Cable tensioned membrane solar collector module with variable tension control

Disclosed is a solar collector comprising a membrane for concentrating sunlight, a plurality of elongated structural members for suspending the membrane member thereon, and a plurality of control members for adjustably tensioning the membrane member, as well as for controlling a focus produced by the membrane members. Each control member is disposed at a different corresponding one of the plurality of structural members. The collector also comprises an elongated flexible tensioning member, which serves to stretch the membrane member and to thereafter hold it in tension, and a plurality of sleeve members, which serve to provide the membrane member with a desired surface contour during tensioning of the membrane member. The tensioning member is coupled to the structural members such that the tensioning member is adjustably tensioned through the structural members. The tensioning member is also coupled to the membrane member through the sleeve members such that the sleeve members uniformly and symmetrically stretch the membrane member upon applying tension to the tensioning member with the control members.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to solar collectors and, more 
particularly, to a cable-tensioned membrane solar collector module with 
variable tension control. 
2. Description of the Prior Art 
Recent developments in the solar heliostat collector art include a trend 
toward manufacturing reflector panels or modules for concentrating 
heliostat collector assemblies with thin, flexible, lightweight, reflector 
materials. Examples of such reflector materials are thin metallic sheets 
of steel or aluminum, which are often called foils. Reflector modules 
manufactured from these materials are commonly referred to as 
stretched-membrane solar collectors. 
A concentrating solar collector may be simply defined as a reflector for 
optically collecting the sun's radiation and concentrating incident 
radiation at a focal area. The reflector is typically a mirror or a 
plurality of mirrors supported by a metal-constructed frame. Independently 
steered solar reflectors are generally referred to as heliostats. Solar 
radiation is commonly known as sunlight and, generally speaking, concerns 
electromagnetic radiation and photons emitted by the sun. The focal area, 
broadly speaking, is a point or region to which the collector reflects all 
incident solar radiation. Concentrating generally means increasing the 
intensities of solar radiation to temperatures needed for industrial 
process heat or thermoelectrical power stations. 
To concentrate solar radiation, individual solar collectors are usually 
employed in an array to point or focus the radiation onto an absorber 
target. In most cases, the absorber target is an absorber/receiver. The 
absorber/receiver, which may be a cavity-type, is normally positioned at 
either an aimpoint or the focal area of the array, as previously 
suggested, to absorb maximum solar energy flux. Solar energy flux 
generally means energy flux transmitted from the sun, which is in the form 
of electromagnetic radiation. The absorbed solar energy flux is usually 
carried away by a suitable heat transfer fluid to provide electrical or 
mechanical power, to operate thermomechanical apparatus, or to provide 
industrial process heat. 
The aforesaid trend toward producing lightweight solar collectors is 
dictated in part by the high manufacturing costs and heavyweight of 
glass/metal-type reflector panels and reflector supports. The reflector 
panels and support structures are often fabricated from thick, heavy 
metal, glass, and composite materials to meet the solar reflectivity and 
specularity imposed by the heliostat collector performance requirements, 
as well as the strength and rigidity standards imposed by the 
heliostat/collector survival requirements. Reflectivity is generally 
associated with the reflector material and specular variation in the 
reflection of radiant energy. Specularity is the degree to which beam 
radiation can be successfully reflected without scattering the light rays 
impinging on the reflector surface. The finish and flatness of a surface 
will affect its specularity. For example, silver-glassed mirrors have 
traditionally provided the highest reflectivity and best specularity. 
Metal is a favorable material for manufacturing the reflector support 
because it gives the reflector panel the capacity to withstand 
environmental loads without warping, bucking, or fracturing, which 
eventually could lead to failure. Examples of such environmental loads are 
gravity loads, wind loads, and ice/snow loads. 
Unfortunately, the heavy deadweight load of the glass/metal reflectors and 
the reflector supports frequently produces stresses and deformation that 
undesirably add to the harmful stresses produced by the environmental 
loads. Additionally, the aforementioned use of heavy glass, metal, and 
other structural materials to fabricate the reflectors and their supports 
is one major reason for their high manufacturing costs. 
In addressing the disadvantages associated with glass/metal-type reflector 
panels by producing lightweight stretched membrane solar collectors which 
greatly simplify and reduce the weight of the reflectors, a problem has 
developed in shaping and tensioning the stretched reflector surfaces 
thereof. For example, it has often been extremely difficult to shape and 
tension a stretched-membrane-type reflector surface so that it produces an 
acceptable focal spot at the absorber/receiver cavity with minimal 
unabsorbed surface reflected solar flux. Also, the absorber/receiver must 
be sufficiently small to minimize the associated radiant and convection 
energy losses. Radiant and convection losses concern solar energy that is 
lost by the absorber/receiver after the solar radiation is absorbed. The 
concepts of the required focal spot size and the radiant and convection 
losses become even more significant when it is realized that the 
characteristics of a stretched membrane reflector surface and a focus 
provided thereby may be used to reduce radient and connection losses. 
A stretched reflector surface will generally have a gravity-induced focal 
length which is a function of the surface tension and a reflector 
elevation angle. Normally, increasing the tension of the stretched 
reflector surface increases the gravity-induced focal length. The ideal 
focal length is equal to a slant range from the reflector to the 
absorber/receiver cavity. Hence, each solar collector in the field will 
have a different focal length and a different associated tension to 
control the gravity-induced focus. Thus, it is evident that the aforesaid 
reflector characteristics can be used to enhance collector system 
performance by reducing the size of the image at the receiver and 
therefore the amount of energy spillover. 
Another problem is that the reflector surfaces of stretched-membrane solar 
collectors usually have to be tensioned and assembled at the manufacturing 
facilities rather than at the collector sites. They also usually require 
skilled workmen to assemble them. Moreover, once the collectors are 
factory-assembled, their focus or aimpoint is usually not easily 
adjustable; therefore it can be difficult to produce various concentration 
ratios to meet specific collector site requirements. Concentration ratios 
are the ratio of the intensity of solar light impinging on the 
absorber/receiver to the solar light impinging on the reflector surface. 
Notably, these ratios may be as small as one for no concentration using a 
single collector to as high as several thousand using a large field of 
collectors. 
Besides, many factory-assembled collectors which do not provide a means for 
immediately adjusting the reflector tension during periods of operation at 
the collector site frequently are incapable of compensating incapable 
reflector tension variations and reflector deformation because of 
long-term reflector creep and environmental loads. Reflector creep may be 
defined as a slow change in reflector tension as a result of prolonged 
exposure to temperature excursions and environmental loads. 
Still another problem related to factory-assembled collectors is that 
shipping constraints usually limit the size of the reflector module which 
can be transported to the collector site from the factory. Another problem 
is that most current membrane solar collectors require fairly 
sophisticated designs to provide the reflector surfaces with the desired 
durability and optics. 
To cope with the aforesaid problems, the reflector surfaces of some solar 
collectors have been designed by tensioning a sheet of aluminized Mylar 
over a plurality of elongated supporting members. The supporting members 
impart a catenary configuration to the aluminized sheet. A prior art 
patent relating to such a design is U.S. Pat. Ser. No. 4,173,397. 
Unfortunately, however, this prior art design as well as others have 
suffered from one or more shortcomings. For example, this earlier design 
is unduly complex, comprises a number of component parts, and has a focus 
that is not easily controllable. 
Some prior art designs have stretched a sheet of aluminized Mylar over a 
top of a hollow cylinder and reduced a pressure therein between to provide 
a desired surface configuration. An example of this design is disclosed in 
U.S. Pat. Ser. No. 4,288,146. Unfortunately, this design may develop 
leaks and changes in the pressure within the cylinder. Such leaks may, in 
turn, lead to undesirable and irreversible degradation of the collector 
focus. It will be noted that the use of a vacuum pump to maintain the 
desired pressure has to some degree been helpful in reducing some aspects 
of the pressure leakage problem. However, such a pump is an additional 
cost element and is power consuming. Moreover, such a vacuum system adds 
complexity to the collector system, requires additional maintenance and 
reduces system reliability. 
Another prior art design somewhat similar to the design of the present 
invention is taught in U.S. Pat. Ser. No. 4,251,135. Here, a solar 
reflector having a flexible triangular reflective membrane with three 
sides thereabout employs a tension cable to place the membrane under 
tension. This design, however, fails to provide a means for adjustably 
varying the tension of the assembled reflector panel at the collector 
site. Thus, this design suffers from the same long-standing problem 
discussed above in connection with factory-assembled, stretched-membrane 
collectors that the present cable tensioned membrane solar collector 
module invention with variable tension control has satisfactorily overcome 
this problem. 
SUMMARY OF THE INVENTION 
Against the foregoing background, it is therefore a general object of the 
present invention to provide a tensioning device for a lightweight 
stretched-membrane solar collector module which overcomes many of the 
aforementioned shortcomings and disadvantages of the prior art lightweight 
solar collectors. 
It is a specific object to provide a lightweight stretched membrane-type 
reflector module which is adequately held in plane and in tension 
substantially solely through low-cost, simply constructed, fairly 
lightweight tensioning components. 
It is another specific object to provide a lightweight stretched 
membrane-type reflector module with variable control tensioning which can 
be used to compensate for reflector surface variations due to reflector 
creep and environmental loads at the collector site, as well as to produce 
desired concentration ratios. 
The above objects, as well as other objects and advantages, are attained by 
the present invention, which may be described briefly as a solar collector 
comprising a membrane member for concentrating sunlight, a plurality of 
elongated structural members for suspending the membrane member thereon, 
and a plurality of control members for adjustably tensioning the membrane 
member and controlling a focus provided by the membrane member. Notably, 
each control member is disposed at a different corresponding one of the 
plurality of structural members. The collector also comprises an elongated 
flexible tensioning member that stretches the membrane member and holds it 
in tension, and a plurality of sleeve members provide the membrane member 
with a desired surface contour during the tensioning thereof. The 
tensioning member is coupled to the structural members such that the 
tensioning member is adjustably tensioned with the control members. The 
tensioning member is also coupled to the membrane member through the 
sleeve members such that the sleeve members uniformly and symmetrically 
stretch the membrane member upon applying a tension to the tensioning 
member with the control members. 
Additional objects, advantages, and novel features of the present invention 
will be set forth in part in a detailed description which follows, and in 
part will become apparent to those skilled in the art upon an examination 
of the following description or upon practicing the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
elements or a combination of elements particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring initially to FIGS. 1-3, there is illustrated a preferred form of 
a cable-tensioned membrane solar collector module 2 with variable 
tensioning control constructed in accordance with the invention. 
Generallly speaking, the cable-tensioned solar collector module 2 may be 
employed in numerous applications where a reflector or collector surface 
is required to retrieve power from solar energy. An example of one such 
application is a central receiver system which, generally speaking, 
employs a field of heliostat collectors to concentrate solar radiation 
into an absorber/receiver to generate fairly large amounts of electrical 
power or thermal energy for industrial processes. The collector module 2 
generally includes a reflector 4, a plurality of sleeve members 6, a 
reflector support member generally designated by the reference numeral 8, 
a reflector surface cable-tensioned member 10, a plurality of a variable 
tensioning control members 12, and a plurality of cable retaining members 
14. 
Referring initially to the reflector 4, it generally functions as a 
lightweight stretched-membrane-type reflector surface for optically 
collecting and concentrating sunlight. In the illustrated form, the 
reflector 4 comprises a composite membrane member having a closed 
polygonal shape. The composite member includes an upper filmlike layer 16, 
which forms a reflector surface, and a lower layer 18 which serves as a 
substrate for the upper layer 16. 
The lower substrate layer 18 is best shown in FIG. 2 and may be formed from 
any number of fairly thin, lightweight, elastic reflector materials, such 
as aluminum, steel foils, or high-strength, polymeric foils. Likewise, the 
reflector surface 16 may be formed from any number of well-known plastics 
which are capable of meeting the mechanical property requirements and 
optical performance requirements for satisfactory reflector surface 
operations. Aluminized polyesters and silvered polycarbonate are examples 
of such reflector surface materials. Incidentally, it will be appreciated 
that the reflector surface 16 can be applied to the lower layer 18 with 
any number of well-known reflector surface forming techniques. Examples of 
such techniques are direct metallization techniques and surface sheet 
lamination techniques. 
Referring now to the reflector support member 8, the reflector support 
member 8, broadly speaking, functions to support and suspend thereon the 
reflector 4. More directly, it also functions to assist the tensioning 
member 10 in holding the reflector 4 in tension. In the illustrated form, 
the reflector support member 8 comprises four elongated metal constructed 
structural members 20. The structural members 20 are connected to a 
centrally located reflector hub member 22 in a spokelike configuration 
such that the structural members 20 radiate from the reflector hub member 
22, as is most clearly shown in FIGS. 1 and 2. 
The reflector hub member 22 is anchored to the ground by a pedestal 24, 
which is of sufficient strength and rigidity to satisfactorily withstand 
collector module system overturning moments transferred thereto from the 
reflector hub member 22. It will be noted that the invention contemplates 
the reflector hub member 22 and the pedestal 24 to provide mounting 
provisions for a two-axis steering and tracking or drive assembly. It will 
be further noted that firstly, the details of the two-axis drive system 
and the mounting provisions thereof have been omitted from the drawings 
for the sake of clarity and brevity since they are well known in the 
heliostat collector art, and secondly, the drive system and its mounting 
provisions along with the pedestal 24 form no part of the present 
invention. 
Referring now to FIGS. 4 and 5 and again to FIG. 3, the reflector support 
member 8 is provided with a plurality of metal-constructed variable 
tensioning control members 12, one control member 12 being located at a 
different peripheral end portion 26 of each structural member 20. The 
control members 12 generally function to adjustably or variably tension 
the tensioning member 10. Each control member 12 also functions to control 
a gravity-induced focus provided by the reflector 4, as well as to provide 
a means for fine tension adjustment of the tension in the reflector 4. It 
will be noted that the tensioning member 10 in response to adjustment of 
the control members 12 functions to tension the reflector 4, as will be 
more fully explained hereinafter. 
In the particular arrangement illustrated, each control device member 12 is 
shown in a lowered position for imparting tension to the tensioning member 
4 and is pivotally connected to a different, corresponding structural 
member 20 through a pin member 36. By the connections with pin member 36, 
control member 12 is enabled to be rotated from a first or raised position 
to the second, lower position. In the raised position tension is relieved 
and a shorter focal length is allowed, while in the lowered position 
tension is increased and longer focal lengths are sustained. 
Also, in the particular embodiment illustrated, each control member 12 is 
provided with a wedgelike shape which defines opposed upper and lower 
portions 28, and 30, respectively. The wedgelike shape and the manner in 
which each control member 12 is pivotally connected to its associated 
structural member 20 allows the control member 12 to form an acute angle 
with an outer surface of the end portion 26 of the related structural 
member 20, as is clearly shown in FIG. 5. By this angle, the two surfaces 
26, and 30 are, generally speaking, radially spaced from one another to 
enable each control member 12 to be rotated in a radial direction relative 
to an imaginary axially extending center line 27, depicted in FIG. 2, 
which passes through the hub member 22. Stated somewhat differently, each 
control member 12 is enabled to be pivotally moved toward the associated 
structural member 20 when tensioning the reflector 4 and to be pivotally 
moved away from the associated structural member 20 when detensioning the 
reflector through the aforesaid pin connection. 
Although the control members 12 are preferably provided with wedgelike 
shapes and are preferably connected to the structural members 20 by 
locating the pin member 36 at upper portions thereof, be it understood 
that the control members 12 may be formed with other shapes and may be 
pivotally connected to the control members 20 using other fastening 
arrangements, as will occur to those skilled in the art. For instance, the 
outer end regions 26 of the structural members 20 may be configured to 
form a triangularly shaped fulcrum located approximately intermediate the 
upper and lower sides 33, and 35, respectively, as is clearly illustrated 
in FIG. 6. Here, the ends 30 of the control 12 members would be provided 
with fairly flat surfaces. The control members 12 would be pivotally 
connected to the structural members 20 by locating the pin members 36 at 
their fulcrums. 
Referring now to the cable-retaining members 14, notably a retaining member 
14 is disposed at an outer region of the upper surface 28 of each control 
member 12, as is clearly illustrated in FIG. 5. Each retaining member 14 
serves to secure the tensioning member 10 to the related control member 
12, as well as serving to secure the tensioning member 10 to the 
structural member 20. In the present instance, each retaining member 14 
is, generally speaking, in the form of a disk that has an outer circularly 
shaped rim portion 40. The rim portion 40 defines a recess. The recess is 
of a size and shape suitable for holding therein the tensioning member 10 
with a minimal amount of crimping and for allowing the tensioning member 
10 to move freely and easily therein. 
The retaining members 14 may be attached to the control members 12 with 
spot welds or with conventional bolt-type fasteners. However, in the 
preferred embodiment each retaining member 14 is pivotally connected to 
one of the associated control members 12 through a pin 38. This pin 
connection allows the tension imparted to the tensioning member 10 to be 
uniformly distributed around the circumference of the reflector 4, as will 
be more fully discussed hereinafter. 
Referring again to the control members 12 by way of FIG. 5, attention is 
now drawn to the fact that the lower portion 30 of each control member 12 
is provided with adjusting members. The adjusting members are generally 
designated by the reference numeral 42, and they serve to impart radially 
indexing movement to the associated control members 12, as will be more 
fully discussed hereinafter. Each adjusting member 42 is in the form of 
two feed screws 44 that are operatively connected between the associated 
control member 12 and the associated structural member 20. 
In this double feed-screw arrangement, a first threadless portion 46 of 
each feed screw 44 is rotatably secured at the outer end portion of the 
associated control member 12 with a pair of washer-shaped retaining rings 
48, one ring 48 being spot welded to an inner surface 34 of the control 
member 12, and the other ring 48 being spot welded to its outer surface 
32. A second threaded portion 50 of each feed screw 44 threadably engages 
a mating nut 54 at an aperture 52 of the associated structural member 20. 
Each nut 54 is welded to the inner surface of the outer end 26 of the 
structural member 20. 
Referring now to the sleeve members 6, and again to FIGS. 2, 3, and 4, the 
reflector member 4 is shown to include a plurality of sleeve members 6. 
The sleeve members 6 generally function to couple the reflector 4 to the 
tensioning member 10 and to bring the reflector 4 to an isotropic, planar 
tension state, during the tensioning of the reflector 4. By bringing the 
reflector member 4 to an isotropic, planar state, the sleeve members 6 
enable the reflector 4 to be uniformly and symmetrically stretched to a 
desired level of constant tension. 
To accomplish imparting isotropic properties to the reflector membrane 4 
during tensioning, each sleeve 6 is provided with a parabolic shape which 
approximates a catenary. The latter shape may be defined as a 
gravity-induced curve assumed by a flexible cable of uniform density and 
cross section hanging freely from two points. More specifically, each 
sleeve member 6 is in the form of an elongated sheet that has been folded 
in a manner to define a longitudinally extending slot 56. Each slot 56 for 
each sleeve member 6 generally functions to seat therein a different 
corresponding portion of the tensioning member 10, and it is of a size and 
shape suitable for this purpose. Each slot 56, and thus each sleeve member 
6, also includes an upper portion 58 and a lower portion 60, which define 
a pair of longitudinally extending, transversely spaced peripheral edges. 
The upper portion 58 of each sleeve member 6 has a bow or parabolic shape 
and primarily functions to assist the tensioning member 10 in providing 
the reflector surface 16 with a certain level of constant tension, whereas 
the lower portion and the spaced edges 60 thereof function to receive and 
retain therein between corresponding boundary portions of the reflector 4 
through spot welds, bonding, or some other suitable fastening technique. 
The upper portion 58 also functions to assist the tensioning member 10 in 
effecting a desired gravity-induced focal length and in substantially 
preventing deterioration of the collector focus due to wind-induced 
deflections. For example, upon the sleeve members 6 being attached to the 
reflector 4, and upon loading the sleeve members 6 with the tensioning 
member 10, the sleeve members 6 act to uniformly stretch the reflector 4 
in opposition to the straightening influence exerted on the upper portions 
58 by the loaded tensioning member 10. This loading technique together 
with the parabolic shape of the sleeve members 6 enables the reflector 4 
to be uniformly tensioned and stiffened to a constant magnitude which 
minimizes deterioration of the collector focus due to high winds and/or 
weight. 
It will be noted that the sleeve members 6 may be formed from any number of 
well-known polymeric materials, such as polimide, or metallic-type 
materials, such as steel and aluminum. Preferably, the sleeve members 6 
are formed from the same material selected for the lower substrate layer 
18 of the membrane reflector member 4. 
Referring now to the tensioning member 10, the tensioning member 10 serves 
to uniformly and symmetrically tension the reflector 4, to hold the 
reflector 4 in constant tension through the sleeve members 6, and to 
connect the reflector 4 to the structural members 20, as is clearly shown 
in FIG. 5. The tensioning member 10 may be fabricated from any number of 
materials, such as metal cables, high-strength ropes, and single filament 
lines. Preferably, the tensioning member 10 comprises a high-strength 
cable. 
Upon mounting the reflector 4 to the reflector support member 8, it is 
obvious that the sleeve members 6 function to couple the reflector 4 to 
the cable 10 and that the cable 10, in turn, functions to couple the 
reflector 4 to the structural members 20 through the tensioning control 
members 12 by way of the retaining members 14. 
To accomplish mounting the reflector 4 to the reflector support member 8, 
the cable 10 is inserted through the slots 56 of the coupled sleeve 
members 6 and the reflector member 4. As previously mentioned, the sleeve 
members 6 are coupled to the reflector 4 by equally spacing and fastening 
them around the boundary of the reflector 4 via the slot edges 60. 
Thereafter, the reflector 4 is suspended at the reflector support member 8 
such that each sleeve member 6 is disposed between two different adjacent 
structural members 20, and the free segments of the cable 10 are within 
corresponding rim portions 40 of the retaining members 14. From the 
aforesaid, it is also obvious that a plurality of separate, fairly 
large-size reflectors 4 can be easily mass mounted to associated support 
members 8 at a collector site, rather than at a factory. 
To accomplish tensioning the reflector 4 with the cable 10, each set of 
screw feeds 44 are initially sequentially rotated a desired number of 
turns in a clockwise direction. Such rotation threadably advances the feed 
screws 44 at the nuts 54 and imparts radially inward movement thereto. 
This radial movement causes the affected control member 12 to pivotally 
move radially inward and downward at the pin member 36 while carrying its 
mounted retaining member 14 with it. The downward and radial inward 
movement of both the control member 12 and its retaining member 14 serves 
to subject the cable 10 to a tension force. 
In response to this tension force, the upper bow-shaped portions 58 of the 
sleeve slots 56, and thus the sleeve members 6 themselves, attempt to 
straighten. As the sleeve members 6 straighten, they subject the edges of 
the attached reflector 4 to a pulling force which acts to uniformly and 
symmetrically tension the reflector 4. 
From the aforesaid, it will be noted that additional rotation of the feed 
screws 44 causes the tension in the reflector 4 to be incrementally 
increased. More particularly stated, increasing the tension in the cable 
10 through the control members 12 reciprocally increases the amount at 
which the upper curved portions 58 of the slots 56 are straightened and, 
thus, also reciprocally increases the tension in the reflector member 4. 
The reflector 4 is fully tensioned when the control members 12 are rotated 
such that the inner surface regions thereof abuttingly engage the outer 
surfaces of the structural member ends 26 or when the feed screws 44 are 
fully advanced. 
It will also be noted that the ability of the tensioning member 10 to slide 
freely within the rims 40 of the retaining members 14 in conjunction with 
the ability of any one or more of the affected retaining members 14 to 
rotate, upon adjusting selected control members 12, allows the tension 
applied to the reflector 4 through the tensioning member 10 and the sleeve 
members 6 to be uniformly distributed around the boundary regions of the 
reflector 4. These abilities also enable the applied tension to remain 
uniformly distributed around the boundaries regions thereafter. 
It will now be appreciated that during the tensioning of the reflector 
member 4, the amount at which the slots 56 are straightened, in part, 
determines the ultimate contour and the degree of tension and stiffness 
that are imparted to the reflector surface 16. Additionally, this slot 
straightening and tensioning characteristic of the present invention 
significantly contributes to controlling the gravity-induced focusing of 
the collector 2 and to protecting the collector 2 from being adversely 
affected by high winds. For example, increasing the tension as aforesaid 
tends to flatten the contour or optical reflector surface 16 of the 
reflector 4, and changing the surface tension and surface contour causes 
the gravity-induced focal point to also change. Moreover, the reflector 4 
can be tensioned and thereby stiffened at levels sufficient to 
substantially prevent wind-induced reflector surface deflections. Here, it 
is contemplated that the magnitude of tension imparted to the reflector 4 
will be optimized to provide sufficient stiffness to minimize 
deterioration of the reflector focus due to environmental loads, as well 
as to produce satisfactory solar flux concentrations at the receiver. 
Having explained the details of tensioning the reflector 4, it will be 
evident that rotating the feed screws 44 in a counter-clockwise direction 
results in initially backing the feed screws 44 from the nuts 54. The 
latter action of the feed screws 44 causes the control members 12 to pivot 
about the pin members 36 in an upward and radially outward direction 
relative to the structural member ends 26. Such upward movement releases 
the tension in the cable 10, as well as in the coupled sleeves 6 and the 
reflector member 4. Consequently, the reflector 4 is detensioned in the 
aforesaid manner and returned to its original nontensioned state. 
Attention is now drawn to the fact that the cable-tensioned membrane solar 
collector module 2 of the present invention has several advantages over 
earlier somewhat similar collector types in that: the reflector panel 
member 4 uses mostly inexpensive, readily available materials and 
components which can be easily and cheaply manufactured; the reflector 
member 4 can be easily assembled, adjustably tensioned, and disassembled 
at the collector site; and the sleeve members 6, cable 10, and control 
members 12 provide the collector 2 with variable control tensioning which 
can be used to compensate for tension reflector variations due to 
reflector creep and environmental loads, as well as to produce desired 
concentration ratios. 
In keeping with the invention, various changes and modifications to 
particularly disclosed embodiments will be apparent to those skilled in 
the art and eventually may be made without departing from the spirit and 
scope of the invention. By way of example, there is illustrated in FIGS. 
7-9 a variant of the embodiment of FIG. 1 wherein the structural support 
members, which in this instance are denoted by the reference character 62, 
are employed to assist the tensioning member 10 in holding the reflector 4 
in a state of plane tension. 
It will be noted that the reflector member 4, the sleeve members 6, the 
tensioning member 10, and the retaining members 14 are connected to one 
another and to the support members 62 in substantially the same manner as 
that described for the embodiment of FIG. 1. The only difference in the 
manner in which the aforesaid components of the embodiments of FIG. 1 and 
FIG. 2 are connected is that the retaining members 14 are directly 
connected to the outer end portions of the structural members 62, as is 
clearly shown in FIG. 7. 
To enable initial attachment and tensioning of the reflector 4 of FIG. 7, 
the reflector support members 62, which are shown in their raised or 
nontension position, are pivotally mounted at a first upper portion of the 
hub member 22 by way of a collar and pin arrangement 66, which arrangement 
is secured thereto by conventional means such as spot welds 68. The collar 
66 is provided with cleaved brackets 70, which have apertures 72 for 
receiving therein the pins 74, and which are of a size and shape to 
receive therein between mating peripheral end portions 76 of the 
structural members 62. The structural end portions 76 are provided with 
apertures 78 for receiving therein the pins 74 on which the structural 
members 62 are enabled to pivotally swing. 
The variable tension control member, which is generally designated by the 
reference numeral 80, comprises a plurality of studs 82 circumferentially 
spaced about a lower portion of the hub member 22 so as to project within 
complementary elongated through slots 84 of the structural end portions 
76. The studs 82 are secured to the hub 22 with a collar 86. End portions 
of the studs 82 are threaded and are fitted with stud heads in the form of 
wing nuts 88. The slots 84 are of a size and shape suitable for allowing 
vertical movement of the structural members 62 during tensioning or 
detensioning. 
When applying and tensioning the reflector member 4, the structural members 
62 are pivotally lowered from their raised or near vertical position until 
a desired amount of tension in the reflector member 4 is acquired. 
Lowering the structural members 62 is accomplished by threadably advancing 
the stud heads 88. As the stud heads 88 are advanced, the structural 
members 62 will be caused to swing downward in a clockwise direction so as 
to place the reflector member 4 under a desired tension. By referring to 
FIGS. 7 and 8, it will be apparent that the reflector member 4 is 
completely tensioned when the ends 76 of the structural members 62 
abuttingly engage the hub 22. 
Upon threadably backing off the stud heads 88, the structural members 62 
can be pivoted in a counterclockwise direction so as to allow the 
structural members 62 to be raised from the lower or near horizontal 
position to the vertical position. Such counterclockwise movement of the 
structural members 62 enables the reflector member 4 to be detensioned. 
Incidentally, it will be appreciated that the initial tension in the 
tensioning member 10 is of sufficient magnitude to keep the support 
members 62 raised when the support members 62 are in a nontensioned 
position and to assist in swinging the members 62 from the horizontal 
position to the raised position when the reflector 4 is being detensioned. 
The present examples and embodiments, therefore, are to be considered in 
all respects illustrative and restrictive, and the invention is not to be 
limited to the details given herein but may be modified with the scope of 
the appended claims.