Patent Publication Number: US-2021184485-A1

Title: Portable solar power management system

Description:
INCORPORATION BY REFERENCE 
     An Application Data Sheet is filed concurrently with this specification as part of this application. Each application to which this application claims benefit or priority as identified in the concurrently filed Application Data Sheet is incorporated by reference herein in its entirety and for all purposes. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a portable system for energy management; in particular, the present invention relates to a portable system for capturing and managing solar energy for use in lighting and other applications of a health care facility in a rural area. 
     2. Discussion of the Related Art 
     Many parts of the world still lack a reliable source of electricity for supporting essential health care services (e.g., mid-wife services or other emergency services) provided after dark. The required source of electricity is essential to provide adequate lighting for patient examination and power to operate simple diagnostic devices or to perform simple medical procedures. In the past, diesel or gasoline-powered local generators are often used. However, such systems are not only costly to acquire and maintain, their operations also depend on fuel being reliably accessible and available, which is often not the case. In addition, these local generation systems require some level of expertise to operate, which may not be readily available in many locations. Consequently, such local generation systems are seldom efficiently used, or are able to remain serviceable over even a significant fraction of their expected lifespan. These local generation systems also require the facility to provide infra-structure support (e.g., semi-permanent wiring), as they are not portable. Thus, the fact still remains that after-dark essential health care services are denied to many communities because of a lack of reliable source of electricity. 
     Therefore, there is a long-felt need for a portable power management system (e.g., one that can be transported in a protective container, such as a suit case) that can provide adequate lighting for patient examination, and power to operate simple diagnostic devices or to perform simple medical procedures. 
     SUMMARY 
     According to one embodiment of the present invention, a power management system includes (i) a solar panel interface to one or more solar panels, the solar panel interface providing wiring for: (a) receiving solar panel sensing signal representative of a voltage in the solar panels and (b) conducting one or more electrical currents received from the solar panels; (ii) an energy storage interface to one or more energy storage devices, the energy storage interface providing wiring for: (a) receiving an energy storage sensing signal representative of a voltage in the energy storage devices and (b) conducting one or more electrical currents received from or provided to the energy storage devices; (iii) a charging circuit which routes the electrical currents from the solar panels to the wiring for conducting electrical currents received from or provided to the energy storage devices; (iv) a load interface to one or more load devices, the load interface providing wiring for: (a) receiving a load sensing signal representative of a voltage in the load devices and (b) conducting one or more electrical currents in each of a primary load circuit and a secondary load circuit; and a (v) controller for operating the solar panel interface, the energy storage interface, the charging circuit and the load interface. 
     According to one embodiment of the present invention, the power management system further includes (i) a programmable controller in the secondary load circuit receiving the solar panel sensing signal, the energy storage sensing signal and the load sensing signal; and (ii) a load control circuit which routes the electrical currents from to the energy storage devices to the wiring for conducting electrical signals in the load interface, the load control circuit being capable of activating or deactivating the secondary load circuit independently of the primary load circuit. Based on the states of these signals, the programmable controller activates and deactivates power supplied to load devices in the secondary load circuit. 
     The power management system may include a housing that encloses the solar panel interface, the energy storage interface, the charging circuit, the load interface, the controller, at least one of the solar panels and at least one of the energy storage devices. In that configuration, the management system is portable. In one embodiment, the housing further encloses the programmable controller and the load control circuit. The energy storage devices may be provided by one or more lead acid batteries or lithium ion batteries. According to one embodiment of the present invention, for lithium ion batteries, the programmable controller may execute a method for waking up the battery. The method may perform the battery wake-up operation when one or more of the following conditions are satisfied: (a) the suitcase battery does not present a usable voltage, (b) the solar panel sensing signal indicates a voltage suitable for performing a charging operation on the battery, (c) previous wake-up operations have not exceed a predetermined maximum number; and (d) an elapsed time between the wake-up operation and an immediately preceding wake-up operation exceeds a predetermined time period. 
     In one embodiment, to ensure that priority is given to lighting, the programmable controller maintains a score relevant to determining whether to activate or to deactivate the secondary load circuit. The score may be increased when the solar panel sensing signal and the load sensing signal both indicate a favorable power condition. The score may be decreased when the solar panel sensing signal and the energy storage sensing signal together indicate an unfavorable condition for charging the energy storage devices, or when the energy storage sensing signal indicates that the energy stored in the energy storage devices is less than a predetermined value. In one instance, the secondary load circuit is activated for a predetermined time period when the score exceeds a predetermined value. In addition, the secondary load circuit may be deactivated when the energy storage sensing signal indicates that the energy stored in the energy storage devices is less than a predetermined value. Under that condition, the score is set to zero upon deactivating the secondary load circuit. 
     According to one embodiment of the present invention, the power management system includes one or more light emitting diode-based (LED) lights operating on the primary load circuit. In that example, each of the LED lights is capable of being dimmed in response to a control signal from the controller. In one example, the amount of dimming depends on the duty cycle of the control signal. The controller determines the duty cycle based on the solar panel sensing signal, the energy storage sensing signal and the load sensing signal. In addition, each of the LED lights is capable of being programmed to be dimmed to a predetermined minimum brightness. 
     The present invention is better understood upon consideration of the detailed description below, in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1( a )  shows a block diagram of portable power management system  100 , in accordance with one embodiment of the present invention. 
         FIG. 1( b )  shows a block diagram of circuit  200 , which is an implementation of an optional plug-in accessory to circuit  152  of power management system  100 , in accordance with one embodiment of the present invention. 
         FIGS. 2 ( a   1 ),  2 ( a   2 ),  2 ( a   3 ), and  2 ( b ) show smart box circuit  200  in further detail schematically, in accordance with one embodiment of the present invention. 
         FIGS. 3( a ), 3( b ), and 3( c )  show circuit  300 , which represents an LED light that can be actively dimmed to under computer control, in accordance with one embodiment of the present invention. 
         FIG. 4  illustrates a method executed in CPU  270  for asserting control signal  212 , which activates battery wakeup circuit  201 , in accordance with one embodiment of the present invention. 
         FIG. 5  illustrates a method for ensuring priority is given to using the battery&#39;s energy to provide lighting, in accordance with one embodiment of the present invention. 
         FIGS. 6( a ) and 6( b )  show, respectively, back and front views of an LED light assembly  600 , according to one embodiment of the present invention. 
         FIG. 6( c )  provides the back view of housing  650  with back plate  602  and a printed circuit board (PCB) removed. 
         FIG. 6( d )  shows PCB  651  on which numerous LED devices may be mounted; PCB  651  may be mounted on housing  650 . 
         FIG. 6( e )  shows hanger  601  by itself. 
         FIG. 6( f )  shows housing  650  being fixed to one of the groves in pattern  606 , with back surface  603  forming a 45° angle relative to arms  601   a  and  601   b.    
     
    
    
     To facilitate cross-referencing among the figures, like elements are assigned like reference numerals. 
     DETAILED DESCRIPTION 
     To overcome the deficiencies of the prior art, the present invention provides a portable solar power management system that receives and stores solar energy in the daytime, and which dispenses power during the day and after dark. Such a portable power management system is suitable for use at a small to medium size health center (HC) in certain parts of the developing world. Typically, such an HC may be on or off a power grid. Thus, the solar power management system may be relied upon as a primary source of energy, a back-up system, or a cost-reduction device for a room in such a facility. In this detailed description, portable solar power management systems designed for maternal and child health (MCH) applications are used to illustrate the present invention. In a MCH application, the portable solar power management system provides sufficient power for illumination and sufficient power to perform delivery services or a C-section. The present invention is, of course, not so limited. As the systems according to the present invention are portable, they can be easily transported to support emergency response after a natural disaster, or to be used in any temporary installation. 
       FIG. 1( a )  shows a block diagram of portable power management system  100 , in accordance with one embodiment of the present invention. Portable power management system  100  is designed to allow its components and selected accessories to be packed in a suit case for portability. In one embodiment, the suit case measures approximately 20×16 by 8 inches and weighs about 35 pounds. In general, such a suit case may be considered portable if it can be transported manually without difficulty using no more than two average able-bodied adults. As shown in  FIG. 1 , portable power management system includes one or more solar panels  101  that are expected to be kept in the sunlight to capture solar power during operation and are sized to fit also in the suit case during transportation. Each of solar panels  101  may be built out of photovoltaic cells to provide a maximum output power of approximately 20 watts, at a nominal output voltage of at least about 12 volts. Under control of controller  102 , output currents of the solar panels  101  may be used to charge energy storage devices  106  and  107 . In one implementation, energy storage device  106  is a battery built into the suit case, while storage device  107  may be an optional additional battery that can be connected to portable power management system  100 . Each of storage devices  106  and  107  may be a commercially available sealed lead acid battery or a lithium iron phosphate battery. These batteries also operate at approximately 12 volts. To prevent an over-voltage condition in the battery charging circuit, the input terminals of the batteries (and, hence, also the output terminals of solar panels  101 ) are limited by controller  102 . When the battery is a type of lithium ion battery, a protective method to recover from battery over-discharge by “waking up” the battery may be provided, in accordance with the present invention, as illustrated in detail by flow chart  400  of  FIG. 4 , which is discussed in further detail below. Other batteries may also be used, with controller  102  providing suitable control of the charging process. 
     The power stored in the batteries is used to supply power to circuits  151  and  152 . Circuit  151  is designed for supplying power to lighting. In one embodiment, circuit  151  may provide high-efficiency, rugged and water-resistant light emitting diode (LED) lights. Typically, each such light may provide very bright white spectrum light (e.g., 5400° to 5600° K) at 2-8 watts, suitable for medical procedure use. As providing lighting after dark is an important purpose for the present invention, to avoid inadvertent inappropriate use or abuse, circuit  151  supplies only sockets for special lighting connectors (e.g., M12 light connectors). In  FIG. 1( a ) , these sockets are represented by primary circuits  103 . In one embodiment, additional circuit sockets, represented extension circuits  108 , may be provided by connecting a satellite kit on which the additional sockets are mounted. The satellite kit may be used to provide lighting, for example, in an adjacent room without its own portable power management system. 
     Circuit  152  is provided to provide power to operate low-power electronic devices, such as handheld medical diagnostic devices, cellular telephones, and portable computers. As after-dark lighting is deemed more essential, circuit  200  is included to activate circuit  152  only when an adequate level of energy has been stored in the batteries. This operation is discussed in further detail below in conjunction with  FIG. 5 . Circuit  152  may supply power through various outlets of different convenient voltages, represented in  FIG. 1( a )  by secondary circuit  105 . These power outlets may be, for example, automotive power outlets (e.g., 12 volts standard cigarette lighter sockets), 12-volt binding posts, and USB sockets. These sockets may supply power to communication or computation devices (e.g., cellular telephones, tablet or notebook computers), or medical or diagnostic equipment (e.g., portable fetal heart rate Doppler sensor, examination headlamps, blood pressure meters). Communication devices have become increasingly useful as diagnostic devices because remote diagnostic techniques have come into greater use. 
     Power switch  104  is prominently located to ensure easy access should system shut down be necessary under emergency conditions. 
     Controller  102  also provides a user interface for communicating operational information regarding power management system  100 . For example, portable power management system  100  includes LED lights to indicate battery charging and battery charge status. In addition, a liquid crystal display (LCD) panel may also be provided to indicate the current output voltage of the batteries, the charging current from solar panels  101 , and the total output currents being drawn in circuits  103 ,  151 , and  152 . 
     In one embodiment, circuit  152  may include an optional “plug-in” accessory (“smart box”) that provides control to “luxury load” and to waking-up an over-discharged lithium ion battery.  FIG. 1( b )  is a block diagram of circuit  200 , which is an implementation of the smart box according to one embodiment of the present invention. As shown in  FIG. 1( b ) , circuit  200  interfaces circuit  152  through connector  172 , which includes solar panel sensing signal  181 , battery sensing signal  182 , and load sensing signal  183 . In one embodiment, (i) solar panel sensing signal  181  indicates a voltage supplied by solar panels  101 , which may be between 0 and 25 volts; (ii) battery sensing signal  182  indicates a voltage supplied by energy storage devices  106  or  107 , which may be between 0 and 14 volts; and load sensing signal  183  indicates a voltage of load devices, which may be between 0 and 14 volts. The sensing signals are received in to microcontroller  176 , which controls lithium battery wake-up circuit  171  for waking-up an over-discharged lithium battery and luxury load switch  174 . Luxury load switch  174  activates circuit  152  in accordance with the load management method described below in conjunction with  FIG. 5 . Power supply circuit  163  provides a supply voltage to operate microcontroller  176 . The operation of microcontroller  176  augments the control operations of controller  102  of  FIG. 1( a ) . 
       FIGS. 2 ( a   1 ),  2 ( a   2 ), ( 2   a   3 ), and  2 ( b ) show smart box circuit  200  in further detail schematically, in accordance with one embodiment of the present invention.  FIG. 2( b )  shows a programmable controller in circuit  200  which is implemented using central processing unit (CPU)  270 .  FIGS. 2 ( a   1 ),  2 ( a   2 ), and  2 ( a   3 ) show the remainder of circuit  200 , including battery wakeup circuit  201 , secondary load circuit  251  and auxiliary input circuit  275 . As shown in  FIG. 2( a ) , battery wakeup circuit  201  is activated by control signal  212  (when conditions illustrated by flow chart  400  of  FIG. 4  are met). 
     As shown in  FIG. 2( b ) , after appropriate low pass filtering, CPU  270  receives sensing signals from (i) the batteries (at terminal  213 ), (ii) solar panels (at terminal  211 ), (iii) load circuit  251  (at terminal  261 ) and auxiliary input circuit  275  (at terminal  264 ), and sending out control signals to activate battery wakeup circuit  201  (at terminal  212 ), the secondary load circuit (at terminal  262 ) and auxiliary input circuit (at terminal  263 ). As shown in  FIG. 2( a ) , each of the sensing signals is low-pass filtered to eliminate glitches. CPU  270  may be implemented, for example, by a microcontroller, such as the ATtiny44, available from Atmel Corporation, San Jose, Calif. 
     Secondary load circuit  105  (“luxury loads”) receives power via secondary load circuit  251  only when solar panels  101  provides an output voltage at terminal  214  that is greater than the battery voltage at terminal  215 . The voltage of solar panels  101  at terminal  215  and the voltage of the battery at terminal  215  are provided to CPU  270  at terminals  211  and  213 , respectively, and are used in the algorithm depicted in flowchart  500  of  FIG. 5 . When conditions discussed in flowchart  500  are met, secondary load circuit  251  is activated by the control signal from CPU  270  at terminal  262 , thereby enabling power to become available to circuit  105  ( FIG. 1 ). 
     Circuit  200  includes power circuit  280 , which supplies the power necessary to operate circuit  200 . As shown in  FIG. 2( a ) , circuit  280  includes a buffer circuit which limits power loss over the wide range of input voltages from the solar power source. Circuit  280  may power circuit  280  from the load (terminal  216 , solar panels (terminal  214 ), or the batteries (terminal  215 ). 
     Auxiliary circuit  275 , which is activated by a control signal at terminal  263  from CPU  270 , switches auxiliary loads as needed. Auxiliary sensing signal at terminal  217  may be an external input signal to circuit  200 , which may be used in conjunction with or separately from auxiliary load circuit  275 , as needed. 
     According to one embodiment of the present invention, an LED light that can be actively dimmed to under computer control may be provided, as illustrated by circuit  300   FIGS. 3( a ), 3( b ), and 3( c ) . As shown in  FIGS. 3( a ), 3( b ), and 3( c ) , circuit  300  includes an array of LEDs  310  being controlled by high-brightness LED driver  311 . High-brightness LED driver  311  may be provided, for example, by a high-brightness LED driver integrated circuit, such as the HV9919, available from Supertex Inc., Sunnyvale Calif., High-brightness LED driver  311  receives a pulse-width modulated (PWM) control signal at terminal  312  whose duty cycles control the brightness of LED  310 . In addition, high-brightness LED driver  311  can be programmed using resistors R 17 , R 18 , R 19 , and R 20  to provide a minimum brightness. CPU  270  may be programmed to provide the PWM controls signal at terminal  312 . 
       FIGS. 6( a ) and 6( b )  show, respectively, back and front views of an LED light assembly  600 , according to one embodiment of the present invention. As shown in  FIGS. 6( a ) and 6( b ) , light assembly  600  includes housing  650  and hanger  601 . As shown in  FIG. 6( a ) , back plate  602  provides a covering to housing  650 . Housing  650  encloses a printed circuit board (PCB) on which numerous LED devices may be mounted. One example of such a PCB is provided by PCB  651  shown in  FIG. 6( d ) . As shown in  FIG. 6( d ) , PCB  651  includes, for example, a 3×12 array of LED devices, together with circuitry for driving the LEDs. PCB  651  may implement, for example, circuit  300  of  FIGS. 3( a ), 3( b ), and 3( c ) . Cable assembly  604  electrically connects PCB  651  to circuit  151  of  FIG. 1( a )  via a through-hole in housing  650 .  FIG. 6( c )  provides the back view of housing  650  with back plate  602  and PCB  651  removed. As shown in  FIG. 6( c ) , housing  650  includes cavity  655  for accommodating PCB  651 , with set-offs  652   a - 652   d  for mounting PCB  651 . Back plate  602  may be a thermally conductive plate (e.g., anodized aluminum), which is designed to contact PCB  651  (e.g., press against a surface of PCB  651 ) to allow heat from the electronics and the LED devices to dissipate through back plate  602 . As shown in  FIG. 6( a ) , back plate  602  is formed with heat sink features (e.g., the parallel raised portions or ridges) to provide increased surface area, so as to facilitate heat dissipation. In one embodiment, front surface  603  is integrally formed on housing  650  using a clear material (e.g., acrylic glass), so that front surface  603  may act as a lens for projection of light from the LED devices in the direction where illumination is desired. A proper treatment of front surface  603  may provide uniform and diffused light from the LED devices. Housing  650  includes through holes  602   a  and  602   b , so that housing  650  may be fixedly mounted on a flat surface, such as a ceiling. Housing  650  also includes threaded hole  605  to allow housing  650  to be screw-mounted in a number of ways, such as a tripod or clamped on to a table top via a “clamp and flexible goose-neck” assembly. 
     As shown in  FIGS. 6( a ) and 6( b ) , housing  650  is attached to hanger  601 , which is independently shown in  FIG. 6( e ) . Hanger  601  allows LED assembly  600  to be relatively portable and be hung at any suitable height to provide illumination. As shown in  FIG. 6( e ) , hanger  601  includes a curved portion for attachment to, for example, a horizontal hanger bar. Hanger  601  also includes arms  601   a  and  601   b  which extend to elbow portions  601   c  and  601   d , respectively. Elbows  601   c  and  601   d  are designed to be inserted into corresponding openings provided on opposite sides of housing  650 , as shown in  FIGS. 6( a ) and 6( b ) . In hanger  601 &#39;s relaxed state, i.e., when not attached to housing  650 , the distance between arms  601   a  and  601   b  at elbows  601   c  and  601   d  is slightly less than the distance between these openings of housing  650 . Radiating from the openings on housing  650  where elbows  601   c  and  601   d  are to be attached is a pattern of groves. In  FIGS. 6( a ) and 6( b ) , the groves are labeled pattern  606 . Each grove in pattern  606  is designed to accommodate one of the arms  601   a  and  601   b . For example, when arms  601   a  and  601   b  are formed with a circular cross section, each grove is formed with a semi-circular cross section with a diameter matching the diameter of arms  601   a  and  601   b . (Arms  601   a  and  601   b  need not have a circular cross section). To attach hanger  601  to housing  650 , arms  601   a  and  601   b  are pulled apart slightly to insert elbows  601   c  and  601   d  into the corresponding openings on housing  650 , so that a spring action in arms  601   a  and  601   b  provides a compressive force to secure arms  601   a  and  601   b  to their respective groves on housing  650 , and thereby to lock housing  650  to a fixed position suitable for providing illumination from a desired angle. As shown in  FIGS. 6( a ) and 6( b ) , pattern  606  includes groves that are 45° apart, so that housing  650  may be fixed at any of eight different positions. For example,  FIG. 6( f )  shows housing  650  being fixed to one of the groves in pattern  606 , with front surface  603  forming a 45° angle relative to arms  601   a  and  601   b.    
     As mentioned above,  FIG. 4  shows a method which recovers from over-discharge of the battery. When a lithium ion battery pack is fully discharged, a conventional charging circuit may fail to recharge the battery. This is a situation frequently seen in an off-grid solar power system. Accordingly, circuit  200  has battery wakeup circuit  201  that allows circuit  200  to run on either battery power or solar power. When the lithium ion battery is fully depleted and is unable to be charged by the conventional charging circuit under control of controller  102 , battery wakeup circuit  201  is energized to allow solar power to flow into the battery pack, until normal solar charging can resume. 
     As shown in  FIG. 4 , state  401  represents a monitoring step in which the battery&#39;s voltage is checked. At step  402 , if the battery&#39;s voltage is found to have dropped below a predetermined threshold (e.g., 3 volts), the voltage at the output terminal of solar panels  101  is checked at step  403 . If the voltage at the output terminal of solar panels  101  is found to be sufficiently high (i.e., exceeding a threshold above which battery charging is feasible), the method proceeds to step  405 . Otherwise, the wake-up procedure is postponed until the next time the battery voltage is checked at step  401 . At step  405 , a “wake up attempt” counter is checked to determine if the battery has undergone more than a maximum number of wake-up attempts. (This maximum number is set to a value that should not be reached under normal usage conditions). If the battery has not reached this maximum number of wake-up attempts, the elapsed time since the last wake-up attempt is checked at step  406 . A battery fault condition is indicated if the elapsed time between wake-up attempts is too short (i.e., the battery&#39;s voltage is dropping too quickly to the over-discharged state). The elapsed time may be determined, for example, from a down-counter set at the end of the last wake-up attempt. If the fault condition is not indicated, i.e., the down-counter has not reached zero, the wake-up procedure is initiated to bring the battery to the boosted voltage. Activation of the wake-up procedure is indicated by an LED controlled by circuit  200  at step  408 . At step  409 , the wake up attempt counter is incremented to account for the current attempt. At step  410 , the down-counter is set at the minimum elapsed time between wake-up attempts. 
     To ensure priority is given to using the battery&#39;s energy to provide lighting, a method that is based on a “power credit” system is provided in accordance with one embodiment of the present invention. This method is illustrated by flow chart  500  in  FIG. 5 . As shown in  FIG. 5 , at step  501 , the solar panel&#39;s output voltage is checked to determine if it is at least one volt higher than the battery&#39;s voltage. The higher solar panel voltage—a favorable condition—indicates that battery charging is complete or nearly complete. If the solar panel voltage is favorable, at step  502 , the voltage across the load is checked if it is at least a predetermined value (e.g., 12.6 volts). This ensures that the battery is full or nearly full. Under that condition, at step  503 , a small value (e.g., 1) is added to a power credit account to indicate the favorable energy condition. 
     Next, step  504  determines if the solar panel voltage is actually less than the battery voltage. If so, a small value (e.g., 1) is deducted from the power credit account. At step  506 , if the battery voltage is also less than, for example, 12 volts, a greater value (e.g., 2) is deducted from the power credit account. 
     At step  508 , the power account balance is checked to see if there is sufficient power credit to allow non-lighting applications. For example, to allow non-lighting applications, the power credit account must have a value exceeding 25. At steps  509  and  510 , the circuit supplying the non-lighting applications (“the luxury circuit”) is activated for a predetermined time period (e.g., 30 minutes). Steps  511  and  512  deactivate secondary load circuit  251  at the end of the predetermined time period. At any time during the predetermined time period, step  513  determines if the battery voltage falls below a predetermined threshold (e.g., 11.5 volts). If so, secondary load circuit  251  is also deactivated (step  514 ) and the power credit account is set to zero (step  515 ), as the rapid battery voltage drop indicates an unfavorable condition. After a period of delay (e.g., one second, at step  516 ), the method returns to step  501 . 
     In one embodiment, a power management system of the present invention may provide at least 350 watt-hours (wh) of power per day and up to about 600 wh per day. In one embodiment, one configuration of a power management system of the present invention may be, for example: 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                 Descriptive power 
                 Daytime 
                 Night time 
               
               
                   
                 consumption 
                 energy 
                 energy (wh) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Lights 
                 2 lights - 300 lumens - 
                 32 
                 132 wh 
               
               
                   
                 12 hours per night 1 
               
               
                   
                 light-100 lumens-12 
               
               
                 Computer 
                 1 computer fully charged 
                 100 
                 0 
               
               
                   
                 per day 
               
               
                 Tablet 
                 1 tablet fully charged 
                 30 
               
               
                   
                 per day 
               
               
                 Cell phones 
                 5 dumb phones (5 wh) + 
                 55 
               
               
                 daytime 
                 2 smart phones (15 wh) 
               
               
                   
                 charged per day 
               
               
                 Cell phones 
                 2 dumb phone 
                 0 
                  10 wh 
               
               
                 nighttime 
               
               
                 Fetal Doppler 
                 Device charged for 3 uses 
                 2 
               
               
                   
                 per day; 30 minutes total 
               
               
                 Headlamps 
                 Rechargeable daily-use 2 
                 20 
               
               
                   
                 Headlamps (total) (full 
               
               
                   
                 battery 
                   
                   
               
               
                 Total 
                   
                 239 wh 
                 142 wh 
               
               
                   
               
            
           
         
       
     
     The power management system of the present invention requires little to no understanding by the user of the operation of a solar energy system, as key visual indicators are provided to inform the user whether or not the system is functioning proper and the level of power available. In addition, with the sensing signals provided to the controller, the controller can be easily programmed to provide a real time estimate of how much power remains at the current rate of power usage. The ability of a controller of the present invention to automatically vary the brightness of the lighting based on the instant power condition through the dimmer circuits allows efficient management of available power. 
     The above detailed description is provided to illustrate specific embodiments of the present invention and is not intended to be limiting. Numerous modifications and variations within the scope of the present invention are possible. The present invention is set forth in the accompanying claims.