Note: Descriptions are shown in the official language in which they were submitted.
CA 02800696 2012-11-23
-1-
Description
Supporting framework for a photovoltaic module and tracking device for a
photovoltaic system
The invention relates to a supporting framework for a photovoltaic module,
having
the features of the preamble of patent claim 1, and also to a tracking device
for a
photovoltaic system having a plurality of such supporting frameworks.
EP 1 710 651 131 discloses a biaxial tracking device, in which both vertical
and
horizontal tracking is provided.
In photovoltaic systems, the achievable energy yield depends on the incidence
angle of the Sun in relation to the photovoltaic module, and so, in order to
increase the energy yield, it is expedient to use devices which make the
photovoltaic modules of the system track the position of the Sun, which
changes
depending on the time of year or day. In this case, mention should first of
all be
made of vertical tracking, in which the photovoltaic module is made to track
the
Sun's path by rotation of the supporting structure that carries the module
about an
axis which is substantially vertical with respect to the surface of the Earth.
In
addition, in the case of biaxial tracking, horizontal tracking is also
possible in that
the photovoltaic module is pivoted or inclined in a horizontal axis, so that
ideally a
right angle with respect to the Sun is ensured.
In the case of the tracking device disclosed in EP 1 710 651 B1, a plurality
of
supporting frameworks for a respective photovoltaic module are provided via a
common drive means, in particular a cable, for transmitting an actuating
movement of a drive motor assigned jointly to the supporting frameworks. The
cable is in this case guided in each case around a driver element, which is in
the
form of an approximately cylindrical drum, and wraps around the latter. The
advantage of this drive arrangement having the one common motor for a large
number of supporting frameworks is that, even in the case of a large number of
installed photovoltaic modules, only one or a few motors are required.
CA 02800696 2012-11-23
-2-
Against this background, it is the object of the present invention to specify
a
supporting framework and also a tracking device, such that reliable
transmission
of the actuating movement is ensured.
The object is achieved according to the invention by a supporting framework
having the features of claim 1, which in the assembled state is part of a
tracking
device for a photovoltaic system having a large number of photovoltaic
modules,
which are made to track the Sun preferably exclusively vertically. The
supporting
framework is designed for automatic vertical tracking of the photovoltaic
module
mounted on the supporting framework in operation. It comprises a supporting
mast and also a, preferably cylindrical, driver element which surrounds the
supporting mast and is connected thereto so as to rotate therewith. An in
particular flexible drive means for transmitting a drive force wraps around
the
driver element in the assembled state. In order to ensure a connection between
the drive means and the driver element that is as slip-free as possible, there
is
provided a friction braking device which acts between the drive means and the
driver element. In the assembled state, a plurality of supporting frameworks
are
connected via the common drive means for vertical tracking.
Specifically, with regard to simple installation, the drive means is usually
connected only loosely, that is to say without a firm and form-fitting
connection, to
the driver element. When use is made of a cable, the latter is guided around
the
driver element. Preferably, the cable wraps around the driver element in this
case
in the manner of a loop, i.e. the cable is guided at least once or a plurality
of times
around the driver element. The drive force is transmitted in this case via the
associated friction between the drive means and the driver element, without a
form fit being formed. Depending on the size of the photovoltaic system,
preferably a plurality of 10 up to for example 30 or 40 supporting frameworks
are
connected together via a common drive motor and via the common drive means.
Tests have shown that in this case the problem can occur that, on account of
slip
between the driver element and the drive means, the different supporting
frameworks undergo different vertical tracking, i.e. in an array having a
large
CA 02800696 2012-11-23
-3-
number of such supporting frameworks there is the risk that the rotational
orientations of the latter will be different, and this should be avoided with
regard to
a solar yield which is as efficient as possible.
In order to avoid this and at the same to maintain the installation which is
as
simple as possible by way of simple wrapping of the driver element, there is
provided the friction braking device, which increases the friction that acts
between
the driver element and the drive means, so that slip between the two elements
is
avoided.
Expediently, the driver element has to this end a lateral surface which has
structuring as a friction braking device. For example, the lateral surface is
provided
to this end with elevations and depressions, i.e. for example radially
protruding
ribs, in order to increase the friction.
In a preferred embodiment, the lateral surface has at least one guide slot
which
extends along a section in the circumferential direction. In the assembled
state,
the driver element is accommodated in this guide slot. On account of the
incorporation of the guide slot, the cable therefore no longer rests smoothly
against the lateral surface in this region, but rather extends in a straight
line along
the length of the guide slot. At the inlet-side and outlet-side ends of the
guide slot,
the cable rests against edges, such that as a result the friction is markedly
increased and slip is avoided. The guide slot extends for example through a
rotation angle of more than 200 and preferably more than 30 around the
circumference of the driver element. The guide slot therefore covers a
comparatively large circumferential angle, and this has a positive effect on
the
desired high frictional force between the cable and the guide slot edges.
In order to ensure reliable guidance of the drive means about the driver
element
and in particular to ensure that the drive means extends through the guide
slot, in
an expedient development there is provided a guide element for guiding the
drive
means. This is formed in particular by elements protruding radially from the
lateral
surface, for example guide ribs, protuberances or the like. The guide element
thus
CA 02800696 2012-11-23
-4-
prevents the driver element from slipping along the lateral surface in the
vertical
direction.
This is advantageous in particular when photovoltaic systems are installed in
open
country with uneven ground, with the individual supporting frameworks not
being
arranged at an identical horizontal height. The drive means can therefore
under
certain circumstances extend at an angle to the vertical axis and be guided to
the
driver element.
Expediently, the guide element has in this case a guide region that converges
toward the friction braking device, such that the drive means is guided to the
friction braking device, in particular the guide slot, even in the event of an
inclined
course. This is achieved for example by two opposite guide ribs which run
toward
one another or are formed in a wedge-shaped manner and protrude radially from
the lateral surface.
Biaxial tracking devices, in which, in addition to vertical tracking about a
vertical
axis, horizontal tracking about a horizontal axis is also provided, generally
require
high structural outlay and/or separate servomotors for the two tracking
movements. In the case of the forced mechanical coupling, to be gathered from
EP 1 170 651 131, between the vertical and horizontal tracking, a high
frictional
force has to be overcome by the drive. In order then to achieve a cost-
effective
structure both of the supporting framework and with regard to the possibility
of
using lower-powered motors, it is provided in an expedient embodiment that the
supporting framework is formed exclusively for automatic vertical tracking.
Automatic horizontal tracking, in which the inclination angle takes account of
the
position of the Sun during the day by way of a varying horizontal inclination,
is not
provided.
In order additionally to ensure at the same time a solar yield which is as
high as
possible depending on the installation location of the photovoltaic system, it
is
additionally provided that a fixing apparatus is provided for manually setting
a
horizontal inclination angle. The supporting framework has to this end a
CA 02800696 2012-11-23
-5-
supporting frame, on which the respective photovoltaic module rests in the
assembled state. This supporting frame is mounted in a movable manner about a
horizontal pivot axis. At the same time, a defined horizontal inclination
angle is
settable manually via the fixing apparatus. Thus, for example, depending on
the
installation location (degree of latitude), a horizontal inclination angle
that is as
optimal as possible is set, preferably once when the system is installed or
set into
operation.
Expediently, the fixing apparatus in this case comprises a plurality of
discrete
locking settings for setting defined horizontal inclination angles. This is
achieved in
particular in that the fixing apparatus comprises a linkage which is arranged
between the supporting mast and the supporting frame and which has a variable
fastening end, which is lockable or fastenable preferably to the supporting
mast in
different positions, in order to be able to set the different inclination
angles. In
particular, to this end a perforated plate is arranged on the supporting mast.
Preferably, the supporting framework comprises an adjusting device, via which
the
rotational orientations of various part regions of the supporting mast are
adjustable
with respect to one another, that is to say are fixable to one another in a
reversible
manner with respect to one another. This adjusting device serves to simplify
assembly or to carry out simple readjustment during operation. In the case of
a
photovoltaic system having a large number of supporting frames which are
connected together and the vertical tracking of which takes place via a common
drive motor, there is the problem that, on account of tolerances and play in
the
drive train, the individual photovoltaic modules assume different azimuth
angles,
i.e. different rotation angles about the vertical axis, after the installation
of the
common drive means. On account of the division of the supporting structure
into
two part regions, which are rotationally adjustable with respect to one
another, the
advantage is achieved that, after installation of the system, when the
vertical
orientation between different supporting frameworks is not entirely
synchronous
on account of such play and tolerance effects, the vertical rotational
position of
individual supporting frameworks is easily settable without the supporting
frame as
a whole having to be rotated with respect to an anchoring element.
CA 02800696 2012-11-23
-6-
The two part regions of the supporting mast are connected together at the
dividing
point preferably via flanges. At least one of the flanges has a slot guide,
which is
preferably curved along a circular path, for a fastening element such as a
screw.
The flanges ensure easy assemblability and high mechanical stability. Usually,
it is
provided that the drive for vertical tracking acts on one of the two part
regions, in
particular the lower part region.
According to a preferred development, the flange of the lower part region of
the
supporting mast forms an upper termination for the driver element, i.e. the
dividing
point is arranged at the upper end of the driver element. In the case of the
hollow
cylindrical configuration of the driver element, this flange preferably forms
a cover,
such that a closed structural unit is formed. A bearing region of the
supporting
mast on the foot plate is better protected as a result.
The object is furthermore achieved according to the invention by a tracking
device
for a photovoltaic system, in which a plurality of such supporting frameworks
are
connected together via a common drive means, in particular a cable. The drive
means is in this case driven via a common drive in order to exert an actuating
movement for the supporting frameworks for vertical tracking. In this case,
the
drive means is guided frictionally about the driver elements, and preferably
the
drive means wraps around said driver elements completely or multiply.
Exemplary embodiments of the invention are explained in more detail in the
following text on the basis of the figures, in which, in each case in
simplified
illustrations:
Fig. 1 shows a perspective illustration of a supporting framework to which a
photovoltaic module is fastened,
Fig. 2 shows a side illustration of the supporting framework according to fig.
1,
Fig. 3 shows a roughly simplified illustration of a tracking device having a
plurality
of supporting frameworks connected via a common drive means and driven
by a common drive motor,
CA 02800696 2012-11-23
-7-
Fig. 4 shows a perspective enlarged illustration of the ground-side region of
the
supporting framework having a cylindrical driver element arranged around a
supporting mast,
Fig. 5 shows a side illustration of the elements according to fig. 3,
Fig. 6 shows a simplified side illustration of a driver having a guide slot
and guide
elements, and
Fig. 7 shows a sectional illustration in the region of the driver to
illustrate the
adjusting device.
In the figures, identically acting parts are provided with the same reference
signs.
Fig. 1 shows a supporting framework 2 to which a photovoltaic module 4 is
attached. The photovoltaic module 4 can in this case be composed again of
individual part modules that are electrically connected together.
The supporting framework 2 - as is illustrated once again in fig. 2 -
comprises a
vertically extending supporting mast 6 which carries at its upper end a
supporting
frame 8 to which the photovoltaic module 4 is fastened. The inclination of the
supporting frame 8 is in this case adjustable about a horizontal pivot axis
10.
Arranged in a manner spaced apart from the pivot axis 10 is a strut 12 of the
supporting frame 8, a linkage 14 consisting of a bar being fastened to said
strut 12
in a rotationally movable manner. The linkage 14 is fastened at its lower end
to the
supporting mast 6. For this purpose, a perforated plate 16 is fastened to the
supporting mast 6 in the exemplary embodiment. The linkage 14 is fastenable in
different vertical positions in this perforated plate 16 with the aid of a
fastening
element. The linkage 14 with the perforated plate 16 therefore forms a fixing
apparatus for manually setting a horizontal inclination angle of the
supporting
frame 8.
The supporting framework 2 has at its lower, ground-side end a fastening foot
17,
by way of which it is intended to be anchored on the ground. To this end, in
the
exemplary embodiment, there is provided a flange-like plate, which can be
anchored in the ground via screws. In the exemplary embodiment, immediately
CA 02800696 2012-11-23
-8-
above the fastening foot 17 there is provided a driver element 18. Via the
latter, an
actuating movement, namely a rotary movement about the vertical axis of the
supporting mast 6, is exerted on the supporting mast 6 with the aid of a drive
means 20 (cf. fig. 3). As a result, vertical tracking of the photovoltaic
module 4,
that is to say tracking in the east-west direction, is made possible. As a
result of
the arrangement in the immediate vicinity of the ground, the tilting moments
(with
respect to the vertical) that are exerted on the supporting framework 2 via
the
drive means 20 are kept small.
In a photovoltaic system, usually a large number of such supporting frameworks
2
having photovoltaic modules 4 are arranged in one or more rows. By way of
example, and in a roughly simplified manner, fig. 3 illustrates a single-row
arrangement with a total of five supporting frameworks 2 which are symbolized
by
the driver element 18. As can be seen therefrom, the individual supporting
frameworks 2 are connected together via the common drive means 20, in
particular a cable (wire cable), and, in order to perform vertical tracking,
the rotary
movement is transmitted synchronously to all of the driver elements 18 via the
drive means 20. In this case, the drive means 20 is wrapped around each of the
driver elements 18, i.e. it runs around each driver element 18 fully at least
once.
Furthermore, there is arranged a common drive 22, in particular an electric
motor,
via which the actuating force is transmitted to the drive means. The
supporting
framework 2 forms, together with the drive means 20 and the drive 22, a
tracking
device for vertical tracking of the individual photovoltaic modules. Tracking
is
controlled in a manner dependent on the time of day.
In order to ensure a synchronous rotary adjustment of the individual
supporting
frameworks 2, there is provided a friction braking device, which is configured
in the
exemplary embodiment as a circumferentially extending guide slot 24 which has
been introduced into a lateral surface 26 of the driver element 18 in the form
of a
hollow cylinder. The configuration of the driver element 18 with the guide
slot 24
can be seen best in figs 3 to 5. The guide slot 24 has for example a width of
5 to
mm and extends preferably over a rotation angle for example in the range of
to 60 in the circumferential direction.
CA 02800696 2012-11-23
-9-
By way of this friction braking device configured in such a way, the friction
force
acting between the drive means 20 (cable) and the driver element 18 is
increased
considerably compared with a configuration without a guide slot 24, and so
slip
between the drive means 20 and the driver element 18 is avoided. When the
cable is tensioned upon setting into operation, it rests against the
peripheral edges
(as seen in the circumferential direction) of the guide slot 24, such that
these
edges form a friction brake that acts in both directions with only little
structural
outlay. As a result, synchronous vertical tracking of all of the supporting
frameworks 2 is ensured.
Fig. 5 shows a variant embodiment, in which, in addition to the guide slot 24,
further guide elements 28 are arranged on the lateral surface 26. In the
exemplary
embodiment, these are arranged in the circumferential direction on both sides
with
respect to the guide slot 24. Each guide element 28 is in this case formed by
two
opposing guide ribs, which protrude radially from the lateral surface 26 and
define
a guide region 30 between one another. In the exemplary embodiment, this guide
region 30 converges towards the guide slot. By way of these guide elements 28,
reliable and secure guidance of the drive means 20 in the desired nominal
position is achieved even in the case of installation in open country, in
which the
various supporting frameworks 2 are fastened at different heights. Slipping in
the
vertical direction is avoided.
As can be seen from fig. 7, the supporting mast 6 is arranged, together with
the
driver element 18, in a rotatable manner on the fastening foot 17. To this
end, in
the exemplary embodiment, the fastening foot 17 has a vertically extending
supporting tube 34 over which the hollow-cylindrically formed supporting mast
6 is
fitted. The supporting mast 6 itself is in this case subdivided into two part
regions
36A, 36B which are connected together via a flange connection. To this end, a
fastening flange 38A, B is arranged at the end of each of the part regions
36A, B,
said fastening flanges being in the form of radially protruding and in
particular
circularly annular plates in the exemplary embodiment. The two fastening
flanges
38A, B and thus the two part regions 36A, B are fastenable to one another in
CA 02800696 2012-11-23
- 10-
different rotational positions. To this end, in particular a slot guide and
fastening
elements are provided. As a result, an adjusting device for the rotational
adjustment of the two part regions 36A, B with respect to one another is
formed
overall. This adjusting device serves to simplify assembly, in order in the
event of
setting into operation, after construction and wrapping of the individual
driver
elements 18 with the drive means 20, to be able to orient the individual
photovoltaic modules 4 exactly in the same east-west angular position. As a
result, in the event of setting into operation, a synchronous orientation of
all of the
photovoltaic modules 4 is made possible in an easy manner. Via the dividing
point, a decoupling possibility between the drive train and the upper part
region is
generally defined.
As can be gathered from fig. 7, the driver element 18 is formed in the manner
of a
hollow cylinder which is connected to the lower part region 36A in a
rotationally
fixed manner via struts. In the exemplary embodiment, the flange 38A of the
lower
part region 36A forms at the same time an upper cover for the hollow-
cylindrical
driver element 18. Overall, this creates a largely closed interior cavity, in
which in
particular the bearing point of the supporting mast 6 rests in a protected
manner.
In order to avoid running difficulties, sliding elements in the form of
bearing
sleeves are provided in the exemplary embodiment. These are arranged in each
case in the lower and upper region of the supporting tube 34. Preferably, both
bearing sleeves have a kind of annular flange. The supporting mast 6 is
supported
by way of its lower end, at which it likewise forms an annular flange, on this
annular flange of the bearing sleeve, such that relatively planar contact is
formed.
The bearing sleeves consist for example of an abrasion-resistant plastics
material
or of a suitable metal.
Furthermore, a storm protection means 40 is provided for the supporting mast
6,
such that the supporting mast is secured against lifting axially off the
fastening
foot 17 while at the same time being rotatable. To this end, in the exemplary
embodiment, a form fit which acts in the axial direction is formed between the
fastening foot 17 and the supporting mast 6, in particular the ground-side
flange
CA 02800696 2012-11-23
-11-
thereof. The storm protection means 40 is in this case formed in a simple
manner
by way of a curved lug, one end of which is fastened to the fastening foot 17
and
the other end of which protrudes over the flange, in particular with a small
axial
spacing.
The supporting framework 2 described here and also the tracking device
described with respect to fig. 3 are distinguished overall by a simple
structure and
high operational reliability. The simple structure is also decisively
characterized in
particular by the supporting framework 2 formed only for uniaxial, vertical
automatic tracking. In this case, it is furthermore particularly advantageous
that,
via the fixing apparatus, manual setting of the horizontal inclination angle
can be
carried out, in order to ensure as high a solar yield as possible in spite of
the
simplified structure. For the simple and cost-effective structure, the
configuration
with the driver element 18 and the common drive 22 and also the common drive
means 20 for a large number of supporting frameworks 2 is furthermore of
particular significance. By way of the friction braking device, reliable
operation with
synchronous vertical tracking is ensured. With regard to the simple
installation, the
adjusting device, which allows exact synchronous adjustment of the individual
photovoltaic modules 4 in the same orientation after installation of the drive
means
20, should also be highlighted. These three aspects, namely the fixing
apparatus
having the possibility of manually setting the horizontal inclination, the
friction
braking device and the adjusting device are in principle also realizable
independently of one another. The fixing apparatus and the adjusting device
can
therefore also be realized independently of the configuration with the
friction
braking device. We reserve the right to file partial applications relating to
these
aspects independently of the configuration with the friction braking device.
CA 02800696 2012-11-23
- 12-
List of reference signs
2 Supporting framework
4 Photovoltaic module
6 Supporting mast
8 Supporting frame
Horizontal pivot axis
12 Strut
14 Linkage
16 Perforated plate
17 Fastening foot
18 Driver element
Drive means
22 Drive
24 Guide slot
26 Lateral surface
28 Guide element
Guide region
34 Supporting tube
36A,B Part region
38A,B Fastening flange
Lug
