WO2011039356A1

WO2011039356A1 - Solar energy harvesting system

Info

Publication number: WO2011039356A1
Application number: PCT/EP2010/064669
Authority: WO
Inventors: Rodolphe Marie; Asger Laurberg Vig; Mads Brøkner CHRISTIANSEN; Anders Kristensen
Original assignee: Danmarks Tekniske Universitet
Priority date: 2009-10-01
Filing date: 2010-10-01
Publication date: 2011-04-07

Abstract

Disclosed is a solar energy harvesting system comprising: a solar radiation redirecting layer, comprising an array of features with a sub millimetre scale, adapted to redirect solar radiation having a predetermined range of wavelengths; a solar radiation guiding layer for guiding solar radiation; wherein the system further comprises solar energy harvesting means adapted to convert solar energy into electric energy; where the solar radiation redirecting layer, redirects solar radiation with the predetermined range of wavelengths, towards the solar energy harvesting means. By providing the system with a solar radiation redirecting layer, a part of the solar radiation incident on the system is refracted with different angle allowing the refracted solar radiation to be guided within the solar radiation guiding layer towards the solar energy harvesting means. By using the solar radiation redirection layer to redirect the solar radiation, solar energy harvesting means having a smaller area can be used.

Description

Solar energy harvesting system

Field of the invention

The present invention relates to solar power cells, more specifically to the use of solar power cells in buildings.

Background of the invention

The increasing environmental awareness of homebuyers and companies has led architects and engineers to search for ways of creating more eco-friendly structures. Modern buildings use large quantities of energy for purposes such as lighting, heating and cooling. As the energy production in most part of the world is dependent on consumption of fossil fuels, this results in a large outlet of greenhouse gases with damaging effects on the environment.

The integration of solar power cells in buildings has been proposed as a way of limiting the damaging effect of buildings on the environment. Buildings fitted with solar power cells can in theory not only be self-sufficient with energy but even produce excess energy for use else where.

One way of using solar power cells in a building is to integrate them in the windows. This is especially beneficial in modern skyscrapers as they typically have large glass facades with a potential corresponding large energy production capacity.

By integrating solar power cells in windows, they may further be used to provide solar shading by limiting the amount of heating from the sun. This will lower the amount of energy used for cooling purposes, thereby further decreasing the damaging effect of the building on the environment. US4137098 discloses an energy absorbing Venetian blind type device for generating electricity, providing heat, and serving as a sun shade. The device comprises a plurality of slats covered with an array of photovoltaic cells enclosed between two panes of glass fitted in a window housing. A heat removal system using forced air cools the photovoltaic cells and collects heat for heating purposes elsewhere. The electricity generated by the photovoltaic cells is collected for immediate use or stored in storage batteries for later use.

However it is a problem with the above prior art that the system comprises a large amount of solar power cells. This makes the production of the device expensive. It is a further problem with the above prior art that view from the window is disturbed due to the plurality of slats. As the value of many buildings is reliant on the view, a deterioration of the view will have a corresponding negative effect on the value of the building.

US20090199893 discloses a device comprising a light collector optically coupled to a photocell. The device further comprises a light turning film or layer comprising volume or surface diffractive features or holograms. Light incident on the light collector is turned by volume or surface diffractive features or holograms that are reflective or transmissive and guided through the light collector by multiple total internal reflections. The guided light is directed towards a photocell. In various embodiments, the light collector is thin (e.g., less than 1 millimeter) and comprises, for example, a thin film. However it is a problem with the above prior art that the photocells needs to be positioned such that they receives the light guided through the light collector. In practice this means that the photocells need to be positioned around the edges of the light collector. As the light collector typically is very thin, this makes the device difficult to produce. Large amount of light guided towards photocells positioned at the small space formed by the thin edges of the light collector may further lead to overheating of the photocells resulting in malfunctions. It is a further problem with the above system that it is sensitive to variations of the angle of the light incident on the light turning film.

Thus there is a need for a low cost device, system and method for harvesting solar energy from building facades.

Summary

Disclosed is a solar energy harvesting system comprising:

- a solar radiation redirecting layer, comprising an array of features with a sub millimetre scale, adapted to redirect solar radiation having a predetermined range of wavelengths; and

- a solar radiation guiding layer for guiding solar radiation;

wherein the system further comprises solar energy harvesting means adapted to convert solar energy into electric energy; where the solar radiation redirecting layer, redirects solar radiation with the predetermined range of wavelengths, towards the solar energy harvesting means. Each of the solar radiation redirecting layer and the solar radiation guiding layer may be a glass of mineral type, such as soda-lime-silica, glass-ceramic or borosilicate or alternatively of an organic type such as polyurethane or a polycarbonate. The layers may be made of the same or different material. The solar radiation redirecting layer and solar radiation guiding layer may be one layer.

The features of the solar radiation redirecting layer may be arranged in a regular 2 dimensional grid. The features may be positioned on the exterior of the solar radiation redirecting layer. They may be holes or alternatively protrusions in the solar radiation redirecting layer. The features may have a large variety of shapes, such as being round, rectangular, pentagonal or hexagonal. The features may create a 2 dimensional photonic crystal on the exterior of the solar radiation redirecting layer. The features may be manufactured using a large variety of methods such as optical litography, electron beam lithography, embossing or the continuous embossing technique disclosed in US20090162623.

The solar energy harvesting means may be any device suitable for converting solar radiation into electrical energy such as a solar power cell. By providing the system with a solar radiation redirecting layer, a part of the solar radiation incident on the system is refracted with different angle allowing the refracted solar radiation to be guided within the solar radiation guiding layer towards the solar energy harvesting means. By using the solar radiation redirection layer to redirect the solar radiation, solar energy harvesting means having a smaller area can be used. This will lower the production cost as fewer solar power cells must be used.

When the system is used as a window or in combination with a window, the sub millimetre scale of the features on the solar radiation redirecting layer secures that the view from the window is undisturbed, and the value of the building having the system is therefore unaffected.

It is a further advantage of the present invention that the system only comprises non movable parts. This further decreases the production cost of the system and lowers the chance of malfunctions.

In some embodiments a part of the solar radiation redirected by the solar radiation redirecting layer is guided towards the solar energy harvesting means by total internal reflection in the solar radiation guiding layer, i.e. in one or more guided optical modes. The solar radiation redirecting layer may be attached to the solar radiation guiding layer. The part of the solar radiation redirected by the solar radiation redirecting layer may be all of the solar radiation redirected by the solar radiation redirecting layer.

By using the principle of total internal reflection to guide solar radiation in the solar radiation guiding layer, an effective, low loss guidance of the light is achieved. This results in a highly efficient system, which increases its energy production capacity.

In some embodiments the system further comprises an intermediate layer attached to said solar radiation guiding layer, wherein said intermediate layer has a refractive index which is lower than the refractive index of the solar radiation guiding layer, allowing solar radiation to be guided within said solar radiation guiding layer. By providing the system with an intermediate layer, a plurality of solar radiation redirecting layers can be used at the same time in the system. This enables the system to harvest energy from solar radiation within a broader range of wavelengths, thereby further increasing the efficiency of the system. To make sure solar radiation is guided within the solar radiation guiding layer, a material with a refractive index lower than that of the solar radiation guiding layer is chosen for the intermediate layer, as light can only be guided within a material in contact with materials with lower refractive indices.

In some embodiments the system comprises a plurality of solar radiation redirecting layers and a plurality of solar radiation guiding layers, wherein a first solar radiation redirecting layer is attached to a first solar radiation guiding layer, and a second solar radiation redirecting layer is attached to a second solar radiation guiding layer, where the first solar radiation guiding layer is adapted to guide at least a portion of the solar radiation redirected by the first solar radiation redirection layer towards a first solar energy harvesting means; and the second solar radiation guiding layer is adapted to guide a portion of the solar radiation redirected by the second solar radiation redirection layer towards a second solar energy harvesting means.

By providing the system with two solar radiation redirecting layers each attached to a separate solar radiation guiding layer, the solar radiation redirected by the first and second solar radiation redirecting layer may be guided independently. This results in a more flexible system.

In some embodiments the first solar energy harvesting means and the second solar energy harvesting means are the same i.e. one solar energy harvesting mean.

When the first and second solar energy harvesting means are the same, fewer solar energy harvesting means are needed, this lowers the production cost of the system.

In some embodiments the solar energy harvesting means are optimized to convert solar radiation within the predetermined range of wavelengths into electric energy.

By optimizing the solar energy harvesting means for the redirected wavelengths a more efficient system is achieved. This will not only increase the production of energy, but also decrease the amount of solar heating of a building fitted with the system.

In some embodiments the system comprises a frame comprising the solar radiation guiding layer, wherein the solar energy harvesting means are fitted at said frame. The frame may be any frame suitable for housing a window. The frame may have any shape such as rectangular, square, round, elliptical or any combination of the mentioned shapes. The solar energy harvesting means may be at the entire frame or a portion of the frame. The frame may further comprise the solar radiation redirecting layer. The solar radiation guiding layer may be in contact with the solar energy harvesting means.

The solar energy harvesting means may be inside the frame or on the frame.

By fitting the system within a window frame an invisible system is achieved. This enables the view out of the window to be left undisturbed. By fitting the solar energy means inside a window frame, the system can be integrated within a single device. This lowers both the production cost and installation cost of the system.

In some embodiments the solar radiation is conducted in a direction approximately perpendicular to the normal of the solar radiation redirecting layer.

Preferably solar radiation is guided with an angle of 90 degrees plus minus 30 degrees, relative to the normal of the solar radiation redirecting layer, more preferably solar radiation is guided with an angle of 90 degrees plus minus 10 degrees, relative to the normal of the solar radiation redirecting layer, even more preferably solar radiation is guided with an angle of 90 degrees plus minus 5 degrees, relative to the normal of the solar radiation redirecting layer.

In some embodiments the solar radiation guiding layer further comprises features with a submillinnetre scale adapted to guide light out of the solar radiation guiding layer, towards solar energy harvesting means positioned on top of the solar radiation guiding layer. In some embodiments, the solar radiation guiding layer further comprises features adapted to guide light, guided within the solar radiation guiding layer by total internal reflection, out of the solar radiation guiding layer, towards solar energy harvesting means positioned on top of the solar radiation guiding layer.

The features may change the incident angle of the light guided within the solar radiation guiding by total internal reflection layer, so that the incident angle between the light and the surface of the solar radiation guiding layer becomes lower than the critical angle and the light is allowed to escape the solar radiation guiding layer. The features may have any scale e.g. the features may be smaller than a centimetre or smaller than a millimetre.

Consequently, the solar energy harvesting means does no longer need to be positioned around the edges of the solar radiation guiding layer. As the solar radiation guiding layer may be thin, this makes the device easier and cheaper to produce. Problems with overheating by the large amount of light guided towards solar energy harvesting means positioned at the small space formed by the thin edges may further be avoided.

When the solar radiation guiding layer further comprises features adapted to guide light out of the layer, the solar energy harvesting means may be fitted directly on the solar radiation guiding layer. This will lower the production costs.

In some embodiments the solar energy harvesting system comprise two to eight solar radiation redirecting layers where each layer is adapted to redirect solar radiation having a predetermined range of wavelengths.

When using 2-8 solar radiation redirecting layers, a broad range wavelengths can be redirected and used for generating electric energy. In some embodiments the solar energy harvesting system comprises four solar radiation redirecting layers where each layer is adapted to redirect solar radiation having a predetermined range of wavelengths.

By using 4 solar radiation layer a broad range of wavelength can be redirected.

In some embodiments the distribution of wavelengths in the visible spectrum of the solar radiation conducted through the system is approximately unaffected.

The colour of the light which lightens a room in a building is of great importance. During a normal day the distribution of wavelengths in solar radiation changes. In the middle of the day, wavelength in the blue spectrum dominates and in the evening wavelength in the red spectrum. The changing colour of the sun light perceived by the human eye, controls a number of hormones in the brain, which affect a wide variety of process such as the general mood and the sleeping rhythm.

By securing that the distribution of wavelengths in the solar radiation conducted through the system is approximately unaffected, a person staying in a room fitted with windows using the system of the present invention, will not experience hormonal disturbances. This will make the system suitable for use in rooms where people spend long hours, such as an office setting.

In some embodiments the solar radiation redirecting layer is adapted to redirect solar radiation with wavelengths in the ultraviolet spectrum. Solar radiation in the ultraviolet spectrum have a wide range of harmful effects such as sun burns, eye damage and DNA damage of cells with possible subsequent oncogenesis. By designing the solar radiation redirecting layer to redirect solar radiation in the ultraviolet spectrum, the system can be further used as an ultraviolet shield. In some embodiments the system comprises at least one solar radiation redirecting layer adapted to redirect solar radiation with wavelengths in the red spectrum of visible light, at least one solar radiation redirecting layer adapted to redirect solar radiation with wavelengths in the green spectrum of visible light, and at least one solar radiation redirecting layer adapted to redirect solar radiation with wavelengths in the blue spectrum of visible light.

In some embodiments the features of the at least one solar radiation redirecting layer is of micron or submicron scale. In some embodiments the features of the solar radiation redirecting layer are arranged with a lateral distance L between them, an axial distance M between them and a height H, where L is in the range 100 nanometers-10 micrometers, M is in the range 100 nanometers-10 micrometers and H is in the range 20 nanometers-10 micrometers.

In embodiments of the invention features of the solar radiation redirecting layer/s and/or solar radiation guiding layer/s and/or intermediate layer/s may be controlled by applying an electrical charge on the layer/s. The features of the layers that may be controlled may be features such as, their refractive index, the effective wave length interval of the solar radiation redirecting layer or the like.

In some embodiments, the solar radiation redirecting layer is configured to redirect light with a particular wavelength, incident on the solar radiation redirecting layer within a range of angles: - wherein the orthogonal distance between the surface of the solar radiation redirecting layer and a reference plane is above 10 micrometers for at least one point on the surface of the solar radiation redirecting layer, wherein the reference plane is orientated and positioned so that the average of the orthogonal distances between all points on the surface of the solar radiation redirecting layer and the reference plane is minimized, and/or

- wherein the lateral distance L between the features forming the 2 dimensional photonic crystal and/or the axial distance M between the features forming the 2 dimensional photonic crystal and/or the height or depth H of the features forming the 2 dimensional photonic crystal across the solar radiation redirecting layer is varied.

In some embodiments, the solar radiation redirecting layer is configured to redirect light with a particular wavelength, incident on the solar radiation redirecting layer within a range of angles, wherein the orthogonal distance between the surface of the solar radiation redirecting layer and a reference plane is above 10 micrometers for at least one point on the surface of the solar radiation redirecting layer, wherein the reference plane is orientated and positioned so that the average of the orthogonal distances between all points on the surface of the solar radiation redirecting layer and the reference plane is minimized.

In some embodiments, the orthogonal distance between the surface of the solar radiation redirecting layer and the reference plane is above 50 micrometers, 100 micrometers, 500 micrometers, 1 millimetre, 2 millimetre, 5 millimetre or 1 cm for at least on point on the surface of the solar radiation redirecting layer. In some embodiments, the distance from the surface of the solar radiation redirecting layer to the reference plane varies along two orthogonal axes. The orthogonal distance between the surface of the solar radiation redirecting layer and the reference plane for at least on point may become larger than the determined value by manufacturing the 2 dimensional photonic crystal on an uneven surface. The uneven surface may be formed with structures having an above micrometer scale, changing the incident angle of a light wave across the surface. The structures may be convex or concave spherical structures formed on the surface.

The 2 dimensional photonic crystal may be formed on the uneven surface by plastic or viscoplastic deformation being carried out by exerting pressure on the uneven surface with a mask element, said uneven surface being translated continuously relative to said mask element and said mask element being moved about an axis parallel to a local plane of the uneven surface.

In some embodiments, the solar radiation redirection layer is configured to redirect a particular wavelength of light, incident on the solar radiation layer within a predetermined range of angles, wherein the lateral distance L between the features forming the 2 dimensional photonic crystal and/or the axial distance M between the features forming the 2 dimensional photonic crystal and/or the height or depth H of the features forming the 2 dimensional photonic crystal across the solar radiation redirecting layer is varied.

In some embodiments, the solar radiation redirecting layer is configured to redirect light with a particular wavelength, incident on the solar radiation redirecting layer within a range of angles with an approximately constant efficiency by, engineering optical dispersion relations fulfilling these requirements and designing photonic crystals having said dispersion relations.

The invention also relates to a method of manufacturing a solar energy harvesting system as disclosed above, wherein the features of the solar radiation redirecting layer are created in a predetermined pattern by plastic or viscoplastic deformation being carried out by exerting pressure on said solar radiation redirecting layer with a mask element, said solar radiation redirecting layer being translated continuously relative to said mask element and said mask element being moved about an axis parallel to the plane of the solar radiation redirecting layer.

In some embodiments the invention relates to a method of manufacturing a solar energy harvesting system, wherein the predetermined pattern is designed by taking into consideration the solar conditions at the location, where the solar harvesting system is to be utilized.

The angle of the sun relative the earth differs both as a function of time and position, and by taking into consideration the position where the system is be utilized when designing it, an efficient redirection of the solar radiation can be achieved. This enables a large portion of the redirected solar radiation to be converted into electrical energy by the solar energy harvesting means.

Brief description of the drawings

The above and/or additional objects, features and advantages of the present invention, will be further elucidated by the following illustrative and non- limiting detailed description of embodiments of the present invention, with reference to the appended drawings, wherein:

Fig. 1 shows refraction of light in a normal window glass. Fig. 2 shows a solar energy harvesting system according to an embodiment of the present invention. Fig. 3 shows the functioning of a solar energy harvesting system according to an embodiment of the present invention.

Fig. 4a shows a solar energy harvesting system further comprising an intermediate layer, according to an embodiment of the present invention.

Fig. 4b shows the functioning of a solar energy harvesting system further comprising an intermediate layer, according to an embodiment of the present invention. Fig. 4c shows the functioning of a solar energy harvesting system according to an embodiment of the present invention, where the solar radiation redirecting layer and the solar radiation guiding layer is combined in a single layer. Fig. 5a shows a solar energy harvesting system comprising four solar radiation redirecting layers, four solar radiation guiding layers and four intermediate layers, according to an embodiment of the present invention.

Fig 5b is a spectrum plot showing the effective range of wavelength for the four solar radiation redirecting layers of Fig. 5a.

Fig. 6a-c shows designs of the submilimetric features of the solar radiation redirecting layer, according to embodiments of the present invention. Fig. 7 shows a side view of a solar energy harvesting system according to an embodiment of the present invention. Fig. 8 shows a front view of a solar energy harvesting system according to an embodiment of the present invention. Fig. 9a-d shows a manufacturing process for making the array of features with a submillimetre scale.

Fig 10a shows a top view of a solar radiation redirecting layer according to an embodiment of the present invention.

Fig 10b shows a side view of a solar radiation redirecting layer according to an embodiment of the present invention.

Fig 10c shows a top view of a solar radiation redirecting layer according to an embodiment of the present invention.

Fig 1 1 a shows a front view of a solar energy harvesting system according to an embodiment of the present invention.

Fig 1 1 b shows a side view of a solar energy harvesting system according to an embodiment of the present invention.

Figs. 12a-d show an embodiment of the present invention where the orthogonal distance between the surface of the solar radiation redirecting layer and a reference plane is above a determined value.

Fig. 13a-b shows designs of the submilimetric features of the solar radiation redirecting layer, according to embodiments of the present invention where the distance between the features are varied across the solar radiation redirecting layer. Detailed description

In the following description, reference is made to the accompanying figures, which show by way of illustration how the invention may be practiced.

Figure 1 shows refraction of an incoming light ray 102 travelling in air, in a standard single layer window glass 101 . As a result of the difference in refractive indices between air and glass, and the incidence angle 121 between the incoming light ray 102 an the normal component of the window 101 , the incoming light ray 102 is refracted with an angle 1 13 given by Snell S law at the air/glass interface 103. The light ray 104 travelling in the glass 101 hits the glass/air interface with an incidence angle 122 and is again refracted with an angle 120, returning the direction of propagation of the outgoing light ray 106, to that of the incoming light ray 102.

Figure 2 shows a solar energy harvesting system 212 according to an embodiment of the present invention. The system comprises a solar radiation guiding layer 201 , a solar radiation redirecting layer 207 and solar energy harvesting means 21 1 . The solar radiation guiding layer may be a glass of mineral type, such as soda-lime-silica, glass-ceramic or borosilicate or alternatively of an organic type such as polyurethane or a polycarbonate. The solar radiation redirection layer 207 comprises an array of features having submillimetre scale, micron scale or submicron scale. The features may be arranged in a regular grid, creating a photonic crystal structure. The solar radiation redirection layer 207 may be formed using the embossing technique, where a mould is pressed against a soft layer deposited on the solar radiation guiding layer 201 . The solar radiation redirection layer 207 has the ability to redirect an incoming light ray, having a wavelength within a certain effective interval. By changing the distance between the features of the solar radiation redirection layer 207, different effective intervals can be achieved. The solar energy harvesting means 21 1 is placed in the periphery of the solar radiation guiding layer 201 . The solar energy harvesting means 21 1 may be any device suitable for conversion of solar energy into electric energy, such as any type of solar cell. Figure 3 shows the function of a solar energy harvesting system 312 according to an embodiment of the invention. An incoming light ray 302 with a wavelength within the effective interval of the solar radiation redirection layer 307, hits the air/crystal interface 303 with an incident angle 321 . The incoming light ray 302 is split into a first light ray 304 and a second light ray 308, both travelling in the glass. The first light ray 304 is refracted with an angle 313 similar to the angle at a conventional air/glass interface. The second light ray 308, is refracted with a large angle 314 as a result of interaction with the solar radiation redirection layer. The first light ray 304, hits the glass/air interface with an angle 322, below the critical angle of the glass/air interface, and is refracted with an angle 320, creating an outgoing light ray 306. The second light ray 308 hits the glass/air interface with an angle 315, which is larger than the critical angle of the glass/air interface and is therefore totally internally reflected with an angle 316. The critical angle Q_c is given by: θ„ = arcsin where n₂ is the refractive index of the less optical dense medium, in this case air, and ^ is the refractive index of the more optical dense medium, in this case glass. The refractive index for glass is typically around 1 .5 and for air around 1 .0, resulting in a critical angle of around 42 degrees. The second light ray 308, hits on the opposite side of the glass, the glass/air interface 319, with an incidence angle 317 of equal size as the incidence angle 315. The second light ray 308, is again totally internally reflected with an angle 318, and hits the solar energy harvesting means 31 1 in the bottom of the window, where at least a part of the energy in the light ray is converted into electric energy. It should be noted that only first order refraction is shown in the figure for clarity, however higher order refraction phenomenas are also present. This means that a plurality of harmonics light rays is generated, resulting in a plurality of light rays travelling in the glass. The photonic crystal structure of the solar radiation redirecting layer 307 may be designed to increase the generation of harmonics as this may increase the amount of light trapped in the solar radiation guiding layer 301 , increasing the efficiency of the system. Figure 4a shows a solar energy harvesting system 412, according to an embodiment of the present invention. The solar energy harvesting system 412 comprises a solar radiation redirection layer 407, a solar radiation guiding layer 401 , solar energy harvesting means 41 1 and optionally an intermediate layer 409. In this embodiment the submillimetre features of the solar radiation redirection layer 407, is formed in the same element 410 as the solar radiation guiding layer 401 . The optional intermediate layer 409 has a lower refractive index than the solar radiation guiding layer 401 , allowing solar radiation to be guided within the solar radiation guiding layer by total internal reflection.

Figure 4b shows the function of a solar energy harvesting system 412, according to an embodiment of the present invention. An incoming light ray 402 with a wavelength within the effective interval of the solar radiation redirection layer 407, hits the air/crystal interface 403, with an incident angle. The incoming light ray 402 is split into a first light ray 404 and a second light ray 408, both travelling in the solar radiation guiding layer 401 . The first light ray 404, is refracted with an angle similar to the angle at a normal air/glass interface. The second light ray 408 is refracted with a larger angle as a result of interaction with the solar radiation redirection layer 407. The first light ray 404 hits the interface between the solar radiation guiding layer 401 and the intermediate layer 409, with a angle under the critical angle and is refracted with an angle, creating a light ray 405 travelling in the intermediate layer 409. The light ray 405 travelling in the intermediate layer 409 hits the intermediate layer 409/air interface and is again refracted creating an outgoing light ray

406. The second light ray 408 hits the interface between the solar radiation guiding layer 401 and the intermediate layer 409 with an angle above the critical angle of the interface of the solar radiation guiding layer 401 and the intermediate layer 409, and is therefore totally internal reflected. The solar radiation guiding layer 401 guides the second light ray 408 towards solar energy harvesting means 41 1 , where a part of the energy of the second light ray 408 is converted into electrical energy.

Figure 4c shows the function of a solar energy harvesting system 412, according to an embodiment of the present invention. The solar energy harvesting system 412 comprises a solar radiation redirection layer 407, a solar radiation guiding layer 401 , solar energy harvesting means 41 1 . In this embodiment the submillimetre features of the solar radiation redirection layer

407, is formed in the same element 410 as the solar radiation guiding layer 401 . An incoming light ray 402 with a wavelength within the effective interval of the solar radiation redirection layer 407, hits the air/crystal interface 403, with an incident angle. The incoming light ray 402 is split into a first light ray 404 and a second light ray 408, both travelling in the solar radiation guiding layer 401 . The first light ray 404, is refracted with an angle similar to the angle at a normal air/glass interface. The second light ray 408 is refracted with a larger angle as a result of interaction with the solar radiation redirection layer 407. The first light ray 404 hits the air/glass interface, with a angle under the critical angle and is refracted with an angle, creating an outgoing light ray 406. The second light ray 408 hits the air/glass interface with an angle above the critical angle of the air/glass interface and is therefore totally internal reflected. The solar radiation guiding layer 401 guides the second light ray 408 towards solar energy harvesting means 41 1 , where a part of the energy of the second light ray 408 is converted into electrical energy.

Figure 5a shows a solar energy harvesting system 501 , according to an embodiment of the present invention. The system comprises four solar radiation redirecting layers 513, 514, 515, 516, four solar radiation guiding layers 505, 506, 507, 508, four intermediate layers 509, 510, 51 1 , 512, and four solar energy harvesting means 517, 518, 519, 520. Each solar radiation redirecting layer 513, 514, 515, 516 is designed to redirect solar radiation having wavelengths within different predetermined ranges, as shown in figure 5b. This may be achieved by choosing different distances between the submillimetre features of the solar radiation redirecting layers 513, 514, 515, 516. The solar radiation redirecting layers 513, 514, 515, 516 may be designed to have a combined effective range covering a part of the spectrum of visible light. Under each of the solar radiation redirecting layers 513, 514, 515, 516 s solar radiation guiding layers 505, 506, 507, 508 is placed. Each set of guiding and redirecting layers 513 and 505, 514 and 506, 515 and 507, 516 and 508 may be formed from a common element. Under each solar radiation guiding layer 505, 506, 507, 508 an intermediate layer 509, 510, 51 1 , 512 is placed. Each intermediate layer has a refractive index that is lower than the refractive index of the associated solar radiation guiding layer 505, 506, 507, 508, it is in contract with, thereby enabling the solar radiation guiding layers 505, 506, 507, 508 to guide solar radiation towards solar energy harvesting means 517, 518, 519, 520. The solar energy harvesting means 517, 518, 519, 520 may be designed to be most effective at the specific range of wavelengths of the solar radiation guided towards them. Meaning that the solar energy harvesting means 517 is most effective around the wavelengths of the solar radiation redirected by the solar radiation redirecting layer 513, the solar energy harvesting means 518 is most effective around the wavelengths of the solar radiation redirected by the solar radiation redirecting layer 514, the solar energy harvesting means 519 is most effective around the wavelengths of the solar radiation redirected by the solar radiation redirecting layer 515, and the solar energy harvesting means 520 is most effective around the wavelengths of the solar radiation redirected by the solar radiation redirecting layer 516.

Figure 5b is a spectrum plot showing a schematic example of the effective range of wavelengths for the four solar radiation redirecting layers 513, 514, 515, 516. Each of the solar radiation redirecting layers 513, 514, 515, 516 is designed to redirect solar radiation with different wavelength. The graphs show the percentage of solar radiation I redirected by a given layer for a given wavelength.

Figure 6a shows a design of the solar radiation redirection layer 601 according to an embodiment of the present invention with the submillimetre features 607 arranged on a rectangular grid creating a crystal like structure. The features 607 are in this embodiment protruding rectangles.

Figure 6b shows a design of the solar radiation redirection layer 601 according to an embodiment of the present invention, where the features 607 are designed as rectangles with a single end protruding, creating a triangular appearance in the elevation plane.

Figure 6c shows a design of the solar radiation redirection layer 601 according to an embodiment of the present invention, where the features 607 are designed as protruding cylinders.

Figure 7 and figure 8 shows a solar energy harvesting system 712 used as a window in a room with walls 705, a floor 709 and a ceiling 710 according to an embodiment of the present invention. Figure 7 shows a side view and figure 8 shows a front view of the solar energy harvesting system 712. The solar energy harvesting system 712 is integrated in a window frame 718. The solar energy harvesting means 71 1 , 713, 714, 715 are attached to the window frame 718. In this embodiment solar energy harvesting means 71 1 , 713, 714, 715 is positioned along the entire window frame 718, however alternatively it may only be present in a portion of the frame. The solar radiation redirecting layer 707 is comprised of a plurality of features arranged in regular grid, creating a 2-dimensional photonic crystal structure. The shape of the solar radiation redirecting layer is in this embodiment rectangular. A first portion of the solar radiation incident on the solar radiation redirecting layer 707 is redirected by the 2-dimensional photonic crystal of the solar radiation redirecting layer 707 and guided by the solar radiation guiding layer 701 , at least partly by total internal reflection, towards solar energy harvesting means 71 1 , 713, 714, 715. A second portion of the solar radiation incident on the solar radiation redirecting layer 704, 706 is conducted through the system and into the room fitted with the system, lighting up the room. Preferably the distribution of wavelength of the light conducted through the system 704, 706 is approximately equal to the distribution of wavelength of the solar radiation incident on the system 712. The size of the system is preferably equal to standard window sizes. The solar radiation 708 guided by the solar radiation guiding layer 701 , may be guided in a direction approximately perpendicular to the normal 719 of the solar radiation guiding layer 701 .

Figure 9a-d shows an example of a manufacturing process for making the array of features with a submillimetre scale. First a glass substrate 901 is coated with a sol-gel material 902 as shown in figure 9a, 9b. Then a stamp 903 with a cast of the desired submillimetre scale features is pressed into the sol-gel 902 as shown in figure 9c. The glass substrate 901 , the sol gel 902 and the stamp 903 is then heated to a temperature of approximately 80 degrees for approximately 2 hours to cross-link the sol-gel such that is becomes a fixed structure. The stamp 903 is then removed and the glass substrate 901 with the imprinted sol-gel layer 904 is anealled at 700 degrees C for approximately 2 hours to densify the silica network and decompose the organic groups of the sol-gel. It should be understood that the manufacturing process described above is only mentioned as an example, the submillimetre scale features may be manufactured in a plurality of different ways including the ones described in the article cSBIass nanostructures fabricated by soft thermal nanoimprintD C. Peroz, C Heitz, E. Barthel, V. Goletto and E.

J. Vac. Sci Technol. B, vol 25, issue 4, L27-L30, 2007, the article [Nano Imprint Lithography on Silica Sol-gels: a simple route to sequential patterning DC. Peroz, V. Chauveau, E. Barthel and E.

Advanched Materials, vol 21 , issue 5, 555-558, 2009 and US20090162623.

Figure 10a-b shows a top and a side view of an example of the solar radiation redirecting layer. The solar radiation redirecting layer 1001 comprises an array of features with a submillimetre scale 1002a-d. The features are arranged with a lateral distance 1004 an axial distance 1003 and a height 1005. The lateral distance is preferably in the range 100 nanometers-10 micrometers, the axial distance is preferably in the range of 100 nanometers-10 micrometers and the height is preferably in the range of 20 nanometers-10 micrometers. Preferably the lateral distance 1004 and axial distance 1003 is in the range of the wavelengths of the solar radiation, which the solar radiation redirecting layer 1001 is designed to redirect.

Figure 10c shows a side view of the solar radiation redirecting layer according to an embodiment of the present invention, where the features are holes with a depth 1006. Preferably the depth is in the range 20 nanometers- 10 micrometers.

Figure 1 1 a-b shows a solar energy harvesting system according to an embodiment of the present invention. Figure 1 1 a shows a front view and figure 1 1 b shows a side view. In this embodiment the solar energy harvesting means 1 105 are placed on top of the solar radiation guiding layer 1 104. The solar radiation guiding layer 1 102 is further fitted with guiding structures 1 104 comprising features with a submillimetre scale for allowing the solar radiation to be guided towards the solar energy harvesting means 1 105. The guiding structures may comprise protrusions with an angle of approximately 45 degrees relative to the normal of the solar radiation guiding layer. The guiding structures may be blazed gratings.

Figs. 12a-c show an embodiment of the present invention where the orthogonal distance between at least on point on the surface of the solar radiation redirecting layer and a reference plane is above a determined value. Fig 12 a shows a side view of a solar harvesting system according to an embodiment of the invention. The solar radiation redirecting layer 1203 is formed with periodical spherical convex and concave structures changing the orientation of the local plane the 2 dimensional photonic crystal is formed on. In other embodiments the spherical convex and concave structures may be arranged in an un-periodic random fashion or other shapes may be used e.g. triangular or pyramid shapes. Shown is a first light wave 1204 and a second light wave 1205 travelling towards the solar radiation redirecting layer with a first and a second angle respectively.

Fig. 12b shows a close up of the region of the solar radiation redirecting layer 1203 marked with the square 1206 in Fig. 12a. The features forming the 2 dimensional photonic crystal is shown as a plurality of protrusions formed on the local plane 1208. Shown is also the first light wave 1204 incident on the local plane with a first angle.

Fig. 12c shows a close up of the region of the solar radiation redirecting layer 1203 marked with the square 1207 in Fig. 12a. The features forming the 2 dimensional photonic crystal is shown as a plurality of protrusions formed on the local plane 1209. Shown is also the second light wave 1205 incident on the local plane with a second angle. As the incident angle of the first and the second light wave 1204 1205 is similar in respect to the local planes 1208 1209 e.g. the 2 dimensional photonic crystal sees the first and the second light wave 1204 1205 in the same way, both the first and the second light wave 1204 1205 may be redirected towards the solar energy harvesting means 1202. This will decreases the angle dependency of the system allowing solar radiation incident on the system with a wider range of angles to be redirected towards the solar energy harvesting means 1202.

Fig. 12d shows a side view of a part of the solar radiation redirecting layer 1203 and the reference plane 1212. The reference plane 1212 is orientated and positioned so that the average distance from the reference plane 1212 to all points on the surface of the solar radiation redirecting layer 1203 is minimized. Shown is a point 121 1 having a orthogonal distance to the reference plane above a determine value e.g. above 20 micrometer, 50 micrometers, 100 micrometers, 500 micrometers, 1 millimetre, 2 millimetre, 5 millimetre or 1 cm.

Fig. 13a-b shows designs of the submilimetric features of the solar radiation redirecting layer, according to embodiments of the present invention where the distance between the features are varied across the solar radiation redirecting layer.

Fig. 13a shows an embodiment of the present invention where the distances between the features of the solar radiation redirecting layer are varied along a single axis. In this embodiment the width of the features is additionally varied.

Fig. 13b shows an embodiment of the present invention where the distance between the features of the solar radiation redirecting layer varies along two axes. Although some embodiments have been described and shown in detail, the invention is not restricted to them, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilised and structural and functional modifications may be made without departing from the scope of the present invention.

In device claims enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims or described in different embodiments does not indicate that a combination of these measures cannot be used to advantage. It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

Claims:

1 . A solar energy harvesting system for collection of solar energy, comprising;

- a solar radiation redirecting layer, comprising an array of features with a sub millimetre scale creating a 2 dimensional photonic crystal, adapted to redirect solar radiation having a predetermined range of wavelengths; and

- a solar radiation guiding layer for guiding solar radiation;

characterized in that the system further comprises solar energy harvesting means adapted to convert solar energy into electric energy; where the solar radiation redirecting layer redirects solar radiation with the predetermined range of wavelengths, towards the solar energy harvesting means.

2. The solar energy harvesting system according to claim 1 , wherein a portion of the solar radiation redirected by the solar radiation redirecting layer is guided towards the solar energy harvesting means by total internal reflection in the solar radiation guiding layer.

3. The solar energy harvesting system according to claim 2, wherein the system further comprises an intermediate layer attached to said solar radiation guiding layer, wherein said intermediate layer has a refractive index which is lower than the refractive index of the solar radiation guiding layer, allowing solar radiation to be guided within said solar radiation guiding layer.

4. The solar energy harvesting system according to any of the preceding claims, comprising a plurality of solar radiation redirecting layers and a plurality of solar radiation guiding layers, wherein a first solar radiation redirecting layer is attached to a first solar radiation guiding layer, and a second solar radiation redirecting layer is attached to a second solar radiation guiding layer, where the first solar radiation guiding layer is adapted to guide a portion of the solar radiation redirected by the first solar radiation redirection layer towards a first solar energy harvesting means; and the second solar radiation guiding layer is adapted to guide a portion of the solar radiation redirected by the second solar radiation redirection layer towards a second solar energy harvesting means.

5. The solar energy harvesting system according to claim 4, wherein the first solar energy harvesting means and the second solar energy harvesting means are the same.

6. The solar energy harvesting system according to any of the preceding claims, wherein the solar energy harvesting means is optimized to convert solar radiation within the predetermined range of wavelengths into electric energy.

7. The solar energy harvesting system according to any of the preceding claims, further comprising a frame comprising the solar radiation guiding layer, wherein the solar harvesting means are fitted at said frame.

8. The solar energy harvesting system according to any of the preceding claims, wherein the solar radiation guiding layer further comprises features with a submillimetre scale adapted to guide light out of the solar radiation guiding layer, towards solar energy harvesting means positioned on top of the solar radiation guiding layer.

9. The solar energy harvesting system according to any of the preceding claims, wherein the solar radiation guiding layer further comprises features adapted to guide light, guided within the solar radiation guiding layer by total internal reflection, out of the solar radiation guiding layer, towards solar energy harvesting means positioned on top of the solar radiation guiding layer.

10. The solar energy harvesting system according to any of the preceding claims, wherein the distribution of wavelengths in the visible spectrum of the solar radiation conducted through the system is approximately unaffected.

1 1 . The solar energy harvesting system according to any of the preceding claims, wherein the solar radiation redirecting layer is adapted to redirect solar radiation with wavelengths in the ultraviolet spectrum.

12. The solar energy harvesting system according to any of the preceding claims, wherein the system comprises at least one solar radiation redirecting layer adapted to redirect solar radiation with wavelengths in the red spectrum of visible light, at least one solar radiation redirecting layer adapted to redirect solar radiation with wavelengths in the green spectrum of visible light, and at least one solar radiation redirecting layer adapted to redirect solar radiation with wavelengths in the blue spectrum of visible light.

13. The solar energy harvesting system according to any of the preceding claims, wherein the features of the solar radiation redirecting layer are arranged with a lateral distance L between them, an axial distance M between them and a height H, where L is in the range 100 nanometers-10 micrometers, M is in the range 100 nanometers-10 micrometers and H is in the range 20 nanometers-10 micrometers.

14. The solar energy harvesting system according to any of the preceding claims, wherein the solar radiation redirecting layer is configured to redirect light with a particular wavelength, incident on the solar radiation redirecting layer within a range of angles:

- wherein the orthogonal distance between the surface of the solar radiation redirecting layer and a reference plane is above

20 micrometers for at least one point on the surface of the solar radiation redirecting layer, wherein the reference plane is orientated and positioned so that the average of the orthogonal distances between all points on the surface of the solar radiation redirecting layer and the reference plane is minimized, and/or

15. A method of manufacturing a solar energy harvesting system according to any of the preceding claims, wherein the features of the solar radiation redirecting layer are created in a predetermined pattern by plastic or viscoplastic deformation being carried out by exerting pressure on said solar radiation redirecting layer with a mask element, said solar radiation redirecting layer being translated continuously relative to said mask element and said mask element being moved about an axis parallel to the plane of the solar radiation redirecting layer.