Internal refractor focusing solar energy collector apparatus and method

A solar energy collector apparatus and method, the apparatus including an open-top shell-like structure. A Fresnel lens system and a mirror system inside the shell structure focus and direct solar energy toward a solar energy absorber apparatus also inside the shell structure. The shell structure is mounted upon a hollow axle in a framework for rotation about its longitudinal axis. The framework supports the longitudinal axis in a position generally parallel to the axis of rotation of the earth to provide an equatorial mounting for the solar energy collector. Rotation about the longitudinal axis adapts the solar collector for following the east-west movement of the sun. The optical apparatus in the shell structure is adapted for movement to follow the north-south seasonal changes in the sun's position. The solar energy absorber apparatus is nonrotatably supported inside the shell structure by the hollow axle and heat transfer conduits pass through the hollow axle to the solar energy absorber apparatus in nonrotable relationship therewith. A photovoltaic apparatus may be included within the shell structure for converting at least a portion of the incoming solar spectrum to electrical energy. This combination of features provides higher solar efficiencies and higher temperatures in the heat transfer fluid. The method includes tracking the sun with the solar energy collector apparatus thereby maximizing the amount of solar energy collected while eliminating coupling failures in the heat transfer conduits.

This application contains patentably distinct subject matter from 
co-pending applications, Ser. No. 970,761 and Ser. No. 970,762, both filed 
on even date herewith. 
BACKGROUND 
1. Field of the Invention 
This invention relates to solar energy collector apparatus and, more 
particularly, to a solar energy collector apparatus and method whereby the 
shell structure for the solar collector is mounted on an equatorial mount 
for east-west tracking of the sun and the optical apparatus therein are 
movable so as to follow the seasonal variations of the sun without 
twisting or otherwise excessively bending the heat transfer conduits 
requiring flexible or rotatable couplings. 
2. The Prior Art 
Currently, the only inexhaustable source of energy available to mankind is 
solar energy. Solar energy or solar flux is customarily measured in 
langleys per minute, one langley being equivalent to one calorie of 
radiation energy per square centimeter. The intensity of the solar flux 
varies with geographical location, time of day, season, cloud cover, 
atmospheric dust, and the like, and this intensity varies between about 
zero and 1.5 calories per square centimeter per minute. Therefore, 
assuming a solar flux of one langley per minute, one square meter receives 
10,000 calories per minute while a house roof, having 100 square meters, 
receives about 1,000,000 calories per minute. With an average of one 
langley per minute for 500 minutes per day (which is slightly more than 8 
hours), the 100 square meter roof receives, in bright sunshine, about 
500,000 kilocalories per day. This energy is the equivalent in thermal 
energy to burning about 14 gallons of gasoline. Therefore, solar energy 
represents a valuable, inexhaustable energy resource. 
When an object such as a solar collector is exposed to solar radiation, its 
temperature rises until its heat losses become equal to its heat gains. 
The losses depend on the emission of radiation by the heated material, 
movement of the surrounding colder air, and thermal conductivity of the 
materials in contact with it. The gains depend upon the intensity of solar 
radiation and the absorptivity of solar radiation by its absorption 
surface. Customarily, solar energy is collected by two general techniques 
to produce higher temperatures: (1) by covering a receiving surface with a 
sunlight-transparent sheet of glass or plastic (flat plate collector), and 
(2) by focusing the solar radiation from a large area onto a receiver of 
small area (focusing collectors). 
Flat plate collectors are usually stationary but should be repositioned 
every few days to follow the seasonal variations in the solar track. Flat 
plate collectors have the advantage of being generally cheaper to 
fabricate and also have the advantage in absorbing heat from diffuse solar 
radiation as well as the direct radiation by being able to operate on 
cloudy but bright days. 
Focusing collectors can produce much higher temperatures although they can 
use direct radiation only and require turning throughout the day to follow 
the sun. Although focusing collectors are useful in obtaining higher 
temperatures from solar energy, (1) they usually cost more, (2) they need 
to be moved continuously to track the sun, and (3) they can use only 
direct solar radiation that is unscattered by clouds or haze. One common 
form of focusing collector is a parabolic mirror which has been used to 
obtain temperatures up to about 3500.degree. C. depending upon the optical 
perfection of the parabolic surface. Unfortunately, parabolic collectors 
are relatively expensive, require sophisticated mountings and the 
absorption surface is usually interposed between the sun and the parabolic 
reflector at a position adjacent the focal point of the parabolic 
curvature. 
Another device for useful focusing solar energy in a focusing collector is 
the Fresnel lens. The Fresnel lens consists of nested grooves cut or 
otherwise formed in one face of a transparent material such as plastic. 
The sides of each successive groove is set in such a way that the light 
passing through each groove is refracted at a slightly different angle so 
as to converge on a common focal point or line. Such lenses have been 
pressed from rigid sheets of plastic material and are, therefore, 
relatively inexpensive while being effective to give a relatively sharp 
focus. A more detailed discussion on the use of a Fresnel lens in a solar 
concentrator can be found in "Large-Scale Fresnel Lens Solar Concentrator" 
Marshall Space Flight Center, Alabama; NASA Tech Briefs; Winter (1977) p. 
461. 
Since focusing collectors require tracking mechanism for tracking the sun, 
various types of tracking devices have been developed. Tracking of the sun 
in its east-west movement only is relatively simple since the sun moves at 
a rate of 15.degree. of arc every hour. This calculation is determined on 
the basis of the earth making one complete revolution of 360.degree. in a 
24 hour period so that in one hour it moves 360.degree. divided by 
24.degree. or 15.degree.. However, the annular motion of the earth 
relative to the sun causes the sun to appear to move in declination by 
about 47.degree.. This wide range from summer solstice to winter solstice 
is a major problem any focusing collector system must face. Thus, any 
fully tracking collector that is focused continuously on the position of 
the sun in the sky requires motion in two coordinates. While the exact 
coordinates in which the motion is made are not deemed important, one set 
of coordinates may be rendered redundant by using an equatorial mounting 
where one axis of rotation is supported parallel to the axis of rotation 
of the earth. The sun then appears to have no significant daily motion in 
the transverse coordinate (declination). Meanwhile, any other set of axes 
of motion requires two motions to track the daily motion of the sun. 
However, in order to accommodate seasonal variations, it is necessary to 
include within the equatorial mounting a mechanism for matching daily 
changes in the seasonal position of the sun. Thus, an equatorial mounting 
presents the more feasible mounting system for a tracking or focusing 
solar collector. 
Additional information regarding solar collectors can be found in Applied 
Solar Energy, Aden B. Meinel and Marjorie P. Meinel, Addison-Wesley 
Publishing Company, Reading, Mass. (1976) Library of Congress Catalog Card 
No. 75-40904, and Direct Use of the Sun's Energy, Farrington Daniels, 
Ballantine Books, New York (1977) Library of Congress Catalog Card No. 
64-20913. 
Utilization of collected solar energy very often occurs at a location other 
than the center of focus for a focusing collector. The exception to this 
statement are those focusing collectors which are used primarily as 
photovoltaic power towers, solar cookers, etc. The technique for 
transferring solar energy from its collection site to its utilization site 
generally involves some form of fluid heat transfer medium. The fluid heat 
transfer medium is conducted through conduits to and from the solar energy 
absorption site. The heat transfer medium is heated by the thermal energy 
produced by the absorbed solar energy and carries the thermal energy to 
the utilization site where the thermal energy is either utilized directly 
or stored for subsequent use. Unfortunately, the combination of movable 
solar collectors and fluid heat transfer conduits presents difficulties 
with regard to fabricating solar collectors which will accommodate flexure 
or otherwise movement of the fluid heat transfer conduits. 
In view of the foregoing, it would be an advantage in the art to provide 
improvements in solar collector apparatus and the method for collecting 
solar energy. It would also be an advancement in the art to provide a 
solar collector apparatus for tracking the sun, the apparatus including 
mechanism for accommodating the movement of the solar collector and the 
optical apparatus therein while minimizing excessive flexure or twisting 
of the fluid heat transfer conduits. Such an invention is disclosed and 
claimed herein. 
BRIEF SUMMARY AND OBJECTS OF THE INVENTION 
The present invention relates to a novel apparatus and method for focusing 
and collecting solar energy for absorption as thermal energy by a fluid 
heat transfer medium. The solar energy collector apparatus is configurated 
to be a focusing collector and includes optical apparatus and structure to 
accommodate tracking the movement of the sun and to focus and direct the 
solar flux toward a solar energy absorber apparatus. Excessive flexure or 
twisting of the fluid heat transfer conduits or use of rotating couplings 
is minimized by mounting the solar energy absorber apparatus in a 
generally stationary position inside the movable shell structure. 
Photovoltaic apparatus may also be used for converting a portion of the 
solar flux into electrical energy. 
It is, therefore, a primary object of this invention to provide 
improvements in solar energy collector apparatus. 
Another object of this invention is to provide an improved method for 
collecting solar energy. 
Another object of this invention is to provide a focusing solar collector 
apparatus which is relatively inexpensive to fabricate. 
Another object of this invention is to provide a solar collector apparatus 
wherein the fluid heat transfer conduits are maintained in a relatively 
stationary position to minimize flexure of the conduits. 
Another object of this invention is to provide a solar collector apparatus 
wherein the solar energy absorber mechanism is relatively stationary while 
the collector apparatus rotates thereabout. 
These and other objects and features of the present invention will become 
more fully apparent from the following description and appended claims 
taken in conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention is best understood by reference to the drawings wherein like 
parts are designated with like numerals throughout. 
Referring now to FIG. 1, the solar collector apparatus of this invention is 
shown generally at 10 on the roof 14 of a building 12. It should be noted 
that the solar collector apparatus 10 is oriented in a north-south 
direction. For example, assuming arrow 24 represents geographic north then 
solar collector apparatus 10 is in position for collecting solar energy in 
a northern latitude. Conversely, if arrow 24 represents the direction for 
geographic south then solar collector apparatus 10 is oriented for 
collecting solar energy in a southern latitude. 
Referring now more particularly to FIG. 2, a portion of solar collector 
apparatus 10 is shown and includes a plurality of solar collectors, shown 
herein as solar collectors 20a and 20b. Solar collectors 20a and 20b are 
supported in a framework 16 with framework 16 supported on a base 18 by a 
riser 19. Arrow 24 also indicates the direction north for the orientation 
of base 18 while framework 16 is supported by riser 19 in a direction 
indicated by arrow 22 representing a line parallel to the axis of rotation 
of the earth. In this manner, framework 16 serves as the basal framework 
for an equatorial mount for solar collectors 20a and 20b. The length of 
riser 19 is determined, therefore, by the latitude of placement of solar 
collector apparatus 10 and, if desired, may be configurated as an 
automatically adjustable lifting assembly for orienting, where necessary, 
the solar collectors 20a and 20b toward the sun. 
Solar collector 20a is supported in framework 16 by a hollow axle 30 
secured thereto. Hollow axle 30 remains stationary relative to framework 
16 and solar collector 20a is rotatably mounted thereto. A gear 32 
accommodates rotation of solar collector 20a about hollow axle 30 or, more 
particularly, the longitudinal axis represented by hollow axle 30 and axle 
48 (FIG. 3). Gear 32 is engaged by a worm gear 34 mounted on a shaft 36. 
Shaft 36 is selectively turned by operation of a motor 38. Turning of 
shaft 36 by motor 38 causes worm gear 34 to advance or reverse gear 32 
correspondingly to thereby rotate solar collector 20a about its 
longitudinal axis. 
Heat transfer fluid is supplied and returned through header conduits 40 and 
42, respectively, and distributed into each of the solar collectors 20a 
and 20b by the appropriate tubing such as tubing 41 and 43 to solar 
collector 20a. Since hollow axle 30 is nonrotatably mounted to framework 
16, tubing conduits 41 and 43 pass in nonrotatable relationship through 
hollow axle 30 as will be set forth more fully hereinafter. 
Referring now more particularly to FIG. 3, the structure of solar collector 
20a is set forth in greater detail. Shell 28 and gear 32 rotate about 
hollow axle 30 to form a nonrotatable passageway through shell 28 and 
framework 16 for tubing conduits 41 and 43 to a solar energy absorber 
apparatus 50. In particular, tubing conduits 41 and 43 pass through a bore 
44 of hollow axle 30 and are carried by a bridge 46 to solar energy 
absorber apparatus 50. The opposite end of bridge 46 terminates in axle 48 
which is nonrotatably mounted in frame 16. Accordingly, shell 28 is 
rotatable about a longitudinal axis between hollow axle 30 and axle 48 to 
accommodate thereby the daily tracking of the sun in its apparent 
east-west movement. 
The open top of shell 28 is covered by a transparent cover 26 to enclose 
the internal apparatus against inclement weather and heat losses to the 
ambient. The bottom of shell 28 could also include additional weight to 
serve as a counter balance to offset the rotational torque resulting from 
the offset configuration of shell 28 and the components therein relative 
to the longitudinal axis. 
It shall be understood that the word shell shall include both enclosed or 
airtight structures (as shown in FIG. 2) as well as non enclosing or non 
airtight structures such as lattice or open framework structures (not 
shown). It shall be understood also that such open structure shells may be 
enclosed either singly or in gangs behind a transparent or greenhouse-like 
cover (not shown) to provide protection from weather. 
Shell 28 also serves as a support for a plurality of focusing means inside 
solar collector 20a. In particular, Fresnel lenses 62 and 64 are supported 
therein and serve as the focusing apparatus for focusing solar flux 80 as 
focused solar flux 82 and 86, respectively. The focused solar flux 82 and 
86 is reflected by mirrors 66 and 68, respectively, to form reflected 
solar flux 84 and 88, respectively. A portion of scattered solar flux 
inherently present inside shell 28 is further concentrated by optional 
parabolic reflectors known in the art as Winston collectors 54 and 58 and, 
more particularly, to the reflective, parabolic surface such as surface 56 
of Winston collector 54. In this manner, the concentrated, focused solar 
flux and portions of the scattered flux which is scattered in a solid 
angle about the incident direct solar flux is received by solar energy 
absorber apparatus 50. The solar flux directed into solar energy absorber 
apparatus 50 is absorbed therein by the heat transfer fluid passing 
through coils 52 between tubing conduits 41 and 43. 
An optional flat plate collector 57 is included as an annulus around 
optional Winston collector 58 to further absorb a portion of the scattered 
solar flux inside shell 28. Clearly collector 57 could be used with 
holorum 50 independently and without Winston Collector 58. Coils 59 are 
attached to the rear face of flat plate collector 57 and may serve as a 
preheater for incoming heat transfer fluid through tubing conduit 41. 
Alternatively, flat plate collector 57 can be configurated as a 
photovoltaic apparatus for converting sunlight into electrical energy with 
coils 59 providing any required cooling. 
Each of Fresnel lenses 62 and 64 is adapted to be moved internally within 
the confines of shell 28 to thereby focus or otherwise concentrate solar 
flux 80 on mirrors 66 and 68, respectively. Movement of Fresnel lenses 62 
and 64 is required since framework 16 and, more particularly, the 
longitudinal axis of solar collector 20a is generally fixed in a position 
parallel to the axis of the earth as represented by arrow 22 (FIG. 2). 
Accordingly, as the sun moves through seasonal changes in its relative 
position with respect to the earth's latitude, Fresnel lenses 62 and 64 
suitably track the sun in its seasonal variations to accommodate focusing 
the solar flux on the respective mirrors and as set forth hereinbefore. 
Mounting of Fresnel lens 64 is accomplished by means of a lever 97 which 
is pivotally mounted to mirror 68. Mirror 68 is supported by a brace 92 
extending from a controller 90. Movement of lever 97 is accomplished 
through an extension 96 attached to the end of an arm 95. Movement of arm 
95 is controlled by controller 90. Controller 90 is selectively controlled 
to provide the appropriate movement of Fresnel lens 64 for solar tracking 
as set forth hereinbefore. 
Mirror 66 is also rotated in coordination with movement of Fresnel lens 64 
so as to reflect the concentrated solar flux 88 into solar energy absorber 
apparatus 50. In the particular embodiment illustrated herein, mirror 68 
requires an angular rotation of only one half that of Fresnel lens 64 to 
thereby accomplish the foregoing purposes. Rotation of mirror 68 is 
accomplished through an extension member 94 which is controlled by a 
moveable arm 93. Movable arm 93 is, in turn, also controlled by controller 
90. 
It should be noted that Fresnel lens 64 and mirror 68 along with controller 
90 are mounted to shell 28 through a bracket 91 thereby permitting the 
foregoing structure to be rotated with shell 20a while solar energy 
absorber apparatus 50 is nonrotatably mounted therein to preclude any form 
of twisting or otherwise turning of tubing conduits 41 and 43. 
While the apparatus of this invention is primarily directed toward 
collecting solar flux 80 and converting the same to thermal energy for 
heating the heat transfer fluid passing between tubing conduits 41 and 43, 
an optimum portion of the solar spectrum can be converted into electrical 
energy by means of photovoltaic converters 70 and 72 attached to the rear 
of mirrors 66 and 68, respectively. In this particular instance, each of 
mirror 66 and 68 is fabricated as a selectively reflective mirrored 
surface to permit a limited portion of the solar spectrum to pass 
therethrough and most efficiently activate the photovoltaic apparatus 70 
and 72. 
Furthermore, the holorum apparatus herein may be fabricated with a beam 
splitter-type device (not shown) having a selective surface thereon for 
reflecting a predetermined portion of the solar spectrum toward a first 
photovoltaic apparatus (not shown) having a higher efficiency with that 
particular spectral range and transmitting the remainder of the solar 
spectrum toward a second photovoltaic apparatus (not shown) having a 
higher efficiency with that particular spectral range. This is 
conventional apparatus and is, therefore, not specifically illustrated 
herein. The conduits would be suitably reconfigured to provide any 
required cooling for the subject photovoltaic apparatus. 
Referring now more particularly to FIG. 4, a second preferred embodiment 
for providing the relative movement of the Fresnel lens and mirror 
apparatus of this invention is shown herein. A Fresnel lens 102 is 
surmounted over a mirror 104 and is mounted on the ends of vertical 
support arms 106a and 106b. Support arm 106a terminates in a gear 123 
while support arm 106b terminates in a bearing 120 on a shaft 108. Shaft 
108 also serves as the support for mirror 104 and is rotatably engaged to 
outer walls 110 of the solar collector apparatus by bearings 112 and 113. 
Walls 110 corresponding to the side walls of shell 28 (FIGS. 2 and 3). 
Gear 123 is rotatably mounted to shaft 108 by a bearing and is engaged by a 
second gear 122 fixed to a motor shaft 116. A second gear 124 is also 
fixed to motor shaft 116 so that motor 114 will turn shaft 116 causing 
each of gears 122 and 124 to be rotated. Gear 122 turns gear 123 causing 
support arm 106a and, correspondingly, Fresnel lens 102 to be moved in an 
arcuate manner about shaft 108. Correspondingly, turning of gear 124 
causes gear 125 to turn and imparts a corresponding rotation to mirror 104 
about shaft 108. It should be noted that the diameters of each of gears 
122-125 is selectively predetermined to accomplish the appropriate 
movement of Fresnel lens 102 relative to mirror 104. For example, the 
diameters of gears 122 and 123 are equal whereas the diameter of gear 124 
is one half of gear 125. In this manner, the angular rotation of mirror 
104 about shaft 108 is one half that of Fresnel lens 102. 
Referring now more particularly to FIG. 5, a third preferred embodiment of 
the focusing apparatus of this invention is shown herein and includes a 
first Fresnel lens 142, a second Fresnel lens 144, and a mirror 146. The 
first Fresnel lens 142 is configurated as a linear Fresnel lens with 
focusing lenslets formed therein as linear grooves parallel to the 
longitudinal axis of first Fresnel lens 142. Correspondingly, the second 
Fresnel lens 144 is configurated with transverse lenslets formed as 
transverse grooves at a position perpendicular to the orientation of the 
lenslets in first Fresnel lens 142. The longitudinal orientation of the 
lenslets of first Fresnel lens 142 focuses the solar flux as rays 152 in a 
generally longitudinal focal pattern 154 along the face of second Fresnel 
lens 144. The transverse or lateral lenslets of second Fresnel lens 144 
further concentrate the solar flux as rays 156 into a generally 
rectangular focal pattern 158 on mirror 146. The focused solar flux is 
reflected as concentrated solar flux 160 into solar energy absorber 
apparatus 148. Any astigmatism resulting from Fresnel lenses 142 and 144 
may be partially compensated by incorporating a Winston collector, such as 
Winston collectors 54 and 58 (FIG. 3), around the opening in each end of 
solar energy absorber apparatus 148. 
The particular configuration of focusing apparatus 140 may be selectively 
placed in solar collector 20a (FIGS. 2 and 3) by replacing clear cover 26 
with first Fresnel lens 42 and mounting second Fresnel lens 144 in place 
of the curvilinear Fresnel lens 62 or 64. Mirror 146 is comparable to 
mirrors 66 and 68. It should be understood further that holorum 50 in FIG. 
3 or holorum 148 in FIG. 5 may be replaced by fluid cooled photovoltaic 
cells. Selective mirrors 66, 68, 104, or 146 and two or more types of 
photovoltaic cells, one type mounted behind the mirrors as shown and one 
type or more replacing the holorum, may be used to provide an optimum 
efficiency system for production of electric power from concentrated 
sunlight. Concentrated solar flux reduces the area of solar cells required 
for electric power production and thus minimizes the cost of this 
expensive item. It is known in the art that the use of two or more 
different types of photo cells (for example galium, arsenide and silicon) 
matched to their optimum spectral ranges, gives an overall system 
performance about double the efficiency of either cell used exclusively. 
Fluid cooling further increases the efficiency of the photovoltaic cells. 
The heated fluid may be used for space heating or air conditioning. 
The invention may be embodied in other specific forms without departing 
from its spirit or essential characteristics. The described embodiments 
are to be considered in all respects only as illustrative and not 
restrictive and the scope of the invention is, therefore, indicated by the 
appended claims rather than by the foregoing description. All changes that 
come within the meaning and range of equivalency of the claims are to be 
embraced within their scope.