Radiant energy collection

Page 1 — bibliographic record

Page 2

Drawing sheet — no readable text.

Page 3

Drawing sheet — no readable text.

Page 4

Drawing sheet — no readable text.

Page 5

Drawing sheet — no readable text.

Page 6

Drawing sheet — no readable text.

Page 7

Drawing sheet — no readable text.

Page 8

Drawing sheet — no readable text.

Page 9

quiring only seasonal solar tracking) is on the order of

RADANT ENERGY COLLECTION 3 or 4.

BACKGROUND OF THE INVENTION

Non-imaging light funnels having utility in collection of light from high energy particles and having a greater

The present invention relates generally to electro concentration capacity than imaging systems have been magnetic energy collection and more particularly to proposed by the inventor and his collaborators in ear devices useful in the collection and utilization of radi lier publications i.e., Review of Scientific Instruments, ant energy from solar and other sources. Vol. 37, No. 8, pp 1094-5 (1966), ibid., Vol. 39, No. 3, The prior art has proposed numerous devices for de O pp. 419-20 (1968), ibid., Vol. 39, No. 8, pp. 1217-8 tection of electromagnetic energy (e.g., infrared scan (1968), and J. Opt. Soc. Am..., Vol. 60, No. 2, pp. 245-7 ners, detectors of light from high energy particles, and (1970). The inventor also noted the similarity between the like) and for collection of such energy (e.g., micro such funnels and the geometry of retinal cones in J. wave antennas, solar collectors, and the like) and is Opt.Soc. Am..., Vol. 61, No. 8, pp. 1 120-1 (1971). Basi particularly rich in suggestions of systems for collection 15 cally, the above publications dealt with proposals for and utilization of solar energy. "ideal', conical-shaped, light collectors which ap Notwithstanding the voluminous proposals of the art, proach an finumber equal to 0.5, a physically unrealiza among the basic, and as yet inadequately resolved, ble limit for lens systems. The field of acceptance of problems inherent in the efficient utilization of solar conical collectors therein proposed may be represented energy are avoidance of energy loss through re-radia by a right circular cone having a gradually diminishing tion (i.e., energy conservation) and avoidance of intri (over about 1) external boundary cut-off. cate, and hence costly, apparatus for tracking the sun SUMMARY OF THE INVENTION in its apparent daily motion through the celestial sphere. According to the present invention a non-imaging A typical attempt to solve solar energy conservation system of exceptional efficiency is provided for the col problems involves providing coatings on energy ab 25 lection and concentration of electromagnetic energy. Comprehended by the invention are longitudinally ex sorbing surfaces as well as elaborate insulation of the particular "trap' employed for the utilization of col tending, generally trough-shaped collection structures lected energy. U.S. Pat. No. 3,277,884, for example, including opposed inner reflective surfaces which func tion to guide and concentrate radiant energy impinging illustrates such a scheme. 30

Another common manner of dealing with energy upon a relatively large entrance opening toward - and conservation involves including in the collection which therethrough if desired, may be - a relatively small exit opening at disposed a trap for detection or uti scheme reflective or refractive concentration appara lization of the concentrated tus to permit collection of solar energy impinging upon ments of the structures of theenergy. Preferred embodi present invention possess a relatively large area and focusing of collected energy 35 an elliptical conical field of acceptance exhibiting an toward a relatively small area of utilization. Typical extremely sharp external boundary cut-off. schemes proposing use of reflector concentrators are It is contemplated that embodiments of the present

3,217,702, for example. (“Shadowing' effects encoun lection andmayutilization invention be most effectively employed in the col of solar energy to provide for tered in disposing an energy utilization body in path of 40 high energy concentration (and hence achievement of Sunlight impinging upon reflectors are to some extent high temperatures and optimal energy conservation) avoided through use of off-axis reflectors, as in U.S. with minimal solar tracking.

Pat. Nos. 3,052,229, 3,613,659 and Tabor, “Stationary Further aspects and advantages of the present inven Mirror Systems for Solar Collectors' Solar Energy, tion will become apparent upon consideration of the Vol. II, No. 3-4, pp. 27 et seq. (1958)). Typical lens 45 following description thereof, reference being made of systems for solar concentration are illustrated in U.S. the following drawing.

Pat. No. 3,125,091 and Meinel et al., “Physics Looks at

Solar Energy' Physics Today, Vol. 25, pp. 684 et seq. BRIEF DESCRIPTION OF THE DRAWING (1972). All of the mirroring and lens systems proposed FIGS. 1 and 2 are schematic representations of radi above are basically imaging systems wherein solar en 50 ant energy collection troughs of the present invention. ergy is reflected or refracted to a system focal point at FIG. 3 is a transverse sectional view taken along line which the “concentrated' energy is utilized for heating 3-3 of FIG. 2.

or power generation. FIG. 4 is a transverse sectional view of a straight Among the solutions proposed for avoidance of diur sided collection trough.

nal solar tracking is the provision of huge, but margin 55 FIG.S is a composite transverse sectional view of col ally efficient, mirrored surfaces such as shown in U.S. lection troughs including troughs of the invention. Pat. No. 3,179,105. FIG. 6 is a graphic representation of the field of ac None of the prior art systems has adequately solved ceptance of a collection trough as shown in FIGS. 1-3. the problems of energy conservation and solar tracking FIG. 7 is a comparative graphic representation of rel and, to a degree, solution of one problem often tends to 60 ative fields of acceptance.

enlarge the difficulties posed by the other. This is to say FIG. 8 is a cross sectional view of an alternative em that systems permitting solar concentration by large bodiment of the invention.

factors generally will require the most careful and fre FIG. 9 is a schematic representation of another alter quent diurnal adjustments for solar tracking. Con native embodiment of the invention. versely, systems requiring little or no diurnal adjust 65 FIG. 10 is a sectional view taken along line 10-10 of ment generally provide lowest factors of concentration. FIG. 9.

Thus, Tabor, infra concludes that the maximum con FIG. 11 is a schematic view of an embodiment of the centration available in a stationary system (i.e., one re invention useful in solar energy collection.

Page 10

FIG. 12 is a graphic representation of relative solar collector of FIG. 4. An included parabolic line as motions. shown in the embodiment of FIG. 3 forms the other FIG. 3 is a variant form of FIG. 12. boundary and is described in greater detail hereafter. FIG. 14 is a graphic representation of the acceptance Concave curving lines of length greater than that of the of a collector of the invention in terms of optical direc above-mentioned parabolic line are also contemplated. tion cosines. The profile curve of a much preferred embodiment FIG. 5 is a graphic representation of relative solar of a collector of the invention is shown in FIG. 3. The motion compared to the field of acceptance of a collec following aspects of that embodiment are of particular tion trough of the present invention. interest in understanding the invention. FIG. 16 is a schematic view of a solar energy collec 10 1. The concentrative capability of the collector, i.e., tor of the present invention. the ratio of exit aperture transverse dimension d to en FIGS. 17-19 are schematic views of radiant energy trance aperture transverse dimension d, is equal to the collectors of the present invention. sine of the half field of view (0) of the trough.

2. The height, L, of the collector is equal to one-half the sum of d and d multiplied by the cotangent of the

FIG. 1 illustrates an embodiment of an electromag half field of view.

netic energy collector of the present invention includ ing a generally trough-shaped body 10 having long of3.a The profile curve of each wall element is a section tiduinally extending, substantially parallel, geometri edge of the exithaving parabola as its focus the laterally opposed aperture and as its axis a line forming

cally similar side wall elements 11, 11, the inner sur an angle with the optical axis of the trough equal to the faces 11a, 11a of which are of energy reflective mate half field of view (0) of the trough. rial. As shown, wall elements 11, 11 taper from an en 4. The embodiment accepts for concentration all en trance aperture 12 to an exit aperture 13. FIG. 2 illus ergy deriving from within an average elliptical conical trates a similar structure including end wall elements field of acceptance developed by the geometric accu 14, 14 which preferably extend from opening 13 to 25 opening 12 and preferably also have energy reflective mulation of all elliptical conical field of acceptance at inner surfaces 14a, 14a. As discussed in greater detail parameterswithin all points

the plane of the entrance aperture, the each of said several fields being as foll later, provision of reflective side wall elements results lows (See FIG. 6):

in donation of optical properties approximating provi a. The apex of the cone is any point, P, in the plane sion of a trough of infinite length. of the entrance aperture;

The optical properties of collectors of the type shown in FIGS. 1 and 2 are best illustrated through consider axis The b.

axis of the cone is a line parallel to the optical the trough;

ation of FIGS. 3, 4 and 5. In FIG. 3 a preferred embodi c. The semi-minor axis of the cone is in a direction ment of a collector of the present invention is seen to transverse to the trough and subtends an angle equal to have an entrance aperture of a transverse dimension d, 35 an exit aperture of a transverse dimension d overall the half field of view (0) of the trough; and height L, an optical axis designated OA, and a half field d. The semi-major axis extends in the longitudinal di of view, designated 8. The optical axis of the trough is ingrection of the trough and subtends an angle approach defined by a line extending from the entrance aperture 90 (as the trough approaches infinite length). to the exit aperture, all points of which are equidistant 40 it will be noted that since the semi-major axis of the from respective opposed edges of each of said aper field of acceptance at any point, P, approaches 90° for tures. The half field of view of the trough of FIG. 3 is a collector of infinite length, and since provision of re defined for the purposes of the present invention as the flective end walls donates optical properties approxi angle formed by the intersection of the optical axis and mating provision of an infinitely long trough, a cross a straight line connecting an edge of one aperture with 45 section (taken parallel to the plane of the entrance ap the laterally opposed edge of the other. erture) of the average field of acceptance of a collector A property common to all collectors of the invention as in FIG.2 approximates the shape of an infinitely long is the collector's "field of acceptance' which is defined rectangular strip. It follows that the area of a sphere of as that three dimensional field from within which radi unit radius intercepted by this field of acceptance (the ant energy (rays) impinging upon a given point in the 50 solid angle in steradians) approaches four times the plane of the collector entrance aperture will reach the half field of view (0), provided the angle 6 is measured exit aperture either directly or by way of one or more in radians (one radian being approximately 57.3. reflections from the collector reflective surfaces. Put It is especially noteworthy that the field of accep another way, rays generated within the field of accep tance of the embodiment is identical at each and every tance of a collector and reaching the entrance plane 55 point, P, in the plane of the entrance aperture. This will invariably reach the exit aperture and those rays being the case, the field of acceptance is not subject to generated outside the field will not. failure or diminution at the edges of the collector For the purposes of the present invention, the shape trough and the maximum angle of acceptance within of a wall element 11 as revealed by the transverse cross the field of acceptance is measured in a plane trans sectional view of the collector 10 will be shown as the 60 verse to the collector, i.e., the angular acceptance of "profile curve' of the element. Accordingly, the profile the entrance aperture, 6m, of the collector is quantita curve of a side wall element of a collector constructed tively equal to the angle of the half field of view (8). according to the present invention may, for example, Another property of interest in the embodiments of be any substantially smooth, non-convex line (connect FIGS. 1-3 is that radiant energy in the plane transverse ing laterally corresponding edges of exit and entrance 65 to the trough which impinges at angles less than but apertures) falling within the shaded area of FIG. 5. It closely approximating 6 with respect to the optic may be noted that the shaded area has as its boundary axis are transmitted to the exit aperture with one or no but does not include a straight line as illustrated in the reflections.

Page 11

S 6

Further illustrative of such a collector's properties is in either direction measured transversely to the trough the comparison of its efficiency to that of a perfectly optical axis.

absorbing flat surface for isotropic radiant energy im Assume further the construction of a second collec pinging on the entrance aperture at all angles up to 90° tor of the form illustrated in transverse section in FIG. with respect to the optic axis. The ratio of energy per 5 4 having dimensions d, d. and L identical to those first second per unit area accepted by the collector to the of the collector. The collector would, of course, pro energy per second per unit area accepted by the ab vide the same theoretical concentration of isotropically sorbing surface is equal to the collector's concentrative impinging energy but the field from which energy could capability (the ratio of exit aperture width, d, to en 10 be gathered would be much less sharply defined. En trance aperture width,d). ergy impinging upon a point, P., near the outermost In practice, numerous departures from the dimen edge of the entrance aperture would be channeled to sional relationships present in FIGS. 1-3 may be made the exit aperture only if it impinged upon P from an in the construction of a collector which will yield satis angle of less than about 1 measured transversely to the factory, albeit. perhaps less than ideal, overall results. 15 trough optical axis in one direction or less than about For example, it may be noted that in FIG. 3 side wall 11 11 from the opposite direction. terminates at a point wherein a line tangent to its para Use of straight or substantially straight side wall ele bolic curvature would lie parallel to the optical axis. It ments as in FIG. 4 would give rise to acceptance of en may be desirable in some embodiments to provide a ergy from marginal angles only after multiple reflec truncated collection trough having a height less than tions with consequent energy loss due to absorption by that of the collector of FIGS. 1-3 and in such cases side less than ideally reflective surfaces. The above example wall 11 would terminate short of the above-mentioned is schematically illustrated in FIG. 7. point. While collection troughs of the invention preferably It may be expedient to increase the overall height of include smoothly curving side walls, it is anticipated the collector by linearly extending reflective side walls 25 that some economic advantage in fabrication might be 11a, 11a beyond the entrance aperture and parallel to derived through use of walls having one or more seg the optic axis. Such virtual extension of the entrance ments revealed in profile curve as straight lines. aperture away from the exit aperture does not serve to It is contemplated that space limitations may develop alter the angular acceptance of the collector but may special utility for "half trough' structures as illustrated diminish the collector's efficiency because of resultant 30 in a preferred embodiment by FIGS. 9 and 10 wherein multiple reflections. It may further be expedient to pro the trough body 15 includes entrance and exit aper vide linear “transition' reflective wall segments ex tures 16 and 17, respectively, along with inwardly ta tending away from the edges of the exit aperture, either pering side wall element 18, a straight wall element 19 parallel to the optic axis or preferably tapering slightly and, preferably, end wall elements 20, 20. Inner wall outwardly, to accomodate transmission of rays passing 35 surfaces 18a, 19a and 20a would be radiant energy re through the exit aperture toward a photocell detector flective. In the embodiment illustrated, dimensional re or the like. lationships maintained in fabrication are similar to Similarly, it is likely that a collector might be more those employed in construction of an embodiment ac economically fabricated in the form more closely ap cording to FIG. 1-3, with expected modifications, i.e., proximating that illustrated in cross section in FIG. 4. 40 entrance and exit apertures have one half the trans As might be predicted from known two dimensional verse dimension, the half angle of view is the same, the analyses of optical collection properties of right circu length is the same, the reflective surface 19a of wall el lar cones (see, e.g., Williamson, "Cone Channel Con ement 19 lies along what would be the optical axis of a denser Optics' J. Opt. Soc, Am..., Vol. 42, No. 10, pp. "full trough,' the focus of the parabolic curvature of 712-15 (1952) and, White, “Cone Channel Optics' 45 the side wall 18 is at what would be the opposite edge Infrared Physics, Vol. 5, pp. 179-85 (1965)), a consid of the exit aperture for a “full trough' (shown in phan erably more diffusely defined field of acceptance exists tom lines), the axis of the parabola would form an angle for such a structure, owing to the fact that the maxi with the optic axis equal to the half field of view and av mum angle of acceptance for given points in the plane erage field of acceptance would be an elliptical cone of the entrance aperture is subject to variance depend 50 approaching an infinitely long rectangular strip in ing upon relative transverse distance from the optical transverse cross section for an infinetely long collector. axis of the trough. This fact may be best illustrated FIG. 8 illustrates in cross section a tandem trough through consideration of the following hypothetical ex collector which, under circmumstances hereafter de ample. scribed, may provide greater factors of concentration 55 than provided by a single trough. In the embodiment

EXAMPLE I

shown, there is a first trough 21 having respective en

Assume the construction of a first collector accord trance and exit apertures 22 and 23, as well as side wall ing to FIGS. 1-3 wherein the ratio of d to d2 (and elements 24, 24 having energy reflective inner surfaces hence the concentration factor) is 9.6 and further that 24a, 24a. Contiguous to exit aperture 23 is a second the half field of view equals approximately 6. The 60 trough 25 having an entrance aperture 26 of transverse height (L) of the collector would be a fixed dimension dimension equal to aperture 23 and an exit aperture 27, according to the relationship described above, i.e., L = as well as side wall elements 28, 28 having energy re 2 (d. -- d.) cot 6. The maximum angle of accep flective inner surfaces 28a, 28a. Trough 21 is filled with tance at all points in the plane of the entrance aperture a medium having a refractive index, n (e.g. air, which would be equal to 6. In particular, radiant energy im 65 has a refractive index of approximately 1.0), and pinging upon a point, P., near the outermost edge of trough 25 is filled with a material having a refractive the entrance aperture would reach the exit aperture if index, n, greater shown than in (e.g., lucite, which has it impinged upon P from an angle of less than about 6 a refractive index of approximately 1.5).

Page 12

in understanding the operation of the embodiment of collector in optical contact with air (n approximately FIG. 8, it should be noted that an energy concentrator equal to i) at the entrance, but filled with a medium of of the type of collector FIGS. 1-3 functions in part to n = 1.5 and having 6, equal to 10.6 and other di reflect energy from within the collector's field of ac mensions according to the relationships above de ceptance to the exit aperture. In practice, some energy 5 scribed.

will directly reach the exit aperture at an angle parallel According to another aspect of the invention, there to the optic axis of the collector while, at the opposite are proposed systems for collection of solar energy extreme, some energy will reach the plane of the exit which include radiant energy collector-concentrators aperture at a grazing angle of nearly 90. To further as above described. The inherent attractiveness of di concentrate such grazing energy toward a tandem sec- 10 rectly using solar light to meet man's energy needs has ond collector exit aperture requires both the refractive motivated an intense search for practical solar power capacity of a medium greater index of refraction than schemes. For most of these, it is necessary to concen that filling the first collector and an angular field of ac trate the sun light by at least an order of magnitude in ceptance for the second collector equal to the critical order to achieve high temperatures. This poses no angle of its medium. With this in mind, the operation of 15 problem in principle because the rays of sunlight are a tandem collector will be best understood through quite parallel (the half-angle 6 subtended by the solar consideration of the following hypothetical example. disk is only as 'A') provided one tracks the sun's loca tion in the sky with an accuracy comparable to 6. Be

EXAMPLE II cause of the formidable technical problems associated Assume one wished to concentrate radiant energy to 20 with tracking to this precision, it would clearly be an the longitudinally-extending photoelectric surface of enormous advantage if the required concentration was an instrument having a transverse dimension dia, equal achievable by a relatively stationary collector, i.e., one to 1 inch. Assume further that one wished to concen requiring little or no diurnal movement. This possibility trate energy from an angular field of acceptance of half was, in fact, explored in Tabor, infra, and the disap angle equal to 16°. To accomplish such a result one 25 pointing conclusion was reached that the maximum might construct a single trough collector as shwon in possible concentration obtainable by a stationary col FIGS. 1-3 filled with a medium having an index of re lector was 3 or 4. This result has been generally ac fraction of 1. Since the exit aperture dimension is 1 cepted to the present time. However, Tabor's analysis inch and the desired maximum angle of acceptance is was based on conventional imaging optics and pre 16, the entrance aperture transverse dimension and 30 dated the inventor's more recent developments which overall height of the trough may be derived from the showed that systems that collect light but do not image relationships heretofore described i.e., the ratio of can achieve a greater concentration than imaging sys transverse exit aperture dimension to entrance aper temS.

ture dimension equals the sine of the half field of view Inasmuch as it is desired to concentrate solar radia (which for the collector of FIGS. 1–3 equals the maxi- 35 the tion with ground based collectors, it is convenient for mum angle of acceptance), and, the overall height of purposes of discussing solar tracking problems to the collector equals half the sum of the entrance and adopt a 'Ptolemaic' description of the sun's motion in exit aperture transverse dimensions multiplied by the the sky. To an adequate approximation, the apparent cotangent of the half field of view. The transverse di motion of the sun as viewed from a fixed point on earth, mension of the entrance aperture would thus equal 3.6 40 describes the cone depicted in FIG. 12. In this figure inches. The concentration factor of the collector would the X axis direction is along north, the Y axis direction be equal to 3.6. along west and Z axis direction along the vertical. The One might instead construct a tandem trough collec cone axis is in the X, Z plane, inclined at angle M, which tor as in FIG. 8 wherein the first trough 21 was filled 45 is the latitude. The cone opening angle, or, is the angle with a medium having an index of refraction, n, of 1, between the earth's axis of rotation and the earth-sun the second trough 26 was filled with a second medium direction. Since the earth's axis is inclined at an angle having an index of refraction, n2, of 1.5 and the photoe of approximately 23.5° with respect to the normal to lectric surface was in optical contact with the second the plane of its orbit (the ecliptic plane), the angle var medium. The maximum angle of acceptance (critical 50 ies between the approximate limits 66.5 s or angle) for trough 25 would be equal to the inverse sine s 1 13.5 during the course of a year. Except at a time of the index of refraction of the medium filling trough of equinox, when a a = 90° and the apparent solar path 21 divided by the index of refraction of the medium fill describes a great circle wherein the sun does not “rise' ing trough 26, i.e., 6m = arc sine ni/ng =r arc sine 1 / 1.5 or “fall' in the vertical, the problem of collecting solar = arc sine 0.6666 = 42. Given dimension d of exit ap 55 light is non-trivial and becomes most demanding at sol erture 27 equal to 1 inch and maximum angle of accep stice (or = 90-23.5'). Collection and concentration of tance equal to 42, d, the transverse dimension of the solar light by high factors at the time of solstice for a entrance aperture 26 would be equal to 1.5 inches and reasonable fraction of the day, say 6 to 8 hours, may be the overall height would be 1.4 inches. With respect to considered the fundamental problem of solar collec trough 21, since the exit aperture 23 transverse dimen 60 tion. This is so because at such times the apparent sion is equal to 1.5 inches and the desired maximum “rise' or “fall" in the vertical requires following or angle of acceptance is equal to 16, the transverse di tracking the solar disk "upwardly' about 12 within the mension, d, of the entrance aperture 22 would be 5.4 three or four hours prior to its reaching the zenith inches and the overall height would be 12 inches. The (noon) position and “downwardly' about another 12 concentration provided by trough 21 would be factor 65 within 3 or 4 hours after its reaching the zenith posi of 3.6 and the concentration of the entire tanden sys tion. Clearly, the stationary collector which would con tem would be equal to 1.5 times 3.6, or 5.4. tinuously accept direct solar radiation throughout the Finally, it may be noted that approximately the same period of the above-mentioned t2 excursion during concentration may be derived through use of a single the time before and after reaching the noon position,

Page 13

and which further was capable of high orders of con Number of hours -2(db/2n) (24) = (dbfat) (24) where centration, approaches the ideal in solar energy collec the factor 2 results from the fact that Cosqb is even in d. tion. The extent to which collectors of the invention ap Table I below approximates the number of accepted proach this ideal is set forth hereafter. hours per day for a collector with 6 F 6 (concentra The acceptance of a collector as shown in FIGS. 1-3 tion factor, 9.6) throughout the year in the approxima may be described using optical direction cosines KX, tion of a point-like sun. w

TABLE I

Collected hours

Season 2 Cos co per day

Equinox O (Full Solar Ellipse Accepted) Full Daylight

Solstice 47° 0.61 524 7.0

KY, KZ (See FIG. 14) where, for a constant index of Averaged over the year this gives approximately 8 refraction, we may take K as the unit energy ray direc hours of collected sunlight. For 6 = 7 (concentra tion. KX, KY become ture Hamiltonian variables con jugate to X, Y when the light ray trajectories are pa proximatelyof98.2) tion factor one may obtain an average day of ap hours of sunlight.

rameterized by Z. Here, Z is measured along the optic 20

Use of concentrator as in FIG. 8 which includes tan axis of the collector. Hence dXdY dKXdKY is conserved dem trough collectors wherein n equals 1 and n.2 Z = constant equals approximately 1.5 would result in achieving In deriving the acceptance of such trough collectors in concentration factors on the order of 12 to 15. the KX, KY plane, the ray trajectories projected on a 25 Table II, below illustrates approximate concentration constant y plane behave as though the collector were factors for collectors having 6m within the range of a two dimensional, so that to 7 along with approximate totals of hours of sunlight KXI (KX + KZ) s Sine which may be collected at solstice (2T=47) in the ap however, proximation of a point-like sun.

KXI (1 - KY) s Sine, 30 TABLE I

KX/Sine -- KY: s 1 6ma 2T Cose d Concentration Hours Thus the acceptance fills an ellipse of semi-minor axis Factor Collected equal to Sinéma and semi-major axis equal to 1, as 70 47 0.567 555 8.2 74 shown in FIG. 14. 6° 47 0.610 52.4 9.6 7.0 (It may be recalled at this point that the collector 35 5° 47 0.657 48.9 1.4 6.5 4° 470 0.709 44.8 14.3 6.0 concentrates by a factor of 1/Sin6, or cosec 0,...) 30 47 0.769 39.8 19.1 5.3 It is easily shown that the apparent motion of the sun 2

in the KX, Ky plane is also an ellipse. A convenient way A. 47 0.954 17.4 14.6 2.3 to visualize this is to reconsider FIG. 12 and take as the

Z' direction the zenith (highest point of the sun in the 40 sky, or noon) keeping the Y' direction West as before. It may be noted from the above that as the angular (See FIG. 13). acceptance of the collector diminishes, the concentra Clearly, the projection of the cone on the X', Y' tion factors increases and the number of hours of sun plane is an ellipse, and light which can be collected at solstice decreases. This Sir 2 or s KX' s 0. 45 inherent property permits flexibility in solar energy col Sinor s KY's Sincy, KY = KY or, in terms of T= Tr/2 - ov, -Sin 2T s KX' s 0, - lection to fit the requirements of a given environment cosT s KY' s cosT. Hence, the semi-minor axis or a given utilization scheme. Thus, when high temper

a = % Sin2a = % Sin2T and the semi-major axis be atures are desired, it may be preferable to employ a -e Sincy = cosT. small angular acceptance to achieve high concentra FIG. 15 shows the ellipse described by the sun on a 50 tion even though a lesser number of hours of sunlight solstice, the most difficult period for collection. On the might be collected at solstice without diurnal move same figure has been added the acceptance of a Sin6 ment. Alternatively, it may be desirable to collect at = 0.1 collector which concentrates the sunlight by a lower concentration for a longer average period of time factor 10. Clearly, such a collector accepts most of the 55 and in such a case a larger acceptance would be pre useful day (7 to 8 hrs.) at solstice. More rigorously, one ferred.

must choose the Z' axis to place the origin in the KX', It should also be noted that variations in the profile KY' plane at the center of the collector ellipse. One curve of collector side walls departing from that shown then finds that for the solar ellipse in FIG. 3 may give rise to diminished, though still ad

-CosT is KY's CosT vantageous, concentrative capacity for a given angular 60 acceptance and/or diminished, though still advanta

Hence, geous, time spans for collection of direct sunlight at sol

b = cosT stice and/or diminished, though still advantageous, Introducing a phase angle is for the solar ellipse, where total energy collection due to energy loss through mul d = 2 at (=360) corresponds to the 24 hour day, we tiple reflections. W find that at the intersection of the two ellipses 65 FIGS. 11 and 16 illustrate solar energy collection de Coscis = a -2a Sin 6 -- (b. Sin 6)/a-(b. Sin vices of the present invention which generally comprise 0na)”). Therefore, the accepted number of daylight one or more collector-concentrator troughs as in FIGS. hours is given by 1-3 and a solar energy trap. As used herein, the term

Page 14

"trap' includes any apparatus having a capacity for ac a trough-shaped body having, cepting radiant energy of various wavelengths either a longitudinally extending radiant energy entrance for direct utilization of such energy or as an intermedi aperture with first and second opposing edges sepa ate in such utilization. As such, the term includes, but rated by a transverse distance d, is not limited to, such direct utilization devices as a longitudinally extending radiant energy exit aper photo- and thermoelectric cells, as well as simple ture, disposed opposite said entrance aperture, 'black body' cavities and variant cavity structures with first and second opposing edges separted by a such as are disclosed in the National Science Founda transverse distance d2, tion publication NSF/RANN/SE/GI-34871/PR/72/4. a pair of symmetrical substantially concave radiant FIG. 11 shows a simple solar energy collector 29 with O energy reflecting and guiding side wall means inter a collector-concentrator 30 as in FIGS. 1-3 having con connecting laterally corresponding edges of said tiguous to its exit aperture 31 a generally cylindrical en apertures, ergy receiving body 32 with coaxial pipe 32 disposed a field of acceptance for radiant energy, therein. Pipe 33 may, for example, contain a fluid to be an angular acceptance for radiant energy within said heated by energy transmitted into cylinder 31 through 15 field of acceptance and determinable at said en concentrator 30. It is proposed the collector 29 may be trance aperture, and, disposed to extend longitudinally in an east-west direc an optical axis determinable by reference to dis tion and that suitable means (not shown) may be em tances separating entrance and exit aperture op ployed to rotate concentrator 30 and cylinder 31 about posing edges, pipe 33 for seasonal tracking of solar movement with 20 wherein the ratio of the distances d to d1 is no less out disturbing the orientation of pipe 33. than the sine of said angular acceptance, the profile FIG. 16 illustrates a solar energy collector 34 includ curve of each of said wall means is a parabola hav ing a plurality of longitudinally-extending troughs 35 in ing as its parabolic focus the opposing edge of said edge to edge relationship within a box frame element exit aperture and as its parabolic axis a line forming 36. In the enclosed space 37 beneath troughs 35 is dis 25 an angle with said optical axis of said body numeri posed a coil element 38 in which a fluid may circulate cally equal to said angular acceptance, and the for utilization of heat energy entering space 37 from field of acceptance of the body, when represented troughs 35. Box frame element 36 is preferably in terms of optical direction cosines, is an ellipse of mounted with troughs 35 extending in an east-west di semi-minor axis equal to the sine of said angular ac rection and the entire frame may be moved for seasonal 30 ceptance and semi-major axis substantially equal to tracking of solar movement. O.

It will be noted that for ease of fabrication it may be 2. A concentrator according to claim 1 wherein the desirable to construct the trough inner side wall ele distance separating said apertures is no more than one ments in the manner shown, i.e., generally triangular half the sum of d and d multiplied by the cotangent of elements 39 may be formed by extrusion (either of re 35 said angular acceptance.

flective material such as aluminum or of a plastic mate 3. A concentrator according to claim 1 further in rial later coated with a reflective material) to provide cluding trough end wall means enclosing the space be side wall surfaces 35a for adjacent troughs. A film 40 of tween by said energy reflecting and guiding side wall a transparent material such as glass may be disposed aS above troughs 35 for the purpose of protecting trough 40 4. A concentrator according to claim 3 wherein said inner side wall surfaces 35a from dust and the like. Due end wall means are radiant energy reflective. to known selective reflective properties (greenhouse 5. A concentrator according to claim 1 wherein said effect), the use of an iron-free glass film may be partic trough is filled with a medium having an index of re ularly advantageous in selectively preventing re-radia fraction greater than 1 and said entrance aperture is in tion of infrared energy by reflecting a portion of re 45 optical contact with a medium having an index of re radiated infrared back toward its exit aperture source. fraction lesser than that of the medium filling said FIGS. 17-19 illustrate concentration devices useful trough.

in collection of radiant energy deriving from within 6. A concentrator according to claim further in fields having a given angularity in one direction and a cluding a second such trough-shaped body disposed differing angularity in another. FIG. 17 (shown in cross 50 contiguous to said exit aperture, the transverse distance section in FIGS. 18 and 3) shows, for example a trough separating first and second edges of the entrance aper 42 of a configuration similar to that of FIG. 2, but ture of said second trough body being identical to the wherein end wall elements 43, 43 extend linearly from transverse distance separating first and second edges of entrance aperture 44 for a given distance and then said exit aperture.

taper toward exit aperture 45 to reveal a partially linear 55 7. A concentrator according to claim 6 wherein said and partially parabolic profile curve (See FIG. 18). trough is filled with a medium having a given index of FIG. 19 (shown in cross section in FIGS. 18 and 3) refrection, said second trough is filled with a medium shows a collector of a shape analogous to that of an el having an index of refraction greater than that of the liptic paraboloid but including parabolic inner surfaces medium filling said trough, and the angular acceptance defined according to the relationships set forth above 60 for energy rays entering the second trough is the in with respect to FIGS. 1-3. verse sine of the ratio of the index of refraction of the Obviously many modifications and variations of the medium filling the first trough to the index of refraction invention will occur to those of ordinary skill in the art of the medium filling the second trough. and therefore only such limitations as appear in the ap 8. A non-imaging radiant energy concentrator, said pended claims should be applied thereto. 65 concentrator comprising:

What is claimed is: a trough-shaped body having, 1. A non-imaging radiant energy concentrator, said a longitudinally extending radiant energy entrance concentrator comprising: aperture with first and second opposing edges sepa

Page 15

rated by a transverse distance d, ent motion of the sun within at least one hour be a longitudinally extending radiant energy exit aper fore and after reaching zenith point at solstice; and, ture disposed opposite said entrance aperture with a solar energy trap at said energy exit aperture. first and second opposing edges separated by a 13. Apparatus according to claim 12, wherein the transverse distance d2, 5 height of said concentrator element is no more than a linear radiant energy reflecting and guiding side one-half the sum of the transverse cross-sectional di wall means interconnecting laterally corresponding mensions of said entrance and exit apertures multiplied first edges of said apertures, by the cotangent of said concentrator angular accep a substantially concave, curving radiant energy re tance.

flecting and guiding side wall interconnecting later 10 14. Apparatus according to claim 12 wherein the ally corresponding second edges of said apertures, ratio of the transverse cross-sectional dimensions of a field of acceptance for radiant energy, said concentrator element exit aperture to said en an angular acceptance for radiant energy within said trance aperture is no less than the sine of said angular field of acceptance and dterminable at said en 15 acceptance.

trance aperture, and, 15. Apparatus according to claim 12 further includ an optical axis determinable by reference to dis ing solar energy reflecting end wall means at the ends tances separating entrance and exit aperture op of said parallel walls of said concentrator element. posing edges, 16. Apparatus according to claim 12 wherein said wherein the ratio of the distances d to d is no less 20 concentrator angular acceptance is 6. than the sine of said angular acceptance, the profile 7. Apparatus according to claim 12 wherein said curve of said curving wall means is a parabola hav concentrator element is filled with a medium having an ing as it parabolic focus a point, in the plane of said index of refraction greater than 1 and said entrance ap exit aperture, spaced away from said first edge of erture is in optical contact with a medium having an said exit aperture a distance equal to d2 and as its 25 index of refraction less than that of the medium filling parabolic axis a line forming an angle with said op said concentrator.

tical axis of said body numerically equal to said an 18. Apparatus according to claim 12 further includ gular acceptance, and the field of acceptance of ing a second concentrator element geometrically simi the body, when represented in terms of optical di lar to said concentrator element and disposesd between rection cosines, is an ellipse of semiminor axis 30 said concentrator element and said solar energy trap equal to the sine of said angular acceptance and contiguous to said concentrator element exit aperture, semi-major axis substantially equal to one. the transverse cross-sectional distance separating op 9. A concentrator according to claim 8 wherein the posing upper edges of said second concentrator ele ment reflecting surfaces being identical to the trans distance separating said apertures is no more than one half the sum of d and d, multiplied by the cotangent of 35 lowerverse cross-sectional distance separating opposing said angular acceptance. edges of said concentrator element reflecting surfaces.

10. A concentrator according to claim 8 further in 19. Apparatus according to claim 18 wherein said cluding trough end wall means enclosing the space be concentrator element is filled with a medium having a tween said wall means.

given index 11. A concentrator according to claim 10 wherein 40 ment is filled with of refraction, said second concentrator ele said end wall means are radiant energy reflective. a medium having an index of refrac 12. Solar energy concentration apparatus, said appa centrator element, andofthetheangular tion greater than that medium filling said con acceptance for en ratus comprising: ergy rays entering said second concentrator element is a concentrator element including, the inverse sine of the ratio of the index of refraction of a pair of longitudinally extending substantially paral 45 the medium filling said concentrator element to the lel walls having substantially concave opposing index of refraction of the medium filling said second inner solar energy reflecting surfaces, concentrator element.

each of said reflecting surfaces being sloped inwardly 20. Solar energy concentration apparatus, said appa from an upper edge at an energy entrance aperture ratus comprising:

to a lower edge at an energy exit aperture, said exit 50 a concentrator element including, aperture being of lesser transverse cross-sectional a pair of longitudinally extending substantially paral dimension than said entrance aperture, lel walls having opposing inner solar energy reflect a field of acceptance for solar energy and an angular ing surfaces, acceptance within said field, determinable at said one of said reflecting surfaces being substsantially entrance aperture, 55 concave and sloped inwardly from an upper edge at an optical axis determinable by reference to dis an energy entrance aperture to a lower edge at an tances separating respective opposing upper and energy exit aperture and the other of said reflecting lower reflecting surface edges, surfaces extending linearly from an upper edge at the profile curve of each of said reflecting surfaces said energy entrance aperture to a lower edge at being a parabola having as its parabolic focus the 60 said energy exit aperture, said exit aperture being lower edge of the opposing reflecting surface and of lesser transverse cross-sectional dimension than as its parabolic axis a line forming an angle with said entrance aperture, said optical axis numerically equal to the angular a field of acceptance for solar energy and an angular acceptance of the concentrator, acceptance within said field, determinable at said the dimensions of said apertures and the slope of said 65 entrance aperture, reflecting surfaces being such that said field of ac an optical axis determinable by reference to dis ceptance is capable of including an arc segment of tances separating respective opposing upper and coordinates equal to those described by the appar lower reflecting surface edges,

Page 16

the profile curve of said sloping reflective surface 21. Apparatus according to claim 20 wherein the being a parabola having as its parabolic focus a height of said concentrator elemenet is no more than point, in the plane of said exit aperture, spaced the sum of the transverse cross-sectional dimensions of away from said linearly extending reflective surface lower edge a distance equal to said exit aperture 5 said entrance and exit apertures multiplied by the co tangent of said concentrator angular acceptance.

transverse cross-sectional dimension and as its par 22. Apparatus according to claim 20 wherein the abolic axis a line forming an angle with said optical ratio of the transverse cross-sectional dimensions of axis of said concentrator numerically equal to said said concentrator element exit aperture to said en angular acceptance, the dimensions of said apertures and the slope of said 10 trance aperture is no less than the sine of said angular sloping reflecting surface being such that the field acceptance.

of acceptance of said concentrator is capable of in 23. Apparatus according to claim 20 further includ cluding an arc segment of coordinates equal to ing solar energy reflective end wall means at the ends of those described by the apparent motion of the sun said parallel walls of said concentrator element. within at least one hour before and after reaching 15 24. Apparatus according to claim 20 wherein said zenith point at solstice; and, concentrator angular acceptance is 6. a solar energy trap at said exit aperture. sk ck ck ck ck

Page 17

UNITED STATES PATENT OFFICE

CERTIFICATE OF CORRECTION

INVENTOR(S) : Roland Winston

It is Certified that error appears in the above-identified patent and that said Letters Patent O are hereby Corrected as shown below:

Col. l, line 26, after "providing" insert -- selective --. Col. 3, line 60, "shown" should be -- known --.

Col. 4, line 26, "field" should be -- fields --.

O Col. 6, line 67 delete "shown".

Col. 9 line l8 "ture" should be -- true --.

Col. 9, line 45 and 46 before each line insert -- - -, to designate the mathematical "minus" quantity.

O Col. 9, line 60 " <" should be -- -- - Col. 10, line 42, "factors" should be -- factor -- . Col. 10, line 54, after "larger" insert -- angular --. Col. 12, line 7, "separted" should be -- separated --.

Col. 12, line 57, "refrection" should be -- refraction --. Col. 13, line l4, "dterminable" should be -- determinable --. Col. 14, line 54 , "substsantially" should be -- substantially -- O Col. 16, line 2, "elemenet" should be -- element --.

signed and eealed this thirteenth Day of April 1976

SEAL

- At testing Officer Commissioner of Patents and Trademarks