The invention relates to the art of solar panel systems, and in particular to actuation systems for controlling the azimuth and elevation angles of a solar panel and to system architectures for controlling large numbers of solar panels.
To obtain the maximum efficiency out of a solar panel it is necessary to change the position the panel to track the position of the sun as it moves across the sky.
It is desirable for the solar panel actuator system to be robust, and have a long service life. In a solar farm, where thousands of panels may be deployed, it may be necessary to utilize thousands of solar panel actuators, so low cost is an important concern. Similar concerns arise for the consumer market.
Likewise, it may be necessary to control large numbers of solar panels in an efficient manner.
According to one aspect of the invention a solar panel assembly is provided which includes: a foundation tube; a rotary actuator mounted in the foundation tube, the actuator having a rotating plate extending out of an end of the foundation tube; a linear actuator having a stationary portion and an extensible portion; a bracket mounted to the rotating plate, the bracket having an arm mounted to one of the linear actuator stationary portion and the linear actuator extensible portion; and a frame for holding a photovoltaic panel, the frame being pivotally mounted to the bracket and the frame having an arm connected to the other of the linear actuator stationary portion and the linear actuator extensible portion.
The rotary actuator preferably includes: a motor; a gearbox driven by the motor; a drive screw connected to and driven by an output of the gearbox; a spindle screw connected to the rotating plate; a drive nut having a first threaded hole for receiving a thread of the drive screw and a second threaded hole for receiving a thread of the spindle screw, the guide nut having a guide fin; and a guide rail interacting with the nut guide fin to constrain the nut from rotating, whereby the rotation of the drive by screw by operation of the motor causes the nut to translate linearly which in turn causes the spindle screw to rotate.
The motor is preferably a low cost, brushed DC motor, of approximately 0.5-3 Nm output. The gearbox provides a gear reduction between an output of the motor and an output the gearbox, and wherein the turns ratio between the drive screw and the spindle screw provides a gear reduction between the drive screw and the spindle screw. Overall, a high reduction, e.g., 7500:1 gear reduction, is provided between the motor and rotating plate.
The guide rail is preferably provided in the form of a tubular housing. The motor and gear box are connected to the tubular housing. The drive screw, spindle screw and nut are each disposed with the tubular housing, and it has a channel for receiving the guide fin of the nut.
The linear actuator preferably includes: a motor; a gearbox driven by the motor; a drive screw connected to and driven by an output of the gearbox; a first tube encompassing the drive screw, the first tube being connected to one of the frame arm and the bracket arm; a second tube partially mounted in and extensible from the first tube, the second tube being pivotally connected to the other of the frame arm and the bracket arm in a manner so as to prohibit substantive rotation of the second tube relative to the first tube; and a drive nut having a threaded hole for receiving a thread of the drive screw, the drive nut being disposed within the second tube and having a splined connection to at least one of the first and second tube in order to prohibit rotation of the drive nut, whereby the drive nut translates linearly causing the second tube to slide linearly relative to the first tube as the drive screw is rotated by said motor and gearbox.
An end portion of the linear actuator drive screw distal of the gearbox output is preferably connected to a concentric post that spaces the drive screw away from inner walls of the second tube. The non-connected end of the second tube preferably includes an end cap disposed within the first tube, the end cap and concentric post spacing the outer wall of second tube away from the inner wall of the first tube. And the end of the first tube distal from the gearbox preferably includes an annular seal contacting the outer wall of the second tube.
According to another aspect of the invention a rotary actuator is provided which includes: a motor; a gearbox driven by the motor; a drive screw connected to and driven by an output of the gearbox; a spindle screw, one end of which provides an output of the rotary actuator; a drive nut having a first threaded hole for receiving a thread of the drive screw and a second threaded hole for receiving a thread of the spindle screw, the guide nut having a guide fin; and a guide rail interacting with the nut guide fin to constrain the nut from rotating, whereby the rotation of the drive by screw by operation of the motor causes the nut to translate linearly which in turn causes the spindle screw to rotate.
According to another aspect of the invention a solar panel assembly is provided which includes a stand and a photovoltaic panel pivotally mounted to the stand about a horizontal axis so as to be adjustable in elevation. A motorized drive adjusts the elevation of the panel. The power source is provided by at least first and second batteries and a motor drive circuit is connected to the batteries for powering the motorized drive. A stow sensor provides a signal indicating a command to move the panel to a horizontal position. A stow circuit receives the stow signal. In the nominal state, the stow circuit connects the at least first and second batteries in parallel and applies an output of the parallel-connected batteries to the motor drive circuit. This lowers the voltage and increases the current capacity of the batteries relative to a serial connection and allows for greater time before the energy in the batteries is depleted. However, in the event the stow signal is activated, the stow circuit connects the at least first and second batteries in series, disconnects the motor drive circuit from the motorized drive, and applies an output of the serial-connected batteries directly to the motor. This provides greater voltage to the motorized drive and enables it to be driven faster. In addition, disconnecting the drive circuit allows the panel to be stowed even in the event of a software error as the stow circuit is preferably provided in the form of hardwired logic.
The stow signal may be activated in response to at least one of: a wind speed sensor reading wind speeds above a predetermined amount; loss of local controller power; loss of charging current; a manual user command to stow; a software malfunction; and a master stow command.
The foregoing and other aspects of the invention will be more readily appreciated having reference to the drawings, wherein:
A. System Summary
More particularly, the panel frame 12 includes a structural cross beam 32 able to support the weight of the panel frame 12 and any photovoltaic modules mounted thereon. The crossbeam 32 includes two spaced apart mounting flanges 34a, 34b for mounting the panel frame 12 onto a bracket 36. The bracket 36 features a mounting plate 38 terminating in two uprising, spaced apart wings 40a, 40b. The hinge shaft 30 is installed through openings in the spaced apart wings 40a, 40b and mounting flanges 34a, 34b. Capstans or nuts 42 secure the hinge shaft 30.
The bracket mounting plate 38 is bolted onto a rotating plate 44 (seen best in
The bracket 36 includes an arm 46 that supports a stationary portion 50 of the linear actuator 24. An extensible portion 52 of the linear actuator 24 is connected to an arm 48 that is rigidly connected to the panel crossbeam 32. Thus, the linear motion of the extensible portion 52 is converted into pivotal motion of the panel frame 12 about the hinge shaft 30.
B. Panel Frame
In the illustrated embodiment the stiffening ribs 406 are arranged as a series of upper and lower rectangular-shaped stiffening members 410. The stiffening members increase the rigidity of the panel 400 to more effectively retain its orientation to the sun. In addition, the two rows of stiffening members 410 define a channel therebetween for mounting the aluminum cross-beam 408. The rear face of the panel 400 can also be used to mount other electrical components thereto such as micro-inverters (not shown).
C. Rotary Actuator
The rotary actuator 16 is shown in greater detail in the isolated views of
More particularly, the guide rail 68 is provided in the illustrated embodiment as a tubular guide 69 (seen best in the cross-sectional view of
By way of example, a suitable motor is 1.2 Nm 12V brushed DC motor manufactured by Harbin Electric of China.
The gearbox 62 preferably provides a large gear reduction, e.g., a 26:1 reduction. The gearbox 62 is preferably identical to a gear box utilized in the linear actuator 24, as shown in
The output gear of the gearbox 62 is rigidly connected to the drive screw 64, thus rotating the drive screw 64. A cover 75 shields the drives screw 64 in the portion between the gearbox 62 and plug 72. This portion of the drive screw need not be threaded, and thus a tight tolerance may be provided between the shaft of the drive screw and a hole 77 formed in the plug 72 for passage of the drive screw therethrough.
The other end of the drive screw 64 is rotatingly mounted via a small axle (not shown) to a base plate 76 that caps and plugs the open end of the foundation tube 14. (The rotating plate 44 lies above the open end of the foundation tube 14.) The drive screw 64 thus rotates in situ. In the illustrated embodiment, the drive screw 64 is preferably formed from steel and has a ¾ inch diameter, 8 turns per inch, Acme thread.
The nut 66 is preferably formed from Acetal or other hard plastic with lubricating properties. As seen best in
As seen best in
The spindle screw 70 preferably features a dual start, low turn ratio, lead thread 88. In the illustrated embodiment, the lead screw has a 0.03 turns per inch thread on a 2.4 diameter, hollow aluminum shaft. The thread 88 preferably has approximately 240° of turn over the length of the spindle screw 70, which is sufficient to meet the east-west tracking requirements of the solar panel. Overall, with the 26:1 reduction provided by the gearbox 62 and an approximately 285 turns ratio between the drive screw 64 and the spindle screw 70, an approximately 7500:1 reduction is provided between the motor 60 and the spindle screw 70. Those skilled in the art will appreciate that a wide variety of other component dimensions and drive ratios may be employed in a commercial rotary actuator.
In operation the motor 60 and gearbox 62 rotate the drive screw 64, which is constrained to spin in situ. The nut 66 receives the torque provided by the drive screw 64, however, the nut 66 is prevented from rotating due to the entrapment of its guide fins 82a, 82b within the channels 84a, 84b of the tubular guide 69. Accordingly, the nut 66 translates linearly upon receipt of the torque imparted by the drive screw 64. As the nut 66 translates, it will in turn impart torque to the spindle screw 70, causing the spindle screw to likewise spin in situ, and in the process turn the rotating plate 44. Clearly, operating the motor in one rotational sense will cause the rotating plate to turn in a first rotational sense and operating the motor in the opposite rotational sense will cause the rotating plate to turn in a second, opposite rotational sense.
Advantageously the rotary actuator 16 may be preassembled as an independent unit and slid into the foundation tube 14 as a unit. An electronics box 60 may also be attached to the guide tube 68 and thus mounted in the foundation tube 14. The base cap 76 seats on a reinforcing flange 92 situated at the top of the foundation tube 14, and a water and dust shield 94 (
The rotary actuator 500 works substantially similar to that of the single screw rotary actuator 16. The addition of another drive screw helps to even out the torques experienced by the assembly and reduce bending moments and other stresses on the relatively long drive components.
D. Linear Actuator
The linear actuator 24 is shown in isolation in
The motor 100 may be the aforementioned 1.2 Nm. 12 volt brushed DC motor. As seen best in
The output gear 118 is fixed at its rotational axis to a drive screw 124. The drive screw 124 has a non-threaded butt end portion which is journaled in the gearbox via two large tapered roller bearings 126. The drive screw in the illustrated embodiment is a ¾ inch diameter, 8 turns per inch, stainless steel screw.
The stationary outer tube 104 is preferably adhesively bonded to the walls of an inlet 128 in the gearbox. A fixture 130 (
The extensible inner tube 106 fits within the stationary outer tube 104 and partially encompasses the drive screw 124. A drive nut 104 is fitted over the drive screw 124 and has threads that matingly receive the threads of the drive screw 124. The drive nut is positioned within extensible inner tube 106 and has two opposing splines 137 that engage two slots (not shown) in the extensible inner tube 106.
The extensible inner tube 106 includes an end cap 136 to seal the inner tube 106 against the interior wall of the outer tube 106. The end cap 136 also enables a small gap to be maintained between the exterior wall of the inner tube 106 and the interior wall of the outer tube 104, and the cap is preferably formed from a slick material in order to minimize friction as the cap slides along the interior wall of the outer tube 104. Likewise the drive screw 124 includes a centralizing post 138 that assists in maintaining good clearance between the drive screw 124 and the walls of the extensible inner tube 106 and the post 138 is preferably formed from a slick material in order to minimize friction as the extensible inner tube 106 slides.
The end of the extensible inner tube 106 distal from the motor includes an attachment member 140 that features a pinned connection 142 for coupling the extensible inner tube 106 to the arm 46 connected to the panel crossbeam 32.
In operation, the motor 100 and gearbox 102 rotate the drive screw 124, which spins in situ. The drive nut 134 receives the torque from the drive screw 124 but is constrained from rotating due to its splined interconnection with the inner tube 106, which is itself precluded from rotating as a result of the pinned connection 142 with the arm 46. Consequently the drive nut 134 translates linearly, moving the inner extensible tube 106 relative to the stationary outer tube 106. Those skilled in the art will appreciate that the drive nut could additionally or alternatively have a splined interconnection with the outer tube and be used to push the inner tube outward or collapse it inwards, for example, by placing the drive nut between two interference features within the inner tube.
It will also be appreciated that while the illustrated embodiment has the arm bracket 46 connected to the stationary portion 50 of the linear actuator and the crossbeam arm 48 connected to the extensible portion 52 of the linear actuator the opposite arrangement may be effected in alternative embodiments. In other words, in an alternative embodiment, arm bracket 46 is connected to the extensible portion 52 of the linear actuator and the crossbeam arm 48 is connected to the stationary portion 50 of the linear actuator 24.
E. Electronics
In this embodiment each solar panel 200 also includes a local controller 220. The local controller 220 includes a microcontroller 222 which communicates with the local controller preferably via a wired communications link 226 such as provided by CAN controller 224. The actuation system for repositioning the solar panel may be controlled by commands received over the communication links 204, 206, 224, 226 and executed by the microcontroller 222 which, in turn, controls the motors of the rotary and linear actuators via motor control lines 228, 230.
In the preferred embodiment motor two rechargeable batteries 310a, 310b are used to power the actuators and the drive electronics. The two batteries 310a, 310b are each preferably 12 volt batteries that are normally connected in parallel. This doubles the current capacity of the system, and increases the amount of time the system can operate without recharging the batteries. However, during a stow condition, the circuit 600 automatically reconfigures the batteries 310a in series to operate at least the linear actuator motor at 24 volts. This increases the speed of the motor(s) thereby reducing the time it takes to bring the photovoltaic panel 12 to the horizontal position.
The stow control circuit 600 is shown in
However, when a stow condition is detected on any of signal lines 604, relays RL1 and RL3 are energized to switch out the motor drive circuitry 602 and directly apply power from the batteries 310a, 310b to the linear actuator motor 100. In this state, relays RL2 and RL4 also energize. Relay RL2 disconnects the negative terminal of battery 310b from ground, and relay RL4 connects the positive terminal of battery 310a to the negative terminal of battery 310b. Thus, the batteries are connected in series to apply 24 volts to the motor 100. As soon as this happens the linear actuator motor 100 starts driving the solar photovoltaic panel to the horizontal position.
Note that all of these actions can be done with or without software algorithm supervision. Thus, upon a software malfunction the hard wired logic provided by the circuit 600 will take control of the system and safely stow the solar photovoltaic panel.
While the above describes a particular embodiment(s) of the invention, it will be appreciated that modifications and variations may be made to the detailed embodiment(s) described herein without departing from the spirit of the invention.
Number | Date | Country | |
---|---|---|---|
61416841 | Nov 2010 | US |