WO2018128942A1

WO2018128942A1 - Solar energy harvesting systems including at least one thermal-mechanical actuator for solar tracking

Info

Publication number: WO2018128942A1
Application number: PCT/US2017/069078
Authority: WO
Inventors: Ivyann OVESON; John Salmon
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-01-03
Filing date: 2017-12-29
Publication date: 2018-07-12
Anticipated expiration: 2019-07-03

Abstract

Embodiments relate to a solar energy harvesting systems that include at least one solar panel configured to adjust an orientation thereof and where the adjustment is obtained solely by thermal-mechanical actuation. In an embodiment, a solar energy harvesting system is disclosed, which includes at least one support structure pivotable about at least one pivot axis, and at least one solar panel supported by the at least one support structure and pivotable about the at least one pivot axis. The system includes at least one thermal-mechanical actuator configured to convert thermal energy to mechanical energy, and at least one actuation link coupling the at least one thermal-mechanical actuator to the at least one solar panel. The link is configured to cause the at least one solar panel to pivot about the pivot axis responsive to the actuator converting the thermal energy to the mechanical energy.

Description

SOLAR ENERGY HARVESTING SYSTEMS INCLUDING AT LEAST ONE THERMAL-MECHANICAL ACTUATOR FOR SOLAR TRACKING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No.

62/441,893 filed on 3 January 2017, the disclosure of which is incorporated herein, in its entirety, by this reference.

BACKGROUND

[0002] Typically, solar panel installations, especially those with solar-tracking capability, may be costly to install and operate. A stationary solar panel installation typically holds a solar panel in a fixed position, which can reduce the output as the sun moves into less-than-optimal positions relative to the solar panel.

[0003] More recently, solar-tracking panels have been developed, which are arranged to move with or track the movement of the sun to thereby improve the energy output. However, the tracking adds a complexity to the system, such as the requirement for a power source to drive the movement of the solar panel. This may make it impractical for solar-tracking panels to be used in remote areas or areas that do not have easy or ready access to grid power, such as developing countries.

[0004] Accordingly, designers and manufacturers of solar-tracking solar energy harvesting systems continue to seek improvements thereto.

SUMMARY

[0005] Embodiments disclosed herein relate to a solar energy harvesting systems that include at least one solar panel configured to adjust an orientation thereof and where the adjustment in orientation is obtained solely by thermal mechanical actuation. In an embodiment, a solar energy harvesting system is disclosed. The solar energy harvesting system includes at least one support structure pivotable about at least one pivot axis, and at least one solar panel supported by the at least one support structure and pivotable about the at least one pivot axis with the at least one support structure. The solar energy harvesting system further includes at least one thermal-mechanical actuator configured to convert thermal energy to mechanical energy, and at least one actuation link coupling the at least one thermal-mechanical actuator to the at least one solar panel. The at least one actuation link is configured to cause the at least one solar panel to pivot about the at least one pivot axis responsive to the at least one thermal-mechanical actuator converting the thermal energy to the mechanical energy. [0006] Features from any of the disclosed embodiments may be used in combination with one another, without limitation. In addition, other features and advantages of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The drawings illustrate several embodiments, wherein identical reference numerals refer to identical or similar elements or features in different views or embodiments shown in the drawings.

[0008] FIG. 1 is an illustration of a solar energy harvesting system, according to an embodiment;

[0009] FIG. 2 is a simplified isometric view of a solar energy harvesting system showing the solar panels in a first orientation, according to an embodiment;

[0010] FIG. 3 is a simplified isometric view of the solar energy harvesting system of FIG. 2, showing the solar panels in a second orientation;

[0011] FIG. 4 is an illustration of a solar energy harvesting system, according to an embodiment;

[0012] FIG. 5 is an illustration of a solar energy harvesting system, according to an embodiment;

[0013] FIG. 6 is an illustration of a solar energy harvesting system, according to an embodiment;

[0014] FIG. 7 is a solar energy harvesting system with individually actuatable solar panels, according to an embodiment; and

[0015] FIGS. 8A-8C are simplified illustrations of a solar energy harvesting system, according to an embodiment.

DETAILED DESCRIPTION

[0016] Solar energy harvesting systems according to embodiments disclosed herein may provide a simplified installation and/or operation with solar tracking capability effected solely by thermal mechanical actuation. In some embodiments, a solar energy harvesting system may include at least one support structure pivotable about at least one pivot axis, and at least one solar panel supported by the at least one support structure and pivotable about the at least one pivot axis with the at least one support structure. The system may further include at least one thermal-mechanical actuator configured to convert thermal energy to mechanical energy, and at least one actuation link coupling the at least one thermal-mechanical actuator to the at least one solar panel. The at least one actuation link may be configured to cause the at least one solar panel to pivot about the at least one pivot axis responsive to the at least one actuator converting the thermal energy to the mechanical energy. The actuation of the solar panel may be calibrated to cause the solar panel's orientation to vary throughout the day such that the solar panel tracks the movement of the sun throughout the day.

[0017] FIG. 1 shows a simplified illustration of a solar energy harvesting system

100, according to an embodiment. The system 100 includes a plurality of solar panels 102, each supported by a support structure 110, a thermal -mechanical actuator 120, and an actuation link 130 connecting the thermal-mechanical actuator 120 to each of the solar panels 102. The components and the arrangement thereof shown in FIG. 1 are merely illustrative, and other variations, including eliminating components, combining components, rearranging components, and substituting components are all contemplated. For example, although the illustrations herein show examples of solar energy harvesting systems with multiple solar panels, it will be understood that the embodiments of the present disclosure apply equally to a system that includes only a single solar panel, or any number of solar panels different that the number of solar panels in the illustrations. In some examples, multiple thermal-mechanical actuators, each associated with individual or a subset of the solar panels in the array, may be used, for examples as described further below with reference to FIGS. 7 and 8.

[0018] As illustrated in FIG. 1, the system 100 may include a plurality of solar panels 102, such as five solar panels, but in other examples, a greater or smaller number of solar panels may be used. Each of the solar panels 102 may be pivotally coupled to a frame 140 via the support structure 110 such that each individual solar panel and the support structure 110 thereof are pivotable about at least one axis 104. In this example, each solar panel is pivotable its respective axis 104, as shown by arrows 103.

[0019] Each solar panel 102 may be attached to a first surface 112, also referred to as support surface, of its respective support structure 110. The support structure 110 may be pivotally coupled to the frame 140 via an axle or any other type of pivot joint. The frame 140 may be configured to remain stationary during use of the solar energy harvesting system. The frame 140 may be rigidly connected or be integral with a structure defining a stationary frame of reference. In some embodiments, the frame 140 may be rigidly connected to or part of a billboard, a mounting rack, a picnic table, a roof , a wall, or other structure of a building, a tree, or otherwise rigidly coupled to the ground. Although not required, in some embodiments, the frame 140 may be mounted to an external structure such that alignment between the tracking path of the solar panels 102 and the observable path of the sun is enhanced. Embodiments disclosed herein may be especially well suited for use in any area that may not have readily- or inexpensively-available grid power, such as camp sites, picnic areas or other remote (off-grid) locations, and developing countries in which grid power may lack access to grid power and/or available skilled labor to install and operate more complex solar tracking systems. In one example, the frame 140 of system 100 may be attached to or integrated into the roof structure of a school or a home in a developing country, e.g., in Africa. In other examples, the frame 140 of the system may be attached to or easily incorporated into the horizontal portion of a picnic table or in the vertical (back) support of a bench in a remote (off-grid) area. Many other advantageous applications will be appreciated in view of the present disclosure. In some embodiments, the frame 140 itself may be mounted such that the frame 140 is movable in relation to the stationary frame of reference. In some embodiments, the frame 140 may be movable to enable reorienting the traversable path of the solar panels such as to remain in alignment with the observable path of the sun, which varies throughout the year. In yet further embodiments, the individual solar panels 102 may be pivotable about multiple axes, one associated with traversing a path to track the movement of the sun during the day and one for adjusting an orientation of the solar panel to take into account variations of the observable path of the sun throughout the year.

[0020] Referring still to FIG. 1, the system 100 may include the thermal- mechanical actuator 120, which is configured to convert thermal energy to mechanical energy. In some embodiments, as in the illustrated example in FIG. 1, the thermal - mechanical actuator 120 may be a linear actuator configured to apply an actuation force along a generally linear path 121. In other embodiments, the thermal-mechanical actuator may be a rotary actuator configured to apply a rotational force, e.g., at or operatively arranged with respect to the pivot joint of each solar panel. In some embodiments, a combination of linear and rotary actuators may be used. The thermal-mechanical actuator 120 may convert thermal energy to mechanical energy without any reliance on electrical energy for powering or controlling the actuator. Such thermal-mechanical actuator may be operable to provide an actuation force solely responsive to variations in temperature. An example of such thermal-mechanical actuator is a wax motor, which converts thermal energy into mechanical energy by exploiting the phase-change behavior of a wax. During melting, the wax expands in volume, thereby powering an extension stroke of the actuator. Inversely, during cooling of the wax, the wax reduces in volume, which may power a retraction stroke. In some embodiments, the retraction of the actuator may be assisted, e.g., using one or more biasing elements as will be further described.

[0021] The thermal-mechanical actuator 120 may use any of a variety of phase- change materials other than a wax, such as a plant oil or other lipid-based material or a polymer-based material. A linear thermal-mechanical actuator according to some embodiments may be implemented using a cylinder 122, which contains a fixed quantity of the phase-change material 124 (e.g., a lipid- or polymer-based material). The phase- change material 124 may be enclosed by the cylinder 122 and a piston 126 housed in the cylinder. A piston rod 128 connected to the piston 126 may extend from and retract into the cylinder 122 to provide linear actuation force responsive to heating and cooling of the phase-change material 124. In some embodiments, the phase-change material 124 may include beeswax or any other type of wax.

[0022] The thermal-mechanical actuator 120 may be coupled to each of the solar panels 102 via the actuation link 130. For example, the actuation end 129 of the actuator 120 (in this case the free end of the piston rod 128) is coupled to the actuation link 130. The actuation link 130 may be coupled to one or more of the solar panels, in this case to each of the solar panels, to cause the solar panels 102 to pivot about their respective pivot axes 104 responsive to the thermal-mechanical actuator 102 converting thermal energy to mechanical energy. The actuation link 130 may include a single actuation link coupling each of the solar panels 102 to the thermal-mechanical actuator 120 or a plurality of links operatively arranged to transmit the actuation force applied by the actuator to each of the solar panels. For example, the actuation link 130 may include at least one rigid member 132 which is connected to the free end of the piston rod 128. The rigid member 132 may be connected to each of the support structures 110 of each of the solar panels 102. The rigid member 132 may be connected to each support structure 110 at a location 105 spaced apart from the pivot location 107, thereby defining a lever arm 106. The location 105 may thus also be referred to as the actuation end of the lever arm 106 and the location 107 may also be referred to as the pivot end of the lever arm 106. In this illustrated example, the pivot end of the lever arm is located near the support surface 112 and the actuation end is located along a portion of the support structure 110 that extends away from the surface 114 opposite the support surface 112. [0023] In operation, an extension of the piston rod 128 causes a force to be applied on the actuation ends of the lever arm 106 of each solar panel 102, thereby causing the solar panels 102 to pivot in a first direction (e.g., clockwise) about the pivot axes 104. Conversely, retraction of the piston rod 128 may actuate the rigid member 132 in the opposite direction (in the illustration, to the right of the page), thereby causing the solar panels 102 to pivot in a second direction (e.g., counter clockwise) about the pivot axes 104. This pivotal action of the solar panels 102 effects a change in the orientation of the solar panel 102 throughout the day, thereby allowing the solar panel to track the movement of the sun. The amount of pivoting and the rate (linear or non-linear) of pivoting of each solar panel 102 may be calibrated to obtain a desired tracking patch which may be specifically tailored to obtain an optimum orientation (e.g., with each panel facing the sun at any given time during the day) of each panel through the day. The calibration of the tracking path can be achieved in part by the configuration of the actuation link and the thermal-mechanical actuator (e.g., size, stroke and other operational parameters) as well as any other components of the system (e.g., relative arrangement of the solar panels, stiffness of rotational components and/or return mechanism, and the inclusion of any mechanical stops, e.g., for limiting the rotation of the solar panels.

[0024] In some embodiments, the actuation link 130 may be configured such that an extension stroke of the actuator causes the same amount of pivotal movement by each solar panel 102. In some embodiments, the actuation link 130 may be configured to provide different amount of force and/or cause a different amount of rotation by one or more of the plurality of solar panels. In some embodiment, e.g., when using a rigid link member, to accommodate the arcuate movement of the free end of the support structure 1 10 while remaining connected to the support structure 120, the actuation link 130 may be pivotally slidably coupled to each support structure 120. For example, as shown in FIG. 1 , the rigid member 132 may include a corresponding number of pins, each received in a slot at the locations 105 of each support structure 1 10 and extending along a length of the portion defining the lever arm 106. Each slot may be sized such that the respective pin moves freely (slidably and pivotally) within the slot. As the rigid member 132 moves responsive to an extension of the rod (i.e., to the left of the page), the pins 134 slide up the length of the slot until the solar panels are substantially horizontal, and then slide down the length of the slot as the solar panels continue to rotate clockwise. As the rigid member 132 moves in the opposite direction, responsive to a retraction of the rod (i.e., to the right of the page), the pins 134 again slide up the length of the slot until the solar panels are substantially horizontal, and slide down the length of the slot as the solar panels rotate counter clockwise returning to their starting orientation.

[0025] In some embodiments, the system 100 may be configured to achieve any desired amount (angle Θ) of pivotal movement of the solar panels about their respective pivot axes. For example, the thermal-mechanical actuator 120, the link 130, and/or the individual panels 102 may be operatively coupled to cause each of the solar panels 102 to pivot up to about 180 degrees or an amount less than 180 degrees, e.g., up to about 150 degrees, up to about 130 degrees, or up to about 100 degrees. In some embodiments, the pivotal movement of each solar panel 102 may be limited to about 90 degrees. The pivotal movement of each panel 102 may be constrained at the pivot joint (e.g., by using a limiter at the axel or pin joint) or by constraining the linear movement of the actuator 120 or actuation link 130 (e.g., by using a mechanical stop operatively associated with the actuation link). In some embodiments, a release mechanism may be included at the actuator 120, which allows the actuator to continue to extend while motion of the link 130 and/or pivoting of the solar panels 102 is constrained to a desired amount. In some embodiments, the release mechanism may be a friction coupling between the free end 129 of the piston rod 128 and the link 130. For example, the friction coupling may be configured to couple the free end 129 of the piston rod 128 to the link 130 to cause the link 130 to actuate when there is relatively low resistance (e.g., equal to any resistance at the pivot joints as needed to pivot the solar panels) and may decouple the free end 129 of the piston rod 128 (e.g., allowing the free end to slip in relation to the actuation link) when there is relatively higher resistance (e.g., as may be caused by a hard stop encountered when the solar panels have reached their maximum pivot angle). Other release mechanisms may be used. In some embodiments, the release mechanism may be implemented by the inclusion of an extendible portion (e.g., an elastic portion) along a length of the link to allow the piston rod to continue to extend substantially unresisted after the solar panels have reached their maximum allowable pivot angle. In some embodiments, the amount of pivotal movement of the solar panels may be adjustable for example to achieve a desired or optimal tracking path during different times of year or at different geographic locations. For example, during a winter day, the solar panels may need to pivot a smaller amount to sufficiently track the sun as compared to the amount needed during a summer day. Similarly a starting orientation and an ending orientation of each panel may be adjustable to accommodate different desired tracking paths of the solar panels. [0026] In some embodiments, the system 100 may also include a return mechanism

150. The return mechanism 150 may assist the return of the solar panels 102 and to their starting orientation and in some cases, with the return of the piston rod 128 to the retracted configuration. The return mechanism 150 may include a spring or any other type of biasing member operable arranged to apply a force on the actuation link 130 in a direction opposite the actuation direction during a power stroke of the cylinder. The return mechanism may be configured to provide minimal or substantially no biasing force until the actuation link has been actuated through the majority of the power stroke (e.g., about 90%, or up to 95% or 98%) so as to minimize any resistance being applied to the actuation of the solar panels. This may be achieved by arranging a spring relative to the frame such that it doesn't engage (e.g., does not begin to compress) until the actuation link has traversed the majority of the power stroke. In some examples, a sufficiently soft spring may be used, which applies just enough force to return the solar panels to their starting orientation (e.g., a force sufficient to overcome any friction at the pivot joints) without otherwise substantially resisting the force applied by the actuator 120.

[0027] FIGS 2 and 3 show simplified isometric views of a solar energy harvesting system, according to an embodiment. The system 200 in FIGS. 2 and 3 includes a plurality of solar panels 202, each including a plurality of solar cells (e.g., photovoltaic cells) for converting solar energy to electrical energy. Each solar panel 202 is supported on a support structure 210, which is pivotally coupled to a frame 240. The system 200 further includes a thermal-mechanical actuator 220 configured to convert thermal energy to mechanical energy, and an actuation link 230 connecting the thermal-mechanical actuator 220 to the solar panels 202 to cause the solar panels to pivot responsive to the conversion of thermal energy to mechanical energy. The solar panels 202 in FIG. 2 are oriented substantially horizontally, which may correspond to a mid-day orientation of the solar panels in some applications, such as when the system 200 is mounted generally parallel with the ground. If differently mounted, such as if mounted to a vertical surface (e.g., a wall of a building), the configuration in FIG. 2 may be a morning configuration, for example a starting orientation of the solar panels. The solar panels 202 in FIG. 3 are oriented at an angle to vertical, which in some applications may correspond with morning of afternoon orientation. It will be understood that the terms horizontal and vertical are used only to reflect relative position of components of the system as illustrated and do not otherwise imply any limitation on the orientation or usage of the system or components thereof. The components and the arrangement thereof shown in FIG. 2 are merely illustrative, and other variations, including eliminating components, combining components, rearranging components, and substituting components are all contemplated.

[0028] The solar panels 202 are arranged generally parallel to one another to form an array 201 . The spacing S between the solar panels 202 may be selected to minimize empty space while reducing or minimizing shadows from any given panel to adjacent panels, as the solar panels 202 traverse their tacking path. The shadow cast by a given panel 202 and, thus the spacing S, which should be greater than the overall length of the shadow of a given panel 202 through the day, may be a function of the width of the solar panel Wp and the height of the support structure. The individual panels 202 are pivotally connected to a frame 240. The frame 240 may include a base 242, a pair of opposing side walls 244, and a rear wall 246. The base 242 may be a generally rectangular plate having a length LB and a width WB. The walls 244, 246 may extend generally perpendicular to the base 242. The frame 240 may also include a front wall (not shown), thereby substantially enclosing the array of solar panels 202 into a box. The box may have an open top side or may be provided with a lid of a transparent material. Each solar panel 202 may be attached to a first (support) surface 212 of the support structure 210. The support structure may have a T-shaped transverse cross-section defined by a horizontal slat 213 and a vertical leg 215. The slat 213 supports the solar panel on its outward facing surface which defines the support surface 212 and the leg 215 extends generally perpendicularly from the opposite (or inward facing) surface 214. In the illustrated example, the leg 215 is generally perpendicular to the slat 213 ; however in other examples, the leg 215 may be at a different angle relative to the slat 213.

[0029] The support structure 210 is pivotably coupled to the frame 240, specifically to the opposing side walls 244 at the pivot locations 205- 1 and 205-2, such that the support structure 210 is pivotable about the pivot axis 204 extending through the locations 205- 1 and 205-2. In this example, the support structure 210 is pivotably coupled to the frame 240 at pivot locations near the support surface 212, for example at pivot joints arranged at the interface between the leg and the slat. The actuation link 230 is coupled to the support structure 210 at an actuation location, in this case near the bottom or free end of the leg 215, defining a lever arm that connects the actuation location to the pivot axis 204. The lever arm extends substantially the full height of the leg 215. In other examples, the actuation location may be at a different location along the leg 215. As such the length of the lever arm may vary in different embodiments. The length of the lever arm may be tailored, along with other aspects of the assembly, to obtain a desired mechanical advantage, and thus a desired amount of rotation or pivotal action of each solar panel. In yet other examples, the relative arrangement of the pivot and actuation locations may be reversed, e.g., positioning the pivot location closer to the free end of the leg 215 and positioning the actuation location closer to the support surface 213 as in the example in FIG. 5 described further below. In this illustrated example, the leg 215, and correspondingly the lever arm, is generally perpendicular to the support surface 212 of the slat and thus to the solar panel 202. In other examples, the leg 215, and thus the lever arm, may be arranged at a different angle to the support surface 212 and thus to the solar panel 202.

[0030] The system 200 may be configured to enable the solar panels 202 to pivot a sufficient amount such that the solar panels 202 remain oriented to face the sun at all times or a selected portion of time (e.g., between the hours of 10am-4pm) during the day. The solar panels 202 are spaced apart from one another by a sufficient distance to ensure that any given panel 202 does not shadow adjacent panels as the solar panels 202 traverse their tracking path. As described, the pivotal action and, thus, solar tracking of the solar panels 202 may be achieved using thermal mechanical actuation. To that end, the system 200 includes at least one thermal-mechanical actuator 220 (e.g., a wax motor 222). The thermal-mechanical actuator 220 may be implemented according to any of the examples herein, e.g., using a linear thermal-mechanical actuator that provides mechanical actuation responsive to changes in temperature and thrusting volumetric expansion and reduction of a phase-change material. The solar panels 202 may be connected to the thermal- mechanical actuator 220 via the actuation link 230, which in this example is a non-rigid member 232 (e.g., a cable, a cord, or any other type of elastic or non-elastic flexible member). A non-rigid member 232 may be operatively associated with the actuator 220 to act as a pull member (i.e., a tension member), which pulls the solar panels 202 from their starting orientation toward the ending orientation during the power stroke of the actuator. In other embodiments, a rigid member may be used, which may transmit force from the actuator to the solar panels both during the power stroke and during retraction of the actuator, thus acting as both a pull member and a push member. Referring back to the example in FIG. 2, one end of the link 230 may be fixed to the last panel 202-6 of the array and the opposite end of the link 230 may be fixed to the actuation end 229 of the actuator 220. The link 230 may also be fixed to each of the other panels 202-1 through 202-5 of the array to transmit the actuation force of the actuator 220 to each of the solar panels 202- 1 through 202-6. In some embodiments, to provide a compact arrangement of components, a non-rigid member 232 may be used for the actuation link 230, and the thermal- mechanical actuator 220 may be enclosed within the box defined by frame 240 and arranged, e.g., along the length of the base or along the width of the base, with the non- rigid member 230 operably routed from the actuation end 229 to the solar panels via one or more pulleys 234-1, 234-2.

[0031] The system 200 may operate similar to the example in FIG. 1. Referring to the illustrated example, during operation, an extension of the rod 228 of wax motor 222 causes a force to be applied to the support structure 210 of each solar panel 202 via the link 230 thereby causing each panel 202 to pivot through an arc corresponding to the tracking path of each panel 202. The system 200 may be configured with a starting configuration in which the solar panels 202 face to one side of the frame (also referred to as starting orientation). As the wax motor 222 heats up during the day causing the phase- change material melts, the extension of the rod 228 causes the non-rigid member 232 to pull each leg 215 of the support structures 210 toward the left side of the page thereby causing the solar panels 202 to rotate toward the right side of the page (e.g., as shown in FIG. 3). When the phase-change material of the wax motor 222 cools and thus contracts, the rod 228 may retract in the cylinder causing the tension on non-rigid member 232 to be released to allow the non-rigid member 232 to return to the starting configuration. In some embodiments, a return mechanism 250 may be used to assist the return of the actuation link 230 to the starting configuration. For example, a return link 252 and a biasing member 254 (e.g., a compression spring or other suitable spring) may be coupled to each of the solar panels 202. The return link 252 may be anchored to the rear wall 246 via the biasing member 254 to apply a return force acting in the opposite direction of the actuation force during a power stroke (e.g., a force that biases the free ends of the legs 215 solar panels towards the rear wall 246). In other embodiments, the return mechanism 250 may be integrated with the actuation system, such as using a one or more spring loaded pulleys for the one or more pulleys 234-1 and 234-2, or by coupling a biasing member (e.g., a spring or an elastic member) to the end of the actuation link that is connected to the last panel 202-6. Other arrangements may be used in other embodiments.

[0032] The return mechanism 250 may be configured to apply sufficient return force to cause the solar panels (and in some cases assist with the retraction of the rod 228) to return to the starting configuration but without significantly resisting the extension of the rod 228 during a power stroke. For example, a spring with a stiffness that is sufficiently low so that it does not significantly resist the actuation force applied by the thermal- mechanical actuator, but such that it is sufficiently high to return the solar panels to their starting position in the absence of actuation force. The stiffness of the spring may be selected or tailored to be sufficient high to return the solar panels (e.g., overcome any friction in the pivot joints and or resistance from the weight of the solar panels) and sufficiently low to reduce or minimize any resistance to the extension of the rod 228. In some examples, the force of the spring may be non-linear such that the spring applies increasingly greater amount of force as the solar panels 202 pivot closer to the end orientation. A non-linear spring may also be used to control the end configuration of the solar panels, e.g., to limit the amount of rotation of each panel.

[0033] FIG. 4 shows a simplified illustration of a solar energy harvesting system, according to an embodiment. The system 400 in FIG. 4 includes an array 401 of solar panels 402, each supported on a support structure 410 pivotably coupled to a frame 440. The system 400 further includes a thermal-mechanical actuator 420, and an actuation link 430 connecting the thermal-mechanical actuator 420 to each of the solar panels 402 in the array. The components and the arrangement thereof shown in FIG. 4 are merely illustrative, and other variations, including eliminating components, combining components, rearranging components, and substituting components are all contemplated.

[0034] In this example, the actuation link 430 includes a non-rigid link member

432 arranged in a closed loop. The link member 432 is connected to each of the plurality of panels (e.g., to a free end of the support structure 410 of each solar panel 402) and to the thermal-mechanical actuator 420. The non-rigid link member 432 may be implemented using, for example, a single or multi-filament cord, string, or rope, a cable, or a belt. The non-rigid link member 432 may be wound around a pair of pulleys 434-1, 434-2 disposed at opposite ends of the solar panel array 401. The thermal-mechanical actuator 420 may be operatively coupled to the link member 432, e.g., along a bottom portion 432-1 of the link member 432, to cause the top portion 432-2 of the link member 432 to translate back and forth responsive to extension and retraction of the piston rod 428, thereby causing pivotal movement of the solar panel 402 about their respective axes 404.

[0035] FIG. 5 shows a simplified illustration of a solar energy harvesting system, according to an embodiment. The system 500 in FIG. 5 includes an array 501 of solar panels 502, each supported on a support structure 510 pivotably coupled to a frame 540. The system 500 further includes a thermal-mechanical actuator 520, and an actuation link 530 connecting the thermal-mechanical actuator 520 to each of the solar panels 502 in the array. The components and the arrangement thereof shown in FIG. 5 are merely illustrative, and other variations, including eliminating components, combining components, rearranging components, and substituting components are all contemplated.

[0036] In this example, the actuation link 530 includes a non-rigid link member

532 arranged in a closed loop similar to the arrangement in FIG. 4. However, in this example, the link 530 is coupled to the support structure 410 of each panel 502 at a location near the solar panels 502. The support structure 510 of each panel 502 is hinged at its free end to the frame 540, defining the lever arm 506 between the hinge point 507 and the actuation point 505. In this example, actuation of the link by the thermal-mechanical actuator 520 causes each of the solar panels 502 to pivot about the axes 504 which are aligned with the hinge axes of the support structures 510. As with the example in FIG. 4, the link member 532 may be wound around pulleys 534-1, 534-2 to operatively route the link member 532 between the actuator 520 and the solar panels 502. As discussed, the pivotal amount to which the solar panels are able to pivot may be limited by a mechanical stop. The mechanical stop may be implemented to limit the amount of rotation of one or more of the hinge joints of the solar panels or to limit the rotation of the pulleys. In other examples, the mechanical stop may be implemented as a hard stop limiting the amount of back and forth travel of the link member 532, or by any other suitable means. In some embodiments, in which a closed loop link is used with a mechanical stop, the actuator 520 may be releasably couple to the link 530 such that actuation provided by the actuator 520beyond the movement allowed by the mechanical stop is not transferred to the link 530.

[0037] FIG. 6 shows a simplified illustration of a solar energy harvesting system, according to an embodiment. The system 600 in FIG. 6 includes an array of solar panels 602, which similar to other examples herein are supported on respective support structures 610 pivotally coupled to a frame 640. The system 600 further includes a linear thermal- mechanical actuator 620 (e.g., a beeswax cylinder 622) and an actuation link 630 coupling the actuator 620 to the solar panels 602 such that the linear movement of the rod end 629 of the cylinder 622 is translated to a rotational movement applied to each panel 602. In this example, the actuation link 630 includes a rack and pinion gear arrangement. The rack gear 633 (or simply rack) is rigidly coupled to the rod end 629 of the cylinder 622 and is configured to translate back and forth (e.g., on a rail 638). The support structure 610 of each panel 602 is provided with a pinion gear 635 (or simply pinion) rigidly connected to one end of the lever arm 605, the center axis of the pinion gear defining the pivot axis 604 for each panel 602. The pinion gears 635 are meshed with the rack gear 633 such that translation of the rack gear 633 causes rotation of the pinion gears 635 about the respective pivot axis 604.

[0038] The opposite end of the lever arm 605 is operatively supported by the frame

640. For example, a post 61 1 extending from the opposite longitudinal ends of the support structure 610 may be received in respective arcuate tracks 649 provided in the side walls 644 of the frame 640 to slidably support the support structure 610 to the frame 640 as the solar panels 602 pivot about the axis 604. During a power stroke of the cylinder 622 (i.e., when the rod end 629 moves away from the cylinder, in this case to the right of the page), the rack gear 633 moves in the same direction (to the right of the page) causing each of the pinions 635 to turn counter clockwise. When the cylinder 622 cools and the rod end 629 retracts (i.e. moving toward the cylinder, in this case to the left of the page), the rack gear 633 moves toward the cylinder 622 causing the pinions 635 to rotate the solar panels 602 in the opposite direction (in this case clock wise). The solar panels 602 may be configured to traverse an arc of up to about 180 degrees, in some cases up to 130 degrees, or up to 90 degrees. As such, the arcuate tracks 649 may have an arc length corresponding to or slightly greater than the arc traversed by the solar panels 602. In some examples, the arc length of the arcuate tracks 649 may be used to limit the amount of pivotal movement of the solar panels and the cylinder 622 may be releasable coupled to the actuation link to allow the rod end 629 to continue to extend after the solar panels have traversed the length of the arcuate tracks.

[0039] As described, the spacing S between the solar panels 602 may be selected to minimize empty space, while reducing or minimizing shadows from any given panel to the adjacent panels, as the solar panels 602 traverse their tacking path (e.g., along the arcuate tracks 649. The shadow cast by a given panel 602 and, thus, a suitable spacing S that avoids shadowing of any panel by adjacent panels may be computed as a function of the width of the solar panel WP and the height of the support structure, which in this example is substantially the same as the length of the lever arm 605. In some examples, the solar panels 602 may be spaced apart from one another by a spacing S which is greater than the linear length LA of the arcuate path traversed by the solar panel. In some embodiments, the actuator 620 may be provided in a thermal control box 650. The thermal control box 650 may be made of and/or filled with a thermally stabilizing material configured to even out fluctuations in temperature and thus enable a smoother operation (e.g., extension/retraction) of the thermal-mechanical actuator. [0040] FIG. 7 shows a simplified illustration of a solar energy harvesting system, according to an embodiment. The system 700 in FIG. 7 includes an array of solar panels 702, each supported on a support structure 710 which is pivotally coupled to a frame 740. The system 700 in this examples includes a plurality of linear thermal-mechanical actuators 720 (e.g., a beeswax cylinders 722), each of which is operatively connected via a respective actuation link 730 to the individual solar panels 702 to cause each of the solar panels 702 to pivot about its respective pivot axis 704 responsive to the conversion of thermal energy to mechanical energy by the thermal-mechanical actuators 720. The actuation link 730 may be a rigid link between the cylinder 722 and the link 730. The link 730 may utilize any suitable (e.g., a pin and slot) arrangement to couple to the free end of the support structure 710 to translate the linear movement of the rod of cylinder 722 to an arcuate movement at the free end of the support structure 710. In further examples, the individual solar panels 702 may be movable relative to one another. For example, the solar panels 702 may be movably (e.g., slidably) coupled to the frame 740 and to at least one additional actuator configured to adjust the spacing between the solar panels, the starting and/or ending orientation of the solar panels 702, or to cause pivotal movement of the solar panels along an axis other than the pivotal axis 704. The additional actuator may also be a thermal-mechanical actuator, which may be configured to vary the spacing of the solar panels throughout a given day or may be calibrated to make adjustments throughout the year.

[0041] FIGS. 8A-8C show another example of a solar harvesting system, according to an embodiment. The solar energy harvesting system 800 includes a solar panel 802 supported on a support structure 810, which is pivotable about the pivot axis 804. The solar panel 802 may be attached, via the support structure 810, to an external structure 803, such as a roof of a building. In some embodiments, the external structure (e.g., roof) may be inclined and the support structure 810 and solar panel 802 associated therewith may be attached to the external structure such that it is substantially parallel to the structure 803, and thus also inclined (e.g., relative to the ground) in its starting configuration. The solar panel 802 may be attached to the structure 803 via a pivotal joint between the support structure 810 and the external structure 803, the pivotal axis of the pivotal joint defining the axis 804, which in the illustrated example is near and extending along one of the longitudinal edges of the solar panel 802.

[0042] The system 800 may include an actuation assembly 801. The actuation assembly 801 includes a thermal-mechanical actuator 820, such as a wax motor or any other type of linear thermal-mechanical actuator that converts thermal energy into mechanical energy, and an actuation link 830, such as a pivot joint or other suitable link between the extension end of the actuator 820 and the support structure 810. In the illustrated example, the thermal-mechanical actuator 820 includes a cylinder 822 with a piston 824 operable to extend from and retract into the cylinder 822 responsive to changes in temperature (i.e., responsive to the heating and cooling of a phase-change material contained in the cylinder 822). For example, the thermal-mechanical actuator 820 may be configured as any of the thermal-mechanical actuators disclosed herein. The thermal- mechanical actuator 820 may be operatively connected (e.g., rigidly fixed) to the external structure 803 and operatively connected (e.g., pivotally fixed via the link 830) to the support structure 810. The actuation link 830 may be configured to translate the linear movement of the piston 824 to a pivotal movement of the solar panel 802. As such the actuation link 830 may be configured to cause the solar panel 802 to pivot about at least the pivot axis 804 responsive to the actuator 820 converting the thermal energy to the mechanical energy. In some embodiments, depending on the starting configuration (e.g., the initial inclination of the panel 802 with the piston fully retracted), the actuation assembly 801 may be configured to pivot the panel clockwise upon extension of the piston and counterclockwise upon retraction, as in the example in FIGS. 8A-8C. In other examples, the rotation direction may be reversed. In some embodiments, the system 800 may have a starting configuration as shown in FIG. 8 A (e.g., with the panel 803 generally in line with the incline of the external structure). The system may be configured such that the panel 802 pivots, for example, clockwise about the axis 804 responsive to actuation by the thermal-mechanical actuator 820 as the ambient temperature increases during the day. The panel 802 may rotate to any number of intermediate positions between the staring position and the end position, e.g., as shown in FIGS. 8B and 8C. For example, the system 800 may be configured such that the panel 802 is substantially horizontal (relative to the ground) in one intermediate configuration, which may correspond to a mid-day configuration, e.g., as shown in FIG. 8B. As described herein, the thermal-mechanical actuator 820 and link 830 may be configured to provide any desired amount of total rotation of the panel as may be suitable for a specific application (e.g., a specific geographic location, or specific time of year).

[0043] While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting.

Claims

CLAIMS What is claimed is:

1. A solar energy harvesting system, comprising:

at least one support structure pivotable about at least one pivot axis;

at least one solar panel supported by the at least one support structure and pivotable about the at least one pivot axis with the at least one support structure;

at least one thermal-mechanical actuator configured to convert thermal energy to mechanical energy;

at least one actuation link coupling the at least one thermal-mechanical actuator to the at least one solar panel, the at least one actuation link configured to cause the at least one solar panel to pivot about the at least one pivot axis responsive to the at least one actuator converting the thermal energy to the mechanical energy.

2. The solar energy harvesting system of claim 1, wherein the at least one thermal- mechanical actuator includes a linear actuator, the at least one actuation link coupling the linear actuator to the at least one solar panel such that linear movement of the linear actuator translates to pivotal movement of the at least one solar panel.

3. The solar energy harvesting system of claim 1, wherein the at least one solar panel includes a plurality of solar panels, wherein the support structure includes a plurality of support structures each of which supports a corresponding one of the plurality of solar panels, each of the plurality of solar panels configured to rotate about a respective pivot axis, and wherein the at least one actuation link includes at least one pull member or push member connected to each of the plurality of solar panels.

4. The solar energy harvesting system of claim 1, wherein the at least one thermal- mechanical actuator includes a wax motor.

5. The solar energy harvesting system of claim 1, wherein the at least one thermal- mechanical actuator includes a cylinder, a piston, and a fixed quantity of a phase-change material sealed within the cylinder such that volumetric expansion and contraction of the phase-change material causes movement of the piston.

6. The solar energy harvesting system of claim 5, wherein the at least one actuation link includes a rigid member coupling the piston to the at least one solar panel.

7. The solar energy harvesting system of claim 6, wherein the at least one actuation link includes a rack connected to the piston, and a pinion meshed with the rack and coupled to the at least one solar panel such that movement of the rack causes rotation of the pinion about the pivot axis.

8. The solar energy harvesting system of claim 5, wherein the at least one actuation link includes a non-rigid member coupling the piston to the at least one solar panel, the system further comprising a biasing member connected to the at least one solar panel and configured to apply a biasing force opposite the force applied by the at least one actuator.

9. The solar energy harvesting system of claim 8, wherein the non-rigid member includes an elastic member.

10. The solar energy harvesting system of claim 1, wherein the at least one solar panel is attached to a first surface of the at least one support structure, and wherein the at least one actuation link is coupled to the at least one solar panel at an actuation point, a lever arm defined between the actuation point and the at least one pivot axis.

1 1 . The solar energy harvesting system of claim 10, further comprising a frame pivotally supporting the support structure, wherein the support structure is pivotally connected to the frame at one end of the lever arm, and wherein the actuation link is coupled to the support structure at the opposite end of the lever arm.

12. The solar energy harvesting system of claim 10, wherein the lever arm is angled relative to the first surface.

13. The solar energy harvesting system of claim 10, wherein the support structure includes a slat defining the first surface and a leg extending from a second surface of the slat opposite the first surface.

14. The solar energy harvesting system of claim 13, wherein the leg includes a free end that is connected to the at least one actuation link, and wherein the at least one solar panel is pivotally coupled to a frame at a location between the free end of the leg and the support surface.

15. The solar energy harvesting system of claim 1 further comprising a mechanical stop associated with the one or more solar panels and configured to limit rotation of the at least one solar panel.

16. The solar energy harvesting system of claim 14, wherein the mechanical stop is configured to limit the rotation of the at least one solar panel to an arc of less than 180 degrees.

17. The solar energy harvesting system of claim 15, wherein the at least one solar panel has a starting configuration associated with an unextended state of the at least one thermal- mechanical actuator and an ending configuration associated with an extended state of the at least one thermal-mechanical actuator, and wherein the mechanical stop is adjustable to adjust at least one of the starting configuration and the ending configuration.

18. The solar energy harvesting system of claim 1, wherein the at least one solar panel includes a plurality of solar panels, each of the plurality of solar panels configured to traverse an arc having a linear length, and wherein the plurality of solar panels are spaced by a distance greater than the linear length.

19. A solar energy harvesting system, comprising:

a plurality of solar panels each of which includes a slat, a plurality of solar cells attached to a first surface of the slat, and a lever arm extending away from a second surface of the slat opposite the first surface;

a frame, wherein a first end of the lever arm of each of the plurality of solar panels is pivotally attached to the frame; and a wax motor coupled to each of the plurality of solar panels via at least one actuation link, wherein a second end of the lever arm of each of the plurality of solar panels is coupled to the at least one actuation link.

20. The solar energy harvesting system of claim 19, wherein the lever arm is defined, at least in part, by a leg extending from to the second surface, and wherein the first end of the lever arm is relatively closer to the second surface than the second end of the lever arm.

21. The solar energy harvesting system of claim 19, wherein the lever arm is defined, at least in part, by a leg extending from the second surface, and wherein the first end of the lever arm is closer to a free end of the leg than the second end of the lever arm.

22. The solar energy harvesting system of claim 19, wherein the frame further includes a plurality of arcuate tracks, each configured to guide movement of the second end of the lever arm relative to the frame.

23. The solar energy harvesting system of claim 19, further comprising a second actuator configured to adjust a spacing between the plurality of solar panels.

24. The solar energy harvesting system of claim 19, wherein the frame includes a base and a pair of opposing walls extending from the base, each of the plurality of solar panels pivotably coupled to the pair of opposing walls, the frame further including a rear wall connecting the pair of opposing walls, and wherein the solar energy harvesting system further includes a biasing member coupling each of the plurality of solar panels to the rear wall.

25. The solar energy harvesting system of claim 24, wherein the wax motor is arranged such that a piston of the wax motor moves in a direction substantially perpendicular to the rear wall of the frame.

26. The solar energy harvesting system of claim 1,9 further comprising a thermal control box around the wax motor.