Photovoltaic panel support assembly

A solar energy power source is provided comprising at least two flat photovoltaic panels disposed in co-planar side-by-side relation and an improved support structure for supporting the panels for pivotal movement on a pivot axis that extends transversely of the panels, the improved structure including a single selectively operable drive means for pivoting all of the panels simultaneously and by the same amount of angular displacement.

This invention relates to solar energy collection systems utilizing a 
multiplicity of photovoltaic ("PV") cells to generate electrical power 
from incident solar radiation, and more particularly to an improved solar 
tracker designed to move and stably position a unified array of 
photovoltaic modules in relation to the sun. 
BACKGROUND OF THE INVENTION 
Prior practice has been to combine a plurality of photovoltaic solar cells 
into a flat rectangular module of selected size, and then form a flat 
array consisting of a plurality of such modules. By way of example, one 
suggested prior art technique involves assembling a plurality of solar 
cells so as to form rectangular modules measuring approximately 
1'.times.4', with each module being surrounded and supported at its edges 
by a rigid frame made of a suitable material, e.g., aluminum. These 
modules are intended to be mounted in a rigid grid-like (i.e., 
trellis-like) framework forming part of a pivotal support structure, with 
the grid-like framework having a plurality of openings each sized and 
adapted to accommodate a single module in a nesting relationship. The 
several modules are electrically connected in parallel or in series, 
according to the power output requirements of the operator. Another 
arrangement consists of mechanically and electrically connecting two or 
more modules as an integrated structure, which structure is frequently 
referred to as a "solar panel". These panels in turn are mounted on a 
pivotal support structure. 
According to efficient practice, the pivotal support structure is oriented 
so as to cause the modules or panels to face the sun. To maximize the 
concentration of incident solar energy, efforts have been made to provide 
a suitable support structure adapted to adjust the orientation of the 
panels to accommodate for variations in the angle of the sun during 
various seasons of the year and during each day of a given season, i.e., 
solar tracking means. 
Photovoltaic solar modules and panels mounted in ground or roof 
installations catch and are stressed by the wind. The buffeting effect by 
winds of even modest velocity, e.g., 10 miles per hour, places the panels 
and their supporting structure under relatively high stress. As an economy 
measure, particularly where two or more panels are mounted in tandem on 
the same support structure, it is common to orient the pivotable support 
structure so that the panels extend north to south and to limit the 
panel-adjusting means to a single axis mode of operation whereby the 
panels can be pivoted east to west on a north/south pivot axis to 
compensate for variations in the angle of the sun from sunrise to sunset. 
Nevertheless, in the interest of withstanding high winds, the common 
practice has been to utilize relatively massive support structures, some 
with cross-braces that serve to provide panels with added deformation 
resistance as well as to connect them to the support structure. These 
relatively massive support structures are costly and cumbersome and 
constitute another factor tending to discourage widespread use of arrays 
of photovoltaic panels as economical sources of electrical power. 
Furthermore, they are especially objectionable from a cost standpoint when 
utilizing a plurality of relatively large silicon solar cell modules, 
e.g., modules that measure 4'.times.6'. 
The primary object of this invention is to provide a photovoltaic solar 
energy collection and conversion system that is characterized by a simple, 
relatively inexpensive solar module support structure. 
Another object is to provide a new and improved mechanical structure for 
pivotally mounting a plurality of photovoltaic modules and panels in a 
planar array that is unified so that a single mechanism may be used to 
simultaneously and correspondingly change the angle of declination of the 
array. 
A more specific object is to provide a solar energy electrical power source 
comprising at least two flat photovoltaic panels disposed in co-planar 
side-by-side relation and an improved support structure for supporting the 
panels for pivotal movement on a pivot axis that extends transversely of 
the panels, the improved structure including selectively operable means 
for pivoting all of the panels simultaneously and by the same amount of 
angular displacement. 
A further specific object is to provide a support mechanism for supporting 
and tracking multiple photovoltaic modules wherein individual structural 
members perform multiple tasks. 
These and other objects and advantages of the invention are achieved by 
providing (1) at least two flat PV panels in side by side and co-planar 
relation, (2) a pivot shaft extending transversely of the side-by-side 
panels, (3) at least two supports spaced apart lengthwise of the shaft, 
(4) means for mounting the pivot shaft to the at least two supports, (5) 
means for connecting the panels to the pivot shaft so that the panels can 
pivot about the longitudinal axis of the shaft, (6) means for mechanically 
coupling all of the panels together so as to form a unified flat array, 
and (7) electro-mechanical drive means for (a) mechanically pivoting the 
unified array about the aforesaid axis and (b) locking the array against 
pivotal movement when the electro-mechanical drive means is deenergized. 
Other objects, features and advantages are set forth in the following 
detailed description of a preferred embodiment of the invention which is 
to be considered together with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 1-6, the illustrated apparatus comprises four 
dual-module (i.e., bi-module) photovoltaic ("PV") panels 2A-2D with the 
modules in each panel being identified as 4A and 4B. These modules are 
formed as described below. These PV panels 2A-2D are mounted on a support 
structure which comprises a plurality of A-frame support units 10 that are 
made of metal and are secured to a base 11 (FIG. 1) which preferably is a 
concrete slab on the ground or a flat roof. The A-frame units are 
preferably made of angle irons. 
Each of the modules 4A and 4B consists of a plurality of silicon 
photovoltaic solar cells which are interconnected in series and/or in 
parallel so that each module has a predetermined voltage and current 
output. 
Although not shown, it is to be understood that preferably, but not 
necessarily, each module 4A and 4B consists of a laminated structure which 
comprises in the order named: (1) a top (front) layer in the form of a 
pane (sheet) of glass, (2) a layer of "EVA", a transparent plastic 
adhesive consisting essentially of an ethylene vinyl acetate copolymer, 
(3) an array of silicon solar cells interconnected in series or in 
parallel according to the output voltage and current requirements, (4) a 
second layer of EVA, and (5) an insulating and water impermeable back skin 
or cover in the form of a layer of Tedlar. The latter is the trade name 
for a polyvinyl fluoride polymer made by DuPont. 
In the preferred form of practicing the invention, each solar module is 
made up of a series of 4".times.4" rectangular silicon solar cells which 
are initially arranged and electrically connected in series in strips of 
18 cells each, and then 12 strips are arranged in side-by-side relation 
and connected in parallel to form 4'.times.6' modules, with each cell 
having a voltage output of about 0.5 volts and each module having a total 
voltage output of about 8.0 volts. In the lamination process (which 
involves heating) the layer of EVA is liquified enough to fill the voids 
between adjacent solar cells and form an integrated, unified structure. 
Each of the panels 2A-2D consists of a pair of side rails or frame members 
12 and 14, a pair of end frame members 16 and 18, and a pair of 
cross-members 22 and 24 that extend between the side frame members 12 and 
14. The PV module 4A is encompassed and supported by the side frame 
members 12 and 14, the end frame member 16 and the crossbar member 22. The 
second module 4B in each panel is encompassed and supported by the side 
frame members 12 and 14, the end frame member 18, and the crossbar member 
24. Preferably a small air gap exists between cross members 22 and 24 to 
allow air to pass between them and thus reduce the total "sail" effect. 
Although not shown, it is to be understood that preferably, but not 
necessarily, each of the photovoltaic solar cells in modules 4A and 4B 
comprises a silicon substrate, a PN junction located within about 0.5 
microns from the front surface of each cell, an AR (anti-reflection) 
coating on the front side of each cell, and ohmic contacts on the front 
and back sides of each cell, with the ohmic contact on the front side of 
each cell comprising a silver grid-shaped contact, while the ohmic contact 
on the rear side of each cell comprises either an uninterrupted aluminum 
layer or an aluminum layer having apertures in which are formed silver 
pads for facilitating soldering of the rear contacts. In each module the 
glass pane overlies the front AR-coated side of the assembled cells, while 
the back skin covers the rear contact. The back skin may be a sheet of 
glass or a plastic material. Preferably, the back skin is made of Tedlar 
as previously described. The back skin and the front pane are hermetically 
sealed to the solar cells by the EVA layers so that the four edges of the 
module and the front and rear surfaces of the solar cells are not exposed 
directly to atmospheric conditions. Although not shown, it is to be 
understood that each module has electrical terminals that are soldered to 
ribbon-like electrical conductors that are used to interconnect the 
modules to an exterior power take-off circuit. 
Turning now to FIGS. 2-4, the A-frame support units 10 preferably comprise 
front and rear angularly-disposed struts 26 and 28 that are welded or 
bolted together and also to a horizontally-disposed connecting member 30. 
The horizontally-extending brace or connecting member 30 is securely 
attached to base 11. A diagonal brace member 31 is provided which extends 
from the juncture of members 28 and 30 of one A-frame unit to the juncture 
of members 26 and 28 of an adjacent A-frame unit. This member distributes 
loads to the base. Diagonal braces 31 need not be used between each pair 
of A-frame units. 
As seen best in FIG. 3, a U-shaped anchor member 32 is attached to the rear 
side of each A-frame support unit. The U-shaped anchor member embraces and 
serves to secure a pivot shaft 34 to each of the A-frame supports. For the 
purpose of illustrating that the number of panels 2A-2D is variable, the 
shaft 34 and also the coupling member 44 hereinafter described, are shown 
in FIGS. 1 and 2 as projecting beyond panel 2A. 
Still referring to FIGS. 2-5, the several panels 2A-2D are pivotally 
secured to pivot shaft 34 by means of like U-shaped journal units 38 which 
are secured to the side frame members 12 and 14 of the panels and are 
provided with roller, ball or sleeve bearing units 40 (FIG. 5) that 
encompass pivot shaft 34. As a result of this arrangement, the several 
panels 2A-2D can rotate on pivot shaft 34. 
The several panels 2A-2D are connected together to form a unified array by 
virtue of a force-applying elongate coupling member 44. The latter may 
take various forms, e.g., it may be a hollow pipe (as shown in the 
drawings) or a hollow or solid flat rod or bar. Preferably, coupling 
member 44 is in the form of a hollow pipe for reasons of cost. Member 44 
is secured to each of the panels 2A-2D by means of U-shaped clamps 60 that 
are bolted to the side frame members 12 and 14 and are arranged so as to 
embrace and secure the member 44 to the several panels. The member 44 is 
rigid and, therefore, because of the connections made by the clamps 60, 
the several solar panels are connected so as to form a unified array. 
Positioning of the array of solar panels 2A-2D is accomplished by means of 
an electro-mechanical drive means 80 that is reversible. The drive means 
80 may take various forms and may, for example, be similar to the 
reversible drive means disclosed in U.S. Pat. No. 4,004,574. Preferably, 
however, the drive means 80 comprises a screw-type ELECTRAK linear 
actuator manufactured by the Warner Electric Division of Dana Corporation, 
located at 449 Gardner Street, South Beloit, Ill. 61080. Although details 
of its construction are not shown in the drawings, it is to be understood 
that the ELECTRAK actuator comprises an electric motor, a gear reduction 
unit driven by the motor, a brake, a clutch, two telescoping tubes 82 and 
84 (FIG. 4), and a screw/nut mechanism coupling the two tubes with the 
screw being driven by the motor. When the motor is operated, the resulting 
rotation of the screw causes the two tubes to telescope in either a 
retracting or extending mode according to the direction of movement of the 
electric motor's drive shaft. The outer end of the inner telescoping tube 
of the ELECTRAK actuator is pivotally secured to a bracket 88 attached to 
the base 11. The other end of the ELECTRAK actuator is attached to a 
collar 90 that is rotatably mounted on the force-applying tube 44. When 
the motor (not shown) of the linear actuator 80 is operated in a first 
direction calculated to extend tube 84 relative to the tubular housing 82, 
the solar panel array comprising the panels 2A-2D will tend to pivot 
clockwise as viewed in FIG. 5. If operation of the motor is reversed so as 
to cause the tubes 82 and 84 to telescope in a contracting fashion, the 
array of solar cell panels will pivot in a counter-clockwise direction as 
viewed in FIG. 5. 
Associated with the electro-mechanical drive system is a dual limit switch 
assembly which comprises a dual limit switch unit 92 characterized by 
first and second operating buttons 94 and 96. This dual switch assembly is 
mounted to one of the A-frame structures in position for the two buttons 
94 and 96 to be operated by angular cam members 98 and 100 that are 
attached to one of the frame members 12 or 14. The cam members are 
arranged so that when the array of panels 2A-2D is pivoted in one 
direction (e.g., clockwise as seen in FIG. 5) by electro-mechanical 
actuator 80, cam member 98 will contact and depress button 94, thereby 
causing operation of the motor of the electro-mechanical actuator to 
reverse. Similarly, when the actuator rotates the panels in the opposite 
direction, pivotal movement of the array will reverse when cam member 100 
engages and depresses the button 96. 
As noted above, the invention is directed to providing a support structure 
for an array of solar cell panels so that the panels may be moved in 
synchronism with movement of the sun on a daily basis Thus, early in each 
day the electro-mechanical actuator 80 positions the solar panels so that 
they face east at a predetermined angle of inclination. As the sun 
traverses the sky from east to west, the electro-mechanical actuator is 
operated so as to cause the panels to rotate in synchronism with movement 
of the sun until the solar panels reach a predetermined limit angle 
relative to the setting sun. Assuming that the viewpoint of FIG. 5 is 
looking south to north, the movement of the solar cell panels in tracking 
the sun involves a counter-clockwise rotation as viewed in FIG. 5. 
The dual limit switch assembly limits the angle of movement of the solar 
panel array. Typically, the cam members 98 and 100 are arranged so that 
when the solar panels are rotated clockwise to a first limit position 
determined by engagement of cam 98 with switch button 94, the panels will 
extend at an angle of approximately 130 degrees to the eastern horizon, 
and when the solar cell array is rotated counter-clockwise to a second 
limit position determined by engagement of cam member 100, with switch 
button 96, the solar cell array will be disposed at an angle of about 130 
degrees to the western horizon. 
Use of a screw-type electro-mechanical actuator for pivoting the solar 
panel array is advantageous in that, particularly when a screw-type 
actuator is used, the position of the solar panels relative to the sun may 
be changed in relatively small increments, while at the same time 
termination of operation of the electric motor that powers the actuator 
mechanism assures that the actuator will prevent movement of the solar 
panels under the effect of moderate wind buffeting. 
FIG. 6 illustrates diagrammatically a control system for operating the 
electro-mechanical drive means so as to cause the solar cell panel array 
to track according to the daily position of the sun. In this control 
system, the electro-mechanical drive 80 is coupled to a clock-controlled 
programmable controller 110 that is adapted to initiate operation of the 
drive daily at a time predetermined according to the day of the year. The 
controller also is designed to reverse the drive means when its second 
limit switch button 96 is depressed, so as to cause the drive means to 
pivot the solar cell array back to a horizontal position to reduce wind 
loading at night, and then hold it in that position until the next day. 
The controller then initiates movement of the array to the original 
eastward-facing position, and then causes it to move as previously 
described in synchronism with movement of the sun. The controller may be a 
conventional electro-mechanical controller or it may be computer 
programmed to provide the desired operating sequence. The essential thing 
is that the controller is programmed so as to cause the electro-mechanical 
actuator 80 to initiate westward pivoting of the solar cell array 
incrementally in a stepwise or slow continuous mode so as to track 
movement of the sun from the eastern to the western horizon commencing at 
a predetermined time and ending when cam 98 engages limit switch button 
96. Additionally, the controller is arranged so that when the solar panel 
array has been moved far enough to actuate the limit switch button 96, the 
motor of the electro-mechanical drive means will reverse its operation so 
as to cause the solar panel array to pivot clockwise back to its 
horizontal position. Once the solar panel array has been returned to its 
horizontal position, it will remain there until the controller initiates a 
subsequent eastward movement for the next consecutive day of solar panel 
tracking. 
An essential advantage of the invention as described above is that various 
electro-mechanical means may be used for pivoting the array of solar cell 
panels. Additionally, by having the solar cell modules disposed in a 
simple, relatively small mass framework, the power required to rotate the 
solar cell array is reduced to practical limits. Also contributing to the 
lower power input is the fact that the pivot shaft 34 is offset from the 
geometric midpoint of the panels so as to moment balance the panels and 
thereby offset the weight of the coupling member. Furthermore, the 
simplified arrangement for mounting the several photovoltaic modules into 
a plurality of solar cell panels reduces the number of required structural 
members and offers the advantage that certain frame members perform dual 
tasks, e.g., the coupling member 44 adds rigidity to the dual module 
panels, couples all of the panels 4A-4D together, and acts to transmit 
forces from actuator 80 to panels 2A-2D. Similarly, the pivot shaft 34 
serves to transmit horizontal forces to the diagonal braces 31. At the 
same time, the foregoing arrangement makes it possible to support the 
photovoltaic modules so as to minimize the "sail" effect. In this 
connection, it is to be noted that the gaps between adjacent panels and 
also between the two modules in each panel, have the effect of reducing 
the "sail" effort. Nevertheless, the framework is adequate to improve the 
resistance of the modules to distortion or fracture under wind-caused 
stress. 
The electro-mechanical actuator, particularly one like the ELECTRAK linear 
actuator that is a screw-type electro-mechanical drive system, makes it 
possible to not only precisely position the solar cell array and to change 
its position at a relatively slow rate, but to also make certain that the 
position of the solar cell array at any given moment in time is 
substantially fixed, due to the fact that there is little or no backlash 
or play in the electro-mechanical drive system. In other words, 
electro-mechanical screw-type linear actuators not only provide precise 
selective positioning of the solar cell array, but they also have the 
advantage of positively locking the array in a particular position. In the 
usual case, the required rate of movement of the solar cell array in the 
course of tracking the sun from morning to evening, is quite small, 
averaging approximately 10 degrees per hour. Hence, an electro-mechanical 
linear actuator as above-described has the advantage of providing the 
required slow movement of the solar cell array while providing a braking 
action preventing movement of the solar cell array during the periods of 
moderate wind buffeting. 
During periods of high winds, the actuator clutch is designed to slip. The 
actuator and the coupling member 44 are thereby protected from having to 
bear large loads. As a result, the actuator and coupling member can be 
formed out of lighter weight and lower strength components, which tend to 
be cheaper to produce. When the array is pivoted to the position shown in 
FIG. 2, excessive wind loads will cause the coupling member 44 to engage 
the A-frame members 28 so as to mechanically prevent further rotation of 
the solar panels. When the panels are in the position shown in FIG. 1, 
further rotation of the panels under wind loads is prevented by virtue of 
engagement of additional mechanical coupling straps 115 that interconnect 
adjacent panels, e.g., 2A and 2B, and are intercepted by the front A-frame 
members 26. 
Other advantages of the invention will be obvious to persons skilled in the 
art. 
It is to be appreciated that the invention is susceptible of various 
modifications. Thus, for example, the number of photovoltaic modules in a 
panel may be as little as one or may be in excess of two. Similarly, the 
number of panels mounted on the same pivotal axis may be greater or less 
than the four panels illustrated in the present drawings. Furthermore, the 
nature of construction of the solar cells and the solar modules, is not 
critical to the invention. Thus, for example, the solar cells may be made 
of some material other than silicon known to persons skilled in the art. 
The essence of the invention is that is provides a new and improved means 
for supporting a plurality of photovoltaic modules and panels for tracking 
purposes, with the electro-mechanical support and tracking structure being 
simple, reliable, and cheaper to construct than corresponding systems 
known to the prior art.