EP2210275A2

EP2210275A2 - Solar collector

Info

Publication number: EP2210275A2
Application number: EP08847472A
Authority: EP
Inventors: Robert Massen
Original assignee: Massen GmbH
Current assignee: Massen GmbH
Priority date: 2007-11-11
Filing date: 2008-11-07
Publication date: 2010-07-28
Also published as: WO2009059785A2; US20100282241A1; WO2009059785A3; DE102007054124A1

Abstract

The invention relates to a solar collector, the absorbent surface thereof only reflecting a small fraction of the sunlight and due to selective reflection properties, simulates a two-dimensional surface or a three-dimensional area or creates a visual impression of the contents.

Description

solar collector

The reduction of energy consumption of private and public buildings through the use of solar collectors, which are mainly installed on roofs and exterior facades, and photovoltaic panels, which convert solar energy into electricity, and solar thermal panels, which convert solar energy into heat, is a worldwide funded measure to reduce energy consumption.

Both photovoltaic cells and solar thermal, liquid-flow panels are optimized for the best possible absorption of sunlight. But this is synonymous with the least possible reflection, since each reflected photon for the

Conversion to electricity (photovoltaic) or heat

(in solar thermal) is lost. Accordingly, these panels or solar panels look dark-black to dark-blue and thus form incalculable interruptions in the architectural-looking structure of roof tiles, slates or green roof occupied roof.

FIG. 1 shows, by way of example, in a photograph reduced to a pure line drawing for printing reasons, a roof of a private house 10 covered with roof tiles, which is provided both with a thermal solar collector 12 and with a photovoltaic solar panel.

Solar collector 14 is occupied. The dark area-like interruption of both the color and the structure of the tiles is visually very disturbing and structurally not tolerable from an architectural point of view.

There is no need to explain further how to obscure the visual impact of such roofs in both private and public buildings, and even more so in historical buildings. As façade surfaces are increasingly being fitted with such systems, the aesthetic disturbance in the overall picture of settlements, industrial buildings, etc. is increasing. As a result, many and in particular practically all historical buildings are not suitable for solar-technical energy generation, despite having a suitable location already be equipped for reasons of monument protection. Even with large solar parks in the field, the panels are visually very disturbing.

There have already been a number of approaches, through a periodic approach

Arrangement of solar cells to reduce this disturbing aesthetic impression in the roof design. Thus, WO 2006/010261 A1 describes a periodic arrangement of smaller photovoltaic cells, which by their size and arrangement at least the periodic arrangement of roof tiles in certain

Imitating way visually. A color adaptation to the roof is provided here by a color-coded anti-reflection layer, but which can produce no spatial impression. Such coloring is also associated with a large reduction in absorbed light.

In DE 19739948 a photovoltaic roof tile is described, in which specially shaped small photovoltaic cells are embedded, so that at least the 3D shape of a roof tile is retained, but not its color impression.

In WO2004 / 079278 a spectrally operating method is described to provide solar cells on its entire surface with narrow-band reflecting layers, which give the usually black cells a colored appearance and still transmit most of the spectrum of sunlight and thus reduce energy production only insignificantly , A number of materials and coatings are described to accomplish this purpose.

The mentioned methods of photovoltaic power generation are expensive special solutions that severely limit the efficiency and run counter to the trend for low-cost mass production of large flat photovoltaic panels.

For solar thermal panels, no economic methods for architectural design are known. In the context of this application, we define the term "architectural design" as the sum of all physical measures of giving a desired visual impression to the human observer for the purpose of generating energy that does not reflect the solar radiation, in which case the two-dimensional coloring is only one aspect often not enough, because a homogeneous colored surface is too simple for most design wishes Design therefore also requires graphic elements such as lines and graphically emphasized elements, textured surfaces, etc.

There is therefore a high public and economic interest in designing thermal or photovoltaic solar collectors in such a way that on the one hand a desired visual impression is created and on the other hand the solar collectors can be produced cost-effectively in a mass production and yet the energy efficiency is reduced as little as possible.

There is an interest in increasing the acceptance of solar energy usage by providing solar collectors that are highly efficient and yet are not perceived as optically disturbing. This solar collectors would be used even where they were previously rejected as aesthetically unreasonable. A small loss in efficiency is thus compensated immediately.

This object is achieved by a solar collector with the features of claim 1.

Only a small fraction of the sunlight is reflected, so that the efficiency is only slightly deteriorated. A small percentage of reflected light is sufficient to simulate a two-dimensional surface or a three-dimensional spatial form, or to create a content-imparting visual impression because the reflection is selective. A simulated area can be, for example, a façade wall with a certain color, which is also patterned in itself, or also edge margins of slate slabs. A simulated three-dimensional spatial form could be a replica of the tiles surrounding the solar panel. A visual image that conveys contents can e.g. convey an advertising message.

Depending on which criterion the reflection is selected, for example, only 1 to 10% of the incident sunlight is reflected, with appropriate design and / or combination of different selections preferably between 1 and 5%. In a first embodiment, the absorbing surface reflects spectrally selective.

Preferably, incident sunlight is selected only in a narrow band selected wavelength range or in narrow band Wavelength ranges reflected, for example, have only a width of about 5 to 15 nm. Advantageously, the reflected wavelength bands are in the range of the highest perception of the human eye. The eye has three perceptual maxima. Typically, the maxima of these reflection bands will be in the values specified for the CIE standard observer:

BLUE = 435.8 nm GREEN = 546.1 nm RED = 600.0 nm, which corresponds to the maximum sensitivity of the human color vision system for the three primary colors blue, green, red. Of course, one can also

For example, reflection may be placed between the maxima for green and red, where the perception of both the green and the red cones is high.

When selecting the reflected wavelengths, it is crucial that as little energy as possible should be reflected in order to achieve a desired visual effect.

The fact that the reflection spectrally accurate and very narrowband adapted to the human perception, a desired visual impression can already be generated by the reflection of a very small percentage of the incident sunlight, it is reflected only a small fraction of sunlight. The energy loss caused by reflection remains low. The choice of which rays to reflect is at the spectral level.

The production of spectrally narrowband reflective coatings is the

The person skilled in the art of optical coating technology is known by the term "narrow band partial reflective coatings"

Coatings are for example from the company Red Optronics Company

(www.optical-components.com).

Preferably, the spectral narrow-band reflection can be wholly or partly supported or formed by a fluorescence effective in the desired wavelength bands. In particular, in the case of black thermal collectors, which can not exploit the UV component of sunlight, it is possible by means of targeted fluorescence to utilize this unused energy of the spectrum in a visible reflection which can be used for aesthetic design. In a second embodiment, the absorbent surface reflects directionally selective.

Preferably, incident sunlight is substantially not reflected in a first solid angle range and reflected only in a second solid angle range which is smaller than the first solid angle range and substantially corresponds to the solid angle range, under which the solar collector is seen in the operational state mainly by human observers.

The fact that the reflection takes place only in the solid angle range from which a human observer usually sees the roof / the outer wall with the solar panels, also satisfies the reflection of a very small percentage of the incident sunlight, it is reflected only a small fraction of sunlight, it Therefore, little energy is lost. The choice of which rays to reflect is spatial. The production of layers with a direction-selective behavior is the

Professional of the optical layers known. The company Merck, Darmstadt, provides e.g. printable and sprayable pigments which reflect certain wavelengths in certain directions ("effect pigments") (see, e.g., Dr. Christoph Schmidt, Merck KGaA, Darmstadt, "The Light Manager: Dyes and Pigments in Our Environment"). The use of nanostructures also makes it possible to produce layers with direction-selective reflection.

Such nanostructures can also be used with classic printing techniques such as

Web-fed printing, digital ink-jet printing and the like be applied, the

Nanoparticles align themselves from an evaporating carrier liquid in a self-organized process on the substrate so that the resulting

Layer shows a certain angle of reflection for incident sunlight.

In a third embodiment, the absorbent surface reflects area-selectively. The reflective surfaces may, for example, the edges of

Imitate roof tiles graphically, so that only a very small area in relation to the absorbing surface reflects and only a small fraction of the sunlight is reflected.

Preferably, the reflective surfaces necessary for the desired optical impression are interrupted so that a human observer does not perceive any interruption. That's depending on the angle under which the solar collector is seen, more or less possible. A person unconsciously supplements surfaces and structures that are interrupted. Thus, the energy removed from the radiation can be reduced, so the efficiency increases. The interruption of the reflective surface, which is not perceived by humans, reflects an even smaller fraction of the sunlight.

All three embodiments mentioned above can be combined as desired.

In a further embodiment, the visual impression is adapted to the surface surrounding the solar collector after installation, ie in the ready state. According to another embodiment, the absorbing solar collector surface can also be used for artworks or billboards - always with very little efficiency limitation, since only a small percentage of the incident light is reflected. The changed reflection properties are preferably achieved by

Printing, coating or texturing of the solar collector surface achieved. For a very cost-effective implementation is possible, which is also suitable for mass production.

The printing, coating or texturing can take place, for example, on a glass plate provided for the protection of the solar collector. It is also possible to provide a printed film which is applied to the absorbing surface of the solar collector.

It is known to those skilled in the optical coatings that optical properties can also be controlled electrically. For example, in electrochromic glasses by applying a voltage, the transparency or the diffuse backscatter of light can be controlled. If such glasses combined with the layers described above with spectrally selective behavior or with a direction-selective reflection, the desired effects can be electrically controlled in addition. This is interesting, for example, for the design of solar collectors for advertising purposes

The invention further provides a method of manufacturing solar panels. The idea of the invention is explained by way of example with reference to the design of a photovoltaic roof panel made of solar cells, which is mounted on a tile covered with roof tiles. For this purpose we use the following representations: Figure 1 shows the disturbing visual impression of photovoltaic and thermal solar collectors in the prior art, which break the architectural-seeming structure and color of a roof tile-covered roof by a continuous dark area;

FIG. 2 shows the spectral sensitivity curves of the human eye;

FIG. 3 shows the solid angle of the required reflection of a printed graphic pattern of simulated roof tiles on a photovoltaic roof panel to be viewed by an observer from the street; FIG. 4 illustrates the exploitation of the principle of the human visual

Continuation of graphic patterns to reduce the total reflecting surface.

As already discussed with reference to Figure 1, the architectural design of solar collectors can be attributed to the following task: the solar collector should be designed by suitable surface processes visually corresponding to the undisturbed roof tile pattern, which expedient for cost reasons with a simple printing process at the end of the manufacturing process of the entire solar collector carried out and may affect the energy efficiency only slightly. Especially in custom designs, a digital printing process such as ink jet printing is suitable. Other pattern-generating processes, such as surface texturing, interference coating, nanoscale wavelength-dependent reflections, etc., are known to those skilled in the surface art. For reasons of simplification, we present the idea of the invention primarily on the basis of a printing process; However, the other known surface design processes such as coating, structuring, etc. are part of the inventive concept. In the context of this description, we use the term "printing process" for the entirety of these visual surface design processes. Any light reflected by a solar collector is lost for conversion into electrical energy (in photovoltaics) or thermal energy (in solar thermal energy). It is therefore of great importance, by suitable design of the printing processes, to minimize the amount of total reflected light in the region of the energetically active wavelengths while still producing visually pleasing color and / or graphic patterns on the surface of the solar collector for the human visual system.

According to the invention, this is done in a first embodiment by applying surface properties which reflect the incident sunlight only in a narrow band selected wavelength range or in narrow band selected wavelength ranges.

FIG. 2 shows in a graph 16 the relative spectral sensitivity of the color receptors of the human retina over the wavelength. The human eye has as color receptors three different types of cones for the primary colors BLUE, GREEN and RED. Their respective sensitivity is shown in the graph of FIG. A line 18 shows the sensitivity of a blue pin, a line 20 the sensitivity of a green pin and a line 22 the sensitivity of a red pin. The sensitivity curves correspond to spectral bandpasses in the range of wavelengths from about 400 nm to 650 nm, these bandpasses overlapping strongly, especially in GREEN and RED. With a curve 24, the energetically effective absorption of sunlight in this spectral range is indicated.

The knowledge of the sensitivity curves 18, 20 and 22 leads to a specific selection of the pigments selected for the colored, areal printing of the surface of the solar collectors. For a blue impression very narrow-band reflective pigments are used, which reflect near the maximum of the sensitivity of the blue pin of 435.6 nm, so for example between about 430-445 nm. For a green impression are very narrow-band reflective Using pigments that reflect near the maximum sensitivity of the green pin at 546, 1 nm, for example, between about 540 to 555 nm. For a red impression very narrow-band reflective pigments are used, which are close to the maximum reflect the sensitivity of the red pin at 600 nm, so for example from about 590 to 605 nm. Thus, any color impression and thus any impression of a three-dimensional spatial form can be caused in the human observer, although compared to traditional broadband pigments only small energy losses occur. The radiation loss by reflection can thus be kept very small, or in other words, the energy gain (1 / loss) is significant compared to the use of classical broadband CMYK pigments (CMYK cyan, magenta, yellow, key).

According to the invention, in the second embodiment, the desired visual color impression is achieved with the lowest possible radiation losses by applying surface properties which reflect the incident sunlight in a directionally selective manner. In the described embodiment, the sunlight is reflected only in the restricted solid angle (s) from which the solar collector mounted on the roof can usually be observed by humans. 3 shows a building 32 with a sloping roof 34, on which a solar collector 36 is mounted. This is illuminated by the large-radiating sun 38 substantially in parallel. As a result of the compressed perspective perception of the solar collector 36 from a person standing on a street 40, the angle valid for the optical perception is reduced to a very small solid angle α, which is only a fraction of the usual diffuse reflection angle of a surface 44 of the solar collector 36 of approx. 180 degrees.

The surface is designed by a printing process (in the sense of the above-mentioned generalization of the term "printing process") so that incident sunlight is reflected only in the narrow solid angle from which the human observer 42 can see the solar collector 36. Upwards or into others lateral directions, no light is reflected, thereby roughly reducing the energy efficiency by a fraction of

α / 180 degrees compared to diffusely reflecting pigments throughout the half-space. Expressed in an equation:

η _r = η ₀ - α / 180 ^* η ₀ with η _r = resulting efficiency and η _o = original efficiency. At a typical value of α = 10 degrees this is a factor of 1/18, ie a small loss.

Of course, this second embodiment can be combined with the first one.

The sunlight is thereby reflected so that the human observer 42 a pattern corresponding to the surrounding area, in the illustrated case, the pattern of a Dachziegeldaches, i. perceives a three-dimensional spatial form, or so that the human observer 42 e.g. a work of art or an advertising message perceives as content mediating impression. This form of sunlight reflection applies equally to the first embodiment. FIG. 4 shows, for the third embodiment, an exemplary printing of the solar radiation-exposed surface of a solar collector, which of course can also be combined with the two embodiments already described. Here, the perception property of the human visual system is used to perceive interrupted graphic structures in the perception as uninterrupted. It is therefore printed by a printing process, a pattern 46 of a Dachziegeldaches as a graphic pattern with a reflective layer. The line-like structures 48 are interrupted again and again at locations 50, so that the total reflecting area is reduced according to the line-to-line ratio, without the human visual system being significantly disturbed in recognizing a roof tile roof. Especially with perspectively drawn graphic structures, lines running into the vanishing point can be interrupted frequently and over substantial lengths without the impression of a closed roof tile pattern being lost. Thus, according to the invention, the energy efficiency increases compared to a pattern traditionally printed with uninterrupted lines pattern, approximately corresponding to the ratio line distance / interruption distance.

It is known from color perception that certain color impressions can be influenced not only by the choice of pigments but also by the spatial frequencies of the linear structures of a multicolored pattern (see for example EP 164 20 98 A1).

Therefore, the effects of perception of linear continuation and color perception, caused by the reflection of narrow - band reflective pigments in the energetic sense, can be optimized by using the accordingly discontinuous dense linear structure and the narrow-band reflective pigments are combined with each other.

The Erfϊndungsgedanke concerns both photovoltaic and thermal solar collectors and includes all processes for architectural, graphic or color design of the absorbent surface of these solar collectors. It does not only include the energetically optimized design in the sense of an optical reconstruction of the solar collectors, e.g. are designed as solar panels, concealed building structures such as roof tiles, facade elements or outdoors set up, the terrain hiding solar panels. The term "architectural design" in the sense of the inventive idea also includes the free artistic design and patterning through artistic motives but also through motifs in the sense of an advertising space or a message.

In summary, the concept of the invention relates to solar collectors and all production methods for the production of optically appealing photovoltaic and thermal solar collectors such that the energy efficiency is only slightly reduced compared to a non-patterned solar collector, which is achieved by individual or combined utilization of the effects: Reflection essentially only in the limited solid angle from which the solar collector is seen b) graphic design by linear structures, which are so interrupted that they do not disturb the human perception as a whole pattern c) colored flat design by pigments with narrow

Wavelength ranges in which a reflection takes place, which lie in the range of the human perceptible wavelengths.

Claims

claims

A solar collector, the absorbing surface of which reflects only a small fraction of the sunlight and which simulates one or more two-dimensional surfaces or three-dimensional spatial forms or creates a visual image that conveys contents through selective reflection properties.

2. Solar collector according to claim 1, whose absorbing surface reflects spectrally selective.

3. Solar collector according to claim 2, wherein the spectrally selective reflection is formed or supported by fluorescence.

4. Solar collector according to claim 3, whose absorbing surface converts a part of the sunlight lying in the ultraviolet wavelength range by fluorescence in visible to human light and reflected spectrally selective.

5. Solar collector according to one of the preceding claims, whose absorbing surface reflects directionally selective.

6. Solar collector according to one of the preceding claims, whose absorbing surface reflects surface selectively.

A solar collector according to any one of claims 2 to 4, wherein the absorbing surface selects incident sunlight only in a narrow band selected wavelength range or in narrow band

Wavelength ranges that only have a width of about 5 to 15 nm

8. A solar collector according to any one of claims 2, 3, 4, 7, wherein the absorbing surface reflects incident sunlight narrowband in one or more wavelength ranges corresponding to the highest perception of the human eye.

9. The solar collector according to claim 5, wherein the absorbing surface substantially does not reflect incident sunlight into a first solid angle range and into a second solid angle range smaller than the first solid angle range and substantially the solid angle range below which the solar collector is in the operative state predominantly human observers is reflected.

10. The solar collector of claim 9, wherein the first solid angle range is about fifteen to twenty times greater than the second solid angle range.

1 1. A solar collector according to claim 6, wherein the reflective surfaces are interrupted so that a human observer perceives no interruption.

12. A solar collector according to any one of the preceding claims, wherein the selective reflection characteristics are selected so that a human observer receives substantially the same visual impression from the solar collector as from the surface surrounding the solar collector in the operative state.

13. Solar collector according to one of the preceding claims, wherein the selective reflection properties of the absorbent surface by printing, coating or texturing are realized.

14. Solar collector according to one of the preceding claims, wherein the solar collector comprises a glass plate which is printed, coated or textured.

15. Solar collector according to one of the preceding claims, wherein the solar collector comprises a plastic plate or plastic film, which is printed, coated or textured.

16. Solar collector according to one of the preceding claims, wherein the selective reflection properties of the absorbing surface are electronically controllable.

17. A method for producing a solar collector for converting sunlight into thermal and / or electrical energy, wherein the reflection properties of the absorbing surface of the solar collector is selectively changed so that simulates a three-dimensional spatial form or a content-conveying visual impression is generated.

18. The method of claim 17, wherein the selective reflection properties of the absorbent surface are realized by printing, coating or texturing.