System for collecting solar energy

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FIG. 6 is a vertical sectional view of a system of this

SYSTEM FOR COLLECTING SOLAR ENERGY invention which is compounded with a number of unit systems of FIG. 4.

BACKGROUND OF THE INVENTION FIG. 7 is a vertical sectional view of a system of this invention which is compounded with a number of unit 1. Field of the Invention systems of FIG. 5.

This invention relates to a new system for collecting the radiant energy of sunlight. DETAILED DESCRIPTION OF THE 2. Description of the Prior Art PREFERRED EMBODIMENTS

Heretofore, several systems for collecting the radiant O The most essential feature of this invention consists in energy of sunlight have been proposed. As an example the faceplate. The faceplate is a plate made by a large seen in a solar-electric power plant or a solar furnace, number of optical fibers tied up coherently in a bundle sunlight is concentrated, to yield a high temperature, on vertically to the plane of the faceplate. Each diameter of a receiver by a large number of mirrors designed to the optical fibers is selected from a range of 0.5 micron follow the sun, or so-called heliostats, wherein each 5 to 2.0 micron, which is the gist of the faceplate. Thick mirror must be individually moved by clockwork for ness of the faceplate is not essential, but may be in a strictly reflecting the solar rays into a fixed direction to range of three to ten millimeters. the receiver, so that it is inevitable for the system to This faceplate works very effectively. According to become very complicated in a large scale. A unit collec this faceplate, the rays departing from each optical fiber tor such as giant parabolic mirror or Fresnel lens as 20 of the faceplate have always a certain intensity compo another example must be also designed to strictly follow nent along the principal axis of each optical fiber, so the sun, otherwise the incident solar rays can not focus that all the rays departing from all optical fibers of the on one point, so that the efficiency for collecting solar faceplate has always some intensity component along energy lowers markedly. Many attempts for improving the direction of principal axis of the faceplate, when the follow-means have been made, but any of those is 25 ever solar rays enter into the faceplate from a direction still complicated and expensive. We have now found being within about the numerical aperture of the optical that collecting the radiant energy of sunlight with a fiber of the faceplate. Hence, numerical aperture stands considerable high efficiency can be accomplished with for sin 6=Vn 12-n2, wherein 0 represents angle of no special follow-means. deviation from principal axis, n represents refractive SUMMARY OF THE INVENTION 30 index of the optical fiber, and n2 represents refractive index of the material surrounding the optical fiber. The

An object of this invention is therefore to provide a value of numerical aperture varys depending on n and system for collecting the radiant energy of sunlight with n2, but is exemplified as about sin 39. Namely, the a considerable high efficiency with no special means for faceplate of this invention can produce, from all of its following the sun. under surface, rays having a certain intensity as a com Another object of this invention is to provide a simple ponent parallel to the principal axis of the faceplate, and cheap collector of solar energy, whenever solar rays enter into the faceplate from the Other objects will be apparent from the following direction area which is formed by a cone formed by the description. revolution around the principal axis of the line having Thus, this invention relates to a system for collecting 40 an angle of about 39” between the line and the principal the radiant energy of sunlight which comprises a face axis of the faceplate. The parallel rays produced can be plate for receiving the parallel rays of sun which is a easily focused by a fixed single means for focusing par thin plate made of a large number of optical fibers hav allel rays having a definite direction. Namely, this face ing respectively a diameter ranging from 0.5 micron to plate enables to obviate the necessity of follow-means of 2.0 micron tied up coherently in a bundle vertically to 45 the sun.

the plane of the faceplate, and a means for focusing the The reason why optical fibers work so effectively in parallel rays departing from optical fibers of the face the diameter range of 0.5-2.0 micron, will be given by plate to concentrate the radiant energy outside the sys the principal of Fraunhofer diffraction and the principle tem, of reversibility of light-path. The illustration will be 50 easier, when the incident rays are rays having a single

BRIEF DESCRIPTION OF THE DRAWINGS wave length. The basic idea of this invention is that FIG. 1 shows directivity patterns based on Fraun each diameter of optical fihers is selected from the di hofer diffraction which is formed when beams of paral ameter not larger than 1.22N, N is the wavelength of the lel light depart from the aperture of an optical fiber incident light. The diameter range of optical fibers of along the principal axis of the fiber. 55 the faceplate of this invention, 0.5-2.0 micron was se FIG. 2 is a vertical sectional view of a system of this lected in due consideration of the effective wave length invention which has a focusing means consisting of two band 0.3-3.0 um of sunlight, and practical efficiencies. parabolic mirrors. The reason why the length of diameter is critical at FIG. 3 is a vertical sectional view of another system 1.22X will be given as follows. If beams of parallel light of this invention which has a focusing means of a Fres 60 depart from the aperture of an optical fiber having an nel lens. appropriate small diameter, Fraunhofer diffraction of FIG. 4 is a vertical sectional view of a system of this beams will occur, so that the beams departing from the invention which has a focusing means consisting of two aperture generally form a three dimensional intensity parabolic mirrors, and a means for transferring the fo distribution pattern, that is, a directivity pattern consist cused energy. 65 ing of a main lobe and subsidery lobes. Generally, some FIG. 5 is a vertical sectional view of another system region of zero intensity is formed between the main lobe of this invention which has a focusing means of a Fres and the subsidery lobes. But, if the diameter of the aper nel lens and a means for transferring the focused energy. ture is adequately selected, only a main lobe can be

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formed. This adequate diameter can be derived from the ter of aperture of the secondary parabolic mirror can be following principle. Fraunhofer diffraction shows a selected from the range of 1/20-1/10 times as much as lobe-like diffraction having a directivity coefficient the diameter of aperture of the primary concave para (2J 1(x)/x)2, wherein J 1(x) is Bessel function, x = mid sin bolic mirror, so that rays reflecting on the convex sur y/\, d is diameter of the aperture, X is wave length of 5 face of the secondary mirror can focus on or below the incident beams of light, and y is the angle formed be surface of primary mirror, according to the purpose of tween the incident direction of beams and the principal using the collecting system.

axis of the aperture. When (2J(x)/x)2 becomes zero, X FIG. 2 shows an example of the collecting system of becomes about 3.83, and d/A becomes 1.22, in which this invention using parabolic mirrors' means, wherein 1 only main lobe is formed. Accordingly, if the diameter O is faceplate, 2 is optical fibers composing the faceplate, of optical fiber is not larger than 1.22N, parallel beams 3 is primary concave parabolic mirror, and 4 is second which enter into the aperture of optical fiber along the ary small convex parabolic mirror. 5 represents focus of principal axis thereof, pass through the fiber and depart the primary concave parabolic mirror. 6 is objective from another aperture thereof from a directivity pattern substance for applying the solar energy collected. 7 is a having only a main lobe and no subsidery lobes as 15 means for fixing the objective substance. a--a is princi shown in FIG. 1. pal axis of the faceplate. The rays of sunlight pass In FIG. 1, lobe L1 is the directivity pattern based on through optical fibers 2 of faceplate 1 to depart there Fraunhofer diffraction which is formed when beams of from as rays having an intensity component parallel to parallel light depart from the aperture of an optical the principal axis a-a, and the parallel rays reflect on fiber, the diameter of which is equal to 1.22N, A being the surface of mirror 3 to focus on the surface of mirror the wavelength of the beams, and lobe L2 is the one 4, and then to reflect thereon to focus on objective when the diameter is 1.00A. In FIG. 1, 2 is optical fiber, substance 6, so that the objective substance 6 is heated. 0, 10, 20, 30', etc. is an angle of deviation from the FIG. 3 shows another example of the collecting sys principal axis of optical fiber, a-a, and the circular line tem of this invention using a Fresnel lens, wherein 8 is of 1.0, 0.9, etc. is the line representing a relative inten 25 Fresnel lens, and 1, 2, 6, 7 represents respectively the sity, assuming that the intensity at the principal axis is same meaning as in FIG. 2.

1.00. The principle of reversibility of light-path teaches As is seen FIGS. 2 and 3, parabolic means makes the that the directivity pattern formed by the beams which collecting system thin, and Fresnel lens means makes advance upward in FIG. 1 can be wholly applied to the the one rather thick.

beams which advance downward in FIG. 1, so that the 30 Focused solar energy can be transferred to a remote beams Bo which enter downward into the optical fiber 2 place. FIG. 4 shows an example of the system for solar along the principal axis a--a depart from the optical energy focused to transfer to a remote place. The rays fiber as the beams having an intensity component along reflected on the surface of secondary mirror 4 focus at the principal axis a--a of 1.0; the beam B which enter the central area on the surface of primary mirror 3. The downward into the optical fiber 2 from the direction 35 focused rays are transferred through a bundle of optical deviated by 10' from the principal axis a--a depart from fibers for transmission 9 to a remote place. The diame the optical fiber as the beams having an intensity com ters of optical fibers for transmission may be defined ponent along the principal axis a-a of 0.89; the beams economically. The bundle of optical fibers are con of 20, 0.63; the beams of 30, 0.36; etc. nected a transparent cone 10 which is connected with As will be clearly understood from above illustra the primary mirror 3 at its central lacked part. tions, the faceplate of this invention enables to let paral FIG. 5 shows another example of the system to a lel rays of sunlight entering into the optical fibers from remote place, in which a Fresnel lens 8 is used as a all directions within the numerical aperture of the opti means for focusing.

cal fibers pass through the optical fibers to depart, from FIG. 6 shows an example of the big system which is the outlet apertures of all the optical fibers, a number of 45 compounded with a number of unit systems shown in rays, any of which is parallel to one another and to the FIG. 4. All of the bundles 9 of optical fibers from unit principal axis of the faceplate, and has a certain intensity systems is gathered to make one big bundle 11 to trans relating to the angle formed between the incident direc fer to one remote place.

tion of sunlight and the principal axis of the faceplate. FIG. 7 shows another example of the big system The parallel rays departed from the faceplate can be 50 compounded with units shown in FIG. 5. easily focused by a single means for focusing fixed to The faceplate can be one big plane plate as in FIG. 6, the faceplate. Thus, the faceplate of this invention ena and can be the one compounded in a jagged sectional bles to eliminate the necessity of strictly following the view as in FIG. 7. The form of faceplate in FIGS. 6 and incident direction of sunlight. 7 is exchangeable with each other. The plane faceplate The means for focusing parallel rays departing from 55 will be suitable to be equipped on the plane facing the optical fibers of the faceplate may be any of conven sun's path, for example declined roofs. The faceplate in tional and new means for focusing parallel rays. An a jagged sectional form will be suitable to be equipped example is a concave parabolic mirror accompanied on horizontal roofs, or especially on vertical walls. with a secondary small convex parabolic mirror posi Many other modifications for compounding units of the tioned at the focal area of the concave parabolic mirror, collecting system will be considered within the scope of Another example is Fresnel lens. this invention.

As shown in FIG. 2, the former parabolic mirrors are Advantages of this invention are as follows. positioned below the faceplate. The concave parabolic (1) The system of this invention obviates the need for mirror is one for focusing parallel rays departing from a mechanism for the strict follow of the solar direction. the faceplate, so that the focus of the concave parabolic 65 (2) The system can be made in very thin form in the mirror surface is formed below the faceplate. Second parabolic mirrors' one.

ary small convex parabolic mirror is positioned at the (3) Collecting solar energy can be conducted under focal area of the concave parabolic mirror. The diame the collecting system.

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(4) Collected solar energy can be easily transferre nected with a transparent cone which is connected with and gathered to a remote place. a bundle of optical fibers for transmission to transfer the ; (5) The system is cheap, and easy to equip on any focused solar rays to a remote place.

place such as roof, wall, water surface, etc. 5. A system as claimed in claim 1, wherein the focus (6) The system promises very high collecting coeffici 5 ing means is a Fresnel lens.

ent of solar energy with no special follow-mechanism. 6. A system as claimed in claim 5, wherein the object This system can be widely used, for example, as col to give solar energy is directly placed at the focus of the lector for solar house heating and cooling and as a high Fresnel lens.

temperature collector used in solar electric power plant 7. A system as claimed in claim 5, wherein the focal or solar furnace. O area of the Fresnel lens is connected with a transparent

What is claimed is: cone which is connected with a bundle of optical fibers 1. A system for collecting radiant energy of sunlight for transmission to transfer the focused solar rays to a which comprises a faceplate for receiving parallel rays remote place.

of sunlight which is a thin plate made of a large number 8. A system for collecting radiant energy of sunlight of optical fibers having respectively a diameter ranging 5 which is compounded with a number of units, the unit from 0.5 micron to 2.0 micron tied up coherently in a of which comprises a faceplate for receiving parallel bundle vertically to the plane of the faceplate, and a rays of sunlight which is a thin plate made of a large means for focusing the parallel rays departing from the number of optical fibers having respectively a diameter optical fibers of the faceplate to concentrate the radiant 20 ranging from 0.5 micron to 2.0 micron tied up coher energy outside the system. ently in a bundle vertically to the plane of the faceplate, 2. A system as claimed in claim 1, wherein the focus a means for focusing the parallel rays departing from ing means is a concave parabolic mirror accompanied the optical fibers of the faceplate, and a bundle of opti with a small convex parabolic mirror positioned at the cal fibers for transmission which is connected with the focal area of the concave parabolic mirror, the concave 25 focal area of the focusing means, and the bundles of parabolic mirror being positioned below the faceplate and having a lacked area at the central part of the mir optical fibers for transmission are collected to a remote ror, and the small convex parabolic mirror reflecting destination.

9. A system as claimed in claim 8, wherein the com the rays reflected from the concave parabolic mirror to pounded faceplate is one big plane faceplate com focus at or below the lacked area of the concave para 30 pounded with a number of unit faceplates. bolic mirror.

3. A system as claimed in claim 2, wherein the object pounded 10. A system as claimed in claim 8, wherein the com to give solar energy is directly placed at the position faceplate is a big one compounded, in a saw toothed sectional which is the focus of the convex parabolic mirror and is in such a manner that form, with a number of unit faceplates below the concave parabolic mirror. one unit faceplate per one tooth is 4. A system as claimed in claim 2, wherein the central 35 equipped in parallel to one k l another.

lacked area of the concave parabolic mirror is con