WO2008100200A1

WO2008100200A1 - Light collecting device

Info

Publication number: WO2008100200A1
Application number: PCT/SE2008/000114
Authority: WO
Inventors: Bengt Steneby
Original assignee: Parans Solar Lighting Ab
Priority date: 2007-02-12
Filing date: 2008-02-12
Publication date: 2008-08-21
Also published as: WO2008100200A9; WO2008100200A8

Abstract

An arrangement for the collection of light within a designated frequency interval, such as visible light, comprising a light- refracting lens (5) and a first light transporting or light- transforming organ (1), wherein the first organ shows a light entry (Ia) that is arranged at or in the proximity of the focal point of the lens for light within the designated frequency interval. The arrangement comprises a frequency selective mirror (4) that is arranged to enable transportation of incoming light within the designated frequency interval to the light entry and to resist transportation of incoming light outside the designated frequency interval to the light entry. The light entry is encased in a body (3, 7) whose outer surface is separated from the focal point of the lens for light within the designated frequency interval.

Description

LIGHT COLLECTING DEVICE

FIELD OF THE INVENTION

The present invention relates to a device for the collection of light within a designated frequency interval, such as visible light, comprising a light-refracting lens and a first light-transporting or light-transforming organ.

BACKGROUND

It has long been of interest to be able to let daylight into buildings. Except for the modern era with electric lights, mankind as been dependant on daylight and has biologically evolved under this premise. For example, changes in the intensity and colour of the daylight affect people's perception of the time lapse, e.g. when different meals are to be eaten, and in that when it is time to be asleep and when it is time to be awake.

With the construction of buildings implementation of daylight is of grave importance. Usually different types of windows and skylights are used. However, these solutions are limited in the ability to transport light into buildings, due to the fact that they only illuminate areas that are located in the vicinity of the windows and/or skylights. In addition, windows and/or skylights take up considerable space on the ceiling and fagade of the building, which leaves less space for equipment such as ventilation equipments and antennas. Furthermore, windows and skylights are often unfavourable with regard to the insulation and energy consumption of the building.

EARLIER STANDPOINT OF TECHNIQUE

As an alternative or complement to traditional windows, skylights and light shafts, devices that collect sunlight and lead said light into the building via for example optic fibres, have started being used. WO 2003/091621 and WO 2006/049560 describe such light collecting devices that can be used for leading sunlight into buildings .

In such devices and the like, light-compressing techniques are used, comprising light collecting devices and/or a light collecting mirror that refracts or reflects the light towards a focal point where the light is further transported inside the optic fibre. Due to the high energy density of the light in the focal point area, problems can occur such as heating and/or ageing of objects.

Problems may also occur with outer impurities that will combust should they enter the area of the focal point. Combustion residue will then blacken down the light entry of the fibre or other materials where the light can focus so that in said blackening the radiation will transform into heat. The result may be an avalanche like heating where discolouration of the fibre or other materials leads to even more transformation of the radiation into heat.

In the case where the light shall be focused into an optic fibre of plastic that could be PMMA, the temperature inside the plastic material should not exceed 7O⁰C approximately, due to the fact that the material starts to soften at such temperatures. Optic fibre of PMMA have in recent times a very good light-conducting capability at a low cost.

Optic fibre may be comprised of glass. Even though glass can endure higher temperatures than plastic the surface coating that encases the glass type may have a lower optical density and be more heat sensitive.

Optic fibre may also be comprised of quartz.

Development is underway in relation to optical light conductors which opens possibilities for new variations in the future. Because huge amounts of radiation are gathered at the entrance to the optic fibre regardless of the material it is made of, measures are required in order to deal with this energy.

Optic fibres of PMMA have a high attenuation of IR- and UV- radiation. This causes most of the heat development to occur in the beginning of the fibre. PMMA is heat insulating which puts extra high demands on leading heat away from the fibre. Thinner fibres are preferred because they have a larger heat-dissipating surface in relation to its volume than a corresponding thicker fibre. The size and focal length of the lens are also factors that need to be taken into consideration when choosing both the size and type of fibre and the degree of radiation intensity and heat development that is to be expected at the area of the focal point.

To be able to follow the path of the sun across the sky it is preferential to use some sort of sensor device. In the case where the sensor device directly measures the focal point of the light problems will occur with heat development.

EP 0 295 152 A2 describes a device for tracking light. The device comprises a casing whose bottom has the end of an optic fibre arranged. At the other end of the casing a lens is assembled and outside said lens a filter. In the device described in EP 0 295 152 foreign particles risk ending up in the focal point of the lens. Furthermore, the use of a filter means that the energy from the light that is being filtered away is absorbed by said filter causing heating of the device.

DESCRIPTION OF THK INVENTION

The invention aims to providing an improved device for the collection of light. The invention also aims to achieving several desired effects for high-capacity sun-catching systems all in the same device. The invention is of the most importance in systems where the visible light is broken into the fibre optic by means of refraction.

According to the invention these aims are achieved with a device of the kind designated in the preamble of claim 1 and that comprises the special technical features set out in the characterizing part of the claim. The device is designed for the collection of light within a designated frequency interval, such as visible light. The device comprises a light-refracting lens and a light- transporting or light-transforming organ, wherein the organ shows a light entry that is arranged at or in the proximity of the focal point of the lens for light within the designated frequency interval. A frequency selective mirror is arranged for allowing transportation of incoming light within the designated frequency interval to the light entry and to counteract transportation of arriving light outside the designated frequency interval to the light entry.

The light entry is encased in a body whose outer surface is separated from the focal point of the lens for light within the designated interval frequency. The device according to the invention comprises a frequency selective mirror that may utilize interference in thin layers, which reflects away unwanted radiation within the infrared and ultraviolet area but that lets visible light through. Due to the unwanted wavelengths reflecting away the unwanted wavelengths of the light, the heat development that would otherwise be caused by said unwanted wavelengths is reduced. The optic fibre's light entry is further encased in a protective body whose outer surface is not situated in the focal point of the lens. In this way the risk of foreign particles ending up at the focal point is eliminated.

The protective body and the light-transporting or light-transforming organ suitably form a solid unit in which the light entry is received. The light entry is sealingly received in the protective body without the light entry being in communication with the surrounding atmosphere or some encased space inside the protective body. In this way there is furthered assured that no foreign particles or impurities breach into the light entry at the focal point. Either particles from the surrounding in use or particles that have been encased in the protective body during the manufacture therefore risk ending up in the focal point. The solid design of the protective body and the light-transporting or light-transforming organ also contributes to there being no cavities in the unit, wherein said cavities could otherwise cause disturbances in the radiation path and form insulating layers that counteract removal of heat.

The reflecting layer may be constructed as a thin coating on a transparent body that constitutes the whole or part of the protective body. The transparent body may be made of glass, quartz glass, diamond, or some other transparent material. The transparent body should be as transparent as possible. This means that if, for example, glass is used the content of iron oxide should be kept at a minimum, which would otherwise dampen certain frequencies of the light, resulting in that a green colouring appears and also a certain transformation of light to heat.

The transparent body is constructed with a thickness sufficient enough so the surface that the converging radiation is gathered to, seen at the surface of said transparent body is significantly larger than at the focal point. The transparent body is made thick enough so that the radiation per unit area is sufficiently low as to eliminate any danger of combustion of particles that enter the radiation area on the transparent body's surface. The particles mentioned may be, for example, airborne impurities. The transparent body can be made so large that it further comprises the light- refracting lens. In this regard the surface of the lens facing towards the sun is coated with the light-reflecting layer that reflects away unwanted radiation but lets through visible light.

A frequency selective mirror that utilizes interferences in thin layers and that lets through visible light and that reflects other radiation has a certain transition that covers a certain frequency width where the mirror successively transitions from refracting to reflecting abilities. There exist a qualitative array of said frequency selective mirrors on the market today in regard to the steepness of flanks bridging the carrying out of reflecting and light passing. A product that lets through the entire spectrum of visible light will therefore also let through small portions of both infrared and ultraviolet light. Because of this it is favourable in a high-capacity system to handle the effects that the remaining portions of unwanted radiation will cause.

The protective body can, apart from the transparent body also comprise a heat-dissipating body. The optic fibre is then suitably arranged in the heat-dissipating body, which contacts that side of the transparent body which is opposite to the frequency selective mirror. The optic fibre's light entry is thus encased in a protective body that is formed by the transparent body and the heat- dissipating body.

The long-wave infrared light is not refracted as much as visible light which is why the focused surface is larger for the focal length that is optimal for visible light. The infrared light that does not connect to the optic fibre's opening can partially, to a certain degree, be reflected away by the surface of the heat- conducting material against the transparent body and partially be taken care of by the heat-conducting material for radial radiation dissipation towards the surrounding from its surface; also through transference to surrounding gas such as ordinary air; also through conduction further into the structures the heat-dissipating body is mounted in and also by conducting heat out into the transparent body that in turn transfers heat to the surroundings, in a fashion similar to the aforementioned heat-dissipating body.

A part of the infrared light will also radiate into the opening of the optic fibre. The optic fibre is mounted with its light entering opening facing towards the transparent body via a medium with the same or approximately the same optical refracting index as said fibre in order to minimize unwanted reflection during the light's transference between mediums with different optical densities. In the case where the optic fibre is comprised of PMMA the infrared light that radiates into the optic fibre will transform into heat. Most of the heat is developed in the beginning of the fibre and is then decayed the further in it goes due to the fact that more and more of the infrared radiation is filtered away. Because most heat is developed in the beginning of the fibre, high demands are here put on that heat dissipating conduction towards the surrounding may be performed here, in the best way. It is preferable if the transparent body is comprised of a material with a high heat- dissipating ability. Glass conducts heat significantly better than PMMA which makes it a suitable material in this regard. In the case where the transparent body is comprised of diamond an optimal heat conduction is achieved.

Through the invention it is possible to achieve higher capacities in a sun-catching system. There is given new possibilities to combine larger lenses and fibres and also to have a higher compression degree for the light inside the fibres. This presents large winnings in the form of leaner light-wiring for the same amount of light which in turn makes it easier to lay out the light-wiring in buildings and also because leaner light-wirings are cheaper. This also leads to that, in a sun-catching system that comprises a number of mechanically connected optical units, it is possible to create a system with fewer units due to the fact that by means of the invention it is possible to use larger lenses and fewer optical fibres for the same amount of light.

The invention may also be of use at photovoltaic techniques. The sun panel's ability to constantly focus the light of the sun may be of use. Photovoltaic elements maintain a higher light intensity than that on the surface of the earth.

The photovoltaic elements function better if they are not excessively heated. Photovoltaic elements further entail a high cost per surface unit. The frequency selective mirror that is based on interferences in thin layers can in photovoltaic applications be designed as a band-pass filter for letting through the photons that have the right wavelength for exciting the electrons inside the photovoltaic element but reflect away the photons with unwanted wavelengths that would otherwise only cause unwanted heating. It is economically preferential that both the photovoltaic elements and the aforementioned frequency selective mirror be held as small as possible due to the fact that they both entail a high price.

The invention also comprises a sensor arrangement for direct light- measuring at the focal point of the light for the optical units used in a sunlight-collecting panel that are intended for controlling of the mechanism for the angle direction towards the sun in its course over the sky. This sensor arrangement gives the highest precision with a momentous reconnection of the feedback value, i.e. where the focal point really is located. This is carried out by light- collecting volumes or cavities surrounding the fibre opening of the light-conducting fibre placed in the central part of the heat- dissipating body. It works in the following way: If the focal point deviates but slightly from the fibre opening, the focal point will be displaced towards an adjacent cavity or alternatively a pair of mutually adjacent light-collecting cavities. In the bottom of said cavities there are mounted light-conducting fibres that conduct the light on to electrical light-sensitive components that in turn are connected to a calculation circuit for controlling the work of the motors that adjust the angles on the optical units.

The focal point, or in other words the imaging of the sun, is when properly calibrated centred over the light-conducting fibre opening. The imaging's size in relation to the light-conducting fibre and, taking into consideration the imperfections of the optical lens, is so big that a small part of light spills over the light-collecting fibre's edge and over into the surrounding light-collecting cavities. When the focal point is correctly calibrated it could be said that it balances on the edges spilling an equal amount of light into all of the surrounding cavities. This is a momentous and ever ongoing act of balance that is being executed where the calculation unit constantly controls the motors work so that a light balance in the light-collecting cavities may be maintained. The cavities are suitably filled with a semi-transparent material that is suitably comprised of heat-conducting material such as silicon but may also be made from glass or plastic. The light- transporting fibres in the bottom of said cavities may at the invention be replaced by light-sensitive electrical components with the same function.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following exemplifying embodiment the invention is described with reference to the attached figures, wherein:

Fig. 1 is a schematically cross-sectional view of an arrangement according to a first embodiment of the invention.

Fig. 2 and 3 is a schematically cross-sectional view and an above plan view respectively illustrating an arrangement according to a second embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

In figure 1 there is shown how rays of the sun 8, that in principal are parallel, are refracted in a convex lens 5. Rays of light in the visible spectrum converges 9 towards the focal point and then generally passes through a reflecting layer 4 on a transparent body 3 and radiates further towards the focal point that substantially coincides with a light entry Ia of an optic fibre 1. The optic fibre 1 is mounted in a heat-conducting body 7. The transparent body 3 and the heat-conducting body 7 together form a protective body 10 in which the optic fibre's light entry Ia is encased. Light rays within the ultraviolet and infrared area are substantially reflected on the reflective layer of the glass. The visible light passes on its way the transparent body 3 before it enters the optic fibre 1 through the light entry Ia at the focal point. Portions of the light that lie within the infrared and the ultraviolet area are substantially reflected at the reflecting layer 4 on the surface of the glass. The fibre 1 is mounted in the heat-conducting body 7 that emits heat partially through radiation and through convection in the surrounding air and also via bridge passing of heat in the structure 2 that it is assembled in. The heat-conducting body comprises surface-increasing means 6 in order to increase the heat-conducting surface against surrounding air. 11 is an arrangement for angle redirection of the combined whole in order to constantly focus towards the sun. 9 represents a light-converging part in the ray path. An infrared beam 12 is not refracted as much as visible light.

Figure 2 and 3 illustrates a part corresponding to the one shown in figure 1 but here designed with details of the sensor organs for controlling and the movement apparatus for tracking of the sun. In fig. 2 and 3 there is shown a light-conducting optical fibre 1 for transporting light for useful purposes, a transparent body 3, a frequency selective mirror 4, surface-increasing means 6 for increasing the heat-conducting surface, a heat-conducting body 7 and sunlight 8 that converges towards a focal point. Ia represents the optical fibre's 1 beginning and entry for sunlight. 20 represents a separation between the different light-collecting cavities 260-290 in the heat-conducting body. 26-29 represents light-conducting fibres that transport light from the cavities to a coupling piece for transference of light to light-sensitive electrical components intended for reading of light levels.

Above, exemplifying embodiments have been described. It shall be known that the invention is not restricted to these examples and that it may be freely varied within the scope of the following claims.

Claims

1. An arrangement for the collection of light within a designated frequency interval, such as visible light, comprising a light- refracting lens (5) and a light-transporting or light-transforming organ (1), wherein the organ shows a light entry (Ia) that is arranged at or in the proximity of the focal point of the lens for light within the designated frequency interval, characterized by a frequency selective mirror (4) that is arranged for enabling transporting of incoming light within the designated frequency interval to the light entry and to resist transportation of incoming light outside the frequency interval to the light entry and also that the light entry is encased in a protective body (3, 7) whose outer surface is separated from the focal point of the lens for light within the designated frequency interval.

2. An arrangement according to claim 1, wherein the body (3, 7) and the light-transporting or light-transforming organ forms a solid unit in which the light entry (Ia) is occupied.

3. An arrangement according to claim 1 or 2, wherein the protective body comprises a transparent body (3) that is arranged between the light entry (Ia) and the surface opposite to the focal point of the lens (5).

4. An arrangement according to claim 3, wherein the transparent body (3) has a dimension in a direction from the light entry (Ia) to the lens (5) such that the light intensity on the surface facing away from the light entry of the transparent body is significantly lower than at the light entry.

5. An arrangement according to any one of claims 1-4, wherein the transparent body comprises the lens.

6. An arrangement according to any one of claims 3-5, wherein the transparent body ( 3 ) is formed from a material with good heat- conducting capabilities, preferably glass.

7. An arrangement according to any one of claims 1-6, wherein the protective body comprises a heat-conducting body (7) that is arranged around the light-transporting or the light-transforming organ ( 1 ) .

8. An arrangement according to any one of claims 1-7, wherein the light transporting or light-transforming organ comprises an optic fibre (1).

9. An arrangement according to any one of claims 1-7, wherein the light-transporting or light-transforming organ comprises a photovoltaic element.

10. An arrangement according to any one of claims 1-9, comprising a guided movable light-refracting lens and a first light-transporting or light-transforming organ (1), wherein the first organ (1) shows a light entry (Ia) that is arranged at or in the proximity of the focal point of the lens for light within the designated frequency interval and a number of second light-transporting or light- transforming organs (26-29) that are arranged around the first organ's light entry (Ia) and connected to a control unit for controlling of the movable lens.