ES2563645A1 - Modular solar concentration system without monitoring by combining conventional optics and holographic optical elements (HOE¿s) (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Modular system of solar concentration without tracking through the combination of conventional optics and holographic optical elements (hoe's). A concentration-free solar panel is shown capable of capturing the summer and winter radiation, throughout the day, by combining a holographic optical element (7) and a conventional optic (8). The holographic optical element performs the passive tracking of solar radiation and sends it in a defined direction. Both optics are placed on a base (9), held by a fixed structure (10). The optical part described can be independent of the generation part. The latter is composed of a structure (11), a radiation receiver (6), and an active or passive heat sink (12). Said coupling between optics and generation may be by reflection or by transmission of sunlight. The concentration is customizable and can vary from 10x. (Machine-translation by Google Translate, not legally binding)

Description

MODULAR SOLAR CONCENTRATION SYSTEM WITHOUT FOLLOW-UP THROUGH THE COMBINATION OF CONVENTIONAL OPTICS AND HOLOGRAPHIC OPTICAL ELEMENTS (HOE’s)

Technical sector

The invention is part of the technical sector of renewable energy, more specifically in relation to both thermal and thermoelectric solar energy, as well as photovoltaic solar.

State of the art

The solar thermal installations mostly commercially available today are of four types, which differ in the optics used to concentrate the light in a pipe through which heat transfer fluid circulates. Parabolic trough systems consist of parabolic mirrors that concentrate on a line located in the focus of the parabola; Fresnel-type solar concentrators use several flat or almost flat mirror surfaces with different orientation from each other, simulating the different faces of a cylindrical Fresnel lens, which concentrate on a line in the focus of the lens; Torre's solar concentrators consist of a multitude of flat or almost flat mirrors, located in concentric circles, which concentrate the light on top of a tower, where the spotlight of for example a spherical Fresnel lens would be located; Finally, Stirling motor systems use spherical pseudo mirrors that concentrate the light in the corresponding focus. They all have a considerable size, are not modular to smaller sizes, and also, for such infrastructures, they need to track the sun on at least one axis, which increases installation and maintenance costs.

It is therefore convenient, in this sector, to develop a product that can be modulated in size and, ideally, without active monitoring.

As for photovoltaic solar modules, the most common in the market are flat, with a front glass, an aluminum frame and virtually the entire surface covered with photovoltaic solar cells. Given that solar cells represent by far the most important part of the cost, there has been an effort for decades to reduce their surface area, replacing it with concentrating elements that are theoretically cheaper to achieve all the light received on them. However, so far the concentration photovoltaic solar systems, of many different types, have not achieved a significant market entry. The main reasons are the price, as well as the major complication of the final structure of the complete system, which requires sun tracking. This adds complexity and cost to these systems.

Holography, as an optical technology, has many advantages over other optical concentrating systems (lenses or mirrors, for example): it is much more versatile and cheaper than them. Used in low or medium concentration, it also eliminates the need for sun tracking, which reduces the complexity of the system.

There have previously been attempts to use holography on solar panels. For example, US4863224, granted to Afian et al., Uses a hologram and a prism or plate. However, this solar concentrator must be aligned with the sun, and has no passive tracking capability. Another invention that also has this disadvantage is US5268985, issued to Ando et al. It comprises a hologram and a total reflection surface, but, in addition to needing monitoring, it is constructed to capture monochromatic light and wastes most of the solar spectrum. Patents US5877874 and US6274860, granted to Rosenberg, present a flat holographic concentrator in which at least one multiplexed holographic film, which achieves high angular and spectral bandwidths, concentrates the light in solar cells placed in the same plane. This invention has the disadvantage of having many optical losses, and the need to use bifacial cells, as well as placing the entire solar system in a flat place with the floor painted white to reflect the albedo. US20080257400, granted to Mignon and Han, also presents a flat holographic concentrator but with two different surfaces, in which there are multiplexed transmission and reflection holograms, with solar cells perpendicular to said collecting surfaces. The great disadvantage of this design, in addition to the losses due to the various reflections and transmissions in the various holograms, is the constructive difficulty, which can take it away from manufacturing at competitive costs. US20120125403, granted to Orlandi, proposes to apply holographic films directly on conventional photovoltaic modules, so that any incident from different angles is used as perpendicular radiation to the plane of the module. This concept, although very marketable due to the limited interference with the original design, does not reduce the manufacturing cost of the current modules.

Many other authors have joined conventional optics and diffractive optics, as proposed herein. However, its intention has not been to take advantage of the entire spectrum to concentrate it on a single device, as the present invention does, but to divide the spectrum and direct each of said divisions to different devices, each selective to the spectral region that arrives Each of these regions, moreover, is usually of narrow angular and spectral bandwidths. Although the concept of separating the spectrum can be useful for specific applications, applying it to a large solar installation increases the number of parts and the complication of the system. This assumes that it is difficult to lower system costs. A concentration without spectral separation, like the one proposed here, only needs a radiation collector and a single angular and spectral design, although it also needs to collect very wide spectral and angular bandwidths.

Examples of patents using conventional and diffractive combination of optics for spectral separation are: US patent 2009/0114266 A1, of Biles and Halter; WO2014036406 A1, by Escarra et al .; US 2010/0212717 A1, by Whitlock et al .; US

6,469,241 B1, of Penn; US 2010/0032005 A1, of Ford and Karp; US 6,015,950 to Converse; US 2007/0277869 A1, by Shan et al.

All of the above approaches introduce some additional complication to existing systems in the market, and most do not solve the problem of wide-angle and spectral bandwidth collection.

Explanation of the invention.

The study of the state of the art reveals that there are two major problems in the implementation of holography in solar applications, both thermal and photovoltaic. The first is the collection of most of the possible solar spectrum without the need for active tracking (the hologram is monitored without system movement). This collection refers both to the variation of angles of incidence throughout the different annual seasons, and to the wide range of energy wavelengths that are necessary to collect.

As for wavelengths, to make a collection of a significant part of the solar spectrum, the hologram should be able to collect at least the region between 500 nanometers (nm) and 1,100 nm. This portion contains 70 percent of all energy in the solar spectrum. Even better would be to collect between 400 nm and 1,200 nm, that is, 80 percent of the spectrum's total energy. However, current holograms have a limitation in terms of spectral bandwidth that they can cover. Therefore, the present invention relies, with current technology, on at least two overlapping diffraction networks, that is, multiplexed, to capture the minimum required 70 percent. Future research will increase the bandwidth per diffraction network and thus reduce the need for multiplexing.

But they also have to collect these wavelengths throughout the year, and from morning to afternoon. Generally, in a wide range of terrestrial latitudes, the annual variation of angles of incidence of sunlight remains at approximately 60 °. As seen in Figure 1, a surface (1) inclined at latitude will receive radiation (2) from a low angle in winter, while in summer it will receive radiation (3) at a higher angle. Radiation (4) in spring and autumn will be received at an angle very close to the perpendicular. The angular variation between (2) and (3) is approximately 60º mentioned. Today, and without taking into account the possible future advances in this field, both reflection and transmission holograms have a restriction in terms of their angular bandwidth, so, in this case, they are also necessary at least two multiplexed diffraction networks. Along with the wavelength requirements, at least four multiplexed networks with current technology are needed. You can multiplex as many high efficiency networks as the linear dynamic range of the material allows. Here too, the possible future reduction in the number of multiplexed networks with the advancement of technology applies.

On the other hand, in a flat configuration like that of Figure 1, there is the additional problem that, if you want to greatly reduce the amount of radiation receivers (in Figure 1 represented as a pipe (6) in a solar panel thermal), that is, if it is desired to increase the concentration significantly, then the radiation exit angle (5) must be very steep. This presents a problem in the construction of holograms: angles so inclined are not viable to obtain commercially without many optical losses in the hologram, especially by Fresnel reflection. This type of reflection occurs in any interface between two media with different index of refraction, and the greater the angle of incidence with respect to the normal one.

The authors have already solved this problem in previous designs (patent EP201331199). In them, the drawbacks were overcome by hologram coupling, several conventional optics and a 3D structure with several planes of different inclination from each other. In this way, a solar panel design was optimized for a concentration of between 2 and 10X. However, it has been observed that, for higher concentrations, the consequent increase in volume of the entire system inherently entails an increase in weight and quantity of structural materials, making said design economically unfeasible, due to the amount of material involved.

It was therefore necessary to evolve towards a new concept in which the commitment between economic competitiveness, that is, low consumption of materials, and optical efficiency, that is, maintaining spectral and angular bandwidths, was maintained.

In this concept, object of this document, it is necessary to maintain a relative flatness so as not to raise the cost. That is, it is not possible to apply complicated 3D structures. Therefore, the holographic optical element (7) is kept flat or slightly curved. The holographic optical element (7) and the conventional optics (8) are attached glued to each other. This is observed in Figures 2 and 3, in which both are represented slightly apart to be able to graphically observe the radiation between them. In addition, their refractive indexes should be similar to avoid or minimize losses due to Fresnel reflection.

The holographic optical element (7) must be designed in such a way that it captures at least the angular widths of 60 ° and spectral of 600 nanometers already mentioned as input. Or even higher ranges, implying, as appropriate, as many multiplexed diffraction networks as necessary without affecting efficiency. In this way, active tracking is avoided, and it is the hologram that performs passive tracking.

On the other hand, the design of the holographic optical element (7) must also ensure that all of that captured radiation is sent with a specific exit angle, for example perpendicular, that ensures the correct operation of the conventional optical element (8) to which it is coupled. .

Conventional optics (8) coupled to the holographic element (7) collects the radiation from it, sent at a specific angle, for example perpendicular as shown in Figures 2 and 3, and concentrates it on the radiation receiver (6). To do this, conventional optics must be designed in such a way as to allow such concentration. For example, a conventional flat-convex lens, a Fresnel lens or a periodic or non-periodic arrangement of conventional optics can be used. The fine design of said conventional optics (8) depends on the desired concentration factor. In fact, it can and should be adjusted to it, which will depend at all times on what is the most expensive element of a solar panel. If at any given time the solar cells are of high price, then it will be convenient to reduce their size in the system, and conventional optics (8) will be designed for a greater concentration. If the materials outside the receiver (6) are the ones that increase in price, it will be convenient to go to lower concentrations. Therefore, the system has high versatility to adapt to market changes. According to the calculations made, the same design can cover concentrations that vary from 10X, only varying the design of conventional optics (8).

The holographic optical element (7) and conventional optics (8) are coupled as seen in Figures 2 and 3, that is, glued to each other. In the case of Figure 2 and also of Figure 4, the holographic optical element (7) is reflective. In this case, the optical elements (7) and (8) can rest on a base (9) of any structural material. The system can also be carried out in a transmission configuration (see Figures 3 and 5), in which the holographic optical element (7) will be transmission.

On the other hand, both the holographic optical element (7) and conventional optics (8) must be designed to capture the wavelengths most favorable to the receiver (6). In this aspect, both the design of holographic networks and the material from which conventional optics are constructed are influenced (8). The only requirements to be demanded from such material are a.) Transparency in the optimum range of wavelengths, b.) Resistance to inclement weather and ultraviolet (UV) radiation, c.) Refractive index similar to that of the holographic optical element ( 7) and d.) The lowest possible density, so that the total weight / cost ratio of the system is economically viable.

All of the above refers to what we call the "optical part" of the system. The so-called "generation part" consists of a radiation receiver (6) and a heat sink (12). The radiation receiver will always be placed at the focal distance with which conventional optics is designed (8).

In the case of a photovoltaic solar module, the radiation receiver (6) is a solar cell, and the heat sink (12) can be active, such as a pipe with heat transfer fluid, or passive, such as a structure of dissipation by convection by metal fins. If an active heatsink is used, the module becomes a hybrid, since in addition to producing photovoltaic electricity it can also heat water, or use said heating to produce steam and thereby more electricity through the movement of a turbine.

In the case of a thermal or thermoelectric solar panel, the radiation receiver (6) and the heat sink (12) are the same: a heat transfer fluid pipe.

An important feature of the present invention is the possibility of physical separation of the optical and generation parts. Both can be supported on separate structures, (10) for the optical part and (11) for the generation part. The advantage of this arrangement is the lower mechanical complexity, providing greater resistance to winds, vibrations, etc. It is also advantageous the greater versatility at the time of transport and assembly, reducing costs in both cases.

Both structures (10) and (11) are variable in position, so that the system can vary its inclination, and the same system is valid for most land latitudes.

The described solar concentration modular system can be manufactured in units of small dimensions, so that it is modular. That is to say, it can be applied to small installations, as well as joining modules, also to large power plants, both photovoltaic and thermoelectric solar.

Description of the drawings

Figure 1. Variation of incident solar radiation angles between winter (2) and summer

(3) on a surface (1) inclined at latitude. Early solar radiation in winter (2) strikes the surface (1) at a lower angle, while solar radiation at noon in summer (3) strikes the same surface (1) at a higher angle. The difference between both angles is approximately 60º for many latitudes. Radiation in spring or autumn (4) affects practically perpendicular on said surface (1). It is desired to influence said radiation on radiation receptors (6), so that its position must be made to coincide with the radiation exit angle (5).

Figure 2. Optical assembly formed by a holographic optical element (7) and a conventional optical element (8), represented in this case as triangular prisms of various sizes, emulating a Fresnel lens. The holographic optical element (7) receives radiation from all angles of incidence between winter (2) and summer (3), and directs them in a specific plane, for example perpendicular, towards the conventional optical element (8). This is designed to concentrate the outgoing radiation (5) at a point determined by the overall design of the system. This Figure shows the configuration for the case of using reflection holograms. In the Figure the holographic (7) and conventional (8) optical elements are shown separated to observe the radiation between them, but in a real configuration they are joined.

Figure 3. Optical assembly formed by a holographic optical element (7) and a conventional optical element (8), represented in this case as triangular prisms of various sizes, emulating a Fresnel lens. The holographic optical element (7) receives radiation from all angles of incidence between winter (2) and summer (3), and directs them in a specific plane, for example perpendicular, towards the conventional optical element (8). This is designed to concentrate the outgoing radiation (5) at a point determined by the overall design of the system. This Figure shows the configuration for the case of using transmission holograms. In the Figure the holographic (7) and conventional (8) optical elements are shown separated to observe the radiation between them, but in a real configuration they are joined.

Figure 4. Scheme of the complete solar concentration modular system, object of the present invention, formed by two structures that can be independent. One of them (10) gives support and rigidity to the optical assembly formed by a base (9), a holographic optical element (7) and a conventional optical element (8). The second structure

(eleven)

it gives support and rigidity to the receiver assembly, composed of a radiation receiver (6), which can be a solar cell or a heat transfer fluid pipe, and a heat sink (12) that can be active (with cooling fluid) or passive (with convection dissipating fins). This system, represented here in the case of a reflection hologram, is able to track radiation without movement at all times of the year, from summer (3) to winter (2), and reflect it

(5)

 until concentrated in the receiver (6).

Figure 5. Scheme of the complete solar concentration modular system, object of the present invention, formed by two structures that can be independent. One of them (10) gives support and rigidity to the optical assembly formed by a holographic optical element (7) and a conventional optical element (8). The second structure (11) gives

support and rigidity to the receiver assembly, composed of a radiation receiver (6), which can be a solar cell or a heat transfer fluid pipe, and a heat sink

(12) which can be active (with cooling fluid) or passive (with convection dissipating fins). This system, represented here in the case of a transmission hologram, is capable of tracking the radiation without movement at all times of the year, from summer (3) to winter (2), and transmitting it (5) until it is concentrated in the receiver (6).

Embodiments of the invention

In a preferred, but not exclusive, configuration, the modular solar concentration system, both thermal and photovoltaic, will consist of several structures (10) and (11) coupled together so that the light received by the optical part is concentrated, ( 7) and (8), in the generation, (6) and (12). The measurements of each unit module to be supported by the structure (10) can be, for example, 1,300x1,000 mm, that is, very close to the magnitudes of any standard panel. The base (9) can be made of any material, for example wood or plastic. The structure (10) can be made of any structural material, for example steel. The hologram (7) will be made of photosensitive material on a transparent rigid or flexible substrate with the same refractive index. Conventional optics (8) will be manufactured with the same characteristics - transparency and refractive index - as diffractive optics, and in suitable materials, such as transparent plastics or glass, resistant to weather and UV radiation, and of minimum density possible.

The structure (11) that supports the receiver (6) will have the necessary measures for concentration in said receiver. Its dimensions will depend largely on the concentration that is desired, and based on which the conventional optics are designed (8). For example, for a concentration of 16X, and the unit module dimensions mentioned above, the structure (11) will place the receiver at a length of 3.3 meters with respect to optical assembly (7) and (8), corresponding distance with the focal length of conventional optics (8). Under these conditions, the width of the receiver (6) is 78 millimeters, that is, half of a conventional solar cell 156 millimeters on its side. All these dimensions vary and the geometries are adapted according to the desired concentration factor, which can vary from 10X.

In various configurations, the receiver (6) can be a solar cell for a photovoltaic system, or a heat transfer fluid pipe for a thermal or thermoelectric solar system. In the event that the receiver (6) is a photovoltaic cell, it must be accompanied by a heat sink (12), which can be active - such as a pipe with cooling fluid, which can have a system solar thermal / photovoltaic hybrid - or passive, such as a static structure of dissipating fins. If it is a thermoelectric or thermal solar system, there is no need for a heat sink (12) and the heat transfer fluid pipe becomes the receiver (6).

In addition, all these configurations can be done in reflection concentrating systems, as shown in Figure 4, where the diffractive optic or holographic optical element (7) is for example a reflection hologram, and the structure (11)

which supports the generation part is located above that which supports the optical part (10). Or, also, they can be carried out in transmission concentrator systems, as shown in Figure 5, where the diffractive optics (7) is for example a transmission hologram, and the structure (11) that supports the generation part is it places below the one that supports the optical part (10).

Claims (9)

one.

Modular solar concentration system characterized by being composed of two parts, an optic that concentrates on one of generation, the first one formed by a holographic optical element (7) coupled to a conventional concentrating optic (8) of the same or very similar index of refraction on a structure (10), and the second by a radiation receiver (6), a heat sink (12) and a structure (11).

2.

Modular solar concentration system according to claim 1, characterized in that the optical and generation parts are physically separated in one configuration, and are together in the other configuration.

3.

Modular solar concentration system according to claim 1, characterized in that the holographic optical element (7) acts so that, being fixed, it captures incident radiation at all times of the year and times of day, thus avoiding active radiation tracking solar, and whose outgoing radiation is effected in the direction or directions determined by conventional optics (8).

Four.

Modular solar concentration system according to claims 1 and 3, characterized in that the conventional optics (8) concentrates its incident radiation, coming from the holographic optical element (7), into the radiation receiver (6) placed at the focal length of the optics conventional (8), and said design welcomes concentration factors from 10X.

5.

Modular solar concentration system according to claim 1, characterized in that the structures (10) and (11) vary in position, such that the inclination of the planes of the optics (7) and (8), as well as that of the receiver (6) fit all latitudes.

6.

Modular solar concentration system according to claim 1, characterized in that the receiver (6) is a photovoltaic solar cell in the case of being used as a photovoltaic solar module, or a pipe with heat transfer fluid in the case of being used as a thermal or thermoelectric solar panel.

7.

Modular solar concentration system according to claims 1 and 6, characterized in that the heat sink (12) coincides with the receiver (6) in the case of being used as a thermal or thermoelectric solar panel, while it is a separate element in the case of photovoltaic solar module, and in the latter case it is either an active heatsink by means of moving fluid, thus forming a hybrid thermal-photovoltaic or thermoelectric-photovoltaic module, or a passive heatsink.

8.

Modular solar concentration system according to claims 1 to 7, characterized in that the conventional optics (8) is located above the holographic optical element (7), and said assembly - optical part - is located below the generation part, thus forming a modular system of solar concentration by reflection.

9. Modular solar concentration system according to claims 1 to 7, characterized in that the conventional optics (8) is located below the holographic optical element (7), and said assembly - optical part - is located above the generation part, thus forming a modular system of solar concentration by transmission. DRAWINGS