancla mayores dentro del espectro solar. Con relación a las propiedades de reflexión/absorción de la capa de metal, ha de observarse que esta capa puede presentar propiedades tanto de reflexión como de absorción en el mismo rango de longitudes de onda (es decir los denominados rangos de longitudes de onda primero y segundo comprendidas dentro del espectro de ¡rradiancla solar pueden ser rangos que se solapan, o Incluso que coinciden). Sin embargo, en esta situación la reflexión en dicho rango normalmente es menos Intensa que en otros rangos de longitud de onda del espectro, debido a la presencia del efecto de absorción. En una realización preferida de la Invención, el espejo comprende además una capa de sustrato y/o una capa protectora aplicada a la capa de metal. Therefore, according to the foregoing considerations, an objective of the invention is a mirror for solar energy applications comprising: a metal layer that exhibits reflection of at least a first range of wavelengths within the solar irradiance and absorption spectrum of at least a second range of wavelengths comprised in said spectrum; and a multi-layer aperiodic structure adjacent to the metal layer, comprising a plurality of layers of different refractive indices and thicknesses, which has reflection within the second range of wavelengths in which the adjacent metal layer exhibits absorption; the distribution of layers in the multilayer aperiodic structure being arranged so that the wavelength ranges with minimal reflection in said multilayer aperiodic structure correspond to wavelength ranges with maximum absorption in the terrestrial solar spectrum. Therefore, the multi-layer aperiodic structure of the invention is configured to reflect the light in the wavelength ranges absorbed by the adjacent metal layer, making the wavelength ranges of low reflectivity (due to, for example, the interference between the layers) coincide with the ranges of wavelengths in which the solar spectrum has occasional drops in irradiance (corresponding to those wavelengths included in the atmospheric absorption bands), so that the multilayer structure reflects the lengths wave with higher values of the radius within the solar spectrum. With regard to the reflection / absorption properties of the metal layer, it should be noted that this layer may have both reflection and absorption properties in the same wavelength range (i.e. the so-called first wavelength ranges and second included within the spectrum of solar radiation can be overlapping ranges, or even matching). However, in this situation the reflection in that range is usually less intense than in other ranges of wavelength of the spectrum, due to the presence of the absorption effect. In a preferred embodiment of the invention, the mirror further comprises a substrate layer and / or a protective layer applied to the metal layer.
En otra realización preferida de la Invención, el grosor de las capas que forman la estructura aperiódica multlcapa está comprendido entre 1 nm y 1 μιτι. Más preferiblemente, el grosor de las capas que forman la estructura aperiódica multlcapa está comprendido entre 10 nm y 400 nm. In another preferred embodiment of the invention, the thickness of the layers that form the multi-layer aperiodic structure is comprised between 1 nm and 1 μιτι. More preferably, the thickness of the layers that form the multi-layer aperiodic structure is between 10 nm and 400 nm.
En una realización adicional preferida de la Invención, el número de capas en la estructura aperiódica multlcapa está entre 2 y 1 000. Más preferiblemente, el número de capas en la estructura aperiódica multlcapa está entre 4 y 200. In a further preferred embodiment of the invention, the number of layers in the multi-layer aperiodic structure is between 2 and 1 000. More preferably, the number of layers in the multi-layer aperiodic structure is between 4 and 200.
En una realización preferida de la Invención, la estructura aperiódica multlcapa está formada por una secuencia alternada de dos materiales de diferente índice de refracción. Más preferiblemente, la estructura aperiódica multlcapa está formada por capas alternadas de óxido de silicio y óxido de titanio o cualquier compuesto derivado de los mismos. In a preferred embodiment of the invention, the multi-layer aperiodic structure is formed by an alternating sequence of two materials of different refractive index. More preferably, the multi-layer aperiodic structure is formed by alternating layers of silicon oxide and titanium oxide or any compound derived therefrom.
En una realización preferida de la Invención, la capa de metal comprende uno o más de los siguientes materiales: cobre, aluminio, cromo, hierro, titanio, níquel, cobalto, paladlo, rodio, plata, oro, platino, o cualquier aleación de los mismos. En una realización adicional preferida de la Invención, la estructura aperiódica multlcapa y la capa de metal están dispuestas para formar un espejo de primera o segunda cara. In a preferred embodiment of the invention, the metal layer comprises one or more of the following materials: copper, aluminum, chromium, iron, titanium, nickel, cobalt, palladium, rhodium, silver, gold, platinum, or any alloy of the same. In a further preferred embodiment of the invention, the multi-layer aperiodic structure and the metal layer are arranged to form a first or second-sided mirror.
En una realización adicional preferida de la Invención, las capas de menor índice de refracción dentro de la estructura aperiódica multlcapa presentan una porosidad comprendida entre el 10% y el 95% y las capas de mayor índice de refracción presentan una porosidad comprendida entre el 0% y el 10%. In a further preferred embodiment of the invention, the layers with the lowest refractive index within the multi-layer aperiodic structure have a porosity between 10% and 95% and the layers with the highest refractive index have a porosity between 0% and 10%.
Un objetivo adicional de la Invención se refiere a un método para fabricar un espejo para aplicaciones de energía solar, que comprende preferiblemente las etapas de: A further objective of the invention relates to a method for manufacturing a mirror for solar energy applications, which preferably comprises the steps of:
- Deposición de una capa de metal, que puede reflejar un rango de longitudes de onda comprendidas dentro del espectro de ¡rradlancla solar, adyacente a una pluralidad de capas de diferente índice de refracción y espesor, que forman una estructura aperiódica multicapa que presenta bandas de reflexión a rangos de longitud de onda en los que la capa de metal adyacente absorbe; - Deposition of a metal layer, which may reflect a range of wavelengths comprised within the spectrum of the sunburst, adjacent to a plurality of layers of different refractive index and thickness, which form a multi-layer aperiodic structure that has reflection bands at wavelength ranges in which the adjacent metal layer absorbs;
- depositar las capas en la estructura aperiódica multicapa, de manera que las bandas de reflexión más débil de la estructura aperiódica multicapa corresponden a rangos de longitud de onda coincidentes con las bandas de absorción más intensas en el espectro solar terrestre.  - depositing the layers in the multi-layer aperiodic structure, so that the weakest reflection bands of the multi-layer aperiodic structure correspond to wavelength ranges coinciding with the most intense absorption bands in the terrestrial solar spectrum.
En una realización adicional preferida del método de la invención, la estructura aperiódica multicapa o la capa de metal se deposita sobre un sustrato (por ejemplo, un sustrato de vidrio). Además, el método de la invención puede comprender la etapa de depositar una capa protectora sobre la capa de metal. In a further preferred embodiment of the method of the invention, the multi-layer aperiodic structure or the metal layer is deposited on a substrate (for example, a glass substrate). In addition, the method of the invention may comprise the step of depositing a protective layer on the metal layer.
En una realización adicional preferida de la invención, la técnica empleada para depositar las capas que forman la estructura aperiódica multicapa o la capa de metal comprende uno o más de la siguiente lista: deposición por rotación (spin-coating), recubrimiento por inmersión (dip-coating), Langmuir-Blodgett, técnicas de deposición química en fase de vapor o deposición física en fase de vapor como evaporación térmica o pulverización catódica.  In a further preferred embodiment of the invention, the technique used to deposit the layers that form the multi-layer aperiodic structure or the metal layer comprises one or more of the following list: spin deposition, dip coating (dip -coating), Langmuir-Blodgett, chemical vapor deposition techniques or physical vapor deposition techniques such as thermal evaporation or sputtering.
Tal como se describe en los párrafos anteriores del presente documento, diseñando el espejo para un ángulo de incidencia de luz solar de libre elección y usando materiales de bajo coste, la invención resulta altamente competitiva, en términos de rendimiento, frente a espejos de plata convencionales. La estructura del espejo basada en la combinación de una capa de metal de libre elección y una estructura aperiódica multicapa prediseñada, permite una alta reflexión fuera de las bandas de absorción del espectro solar terrestre (es decir, la estructura aperiódica refleja intensamente las longitudes de onda incidentes que el metal absorbe), y presenta valores de SWIR tanto estables como constantes con respecto a la dirección de incidencia de la luz. As described in the previous paragraphs of the present document, designing the mirror for an angle of incidence of free-choice sunlight and using low-cost materials, the invention is highly competitive, in terms of performance, compared to conventional silver mirrors. . The mirror structure based on the combination of a metal layer of free choice and a pre-designed multilayer aperiodic structure, allows high reflection outside the absorption bands of the terrestrial solar spectrum (that is, the aperiodic structure strongly reflects wavelengths incidents that the metal absorbs), and presents both stable and constant SWIR values with respect to the direction of incidence of the light.
DESCRIPCIÓN DE LAS FIGURAS La figura 1 muestra dos realizaciones de la distribución multicapa de un espejo de segunda cara (figura 1 a) y un espejo de primera cara (figura 1 b) según la presente invención. DESCRIPTION OF THE FIGURES Figure 1 shows two embodiments of the multilayer distribution of a second-sided mirror (Figure 1 a) and a first-sided mirror (Figure 1 b) according to the present invention.
La figura 2 muestra una distribución gráfica del espectro solar terrestre según la norma ASTM G173-03 en el que las regiones espectrales de menor intensidad de la radiación solar se resaltan en vertical. Figure 2 shows a graphic distribution of the terrestrial solar spectrum according to ASTM G173-03 in which the spectral regions of lower intensity of solar radiation are highlighted vertically.
La figura 3 muestra un diagrama de flujo que incluye las etapas principales de un proceso de optimización empleado para el diseño de la estructura aperiódica multicapa para un espejo según la presente invención. La figura 4 muestra las partes real (n) e imaginaria (k) del índice de refracción de los materiales usados para construir una estructura multicapa según la invención, que comprende T1O2 (figuras superiores) y S1O2 (figuras inferiores). La figura 5 muestra la reflectancia calculada teóricamente de un espejo de primera cara según la invención, cuyas composiciones de capa y espesores de capa se describen en la tabla 1 del presente documento. Se incluye el espectro de masa de aire (AM) de 1 ,5 así como el valor de SWIR obtenido. La figura 6 muestra valores de obtenidos a diferentes ángulos de incidencia para la composición multicapa descrita en la tabla 1 del presente documento. Figure 3 shows a flow chart that includes the main stages of an optimization process used for the design of the multi-layer aperiodic structure for a mirror according to the present invention. Figure 4 shows the real (n) and imaginary (k) parts of the refractive index of the materials used to construct a multilayer structure according to the invention, comprising T1O2 (upper figures) and S1O2 (lower figures). Figure 5 shows the theoretically calculated reflectance of a first-sided mirror according to the invention, whose layer compositions and layer thicknesses are described in Table 1 of this document. The air mass spectrum (AM) of 1.5 is included as well as the SWIR value obtained. Figure 6 shows values obtained at different angles of incidence for the multilayer composition described in Table 1 of this document.
La figura 7 muestra la parte real (n) e imaginaria (k) del índice de refracción de los materiales usados para construir una estructura apilamiento multicapa según la invención, que comprende T1O2 (figuras superiores) y S1O2 poroso (figuras inferiores). Figure 7 shows the real (n) and imaginary part (k) of the refractive index of the materials used to construct a multilayer stacking structure according to the invention, comprising T1O2 (upper figures) and porous S1O2 (lower figures).
La figura 8 muestra la reflectancia calculada teóricamente de un espejo de primera cara cuya composición de capa y espesores de capa se describen en la tabla 3 del presente documento. Se incluye un espectro AM de 1 ,5 así como el valor de SWIR obtenido. La figura 9 muestra valores de SWIR obtenidos a diferentes ángulos de incidencia para el sistema según la invención descrito en la tabla 3 del presente documento.  Figure 8 shows the theoretically calculated reflectance of a first-sided mirror whose layer composition and layer thicknesses are described in Table 3 of this document. An AM spectrum of 1.5 is included as well as the SWIR value obtained. Figure 9 shows SWIR values obtained at different angles of incidence for the system according to the invention described in Table 3 of this document.
La figura 10 muestra imágenes de sección transversal obtenidas a través de microscopía electrónica de barrido por emisión de campo (FESEM) de un sistema de 20 capas de SÍO2/TÍO2 con una capa de cobre encima. En el lado izquierdo y derecho de la figura, se muestra respectivamente una imagen de electrones secundarios y una imagen de electrones retrodispersados. La barra de escala mostrada en la figura es de 2 micrómetros. Figure 10 shows cross-sectional images obtained through field emission scanning electron microscopy (FESEM) of a 20 layer system of SIO2 / TIO2 with a copper layer on top. On the left and right side of the figure, an image of secondary electrons and an image of backscattered electrons are shown respectively. The scale bar shown in the figure is 2 micrometers.
La figura 1 1 muestra espectros de reflectancia de una película de SÍO2/TÍO2 multicapa calculada teóricamente (línea intensa) y experimental (línea tenue) construida según la invención, usando los valores de grosor descritos en la tabla 5 del presente documento. También se incluyen los valores de SWIR. Figure 1 1 shows reflectance spectra of a theoretically calculated (intense line) and experimental multilayer SIO2 / TIO2 film constructed according to the invention, using the thickness values described in Table 5 of this document. SWIR values are also included.
La figura 12 muestra valores de SWIR obtenidos a diferentes ángulos de incidencia para el sistema según la invención descrito en la tabla 5 del presente documento. Figure 12 shows SWIR values obtained at different angles of incidence for the system according to the invention described in Table 5 of this document.
La figura 13 muestra espectros de reflectancia de una película de SÍO2/TÍO2 multicapa calculada teóricamente (línea intensa) y experimental (línea tenue) construida según la invención, usando los espesores descrito en la tabla 7 del presente documento. También se incluyen los valores de SWIR. La figura 14 muestra valores de SWIR obtenidos a diferentes ángulos de incidencia para el sistema según la invención descrito en la tabla 7 del presente documento. DESCRIPCIÓN DETALLADA DE LA INVENCIÓN Figure 13 shows reflectance spectra of a multi-layer SIO2 / TIO2 film calculated theoretically (intense line) and experimental (dim line) constructed according to the invention, using the thicknesses described in Table 7 of this document. SWIR values are also included. Figure 14 shows SWIR values obtained at different angles of incidence for the system according to the invention described in Table 7 of this document. DETAILED DESCRIPTION OF THE INVENTION
A continuación se procede a describir algunas de las realizaciones preferidas y no limitativas de la invención, con relación a las referencias numéricas de las figuras 1 -14 en el presente documento. Las definiciones proporcionadas pretenden facilitar la comprensión de determinados términos y, de ningún modo limitarán el alcance de las reivindicaciones del presente documento. Some of the preferred and non-limiting embodiments of the invention will now be described, in relation to the numerical references of Figures 1-14 herein. The definitions provided are intended to facilitate the understanding of certain terms and will in no way limit the scope of the claims in this document.
Tal como se muestra en la figura 1 (a) del presente documento, una realización de la invención se refiere a un espejo de segunda cara que combina: - una estructura aperiódica multicapa (1 ) hecha de capas de espesores e índices de refracción prediseñados, que pueden reflejar la luz del sol de manera eficiente, en la que las bandas de menor reflectividad de dicha estructura aperiódica multicapa (1 ) se hacen coincidir con las bandas de absorción atmosférica en el espectro solar terrestre, reflejándose de ese modo de manera intensa en las bandas de alta energía del espectro solar terrestre. La estructura aperiódica multicapa (1 ) se deposita sobre una capa de vidrio de sustrato (2) transparente plana; As shown in Figure 1 (a) of the present document, an embodiment of the invention relates to a second-sided mirror that combines: - a multi-layer aperiodic structure (1) made of pre-designed layers of thicknesses and refractive indices, which can reflect sunlight in an efficient manner, in which the bands with the lowest reflectivity of said multi-layer aperiodic structure (1) are matched with the atmospheric absorption bands in the terrestrial solar spectrum, thereby reflecting intensely in the high energy bands of the solar solar spectrum. The aperiodic multi-layer structure (1) is deposited on a layer of flat transparent substrate glass (2);
- una capa de un metal (3) a elección depositado sobre tal estructura aperiódica multicapa (1 ), que puede reflejar de manera eficiente una determinada región espectral de luz del sol; - una capa de recubrimiento protectora (4), tal como pintura de esmalte, cuya función es impedir la degradación de toda la estructura aperiódica multicapa (1 ). Este diseño está orientado hacia la luz incidente desde el lado que termina en la capa de vidrio (2). - a layer of a metal (3) of choice deposited on such a multi-layer aperiodic structure (1), which can efficiently reflect a certain spectral region of sunlight; - a protective coating layer (4), such as enamel paint, whose function is to prevent the degradation of the entire multi-layer aperiodic structure (1). This design is oriented towards the incident light from the side that ends in the glass layer (2).
El diseño de la estructura aperiódica multicapa (1 ) es tal que refleja de manera eficiente la región espectral en la que el metal absorbe, teniendo el efecto de dar lugar a un espejo de banda ancha de alta reflexión que cubre el espectro solar completo para todo un cono de direcciones de incidencia de la luz incidente. La capa de recubrimiento protectora (4) de pintura de esmalte sirve para proteger la cara trasera de la capa de metal (3) frente a la corrosión u otras amenazas ambientales. The design of the multi-layer aperiodic structure (1) is such that it efficiently reflects the spectral region in which the metal absorbs, having the effect of giving rise to a high-reflection broadband mirror that covers the entire solar spectrum for all a cone of directions of incidence of the incident light. The protective coating layer (4) of enamel paint serves to protect the back face of the metal layer (3) against corrosion or other environmental threats.
Otra realización de la invención se refiere a un espejo de primera cara con un diseño que combina una capa de un metal (3) de libre elección, que puede reflejar de manera eficiente una determinada región espectral, que se deposita sobre una capa de sustrato (2). El espejo también comprende una estructura aperiódica multicapa (1 ) hecha de capas de espesores e índices de refracción prediseñados, que puede reflejar de manera eficiente la región espectral en la que el metal absorbe. Este efecto se obtiene forzando que las bandas de menor reflectlvldad de la estructura coincidan con las bandas de absorción atmosférica en el espectro solar terrestre y mediante la alta reflexión en las bandas de alta energía del espectro solar terrestre (véase la figura 2 del presente documento, en la que se muestra una distribución gráfica de bandas de baja energía en el espectro directo y circunsolar). En este caso, el espejo está diseñado para que la luz incida en el mismo desde el extremo que termina en la estructura aperiódica multicapa (1 ). Este diseño da lugar a un espejo de alta reflexión en un amplio rango espectral que cubre las bandas de alta energía del espectro solar terrestre para un cono ancho y ajustable de ángulos de incidencia de la luz. Another embodiment of the invention relates to a first-face mirror with a design that combines a layer of a metal (3) of free choice, which can efficiently reflect a certain spectral region, which is deposited on a substrate layer ( 2). The mirror also comprises a multi-layer aperiodic structure (1) made of pre-designed layers of thicknesses and refractive indices, which can efficiently reflect the spectral region in which the metal absorbs. This effect is obtained by forcing the lower reflectivity bands of the structure to coincide with the atmospheric absorption bands in the terrestrial solar spectrum and by high reflection in the high energy bands of the terrestrial solar spectrum (see Figure 2 of this document, in which a graphic distribution of low energy bands in the direct and circumsolar spectrum is shown). In this case, the mirror is designed so that the light strikes it from the end that ends in the multi-layer aperiodic structure (1). This design results in a high-reflection mirror in a wide spectral range that covers the high-energy bands of the Earth's solar spectrum for a wide and adjustable cone of light incidence angles.
Un objetivo adicional de la presente invención se refiere a un método para fabricar un espejo de segunda cara que comprende las siguientes etapas: A further objective of the present invention relates to a method for manufacturing a second-sided mirror comprising the following steps:
(a) Preparación de una estructura aperiódica multicapa (1 ), en la que las capas de materiales de índices de refracción altos y bajos de diferente espesor se alternan de manera aperiódica (es decir, no periódica pero no caótica). Esta estructura aperiódica multicapa (1 ) se forma sobre la superficie inferior de una capa de vidrio (2) que actúa como capa protectora (4) superior de la estructura de espejo completa. Es el resultado de la deposición alternada de capas de espesor controlado de diferentes materiales a elegir de modo que se consigue una modulación espacial aperiódica del índice de refracción a través de la estructura aperiódica multicapa (1 ). Esta modulación es responsable de las propiedades de reflexión de la multicapa y está diseñada para proporcionar la máxima reflectividad solar (R.S también llamada SWIR en inglés) posible en el rango de longitudes de onda de 350-2500 nm para la estructura completa del espejo, teniendo en cuenta las pérdidas ópticas específicas provocadas por la absorción de los materiales que la constituyen, particularmente la capa de metal (3), y las capas de sustrato (2) y protectora (4). La deposición de estas capas puede conseguirse mediante cualquier tipo de técnica de recubrimiento de película delgada tal como deposición por rotación (spin-coating), deposición por inmersión (dip- coating), Langmuir-Blodgett, deposición química en fase de vapor o un método de deposición física en fase de vapor, tal como evaporación o pulverización catódica, y a partir de un amplio rango de precursores. El espesor de cada una de las capas que forman la multicapa está comprendido entre 1 nm y 1 micrómetro. El número de capas en las multicapas puede variar entre 2 y 1000. La estructura de este espejo de múltiples capas que conduce a una alta reflectividad solar (R.S o SWIR) que es máxima para un ángulo de incidencia a elegir, y que es tan constante como sea posible para un amplio rango de direcciones de incidencia alrededor de ese, es la clave de la innovación propuesta en esta invención. (a) Preparation of a multi-layer aperiodic structure (1), in which the layers of high and low refractive index materials of different thickness alternate in an aperiodic manner (ie, not periodically but not chaotically). This multi-layer aperiodic structure (1) is formed on the lower surface of a glass layer (2) that acts as the upper protective layer (4) of the complete mirror structure. It is the result of the alternating deposition of layers of controlled thickness of different materials to be chosen so that an aperiodic spatial modulation of the refractive index is achieved through the multi-layer aperiodic structure (1). This modulation is responsible for the reflection properties of the multilayer and is designed to provide the maximum solar reflectivity (RS also called SWIR in English) possible in the wavelength range of 350-2500 nm for the entire mirror structure, having take into account the specific optical losses caused by the absorption of the materials that constitute it, particularly the metal layer (3), and the substrate (2) and protective layers (4). The deposition of these layers can be achieved by any type of thin film coating technique such as rotation deposition (spin-coating), dip deposition (dip-coating), Langmuir-Blodgett, chemical vapor deposition or a method physical vapor deposition, such as evaporation or sputtering, and from a wide range of precursors. The thickness of each of the layers that form the multilayer is between 1 nm and 1 micrometer. The number of layers in the multilayers can vary between 2 and 1000. The structure of this multi-layer mirror that leads to a high solar reflectivity (RS or SWIR) that is maximum for an angle of incidence to choose, and that is so constant As possible for a wide range of incidence addresses around that, it is the key to the innovation proposed in this invention.
(b) Deposición de una capa metálica (3) de composición de libre elección sobre la estructura aperiódica multicapa (1 ) descrita en la etapa (a). La deposición de esta capa de metal (3) puede conseguirse mediante cualquier tipo de técnica de recubrimiento de película delgada tal como deposición por rotación (spin-coating), deposición por inmersión (dip-coating), Langmuir-Blodgett, deposición química en fase de vapor o una técnica de deposición física en fase de vapor, tal como evaporación o pulverización catódica, y a partir de un amplio rango de precursores. (b) Deposition of a metal layer (3) of free choice composition on the multi-layer aperiodic structure (1) described in step (a). The deposition of this metal layer (3) can be achieved by any type of thin film coating technique such as rotation deposition (spin-coating), dip deposition (dip-coating), Langmuir-Blodgett, chemical vapor deposition or a physical vapor deposition technique, such as evaporation or sputtering, and from a wide range of precursors.
(c) Deposición de una capa protectora (4) de esmalte que protege la capa de metal (3) frente a la corrosión o cualquier tipo de degradación. (c) Deposition of a protective layer (4) of enamel that protects the metal layer (3) against corrosion or any type of degradation.
En una realización alternativa de la presente invención, el procedimiento tiene como objetivo la fabricación de un espejo de primera superficie que comprende las siguientes etapas: (a) Deposición de una capa metálica (3) de composición de libre elección sobre el sustrato (2) de vidrio. La deposición de esta capa metálica (3) puede llevarse a cabo mediante cualquier tipo de técnica de recubrimiento de película delgada tal como deposición por rotación (spin-coating), deposición por inmersión (dip-coating), Langmuir-Blodgett, deposición química en fase de vapor o deposición física en fase de vapor, tal como, evaporación o pulverización catódica, y a partir de un amplio rango de precursores. In an alternative embodiment of the present invention, the process is aimed at manufacturing a first surface mirror comprising the following steps: (a) Deposition of a metal layer (3) of free choice composition on the substrate (2) of glass. The deposition of this metallic layer (3) can be carried out by any type of thin film coating technique such as rotation deposition (spin-coating), dip deposition (dip-coating), Langmuir-Blodgett, chemical deposition in vapor phase or physical deposition in vapor phase, such as evaporation or sputtering, and from a wide range of precursors.
(b) Preparación de una estructura aperiódica multicapa (1 ) en la que se alternan capas de materiales de índices de refracción altos y bajos de diferente espesor de manera aperiódica (es decir, no periódica pero no caótica). La estructura aperiódica multicapa (1 ) según esta realización particular de la invención se forma preferiblemente sobre la superficie libre de la capa de metal (3) depositada en la etapa (a). (b) Preparation of a multi-layer aperiodic structure (1) in which layers of high and low refractive index materials of different thickness alternate in an aperiodic manner (ie, not periodically but not chaotically). The multi-layer aperiodic structure (1) according to this particular embodiment of the invention is preferably formed on the free surface of the metal layer (3) deposited in step (a).
Para conseguir la modulación mencionada anteriormente del índice de refracción, la estructura aperiódica multicapa (1 ) puede estar compuesta por cualquier secuencia de capas de materiales de diferente índice de refracción y espesores, sin limitación alguna impuesta en cuanto al número y el tipo de composiciones de material que va a emplearse, su micro o nanoestructura, o su porosidad. Los espejos descritos en el presente documento pueden usarse para cualquier fin adecuado, incluyendo pero sin limitarse a heliostatos y cualquier tipo de elemento óptico que va a implementarse en una central solar térmica, fotovoltaica, o central combinada solar térmica y fotovoltaica. In order to achieve the aforementioned modulation of the refractive index, the aperiodic multilayer structure (1) may be composed of any sequence of layers of materials of different refractive index and thicknesses, without any limitation imposed as to the number and type of compositions of material to be used, its microstructure or nanostructure, or its porosity. The mirrors described herein can be used for any suitable purpose, including but not limited to heliostats and any type of optical element to be implemented in a thermal, photovoltaic, or combined solar thermal and photovoltaic solar power plant.
- PROCEDIMIENTO DE OPTIMIZACIÓN DEL DISEÑO DEL ESPEJO: - MIRROR DESIGN OPTIMIZATION PROCEDURE:
Se define la reflectividad solar o factor de reflexión de la energía solar, en inglés "solar spectrum weighted integrated reflectance" (SWIR o R.S) como el resultado de integrar, entre el rango de longitudes de onda seleccionado, el producto de cualquier espectro solar objetivo (que puede ser un espectro estándar tal como AMO, AM1 ,0, AM1 ,5... o cualquier otro) y el espectro de reflectancia fí(X) (es decir, la intensidad de luz reflejada dividida entre la intensidad de luz incidente para cada longitud de onda), normalizado por el espectro solar integrado. Todos los ejemplos proporcionados en este documento presentan valores de R.S o SWIR calculados según: 2500 The solar reflectivity or solar energy reflection factor is defined, in English "solar spectrum weighted integrated reflectance" (SWIR or RS) as the result of integrating, between the selected wavelength range, the product of any target solar spectrum (which can be a standard spectrum such as AMO, AM1, 0, AM1, 5 ... or any other) and the reflectance spectrum f (X) (that is, the intensity of reflected light divided by the intensity of incident light for each wavelength), normalized by the integrated solar spectrum. All the examples provided in this document present RS or SWIR values calculated according to: 2500
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Todos los cálculos de propiedades ópticas se han realizado usando el método de la matriz de transferencia en el que se ha tenido en cuenta la propagación de la luz como un vector de onda. Todos los materiales se han modelado usando datos bien establecidos procedentes o bien de bibliografía relacionada o bien estimados a partir de mediciones fiables. El valor de R.S o SWIR, según se define en esta sección, se usa como factor de mérito para encontrar un diseño optimizado. El método de optimización se basa en un algoritmo genético que muestrea una población inicial, por ejemplo una población de 150 individuos (diseños de espejo), y conserva, de cada generación a la siguiente, sólo un porcentaje (por ejemplo del 10%) que muestra un mejor valor de R.S o SWIR. Esto proceso se itera tanto como sea necesario para alcanzar un valor máximo estable, que normalmente tiene lugar tras evaluar 45.000 individuos (300 generaciones) cuando la R.S o SWIR se optimiza para un ángulo de incidencia específico. Cuando la meta es optimizar la R.S o SWIR para un amplio rango simultáneamente (lo que significa que el R.S o SWIR para cada ángulo pudiera no ser óptimo para ese ángulo específico, pero la eficiencia global del reflector es superior cuando se tienen en cuenta todas las direcciones de incidencia), entonces el número de generaciones requeridas para alcanzar una configuración optimizada está cerca de 1000. En cualquier caso, el número máximo de generaciones que se someten a prueba es de 5000, aunque tal valor nunca se alcanzó en los cálculos realizados para encontrar los diseños descritos en el presente documento. En cada individuo, los índices de refracción de las capas de las que está hecho, se consideran valores fijos de entrada, mientras que el espesor puede variar libremente. En general, se consideran un máximo de 30 capas dieléctricas para la estructura aperiódica multicapa (1 ), aparte de la capa de metal (3) y el sustrato (2). Tal restricción se impone para encontrar soluciones que sean realmente viables. Para la mayoría de materiales considerados, los resultados optimizados consideran algunas capas de espesor nulo, lo que indica que el valor superior impuesto no sólo es práctico, sino que está por encima del número necesario para optimizar la estructura en términos absolutos. A continuación se proporciona un diagrama de flujo del proceso de optimización y un sumario de los parámetros de entrada. Se usa una tolerancia de 10 12 como criterio para detener los cálculos. En esta divulgación, "tolerancia" se define como la diferencia entre la R.S. o SWIR obtenida para los diseños optimizados de dos generaciones consecutivas. En la figura 3 del presente documento se muestra una descripción esquemática del proceso de optimización descrito. En los siguientes párrafos, se describen realizaciones preferidas de las técnicas de preparación y caracterización de espejos: - PREPARACIÓN DEL ESPEJO: All calculations of optical properties have been performed using the transfer matrix method in which the propagation of light as a wave vector has been taken into account. All materials have been modeled using well established data from either related literature or estimated from reliable measurements. The RS or SWIR value, as defined in this section, is used as a merit factor to find an optimized design. The optimization method is based on a genetic algorithm that samples an initial population, for example a population of 150 individuals (mirror designs), and retains, from each generation to the next, only a percentage (for example 10%) that It shows a better value of RS or SWIR. This process is iterated as much as necessary to reach a stable maximum value, which normally takes place after evaluating 45,000 individuals (300 generations) when the RS or SWIR is optimized for a specific incidence angle. When the goal is to optimize the RS or SWIR for a wide range simultaneously (which means that the RS or SWIR for each angle may not be optimal for that specific angle, but the overall efficiency of the reflector is higher when all the dimensions are taken into account directions of incidence), then the number of generations required to achieve an optimized configuration is close to 1000. In any case, the maximum number of generations under test is 5000, although such value was never reached in the calculations made for Find the designs described in this document. In each individual, the refractive indexes of the layers from which it is made are considered fixed input values, while the thickness can vary freely. In general, a maximum of 30 dielectric layers are considered for the multi-layer aperiodic structure (1), apart from the metal layer (3) and the substrate (2). Such restriction is imposed to find solutions that are really viable. For most of the materials considered, the optimized results consider some layers of null thickness, which indicates that the higher value imposed is not only practical, but is above the number needed to optimize the structure in absolute terms. A flowchart of the optimization process and a summary of the input parameters are provided below. A tolerance of 10 12 is used as a criterion to stop the calculations. In this disclosure, "tolerance" is defined as the difference between the RS or SWIR obtained for the optimized designs of two consecutive generations. A schematic description of the optimization process described is shown in Figure 3 of this document. In the following paragraphs, preferred embodiments of mirror preparation and characterization techniques are described: - MIRROR PREPARATION:
Aunque existe una amplia variedad de métodos que pueden usarse para fabricar los espejos propuestos en el presente documento, tal como se indica en las reivindicaciones y entiende un experto en la técnica con conocimientos medios, se proporcionan detalles de dos de los mismos como ejemplos no limitativos de realizaciones de la invención: Although there is a wide variety of methods that can be used to make the mirrors proposed herein, as indicated in the claims and understood by one of ordinary skill in the art, details of two of them are provided as non-limiting examples. of embodiments of the invention:
Sol-Gel: De entre las diversas rutas de procesamiento de líquido, el método sol-gel proporciona una opción versátil y de bajo coste para preparar óxidos metálicos con diferentes microestructuras y estados de agregación. Además, los métodos sol-gel pueden combinarse con técnicas de deposición de líquido para obtener películas con estructuras estables y libres de grietas. Se preparó la estructura aperiódica multicapa (1 ) usando dispersiones de capa de S1O2 y T1O2 obtenidas mediante técnica sol-gel. Se obtuvo una dispersión de S1O2 mezclando tetraetóxido de silicio en una disolución etanólica de ácido clorhídrico, mientras que se preparó una dispersión de T1O2 a partir de una disolución de ácido nítrico en isopropanol, a la que se añadió lentamente tetraisopropóxido de titanio. Se depositaron ambas dispersiones sobre una capa de sustratro (2) de vidrio usando un dispositivo de recubrimiento por rotación (Laurell WS-400E-6NPP), en el que pueden determinarse de manera precisa tanto la rampa de aceleración como la velocidad de rotación final. Se centrifugaron las muestras durante 1 minuto y después se trataron a una temperatura de entre 300SC y 550SC en una placa de calentamiento durante un intervalo de entre 10 y 300 segundos. Tras el enfriamiento en una capa metálica (3), se repite el procedimiento de recubrimiento tantas veces como sea necesario para obtener la estructura aperiódica multicapa (1 ) deseada. Se realizó el mismo proceso mediante recubrimiento por inmersión (ND-RDC, Nadetech Innovation) sumergiendo los sustratos en las mismas dispersiones de óxido de metal. Ambos procesos dan como resultado una estructura aperiódica multicapa (1 ) densa. Sol-Gel: Among the various liquid processing routes, the sol-gel method provides a versatile and low-cost option for preparing metal oxides with different microstructures and aggregation states. In addition, sol-gel methods can be combined with liquid deposition techniques to obtain films with stable and crack-free structures. The multi-layer aperiodic structure (1) was prepared using S1O2 and T1O2 layer dispersions obtained by sol-gel technique. A dispersion of S1O2 was obtained by mixing silicon tetraethoxide in an ethanolic solution of hydrochloric acid, while a dispersion of T1O2 was prepared from a solution of nitric acid in isopropanol, to which titanium tetraisopropoxide was slowly added. Both dispersions were deposited on a glass substrate layer (2) using a rotation coating device (Laurell WS-400E-6NPP), in which both the acceleration ramp and the final rotation speed can be precisely determined. Samples were centrifuged for 1 minute and then treated at a temperature between 300 S C and 550 S C on a heating plate for a range of 10 to 300 seconds. After cooling in a metal layer (3), the coating procedure is repeated as many times as necessary to obtain the desired multi-layer aperiodic structure (1). The same process was carried out by immersion coating (ND-RDC, Nadetech Innovation) by submerging the substrates in the same metal oxide dispersions. Both processes result in a dense multi-layer aperiodic structure (1).
Deposición física en fase de vapor: Este método implica la deposición de la capa metálica (3) y las láminas de óxidos metálicos para la estructura aperiódica multicapa (1 ). El metal es depositado mediante una técnica de evaporación térmica o mediante pulverización catódica. Ambos métodos de deposición implican una cámara de alto vacío (Leica EM SCD500) equipada con una balanza de cuarzo (Leica EM QSG100) que monitoriza el espesor depositado. Se evaporó el metal (conformado como alambre) a través de una resistencia de tungsteno polarizada a 4 V y con una corriente aplicada de 30 mA. Se realizó la pulverización catódica de metal usando un blanco específico polarizado a alta tensión a una presión de argón de entre 5x10-3 y 1 x1 0-2 mbar. Physical vapor deposition: This method involves the deposition of the metal layer (3) and the metal oxide sheets for the multi-layer aperiodic structure (1). The metal is deposited by a thermal evaporation technique or by sputtering. Both deposition methods involve a high vacuum chamber (Leica EM SCD500) equipped with a quartz scale (Leica EM QSG100) that monitors the deposited thickness. The metal (formed as wire) was evaporated through a tungsten resistance polarized at 4 V and with an applied current of 30 mA. Metal sputtering was performed using a specific target polarized at high voltage at an argon pressure between 5x10 -3 and 1 x1 0 -2 mbar.
- CARACTERIZACIÓN ESTRUCTURAL: - STRUCTURAL CHARACTERIZATION:
Caracterización de los espejos: Se tomaron imágenes por microscopía electrónica de barrido por emisión de campo (FESEM) de las capas depositadas sobre silicio usando un microscopio Hitachi 5200 funcionando a 5 kV. Se sumergieron muestras en nitrógeno líquido antes de ser cortadas para analizar la sección transversal. Mirror characterization: Images were taken by field emission scanning electron microscopy (FESEM) of the layers deposited on silicon using a Hitachi microscope 5200 running at 5 kV. Samples were immersed in liquid nitrogen before being cut to analyze the cross section.
Mediciones de reflectancia óptica: Se obtuvieron espectros de reflectancia especular de incidencia normal usando un espectrofotómetro de barrido en el UV visible (SHIMADZU UV-2101 PC) unido a una esfera de integración y un espectrofotómetro de transformada de Fourier (BRUKER) acoplado a un microscopio que funciona en el rango de longitud de onda de 450 nm-2500 nm Optical reflectance measurements: Normal incidence specular reflectance spectra were obtained using a visible UV scan spectrophotometer (SHIMADZU UV-2101 PC) attached to an integration sphere and a Fourier transform spectrophotometer (BRUKER) coupled to a microscope which works in the wavelength range of 450 nm-2500 nm
EJEMPLOS DE REALIZACIONES DE LA INVENCIÓN EXAMPLES OF EMBODIMENTS OF THE INVENTION
EJEMPLO 1 : En una primera realización de la invención descrita en el presente documento, se presenta en este caso un diseño optimizado de un espejo de primera cara o de primera superficie que maximiza la R.S o SWIR para un amplio rango de ángulos de incidencia de la luz simultáneamente, suponiendo en este caso valores de índice de refracción estándar de las fases densas de los materiales empleados (S1O2 y T1O2). La dependencia espectral del índice de refracción y el coeficiente de absorción supuestos para estos cálculos se presentan en la figura 4. Tal espejo está hecho de una secuencia de capas cuya composición y espesor se enumera en la tabla 1 del presente documento. Este diseño calculado se consiguió en la generación 1001 . La figura 5 visualiza su reflectancia calculada a incidencia normal. Los valores de R.S o SWIR para diferentes ángulos de incidencia se enumeran en la tabla 2 del presente documento y se representan gráficamente en la figura 6, en la que puede observarse la R.S o SWIR casi constante entre ángulos de incidencia de 0s y 40s, que es una de las propiedades novedosas más relevantes de las estructuras (1 ) multicapa descritas en el presente documento. EJEMPLO 2: En una segunda realización de la invención descrita en el presente documento, se presenta en este caso un diseño optimizado de un espejo de primera cara o de primera superficie que maximiza la R.S o SWIR para un amplio rango de ángulos de incidencia de la luz simultáneamente, suponiendo en este caso un contraste de índice de refracción muy grande pero realista entre los dos tipos de capas consideradas (S1O2 poroso y T1O2 denso). La dependencia espectral del índice de refracción y el coeficiente de absorción supuestos para estos cálculos se presentan en la figura 7. Tal espejo está hecho de una secuencia de capas cuya composición y espesor se enumeran en la tabla 3 del presente documento. Este diseño calculado se consiguió en la generación 1001 . La figura 8 visualiza su reflectancia calculada a incidencia normal. Los valores de R.S o SWIR para diferentes ángulos de incidencia se enumeran en la tabla 4 y se representan gráficamente en la figura 9, en la que puede observarse la reflectancia optimizada a un ángulo de incidencia de luz incidente a 25s, así como la R.S o SWIR casi constante entre ángulos de incidencia de 0s y 40s, que es una de las propiedades novedosas más relevantes de las estructuras multicapa descritas en el presente documento. EXAMPLE 1: In a first embodiment of the invention described herein, an optimized design of a first-face or first-surface mirror that maximizes the RS or SWIR is presented in this case for a wide range of angles of incidence of the light simultaneously, in this case assuming standard refractive index values of the dense phases of the materials used (S1O2 and T1O2). The spectral dependence of the refractive index and the assumed absorption coefficient for these calculations are presented in Figure 4. Such a mirror is made of a sequence of layers whose composition and thickness are listed in Table 1 of this document. This calculated design was achieved in the 1001 generation. Figure 5 visualizes its reflectance calculated at normal incidence. The RS or SWIR values for different angles of incidence are listed in Table 2 of this document and are plotted in Figure 6, in which the almost constant RS or SWIR can be observed between incidence angles of 0 s and 40 s , which is one of the most relevant novel properties of the multilayer structures (1) described herein. EXAMPLE 2: In a second embodiment of the invention described herein, an optimized design of a first-face or first-surface mirror that maximizes the RS or SWIR is presented in this case for a wide range of angles of incidence of the light simultaneously, assuming in this case a very large but realistic refractive index contrast between the two types of layers considered (porous S1O2 and dense T1O2). The spectral dependence of the refractive index and the assumed absorption coefficient for these calculations are presented in Figure 7. Such a mirror is made of a sequence of layers whose composition and thickness are listed in Table 3 of this document. This calculated design was achieved in the 1001 generation. Figure 8 visualizes its reflectance calculated at normal incidence. The RS or SWIR values for different angles of incidence are listed in Table 4 and plotted in Figure 9, in which the optimized reflectance can be observed at an incident angle of incident light at 25 s , as well as the RS o SWIR almost constant between angles of incidence of 0 s and 40 s , which is one of the most relevant novel properties of the multilayer structures described herein.
EJEMPLO 3: En una tercera realización de la invención se describe cómo preparar un espejo de segunda cara de alta reflectlvldad solar usando el método sol-gel para depositar una estructura aperiódica multicapa (1 ) combinada con un proceso de evaporación para depositar una capa de metal (3) de cobre. El diseño seguido, obtenido a partir de los cálculos de optimización descritos en párrafos anteriores, se proporciona en la tabla 5 del presente documento, y se consiguió tras 162 generaciones. Se emplearon dos suspensiones de precursor diferentes para crear películas delgadas de óxido de silicio y óxido de titanio mediante deposición por rotación. Para el primero, se usaron tetraetóxido de silicio (0,50 M), ácido clorhídrico (10-3 M), agua (2,37 M) y etanol (14,44 M), mientras que para el último, se usó tetraisopropóxido de titanio (0,30 M), ácido nítrico (5,60- 10" 3 M), agua (0,1 6 M) e isopropanol (1 1 ,78 M). La deposición alternada mediante deposición por rotación (spin-coating), seguida por estabilización térmica a 600SC durante 1 0 segundos de cada tipo de capa, proporcionó una estructura aperiódica multicapa (1 ) estable que presentó una fuerte reflectancia a aquellas frecuencias a las que el cobre, el metal a elegir seleccionado para esta realización, absorbe fuertemente. Tras ello se depositó una capa metálica (3) de cobre de 100 nm sobre la estructura aperiódica multicapa (1 ) para conseguir un reflector de alta intensidad para todo el espectro solar. En la figura 10, se muestran una típica imagen de electrones secundarios (izquierda) e imagen de electrones retrodispersados (derecha) de una sección transversal de la estructura multicapa, según se observó en el microscopio electrónico de barrido funcionando a 5 kV. En este caso, pueden observarse 20 capas. Tal espejo está hecho de una secuencia de capas cuya composición y espesor se enumera en la tabla 5 del presente documento. La capa (3) de cobre se observa como una capa brillante más gruesa en la parte superior. En la figura 1 1 , se visualiza la reflectancia del espejo para el rango de longitud de onda objetivo tanto para la realización de multicapa calculada como para la experimental, que muestran una concordancia muy buena en todo el rango espectral. La dependencia angular de la R.S o SWIR se presenta en la figura 12 y los datos correspondientes se visualizan en la tabla 6. EXAMPLE 3: In a third embodiment of the invention it is described how to prepare a mirror of second face of high solar reflectivity using the sol-gel method to deposit a multi-layer aperiodic structure (1) combined with an evaporation process to deposit a metal layer (3) of copper. The design followed, obtained from the optimization calculations described in previous paragraphs, is provided in Table 5 of this document, and was achieved after 162 generations. Two different precursor suspensions were used to create thin films of silicon oxide and titanium oxide by rotational deposition. For the first, silicon tetraethoxide (0.50 M), hydrochloric acid (10 -3 M), water (2.37 M) and ethanol (14.44 M) were used, while for the latter, tetraisopropoxide was used of titanium (0.30 M), nitric acid (5.60-10 " 3 M), water (0.1 6 M) and isopropanol (1,178 M). Alternate deposition by rotational deposition (spin- coating), followed by thermal stabilization at 600 S C for 10 seconds of each type of layer, provided a stable multi-layer aperiodic structure (1) that showed a strong reflectance at those frequencies at which copper, the metal of choice selected for This embodiment is strongly absorbed, after which a metallic layer (3) of 100 nm copper was deposited on the multi-layer aperiodic structure (1) to achieve a high intensity reflector for the entire solar spectrum. typical secondary electron image (left) and backscattered electron image (right) of a se Transverse ction of the multilayer structure, as observed in the scanning electron microscope operating at 5 kV. In this case, 20 layers can be observed. Such a mirror is made of a sequence of layers whose composition and thickness are listed in Table 5 of this document. The copper layer (3) is seen as a thicker shiny layer at the top. In Figure 1 1, the reflectance of the mirror for the target wavelength range is displayed for both the calculated and experimental multilayer realization, which show a very good concordance throughout the spectral range. The angular dependence of the RS or SWIR is presented in Figure 12 and the corresponding data is displayed in Table 6.
EJEMPLO 4: En una cuarta realización de la invención, se describe cómo preparar un espejo de primera cara de alta reflectividad solar usando sólo un método de deposición física para construir una estructura aperiódica multicapa (1 ). Tal espejo está hecho de una secuencia de capas cuya composición y espesor se enumeran en la tabla 7 del presente documento. Este diseño calculado se consiguió en la generación 1001 . Encima del sustrato se depositó una capa (3) de cobre mediante pulverización catódica. Se emplearon dos blancos diferentes para crear películas delgadas de óxido de silicio y óxido de titanio mediante pulverización catódica. En la figura 13, se visualiza la reflectancia del espejo para el rango de longitud de onda objetivo tanto para la realización de multicapa calculada como para la experimental, que muestran una concordancia muy buena por todo el rango espectral. Presenta una reflectividad solar del 94,3% y demuestra que la realización de los diseños de espejo según la invención es absolutamente viable. Los valores de R.S o SWIR para diferentes ángulos de incidencia se enumeran en la tabla 8 y se representan gráficamente en la figura 14. A lo largo de los ejemplos 1 -4 descritos anteriormente y las correspondientes tablas 1 , 3, 5 y 7 del presente documento, se proporcionan todas las distribuciones de espesor para la estructura aperiódica multicapa (1 ), la capa de vidrio de sustrato (2) y la capa de metal (3) como valores medios de referencia. Sin embargo, también se ha encontrado que variaciones de dichos valores dentro de ±20% en cada capa proporcionan las propiedades deseadas de alta reflexión fuera de las bandas de absorción de espectro solar terrestre, y valores de R.S o SWIR estables con respecto a la dirección de incidencia de la luz. EXAMPLE 4: In a fourth embodiment of the invention, it is described how to prepare a first-face mirror of high solar reflectivity using only a physical deposition method to construct a multi-layer aperiodic structure (1). Such a mirror is made of a sequence of layers whose composition and thickness are listed in Table 7 of this document. This calculated design was achieved in the 1001 generation. A layer (3) of copper was deposited on top of the substrate by sputtering. Two different targets were used to create thin films of silicon oxide and titanium oxide by sputtering. In Figure 13, the reflectance of the mirror for the target wavelength range is displayed for both the calculated and experimental multilayer realization, which show a very good concordance throughout the spectral range. It has a 94.3% solar reflectivity and demonstrates that the realization of the mirror designs according to the invention is absolutely viable. The RS or SWIR values for different angles of incidence are listed in Table 8 and plotted in Figure 14. Throughout Examples 1-4 described above and the corresponding Tables 1, 3, 5 and 7 of the This document provides all thickness distributions for the multi-layer aperiodic structure (1), the substrate glass layer (2) and the metal layer (3) as average reference values. However, it has also been found that variations of said values within ± 20% in each layer provide the desired properties of high reflection outside the terrestrial solar spectrum absorption bands, and stable RS or SWIR values with respect to the direction of incidence of light.
TABLAS BOARDS
Figure imgf000016_0001
29 150 Cu
Figure imgf000016_0001
29 150 Cu
30 1 ,6-106 Vidrio 30 1, 6-10 6 Glass
Tabla 1  Table 1
Figure imgf000017_0001
Figure imgf000017_0001
Tabla 2  Table 2
Figure imgf000017_0002
1 1 57 T¡02
Figure imgf000017_0002
1 1 57 T. 02
12 95 S¡0212 95 S02
13 87 T¡0213 87 Q02
14 77 S¡0214 77 S02
15 97 T¡0215 97 Q02
16 63 S¡0216 63 S02
17 103 T¡0217 103 Q2
18 81 S¡0218 81 S02
19 78 T¡0219 78 Q02
20 148 S¡0220 148 S02
21 224 T¡0221 224 T. 02
22 78 S¡0222 78 S02
23 126 T¡0223 126 Q2
24 86 S¡0224 86 S¡02
25 241 T¡0225 241 T. 02
26 1 17 S¡0226 1 17 S¡02
27 152 T¡0227 152 Q2
28 125 S¡0228 125 S02
29 150 Cu29 150 Cu
30 1 ,6-106 Vidrio 30 1, 6-10 6 Glass
Tabla 3 Table 3
Figure imgf000018_0001
70 0,9766
Figure imgf000018_0001
70 0.9766
75 0,975575 0.9755
80 0,974980 0.9749
85 0,9752 85 0.9752
Tabla 4 Table 4
Figure imgf000019_0001
Figure imgf000019_0001
Tabla 5 Table 5
Figure imgf000019_0002
60 0,901
Figure imgf000019_0002
60 0.901
65 0,89765 0.897
70 0,89670 0.896
75 0,89475 0.894
80 0,89480 0.894
85 0,91 0 85 0.91 0
Tabla 6 Table 6
Figure imgf000020_0001
29 150 Cu
Figure imgf000020_0001
29 150 Cu
30 1 ,6-106 Vidrio 30 1, 6-10 6 Glass
Tabla 7  Table 7
Figure imgf000021_0001
Figure imgf000021_0001
Tabla 8  Table 8

Claims

REIVINDICACIONES
Espejo para aplicaciones de energía solar que comprende: Mirror for solar energy applications comprising:
- una capa de metal (3) que presenta una reflexión de al menos un primer rango de longitudes de onda comprendidas dentro del espectro de irradiancia solar y una absorción de al menos un segundo rango de longitudes de onda comprendidas en dicho espectro;  - a metal layer (3) having a reflection of at least a first range of wavelengths comprised within the solar irradiance spectrum and an absorption of at least a second range of wavelengths comprised in said spectrum;
- una estructura aperiódica multicapa (1 ) adyacente a la capa de metal (3), que comprende una pluralidad de capas de diferentes índices de refracción y espesores, que presenta una reflexión dentro del segundo rango de longitudes de onda en el que la capa de metal (3) adyacente presenta absorción ;  - a multi-layer aperiodic structure (1) adjacent to the metal layer (3), comprising a plurality of layers of different refractive indices and thicknesses, which has a reflection within the second range of wavelengths in which the layer of adjacent metal (3) has absorption;
caracterizado por que la distribución de capas en la estructura aperiódica multicapa (1 ) está dispuesta de manera que los rangos de longitud de onda con reflexión mínima en dicha estructura aperiódica multicapa (1 ) corresponden a rangos de longitud de onda con absorción máxima en el espectro solar terrestre.  characterized in that the distribution of layers in the multi-layer aperiodic structure (1) is arranged such that the wavelength ranges with minimal reflection in said multi-layer aperiodic structure (1) correspond to wavelength ranges with maximum absorption in the spectrum land solar.
Espejo según la reivindicación anterior, que comprende además una capa de sustrato (2) y/o una capa protectora (4) aplicada a la capa de metal (3). Mirror according to the preceding claim, further comprising a substrate layer (2) and / or a protective layer (4) applied to the metal layer (3).
Espejo según cualquiera de las reivindicaciones anteriores, en el que el espesor de las capas que forman la estructura aperiódica multicapa (1 ) está comprendido entre 1 nm y 1 μιτι. Mirror according to any of the preceding claims, wherein the thickness of the layers that form the multi-layer aperiodic structure (1) is between 1 nm and 1 μιτι.
Espejo según la reivindicación anterior, en el que el grosor de las capas que forman la estructura aperiódica multicapa (1 ) está comprendido entre 10 nm y 400 nm. Mirror according to the preceding claim, wherein the thickness of the layers that form the multi-layer aperiodic structure (1) is between 10 nm and 400 nm.
Espejo según cualquiera de las reivindicaciones anteriores, en el que el número de capas en la estructura aperiódica multicapa (1 ) está entre 2 y 1000. Mirror according to any of the preceding claims, wherein the number of layers in the multi-layer aperiodic structure (1) is between 2 and 1000.
Espejo según la reivindicación anterior, en el que el número de capas en la estructura aperiódica multicapa (1 ) está entre 4 y 200. Mirror according to the preceding claim, wherein the number of layers in the multi-layer aperiodic structure (1) is between 4 and 200.
Espejo según cualquiera de las reivindicaciones anteriores, en el que la estructura aperiódica multicapa (1 ) está formada por una secuencia alternada de dos materiales de diferente índice de refracción. Mirror according to any of the preceding claims, wherein the multi-layer aperiodic structure (1) is formed by an alternating sequence of two materials of different refractive index.
Espejo según la reivindicación anterior, en el que la estructura aperiódica multicapa (1 ) está formada por capas alternadas de óxido de silicio y óxido de titanio o cualquier compuesto derivado de los mismos. Espejo según cualquiera de las reivindicaciones anteriores, en el que la capa de metal (3) comprende uno o más de los siguientes materiales: cobre, aluminio, cromo, hierro, titanio, níquel, cobalto, paladio, rodio, plata, oro, platino, o cualquier aleación de los mismos. Mirror according to the preceding claim, wherein the multi-layer aperiodic structure (1) is formed by alternating layers of silicon oxide and titanium oxide or any compound derived therefrom. Mirror according to any of the preceding claims, wherein the metal layer (3) comprises one or more of the following materials: copper, aluminum, chromium, iron, titanium, nickel, cobalt, palladium, rhodium, silver, gold, platinum , or any alloy thereof.
Espejo según cualquiera de las reivindicaciones anteriores, en el que la estructura aperiódica multicapa (1 ) y la capa de metal (3) están dispuestas para formar un espejo de primera cara. Mirror according to any of the preceding claims, wherein the multi-layer aperiodic structure (1) and the metal layer (3) are arranged to form a first-sided mirror.
Espejo según cualquiera de las reivindicaciones 1 -9, en el que la estructura aperiódica multicapa (1 ) y la capa de metal (3) están dispuestas para formar un espejo de segunda cara. Mirror according to any of claims 1-9, wherein the multi-layer aperiodic structure (1) and the metal layer (3) are arranged to form a second-sided mirror.
Espejo según cualquiera de las reivindicaciones anteriores, en el que las capas de menor índice de refracción dentro de la estructura aperiódica multicapa (1 ) presentan un valor de porosidad comprendido entre el 10% y el 95% y las capas de mayor índice de refracción presentan un valor de porosidad comprendido entre el 0% y el 10%. Mirror according to any of the preceding claims, wherein the layers with the lowest refractive index within the multi-layer aperiodic structure (1) have a porosity value between 10% and 95% and the layers with the highest refractive index have a porosity value between 0% and 10%.
Espejo según la reivindicación 2, en el que la estructura aperiódica multicapa (1 ) , la capa de sustrato (2) y la capa de metal (3) comprenden la siguiente composición de materiales con un valor medio de espesor, en el que el grosor de cada capa está comprendido entre ±20% de dicho valor medio: Mirror according to claim 2, wherein the multi-layer aperiodic structure (1), the substrate layer (2) and the metal layer (3) comprise the following composition of materials with an average thickness value, in which the thickness of each layer is between ± 20% of said average value:
Figure imgf000023_0001
16 63 SI02
Figure imgf000023_0001
16 63 SI02
17 1 1 1 T¡02  17 1 1 1 T. 02
18 80 SI02  18 80 SI02
19 72 T¡02  19 72 Q02
20 106 SI02  20 106 SI02
21 225 T¡02  21 225 T. 02
22 78 SI02  22 78 SI02
23 129 T¡02  23 129 Q02
24 87 SI02  24 87 SI02
25 241 T¡02  25 241 T. 02
26 95 SI02  26 95 SI02
27 149 T¡02  27 149 Q2
28 123 SI02  28 123 SI02
29 (metal) 150 Cu  29 (metal) 150 Cu
30 (sustrato) ,6- 06 Vidrio 30 (substrate), 6- 0 6 Glass
Espejo según la reivindicación 2, en el que la estructura aperiódica multicapa (1 ) , la capa de sustrato (2) y la capa de metal (3) comprenden la siguiente composición de materiales y valor medio de espesor, en el que el espesor de cada capa está comprendido entre ±20% de dicho valor medio: Mirror according to claim 2, wherein the multi-layer aperiodic structure (1), the substrate layer (2) and the metal layer (3) comprise the following material composition and average thickness value, in which the thickness of each layer is between ± 20% of said average value:
Figure imgf000024_0001
16 63 SI02
Figure imgf000024_0001
16 63 SI02
17 103 T¡02  17 103 Q2
18 81 SI02  18 81 SI02
19 78 T¡02  19 78 Q02
20 148 SI02  20 148 SI02
21 224 T¡02  21 224 T. 02
22 78 SI02  22 78 SI02
23 126 T¡02  23 126 Q2
24 86 SI02  24 86 SI02
25 241 T¡02  25 241 T. 02
26 1 17 SI02  26 1 17 SI02
27 152 T¡02  27 152 Q2
28 125 SI02  28 125 SI02
29 (metal) 150 Cu  29 (metal) 150 Cu
30 (sustrato) ,6- 06 Vidrio 30 (substrate), 6- 0 6 Glass
Espejo según la reivindicación 2, en el que la estructura aperiódica multicapa (1 ) , la capa de sustrato (2) y la capa de metal (3) comprenden la siguiente composición de materiales y valor medio de espesor, en el que el espesor de cada capa está comprendido entre ±20% de dicho valor medio: Mirror according to claim 2, wherein the multi-layer aperiodic structure (1), the substrate layer (2) and the metal layer (3) comprise the following material composition and average thickness value, in which the thickness of each layer is between ± 20% of said average value:
Figure imgf000025_0001
Figure imgf000025_0001
16. Espejo según la reivindicación 2, en el que la estructura aperiódica multicapa (1 ) , la capa de sustrato (2) y la capa de metal (3) comprenden la siguiente composición de materiales y valor medio de espesor, en el que el espesor de cada capa está comprendido entre ±20% de dicho valor medio: 16. Mirror according to claim 2, wherein the multi-layer aperiodic structure (1), the substrate layer (2) and the metal layer (3) comprise the following material composition and average thickness value, in which the thickness of each layer is between ± 20% of said average value:
Figure imgf000026_0001
Figure imgf000026_0001
Método para fabricar un espejo para aplicaciones de energía solar, que comprende las etapas de: Method for manufacturing a mirror for solar energy applications, comprising the steps of:
deposición de una capa de metal (3), que presenta una reflexión de al menos un primer rango de longitudes de onda comprendidas dentro del espectro de irradiancia solar y una absorción de al menos un segundo rango de longitudes de onda comprendidas en dicho espectro; y una estructura aperiódica multicapa (1 ) adyacente a la capa de metal (3), en el que dicha estructura aperiódica multicapa (1 ) comprende una pluralidad de capas de diferentes índices de refracción y espesores, que presenta una reflexión dentro del segundo rango de longitudes de onda en el que la capa de metal (3) adyacente presenta absorción; y caracterizado por que las capas en la estructura aperiódica multicapa (1 ) se depositan de manera que se hace que los rangos de longitud de onda con una reflexión mínima en dicha estructura aperiódica multicapa (1 ) correspondan con rangos de longitud de onda con una absorción máxima en el espectro solar terrestre. deposition of a metal layer (3), which has a reflection of at least a first range of wavelengths within the solar irradiance spectrum and an absorption of at least a second range of wavelengths comprised in said spectrum; and a multi-layer aperiodic structure (1) adjacent to the metal layer (3), wherein said multi-layer aperiodic structure (1) comprises a plurality of layers of different refractive indices and thicknesses, which has a reflection within the second range of wavelengths in which the adjacent metal layer (3) exhibits absorption; and characterized in that the layers in the multi-layer aperiodic structure (1) are deposited so that the wavelength ranges with minimal reflection in said multi-layer aperiodic structure (1) are made to correspond with wavelength ranges with an absorption maximum in the solar solar spectrum.
18. Método según la reivindicación anterior, en el que la estructura aperiódica multicapa (1 ) o la capa de metal (3) se deposita sobre un sustrato (2). 18. Method according to the preceding claim, wherein the multi-layer aperiodic structure (1) or the metal layer (3) is deposited on a substrate (2).
19. Método según la reivindicación anterior, que comprende además depositar una capa protectora (4) sobre la capa de metal (3). 19. A method according to the preceding claim, further comprising depositing a protective layer (4) on the metal layer (3).
20. Método según cualquiera de las reivindicaciones 17-19, en el que la técnica empleada para depositar las capas que forman la estructura aperiódica multicapa (1 ) o depositar la capa de metal (3) comprende uno o más de la siguiente lista: recubrimiento por rotación (spin-coating), recubrimiento por inmersión (dip-coating), Langmuir-Blodgett, técnicas de deposición química en fase de vapor o una técnica de deposición física en fase de vapor como evaporación térmica o pulverización catódica. 20. The method according to any of claims 17-19, wherein the technique used to deposit the layers that form the multi-layer aperiodic structure (1) or deposit the metal layer (3) comprises one or more of the following list: coating by rotation (spin-coating), dip coating (dip-coating), Langmuir-Blodgett, chemical vapor deposition techniques or a physical vapor deposition technique such as thermal evaporation or sputtering.
21 Método según cualquiera de las reivindicaciones 17-20, en el que la disposición de capas en la estructura aperiódica multicapa (1 ) se ajusta de manera que su reflectividad solar se maximiza a un rango predeterminado de ángulos de incidencia de la luz. Method according to any of claims 17-20, wherein the arrangement of layers in the multi-layer aperiodic structure (1) is adjusted so that its solar reflectivity is maximized to a predetermined range of angles of incidence of light.
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CN108613423A (en) * 2016-12-02 2018-10-02 北京有色金属研究总院 A kind of high temperature selective solar spectrum absorbing membrane and preparation method thereof

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