CA1075510A - Solar collector - Google Patents

Abstract

A SOLAR COLLECTOR

ABSTRACT OF THE DISCLOSURE:
A solar collector composed solely of beam concentrating fresnel segments having surfaces formed on the basis of adjacent ones of a number of overlapped imaginary beam concentrating surface units, getting rid of stepping surfaces in existing fresnel refractor or reflector which do not contribute to the beam concentration.

Description

~ ~ 075510 . .
B ~anoullD or TIID II~DII~0ll:
This invention relates to solar collectors employing integrated fresnel refractors and/or reflectors for efficiently concentrating solar beam radiations of various incident angles.
S The invention is based on improvements of the so-called fresnel lens which was originally invented by a French physician A. J.
Fresnel (1788 - 1827).
The collectors or concentrators for the solar water , heater, solar battery or large-scale solar power plant (herein-after representing these/as~'solar water heater") usually have a number of plano-convex cylindrical lens segments aligned I parallel to each other on one plane of a transparent plate to ¦ concentrate solar beam radiation on predetermined lines of concentration where receiving elements such as heat absorbing pipes are located.
Solar collector lenses of shorter focal lengths generally require a smaller sun tracking movement in the lateral direction and can attain higher concentration of incident solar beam radiation, allowing/use of thinner heat absorbing pipes.
Moreover, lenses having greater apertures can concentrate a greater amount of flux, resulting in a reduced number of heat absorbing pipes to an economical advantage.
For these reasons, it is advantageous to use a collecting lens with a short focal length and a large aperture. Such , lens, however,have a great convexity and thickness and requixes ¦~ a large amount of lens material. It is the general practice *o avoid this problem by prov~iding a collector in the form of a fresnel refractor or reflector having fresnel surfaces, which re much thinner.
3~ For example, one can provide a collector in the form of ...~ .... ,. . . . ....................... .
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a refractor consisting of a number of cylindrical fresnel lens segments as shown in Fig. 1. The individual fresnel lens segments 415, 425 and 435 are formed on the basis of imaginary cylindrical refracting surface units 410, 420 and 430, respec-tively with the respective lens segments 415, 425 and 435 con-nected by vertically rising surfaces 414, 424 and 434, respectively. The number and positioning of the fresnel lens segments have theoretically no restrictions and a great freedom is allowed in designing.
For the purpose of reducing the thickness of the refractor, the fresnel lens segments are usually provided in a number greater than in Fig. 1 where each fresnel lens unit is shown as having only a small number of refracting segments for the simplicity of illustration. The reference numerals 4142 and 4243 indicate the boundarylines between two adjacent lens units.
The conventional solar water heaters using a fresnel lens as a concentrator have an inherent drawback that a substan- ;
tial loss of beam radiation occurs unless the incident beam radiation is parallel to the rising surface 414 as at 4110, because the slantingly incident rays as at 4111 are irregularly refracted or reflected by the rising surfaces 414 and scattered in random directions without contributing to the concentration.
The existence of the rising surfaces also present difficulties during the fabrication of the lenses. In addi-tion, the rising surfaces form acute angles with the refracting or reflecting fresnel segments to prohibit drastic reductions ;
in the thickness of the concentrator.
According to the invention, there is provided an "integrated fresnel" solar collector. The construction of this integrated collector completely eliminates the rising .
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surfaces which are present to convert the individual refrac-ting or reflecting segments in the conventional refractor or reflectors.
This integrated fresnel solar collector comprising an integrated array of Fresnel units, each unit including a plu-rality of Fresnel segments all derived from and confocal with a respective common imaginary beam-concentrating surface, the surfaces of the Fresnel segments meeting each other along lines (in the case of cylindrical surface) or at points (in the case of a surface of a body of revolution) which lie sub- `
stantially in a common plane (hereinafter referred to as "plane cp") which i6 perpendicular to the optic axes or planes of the units, consecutive Fresnel segments of one unit formed from one imaginary surface bei~ng separated by Fresnel seg-ments of an adjacent unit formed from a different imaginary surface.
This "particular arrangement" of the refracting or reflecting segments will be hereinafter referred to as "integrated fresnel segments" for the convenience of explan-ation.
The "optical axes" mentioned in this specificationhave the following meaning. In the case of a cylindrical surface, the cylindrical surface may be shown by a curve appearing at a cross-section which is normal to a generatrix of the surface. This curve is in symmetry with its middle line. This line is referred to as "an optical axis of the cylindrical surface" in cross-section. The expression "optical plane" in this specification means locus of the optical axis if the axis in the cross-section is moved parallel to the generatrix.
In the case where a cylindrical surface is a cir-cular cylindrical surface, an optical axis or an optical plane ~ 4 -~075510 is defined as a line or a plane normal to a plane cp.
In the case of a collector surface formed by rota-ting a curve about the optical axis (hereinafter referred to as a revolutional surface), a cross-section including the revolutional axis is considered and by the curve appearing in the cross-section the surface is represented.
In this case the revolutional axis is termed "an optical axisn. The optical axis of a spherical surface is also normal to plane cp.
On the other hand, "the focal point" of an optical cylindrical surface means a focal point of the curve appearing in a transverse-section of the cylindrical surface. The focal line means locus of the focus when said transverse section is moved along the direction of the generatrix.
The fresnel segments derived from and confocal with (or formed on the basis of or derived from or belong to) an imaginary cylindrical beam concentrating surface are formed on the basis of conventional design concepts for fresnel segments, such design concepts may include the following steps of (a), (b), (c) and (d).

(a) At first an imaginary beam concentrating cylindrical surface is assumed as shown by the chain line in Fig.l. Then the imaginary cylindrical surface is divided into parallel units along parallel surfaces in parallel with the optical plane. Each of these units is termed an imaginary segment.
(b) The imaginary segments expressed by the chain line are moved in parallel with the optical axis (in Fig.l, at the position of 415) to prepare "real fresnel segmentsl'. By this arrangement the whole thickness can be decreased.
(c) The step between adjacent real fresnel segments is connected by vertically rising surface (in Fig. 1, the surface 514, for example) in parallel with the optical plane.
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~0755~0 (Crude fresnel segments are accomplished by the above st(ps (a), (b) and (c), in which case, the focal points are however, displaced along the optical axis by the amount of displacement to result in dissipation of focal points.) To obtain a correct concentration, it is necessary to carry out the following process (d) -(d) Correction is applied to the moved segment in accor-dance with the amount of movement in a manner that focal point is located at the position before the movement of the segment.
The features of the integrated collector construc-tion according to the invention can be summarized as follows:
(1) The above-mentioned inherent drawbacks of the con-ventional fresnel collectors are remedied completely. Namely, the solar beam radiation can be concentrated without material losses even when the incident beam is slanted at a relatively large angle. Therefore, it is not required to change the angle of inclination of the collector for tracking the sun as with the conventional fresnel lenses. The lines of con-centration can be fixed simply by shifting the collector.

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(2) The adjacent segments of the integrated fresnel refractor or reflector form ridges of low and obtuse angle to allow fabrication of collectors thinner and with a lesser number of segments as compared with conventional counterparts. As a result, the fabrication of the collector becomes easier. For i example, the collector lens can be produced from glass continuou sly and on a mass scale by the existing sheet-glass producing I methods or alternatively from a synthetic resin material by the use of the known molding methods and processes with high precision but at a low production cost. The fabrication of the integrated fxesnel reflector from a metal sheet can also be facilitated, not mention to the polishing and other finishing treatments. a a

(3) It becomes easy to produce/collector of/short focal length and large aperture diameter. It follows that, if the receivers or heat absorbing pipes are mounted close to the collectors the structure of the collector as a whole can be made thinner and compact to an economical advantage. The compact construction of the collector makes the sun tracking operation easier, reducing the relative movement of the collector and the receivers.

(4) Particularly, the lens refractors and mirror reflector , formed with integrated cylindrical fresnel segments have a number of advantageous points. Where the axes of the cylindrica 1 segments are disposed in the direction of east - west, the lines of concentration to the movement of the sun for the period of on~ ~ -~ear are moved /slightly in a lateral direction or in a direction perpendicular to both the optical axis of the cylindrical refractor or reflector segments and the axis of the cylindrical segment surface (hereinafter referred to simply as "lateral

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direction" for brevity). This lateral shift is, in practice a little in practical several hours about the noon so that the tracking of the sun may be easy to have the loss lessened.
Further, as will be mentioned hereinafter in detail, these collectors may be split into sections in parallel to the axes of the cylindrical segments, whereby the split sections can be made slanted for tracking of the sun to provide an effec-tive and low-cost solar collector. The easiness of fabrication as mentioned in (2) is also more effective.
In the accompanying drawings:
Fig.l is a diagrammatic transverse cross-section of a conventional plano-convex cylindrical fresnel refractor;
Fig. 2 is a diagrammatic transverse section of a solar concentrator according to the invention with integrated convex cylindrical fresnel lens segments;
Fig. 3 is a diagrammatic transverse cross-section of another embodiment of the invention with integrated fresnel lens segments formed on opposite sides of the concentrator in parallel relation;
Fig. 4A is a plan view of another embodiment of the invention with the integrated fresnel lens refractor formed on opposite sides of the concentrator in perpendicu-larly intersecting relation;

10755~0 ~, . 1, Fig. 4B is a sectional view taken on line X - X of Fig. 4A;
Fig. 5 is a diagrammatic transverse section of another embodiment of the invention using an integrated fresnel concentrator with concave cylindrical reflecting surfaces.
Fig. 6 is a diagrammatic transverse section of still another embodiment of the invention employing an integrated fresnel refractor with convex cylindrical lens segments and an integrated fresnel reflector with concave cylindrical reflecting surfaces formed respectively on another different concentrator in perpendicularly intersecting relation with each other;
Fig. 7 is a diagrammatic transverse cross-section of a further embodiment of the invention;
Fig. 8A is a plan view of a concentrator having arrays of conventional hemispherical convex lenses;
Fig. 8B is a sectional view of the concentrator of Fig. 8A;
Fig. 9A is a plan view of a solar concentrator embodying the invention and having integrated hemispherical fresnel lens ~.
segments;
Fig. 9B is a sectional view of the concentrator of Fig. 9A;
Fig. lOA is a plan view of an integrated fresnel reflector . , zig-zag having revolutional reflecting surfaces with/boundaries of revolutional surfaces shown in solid lines !
Figs. lOB and lOC are transverse and longitudinal sectional views of the concentrator of Fig. lOA;
Fig. 11 is a graphic representation of variations in the angle of incident beam radiation in one year, half a month and one day;
Fig. 12 is a diagrammatic transverse section of a solar concentrator having split reflecting sections;
Fig. 13 is a diagrammatic transverse section of a solar _ 7 -~t................. . . , concentrator having split refracting sections;
Fig. 14 is a diagrammatic transverse section of an integrated fresnel concentrator using a combination of split refracting and reflecting sections;
Fig. 15 is a diagrammatic transverse section of an integrated fresnel concentrator using a combination of a number of split refracting sections; and Fig. 16 is a fragmentary perspective view showing unit pattern~ of split type solar beam concentrator according to the invention employing two-dimensionally integrated fresnel reflecting segments.
EMBODIMENT 1 (Fig. 2) The integrated fresnel lens of the invention consists of a series of lens segments formed on the basis of imaginary cylindrical lens surface units 510, 520 and 530 as shown in Fig. 2. The integrated fresnel lens according to the inven-tion distinctively differs from the conventional counterpart of Fig. 1 in that the cylindrical refracting segments of one lens unit is connected by cylindrical refracting segments of adjacent or adjoining lens unit instead of flat rising ~ dividing surface 414 and 424 of Fig. 1. (Now assume that ,~ these rising positions 514,,524 and in Fig. 1 which are a number of parallel lines are disposed substantially on a single or common plane CP which is perpendicular to the optical axes OA thereof.) More particularly, the cylindrical refracting ~;
segments 515 which are one group of fresnel segments formed on the basis of the imaginary cylindrical beam concentrating surface unit 510 are connected by similar cylindrical refrac-: ting segments 525 of imaginary adjoining lens .

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unit, so that solar beam radiations are concentrated at either concentrating lines 5120 and 5220.
As mentioned hereinbefore, the integrated fresnel concentrator is a modification of the conventional solar collector using simple arrays of fresnel lens segments as shown in Fig. 1. Theoretically there is no limit to the number and positioning of thc individual lens segments so that a great freedom is open to the designer in constructing concentrators which may suit particular requirements. The integrated fresnel refractor of Fig. 2 is obtained simply by providing the cylindrical refracting segments of the adjacent lens unit in place of the upright rising dividing surfaces 414 and 424.
The rising positions 514 and 524 of Fig. 1 and the rising positions 514' and 524' of Fig. 2 are corresponding respectively to each other.
. EM~ODIMENT 2 (Fig. 3) The embodiment of Fig. 3 has the integrated fresnel refractor of Fig. 2 on opposite sides of a transparent plate with the axes of the cylindrical lens segments formed on the upper and lower sides of the plate, which are located in parallel and vertically aligned relation with each other to give increased effects of short focal length. The symmetric arrangement of the lens segments on opposite sides of the concentrator may cause a slight degree of scattering to the incident beam radiation. Such scattering of beam radiation, however, can be reduced to a minimum by reducing the thickness of the lens and increasing the focal length of the lens on the upper side of the concentrator or on the side which firstly receives the incident beam radiation.
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' 30 EMBODIMENT 3 (Figs. 4A and 4B) The embodiment of Figs. 4A and 4B has the ~ntegrated _9_, 1'.
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~ 1075510 fresnel refractor of Fig. 2 on opposite sides of a transparent plate with the axes of the cylindrical lens segments on the upper and lower sides of the plate in perpendicularlY inter-secting relation with each other. Generally, the axes of the upper and lower cylindrical lens segments are not necessarily required to be intersected perpendicularly. If the focal lines of the upper and lower lenses are on the same plane, the incident beam radiation is concentrated at the intersecting points of the respective focal lines, concentrating the beam radiation to a far increased flux density. Where the upper and lowex lenses have focuses on different planes, the beam radiatio is concentrated in the form of line segments or in a rectangular shape depending upon the shape and position of the receivers.
The ratio of the longer and shorter sides of the rectangle (usually parallelogram) can be changed arbitrarily to suit particular needs.
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EMBODIMENT 4 (Fig. 5) Fig. 5 illustrates an embodiment employing a concave cylindrical reflector. Where the concave cylinders (usually parabolic cylinders) of the reflector has a large aperture diameter, it is advantageous to integrate the reflecting surface ¦ of the adjacent units in a manner similar to the integrated ! fresnel refractor discussed hereinbefore. For example, the .
reflector of Fig. 5 is composed of a series of reflec-ting segments which are formed based on imaginary concave cylindrical surface units 691, 692 and so forth, integrating cylindrical reflecting segments of adjacent units with each other as the rising positionsof a plurality of parallel lines 690 substantial Y
on a plane which is perpendicular to the optical axes and gettin ' . .
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rid of the useless rising surfaces in the same manner as in the integrated fresnel refractor of Fig. 2. The conventional concave-cylindrical fresnel reflectors are susceptible to beam ,; collection losses since part of/reflected beam radiation is scattered upon hitting on the rising surfaces even when the incident beam radiation is parallel to the optical axes of the reflecting parabolic cylinders. The integrated fresnel reflecto according to the invention, however, is completely free from this sort of losses.
The above-mentioned integrated fresnel refractor and 1 reflector may be employed independently as a solar concentrator f but may be combined together to provide concentrators of particular constructions as will be discussed in the following embodiments.
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EMBODIMENT 5 (Figs. 6 and 7) ;~ Fig. 6 shows a solar concentrator employing the I integrated fresnel refractor 416 of Fig. 2 in combination with the concave-cylindrical reflector 426 of Fig. 5. The axes of I the cylindrical segments of the refractor and reflector are disposed perpendicular to each other so that their focal lines fall on the same plane as at 406. The receivers are located on the beam concentrating points or lines on the common focal . plane 406. Here, what is c~nsidered to be the focal length of , the lens 416 is the length of the reflected beam passage 416-426-406.
. With the- solar collector of Fig. 7, the receivers are located on the upper side of the collector. This embodiment also has the axes of the cylindrical refracting and reflecting _ segments disposed perpendicular to each other. The incident -11-, ' '`Cl ~ ~ ,; . - t9"' .

solar beam radiation is, after passing through the refractor 44, reflected on the reflecting mirror segments/and concentrated after passing again through the refractor/so that the integrated fresnel lens has an extremely short apparent focal length.
The shorter the distance between the refractor/and the 45, reflector /the better from the standpoint of reducing the scattering which is otherwise caused to the beams re-entering the refractor. The concentrator of Figs. 6 and 7 can contribute to reduce the thickness of the solar water heaters.
If the concave-cylindrical reflectorof the embodiment of Figs. 6 and 7 is replaced by a plane mirror, the result is linear concentration of the beam radiation.
Beam concentrating functions similar to the embodiment of Fig. 7 can be obtained also by providing a reflecting layer lS on the back side of a concentrator which has an integrated fresnel surface on one or opposite sides thereof. In/case of integrated fresnel lens segments formed on opposite sides of the transparent plate or on the one side thereof, as mentioned above, even if/metallic film is attached to the back side of -¦ 20 the transparent plate with respect to light transmission so as to allow the surface to be served as a mirror, such the equivalent function can be obtained that the collector combined with `/ integrated fresnel lens segments and a mirror 45 of Fig. 7 which includes a plane mirror.
! 25 It is possible to construct many other solar concentrators of different constructions by using the integrated fresnel collector according to the invention. For example, the integrat ed fresnel reflector 45 of the embodiment of Fig. 7 may be substituted by an integra~ed fresnel reflector of a shape 30- complementary to and coextensive-with the integrated fresnel - 12 -, lens segments of the lens 44. In such-a case, if the integrated fresnel reflector and refractor are positioned opposingly in a small gap relation with each other, the light flux is concentrated at a very high rate with almost no scattering.
The foregoing description has dealt with concentrators with cylindrical or parabola-cylindrical surfaces. However, in order to concentrate the beam radiation on a single line or .;
a single point, (in certain arrangements of optical systems) it is necessary to employ a refractor or reflector with surfaces of quadratic curve such as/parabola, hyperbola or ellipse in section. Strictly speaking, in integrating such refracting or reflecting segments, the curved surfaces have to be modified 1 in order to compensate for the variation in thickness of the; lens.
; 15 However, solar collectors with an excessively high concentration power are unnecessary in certain cases, for example, in water heaters and solar batteries. Therefore, the circular ~¦use of si~ple/lylindrical segments can be advantageous.
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! Alternatively, the shape of concentration may be extended , purposely in the direction of the optical axes by using an imaginary cylindrical surface unit of a sectional shape other as will be hereinafter mentioned.
.t ' ,than the afore-mentioned quadratic curves or polygonal shapes/
Furthermore, a combination of various and different concentrat-ing segments may be employed to cope with different angles of -30 incidence of the solar radiation or in consideration of particul 'r . .
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. , shape and construction of the receiver or the relative movement of the sun. formed from imaginary units It is also useful to integrate cylindrical fresnel segments of polygonal shape in section. In this instance, manufacture made is further/easier because the respective integrated cylindrical fresnel segments come into simple plane or polygonal cylindrical surface or the combination thereof.
In the foregoing embodiments, the concentrating segments of the adjacent imaginary cylindrical surface units are integrated with each other one-dimensionally or in the lateral direction. However, the integration of the concentrating segments can be effected two-dimensionally by using imaginary units of revolutional curved surfaces. In this instance, it is also possible to provide at a low cost a solar collector which is capable of concentrating beam radiations of a wide range of anglesof incidence at a high concentration ratio and without losses, as will be discussed more particularly hereinlat r.

:, . EMBODIMENT 6 (Figs.- 9A and 9B) ~i Figs. 8A and 8B illustrate an array of conventional ¦ 20 hemispherical fresnel lenses with concentrating segments 112, ¦ 212 and 312 formed on the basis of imaginary hemispherical surfa e units of the same shapes 110, 210 and 310 which are disposed in the most density. The concentrating segments are stepped segments out toward the hems of the respective adjacent /by cylindrical rising planes 111, 211 and 311. Theoretically, there are no particular restrictions to be imposed on the number or position-ing of the lens segments 112, 212 and 312 though the illustrated lenses are divided into a small number of segments for the simplicity of illustration. However, in actual applications, ..
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, 1~75510 the lenses are divided into a greater number of segments to reduce the thickness of the lenses.
A problem arises when the above-described conventional fresnel lens is used as a solar concentrator. More particularly .-S solar beam radiation incident at a slanting angle, is caused to scatter uppon hitting on the rising cylindrical planes resulting in a reductlon ln gain.
The existence of the rising cylindrical planes also causes difficulties in molding the concentrating lenses, particularly in ejecting the lenses from molds. In order to facilitate the ejection from molds, the rising planes are usually formed in a conical shape which, however, causes the losses to occur even ~ in collecting beam radiations in the direction of the optical ¦ axes.
Similar difficulties are also encountered with a fresnel reflector having a number of reflecting segments of paraboloid of revolution (formed in a complem~ntarily shaped molds instead I of the hemispherical planes of the fresnel lenses in Figs. 8A
and 8B), suffering from losses due to scattering of beam radiation by reflections on the dividing riser planes which is caused by the incident rays which are in the direction of the optical axes of the respective refracting segments.
Figs. 9A and 9B illustrate an integrated fresnel refractor which corresponds to the conventional collector of Figs. 8A
and 8B. In Figs. 9A and 9B, the refracting segments of the adjacent imaginary hemispherical refracting surface units 230, 310 and 420 which are arrayed ln overlapping relation are integrated with each other. The dividing riser planes in the conventional hemispherical fresnel lenses are replaced by imaginary ~30 refracting segments of adjacent/lens units as indicated at 2301 ., -'15- 1, . .
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and 3101.
As seen in the plan view of Fig. 9A, the hemispherical fresnel concentrator has a recurring pattern of triangle 12, 23 and 31, more precisely, triangle 12, 23 and 333. The paths of the incident beam radiation are indicated by fine lines. It will be seen that all the incident-beam radiation is concentrate either at the polnt 2300 or 3100 or so forth.
It is also easy to integrate the concentrating segments two-dimensionally, with no particular limits to the number and ~ 10 positions of the individual segments. For example, the collecto ; of Figs. 9A and 9B is so formed as to use on the respective ; sides of the triangle 12-23-31 the dividing positions 100 ofFigs. 8A and 8B as these exist which are corresponding to 100' in Figs. 9A and 9B and indicate the points arranged in a single plane which is perpendicular to the optical axes in Fig. 9, and to integrate the segments 2340 and 234ijof the imaginary unit hemisphere 230 with segments 3140 and 3141/of the imaginary unit 310 or with segments 3140 and 314ijof an imaginary unit 120 (not shown) at the dividing points 100' (segments of same imaginary unit are indicated by same hatching).
Where it is desired to make uni-thickness the point 333 whi h has a relatively small thickness~
segments of adjacent imaginary units may be further integrated at positions indicated by dots 431 to 434. The dots 431 to 434 are located at the same level as the points 100'. This subdividing method is useful when it is desired to obtain a concentrator of uniform or r~duced thickness. There is no particular limit to the position of the subdividing point so that it is possible to make the thickness further equilized, whlch results in enabling the further reduction of the thicknes ¦-. . ~

.~.~,. . . , .. . ~, 10755~0 It has been confirmed that the two-dimensionally integrated fresnel concentrator has the effects equivalent to those of the one-dimensionally integrated fresnel concentrator discussed hereinbefore.
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. 5 EMBODIMENT 7 ., There may be employed a concentrator which has the integratl ~d hemispherical fresnel lenses on opposite sides of a transparent plate. In this instance, it is possible to obtain a concentrato r of an extremely short focal distance by aligning the fresnel lens patterns on opposite sides of the substrate.
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EMBODIMENT 8 (Figs. lOA, lOB and lOC) A reflector having a number of reflecting segments having surfaces of paraboloid of revolution has been used also for the concentration of solar beam radiation. This type of reflector can also be made thinner by two-dimensionally integrating the reflecting segments in a similar manner. For example, an integrated parabolic fresnel reflector is obtained by providing reflecting segments having surfaces of paraboloid of revo]ution instead of hemispherical segments of the fresnel lenses of Figs. 9A and 9B. , Figs. lOA to lOC illustrate an example of an integrated fresnel reflector using reflecting segments based on paraboloid , of revolution and having a quadrilateral unit pattern 56-67-78-8 3 which corresponds to the triangular unit pattern 12~23-31 of ~5 - Fig. '3A. / Fig. lOB shows the reflector in a section as taken on line 67-78 of Fig. lOA. As seen in Fig. lOB, the reflector has a number of integrated reflecting segments of one direction which are formed on the basis of imaginary units of paraboloid . - 17 ~.

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Fig. lOA shows zig-zag boundary lines of each fresnel segments which actually has complicated mosaic pattern but . . outline briefly as simple orthogonal lattice lines, which . case is corresponding to the case where the forcal length is considerably longer than that of Figs. lOB and lOC.
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~, ., of revolution 670 and 780 in short distance of cuttings.
While, Fig. lOC which is a section taken on line 78-89 of Fig.
- lOA shows the integrated reflecting segments of another directiowhich are formed on the basis of imaginary unit paraboloids of revolution 780 and 890 in large distance of cuttings. The four curved planes which share one apex point (or bottom point) are reflecting segments when forming on basis of adjacent imaginary unit paraboloids of revolution which concentrate the solar beam which has the direction of the optical axes radiation/on four different focal points 6700 and 7800 which are located immediately above the points 67 and 78 ... ~., respectively. Thus, the reflector contains no useless planes which do not participate in the beam concentration.
Similar integration can be applied to a unit pattern of pentagonal shape (with five focal points) or more complicated polygons. The unit pattern does not necessarily need to be a regular triangle or square, or the like and the two-dimensional-ly integrated segments may have the respective focuses located on an arbitrary plane or planes and may have different or same focal lengths. In principle, a multitude of points are uniforml Y
distributed over the entire surface of the concentrator to form apex or bottom points of the planes of the segments which have focal points on a predetermined plane or planes.
However, with an increased number of ridges which divides the individual segments, it becomes more difficult to fabricate .
¦ 25 the molds and scattering of the beam radiation is increased.
Therefore, it is more advantageous to employ a relatively simple construction a in Figs. 9A and 9~. -. .,.~ , .
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The solar concentrator may be composed of an integrated hemispherical fresnel reflector and a complementary shaped ~; fresnel refractor which is disposed in a small gap relation with the reflector, with the respective unit patterns in alignment with each other. As mentioned hereinbefore, a collector which is provided with a complementary shaped reflector and refractor has a very strong concentr'ating power.
¦ Instead of combining an integrated fresnel lens with an I 10 integrated fresnel reflector or with the plane minor, a reflect-ing surface may be provided on one face of a concentrator which has an integrated fresnel surface on one or opposite sides thereof. It will be understood that a variety of solar concentrator constructions are available with use of the integrated fresnel reflector and/or refractor.
With an integrated fresnel concentrator which has small and finely divided segments based on imaginary unit surfaces of revolution, the respective segments may be substituted by an approximating plane-or planes without substantially impairing the solar beam concentrating function of the collector. Such substituted planes are equivalent to integrated fresnel segments ' based on imaginary unit polyhedral planes (with concentrating function). In addition to the above, the facts stated in the embodiment 5 may be applied to this embodiment of the collector .
I 25 using two-dimension integrated fresnel segments.
¦~ As mentioned hereinbefore, one of the features of the integrated fresnel concentrator resides in that the sun tracking is accomplished simply by moving the receiver parallel to the plane of the concentrator lens plane. However, as the incident beam radiation is slanted considerably, the losses due to '. ' i 2i~-.~, . . . . . . . . .....

:: 107551o reflections on the lens surfaces become largex and the image of the sun at the concentrating plane is blurred due to various aberrations, failing to ensure the intended strong concentration (These phenomena occur with the conventional concentrating S lenses, too.) Fig. 11 is a gr~phic representation of the lateral in a day displacement of the incident beam radiation of Fig. 2/in every - half a month of the year. The scale on the vertical axis represents the amount of displacement in terms of the ratio of the distance d of Fig. 2 to the focal length f of the cylindrica L
lens, while the scale on the horizontal axis represents the hours of the day. The graph of Fig. ll presumes that the axis of the cylindrical plane is oriented east-west and the plane of the concentrator is disposed normal to the sun at noon of autumnal equinox point. The angle q of Fig. 2 (hereinafter referred to as angle of skew of the sun) changes in a similar manner as in Fig. 11.
It will be understood from Fig. 11 that the incident rays show complicate and large displacement in the lateral direction to increase the value of the skew angle of the sun. This means that the loss due to the reflections of the slanting rays is increased. The same thing happens with the integrated hemispherical fresnel concentrator of Figs. 9A and 9B
to deteriorate its performance quality. The same , problem is encountered with an integrated fresnel reflector(as ,l in non-integrated fresnel reflector). The line of the concentrated beam is blurred,all the more and the reflector looses practicality even with slightly slanting beam radiation.
The following description is directed to this problem, providing means for lessening the losses in one- and two-dimensionally . 21 .
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- ~ ., . v integrated fresnel concentrators.
. 1, EMBODIMENT 10 (Fig. 12) ;' Fig. 12 shows a sun tracking solar collector having a . number of split type integrated cylindrical frèsnel reflectors 400 each with cylindrical reflecting segments 401 and 402 which concentrate normal incident rays 411 and 412 at focal lines 421 and 422 ...., respectively. Fig. 12 shows the reflecto G
in a section taken on a plane perpendicular to the axes of the cylindrical segments the number of which is reduced for the simplicity of illustration.
It is to be noted that cylindrical reflecting segments may be replaced by approximating plane mirrors. In a large-sized solar collector with a great number of concentrating i segments, plane mirrors are actually used in place of cylindrica 1 ones. For example, the adjoining segments 401 and 402 or segments 402 and 403 .. ......are disposed pèrpendicular to a straight line which bisects the angle formed by the normal incident ray 411 ...... and its reflection directed to the focal lines 422 and 421 ..... ., the angle of intersections of the two adjacent segments being 180 minus half the angle 01 between the lines leading from the reflecting point toward the focal lines 421 and 422. This is a value constant respecti-vely to each reflecting point irrespective of the relative position of the sun. When the rays are incident as indicated at 431 and 432 ..... , the segments 401 and 402/has to be shifted to the positions 4011 ....
and 4021~ respectively, in order to concentrate the beam radiation at the focal lines 421 and 422 but the angle of the two adjacent segments remains the same as the value mentioned --~ 22 .~

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above.
Thus, in order to fix the concentrated flux at the predetermined focal lines, it suffices to orient the individual cylindrical segments in their respective positions half the angle of skew ~ of the sun.
Independent orientation of the individual cylindrical segments/too complicatedand troublesome. To avoid this, the - integrated fresnel reflector is divided parallel to the axes of the cylindrical reflecting segments, into a number of independen :
1 10 sections 441, 442 and so forth. The width of each divided section is preferred to be smaller than that of the imaginary cylindrical unit planes. The smaller the width of the divided section, the greater become the resultant effects as will be explained in greater detail hereinlater. The divided sections are tilted separately for an angle of ~/2 to track the sun as indicated by broken lines.
As the respective sections are tilted, the cylindrical segments on the edges of the adjacent sections are parted away from each other and slightly shifted parallel to the plane of the collector. As a result of the displacement, the angle of the reflected rays is varied depending upon the amount of displacement and the concentrated flux is deviated from the fixed focal lines 421 and 422. However, the displacement is very small and can be ignored in a large-sized collector which has relatively ~arge number of divided sections and large receivers or heat absorbers. Ideally, the mounting position of the rotating shaft 461 should~ be selected such that the mean value of the deviations is smallest.
As shown in Fig. 12, the divided sections are rotatable about the respective rotating shafts 461, 462 and 463 which are disposed parallel to the axes of the cylindrical reflecting seym ~nts.
- ~-` 23 .. . .. - . '~ . - ,. . . .

*B
Where the range of oriented angle of split section is ~' approximately constant, it is effective for the angle of . segments to be adjusted to have the deviation zero at the time .~ . of the constant angle. This adjustment is in general small.
l In order to make the deviation zero throughout all the .. orientation, each section is formed of flexible material so as to allow the section to be bent slightly in the shape of "S" .
figure or "inversed S" figure according to the amount of the inclination with being parallel with the axes of cylindrical surface.

. -' 24 10755~0 The divided sections are /supported on arms 451, 452 ... which are fixed at the ends of the divided sections respectively in the direction of axes of cylindrical segments.
The arms are provided with grooves 4610, 4620/for receiving pins 471, 472 ..... which are I fixedly provided on a control rod 48 so that the respective i through sections can be driven simultaneously/the control rod 48.
~ With the conventional solar collector using a reflector ¦ with reflecting surfaces of parabolic cylinders, it has been ¦ 10 necessary to move the whole structure of the collector including the heat receivers for the sun-tracking purposes, requiring sturdy support structure and powerful driving means.
In contrast with the solar collector according to the invention, the sun tracking operation can be accomplished by simple and low cost orientation mechanism with a simple support structure. This advantage becomes more conspicuous with larger concentrators. The principles of the foregoing embodiment can also be applied to a case where the focal lengths of adjacent imaginary reflecting surface units are different from each other. Alternatively, the orientation of the cylindrical reflecting sections for the sun tracking can be accomplished by tilting the respective sections of Fig. 12 simultaneously through the angle ~. In such an instance, howeve , the line of concentration is shifted and divided into a plural number of segments(depending upon the number of the concentrat-ing sections) and distributed on the tilted optical axis.
Therefore, it becomes necessary to select a receiver which has suitable shape and construction and which is movable for tracking purposes.
3d The divided concentrating sections only need to be tilted , ~
.

' t7 :r - .~ . , . __, in the respective positions- It sh~uld be understood that the manner of supporting and driving the individual sections is not limited to the particular method shown in the drawing.
.,', EMBODIMENT 11 (Fig. 13) Fig. 13 illustrates an integrated fresnel refractor 500 which has cylindrical refracting segments 501 and 502 and so forth. Normal solar beam radiations 511 and 512 incident on the segments 501 and 502 are concentrated at focal points 521 and 522, respectively. The figure shows the refractor in a section taken on a plane perpendicular to the axes of the cylindrical refracting segments.
If the refractor 500 of Fig. 13 is located so that the axes of the cylindrical segments is disposed east-west and normal to the sun at noon of autumnal equinox, the line of concentration shows lateral displacement d as shown in Fig. 11.
At this time, the total amplitude of the angle of skew/q is relatively large, as shown in Fig. 2.
The skew angle of the sun should be reduced from the standpoint of reducing the losses of beam radiation. However, 2~ in order to tilt the whole structure of the collector, it become necessary to provide large supporting structure and driving apparatus. Considerations have to be also taken of the winds.
In this connection, the embodiment of Fig. 13 has the .
integrated cylindrical fresnel lens divided into a suitable number of sections 541, 542 and so forth which extend parallel to the axes of the cylindrical refracting segments. The widths I of the respective sections are preferred to be smaller than the width of the imaginary unit lens plane.
- As the incident solar beam radiation is slanted as at 531 . .

.~ 6 . ,.
.
~, ................ . ^i.... .. ,, ...

and 532, the respective sections are tilted simultaneously and equivalently to avoid slanting of the incident rays. Indicated at 551 and 552/are arms which are located at the east and west ; ends for rotating the respective sections about the shafts 561 -- the axes of and 562/which are disposed parallel to/the cylindrical refract-ing segments. The individual sections are driven by fixed pins . ...
571 and 572/on a control rod 58 in a mannertsimilar to the foregoing embodiment. Arrow 580 indicates the amount of displacement of the rod 58.
The rotation of the divided sections causes the concentrat-ing lines to shift as indicated by bro]cen lines and at 5211 and 5221. The positions of the concentrating lines are corrected by moving the concentrator parallel to the receiver by the distance of 5211 - 521, fixing the concentrating line at the predetermined positions.
The parallel movement can be effected by shifting a support frame (which is disposed east-west though not shown in Fig. 13) to which the shafts 561 and 562/are secured.
The collector sections 541 and 542/are not required to bs rotated until they face the sun at normal angle.
The rotation of the concentrator sections may be effected once in half a month, holding them in fixed positions until next orientation. This is because the daily tracking of the sun can be attained by the displacement in the direction of , arrow 590. The plots by broken lines in Fig. 11 represent the amount of displacement 590 from a shifted new focal point, for a concentrator which is fixedly tilte-d 12 degrees toward the north, on the day of summer solstice Sl and the days one month before and after the summer solstice.
As shown in the figure, generally the light beams collected ., . .
, ~ 27 ,.. ... . . .,; .. . .
.. . ,, ~ . . . ~ .
, by the respective sections are not brought on one line during the rotation of the concentrating sections but are distributed in the direction of the optical axis over a distance g in proportion to the rotational angle. Where a receiver is influenced by blurring of the concentrated flux, it is necessary to hold the rotation of the collector sections 541, 542 within a limited range (e.g., 5 - 10 degrees) thereby to reduce the value of the blur g at the concentrating line 5211.
This embodiment also has the advantages of simple construction, simple supporting and orienting mechanisms, and low cost production, and these advantages becomes more pronounce with large-scale sollar collectors with a large number of concentrating sections.

. EMBODIMENT 12 ~Fig. 14) There may be provided a solar collector using a combination of sections of integrated fresnel reflector and sections of integrated fresnel refractor, with axes of the cylindrical reflecting and refracting segments disposed in parpendicularly intersecting relation to obtain beam concentration on points, segments line /or in rectangular forms,as shown in Fig. 14.
In Fig. 14, showing the collector in a transverse section, indicated at 60 is an integrated cylindrical fresnel refractor as used in Embodiment 11 (or more specifically the reference , numeral 60 denotes one of the divided sections of the refractor) .
The east and west ends of the respective concentrating sections of the refractor are supported on common frames 611 and 612.
The individual concentrating sections are rotatable through the arms 621, 622 control rods 631 and 632 by and with /which are secured to the respective sections. Though omitted in the embodiment of ~-; 28 . ,,.

~: ,......... .. . ~.;

Fig, 13, the supporting frames 611 and 612 function to move the collector for tracking purpose in a direction perpendicular to the surface of the drawing. ~
Indicated at 651 and 652/are split sections of an integrate cylindrical fresnel reflector as used in Embodiment 10, which are rotatable through a common control rod 66. The solar collector of this embodiment is located, for example, such that the axes of the refracting segments are disposed east-west while those of the reflecting segments are disposed in the direction of south and north poles of the celestial sphere.
Designated at 681, 682 and 683 are receivers or heat absorbers.
Ll-~L2 Ll and /are focal lengths of the reflector and refractor, respectively. The beam radiations refracted by the lens segment of the refractor are concentrated by the mirror segments of the reflector. The above-mentioned location is advantageous to the reflecting type collector in that good concentration of beam radiation is ensured even with a large skew angle of the sun.
, EMBODIMENT 13 (Fig. 15) The collector may be constructed using a combination of two split type integrated fresnel refractors, with the axes of the respective cylindrical lens segments disposed perpendicularl intersecting relation as shown particularly in Fig. 15. As seen in Fig. 15, a transverse section of the collector, the lower , and upper integrated fresnel refractors are split into a number of sections as indicated at 70 and at 731, 732 and 733 jThe refracting sections of the upper and lower refractors are controllable similarly through control rods 71 and 74, , respectively. The reference numeral 72 denotes a support frame.
, The upper and lower refractors are located close to each other .
. ` 2~
'.'................ ...

1~75510 with the axes of the cylindrical lens segments disposed in perpendicularly intersecting relation to concentrate the beam radiation at 751, 752 and so forth.
As mentioned hereinbefore, a blur g is produced in the direction of the optical axes when the collector is tilted at a large angle and the blur g becomes larger with a greater tilting angle of the collector. With this particuiar embodiment satisfactory concentration would therefore be obtained only for five or six hours of midday. However, the blurring g does not impair the practicality of the collector. For example, a ! as shown by 78 in Fig. 15 receiver or a heat absorber/may be held in an upright position parallel to the optieal axis.
The foregoing description has dealt with tracking type collectors with one-dimensionally integrated eoncentrating segments. Orientation or sun-tracking is also feasible with sollar collectors employing two-dimensionally integrated concentrating segments, as will be explained in greater detail hereafter.

EMBODIMENT 14 (Fig. 16) Fig. 16 illustrates principles of a sun-tracking type solar collector using a two-dimensionally integrated fresnel reflector, showing a part of the reflector which corresponds to triangle 12-23-31 of Fig. 9A. The triangular part of the , reflector is divided into 9 (nine) sections 841, 842 and so forth of uniform area. The divided seetions have rods 851, and so forth 852/seeured to the respeetive center portions for the tilting operation. These tilting rods, and a sun-tracking needle 340 and receivers 129, 239 and 319 are tiltably passed through small apertures 8417, 8427/ 3407, 1297 (not shown), 2397 and ' . ' ~ .0 , ~ -.

3197 in a common supporting fixed sheet 309 and then through small apertures 8518, 8528 /3408, 1298 (not shown), 2398 and 3198 in a common control sheet 409 which is provided parallel to the sheet 309. The digital end of the tracking needle 340 is rocked to track the sun (for several hours of the daytime) throughout a year. Such needle tracking is feasible by mechanical drive using an equatorial telescope as a prime mover or electromechanically under computer control.
! As the tracking needle 340 is tilted, it pushes the smallaperture 3408 to urge a parallel movement to the control sheet 409. As a result, all the collector sections and the receivers which are in engagement with the apertures 8518, 2398/are tilted to track the sun.
When the collector sections are inclined, the concentrated flux is spread in the axial direction on the tilted receiver.
Therefore, the receiver should have a shape and a length suitable for the particular conditions of the concentrated flux.
Instead of the above-described"total tracking"which completely follows the movement of the sun, there may be employed the so-called "half tracking'1. For this purpose, the needle 340 of Fig. 16 is replaced by "a half-tracking needle"
which is mechanically or electromechanically controlled to move half the amount of displacement of the sun,*C
As the sun moves, the half tracking causes a greater ! 25 blurring to the concentrated fiux (especially in the lateral direction) than the total tracking, limiting the shape of the receivers and the operable hours. An advantage of the half tracking is that the parallel movement of the receivers is not xequired.

. ,- ~1 . ' '.

~075510 ,' *C - .
(continued) and large apertures 2399, 3199, .... are replaced with small ap tures 2398, 3198, ... to fix beam receivers.
. .

__ The above-described tracking principles can be easily applied to solar collectors of integrated spherical fresnel ; refractors. In such a case, however, the flxed and control sheet are required to be transparent to allow passage of incident beam radiation. The sheets may be formed from a transparent material or alternatively from wire mesh or other light permeable material. Different from the reflecting eollector, the half tracking of the refracting collector is carried out for the purpose of lessening the degree of inclina-tion of the incident beam radiation (thus not limited to 1/2~, and parallel movement of the receivers is always required.
The above-mentioned half and total tracking may be unsatisfactory for a concentrating operation extending over a long per od of time but is economically very advantageous for the simplieity of the supporting and tracking structures. It will be understood that the same tracking method can be applied to the embodiment of Fig. 4 which has the integrated cylindrica I
fresnel refractors on opposite sides in perpendicularly intersecting relation.

EMBODIMENT 16 .
In splitting a solar collector which has an integrated cyLindrical reflector and an integrated-eylindrical refractor on the back and front sides of a thin plate with the axes of the reflecting mirror and refracting lens segments in perpendi-cularly intersecting relation, the collector is severed parallel to the axes of the cylindrical reflecting segments on the back ; side. Upon installing the so divided collector, the axes of the refracting lens segments are disposed east-west and the ~ 1075510 axes of the reflecting mirror segments are disposed in the direction of the south and north poles of the celestial sphere.
It is advantageous to orient the respective collector sections by tilting them simultaneously half the angle of skew of the sun in a manner similar to the Embodiment 10. In this instance, the collector is moved only in the south-north direction and the amount of the required displacement is very small (with regard to 5 or 6 hours of the midday). Where it is desired to semi-fix the collector and adjust it normal to the sun at noon only once in half a month, the tracking may be omitted if receivers of suitable shape and size are selected.

The embodiments as aforementioned are solar collectors of plane-like such that imaginary beam concentrating surface units are formed as rising positions from lines or points located substantially on a plane to integrated fresnel segments.
Instead of this "plane-like", there is used a "parabolic cylindrical-like" collector, the fresnel segments of which are integrated as rising positions from a plurality of points located on a line which is the bottom center line of the parabolic cylindrical-like surface and the optical axes of imaginary revolutional units are intersected.
This embodiment is a useful mirror type of curved solar , collector which may be obtained by the modification such that i~
explaining with reference to Fig. 10, the imaginary revolutional li parabolic beam concentrating~surface units 560 (not shown), 890, .... are erased from the drawing, and the chain line 780 t of Fig. lOC becomes a solid line and a sectional line in this embodiment and the integrated fresnel segments are formed as . .
-c 34 ;

~, . ! ' . .
' ', ~ 075510 starting positions from a plurality of points on the straight . line 67-78 on which imaginary revolutional beam concentrating surface units 670 and 780 .... are aligned. The optical axes of these units are parallel to each other and are intersected perpendicularly with this straight line 67-78.
The sectional view of this embodiment taken along the line 67-78 is identical /Fig. lOB. In the direction of 78-89 of , chain this embodiment, the parabolic/line 780 becomes the sectional line, that is, describes a solid line on the drawing because j 10 integration of fresnel segments in the direction of 78-89 is not performed and thus parabolic chain line 890 and other so]id ~¦ lines are all removed from the drawing of Fig, lOC. In Fig.lOA, traverse lines are erased except for the only one line which is corresponding to edge end of the sectional line 780 and the part ;
, end line should be er ~sed.
of vertical solid lines which are upper side of the traverse edg '/
In the Fig. lOA, the vertical solid lines all are outlined as straight lines, but to be more aceurate, the distanee between these lines should be wider as thé lines go eloser to the edge end, whieh beeome eurved lines.
Even if respective revolutional parabolie imaginary beam eoneentrating surfaee units have different foreal length one another, the function of eoncentrating is obtainable, but in ease the foreal lengths between the respeetive units are extremely different, it follows that the overallshape of solar eolleetor eomes into distortion. Where forcal lengths Gf the units are too short eompared with the distance between adjaeent two units, it also results in distortion of the solar colleetor ~ whieh impairs praetieality.
! It is also possible to adopt as imaginary beam eoncentrat-ing surface units another revolutional surfaee than revolutional parabolic surfaee whereby it is easy to form optical system by combining with lens etc. Furthermore, effectiv~ solar collector .
.

. 1075510 .' .
r in tracking of sun and beam concentration, too is obtainable by extending optionally the forcal points in the direction of optical axes. This mirror type of solar collector may be formed in the parabolic cylindrical-like shape from the beginning of the working, or particularly large solar collector may be formed by the steps of manufacturing firstly on the plane base which is bent thereafter as shown at 780 in the drawing. This solar collector is used in a manner that optical axes are directed toward the sun and the axis of the curved surface, that is, the line 67-78 of the drawing is directed toward north-south of celestial sphere. Due to forcal points of concentration, the degree of concentration is intensified. The fresnel segments of the solar collector is replaced with approximate polyhedral surface; in other words, the imaginary beam concentrating surface unit has a polyhedral surface, whose solar collector is easily fabricated and useful~ particularly in large size.
There has been disclosed heretofore the best embodiment of the invention presently contemplated. However, it is to be understood that various changes and modifications may be made thereto without departing from the spirit of the invention.

~,. .. . ., ~.

Claims (36)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A solar collector comprising an integrated array of fresnel units, each unit having a succession of concentric cylindrical beam concentrating fresnel segments derived from and cofocal with a respective common imaginary cylindrical beam concentrating surface, the generatrices of all the cylindrical surfaces of said units being mutually parallel, the optical planes of all the cylindrical surfaces of said units being mutually parallel and the focal lines of all the cylindrical surfaces of said units being mutually parallel, the surfaces of said fresnel segments meeting each other along a plurality of parallel lines which lie substantially on a common plane which is perpendicular to the optical planes of said cylindrical surfaces of the units, adjacent imaginary cylindrical surfaces overlapping to overlap adja-cent units and integrate the fresnel segments, such that all the adjacent fresnel segments of one unit formed of one imaginary cylindrical surface are separated by fresnel seg-ments of an adjacent unit formed of a different imaginary cylindrical surface.

2. A solar collector as set forth in claim 1, in which integrated fresnel segments are beam refracting lens segments of light transmissive material.

3. A solar collector as set forth in claim 2, in which at least one of the imaginary cylindrical beam concentrating surfaces has a section of a quadratic curve.

4. A solar collector as set forth in claim 2, in which at least one of the imaginary cylindrical beam concentrating surfaces has a polygonal shape in cross section.

5. A solar collector as set forth in claim 2, in which said integrated cylindrical fresnel segments are provided on both sides of a light transmissive material, the optical planes on both sides being parallel, and the generatrices of the cylindrical surfaces of both sides also being parallel with each other.

6. A solar collector as set forth in claim 2, in which said integrated cylindrical fresnel segments are provided on both sides of the light transmissive material, the optical planes on both sides being parallel to each other, and the generatrices of the cylindrical surfaces on both sides being in an intersecting relation with each other.

7. A solar collector as in claim 2 and further compri-sing a second integrated array of fresnel units having integrated fresnel segments as beam refracting lens segments, one array being provided on a first light transmissive material and the other array being provided on a second light trans-missive material located on the back side of the first material with respect to light transmission, the optical planes of said two arrays being parallel to each other, and the generatrices of the cylindrical surfaces also being parallel to each other.

8. A solar collector as in claim 2 and further com-prising a second integrated array of fresnel units having ingetrated fresnel segments as beam refracting lens segments, one array being provided on a first light transmissive material and the other array being provided on a second light transmissive material and located on the back side of the first material with respect to light transmission, the optical planes of the two arrays being parallel to each other, and the generatrices of the cylindrical surfaces of the two arrays intersecting with relation to each other.

9. A solar collector as set forth in claim 2 and further comprising a second integrated array of fresnel units having integrated fresnel segments as cylindrical beam reflecting mirror segments formed on a second light trans-missive material and located on the opposite side of the first material than the incident light side, the optical planes of refracting and reflecting segments being parallel, and the generatrices of the respective cylindrical surfaces being in intersecting relation with each other.

10. A solar collector as set forth in claim 2, and further comprising a flat mirror disposed on a second material in parallel to said cylindrical integrated fresnel segments and on the opposite side of the first material than the light incident side, and perpendicular to the optical planes of said integrated fresnel segments.

11. A solar collector as set forth in claim 1, in which said integrated fresnel segments are beam reflecting mirror segments.

12. A solar collector as set forth in claim 11, in which at least one of the imaginary cylindrical beam concen-trating surfaces has a section of a quadratic curve.

13. A solar collector as set forth in claim 11, in which at least one of the imaginary cylindrical beam concen-trating surfaces has a polygonal shape in section.

14. A solar collector as set forth in claim 1, in which said integrated cylindrical fresnel segments form refracting fresnel lens segments on the front side of a light transmissive material, and further comprising a reflec-ting mirror surface provided on the back side of said material.

15. A solar collector as set forth in claim 14, in which said reflecting mirror surface is also formed of integrated cylindrical fresnel segments, the optical planes on both sides of said material being parallel to each other and the generatrices of the imaginary cylindrical surfaces on both sides being in intersecting relation with each other.

16. A solar collector as set forth in claim 14, in which said reflecting mirror surface is a plane mirror surface which is formed at a right angle to the optical planes of the imaginary cylindrical beam concentrating surfaces.

17. A solar collector as set forth in claim 1 in which said integrated cylindrical fresnel segments are split into collector sections, each having an area smaller than that of said imaginary beam concentrating surface, and the dividing direction being normal to the plane of the generatrices of the cylindrical surfaces and wherein said collector sections are rotatably supported on axes normal to the plane of the gener-atrices of said cylindrical surfaces.

18. A solar collector as set forth in claim 17, in which said cylindrical integrated fresnel segments are beam reflecting mirror surfaces.

19. A solar collector as set forth in claim 18, for use in sun tracking in which the angle of rotation of said collector sections about their axes is half the angle of rotation of the sun in the plane including both the sun and the generatrices of the cylindrical surfaces.

20. A solar collector as set forth in claim 18, and further comprising at least one refractor of integrated cylin-drical fresnel lens segments in parallel with reflecting mirror surfaces, and having the axes of said cylindrical lens segments disposed in intersecting relation with the axes of the reflecting mirror surfaces, and the optical planes of the refractor segments of the reflecting surfaces being in parallel with one another.

21. A solar collector as set forth in claim 17, in which said cylindrical integrated fresnel segments are beam refracting lens surfaces.

22. A solar collector as set forth in claim 21, in which said collectors comprise at least two refractors of said integrated cylindrical fresnel segments, the optical planes of which are in parallel with one another and the generatrices of the cylindrical surfaces of said refractors being in intersecting relation with one another.

23. A solar collector comprising an integrated array of fresnel units, each unit having a succession of concen-tric revolutional beam concentrating fresnel segments all derived from and cofocal with a respective common imaginary revolutional beam concentrating surface, the axes of revolu-tion of all the surfaces and the optical axes of said units being mutually parallel, the focal points of said units being located in different positions, the surfaces of the fresnel segments meeting each other at points which lie substantially on a plane which is perpendicular to the optical axes of the revolutional surfaces of the units, adjacent imaginary revolutional surfaces overlapping to overlap adjacent units and integrate the fresnel segments, such that all the adjacent fresnel segments of one unit formed of one imaginary revolutional surface are separated by fresnel segments of an adjacent unit formed of a different imaginary revolutional surface.

24. A solar collector as set forth in claim 23, in which said integrated fresnel segments are beam refracting lens segments of light transmissive material.

25. A solar collector as set forth in claim 24, in which at least one of the imaginary revolutional beam con-centrating surfaces has a section of a quadratic curve.

26. A solar collector as set forth in claim 24, in which at least one of the imaginary revolutional beam con-centrating surfaces has a polyhedral surface.

27. A solar collector as set forth in claim 24, in which said revolutional fresnel segments are provided on both sides of the light transmissive material, the axes of the revolutional surfaces of both which sides being in parallel with each other.

28. A solar collector as set forth in claim 24, and further comprising a flat mirror disposed on a second material in parallel to said revolutional integrated fresnel segments and on the opposite side of the first material than the light incident side and perpendicular to the optical axes of said integrated fresnel segments.

29. A solar collector as set forth in claim 23, and further comprising a reflecting mirror surface containing a plan mirror surface which is formed at a right angle to the optical axes of the imaginary revolutional beam concentrating surfaces.

30. A solar collector as set forth in claim 23, in which said integrated fresnel segments are beam reflecting mirror segments.

31. A solar collector as set forth in claim 30, in which at least one of the imaginary revolutional beam con-centrating surfaces has a section of a quadratic curve.

32. A solar collector as set forth in claim 30, in which at least one of the imaginary revolutional beam con-centrating surface units has a polyhedral surface.

33. A solar collector as set forth in claim 23, in which said integrated revolutional fresnel segments are split into collector sections, each having an area smaller than that of said imaginary beam concentrating surface unit, and wherein said collector sections are rotatably supported.

34. A solar collector as set forth in claim 33, in which said revolutional integrated fresnel segments are beam reflecting mirror surfaces.

35. A solar collector as set forth in claim 33, for use in suntracking in which said collector sections are rotatable through half the rotation angle of the sun.

36. A solar collector as set forth in claim 33, in which said revolutional integrated fresnel segments are beam refracting lens surfaces.