WO2013040672A1

WO2013040672A1 - Solar to electric energy transformer based on luminescent glass solar radiation concentrator

Info

Publication number: WO2013040672A1
Application number: PCT/CA2011/001036
Authority: WO
Inventors: George BITSADZE; Vasily JORJADZE; Vladimir Ivanovich Rykalin; Natalia Vladimirovna RYKALINA
Original assignee: Bitsadze George
Priority date: 2011-09-20
Filing date: 2011-09-20
Publication date: 2013-03-28

Abstract

The goal of this work is a creation of construction glass, which converts part of the light passing through it into the electrical energy. The use of such glasses in the construction industry will convert part of the incident on the structure of the building a solar energy into the electricity, which allows having an additional constant source of electrical energy, which can reduce dependence on external electric power source, and in some cases will have an independent power source. Based on the luminescence phenomenon, a sample of multilayer luminescent glass was designed, which converts part of the light passing through it into an electrical energy. Designed sample of glass or the working module meets all the characteristics of glass as a building material and has an extra feature - re-emits part of the incident on the glass surface light at an angle with respect to the incident beam, transports most of the re- emitted light towards the semiconductor converters of the light energy into electricity, placed on the core plate of the glass.

Description

Solar to Electric Energy Transformer based on Luminescent

Glass Solar Radiation Concentrator

Introduction

The vast majority of energy on the Earth in some or other form is a solar energy received from the sun. To transform a solar energy into electricity in most convenient way of usage, a semiconductor converters of photon energy into the electrical energy - a solar batteries, or as they are commonly referred to as solar panels, got a great widespread. The range of solar panels application is wide: batteries from a few milliWatts to industrial projects - commercial solar power plants. Remains an open question about the possibility of using semiconductor transducers for generating commercial power because of the high cost of converters and the need for alienation of relatively large areas in the vicinity of electricity users.

Adding new features to the building materials, namely the conversion of light energy incident on the buildings into electrical energy, represents a great interest. The outer surfaces of modern buildings have a fairly large area, and consequently their surface gets as much of the direct sunlight as reflected and diffusive scattered light. Transformation of the entire incident light energy into electrical energy by the materials from which the building is constructed, and use that same energy to meet the needs of the building, thus reducing the consumption of external commercial sources of energy, or work independently, in our opinion, is one of the challenges of the future of energetics.

Glass as a building material has a very long history. Particular importance is attributed to the glass in modern architecture, where it is used not only in windows and doors, for the passage of light and weather protection, but also as a lining material for the building. Thus, in modern architecture, the use of glass as a building material has increased many times. Key properties of glass as a building material are: sufficient mechanical strength, high transparency, chemical inertness, the ability of ease clean from the dust contamination, repeated withstand to winter-summer cycle.

Any newly developed glass must first meet all the above properties of the glass, and adding new features, such as getting electricity from the part of the incident on the glass light during extended period of time, makes the glass more attractive building material.

Article [1] studied the effect of sunlight, passed through the liquid fluorescent substances, on plants and proposed an idea of greenhouse construction transmitting a specific wavelength of light and use of part of energy of re-emitted light.

In this paper we propose a working sample of the glass. When light passes through it, the portion of the light is transported to the small edges on the perimeter of the glass, where semiconductor converters transferring light into electrical energy with significantly less working surface are located.

Offered Solar to Electric Energy Transformer based on Luminescent Glass Solar Radiation Concentrator is a multilayered luminescent glass or multilayered luminescent concentrator, has all the above characteristics of ordinary glass and adds an important new characteristic - when light passes through the glass, portion of the incident light is converted into the electrical energy.

We describe our sample glass and present experimentally measured results with this sample glass. The results of simulation of light output are also presented.

Principle of operation

Window glass or glasses used in architecture when constructing high-rise buildings, can be considered as a plane-parallel plate with finite dimensions or as a prism whose height is significantly less than its length and width, but much longer than the wavelength of light. Let's consider the release of the fluorescent light in such a plate.

In [2,3] the output of fluorescent light from the symmetrical radiator surrounded by air or other medium is considered in detail, in particular from rectangular prism, to an infinite slab (flat parallel plate]. In [2] data on output of fluorescent light for rectangular prism and a parallel plane plate of unlimited size, surrounded by air, for different refractive indexes n are given.

Lets consider a case of fluorescent light output through a rectangular prism faces, the length and width of which have finite dimensions, much larger than the height of the prism, or that is the same as the parallel plane plate of finite dimensions with a refractive index n.

Lets consider a three-dimensional coordinate system (Fig. la), in which the length and width of the plate are parallel to the axes OX and OY respectively, and the axis OZ, respectively is perpendicular to the two large faces of the plates, which are parallel to the XOY plane and are in optical contact with the material, with refractive index n_h so that n> n₃. Four small area faces of the plate are parallel to the planes XOZ and YOZ respectively, are in optical contact with the material, with refractive index of n₂ (Fig. lb.). When rij = n₂, we have the cases described in [2,3].

The yield of luminescent light in this geometry is as follows: through two large faces, that are in optical contact with a material with a refractive index n will leave a light caught inside a cone, the symmetry axis of which is parallel to the axis Z, perpendicular to the surface of the large face, a half opening angle of which is:

a_c = arc sin (rii / n), and through small face, which are in optical contact with a material whose refractive index n₂, the light will leave, caught in a cone with symmetry axis parallel to the X or Y, respectively, perpendicular to the surfaces of the corresponding face, the half opening angle of which is:

β_ε = arc sin (n₂ / n).

Light rays, do not fall into these cones will not be able to leave the plate, when the small edges around the perimeter of the plate are perpendicular to the large faces, that is when we have a rectangular prism [2,3].

The solid angle corresponding to the cone of large face is equal to:

Ω_α = 2π (1-cos _c).

Accordingly, for the small faces the solid angle is:

Ω_β = 2n[l-cos p_c).

The amount of light emitting from the plate is equal to:

F_E = 2F_A + 4F_B = (2Ω_α + 4Ω_β) / 4π,

where F_A - the amount of light escaping through the large face, and the F_B - the amount of light escaping through the small face.

Accordingly, the amount of light not released from the plate or the number of trapped light is [2,3]:

F_T = 4π - F_E

It should be noted that when the prism or plate with six faces are in contact with the same substance, starting from the critical angle equal to 6_C > 45, the cones begin to overlap and caught in the overlap area light can leave through any of the mutually perpendicular faces. If the value of θ > 54.7, radiation cones overlap so, that the whole light can come out of the plate, that is no trapped light in the plate.

Reduction of amount of trapped light F_T, not leaving the plate and increase by the same amount of escaping light through the small faces, can be achieved by following ways:

1. Changing the geometry of the plane of lateral faces, which is equivalent of changing the geometric shape of rectangular parallelepiped into a more complex geometric shape, namely the replacement of one side face of the plane, into two planes at an angle to each other - a convex polygon;

2. Locating in an optical contact of small edge of the plate material with the same refractive index as the plate [3]. In this case, the entire luminous flux F_T will go outside of the plate and accordingly will leave the plate, going into the FB.

Thus, if small faces on the perimeter of the plate are in optical contact with the adjacent material with a refractive index equal to the refractive index of the plate, then all trapped light F_T will leave the plate through the small faces.

If one adds luminescent material inside the plate, that can intercept photons of light, and then re-emit them isotropic, one can achieve significant yield of re-emitted light along the perimeter of the plate. Those types of plates are widely commercially available in many countries. Having installed around the plate perimeter a semiconductor wafer converters of light energy into electrical energy, one can transfer light flux released through a small edges into the electrical energy. Thus we will obtain the optically transparent plate, with the passage of light through it, with substantial portion of incident light converted into the electrical energy.

Working module

We have created a working module of Luminescent Glass Solar Radiation Concentrator - a multilayered luminescent concentrator, which consists of a central luminescent plate (core) based on polystyrene with a refractive index of n = 1.58, in which we added spectral converters shown in Table 1 (see Appendix 1). The core plate should have the widest possible range of absorption of solar radiation and close to 100% conversion efficiency of absorbed light into the fluorescent light with photon energy slightly above the band gap of semiconductor converters of solar batteries, as well as high transparency to luminescent light.

As noted above, in order to reduce the yield of the luminescent light through two large front faces of the plate, parallel to the plane XOY, both these two faces need to be in optical contact with the substance with the smallest possible refractive index, than the plate. As such a shell, a silicone organic compound SIEL with a refractive index of /?3 = 1.44 was used. In order that the core plate, covered with compound, was mechanically strong and a chemically inert, was covered on both sides by regular mineral glass of 6 mm thick. During manufacturing of the prototype the core was covered with a liquid SIEL with a hardener. It was superimposed by glass plates and then carried out the thermal polymerization of the compound. The result of this is a monolithic multilayer plate - luminescent light radiation concentrator or multilayer luminescent glass (hereinafter - the glass). All this five-layer system after heat treatment is optically transparent and mechanically rigid. Working model of the plate core has a size of 2x120x105mm³. The perimeter of the core plate is L - 450 mm. The average total thickness of the glass is 14.6 mm. Thus, the thickness of the compound on each side of SIEL is 0.3 mm.

Figure 2 shows a schematic cross-section, and the Figures 3a,b,c, shows the photos of the working sample of the multilayer luminescent light concentrator.

To measure the characteristics of the multilayer luminescent concentrator, different semiconductor converters of light into the electricity, such as highly sensitive broadband photo diode S1723-05 7G of Hamamatsu, with the size of the photo cathode of 10 x 10 mm², and solar panels BP-Z911-C4 of Panasonic, consisting of four elements of the amorphous silicon, each of 7 x 9 mm² on a glass substrates, that are specifically designed for operation on diffuse scattered light, were used. These batteries are less effective in direct sunlight and more efficient for luminescent and diffusively scattered light. In particular, these batteries are used in calculators of the Texas Instruments company, not as a charger for the calculator electric circuit, but as the only source of power without any additional DC source. It should be noted that these calculators are working well in any light.

Semiconductor converters were glued around the perimeter of the plate core with an optically transparent epoxy resin and sealed by opaque cover, in order to avoid direct light falling onto the photo detectors. As a result, the prototype has the active size of 90 x 72 mm² (Fig. 3c], which gets direct light.

All six sides of the plate core with refractive index n - 1.58 was surrounded by agents as shown in Figure lb. Big faces are in optical contact with the shell core SIEL compound with a refractive index of n₃ - 1.44, and four small faces on the perimeter with a mineral glass, the substrate of solar panels BP-2911-C4, with a refractive index in the worst case, equal to n₂ = 1.46.

In this geometry, for large faces parallel to the plane XOY, the critical angle for total internal reflection of luminescent light, arising in the core plate, is determined from the expression:

c = arc sin (nt / n) = arc sin (1.44 / 1.58) = arc sin (0.9113924) = 65.7°

Consequently, through each of the large faces will leave the light caught in the cone with an angle of 2a_c = 131.4°, whose axis is perpendicular to the large faces or are inside the solid angle:

Ω_α - 2 n (l-cos _c) = 3.697413 Steradian

Thus, through two large faces of the core will leave a light caught in the solid angle:

F_A = 2 Ω_α = 7.394826

which is 58.85% of the luminescent light.

When the small faces of the plate core are in contact with an air, the critical angle of total internal reflection for small faces of the plate around the perimeter of the core will be:

β₀ = arc sin (1.0002926 / n) = arc sin (1.0002926 / 1.58) = arc sin (0.633096) = 39.3° In our case, the small faces of the plate core are parallel to the planes XOZ and YOZ respectively, and are in optical contact with the glass, refractive index of which, taking it as for a mineral glass, will consider to equal to n₂ = 1.46. In this case the critical angle for small faces will be:

β = arc sin (n₂/ n) = arc sin (1.46 / 1.58) = arc sin (0.924051) = 67.5° The sum of critical angles for both large and small faces is:

a_c + _c = 67.5° + 65.7° = 133.2° > π/2

exceeds π / 2. When the sum of cones opening angles, axes of which are perpendicular to the large and the small faces exceeds π / 2, cones will partly overlap each other and the light, caught in the area of cones intersection, has the opportunity to go through the large surface, and as well through the small surface, depending on at which point in the core the radiation has occurred. In addition, when the critical reflection angle exceeds:

a_c > 54.7°; β > 54.7°

in this case there is no trapped light or the radiation which does not leaves the plate. Therefore, the lower limit of the amount of light leaving through four small edges around the perimeter of the plate, is:

F_B = 4 n - F_A = 12.566371 - 7.394826 = 5.171491

or 41.15% of the total luminescent light.

Simulation of the luminescent light output

Luminescent light output from a variety of geometric shapes is described in the literature in detail, for example in [2,3]. Window glass can be considered as a rectangular prism, whose height is much smaller than the length and width and as an infinitely large parallel plane plate. However, the amount of trapped light of two geometric shapes, a rectangular parallelepiped and an infinitely large parallel-plane plate are different (see Table 1 in [2]). Therefore we need to figure out which considered geometric figure corresponds to a pane glass, depending on its size.

In order to determine the yield of the luminescent light through a small edge around the perimeter of the core plate, as well as to determine the amount of light trapped in the plate, we used simulation program GEANT [4]. Point of luminescent light was simulated uniformly throughout the volume of the core plate of size of 100x100x2 mm³ in the coordinate system shown in Figure la, and the light output through the plate faces was determined. We simulated output of luminescent light from all sides of the plate surrounded by air. Figure 4 shows the results of simulations comparison with the data of [2] for the rectangular prism. The agreement is more than satisfactory.

Further we simulated the output of luminescent light from the core plate size of 100x100x2 mm³, with a refractive index of n - 1.58, large and small faces of which are in optical contact with substances with different refractive indexes ranging from air πι = 1.0002926, and finishing material with a refractive index equal to the refractive index of the plate core. Figure 5 shows the results of the simulation. From Figure 5 it is evident that the total yield of light through four small edges of the core plate with a refractive index n = 1.58 reaches maximum of 62% at the rti = 1.2. At the same time through two large faces leaves about 35% of the light and about 3% of the light does not leaves the core plate at all, being in captivity. Starting from n₃ = 1.29, when the critical angle is _c > 54.7°, all the light leaves the plate, and through four small faces its amount is about 60% of the light.

Obviously, light trapped in the rectangular prism after multiple reflections necessarily will be reflected from the small faces. Figure 6 shows number of reflections from the large faces of the rectangular prism until the first hit on the small faces for the plate of size of 100x100x2 mm³.

Luminescent light output of a rectangular prism and a parallel plane plate is different, when the length and width of the plate substantially exceeds of its thickness. To study this phenomenon, we simulated amount of light trapped in a plate with different geometric dimensions at a constant thickness. Figure 7 shows the dependence of the number of trapped light in slabs of various sizes with thickness of 2 mm, from the refractive index of the plate substance for different plate sizes. The results are compared with those of [2]. It is seen that when the ratio of the length and width of the plate to its thickness LXY / LZ = 50, a plate can be considered as a rectangular prism. When this ratio rises, the light output is close to an infinitely large plate or a parallel plane plate. Figure 8 shows the dependence of the trapped light amount on the ratio of LXY / LZ for a plate with a refractive index of n = 2.00. Left lower plateau, for which LXY / LZ < 10² coincides with the results of [2] for a rectangular prism, and after the values of LXY / LZ > 10⁵, right upper plateau, coincides with the results of [2] for an infinitely large plates. This coincidence is due to the fact that the program GEANT makes 10000 steps in the volume for each simulated photon and after stops it propagation. When we increase the number of steps in GEANT to larger values (10⁵ or to largest we did, 2xl0⁶), more photons, which for default step number were considered as trapped, start to leave the volume. At infinite limit all trapped photons will leave the volume, but this difficult to check, because calculation time of simulation increases dramatically with increasing of step numbers.

Study of characteristics

Characteristics of the working module of luminescent multilayer glass were studied for different wavelengths of incident light on the glass surface, for the sun and diffusive scattered light on clouds, as well as for daylight from the gas discharge lamp. When illuminating frontal part of the glass through the collimator, limiting the spot size and hence the amount of the light on glass, the semiconductor light converters delivers an electrical power on a resistor R, which is measured by the ammeter and the voltmeter in the circuit, as shown in Figure 9. The electrical circuit of the semiconductor converters can measure a single element independently, as well as all twelve elements arranged in optical contact to small edges around the perimeter of the core plate in serial or in parallel circuit of the connection. On the reverse side, the glass is closed by opaque, reflective material for protection from the stray light.

To determine the efficiency of the glass to different wavelengths, the glass was illuminated with blue, green and red LEDs. The registration of luminescent light was carried out using photodiode S1723-05 7G, 10 x 10 mm² of company Hamamatsu, plugged in the current mode. At the beginning the LED was directly illuminating a spot of 10 x 10 mm² of the appropriate wavelength and power on the resistor R was measured. The results are shown in Figures 10a and 11a. Then the photodiode was mounted on a small surface of the plate and the central part of the glass was illuminated by the LED from the same distance, with a light spot of same 10 x 10 mm² size, and the power on the resistor R was measured. The results are shown in Figures 10b and l ib.

From Figures 10a, 10b one can determine the amount of light as a percentage of light collected around the perimeter of the core plate, and respectively, proportional to that light, the amount of the power. For the blue light with a wavelength of λ = 445 nm, the spot of 10 x 10 mm² directly on photodiode delivers a power of 329.6 microWatts frWatt]. Mounted on a small face of the plate the core photodiode, with illuminated spot of the same size in the center of the plate, delivers the power of:

P_B = 0.7137[μ αϋ] x 45[cm] (the core plate perimeter] = 32.1165 [pWatt], which corresponds to 9.74% of incident light, of 329.6 faWatt] incident on the center of the plate through the mineral glass, of thickness of 6 mm and a thickness of compound SIEL of 0.3 mm.

For the green light with a wavelength of λ - 514 nm, similar measurements are shown in Figure 11 a, b. Similarly, as for blue light, the amount of light released through the perimeter of the core plate for the green light is:

P_G = 0.1275[pWatt] x 45[cm] = 5.7375[μΨαίί]

which is 3.54% of the total incident light of 161.99 [μΨαίί].

For the red light with a wavelength of λ = 645 nm, the core plate is absolutely insensitive, while photodiode at this wavelength is sensitive enough.

Thus, the spectral study of core plates show the maximum sensitivity to the blue part of the light, falling at the green part about three times and not sensitive to the red part of the light.

Figures 12, 13 and 14 shows the results of measurements for the gas-discharge lamps with solar panel BP-2911-C4. From Figure 13 and Figure 14 one can determine the amount of light as a percentage of light collected around the perimeter of the plate core, and respectively, proportional to this amount of light the power at full illumination of the active surface of the module at a distance of one meter from the light source, which is:

Pj = 60.1 frWatt] / {((90x72) [mm²] / 56[mm²] x 450[mm] / 28[mm])} = 8.35[μ αΚ], which represents 5.91% of the incident power of 141.3 [^Watt]. For the distance of two meters from the light source to the glass surface, we have:

P₂ = 26.7frWatt] x / ((90x72) [mm²] / 56[mm²]) x 450 [mm] / 28[mm]j = 3.71[μ αίί], which represents 4.71% of the incident power of 78.8 [^Watt].

For the sunlight, the measurements were made on a cloudless days at 45°.26' north latitude for two light to electrical converters, the solar panel BP-2911-C4 and for the photodiode S1723-05 7G.

Figures 15, 16 and 17 show the solar panel BP-2911-C4 respond for direct sunlight on the working module of multilayer luminescent glass. The results of measurements for direct sunlight and for luminescent lights produced by sunlight in the core plate is shown on Fig. 15. From Fig. 15, one can determine the amount of luminescent light on the perimeter of the core plate for direct sunlight:

PSUN = i frWatt] /{((90 x72)[ mm²] / 56[mm²]) x (450[mm] / 28[mm])} = 30.00 frWatt] which represents 8.22% of the incident on the surface of 56mm² of the sunlight power.

Further study of the working module was done with a photodiode S1723-05 7G, which has an active surface area of 10 x 10 mm². We have measured power of the electric energy caused by direct sunlight on the photodiode. Result of measurement is shown on Fig. 18. Afterwards the photodiode was mounted on the side of the core plate using an optical contact. The sunlight spot size of the module was 90 x 72 mm², where sunlight hits it perpendicular and luminescent light from the core was detected by the attached photodiode S1723-05 7G. Measured power of the electric energy in this case is shown in Fig. 19. From Figures 18 and 19 we can determine efficiency of power transformation of solar energy into electric power for the module with S1723-05 7G photodiode. When the sunlight hits directly the photodiode size of 10 x 10 mm² or 100mm² we have maximum electrical power P_PD = 3360faWatt], which gives incident power on the working module of:

PSUN = 3360faWatt] x ((90 x 72) / 100) = 217728[μ αίί] Total power of luminescent light transported to the four small surface of the core plate is:

P_LUM = 287A6frWatt] x 45 = 12935.7 frWatt]

which gives 5.94 % of efficiency of transformation.

Conclusion

1. Constructed working example of the multilayer luminescent light concentrator is working and has the following features: for blue light of λ = 445 nm the efficiency is 9.74%, for the green light λ = 514 nm, the efficiency is 3.54%, for the light from the gas- discharge lamp, the efficiency is between 4 to 6 % depending on distance of irradiation, and efficiency from of direct sunlight is 8.22% for the solar panels BP-2911-C4 of Panasonic and 5.94% for the photodiode S1723-05 7G Hamamatsu.

2. It is necessary for fluorescent additives to "work" across all visible light and their wavelengths to be in coincidence with working wavelength of the light converters into electricity.

3. Reducing the surface of semiconductor converters leads to a reduction of electrical power at the same luminous flux. Hence: it is necessary to increase the area of semiconductor converters.

4. How to increase the area of semiconductor converters? For example, the core plates are divided into squares and along the perimeter of each square two-side converters of light into electricity are installed, which are then displayed on the outer perimeter of the core. That is, semiconductor converters make a grid whose cells are filled with a material the of core plate. Other layers are just like in the layout.

References

1. N.V.Rykalina, Screening of the Photo Selective Materials for Growing of the Plants, Diploma work, Russian State Agrarian University - K.A. Timiriazev Moscow,

Agricultural Academy, Moscow, June 19, 2005.

2. W.A. Shurcliff and R. Clark Jones, The Trapping of Fluorescent Light Produced within Objects of High Geometrical Symmetry, Journal of the Optical Society of America, Vol.39, No.ll, November, 1949.

3. G. Keil, Design Principles of Fluorescence Radiation Converters, NIM 87 (1970) 111- 123.

4. GEANT - CERN Program Library Long Writeup W5013, CERN, 1993 Appendix 1.

Table 1. The type and concentration of luminescent additives.

Claims

Claim

1. The converter of solar energy into electrical energy, comprising of semiconductor solar cells, is characterized by following, that in order to reduce required area and, consequently, the cost of batteries, and eliminate necessity of orientation of batteries in space, a solar energy concentrator is used, which consists of a thin plate of an organic or mineral glass containing fluorescent additives, that absorbs sunlight and then emits fluorescent light with longer wavelength, part of which propagates through the total internal reflection to the ends of the plate, to which a semiconductor solar cells are attached with a common area, not exceeding the total area of the ends of the plate.

2. The converter of solar energy into electrical energy given in claim 1 , is characterized by following, that in case of large fluorescent plate, to reduce the attenuation of the radiation, propagating along the plate, and leaving plate through the ends and hitting the solar panels, a multilayer plates are used, with a core fluorescent plate having refractive index greater than the refractive indexes of one or several surrounding shells.

3. The converter of solar energy into electrical energy given in claim 1 , is characterized by following, that in order to improve the efficiency of solar energy conversion into the electrical energy, fluorescent plate is used, containing one or more fluorescent additives, displacing the solar radiation in to the red or infrared region of the spectrum, corresponding to the optimum of the conversion efficiency of solar energy in to the electrical for the type of solar cell used.

4. The converter of solar energy into electrical energy given in claim 1 , is characterized by following, that in order of using of luminescent plastics-concentrators of the solar radiation as a transformers of solar energy into the electric, as well for glazing of the buildings, greenhouses, vehicles, a fluorescent additives are embedded into the luminescent plates, ensuring exit of the part of solar or luminescent radiation through the front surfaces of the plates in a desired region of the spectrum.

5. The converter of solar energy into electrical energy given in claim 1 , is characterized by following, that in order to reduce the required area of solar panels, two-sided solar panels are used, both sides of which are attached to the ends of the luminescent plates.

6. The converter of solar energy into electrical energy given in claim 1, is characterized by following, that in order to increase the stability of the converter, fluorescent plates are protected from the weather by transparent films or plates.