Patent Publication Number: US-10771009-B2

Title: Maintaining a solar power module

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of, and claims priority to, U.S. patent application Ser. No. 15/397,205, entitled “MAINTAINING A SOLAR POWER MODULE,” and filed on Jan. 3, 2017, the entire contents of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This document relates to systems and methods for maintaining a solar power module and, more particularly, cleaning and cooling surfaces of a solar power module. 
     BACKGROUND 
     Solar power systems and modules, such as photovoltaic (PV) systems and heliostat systems, operate most efficiently in climates and ambient environments that experience a large number of sunny, daytime hours. In such climates and ambient environments, however, the large number of sunny hours can produce conditions that are not optimal for solar power system operation. For example, many locations around the Earth that experience sunny climates also experience high daytime temperatures coincident with the sunny hours. Further, many sunny climates are in locations in which sand, dust, and other particles are prevalent in the ambient atmosphere. Climate conditions such as high temperature and atmospheric particles can add challenges to efficient operation of solar power systems, such as PV cells used in solar panel arrays. For example, while sunny weather increases power output from the solar power arrays, dust and high temperature reduce the efficiency leading to lower solar power output. 
     SUMMARY 
     In a general implementation, a solar power system includes a plurality of solar power cells mounted on an outer surface of a spherical frame, the spherical frame including an inner surface that defines an interior volume; a heat sink that includes a hollow housing mounted within the interior volume of the spherical frame; and a phase change material positioned in the hollow housing of the heat sink, the phase change material thermally coupled to the inner surface of the spherical frame to receive heat from the outer surface of the spherical frame. 
     In an aspect combinable with the general implementation, the plurality of solar power cells include a plurality of photovoltaic (PV) cells. 
     In another aspect combinable with any of the previous aspects, the phase change material includes at least one paraffin wax. 
     Another aspect combinable with any of the previous aspects further includes at least one permanent magnet mounted within the interior volume. 
     In another aspect combinable with any of the previous aspects, the at least one permanent magnet is mounted within the interior volume on a shaft that extends through a diameter of the spherical frame and the heat sink. 
     In another aspect combinable with any of the previous aspects, the at least one permanent magnet includes a hollow magnet that encloses the heat sink. 
     Another aspect combinable with any of the previous aspects further includes a magnetized heat transfer fluid disposed and flowable within the interior volume of the spherical frame between the hollow magnet and the inner surface of the spherical frame based, at least in part, on an amount of heat transferred from the outer surface of the spherical frame into the magnetized heat transfer fluid and a magnetic field generated by the hollow magnet. 
     Another aspect combinable with any of the previous aspects further includes a plurality of baffles mounted within the interior volume of the spherical frame between the heat sink and the inner surface of the spherical frame. 
     In another aspect combinable with any of the previous aspects, the plurality of baffles form at least one flowpath for the magnetized heat transfer fluid within the interior volume that is oriented along a circumference of the interior surface of the spherical frame. 
     Another aspect combinable with any of the previous aspects further includes at least one permanent ring magnet circumferentially mounted adjacent an outer surface of the spherical frame. 
     Another aspect combinable with any of the previous aspects further includes a magnetized heat transfer fluid disposed and flowable within the interior volume of the spherical frame between the heat sink and the inner surface of the spherical frame based, at least in part, on an amount of heat transferred from the outer surface of the spherical frame into the magnetized heat transfer fluid and a magnetic field generated by the permanent ring magnet. 
     In another general implementation, a method for cooling a solar power system includes operating a solar power system that includes a plurality of solar power cells mounted on a spherical frame; transferring heat from an outer surface of the spherical frame to an inner surface of the spherical frame and to a heat sink mounted within an interior volume of the spherical frame; transferring the heat from the heat sink to a phase change material positioned in the heat sink; and transforming at least a portion of the phase change material from a solid phase to a semi-solid or liquid phase based on the heat received from the outer surface of the spherical frame. 
     In an aspect combinable with the general implementation, the plurality of solar power cells include a plurality of photovoltaic (PV) cells. 
     In another aspect combinable with any of the previous aspects, the phase change material includes at least one paraffin wax. 
     Another aspect combinable with any of the previous aspects further includes generating a magnetic field within the interior volume of the spherical frame with at least one magnet; transferring heat from an outer surface of the spherical frame to a magnetized fluid contained within the interior volume; and circulating the magnetized fluid within the interior volume between the inner surface of the spherical frame and the heat sink based on the generated magnetic field and an amount of heat transferred from the outer surface to the magnetized fluid. 
     In another aspect combinable with any of the previous aspects, the magnetized heat transfer fluid includes a ferrofluid liquid that includes a plurality of magnetized particles. 
     In another aspect combinable with any of the previous aspects, the at least one magnet includes a permanent magnet. 
     In another aspect combinable with any of the previous aspects, generating the magnetic field includes generating the magnetic field from the at least one magnet mounted within the interior volume on a shaft that extends through a diameter of the spherical frame. 
     In another aspect combinable with any of the previous aspects, the at least one magnet includes a spherical magnet that encloses the heat sink. 
     In another aspect combinable with any of the previous aspects, generating the magnetic field includes generating the magnetic field with a plurality of ring magnets mounted adjacent the spherical frame. 
     In another aspect combinable with any of the previous aspects, circulating the magnetized fluid within the interior volume includes circulating the magnetized fluid through a flowpath within the interior volume formed by a plurality of baffles mounted within the interior volume of the spherical frame. 
     Another aspect combinable with any of the previous aspects further includes rotating, based at least partially on circulation of the magnetized fluid within the interior volume, the spherical frame about an axis of rotation. 
     One, some, or all of the implementations according to the present disclosure may include one or more of the following features. For example, a solar power system according to the present disclosure may increase efficiency (for example, electrical power output) of a photovoltaic power system. A solar power system according to the present disclosure may facilitate in-situ cleaning of PV cells with little to no disassembly of the solar power system. As another example, multiple self-cleaning arrays of solar power systems can be linked easily in areas such as sun shades and car parks. Also, a solar power system according to the present disclosure may include a spherical design that provides 150% more surface area for the exposed hemispherical region for solar absorption than a planar solar panel. As another example, a solar panel cleaning system of a solar power system may also act as a heat transfer mechanism to reduce a surface temperature of a solar panel of the system. As another example, the cleaning system of a solar power system of the present disclosure may experience little to no evaporation of a cleaning solution, as well as little to no friction between the solar panel and the cleaning system, through a ferrofluid seal. 
     One, some, or all of the implementations according to the present disclosure may also include one or more of the following features. For example, a solar power system according to the present disclosure may also use a low or no energy magneto-caloric pump mechanism to circulate a cooling fluid to cool a solar panel of the power system. A solar power system according to the present disclosure may utilize permanent magnets to drive the magneto-caloric pump, which in turn may rotate a spherical solar panel of the system. A solar power system according to the present disclosure may also utilize a heat transfer material which requires no power to cool the solar panel of the power system. As another example, the solar power system may include cooling and cleaning systems that use little to no power and require little to no maintenance. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a schematic illustration of at least a portion of a solar power system. 
         FIG. 1B  is a schematic illustration of at least a portion of a solar power system that includes a solar panel cleaning assembly. 
         FIG. 2  is a schematic illustration of an internal sectional view of at least a portion of a solar power system that includes at least one magnet and a magnetized fluid to cool the solar power system. 
         FIG. 3  is a schematic illustration of at least a portion of another solar power system that includes at least one magnet and a magnetized fluid to cool the solar power system, along with a solar panel cleaning assembly. 
         FIG. 4  is a schematic illustration of an example operation of a magnetic fluid pump. 
         FIG. 5  is a schematic illustration of at least a portion of a solar power system that includes at least one magnet and a solar panel mounting assembly. 
         FIG. 6  is a schematic illustration of at least a portion of a solar power system that includes an inner spherical housing. 
         FIG. 7  is a schematic illustration of at least a portion of a solar power system that includes at least one magnet mounted in an inner spherical housing and a magnetized fluid to cool the solar power system, along with a phase change heat transfer material. 
         FIG. 8A  is a schematic illustration of at least a portion of a solar power system that includes at least one toroidal magnet and a magnetized fluid to cool the solar power system. 
         FIG. 8B  is a schematic illustration of a magnetic fluid seal system that may be implemented with a solar power system that includes a solar panel cleaning assembly. 
         FIGS. 9A-9B  are schematic illustrations of at least a portion of another solar power system that includes at least one ring magnet and a magnetized fluid to cool the solar power system, along with a solar panel cleaning assembly. 
         FIG. 10  is a chart that illustrates solar panel module efficiency as a function of module temperature. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is a schematic illustration of at least a portion of a solar power system  100 .  FIG. 1A  shows the solar power system  100  from a side view, where the solar power system  100  includes a solar panel  105 . In this example embodiment, the solar panel  105  is spherically-shaped and mounted on mounting assemblies  115  along an axis (for example, an axis of rotation)  210 . In alternative implementations, the solar panel  105  may be, for example, cylindrically-shaped, cubically-shaped, or other form that may be rotated about an axis. Other example shapes of the solar panel  105  include, for instance, cylinders with hemispherical ends, as well as cylinders with solar power cells (for example, photovoltaic cells) mounted on gears or spines that extend from a lateral surface of the cylinder. As another example, solar power cells may be mounted to fins or spines that extend from a shaft (rather than a cylinder). 
     As shown in this example, the axis  215  extends through a diameter of the solar panel  105 . Generally, the mounting assemblies  115  (for example, brackets, rotatable armatures, piston/cylinder assemblies, or otherwise) may facilitate installation of the solar power system  100  to a support structure (not shown), such as a roof, a terranean surface, a building structure, or other support structure. The solar power system  100  may be one of multiple solar power system  100  arranged in an array to generate electrical power from solar energy. Turning briefly to  FIG. 5 , this figure shows a schematic illustration of at least a portion of the solar power system  100  that includes at least one magnet  185  (described later) and a more detailed view of the solar panel mounting assembly  115 . As shown in  FIG. 5 , the solar panel mounting assembly  115  includes a bracket  121  from which a shaft or coupling  240  extends into a bearing  235 . The bearing  235 , as shown receives the coupling  240  and a shaft  175  that extends through the spherical frame  120  at the axis  215 . In some aspects, the shaft  175  and coupling  240  may be integral such that the coupling  240  is part of the shaft  175 . A spacer  230  (for example, that comprises bearing surfaces) is mounted to the shaft  175  between the outer surface  125  of the spherical frame  120  and the bearing  235 . As shown, the solar panel mounting assembly  115  may provide for reduced friction rotation of the spherical frame  120  attached to the shaft  175 , when the shaft  175  is actuated to turn. 
     Generally, the solar power system  100  receives solar energy from the Sun through multiple photovoltaic (PV) cells  110 , and converts the received solar energy to direct current (DC) electricity. The solar energy consists of light energy (i.e., photons), from the Sun that can be transformed to electricity through the photovoltaic effect. Generally, each PV cell  110  absorbs the photons, which excites an electron residing on a semiconductor material to a higher-energy state. The excited electron (or electrons, as this process occurs for millions of electrons during operation of the PV cell  110 ) produces a voltage, which in turn can produce a DC through conduits (not shown) that are electrically coupled to the solar panel  105  (to the PV cells  110  in series). The DC carried in the conduits are delivered, typically, to an inverter system to convert the DC to alternating current (AC). Such electrical connections are made with the PV cells  110  in series to achieve an output voltage and a parallel desired current. 
     As shown in  FIG. 1A , the solar panel  105  includes a spherical frame  120  with an outer surface  120  to which the PV cells  110  are mounted. In this example implementation, the spherical frame  120  may be solid or may be hollow. The spherical frame  120  is coupled to the mounting assemblies  115  to support the solar panel  105  and, in some aspects, allow rotational movement of the solar panel  105  about the axis  210 . 
       FIG. 1B  is a schematic illustration of at least a portion of the solar power system  100  that includes a solar panel cleaning assembly. In this implementation, the solar panel cleaning system of the solar power system  100  includes, as shown, a reservoir  130  that surrounds a lower hemisphere  220  of the solar panel  105  and a cleaning solution  135  that is enclosed at least partially within the reservoir  130 . Generally, the solar panel cleaning system in this example implementation may provide for automated cleaning of the solar panel  105 , for example, to remove collected dust and other particles from the PV cells  110  by rotating the spherical frame  120  on the axis of rotation  210  to immerse an upper hemisphere  215  of the solar panel  105  within the cleaning solution  135  (for example, a cleaning liquid). 
     For example, in some aspects, deposits of dust and other particles on the surface of the PV cells  105  may block or partially block solar radiation from reaching the cells  110  (for example, through a glass cover on the cells  110 ). A density of deposited dust, as well as particle composition and particle distribution, can have an impact on the power output and current voltage and characteristics of the solar power system  100 . For example, in certain Middle Eastern environments (for example, Dhahran, Saudi Arabia) the effect of dust accumulation on the power output of the PV cells  110  (for example, as mono-crystalline PV cells or polycrystalline PV cells) can gradually decrease power output if no cleaning is performed to remove the dust. In some cases, such deleterious effects can reduce power output by more than 50% with no cleaning. In some cases, even a single dust storm that deposits particles at on the PV cells  110  may decrease the power output by 20%. 
     The cleaning solution  135  may include or more chemicals formulated to remove particles from the PV cells  110 , prevent or help prevent mineralization buildup on the PV cells  110 , or both. For example, in some aspects, commercial products such as Solar Panel Wash from American Polywater® Corp., NuRinse (several products) from NuGenTec®, Aquaease from Hubbard-Hall, or Solar Clean, Powerboost and Titan Glass Gleam Solar from J.Racenstein®. In some aspects, the cleaning solution  135  may be a water-based solution mixed with ethoxylated alcohols. In some aspects, the cleaning solution  135  may be a diluted soap-water mixture. 
     As further shown in  FIG. 1B , an actuator  117  may be mounted to one or more of the mounting assemblies  115  to provide rotation of the spherical frame  120  so as to rotate the upper hemisphere  215  through the cleaning solution  135 . For example, the actuator  117  may be coupled to a shaft (shown in other figures) that extends through or from the mounting assembly  115  and to or through the spherical frame  120 . In some aspects, the actuator  117  may include or be a manual actuator, such as a handle or lever, thus allowing a human operator to rotate the spherical frame  120 . In some aspects, the actuator  117  may include or be a motorized or automatic actuator, such as a hydraulic, electric, or solar powered motor, that can automatically (for example, upon receipt of a command from a control system, at a predetermined time, within prearranged time periods, or based on a density of particles on the PV cells  110 ) rotate the spherical frame  120 . 
     Upon rotation (for example, by a manual or motorized actuator), the PV cells  110  mounted on the upper hemisphere  215  of the solar panel  105  may be immersed in the cleaning solution  135  within the reservoir  130 . In some aspects, PV cells  110  may be mounted only on the upper hemisphere  215 . Thus, in such aspects, the upper hemisphere  215  with the PV cells  110  may be rotated into the reservoir  130  to reside in the cleaning solution  135  for a particular time duration. As no PV cells may be mounted on the lower hemisphere  220 , the solar power system  100  may not be operational (for example, produce DC) during this cleaning operation. Subsequently, the upper hemisphere  215  may be rotated out of the reservoir  130  to resume operation (for example, producing DC). 
     In some aspects, PV cells  110  may be mounted on the upper hemisphere  215  and the lower hemisphere  220  (for example, on the whole outer surface  125  of the spherical frame  120 ). Thus, in such aspects, the upper hemisphere  215  with the PV cells  110  may be rotated into the reservoir  130  to reside in the cleaning solution  135  to be cleaned, while the PV cells  110  mounted to the lower hemisphere  220  operate to produce DC. The solar power system  100  may remain in such a position for a time duration that may be longer than the particular time duration in the case of PV cells  110  only being mounted to the upper hemisphere  215 . Subsequent to that longer duration, or when the PV cells  110  mounted on the lower hemisphere  220  are in need of cleaning, the upper hemisphere  215  may be rotated out of the reservoir  130  to continue of the solar power system  100  with little to no interruption of operation (for example, producing DC). 
     In some aspects, the cleaning solution  135  within the reservoir  130  may also provide a cooling fluid for the solar power system  100 . For example, the PV cells  110  mounted to whichever hemisphere (for example, upper  215  or lower  220 ) of the solar panel  105  that is immersed in the reservoir  130  may be cooled to or sustained at a particular desired temperature that is a temperature (or close to a temperature) of the cleaning solution  135 . 
     As shown, the solar panel cleaning system of the solar power system  100  may also include a seal  140  mounted to the top of the reservoir  130 . The seal  140  may be a cover for the reservoir  130 , for example, to prevent loss (for example, due to evaporation, spillage, or otherwise) of the cleaning solution  135  from the reservoir  130 . The seal  140 , in some aspects, may also contact the PV cells  110  to prevent leakage of the cleaning solution  135  from the reservoir  130  (for example, due to tipping of the solar power system  100 ). Other seals, such as magnetic fluid seals, are also contemplated by the present disclosure and are explained with reference to  FIGS. 8A-8B . 
     The example embodiment of the solar power system  100  shown in  FIG. 1B  also includes a fill conduit  145  and a drain  145  that are fluidly coupled to the reservoir  130 . For example, a volume of the cleaning solution  135  may be replenished from a cleaning solution source  160  (for example, tank, bottle, or other liquid holding device) through the fill conduit  145 . In some cases, for example, the cleaning solution source  160  may also include, for example, a float valve and a pump that operate to circulate cleaning solution  135  to the reservoir  130  through the fill conduit  145  when the float valve determines that a volume of the solution  135  in the reservoir  130  is below a predetermined or desired minimum volume. 
     The drain  150  may be fluidly coupled to the reservoir  130  to a solution recapture system  165 . In some aspects, because the used cleaning solution  135  within the reservoir  130  may contain dissolved particles, dust, or other contaminants, a filter  155  may be provided in the drain  150 . The drain  150  may be opened (for example, by a valve or other orifice control device) manually or automatically to circulate used cleaning solution  135  from the reservoir  130  to the solution recapture system  165 . Subsequently, the solution recapture system  165  may recycle (for example, further clean) the used cleaning solution  135  and supply the recycled solution to the cleaning solution source  160 , or may include a tank or other enclosure to store used cleaning solution that is to be disposed. 
     In an example operation of the solar power system  100  shown in  FIG. 1B , the solar panel  105  may operate to generate electricity in a normal operation mode. At a particular time, a determination may be made to clean the portion of PV cells  110  that are exposed to an ambient environment (for example, the cells  110  on the upper hemisphere  215 ), such as at a particular predetermined time interval, upon visual inspection of the exposed PV cells  110 , or when a determined density of particles on the exposed PV cells  110  exceeds a threshold value. The actuator  117  may be operated (for example, manually or automatically) to rotate the spherical frame  120  about the axis  210 . Upon rotation, the exposed PV cells  210  may be immersed into the cleaning solution  135  that is contained in the reservoir  130 . The immersed PV cells  110  may remain in the solution  135  for a particular time duration (for example, determined based on an amount of time necessary to remove particles from the cells  110 ). 
     In some aspects, during cleaning of a portion of the PV cells  110  mounted on the solar panel  105 , another portion of PV cells  110  (for example, mounted on the lower hemisphere  220 ) may continue electricity production for the solar power system  100 , as rotation of the spherical frame  120  exposes the other portion of the PV cells  110  to the ambient environment. After the particular time duration expires, the actuator  117  may rotate the spherical frame  120  to move the cleaned (and cooled) PV cells  110  into exposure to the ambient environment. Intermittently or periodically, the cleaning solution  135  in the reservoir  130  may be replenished by circulating new solution  135  from the cleaning solution source  160 , through the fill conduit  145 , and into the reservoir  130 . Also, intermittently or periodically, used cleaning solution  135  that contains, for example, dissolved particulates, may be circulated from the reservoir  130  and through the filter  155  to the drain  150 . The filtered solution  135  may be circulated to the solution recapture system  165  for recycling or disposal. 
       FIG. 2  is a schematic illustration of an internal sectional view of at least a portion of the solar power system  100  that includes at least one magnet  185  and a magnetized fluid  180  to cool the solar power system  100 .  FIG. 2 , as shown, illustrates a side-sectional view of the solar power system  100  taken through a diameter of the spherical frame  120 . Generally,  FIG. 2  shows an example embodiment of a solar power system cooling system that uses magnet  185  to circulate magnetized fluid  180  through an interior volume  190  of the spherical frame  120 . By circulating the magnetized fluid  180  within the interior volume  190 , heat from the PV cells  110  (not shown in this figure) may be transferred through the spherical frame  120  (for example, from the outer surface  125  to an inner surface  170 ) and into the magnetized fluid  180 . Heat received into the magnetized fluid  180  may be transferred, for example, to a heat sink (described later), the cleaning solution  135 , or other cooling source (for example, a cooling coil, Peltier cooler, or other cooling source in thermal communication with the magnetized fluid  180 ). 
     In some aspects, overheating (or heating) of solar power systems, such as the solar power system  100 , may have deleterious effects on the operation of the system in producing electricity. For example, PV cell performance may decrease with increasing temperature, as operating temperature may affect the photovoltaic conversion process. Both the electrical efficiency and the power output of a PV cell decrease with increasing cell temperature. In desert applications, for instance, PV cells are often sensitive to overheating. For example, PV cells in the Middle East (for example, Dhahran, Saudi Arabia) may experience a loss of efficiency as operating temperature increases, as shown in chart  1000  in  FIG. 10 . 
     As shown in chart  1000 , PV cell efficiency can decrease from 11.6% to 10.4% when module temperature increases from 38° C. to 48° C., which corresponds to 10.3% losses in efficiency and a temperature coefficient of −0.11 ΔE/%° C. PV cell operating temperatures over 26° F. can begin reducing output efficiency, and as the temperature of a solar panel increases, the output current increases exponentially while the voltage output is reduced linearly. The cooling system illustrated in  FIG. 2  can counter the efficiency loss of PV cells  110  in high temperature environments. 
     As shown, the magnetized fluid  180  is contained within the spherical frame  120  and free to circulate within the interior volume  190 . Circulation of the magnetized fluid  180  may be at least partially generated by the magnet  185  mounted on shaft  175  that extends through the diameter of the spherical frame  120 . In this example implementation, the magnet  185  is a spherically-shaped permanent magnet and generates a magnetic field  225  within the interior volume  190  of the spherical frame  120 . 
     In some aspects, the magnetic fluid  180  is a ferrofluid (for example, liquid). Ferrofluids consist of a carrier fluid loaded with small (for example, nanometer sized) magnetic particles. The behavior of ferrofluids varies due to, for example, the carrier fluid, temperature, particle size, shape and loading, magnetic characteristics of the particles and the applied magnetic field (for example, magnetic field  225 ). When exposed to the magnetic field  225 , the magnetized particles in the magnetized fluid  180  produce a body force. In addition, ferrofluid particle size ensures that thermal agitation in the fluid keeps the particles in suspension. Ferrofluids may be expected to perform at temperature of 150° C. (for example, continuously) or 200° C. (for example, intermittently). 
     As shown in  FIG. 2 , circulation curves represent the circulatory movement of the magnetized fluid  180  that is due, at least in part, to the magnetic field  225  (directed to cause the illustrated rotation) generated by the spherical magnet  185 . As heat is being transferred to the magnetized fluid  180  during circulation (for example, heat from the PV cells  110 ), the system acts as a ferrofluid, or magneto-caloric, pump. For example, with reference briefly to  FIG. 4 , a magneto-caloric pump is a device which moves magnetic substances (the magnetized fluid  180 ) from a region of low pressure to a region of high pressure created by a heat source (the PV cells  110  that transfer heat into the interior volume  190  of the spherical frame  120 ). 
       FIG. 4  shows a generic schematic illustration of the operation of a magneto-caloric pump applied to the solar power system  100 , which represents an example operation of the described cooling system of the solar power system  100  shown in  FIG. 2 . The “pump,” in this case, refers to a flowpath of forced circulation due to the magnetic field  225  and a pressure differential caused by heating of the magnetized fluid  180  within the interior volume  190 . The pump contains a magnetic field (field  225 ) and a heat source (heat from the PV cells  110 ). Under the influence of the magnetic field  225 , magnetized fluid  180  is drawn into the pump. As it proceeds along the pump, the fluid  180  is heated by the heat source until the temperature of the magnetized fluid  180  reaches a point where there is a significant reduction in the ferromagnetic properties of the material (for example, the nanoparticles in the fluid). Generally, this happens when the material temperature approaches the “Curie Point” (for example, the temperature at which a material loses its permanent magnetic properties, to be replaced by induced magnetism). 
     The low temperature incoming magnetized fluid (for example, magnetized fluid  180  that flows through the lower hemisphere  220 ) is attracted by the magnetic field contained in the pump. The heated material (for example, heated magnetized fluid  180  flowing in the upper hemisphere  215 ) in the pump is no longer influenced by the magnetic field and is expelled from the pump by the incoming material (for example, cooler magnetized fluid  180  flowing upward from the lower hemisphere  220  to the upper hemisphere  215 ). A pressure head is created in the pump. The hot material (for example, magnetized fluid  180  from the upper hemisphere  215 ) from the pump is dissipated and returned to the pump input (for example, volume of the spherical frame  120  within the lower hemisphere  220 ), completing the pumping cycle. 
       FIG. 3  is a schematic illustration of at least a portion of another embodiment of the solar power system  100  that includes at least one magnet  205  to circulate a magnetized fluid to cool the solar power system  100 .  FIG. 3  also shows the components of the solar panel cleaning assembly described previously with reference to  FIG. 1B .  FIG. 3  shows a side-view of this example of the solar power system  100 . In this example embodiment, in addition to, or alternatively to, a spherical permanent magnet  185  mounted within the interior volume  190  of the spherical frame  120  (not shown in this figure, but shown in  FIG. 2 ), one or more permanent ring magnets  205  may be mounted circumferentially adjacent the outer surface  125  of the spherical frame  120 . 
     As shown, the permanent ring magnets  205  may be mounted to a cage ring  195  that is a circular structure that circumferentially surrounds the spherical frame  120 . The permanent ring magnets  205  can also be mounted, as shown, to one or more cages  200  that are also mounted to the cage ring  195  circumferentially around the spherical frame  120 . As illustrated, the cages  200  are mounted such that a diameter of each cage  200  is orthogonal to a diameter of the cage ring  195 . 
     The operation of the embodiment of the solar power system  100  shown in  FIG. 3  is similar to the operation of the solar power system  100  shown in  FIG. 2 , with the difference being that the magnetic field within the interior volume  190  of the spherical frame  120  is generated by the permanent ring magnets  205  rather than, or in addition to, a permanent magnet mounted within the interior volume  190  (for example, magnet  185 ). Thus, the permanent ring magnets  205  may generate the magnetic field that at least partially powers the magneto-caloric pump applied to the solar power system  100  as described previously. 
     As further shown in  FIGS. 2 and 3 , the spherical frame  120  may also be rotated (shown by rotations  187 ) by operation of the magneto-caloric pump described above. For example, ferrofluid migration (for example, movement of the magnetized fluid  180  within the volume  190 ) from cool to warm portions of the volume  190  may create a pressure differential sufficient to rotate the spherical frame  120  on the shaft  175 . In some aspects, as shown and discussed later with reference to  FIGS. 9A-9B , the rotation can be realized or enhanced through a balanced spherical frame  120  (for example, on the shaft  175 ) and the flow of the magnetized fluid  180  through flow channels formed by baffles mounted on the inner surface  170  of the spherical frame  120 . 
     For instance, as the magnetized fluid  180  circulates within the interior volume  190  as shown, a rotational force may be exerted on the interior surface  170  of the spherical frame  120  by the moving fluid  180 . This rotational force may cause the spherical frame  120  (if free to rotate on the shaft  175 ) to rotate as well about the axis  210 . In some aspects, such rotation of the frame  120  may be desirable, for example, for automatic cleaning of the PV cells  110  by periodically rotating the solar panel  105  through the cleaning solution  135  (shown in  FIGS. 1B and 3 ). In some aspects, the rotational speed of the spherical frame  120  may be based at least partially on a temperature gradient between the heated material (for example, magnetized fluid  180  within the upper hemisphere  215 ) and the cooled material (for example, magnetized fluid  180  within the lower hemisphere  220 ). 
       FIG. 6  is a schematic illustration of at least a portion of the solar power system  100  that includes an inner spherical housing  245 .  FIG. 2 , as shown, illustrates a side-sectional view of the solar power system  100  taken through a diameter of the spherical frame  120  and the inner spherical housing  245 . The inner spherical housing  245  is mounted on the shaft  175  and defines an additional interior volume of the interior volume  190  of the spherical frame  120 . An annulus  191  is further defined between the inner surface  170  of the spherical frame  120  and the inner spherical housing  245 . 
     Generally, the inner spherical housing  245  provides an enclosure for, as some examples, one or more permanent magnets (such as magnet  185 ) mounted on the shaft  175 , a heat sink (as described later), or to enclose other components of the solar power system  100 . For example,  FIG. 7  is a schematic illustration of at least a portion of the solar power system  100  that includes at least one magnet  250  mounted in the inner spherical housing  245 , along with a heat transfer material  260  that is disposed within a volume encompassed by the magnet  250 . In this implementation, the inner spherical housing  245  is separate from the spherical (permanent) magnet  250 , which is mounted within the volume of the housing  245 . In alternative implementations, the spherical magnet  250  may form a housing that defines the volume into which the heat transfer material  260  is disposed. 
     The spherical magnet  250  may be mounted on the shaft  175  and generates a magnetic field (not shown here) much like the magnetic field  225  is generated by spherical magnet  185  in  FIG. 2 . Thus, the spherical magnet  250  may generate a magnetic field within the interior volume  190  of the spherical frame  120  that at least partially powers the magneto-caloric pump applied to the solar power system  100  as described previously. In this example, therefore, the spherical magnet  250  generates the magnetic field that drives (along with a temperature gradient) the magnetized fluid  180  within the interior volume  190  and in the annulus  191 . 
     The inner volume of the inner spherical housing  245  may include or define a heat sink (for example, in embodiments with or without the spherical magnet  250 ). The hint sink includes the heat transfer material  260 . For example, the heat sink within the housing  245  may provide for a central volume available for absorbance of thermal energy, for example, from the PV cells  110 . This central volume can be used in the form of various heat exchange technologies including chemical absorption through the melting of calcium hydroxide (Ca(OH) 2 ) crystals in a aqueous solution or through the use of a tunable phase change material (PCM). Either material, as well as other examples, can be used as the heat transfer material  260 . Further, an amount of material may be adjusted (and adjustable) based on the formulation of heat transfer material included within the heat sink and by adjusting the size of the inner spherical housing  245 , spherical frame  120 , solar panel  105 , or a combination thereof, to provide a desired heat transfer amount. Further, in some aspects, the heat transfer material  260  can absorb thermal energy from the PV cells  110  during a daylight operation time of the solar power system  100  and phase change from solid to liquid by absorbing the thermal energy. The heat transfer material  260  can then solidify during a nighttime non-operational time (for example, when no or negligible solar energy is incident on the solar power system  100 ) as ambient temperature surrounding the solar power system  100  decreases. 
     In some aspects, the heat transfer material  260  is a PCM such as one or more paraffin waxes. For example, paraffin wax is typically found as a white, odorless, tasteless, waxy solid, with a typical melting point between about 46° C. and 68° C. (115° F. and 154° F.). Some paraffin products have melting temperatures of 270° F. In some aspects, the heat transfer material  260  may be a blend of paraffin waxes with different melting points to more evenly and slowly change phase from solid to liquid as thermal energy is absorbed. For example, a combination and quantity of low, middle, and high temperature compositions may be formulated based on the amount of heat required for removal from the PV cells  110 . In some cases, the melting point of a paraffin wax can be depressed using mixtures of high long chained organic acids and salt solutions. Table 1 shows example commercial paraffin waxes from International Group Inc. that could be used, individually or in combination, as the heat transfer material  260 . 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Astorstat ® 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Start to Open 
                   
                 Volume of 
                   
               
               
                   
                 Congealing 
                 Point 
                 Terminal Point 
                 Expansion 
               
               
                   
                 Point 
                 (Astor ® DST- 
                 (Astor DST- 
                 (Astor DST- 
                 Travel 
               
               
                 Product 
                 (ASTM D938) 
                 007) 
                 007) 
                 007) 
                 (Astor DST-007) 
               
               
                   
               
            
           
           
               
            
               
                 Low Operating Temperature Range 
               
            
           
           
               
               
               
               
               
               
            
               
                 Astorstat HA16 
                 17.8-18.9° C. 
                 17.8-18.9° C. 
                 23.4-24.5° C. 
                 14-18% 
                 5.88-6.89 mm 
               
               
                   
                    64-66° F. 
                    64-66° F. 
                    74-76° F. 
                   
                 0.23-0.27 in 
               
               
                 Astorstat HA18 
                 27.2-28.3° C. 
                 27.2-28.3° C. 
                 32.8-33.9° C. 
                 14-18% 
                 5.88-6.89 mm 
               
               
                   
                    81-83° F. 
                    81-83° F. 
                    91-93° F. 
                   
                 0.23-0.27 in 
               
               
                 Astorstat HA20 
                 36.7-37.8° C. 
                 36.7-37.8° C. 
                 42.3-43.4° C. 
                 16-20% 
                 6.37-7.41 mm 
               
               
                   
                    98-100° F. 
                    98-100° F. 
                   108-110° F. 
                   
                 0.25-0.29 in 
               
               
                 Astorstat HA300B 
                   41-42.5° C. 
                    26-28° C. 
                    46-48° C. 
                  9-13% 
                 4.85-5.62 mm 
               
               
                   
                 106-108.5° F.  
                 78.8-82.5° F. 
                 115-118.5° F. 
                   
                 0.19-0.20 in 
               
            
           
           
               
            
               
                 Mid Operating Temperature Range 
               
            
           
           
               
               
               
               
               
               
            
               
                 Astorstat 75 
                 80.1-81.2° C. 
                 74.5-75.6° C. 
                 85.6-86.7° C. 
                 14-16% 
                 5.88-6.37 mm 
               
               
                   
                   176-178° F. 
                   166-168° F. 
                   186-188° F. 
                   
                 0.23-0.25 in 
               
               
                 Astorstat 80 
                 85.1-86.2° C. 
                 79.5-80.5° C. 
                 90.6-91.7° C. 
                 14-16% 
                 5.88-6.37 mm 
               
               
                   
                   185-187° F. 
                   175-177° F. 
                   195-197° F. 
                   
                 0.23-0.25 in 
               
               
                 Astorstat 90 
                 95.1-96.2° C. 
                 89.5-90.6° C. 
                 100.6-101.7° C.  
                 14-16% 
                 5.88-6.37 mm 
               
               
                   
                   203-205° F. 
                   193-195° F. 
                   213-215° F. 
                   
                 0.23-0.25 in 
               
               
                 Astorstat 95 
                 100-101.2° C.  
                 89.0-90.1° C. 
                 105.6-106.8° C.  
                 14-16% 
                 5.88-6.37 mm 
               
               
                   
                   212-214° F. 
                   192-194° F. 
                   222-224° F. 
                   
                 0.23-0.25 in 
               
            
           
           
               
            
               
                 High Operating Temperature Range 
               
            
           
           
               
               
               
               
               
               
            
               
                 Astorstat 6920 
                 124-129.5° C.  
                 107.3-112.9° C.  
                 126.8-132.3° C.  
                 16-18% 
                 6.37-6.89 mm 
               
               
                   
                   255-265° F. 
                   225-235° F. 
                   260-270° F. 
                   
                 0.25-0.27 in 
               
               
                 Astorstat 6988 
                   130-135° C. 
                 115.6-121.2° C.  
                 129.5-135.1° C.  
                 16-18% 
                 6.37-6.89 mm 
               
               
                   
                   265-275° F. 
                   240-250° F. 
                   265-275° F. 
                   
                 0.25-0.27 in 
               
               
                 Astorstat 10069 
                   105-106° C. 
                 98.4-100.0° C.  
                 114.5-116.2° C.  
                 14-16% 
                 5.88-6.37 mm 
               
               
                   
                   221-223° F. 
                   209-212° F. 
                   238-241° F. 
                   
                 0.23-0.25 in 
               
               
                 Astorstat 10316 
                 109-110.6° C.  
                 104-105.6° C. 
                 125.7-127.9° C.  
                 15-17% 
                 6.13-6.63 mm 
               
               
                   
                   228-231° F. 
                   219-222° F. 
                   258-262° F. 
                   
                 0.24-0.26 in 
               
               
                   
               
            
           
         
       
     
       FIG. 8A  is a schematic illustration of at least a portion of the solar power system  100  that includes at least one toroidal magnet  265  and the magnetized fluid  180  to cool the solar power system  100 .  FIG. 8A , as shown, illustrates a side-sectional view of the solar power system  100  taken through a diameter of the spherical frame  120 . Generally,  FIG. 8A  shows an example embodiment of a solar power system cooling system that uses the toroidal magnet  265  to generate a magnetic field  270  to circulate the magnetized fluid  180  through the interior volume  190  of the spherical frame  120 . By circulating the magnetized fluid  180  within the interior volume  190 , heat from the PV cells  110  (not shown in this figure) may be transferred through the spherical frame  120  (for example, from the outer surface  125  to an inner surface  170 ) and into the magnetized fluid  180 . Heat received into the magnetized fluid  180  may be transferred, for example, to a heat sink (described previously), the cleaning solution  135 , or other cooling source (for example, a cooling coil, Peltier cooler, or other cooling source in thermal communication with the magnetized fluid  180 ). As shown, the magnetized fluid  180  is contained within the spherical frame  120  and free to circulate within the interior volume  190 . Circulation of the magnetized fluid  180  may be at least partially generated by the magnet  265  mounted on shaft  175  that extends through the diameter of the spherical frame  120 . 
       FIG. 8B  is a schematic illustration of a magnetic fluid seal system that may be implemented with the solar power system  100  that includes a solar panel cleaning assembly. For example, as illustrated  FIG. 8A  includes the solar panel cleaning assembly which includes the reservoir  130  hemispherically positioned around the lower hemisphere  220  of the spherical frame  120 . The reservoir  130  holds the cleaning solution  130 . The magnetic fluid seal system, in this example implementation, comprises a ferrofluid seal that uses a magnetized fluid to create a seal so that a liquid (for example, the cleaning solution  135 ) does not escape a container (for example, the reservoir  130 ). As illustrated, the magnetic fluid seal system includes a magnet  275  mounted between the reservoir  130  and the outer surface  125  of the spherical frame  120 . The magnet  275  includes pole pieces  280  and generate a magnetic flux  285 . The magnetic flux  285  travels through a ring of magnetic fluid  290  to energize the particles within the fluid  290 . The magnetic fluid  290 , which is held against the outer surface  125  of the spherical frame  120  and the pole piece  280  by the flux  285 , creates a fluidic seal to prevent or help prevent the cleaning solution  135  from escaping the reservoir  130 . 
       FIGS. 9A-9B  are schematic illustrations of at least a portion of another embodiment of the solar power system  100  that includes at least one ring magnet  300  the solar panel cleaning assembly.  FIG. 9A , as shown, illustrates a side-sectional view of the solar power system  100  taken through a diameter of the spherical frame  120 .  FIG. 9B , as shown, illustrates a top-sectional view of the solar power system  100  taken through the ring magnet  300 . Generally,  FIGS. 9A-9B  show an example embodiment of a solar power system cooling system that uses the ring magnet  300  (for example, mounted circumferentially around the spherical frame  120  at the axis  210 ) to generate a magnetic field to circulate a magnetized fluid (not shown in this figure) through the interior volume  190  of the spherical frame  120 . By circulating the magnetized fluid within the interior volume  190 , heat from the PV cells  110  (not shown in this figure) may be transferred through the spherical frame  120  (for example, from the outer surface  125  to an inner surface  170 ) and into the magnetized fluid  180 . Heat received into the magnetized fluid may be transferred, for example, to a heat sink (described previously), the cleaning solution  135 , or other cooling source (for example, a cooling coil, Peltier cooler, or other cooling source in thermal communication with the magnetized fluid  180 ). 
       FIGS. 9A-9B  also show an example embodiment of the spherical frame  120  that includes one or more baffles  305  formed (for example, attached to or integral with) the inner surface  170  of the frame  120 . The baffles  305  form flow paths  310  through which the magnetized fluid flows during circulation of the fluid through the interior volume  190 . For example, as previously described, ferrofluid migration (for example, movement of the magnetized fluid within the volume  190 ) from cool to warm portions of the volume  190  may create a pressure differential sufficient to rotate the spherical frame  120  on a shaft (for example, shaft  175 , not shown in these figures). In some aspects, the rotation can be realized or enhanced through a balanced spherical frame  120  (for example, on the shaft) and the flow of the magnetized fluid through flow channels formed by baffles  305  mounted on the inner surface  170  of the spherical frame  120 . For instance, as the magnetized fluid circulates within the interior volume  190  as shown, a rotational force may be exerted on the interior surface  170  of the spherical frame  120  by the moving fluid. This rotational force may cause the spherical frame  120  (if free to rotate on the shaft) to rotate as well about the axis  210 . In some aspects, such rotation of the frame  120  may be desirable, for example, for automatic cleaning of the PV cells  110  by periodically rotating the solar panel  105  through the cleaning solution  135 . In some aspects, the rotational speed of the spherical frame  120  may be based at least partially on a temperature gradient between the heated material (for example, magnetized fluid within the upper hemisphere  215 ) and the cooled material (for example, magnetized fluid within the lower hemisphere  220 ). 
     While this disclosure contains many specifics, these should not be construed as limitations on the scope of the disclosure or of what may be claimed, but rather as descriptions of features specific to particular implementations of the disclosure. Certain features that are described in this disclosure in the context of separate implementations can also be provided in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be provided in multiple implementations separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     Thus, particular implementations of the present disclosure have been described. Other implementation s are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results.