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|United States Patent Application
;   et al.
July 13, 2006
The invention relates to a solar collector for focusing solar radiation
onto a focal line, said solar collector comprising a carrier for a
grooved, arched reflector. According to the invention, the carrier
comprises a plurality of molded grooves which each have a parabolic
lateral edge; the molded grooves are surrounded by an outer film; the
reflector consists of an elastic reflector material; and the form of the
reflector is impressed on the elastic reflector material, directly or by
inserting a carrier, by means of the parabolic lateral edge.
Hoelle; Erwin; (Rosenfeld, DE)
; Jakob; Klemens; (Isingen, DE)
DREISS, FUHLENDORF, STEIMLE & BECKER
POSTFACH 10 37 62
January 23, 2004|
January 23, 2004|
July 18, 2005|
|Current U.S. Class:
|Class at Publication:
||F24J 2/12 20060101 F24J002/12|
Foreign Application Data
|Jan 24, 2003||DE||103 03 476.5|
12. A solar collector module to focus the sun's rays onto a focal line,
the module comprising: a support structure, said support structure having
a plurality of form ribs, each of said form ribs having parabolic lateral
edges; an outer skin, said outer skin surrounding said support structure
such that said form ribs are clad in said outer skin; and a
trough-shaped, arched reflector, said reflector having a pliable
reflector material and a shape defined by said parabolic lateral edges of
said form ribs.
13. The module of claim 12, wherein said reflector is disposed directly on
said outer skin.
14. The module of claim 12, further comprising a carrier disposed between
said outer skin and said reflector.
15. The module of claim 12, wherein said form ribs have a sickle shape.
16. The module of claim 12, wherein said parabolic lateral edges of said
form ribs are established by folding or corrugating said form ribs.
17. The module of claim 12, wherein an opposing side of said parabolic
lateral edges has a partially circular contour.
18. The module of claim 12, wherein said form ribs and said outer skin
constitute an enclosed rigid box structure.
19. The module of claim 12, further comprising a trapezoidal metal sheet
disposed between said reflector material and said outer skin to seat on
said parabolic lateral edges of said form ribs, said metal sheet having
longitudinal grooves running along said trough-shaped reflector, wherein
said reflector material seats on said metal sheet.
20. The module of claim 19, wherein said grooves form channels, structured
to be sealed at ends thereof.
21. The module of claim 19, wherein said trapezoidal metal sheet and said
outer skin are attached to said form ribs.
22. The module of claim 21, wherein said metal sheet and said outer skin
are attached to said form ribs using screws, rivets, or adhesive.
23. The module of claim 19, wherein said reflector material is glued to
said grooves of said trapezoidal metal sheet.
24. The module of claim 12, wherein said reflector material comprises a
metal, a plastic foil, or a thin glass layer, wherein said foil has a
reflective surface on its upper side and said glass has a reflective
surface on one or both sides.
25. The module of claim 24, wherein said foil or said glass layer has a
thickness on the order of 1 mm.
26. The module of claim 12, further comprising means for a receiving tube
disposed along the focal line and supported by support arms, wherein said
support arms are connected to said form ribs and/or to an upper surface
of said reflector.
 The present invention relates to a solar collecting module
characterized by the terms in claim 1.
 Solar collectors of the above type use a parabolic shaped
reflecting surface to collect and focus sunlight onto a focal line. The
reflecting surface is moved along its horizontal axis to follow the
movement of the sun during the day.
 These solar trough collectors have proved themselves over many
years and are manufactured with different mirror support structures.
 Modern solar collectors are up to 100 meters long and are
approximately 6 meters wide.
 They are driven using one or more electric motors.
 As is evident from the dimensions of these collectors and the fact
that they stand exposed to the weather they are subject to high wind
forces. These wind forces place high demands on the collecting modules in
relation to the stability of the mirror support structures.
 These forces are especially high in relation to the twisting or
torsional rigidity of the structure. The reflecting and concentrating
properties of the collectors are adversely affected by even small
deformation and this affects the efficiency of the installation.
 In order to provide enough resistance to these torsional
deformation forces reticular tube structures are used to support the
parabolic shaped mirrors. This uncoupling of support structure and
pre-formed reflectors results in an extremely complex overall structure.
 An example is the solar collector DE-A-198 01 078 which uses such a
reticular tube structure to support the reflector surface. The support
structure is connected to a carrier tube, which provides the torsional
rigidity. The reticular support, however, does not contribute to the
torsional strength, which means that these constructions are still prone
to torsional deformation.
 Another example is the parabolic trough concentrator DE-A-197 44
767 that likewise uses a reticular support structure.
 Diagonal tubes connected to the individual support arms provide the
torsional rigidity. This type of construction is suitable solely for
short collector modules as the torsional rigidity is not optimal.
 DE-A-199 52 276 presents a parabolic trough collector in which
swiveling support arms are arranged on a central axis. Here also the
torsional rigidity originates only from the central axis tube. The arms
themselves do not contribute to the torsional strength.
 WO-A-02 103 256 demonstrates a parabolic solar collector which has
a central tube onto which side arms are mounted. This type of reflector
is indeed relatively resistant to bending but has almost no torsional
 The present invention is based on the task of building a solar
collector, which provides torsional rigidity in a simple construction.
 This task is resolved by a solar collector module having the
features of claim 1.
 In the present invention forming ribs are surrounded by an outer
skin layer. Together these form an enclosed box construction, which
possesses very high torsional strength. In addition, the form ribs are
also parabolic shaped on their concave edge so that the reflector
material takes on the parabolic trough shape when impressed upon the
reflector. This means that the reflecting surface material need not be
rigid. Pre-formed parabolic mirrors, which are relatively expensive, are
not necessary. Instead, the material can be pliable.
 This pliable reflector material can, for example, be delivered on a
roll and then cut to the required size on site. Transport costs are, in
this way, considerably reduced and the reflector surface material itself
is also considerably cheaper than pre-formed parabolic mirrors.
 The present invention has the advantage of high torsion strength
and that, not only pre-formed parabolic mirrors, but also pliable
reflector material can be utilized because the parabolic trough shape is
impressed on the outer skin in the concave area of the form ribs.
 A further embodiment provides that the form ribs demonstrate a
sickle shape. Because of this sickle shape the whole support structure
with its outer skin has, essentially the form of a supporting wing. This
is, for example, familiar in aircraft or ship construction and possesses
high rigidity in regard to bending and torsion factors.
 In order to give the form ribs the desired shape in a simple manner
they are manufactured using a folding or rippling process so that a
concave lateral edge results that is essentially parabolic shaped. At the
same time the edge opposite the parabolic edge can be arched.
 Onto this closed, torsion rigid support construction, formed by the
form ribs and the outer skin the pliable reflector material is applied so
that it adopts the parabolic shape.
 Preferably a trapezoidal metal sheet is laid onto the outer skin,
which lies on the parabolic lateral edge. This sheet has grooves running
lengthways along the curved trough shaped collector onto which the
reflector material is laid. This has the advantage that the supporting
surfaces of the reflector material, formed by the grooves in the
trapezoidal sheet, are free from obstructions, for example, screw or
rivet heads and that the grooves form parallel running, strip surfaces
which support the shape of the reflector material. Thereby, too,
compensation for materials with different heat expansion coefficients,
for example, glass reflector materials and metal outer skin or support
structure is achieved.
 The grooves of the trapezoidal metal sheet form channels that are
apt to be sealed at their lateral ends. These kind of closed channels
have the advantage that they can be evacuated so that, when the pliable
reflector surface material is placed onto the support surfaces of the
grooves with a layer of adhesive between, the channels of the grooves can
be evacuated and the reflector material is held in place. This can be
continued until the adhesive layer has sufficiently hardened. By this
means, special clamping systems can be spared. Another possible method
for pressing the pliable reflector material in place is that, after
laying the reflector in place, the trough is closed at the lateral ends
and filled with water. Through the water pressure the reflector material
is pressed onto the grooves while the adhesive hardens.
 In an embodiment, the trapezoidal metal sheet is fixed, together
with the outer skin, to the form ribs using, for example, screws or
rivets. In this way, a separate riveting or screwing process is avoided
because the outer skin lies between the form ribs and the grooves of the
trapezoidal sheet and is held in place by the fastening of the
trapezoidal sheet to the form ribs.
 As already mentioned, it is advantageous to glue the reflector
material to the grooves of the trapezoidal sheet. In this way, small
deformations in the surface of the reflector material are avoided. Apart
from this, different materials, as well as glass, can easily be fixed to
the trapezoidal sheet.
 In this way, the reflector material used in the present invention
can be a metal or synthetic foil or a thin glass layer with a thickness
of, for example, 1 mm. The foil material having a reflecting upper
surface and the glass a reflecting surface on one or both sides.
 These thin materials have the special advantage that a second or
more layers can be added to them. In this way repair is considerably
simplified. Due to environmental effects the reflector surfaces become
gradually "blind" in that the reflecting properties are adversely
affected. They must then be either exchanged or the mirror surface
renewed. Whereas the present invention allows for new layers of
reflecting material to be added.
 Along the focal line of the collector provision is made for a
receiving tube, which is supported by support arms. These are attached to
the form ribs and/or the upper surface of the reflector (16).
 This simple structure contributes to an inexpensive construction of
the present invention.
 Further advantages, characteristics and details of the present
invention are contained in the following description in which especially
preferred embodiments are represented in detail with reference to the
 The characteristics represented in the drawings as well as those
mentioned in the description and/or the claims can relate individually or
in any combination to the present invention.
 The drawings show:
 FIG. 1 A perspective representation of a reflector module.
 FIG. 2 The support structure of a reflector module.
 FIG. 3 Lateral view of a form rib in the direction of arrow 111 in
 FIG. 4 A blank cutting for form ribs.
 FIG. 5a to 5c Details of production steps in the manufacture of a
 FIG. 6 An alternative drive for a reflector module installed on a
 FIG. 1 shows a reflector module (10), a plurality of which
constitute a solar collector plant.
 This reflector module (10) is fastened to a support structure (not
shown) and is arranged so that the incident sun's rays strike the concave
area (12) and from there are reflected onto a receiving tube (14) (see
FIG. 3). For this the concave area (12) is formed from a parabolic shaped
 The reflector module (10), as schematically represented in FIG. 2,
consists of a plurality of form ribs (18), which lay parallel to each
other. The form ribs (18) are clad on their concave edge (12) and their
convex edge (20) with an outer skin (22) as represented in FIG. 1. The
outer skin (22) is fixed to the form ribs (18) by means of screws, rivets
or some other means. In this manner the form ribs (18) and the outer skin
(22) form an enclosed support structure.
 In FIG. 3 rivets are schematically represented by means of which
the form ribs (18) and the lower section (26) of the outer skin are
 An upper section (28) of the outer skin (22) is laid onto the
concave edges (12) of the form ribs (18) and onto this upper section (28)
of the outer skin (22) a trapezoidal metal sheet (30) is laid. The lower
bridges (32) of the trapezoidal sheet (30) together with the interposed
upper section (28) of the outer skin (22) are then riveted to the form
ribs (18). The upper bridges (36) of the trapezoidal sheet (30) now form
the laying surface for a reflector material (38), which is pliable and
rests on the upper bridges (36).
 In this way the reflector material (38) adopts the characteristic
shape of the concave surface of the trapezoidal sheet (30). This shape is
the desired parabolic form, which allows the incident sun's rays to be
directed onto the receiving tube (14). The reflector material (38), which
can consist of a reflecting metal or synthetic foil or a layer of thin
glass mirror having a thickness of, for example, 1 mm is then glued to
the upper bridges (36).
 FIG. 3 shows, in addition, a support arm (40) apt to carry the
receiving tube (14). These arms are fastened by rivets or some other
means to the reflector (16) together with the upper bridges (36) of the
trapezoidal sheet (30) and or with the underlying form ribs (18).
 FIG. 4 shows a metal strip (ref. No 42) with a width of 1200 mm out
of which alternating blanks (44) are cut each blank being 6000 mm long.
These blanks (44) or (46) as shown in FIG. 5a are further processed with
a metal folding machine (not shown) in that they are bent to form the
concave area (12) contained in the lateral edge (48). This is achieved by
rippling (50) or folding. The section thus formed still has an
essentially angular outer form that is chamfered in the next production
stage by pressing or folding. During this production stage the lateral
edge (48) is cut and or flanged so that, after laying the outer skin
(22), the trapezoidal sheet (30) and the reflector material (38) onto the
upper section (26), all have the desired parabolic shape.
 In addition recesses (52) are introduced through which pipes for
liquids and electric power cables can run inside the reflector module
(10). The rivets are fastened through the flanged edges.
 Altogether it can be see that the present invention comprising a
plurality of reflector modules (10) possesses the considerable advantage
that each reflector module (10) has the required torsion rigidity and
that pliable reflector material (38) can be used onto which the parabolic
shape is impressed by the trapezoidal sheet (30) and the form ribs (18).
It is therefore not necessary to use expensive pre-formed rigid mirrors.
Relatively inexpensive foil materials can be utilized or thin glass
mirror, which are also less expensive.
 The bonding bridges (54) connecting the upper bridges (36) and the
lower bridges (32) balance different heat expansion coefficients between
the reflector material (38) and the outer skin (22) without problem. In
this way heat stress factors do not build up.
 In an embodiment represented in FIG. 6 the reflector modules (10)
lie on a level base and can be swiveled by means of a suitable drive. The
lower section (26) of the outer skin (22) is provided with a cogging,
which engages, with another cogging or a pair of cogwheels mounted on the
base. This type of fixed reflector module (1) is even more resistant to
buckling than hanging modules. They are also less exposed to the wind.
* * * * *