FI126010B

FI126010B - Solar collector integrated in a window at a wavelength selective translucent element

Info

Publication number: FI126010B
Application number: FI20130276A
Authority: FI
Inventors: Ari Järvinen; Antti Pennanen; Jussi Toppari
Original assignee: Jyväskylän Yliopisto
Priority date: 2013-09-25
Filing date: 2013-09-25
Publication date: 2016-05-31
Also published as: WO2015044525A1; FI20130276A

Description

A WINDOW INTEGRATED SOLAR COLLECTOR BY WAVELENGTH SELECTIVE TRANSPARENT ELEMENT

The present invention relates a window including - a transparent element, including - a substrate made of glass or other optically similar material, - a layered structure arranged on at least one side of the substrate which is wavelength selective for an electromagnetic radiation, a frame construction arranged to border the edges of the transparent element at least partially.

Common tendency for buildings today is to have large window areas. This allows natural lighting of the building space but has the side effect of excessive heating of room air by longer wavelengths of solar radiation, i.e. infrared radiation (IR) or heat radiation. This excess heat needs to be removed by using air conditioning, which is very energy consuming and costly.

This problem has been commonly dealt with wavelength selective coatings on glass, which prevents the excess IR-radiation from penetrating to inner parts of the buildings. These so-called energy saving windows indeed help in solving the problem of excess heating and lower the expenses needed for the air conditioning, but simultaneously waste all the energy of the incoming IR.

Some means are known for collecting of solar energy. However, adoption of solar energy by consumers is hindered by the conceived difficulty of installation and need of large open areas. Conventional solar collectors and panels require substantial amount of open space to be arranged for installation.

The transparent solar panels on the market today use the visible part of the solar spectrum for energy production and thus cause significant dimming of light transmitted through the window, hindering the natural lighting. Or they are built from alternating pieces of transparent glass and opaque solar cells. This is mostly due to the higher efficiency of the electrical solar cells on the shorter wavelengths.

In addition to the drawbacks above, in the solar panels (and other photovoltaic cells) lay also the problem concerning their efficiency that is typically only 15 - 18%. The efficiency of the panel is partly limited by the temperature. By the lower temperature the efficiency of the panels would be higher. This could be achieved by removing the IR radiation from the arriving light. However, naturally this energy would be good to be collected also.

The present invention is intended to create a window by means of which the selected part of the radiation spectrum can be collected for energy use without essentially affecting to the rest of the light transmitted through the window. Especially, the non-visible IR radiation is collected for energy use and the visible light is transmitted intact, e.g., for lightning purposes. The present invention includes creation of a transparent element by means of which the radiation can be selectively collected without essentially effecting to the rest of the light transmitted through the element. In addition, the present invention is also intended to create a photovoltaic cell achieving higher efficiency by means of the transparent element. The characteristic features of the window according to the invention are stated in the accompanying Claim 1 and those of the solar thermal collector in Claim 11, respectively.

In the invention, the transparent element will be applied in a window in order to selectively guide IR radiation to the window frame while letting the visible light through intact. The window also includes collector means at its frame for collecting the radiation from the waveguide layer of the transparent element. The layered structure of the transparent element includes at least one plasmonic nanoparticle layer arranged to filter out at least part of the radiation and at least one waveguide layer arranged to collect at least part of the radiation filtered out by means of at least one plasmonic nanoparticle layer. By this kind of structure it is possible to filter the radiation selectively which opens many interesting applications in addition to the window.

By means of the invention, several important benefits are gained. First of all, the window including integrated solar collector according to the invention uses a coating that prevents IR radiation i.e. the longer wavelengths from entering the building. Instead of wasting the energy, it collects and possibly converts it to useful energy. Thus, the benefits from such a window glass will be at least double compared to a usual selective window glass. In other words, the window integrated solar collector at the same time decreases energy consumption of a building by avoiding the need of air conditioning and provides additional energy by harvesting IR radiation.

The window integrated solar collector may be installed in place of conventional windows, thus allowing the use of designed and constructed window area for harvesting of solar energy, too. Also pre-existing windows from older buildings could be changed and used for harvesting of solar energy.

Another interesting application of the window is in photovoltaic cells. Owing to the window's transparent element the temperature of the photovoltaic cell may be lowered by filtering out part of the radiation and guiding that away. The lowered temperature makes possible higher output currents and improved efficiency. In addition, if desired the radiation filtered out may also be applied for energy harvesting, too, by the means of the window frames including the collection. The other characteristic features of the window and element according to the invention are stated in the accompanying Claims while additional benefits achieved are itemized in the description portion .

In the following, the invention, which is not restricted to the embodiments presented in the following, is described in greater detail with reference to the accompanying figures, in which

Figure 1 shows a rough diagram of the principle of one embodiment of the transparent element as a cross-section,

Figure 2 shows the window in which the solar panel comprising the element have been applied for energy collection and

Figure 3 shows a rough diagram of the principle of another embodiment of the transparent element as a cross-section in connection with a photovoltaic cell.

Figure 1 illustrates an example of the element 30 as a rough diagram of the principle. In this case the element 30 that is applied in a window 10 having integrated solar collector functionality, includes a substrate 11 made of glass or other optical similar material. In addition, the element 30 includes also a layered structure 12 arranged on the substrate 11. In the window 10 the substrate 11 is transparent acting as a conventional window glass. The layered structure 12 may be understood as a coating having at least one layer. In addition, the layered structure 12 is now on at least one side of the substrate 11. The layered structure 12 is wavelength selective. This means the selectivity for an electromagnetic radiation.

The layered structure 12 on the window glass 11 includes at least one waveguide 14. In addition, the layered structure 12 on the window glass 11 includes also at least one plasmonic nanoparticle layer 13. The plasmonic nanoparticle layer 13 is arranged effectively into vicinity of the waveguide 14. Here the "vicinity" means that the energy from the plasmonic nanoparticle layer 13 is able to transfer to the waveguide 14. According to one embodiment the waveguide 14 may be next to the plasmonic nanoparticle layer 13 but this is not necessary in any case.

The function of the waveguide 14 is to transfer at least part of the radiation, especially longer wavelengths, scattered from at least one plasmonic nanoparticle layer 13. The waveguide 14 may be a planar layer of material which has high refractive index relative to the surrounding material. In addition, the waveguide 14 supports trapped propagating electromagnetic modes. The function of the waveguide 14 is to transfer the radiation filtered out by means of the plasmonic nanoparticle layer 13 in order to collect that. The transfer of the radiation filtered out takes place in the planar direction within the waveguide 14. The radiation may be collected to the edges of the waveguide layer 14 i.e. of the element 30. Waveguide 14 may be situated on either or both sides of the glass 11 and in any or all glasses of multi-glass windows 10. Also the window glass 11 may itself act as a waveguide 14.

At least one nanoparticle layer 13 may be situated on top of or below the waveguide 14, or on the opposing side of the glass 11 relative to the waveguide 14, or some combination of the aforementioned positions. Plasmonic nanoparticles 19 form- ing the layer 13 may be particles 19 that have dimensions of 1 - 1000 nm. Plasmonic nanoparticles 19 exhibit localized surface plasmon resonance under electromagnetic radiation.

The nanoparticle layer 13, i.e. the plasmonic particles 19, may also be separated from the waveguide 14 by at least one spacer layer 16. The refractive index of the material forming the spacer layer 16 may be less than that of the waveguide 14. In other words, a spacer structure 16 is arranged between the at least one plasmonic nanoparticle layer 13 and the waveguide 14. The spacer structure may have a variable thickness.

The effect of at least one nanoparticle layer 13 is to scatter the longer wavelengths of incident solar radiation into the waveguide layer 14 while allowing the visible portion of the spectrum to be transmitted through the waveguide 14 and the substrate 11 i.e. through the window 10. In other words, the nanoparticle layer 13 acts as a low-pass filter. This is achieved by exploiting the so called localized surface plasmon resonance (LSPR) phenomenon. By altering the particle composition, size, shape and/or refractive index at the vicinity of the particle 19 the plasmonic resonance may be tuned to at least one desired wavelength or wavelength range in order to target the scattering effect to longer wavelength radiation while minimizing the effect on visible part of the spectrum. The scattering effect is largest on the wavelengths longer than the surface plasmon resonance wavelength. Here longer wavelength radiation means radiation with wavelength λ > 750 nm (i.e. wavelengths above the visible spectrum). This is also known as infrared radiation (IR).

The waveguide layer 14 traps/converts the longer wavelengths scattered by the particle layer 13 into the guided modes of the waveguide 14 which further transmit, generally collects, the radiation to the edges of the window glass 11 where it may be harvested. For this purpose collector means 15 have been arranged in connection with the element 30 at the window 10 frame, i.e., for collecting the radiation from the waveguide layer 14. Figure 2 presents the window 10 having the element 30 as a window material. Some portion of the radiation may be lost to heat in the particles 19 or in the waveguide 14, but also this heat may be partially collected and converted into useful energy via heat conductivity of the element 12 and glass 11.

Spacer layer 16 may be used to separate the particle layer 13 from the waveguide 14 to prevent outcoupling of the trapped modes by the particles 19. The window glass 11 may itself act as spacer layer, too. Outcoupling means herein loss of electromagnetic radiation from the waveguide 14 via scattering by the nanoparticles 19. Trapped modes mean herein electromagnetic radiation that propagates in the waveguide 14 and decays exponentially outside.

Harvesting of the light from the edges of the window 10 may be realized by any suitable solar energy method, i.e. basically either via photovoltaics (electric solar cells) or solar thermal (liquid heated by the radiation). Even both of these methods are well-known the benefit of window integrated solar collector is that the needed active area is many times smaller than in classic solutions, since the window 10 concentrates all the harvested radiation to the edges. From the above methods solar thermal may be more suitable and convenient since the needed liquid tubes 18 are relatively easy to integrate to the window frame 17 (Figure 2) which borders the edges of the transparent element 30 at least partially. It is also more efficient (efficiency usually > 90%) since the photovoltaic have the lowest efficiency exactly on the IR range. Integration of the solar thermal tubing 18 and collecting the IR energy to that is also a major part of the invention. The col lected heat could be used e.g. to heat the house water or to generate other energy, or even for air conditioning via thermal pumps. Reference sign 22 relates to this generally. Yet, especially in Finland and other Nordic countries at the winter times the heat could also be returned to the interior via radiators .

Figure 1 discloses schematically an example of the element 30 according to the invention that is applied as a window integrated solar collector according to the invention. In the outermost layer 13 facing in this case the solar radiation there are plasmonic nanoparticles 19 made of metal with a clear surface plasmon resonance. The plasmonic nanoparticle layer 13 is arranged to filter out at least part of the incoming radiation. The material of the nanoparticles 19 may be, for example, silver or gold. Gold is advantageous since it does not oxidize. Next is spacer layer 16. That is made of material with relative low refractive index, n, for example, same as glass 11 (n ~ 1.5) or lower. Easiest to fabricate and suitable choice would be silicon dioxide, for example. Next is the waveguide layer 14. That can be made of high refractive index material with low absorbance, i.e., real part of the index much higher than that of the glass 11 [Re(n)>>1.5, desirable Re(n)>2] and low imaginary part of the index [Im{n)<<Re{n)] . Suitable materials include e.g. titanium dioxide, hafnium dioxide, and silicon nitride. Waveguide 14 is on the window glass 11 which may be regular window glass without any surface treatments.

It should be noted that there may be one or more waveguides 14 and they may be situated on either or both sides of the glass 11. There may be one or more nanoparticle layers 13 and they may be situated on top of or below the waveguide 14 or on the opposing side of the glass 11 relative to the waveguide 14, or some combination of the aforementioned positions. At least one spacer layer 16 is now also arranged on the element 30 which has a refractive index less than that of the waveguide 14. The glass 11 may also itself act as a spacer layer. Thickness dwc of the waveguide layer 14 may be 0.1 - 100 pm. Thickness dspc of the spacer layer 16 may be 0-2 pm. Examples of the dimensions of the nanoparticles 19 are: height 1lnp= 20 - 200 nm, diameter dNP = 10 - 500 nm (circular discs) . Also similar sized totally spherical nanoparticles could be used.

The window integrated solar collector 10 may be installed in place of conventional windows thus allowing solar energy to be harvested from the large window areas of modern buildings. The window integrated solar concentrator, on comparison, uses the longer wavelengths (IR radiation) of solar radiation for energy production while allowing the visible part of the solar spectrum to enter through the window, thus not affecting the visible light at all (or very little) .

Figure 3 discloses another embodiment for the transparent element 30 that is now in connection with the photovoltaic cell 20 (Figure 2). Typically these cells 20 include a photovoltaic cell element 21 producing electric current in a known manner. The transparent element 30 has been integrated on the surface of the cell element 21. The layer structure 11, 12 of the transparent element 30 may be similar like disclosed in connection with the Figure 1. According to the first embodiment the waveguide layer 14 may only transfer the heat radiation away from the cell 20 without any energy harvesting. According to another embodiment the heat radiation transferred by the waveguide 14 may be harvested, like in the case of the window 10 presented in Figure 2. In this case the photovoltaic cell 20 includes the collecting means around it. The transparent element 30 raises the efficiency of the photovoltaic cell 20 since it filters out and guides the heat radiation away before the radiation arrives to the cell 21.

The present invention relates to a solar thermal collector system, too. That include a collector, i.e., heat source 10, 20 and means 22 for distribute heat from the heat source 10, 20. The heat source may be a window 10 or a photovoltaic cell 20 disclosed above. The heat distributor may be a device 22 known as such.

It must be understood that the above description and the related figures are only intended to illustrate the present invention. The invention is thus in no way restricted to only the embodiments disclosed or stated in the Claims, but many different variations and adaptations of the invention, which are possible within the scope on the inventive idea defined in the accompanying Claims, will be obvious to one skilled in the art.

Claims

A window comprising: - a transparent element (30) comprising: - a substrate (11) made of glass or other optically similar material, - a layered structure (12) arranged on at least one side of a substrate (11) wavelength-selective for electromagnetic radiation, a frame structure (17) adapted to border at least partially the edges of the transparent element (30), characterized in that - the layered structure (12) of the transparent element (30) comprises - at least one layer (13) of plasmonic nanoparticles arranged to filter out at least part of the radiation, one waveguide (14) adapted to collect the filtered radiation filtered off by at least one plasmonic nanoparticle layer (13), - the IR radiation being selectively collected by the transparent element (30), - the visible wavelengths being passed substantially unchanged, the window (10) Ceramic a transparent element (30).

Window according to Claim 1, characterized in that an intermediate layer (16) is arranged between the waveguide (14) and the at least one plasmonic nanoparticle layer (13).

Window according to Claim 1 or 2, characterized in that the waveguide (14) is a planar layer of material having a high refractive index compared to the surrounding material and adapted to maintain bound propagating electromagnetic modes.

Window according to Claim 2 or 3, characterized in that the refractive index of the material of the intermediate layer (16) is arranged to be lower than the refractive index of the waveguide (14).

Window according to one of Claims 1 to 4, characterized in that the plasmonic nanoparticle layer (13) comprises gold nanoparticles (19).

Window according to one of Claims 1 to 5, characterized in that the real part of the refractive index of the material of the waveguide (14) is Re (n) >> 1.5, more particularly Re (n)> 2 and the imaginary part of the refractive action is Im (n) << Re of).

Window according to one of Claims 2 to 6, characterized in that - the thickness (dWc) of the wave jet (14) is 0.1 - 100 µm, - the thickness (dSpc) of the intermediate structure (16) is 0 - 2 µm.

Window according to one of Claims 5 to 7, characterized in that - the nanoparticles (19) have a height (hNP) of 20 - 200 nm, - the nanoparticles (19) have a diameter (dNP) of 10 - 500 nm.

Window according to one of Claims 1 to 8, characterized in that the collecting means (15) comprise fluid pipes (15) integrated in the frame structure (17) of the window (10).

Window according to one of Claims 1 to 9, characterized in that the collecting means (15) comprise at least one solar cell element integrated in the frame structure (17) of the window (10).

A solar thermal collector system comprising: - a heat source (10, 20), means (22) for distributing heat from a heat source (10, 20), characterized in that the heat source is a window (10) according to any one of claims 1 to 10.