Abstract:
A method of determining an energy harvesting capability of a location harvests energy at a location using an energy harvester and charges an energy storage device using the harvested energy. The energy storage device is discharged into a test circuit to provide a notification. The steps of charging the energy storage device and discharging the energy storage device are selectively repeated such that the notification is provided at a rate proportional to an amount of energy being harvested at the location.

Description:
BACKGROUND 
       [0001]    This application relates to energy harvesting, and more particularly to a system and method for determining an energy harvesting capability of a location. 
         [0002]    Solar cells have been used to harvest power for various loads. Solar cells require adequate levels of light in order to harvest sufficient amounts of energy to power their respective loads. Determining acceptable locations for solar cells has involved using expensive equipment such as a lux meter. 
       SUMMARY 
       [0003]    In one embodiment, a method of determining an energy harvesting capability of a location harvests energy at a location using an energy harvester and charges an energy storage device using the harvested energy. The energy storage device is discharged into a test circuit to provide a notification. The steps of charging the energy storage device and discharging the energy storage device are selectively repeated such that the notification is provided at a rate proportional to an amount of energy being harvested at the location. 
         [0004]    In one embodiment, a circuit for determining an energy harvesting capability of a location includes an energy harvester operable to harvest energy from environmental conditions at a location and a notification device operable to provide a notification at a rate proportional to an amount of energy being harvested by the energy harvester at the location. 
         [0005]    In one embodiment, a method of determining an energy harvesting capability of a location connects an energy harvester to a first energy storage device in a test mode. A system load is not powered in the test mode. The first energy storage device is charged using energy harvested by the energy harvester at a location. A charge of the first energy storage device is compared to a desired charge, and a notification is provided to indicate the result of the comparison. The first energy storage device is disconnected from the energy harvester and the energy harvester is connected to a second energy storage device in an operational mode in response to the capacitor charge being greater than or equal to a desired charge. The second energy storage device has a greater energy storage capacity than the first storage device, and in the operational mode the system load is powered by the energy harvester via the second energy storage device. 
         [0006]    In one embodiment, a circuit for determining an energy harvesting capability of a location includes an energy harvester operable to harvest energy from environmental conditions, a first energy storage device being charged by the energy storage device in a test mode, and a second energy storage device being charged by the energy storage device in an operational mode. The second energy storage device has an energy storage capacity that is greater than an energy storage capacity of the first energy storage device. The circuit also includes at least one notification device operable to provide a notification if a charge of the first energy storage device is greater than or equal to a desired charge. A system load is powered by the energy harvester via the second energy storage device in the operational mode, and is not powered in the test mode. A switch is operable to change between the test mode and the operational mode by connecting or disconnecting the energy storage devices from the energy harvester. 
         [0007]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  schematically illustrates a first circuit for determining an energy harvesting capability of a location. 
           [0009]      FIGS. 2-5  schematically illustrate various portions of another circuit for determining an energy harvesting capability of a location. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  schematically illustrates a circuit  10  for determining an energy harvesting capability of a location to determine an optimal placement for an energy harvester  12  at that location. The energy harvester  12  is operable to harvest energy from environmental conditions at the location. The energy harvester may include one or more photovoltaic cells operable to harvest solar energy, for example. 
         [0011]    A switch  14  is operable to command the circuit to switch between powering a test portion  16  of the circuit  10  (in a “test mode”) and powering a load  18  of the circuit  10  (in an “operational mode”). If the test portion  16  indicates that a sufficient amount of energy is being harvested at the location, the switch  14  may cause the circuit  10  to enter the operational mode such that the energy harvester  12  powers the load  18 . 
         [0012]    An energy storage device  20  repeatedly charges from the energy harvester  12  and discharges to power a notification device  22  such that the notification device  22  provides notifications at a rate proportional to an amount of energy being harvested by the energy harvester  12  at the location. In one example the energy storage device  20  includes a capacitor and the notification device  22  includes a light-emitting diode (“LED”). Of course, other energy storage and notification devices could be used. 
         [0013]    A resistor  24  connected in parallel to the energy storage device  20  is used to simulate an energy demand of the load  18 . A plurality of additional resistors  26   a - d  are connected to each other (with resistors  26   a - b  connected in series and resistors  26   c - d  connected in series), and are collectively connected to comparator  28  to exhibit a hysteresis effect such that the resistors  26   a - d  and comparator  28  establish a voltage threshold required to turn the comparator output ON. Thus, once the charge of the energy storage device  20  reaches a level sufficient to meet or exceed the voltage threshold, the comparator  28  turns ON and the energy storage device  20  discharges to power the notification device  22 . The energy storage device then repeatedly charges and discharges such that the notification device  22  provides a notification at a rate proportional to an amount of energy being harvested by the energy harvester  12  at the location. Optional current limiting resistors  30 ,  32  may be used to control an amount of current that flows through the test portion  16  of the circuit  10 . A diode  34  prevents backcharging from the energy storage device  20  back into the energy harvester  12 . 
         [0014]    The notification rate of the notification device  22  is compared to a desired notification rate that represents an amount of energy being sufficient to power the load  18 . If the notification rate is less than the desired notification rate, the energy harvester  12  or the entire circuit  10  may be moved to another location to determine whether the other location enables the energy harvester  12  to harvest more energy. If the notification rate is greater than or equal to the desired notification rate the switch  14  may be used to command the circuit  10  to enter the operational mode such that the load  18  is powered by the energy harvester  12  and the test portion  16  of the circuit  10  is disconnected from the energy harvester  12 . 
         [0015]    A technician could use the circuit  10  to determine where to place a solar panel. If the notification rate was too low the technician would know that an insufficient amount of light would be available to power a load of the solar panel, and if the rate was high enough the technician would know that the solar panel location was acceptable. Thus, the technician could avoid the use of complicated and expensive tools such as lux meters in determining an optimal solar panel location. 
         [0016]      FIGS. 2-5  schematically illustrate various portions of another circuit  40  for determining an energy harvesting capability of a location. Referring to  FIG. 2 , the circuit  40  includes an energy harvester  42  and a switch  43  operable to connect the energy harvester  42  to one of a first energy storage device  44  (in a “test mode”) or a second energy storage device  46  (in an “operational mode”), with the second energy storage device  46  having a greater energy storage capacity than the first energy storage device  44 . In one example, the energy storage devices  44 ,  46  include capacitors. Of course, other energy storage devices could be used. The switch  43  may be a double pole, double throw (“DPDT”) switch that has six terminals and controls two separate flows of current. A diode  47  prevents the energy storage devices  44 ,  46  from backcharging into the energy harvester  42 . 
         [0017]    Referring to  FIG. 3 , a microcontroller  48  has memory  50  that stores both main code  52  and test code  54 . In the operational mode the energy storage device  46  is connected to the energy harvester  42 , and the signal PWR_TEST_MODE is pulled high, commanding the microcontroller  48  to execute the main code  52 . In one example the main code involves powering system loads  56 , which may include one or more motion sensors, for example. 
         [0018]    In the test mode the energy storage device  44  is connected to the energy harvester  42 , and the signal PWR_TEST_MODE is pulled low, commanding the microcontroller  48  to execute the test code  54 . In one example the test code  54  prevents the microcontroller from powering the system loads  56 . 
         [0019]    The signal COMPOUT is used to indicate if the energy harvester  42  is harvesting a sufficient amount of energy to power both the microcontroller  48  and the system loads  56 . The COMPOUT signal is determined using comparator  60 , regulator  62 , and comparator  64  (see  FIGS. 4-5 ). 
         [0020]    Referring to  FIG. 4 , the comparator  60  is used to determine if the energy harvester  42  is harvesting a sufficient amount of energy to power the microcontroller  50 . A first plurality of resistors  66   a - d  are configured to exhibit a hysteresis effect such that the resistors  66   a - d  and comparator  60  collectively establish a first voltage threshold required to turn ON the output of comparator  60 . A voltage V DD  is connected to the output of the energy harvester  42 . If the comparator  60  is turned ON, regulator  62  regulates the voltage V DD  to provide a regulated system voltage S VDD . 
         [0021]    Referring to  FIG. 5 , the comparator  64  is used to determine if the energy harvester  42  is harvesting a sufficient amount of energy to power both the microcontroller  50  and the system loads  56 . A second plurality of resistors  68   a - d  are configured to exhibit a hysteresis effect such that the resistors  68   a - d  and comparator  64  collectively establish a second voltage threshold required to turn ON the output of comparator  64 . In one example the second voltage threshold (of resistors  68   a - d  and comparator  64 ) is greater than the first voltage threshold (of resistors  66   a - d  and comparator  60 ). If the energy storage device  44  has a charge that is greater than or equal to the second voltage threshold, the comparator  64  output turns ON such that the COMPOUT signal is ON. 
         [0022]    The LEDs  70 ,  72  act as notification devices to indicate an amount of energy being harvested by energy harvester  42 . The COMPOUT signal is OFF by default, causing the microcontroller  50  to turn LED  70  ON. However, if the comparator  64  is turned ON, the COMPOUT signal is turned ON, which commands the microcontroller  50  to turn LED  70  OFF and to turn LED  72  ON, indicating that the energy harvester  42  is harvesting a sufficient amount of energy to power both the microcontroller  50  and the system loads  56 . In one example the LED  70  emits red light and the LED  72  emits green light. Of course, other LEDs and other notification devices could be used. 
         [0023]    In one example a first notification could be provided to indicate that the energy harvester  42  was harvesting enough energy to power only the microcontroller  48 , and a second notification could be provided to indicate that the energy harvester  42  was harvesting enough energy to power both the microcontroller  48  and the system loads  56 . The first and second notifications could include turning ON one or both of the LEDs  70 ,  72 , or could include flashing one or both of the LEDs  70 ,  72  ON/OFF at a certain rate, for example. 
         [0024]    Thus, as with the circuit  10  of  FIG. 1 , a technician could use the circuit  40  to determine where to place a solar panel. If the LED  70  was emitting light, the technician would know that an insufficient amount of light would be available to power a load of the solar panel, and if the LED  72  was emitting light the technician would know that the solar panel location was acceptable, and the technician could cause switch  43  change from the test mode to the operational mode. Thus, the technician could avoid the use of complicated and expensive tools such as lux meters in determining an optimal solar panel location. 
         [0025]    Although multiple embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.