Abstract:
A personal solar appliance (PSA) is presented that collects and stores solar energy. The PSA may be resilient enough to suffer all the knocks of extended human use and to have extensive exposure to the elements. Further, the PSA may be waterproof and provide thermal cooling. As such, some embodiments of the PSA includes a base with ventilation holes; a heat sink coupled to the base; a solar cell mounted to the heat sink opposite the base; a printed circuit board mounted to the heat sink opposite the solar cell; and a battery mounted to the base.

Description:
RELATED APPLICATIONS 
       [0001]    The current application claims priority to U.S. Provisional Application 61/224,835, filed on Jul. 10, 2009, and to U.S. Provisional Application 61/357,929, filed on Jun. 23, 2010, both of which are herein incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention is related to solar energy generation and storage and, in particular, to a personal solar appliance for generation and storage of solar energy. 
         [0004]    2. Discussion of Related Art 
         [0005]    Solar cells or photovoltaic cells can be considered large area semiconductor diodes that convert sunlight into electrical current, which is used to produce usable power. The output power of the solar cell depends on multiple factors such as sunlight intensity, temperature, orientation of the cells with respect to the sun, and efficiency of the solar cells. 
         [0006]    Photovoltaic systems, using solar panels, directly convert sunlight into energy using the principles of the photoelectric effect. The photoelectric effect takes advantage of the properties of semiconductor materials, with silicon being the primary material used in photovoltaic solar cells. When photons strike the solar cell, electrons in the semiconductor material are freed and allowed to flow as electricity. The direct current (DC) electricity produced can be directly used to charge batteries. The DC current can also be coupled to an inverter to power alternating current (AC) components or the AC current be connected to a local electrical power grid. 
         [0007]    Traditional photovoltaic systems are based on silicon. Silicon ingots are sliced into wafers that are fabricated into cells. Cells are combined into modules, which are packaged into end-user systems. Silicon-based solar cells typically have efficiencies up to about 18%. Semiconductor materials, like gallium arsenide, have efficiencies that approach 40%, but are much higher costs than silicon. Gallium arsenide, therefore, is not currently economically practical for many terrestrial applications and is used for the most part on spacecraft and interplanetary robots. Thin film technologies use a variety of semiconductors but their efficiency is typically less than 10%. 
         [0008]    A battery charger is a device used to put energy into a rechargeable battery by forcing an electric current into the battery. The charge current for a battery depends upon the technology and capacity of the battery being charged. For example, the current that should be applied to recharge a 12 volt car battery (several Amps) will be very different from the current that should be applied for recharging a mobile phone battery (250 mA to 1000 mA). However, solar cell output current can be utilized to charge any battery. 
         [0009]    In many areas, especially where electrical power is unavailable or unreliable, there is a need for devices that are capable of powering user devices such as lights, radios, MP3 players, cell phones, or other devices, or are capable of charging batteries directly. 
       SUMMARY 
       [0010]    In accordance with the present invention, a personal solar appliance according to some embodiments of the present invention can include a base with ventilation holes; a heat sink coupled to the base; at least one solar cell mounted to the heat sink opposite the base; a printed circuit board mounted to the heat sink opposite the solar cell; and a battery mounted to the base. 
         [0011]    A method of forming a personal solar appliance according to some embodiments of the present invention includes affixing a printed circuit board to a bottom of a heat sink; affixing a solar cell to a top of the heat sink; attaching the heat sink to a ventilated base; and attaching a battery to the base opposite the heat sink. 
         [0012]    These and other embodiments are further discussed below with reference to the following figures, which are incorporated in and considered a part of this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0013]      FIG. 1  illustrates a personal solar appliance according to some embodiments of the present invention. 
           [0014]      FIGS. 2A and 2B  illustrate a personal solar appliance according to some embodiments of the present invention. 
           [0015]      FIG. 3  illustrates a personal solar appliance with a solar concentrator according to some embodiments of the present invention. 
           [0016]      FIGS. 4A ,  4 B, and  4 C illustrate a base of a personal solar appliance according to some embodiments of the present invention. 
           [0017]      FIGS. 5A and 5B  illustrates assembly of the components of a personal solar appliance according to some embodiments of the invention. 
           [0018]      FIGS. 6A and 6B  illustrate assembly of the components of a personal solar appliance according to some embodiments of the invention. 
           [0019]      FIGS. 7A and 7B  further illustrate assembly of the legs of a personal solar appliance according to some embodiments of the present invention illustrated in  FIG. 6 . 
           [0020]      FIGS. 8A and 8B  illustrate aspects of a top cover of a personal solar appliance according to some embodiments of the present invention. 
           [0021]      FIGS. 9A through 9D  illustrates assembly of certain components of the personal solar appliance illustrated in  FIG. 6 . 
       
    
    
       [0022]    In the figures, components having the same designation have the same or similar function. In the figures, components are not drawn to size. 
       DETAILED DESCRIPTION 
       [0023]    Aspects of various embodiments of PSA according to the present invention are described below. One skilled in the art will recognize that particular embodiments of PSA according to the present invention can include any number of the individual features that are described. Further, one skilled in the art may recognize various modifications or alternatives to the particular embodiments described here. Those modifications and alternatives are intended to be within the scope of the present disclosure. 
         [0024]    In some embodiments, the PSA is rugged. In some embodiments, the PSA is a waterproof device. In some embodiments, the PSA includes photovoltaic cells, a battery, a connector to extract power from the PSA, and electronics to manage the power and charging of the battery. In some embodiments, the PSA includes status indicators to provide information on the photovoltaic performance and the battery charge state. In some embodiments, the PSA includes reflectors to increase energy production. In some embodiments, components of the PSA, for example the device&#39;s legs, reflectors, battery, and electronics, can be user replaceable. 
         [0025]    In some embodiments of a PSA according to the present invention, the PSA can include one or more solar cells; electronics coupled to the one or more solar cells; and a battery coupled to the electronics for storing the photovoltaic energy. In some embodiments, the electronics performs power, charge, and telemetry management. In some embodiments, the PSA further includes a system of cables and connectors to couple with user devices. 
         [0026]    U.S. patent application Ser. No. 12/340,500, which is herein incorporated by reference in its entirety, describes a concentration system, a liquid crystal display or similar type display, and a customizable reflective layer to provide visual appeal for a device with a photovoltaic system. U.S. patent application Ser. No. 12/351,105, which is herein incorporated by reference in its entirety, describes an intelligent protective case with photovoltaic, battery, and electronics for use by an intelligent user device. U.S. patent application Ser. No. 12/351,105 also describes the architecture whereby software is obtained and installed for use on the intelligent user device including utilization of the Internet. A discussion of the charging electronics is provided in U.S. patent application Ser. No. 12/831,932, filed on Jul. 7, 2010, which is herein incorporated by reference in its entirety. 
         [0027]      FIG. 1  illustrates an embodiment of intelligent charger  100  consistent with the present invention. Intelligent charger  100  includes one or more solar panels  124 , a battery pack  122 , and electronics  130 . Electronics  120  includes a microprocessor  120  and electronic circuit  102  and controls the charging of battery  122  from solar cell  124 . As shown in  FIG. 1 , microprocessor  120  can include a processor, volatile and non-volatile memory, and an interface. Programming and operating parameters can be stored in non-volatile memory while operating parameters and interim results can be stored in volatile memory. The interface allows microprocessor  120  to communicate, for example with wireless transceiver  104 , physical connector  106 , and electronic circuit  102 . In some embodiments, intelligent charger  100  may include a display  108  and may further include a user input device  109  in order to communicate with a user. Additionally, microprocessor  120  may receive location data through a GPS device  126 , which can be communicated either through connector  106  or through transceiver  104 . 
         [0028]    As shown in  FIG. 1 , microprocessor  120  is coupled to electronic circuit  102 . Electronic circuit  102  is coupled to solar panel  124  and battery pack  122 . In some embodiments, electronic circuit  102  can use a boost or buck mode of power management to output current and voltage compatible with battery  122  based upon incoming current and voltage from solar panel  124 . Battery  122  can be any rechargeable battery, but in some embodiments is a lithium-ion polymer. Electronic circuit  102  is also coupled to physical connector  106  in order to provide a charging current and voltage to an external device (not shown) that is coupled to connector  106 . 
         [0029]    Electronic circuit  102  is coupled to microprocessor  120 , which stores and executes charge management software. The charge management software operating on microprocessor  120  ensures that battery pack  122  and any battery coupled to connector  114  receives current and voltage appropriate to charge those batteries. As such, electronic circuit  102  receives power from solar panel  124  and converts that power to voltage and current appropriate to charge battery pack  122 . Electronic circuit  102  may also convert power to voltage and current appropriate to charge a battery pack coupled to connector  106 . 
         [0030]    In some embodiments, electronic circuit  102  also includes monitoring electronics to monitor the power output and status of solar panel  124  as well as the charge and status of battery  122 . In some embodiments, electronics  102  can also monitor the charge and status of a battery in a device coupled to connector  106 . Microprocessor  120 , then, can monitor and provide statistics on, for example, power production in solar panel  124 , temperature, and battery charging. 
         [0031]    As shown in  FIG. 1 , intelligent charger  116  may also include a wireless transceiver  104  that is coupled to microprocessor  120 . Wireless transceiver  104  may include a cell phone transceiver and may be capable of communicating directly to servicers coupled to the internet. In some embodiments, wireless transceiver  104  may include a local transceiver such as, for example, a Bluetooth transceiver. In which case, intelligent charger  116  can communicate wirelessly smart devices or to personal computers through wireless transceiver  104 . 
         [0032]    In some embodiments, information regarding charging or discharging of battery  122  may be displayed on display  108 . In some embodiments, a smart device coupled to connector  106  may communicate information to electronic circuit  102  that may then be displayed on display  108 . Several status parameters can be provided on display  108 . In some embodiments, display  108  may be a liquid crystal or electronic paper device. Status information that may be displayed can include, for example, power produced by the solar cells, state of charge of the internal battery, power drawn by an external device, or any other parameter. 
         [0033]    In some embodiments, an input device  109  can also be included. Input device  109  may be, for example, an electrostatic touch sensor or other user input device may be utilized so that a user may request status information from the PSA. 
         [0034]    In some embodiments, the PSA can include a global positioning system (GPS)  126  to determine its position. In some embodiments, the PSA can also include a transceiver  104  that can communicate with a remote system via wireless communications or an internet link in order to report its position and status. In some embodiments, the PSA can report to the remote system when prompted by the remote system. In some embodiments, the PSA can report its position and a fault condition to the remote system. A telemetry system that can be utilized for connecting the PSA to a remote monitoring system is described in U.S. patent application Ser. No. 12/351,105. In general, position, statistical data, or fault conditions can be reported to a remote monitor. 
         [0035]    Connector  106  of PSA  100  can be utilized to provide power, telemetry, and configuration management. Connector  106  can be one or more of the families of USB connectors (microUSB, miniUSB, and USB), which may be appropriately protected for outdoor protection when used on PSA  100 . The USB family is able to perform telemetry functions from the PSA and enables the PSA to be configured by a remote computer. Power is delivered by the PSA using a female axial power connector that, in some embodiments, is waterproof and structurally strong. The non-PSA side of the cable may have a number of different devices to receive the power. The power supplied could be at a number of different voltages. The USB family is supplied 5 V at 500 mA to 1000 mA. A cigarette lighter adaptor would take over 13 V at several amps if possible. Other variations are possible. In order to determine what voltage and current should be provided, the PSA can use a sense resistor on a cable pin to determine the nature of the load and dynamically adjust the voltage of its power output accordingly. 
         [0036]    Some embodiments of PSA  100  according to the present invention provide for charging of battery  122  in any charge state, including completely discharged, from solar cell  124  with no other source of power provided. Such a charging system has been described in U.S. application Ser. No. 12/831,392. 
         [0037]      FIGS. 2A and 2B  illustrate an example of PSA  100  according to some embodiments of the present invention. As shown in  FIG. 2A , PSA  100  includes a base  212  and a top cover  214 . Base  212  houses the electronics shown in  FIG. 2A  as well as solar cell  124 . Cover  214  attaches to base  212  and covers solar cell  124 . Further shown in  FIG. 2A  is connector  106 , which is covered by a protective covering  218 . Further, PSA  100  may include foldable legs  210  that can be adjusted to position PSA  100  for best collection of solar radiation. In some embodiments, foldable legs  210  open to locking positions and are attached to base  212  using detents that allow movement of legs  210  in one direction. In some embodiments, legs  210  lock into place at locations designed to provide optimal photovoltaic performance depending upon the PSA&#39;s latitude or the amount of daily solar variation encountered. 
         [0038]    Further, one or more mounting holes  216  may be included to allow PSA  100  to be firmly attached to another platform. Further, in some cases, a locking mechanism (for example a chain and lock) can be provided to fix PSA  100  to an external structure through mounting holes  216 . 
         [0039]    As is further shown in  FIG. 2A , PSA  100  may include indicator access  222  through which lighted indicators can be viewed. In general, indicator access  222  can provide access for the viewing of any number of indicator lights. Further, although not shown in the embodiment shown in  FIG. 2A , access cover  214  may further include access for viewing of display  108   
         [0040]      FIG. 2B  illustrates a slightly different perspective of the embodiment of PSA  100  illustrated in  FIG. 2A . In  FIG. 2B , ventilation holes  220  in base  212  are shown. Further, ventilation  224  under top cover  214  is shown. Ventilation holes  220  and  224  provide cooling for PSA  100  by providing cooling flow for electronics and, through top cover  214 , providing cooling to solar cell  124 . 
         [0041]      FIG. 2C  illustrates an embodiment of PSA  100  that includes a display  108 . Display  108  can be visible through cover  214 , as shown in  FIG. 2C . Display  108  can be positioned anywhere on the face of PSA  100 . Some embodiments of the invention can utilize both display  108  and indicators  222 . 
         [0042]      FIG. 3  illustrates another embodiment of PSA  100  that includes a solar concentrator  310 . Solar concentrator  310 , as shown in  FIG. 3 , includes reflectors  322  and  324  that concentrate solar radiation onto solar cell  124 . The dominant cost in any solar energy system is the solar cells. By comparison reflective materials such as reflectors  322  and  324 , whether made out of metals, Mylar, or other materials, are very inexpensive. Increasing the amount of incoming solar radiation by using reflectors  322  and  324 , therefore, can make economic sense. 
         [0043]    Reflectors  322  and  324 , if made of a heat conductive material, may provide a heat sink capability for PSA  100 . There are several reasons why this matters. The performance of solar cell  124  degrades as its temperature warms, so keeping solar cell  124  cool improves its performance. Electronics  130  may fail if the temperature gets too warm as they are typically the weakest link from a temperature perspective with circuits starting to fail when the temperature rises above 65° C. In some embodiments, reflectors  322  and  324  can dissipate a large amount of heat in order to help cool PSA  100 . 
         [0044]    For a given solar cell, the size of reflectors  322  and  324  and their orientation to the plane of the solar cell are important considerations. Studies of the performance of reflectors have shown that a pair of reflectors  322  and  324 , each twice as long as solar cell  124 , and mounted at a 60° angle relative to the plane of solar cell  124  represent an optimal arrangement with PSA  100  oriented north/south. In some embodiments, reflectors  322  and  324  are twice as long as solar cell  124 . In some embodiments, reflectors  322  and  324  are mounted at an angle of about 60° from the plane of solar cell  124 . In some embodiments, reflectors  322  and  324  are centered on the plane of solar cell  124 . In some embodiments, PSA  100  can be oriented such that solar cell  124  is oriented north/south such that reflectors  322  and  324  are in the east/west position. 
         [0045]      FIG. 3  illustrates an embodiment of PSA  100  with reflectors oriented at about a 60° angle to solar cell  124  and which are twice the length of solar cell  124 . Although these parameters are utilized in the specific embodiment, one skilled in the art will recognize that other shapes and orientations may also function. Further, in some embodiments, reflectors  322  and  324  may be shaped to provide focusing of light onto a smaller solar cell surface. 
         [0046]    As is further shown in  FIG. 3 , mounting holes  216  can include multiple mounting holes. Further shown in  FIG. 3  are electrical connections  312  and  314  from solar cell  124  to a circuit board at connections  316  and  318 . In some embodiments, solar concentrator  310  may be added or removed to the photovoltaic system. In some embodiments, the reflectors of solar concentrator  310  possess an optimal geometry with respect to the solar cell. 
         [0047]    Some embodiments of PSA  100  provide solar charging capability of small appliances in sometimes severe environmental conditions. Therefore, some embodiments of PSA  100  are structurally strong and resist damage due to rough handling and rough conditions. Further, some embodiments of PSA  100  are waterproof to resist damage due to water immersion or wet conditions. 
         [0048]    A solar cell, such as solar cell  124 , which may be utilized in PSA  100 , is expected to have a long lifetime. Expectations of over 20 years for solar cell  124  are not unreasonable if PSA  100  is not mistreated. However, electronics  130  and battery  122  are both expected to have different lifecycles which are significantly shorter than that of solar cell  124 . In some embodiments, components like reflectors  322  and  325 , batteries  122 , legs  210 , and electronics  130  can be individually replaceable in order that the lifetime of PSA  100  is not limited to the shortest lifetime component. 
         [0049]    In some embodiments, PSA  100  as shown in  FIGS. 1 ,  2 A,  2 B, and  3  includes one or more solar cells  124 , a battery  122 , electronics  130  coupled to store photovoltaic energy from the one or more solar cells in the battery, and a structurally resilient base  212  that houses the one or more solar cells  124 , the electronics  130 , and the battery  122 . In some embodiments, the PSA further includes reflectors  322  and  324  coupled to the base to increase solar power incident on the one or more solar cells  124 . 
         [0050]      FIGS. 4A ,  4 B, and  4 C illustrate embodiments of a base  212  according to some embodiments of the invention. As shown, base  212  can be formed of polycarbonate and includes ventilation holes  220  for heat dissipation. In some embodiments, solar cell  124 , battery  122 , and electronics  130  are mounted to base  212 , as shown below. In some embodiments, base  212  includes rib supports  414  and  412  on which a plate can be fixed. Supports  412  and  414  distribute any load stress placed on PSA  100  to base  212 . As is further shown, base  212  includes one or more holes  216  for the purpose of securing PSA  100  to an external structure. Further, base  212  can include a mount  416  to hold connector  106 . In addition, rib supports  414  and  412  can be placed to facilitate the flow of air through base  212 , thereby more efficiently cooling PSA  100 . Support ribs  412  provide further support and structure on which a plate (not shown) that includes some further components of PSA  100  can be mounted. 
         [0051]      FIGS. 5A and 5B  illustrate assembly of a PSA  100  according to some embodiments of the invention. As shown in  FIG. 5A , solar cell  124  is mounted on a heat sink  510  and electrically coupled to wiring  512 . Wiring  512  is coupled to printed circuit board (PCB)  514 , that is mounted onto heat sink  510 . Heat sink  510  and circuit board  514  are mounted in base  212 . In some embodiments, an o-ring seal  516  is made between PCB  514  and base  212  in order to provide a water proof environment for the electronics on PCB  514 . Electronics  130  is at least partially included on PCB  514 . Legs  212  are mounted to base  210 . As shown in  FIG. 5A , heat sink  510  can be attached to base  212  with screws  524 . Battery  122 , which can include a base plate  518 , battery component  520 , and cover  522 , are mounted in base  212  opposite heat sink  510 . In the embodiment shown in  FIG. 5A , cover  526 , which may be a polyurethane sheet or may be cover  214 , is mounted over heat sink  510  in order to cover solar cell  124 . 
         [0052]      FIG. 5B  illustrates another assembly of a PSA  100  according to some embodiments of the present invention. As shown in  FIG. 5B , solar cell  124  is mounted on heat sink  510 . Leads  312  and  324  are coupled to circuit board  514  through access holes  542 . A metal plate gasket  530  is mounted between circuit board  514  and heat sink  510 . Heat sink  510  is screwed into base  512  with screws  524 . Gasket  516  helps seal the electronics on PCB  514 . Further, a resin injection gasket  544  can be included to help in potting the electronics. Reflectors  322  and  324  can be screwed into base  212  with screws  536  and nuts  534 . In the embodiment shown in  FIG. 5B , battery  520  is placed in base  212  and sealed in place with gasket  538  between base  212  and cover  522 . Cover  522  is mounted to base  212  with screws  540 . 
         [0053]    Some embodiments of PSA  100  according to aspects of the present invention can withstand shocks. In particular, these embodiments may withstand shear forces which are parallel or tangential to the face of solar cell  124 . Some embodiments of the PSA may also withstand normal forces which are perpendicular to the face of solar cell  124 . These forces can be visualized as dropping the PSA from a height, or riding over the PSA with a cart, for example. In some embodiments, PSA  100  dissipates heat. In some embodiments, the one or more solar cells  124  are encapsulated with a resin (for example, urethane) to a metal substrate heat sink  510 . In some embodiments, the thickness of the resin is determined by the Young&#39;s modulus (E) and Poisson ratio of the resin. 
         [0054]    Solar cell  124  itself is as delicate as a potato chip. Without proper protection, solar cell  124  will crack and become nonfunctional. As shown in  FIGS. 5A and 5B , solar cell  124  is attached to a heat sink  510 . Heat sink  510  can be made from steel, although other substances such as a tin-aluminum alloy may be utilized. In some embodiments, solar cell  124  is bonded to heat sink  510  using a very hard resin. As shown, heat sink  510  can then be mounted on a base  212 , which can be a polycarbonate base with supports  414  and  412  that deflect any loading stress to the bottom of PSA  100 . Solar cell  124  and heat sink  510  together can be encapsulated with a resin of urethane  526 , as shown in  FIG. 5A . 
         [0055]    This encapsulation of solar cell  124  with urethane achieves several things: It protects solar cell  124  from environmental factors; It allows light to reach solar cell  124  because resin cover  526  has a high transmissivity and permits light of the right wavelength to hit solar cell  124 ; It performs heat conduction to heat sink  510 , thereby cooling solar cell  124 ; and It will self heal small scratches over time. In some embodiments, the gap between solar cell  124  and the heat sink  510  can be minimized, maximizing thermal transfer and keeping the temperature of solar cell  124  down. The metal plate of heat sink  510  can dissipate heat into ventilated base  212 . However, the gap between solar cell  124  and heat sink  510  can not be too small otherwise the urethane will transfer too much stress, which results from the thermal expansion of heat sink  510 , to solar cell  124 . Under stress, solar cell  124  may form cracks. 
         [0056]    Embodiments of PSA  100  can be constructed with many mechanical factors in mind: shear modulus G of cover  526 ; Young&#39;s modulus of solar cell  124 ; Young&#39;s modulus of heat sink  510 ; coefficient of thermal expansion of solar cell  124 ; and the coefficient of thermal expansion of heat sink  510 . In some embodiments, the various factors can be balanced to protect solar cell  124  from the environment and to maximize the transmissivity of light to solar cell  124 . Because light heats solar cell  124 , the heat should be diverted as much as possible to prevent the degradation of the performance of solar cell  124 . To dissipate the heat effectively, heat sink  510  should be excellent at thermal conduction, should be mechanically strong, and should have a low coefficient of thermal expansion. A metal substrate such as steel or aluminum has many of these characteristics. Steel is heavier but does not thermally expand as much as aluminum. Aluminum is lighter, but expands nearly twice as much as steel. 
         [0057]    The gap between solar cell  124  and heat sink  510 , the mechanical properties of the urethane, and the mechanical properties of heat sink  510  can all be varied. As a heat sink, aluminum expands twice as much as steel, however steel is heavier. All other variables are fixed: solar cell yield strength, the solar cell&#39;s Young&#39;s modulus, and the thermal coefficient of expansion of the solar cell. Once the substrate material for heat sink  510  is chosen, the substrate&#39;s Young&#39;s modulus, and the substrate&#39;s coefficient of thermal expansion are also fixed parameters. However, the thickness and composition of the urethane can still be modified. 
         [0058]    The Young&#39;s modulus and the Poisson ratio of the urethane separating solar cell  124  and heat sink  510  determine the size of the gap (e.g., the thickness of the urethane). Young&#39;s modulus (E) is a measure of the stiffness of an isotropic elastic material. Modulus E is the ratio of stress, which has units of pressure, to strain, which is dimensionless. Therefore, Young&#39;s modulus itself has units of pressure. Poisson&#39;s ratio is defined as the ratio of the relative contraction strain, or transverse strain, normal to the applied load to the relative extension strain, or axial strain, in the direction of the applied load. The general formula for sheer modulus G, which describes a material&#39;s response to shearing strains, is G (shear modulus)=E (Young&#39;s modulus)/2(1+Poisson&#39;s ratio)=(F/A)(d/x), where F/A is the pressure applied (for example due to thermal expansion), d is the initial thickness of the urethane resin, and x is the lateral displacement of the urethane resin due to the stress. Ideally, the urethane resin should be hard to the touch and hard to scratch, but not so hard that the Young&#39;s Modulus gets larger, which in turn can increase the desired thickness of the urethane resin. 
         [0059]    Additionally, as is shown in  FIGS. 4A ,  4 B, and  4 C, in some embodiments heat sink  510  is supported against a series of supports  414  and  412  in base  212  in order that forces applied to PSA  100  do not bend heat sink  510 , and thereby crack solar cells  124 . In some embodiments, base  212  is structurally resilient to help withstand rough handling. In some embodiments, base  212  can be formed of polycarbonates. Polycarbonates are a particular group of thermoplastic polymers. They are inexpensive, easily worked, molded, and thermoformed. Polycarbonates have temperature and impact resistance. Injection molded polycarbonates are very strong. Typical mechanical properties of a polycarbonate for forming a base such as that shown in  FIGS. 4A ,  4 B, and  4 C are as follows: the Young&#39;s modulus (E) of 2-2.4 GPa, tensile strength (σt) of 55-75 MPa, and compressive strength (σc)&gt;80 MPa. The thermal properties of a typical polycarbonate material are as follows: working temperature range is from 130° C. to −135° C., the linear thermal expansion coefficient (σ) is 70×10 −6 /K, the specific heat capacity (c) is 1.3 kJ/kg·K, the thermal conductivity (k) at 23° C. is 0.21 W/(m·K), and the heat transfer coefficient (h) is 0.21 W/(m 2 ·K). 
         [0060]    In some embodiments, as shown in  FIGS. 4A ,  4 B, and  4 C supports  414  provided by base  212  are arranged to provide air flow cooling to the back of heat sink  510  in order to help cool PSA  100 . In addition to the physical stresses applied to solar cells  124  by temperature changes, the efficiencies of solar cells  124  are affected by heat. As the cells warm they become less efficient. A typical degradation in efficiency percentage would be −0.41% per ° C. for temperatures above 25° C. On Sep. 13, 1922, a temperature of 136° F. (57.8° C.) was recorded in the city of Al &#39;Aziziyah, Libya. This is the highest temperature ever recorded. Assuming PSA  100  can be kept at thermal equilibrium the worst case environmental circumstance would be about 58° C. In some embodiments of the invention, thermal load management by PSA  100  can be an important issue. 
         [0061]    As shown in  2 B and  4 A,  4 B, and  4 C, some embodiments of PSA  100  have positioned vents  220  and supports  414  to provide for air circulation through PSA  100  under heat sink  510 . The base also holds battery  122  and electronics  130 , which may also be cooled with vents  220  and supports  414 . 
         [0062]    In addition, some embodiments of PSA  100  can be waterproof. This is illustrated in  FIGS. 5A and 5B  where various gaskets and seals are shown in the construction. In some embodiments, for example, a NEMA classification of 6P can be achieved, providing for a PSA  100  that can be submersible to a depth of several feet. As shown in  FIG. 5B , battery  122 , which can be a lithium-ion polymer, can be kept in a watertight compartment formed by base  212  and cover  522  with a rubber gasket  538  as a seal. When battery  122  is replaced, the entire battery cover  522  with a new rubber gasket  538  can be installed. In some embodiments, PSA  100  can have positive buoyancy in water so that it floats. 
         [0063]      FIG. 6A  illustrates assembly of PSA  100  according to some embodiments for the present invention. As shown in  FIG. 6A , solar cell  124  and PCB  514  can be mounted to heat sink  510 . A metal gasket  530  may be placed between PCB  514  and heat sink  510 . A gasket  620  can be placed over PCB  514  and PCB  514  be covered with cover  622 . The electronics on PCB  514  may be potted through cover  622 . Solar cell  124  may be epoxyed to heat sink  510  and then encapsulated with, for example, a urethane layer over solar cell  124 . As shown in  FIG. 6A , cell leads  312  and  314  are coupled to solar cell  124  and connected to PCB  514  during the assembly process. Cover  214  may then be placed over heat sink  510  and the assembly connected, for example by screws, to base  212 . 
         [0064]    As further illustrated in  FIG. 6A , foot assembly  612  and legs  610  may also be provided. Foot assembly  612  can include plastic detents  532  as shown in  FIG. 5B , or may include metal spring parts as illustrated in  FIG. 6A . Once assembled, a connector cover  218  can be inserted into base  212 . 
         [0065]    As shown in  FIG. 6A , battery  122  includes a base  518 , a battery component  520 , and a cover  522 . Battery  122  can be inserted into the bottom of base  212  and screwed into place through cover  522 . 
         [0066]      FIG. 6B  further illustrates assembly of PSA  100  according to some embodiments of the present invention. As shown in  FIG. 6 , PSA  610  is formed by cell assembly  610 , foot assembly  612 , legs  216 , and base  212 . A battery  122  such as that shown in  FIG. 6A  is also included. As shown in  FIG. 6B , cell assembly  610  includes solar cell  124  and PCB  514 . Further, cell assembly  610  can include cover  214 . 
         [0067]      FIGS. 7A and 7B  illustrate foot assembly  612  according to some embodiments of the present invention. As shown in  FIG. 5B , legs  210  can be mounted with detents  532 . Detents  532  can be formed from plastic or from metal. Foot assembly  612  shown in  FIGS. 6 ,  7 A, and  7 B provide a more robust mounting for legs  212 . The leg supports  212  for PSA  100  should be robust and undergo extension and retraction multiple times over the lifetime of the PSA. Foot assembly  612  includes several metal springs  712 ,  714 , and  716  along with a foot detent  710 , which can be made from spring metal or from spring plastic. Metal springs provide a substantially increase in the lifecycle of detent  532  over plastic. Metal springs  712 ,  714 , and  716  along with detent  710  can be held in place by screws  718  to base  212 . Legs  212  are held in place by springs  710 ,  712 ,  714 , and  716 . 
         [0068]      FIGS. 8A and 8B  illustrate utilization of a light pipe  810  to carry light from printed circuit board  514  through cover  212  to indicates  222 . Light pipes  810  can be utilized to carry colored LED light signals from electronics on printed circuit board  514  through cover  212  so that they are visible to a user. In some embodiments, light pipes  810  can be potted with urethane. 
         [0069]    As is further illustrated in  FIGS. 8A and 8B , cover  212  may include ventilation access  820 . Ventilation access  224  allow for cooling of the front side of solar cell  124  during operation. Top cover ventilation helps to keep PSA  100  at ambient temperature. With base  212  ventilated with vent holes  220 , top portion vents  224 —help to prevent additional heat buildup. Solar cell performance declines with increasing heat and therefore additional ventilation can help improve performance. The PSA top cover  212  can be ventilated on each side and can be anchored to PSA  100  with screws at each corner. The top cover can further be attached to PSA  100  when solar cell  124  is encapsulated with urethane adding additional stability. 
         [0070]      FIGS. 9A ,  9 B,  9 C, and  9 D illustrate formation of cell assembly  610  according to some embodiments of the present invention.  FIGS. 9A and 9B  illustrate mounting of PCB  514  on heat sink  510  while  FIGS. 9C and 9D  illustrate mounting of solar cell  124  on the opposite side of heat sink  510 . 
         [0071]    The electronics of PSA  100  can be potted. In electronics, potting is a process of filling a complete electronic assembly with a solid compound for a specific purpose. Thermosetting plastics are typically used, and some embodiments of PSA  100  include a colored thermo-plastic potting material. In some embodiments, the PSA electronics can resist both shock and vibration. In addition, the electronics can be immune from the effects of moisture and corrosive agents. Potting will exclude these to a great extent. Another rational for potting has to do with replacement. When the electronics fail they can be replaced. Potted electronics will be easier to handle throughout this process. Using a colored potting agent will provide a level of security with respect to the electronics design and the components used. 
         [0072]    As shown in  FIG. 9A , circuit board  514  is mounted on heat sink  510 . Heat sink  510  includes through holes  910  for mounting to base  212  and mounting hole  216  as described above.  FIG. 9B  shows a cross sectional view of PCB  514  mounted to heat sink  510 . As shown in  FIG. 9B , PCB  514  can be attached to heat sink  510  with an epoxy layer  920 , or layer  920  may be a metal gasket  530  as shown in, for example,  FIG. 6A . In general, PCB  514  can be affixed to heat sink  510  in any way, including screwing PCB  514  into heat sink  510 . As shown in  FIG. 9B , light guide  810  can be mounted to printed circuit board  514  as PCB  514  is mounted to heat sink  510 . A cover  622  can be placed over PCB  514 . Cover  622  can include holes  924  and  926  to serve as vent and access for potting. In general, there can be any number of holes  924  and  926 . 
         [0073]    Cover  622  creates a small but sufficient volume for urethane to pot the electronics on PCB  514 . Cover  622  is placed over PCB  514  and gasket  620 , which can be a very high bond (VHB) tape, ensures that there is no urethane leak during potting. During injection through one of holes  926  and  924 , the tip of the static mixer sits against an off the shelf O-ring to ensure once again a leak free operation since urethane can be very messy, creates a quality control issue, and may increase the cost and weight of PSA  100 . The other of holes  926  and  924  allow the air to exhaust as urethane is filling the volume of cover  622 . Although two holes, holes  926  and  924 , are shown in  FIG. 9B , there may be any number of holes to facilitate the potting process. For example, in some embodiments holes  926  and  924  may include one fill hole through which the urethane is inserted and two vent holes through which air is vented. Once the urethane has cured, holes  926  and  924  are cut-off. Typically, urethane takes at least two hours to cure. 
         [0074]      FIGS. 9C and 9D  illustrate bonding and potting of solar cell  124  on the opposite side of heat sink  510  from PCB  514 . This process can be accomplished in parallel with the mounting and potting of PCB  514  described with  FIGS. 9A and 9B . 
         [0075]    As shown in  FIG. 9C , multiple drops  930  of urethane are positioned onto the surface of heat sink  510  and are allowed to cure for a set period of time. For example, for Z-6644 urethane, a cure time of two hours is possible. With a different urethane the time could be very different). This bonding can be done in parallel with the potting of the electronics as shown in  FIGS. 9A and 9B . In some examples, 16 drops  930  of urethane can be positioned on heat sink  510 . Curing can be accomplished in a curing chamber. 
         [0076]    While drops  930  are curing, a Solar Cell  124  can be positioned in a bonding station. After 2 hours heatsink  510  is removed from the curing chamber and drops  930  are soft enough to still be deformed, sticky enough to still bond to solar cell  124  and stiff enough to push solar cell flat  124  against the bottom surface of the bonding station. This combination insures that solar cell  124  becomes flat after tabbing wires  312  and  314  have been soldered to it. A flat solar cell  124  with an even gap between solar cell  124  and heatsink  510  to facilitates a successful encapsulation. The clamps on the bonding station ensure that heatsink  510  is as flat as possible. 
         [0077]    When heatsink  510  is clamped on the bonding station, the urethane drops  930  are compressed and deformed to create, after cure, a great way to firmly hold solar cell  124  in place until encapsulated. Also, since urethane sticks very well to urethane these urethane drops  930  get immersed by fresh urethane during encapsulation to form an homogeneous layer of bubble free urethane under solar cell  124 . This process is shown in  FIG. 9D . As shown in  FIG. 9D , a urethane film  932  is applied over solar cell  124 . 
         [0078]    Currently the nominal gap between solar cell  124  and heatsink  510  can be as low as 0.3 mm. The gap between solar cell  124  and heatsink  510  should be as low as possible in order to maximize heat transfer and keep solar cell  124  as cool as possible. As discussed above, solar cells reduce their power performance as temperature increases. For mono-crystalline cells, for example, the reduction in performance is about 0.41±0.05%/° C. above 25° C. After encapsulation, cover  214  can be installed over heatsink  510  to form cell assembly  610 , which is affixed to base  212  by screws. 
         [0079]    In some embodiments, the system is waterproof. In some embodiments, the system is waterproof to a depth of at least one meter. In some embodiments, the electronics, substrate, and solar cell are encapsulated and potted simultaneously. In some embodiments, PSA  100  has positive buoyancy in water or seawater. 
         [0080]    Embodiments described here are exemplary of the invention only and are not to be considered limiting. One skilled in the art will recognize numerous variations on the embodiments described here. Those variations should be considered to be included in the scope of this disclosure. As such, the invention is limited only by the following claims.