Abstract:
Apparatuses and methods to reduce safety risks associated with photovoltaic systems by providing a safety switch on a photovoltaic panel. In one embodiment, a photovoltaic panel includes: at least one photovoltaic cell; a connector to output energy from the photovoltaic panel; and a switch coupled between the at least one photovoltaic cell and the connector. The switch is configured to disconnect the at least one photovoltaic cell from the connector during installation of the photovoltaic panel, and to connect the at least one photovoltaic cell with the connector after installation of the photovoltaic panel.

Description:
RELATED APPLICATIONS 
     The present application is a continuation application of a copending U.S. patent application Ser. No. 12/254,780, filed Oct. 20, 2008, which claims priority to provisional U.S. Patent Application Ser. No. 61/001,587, filed on Nov. 2, 2007 and entitled “Photovoltaic Safety Switch.” The disclosures of the above referenced applications are hereby incorporated herein by reference. 
    
    
     FIELD OF THE TECHNOLOGY 
     At least some embodiments disclosed herein relate to photovoltaic systems in general and, more particularly but not limited to, safety devices for the shipment, installation and/or maintenance of photovoltaic systems. 
     BACKGROUND 
     When a photovoltaic panel or laminate is exposed to direct or diffuse light, a lethal voltage potential may be present. In the United States the possible voltage could be as high as 600 volts, while in Europe and the rest of the world this voltage could approach a kilovolt. 
     Because of this potential danger from electrical shock, solar panel manufacturers and code and standards development organizations have made some recommendations to minimize or eliminate this danger. 
     One suggestion has been to cover the photovoltaic panel with an opaque material such as a tarpaulin. However, this approach proposes its own safety risk from having the wind catch the tarpaulin and pull installation personnel off the roof as they try to control the unstable sheet material against the wind. 
     Another recommendation is to install and/or service the photovoltaic panels at night when there is minimal risk of the panels being energized. This approach presents the potential safety risks associated from working in a poorly lighted environment. 
     In addition to the potential personnel safety issues there are also significant risks to equipment and hardware. Connecting or disconnecting energized plugs can cause arcing and damage to these connectors, junction boxes, and other electrical components. 
     SUMMARY OF THE DESCRIPTION 
     Apparatuses and methods to reduce safety risks associated with photovoltaic systems by providing a safety switch on a photovoltaic panel. Some embodiments are summarized in this section. 
     In one embodiment, a photovoltaic panel includes: at least one photovoltaic cell; a connector to output energy from the photovoltaic panel; and a switch coupled between the at least one photovoltaic cell and the connector. The switch is configured to disconnect the at least one photovoltaic cell from the connector during installation of the photovoltaic panel, and to connect the at least one photovoltaic cell with the connector after installation of the photovoltaic panel. 
     In one embodiment, the photovoltaic panel further includes a junction box to host the connector, wherein the switch is integrated in the junction box. 
     In one embodiment, the switch includes a first conductive contactor, a second conductive contactor, and a removable portion which when removed connects the at least one photovoltaic cell with the connector. For example, the removable portion may include a dielectric separator; when the dielectric separator is inserted between the first and second contactor, the switch is not connected; and when the dielectric separate is removed, the switch is connected. In one embodiment, the first and second conductive contactors are spring loaded toward each other. 
     In one embodiment, the removable portion further includes a flag attached to the dielectric separator. The flag may have a visual indication of warning for electric shock. 
     In one embodiment, the switch includes a reed switch; and the removable portion includes a magnet. The reed switch may be a normally closed reed switch, or normally open reed switch. 
     In one embodiment, the switch includes an optical sensor to turn on or off the switch based on light detected by the optical sensor; and the removable portion includes a pull-tab configured to shield the optical sensor. The at least one photovoltaic cell may be used to power the optical sensor. 
     In one embodiment, the switch further includes a semiconductor switch device (e.g., a Field-Effect Transistor (FET)) or a relay. 
     In one embodiment, the switch includes a relay and a wiring connector to control the relay from a remote location. 
     In one embodiment, the photovoltaic panel further includes a circuit to detect a load from an inverter. The switch is to connect an output of the photovoltaic panel to the connector when the circuit detects a load from an inverter and to disconnect the output in absence of a load from an inverter. 
     In one embodiment, a photovoltaic panel module includes: a voltage module to adjust an output of a plurality of photovoltaic cells; and a switch coupled the voltage module to selectively provide the output. In one embodiment, the voltage module outputs an alternating current (AC) output. The switch may include a semiconductor switch, a relay, a reed switch, a spring loaded switch, and/or an optical sensor to control a state of the switch. 
     In one embodiment, the photovoltaic panel module further includes connectors for wirings to control a state of the switch. 
     The disclosure includes methods and apparatuses which perform these methods, including data processing systems which perform these methods, and computer readable media containing instructions which when executed on data processing systems cause the systems to perform these methods. 
     Other features will be apparent from the accompanying drawings and from the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG. 1  illustrates a solar panel having a safety switch according to one embodiment. 
         FIGS. 2-5  illustrate a spring loaded safety switch for a photovoltaic panel according to one embodiment. 
         FIGS. 6-7  illustrate a junction box with a reed switch for a photovoltaic panel according to one embodiment. 
         FIG. 8  illustrates an optical sensor to control a safety switch for a photovoltaic panel according to one embodiment. 
         FIG. 9  illustrates a solar panel having a safety switch controlled via auxiliary wiring according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding. However, in certain instances, well known or conventional details are not described in order to avoid obscuring the description. References to one or an embodiment in the present disclosure are not necessarily references to the same embodiment; and, such references mean at least one. 
     One embodiment of the disclosure provides a method and system to reduce the safety risks during the shipment, installation and/or maintenance of photovoltaic systems, without introducing the risks associated with other approaches, such as covering them with an opaque material or working on them at night. 
     In one embodiment, safety protection is provided via the inclusion of a normally closed switch integral to the panel junction box or integral to the panel module when alternating current (AC) or direct current (DC) modules are used. 
       FIG. 1  illustrates a solar panel having a safety switch according to one embodiment. In  FIG. 1 , a solar panel  10  (e.g., a photovoltaic panel) includes at least one solar cell  12  (e.g., a photovoltaic cell) to generate power when exposed to direct or diffuse light, in some cases a voltage module  14  to adjust or regulate the output voltage (or in some other cases a current module to regulate current), and a switch  16  to selectively isolate the solar cell  12  from the output connectors of the solar panel. In yet other cases, the switch may be incorporated into regulator modules, such as voltage module  14 . 
     In one embodiment, the switch  16  is a normally closed switch. During the shipment, installation and/or maintenance, the switch  16  is placed in an open state to isolate the solar cell  12  from the output. After the installation or maintenance, the switch  16  is placed into a closed state to allow the solar cell  12  to energize the output connectors of the solar panel and to supply power through the output connectors of the solar panel. 
     The switch  16  and the voltage module can be integrated into the junction box of the solar panel. In some embodiment, the switch  16  is integrated with the voltage module  14  as a panel module. 
       FIGS. 2-5  illustrate a spring loaded safety switch for a photovoltaic panel according to one embodiment. In  FIGS. 2-5 , the switch includes two contactors  102  and  103  made of a conductive metal or plated hybrid. The contactors  102  and  103  are normally made of a spring alloy metal or have an integral spring plunger design (not shown). The contactors  102  and  103  are positioned or fixed in such a way that the two contacts  102  and  103  are spring loaded toward each other to maintain electrical continuity between the two contactors  102  and  103 . Thus, the switch is normally closed (NC) and not in a safe mode for installation or maintenance. 
     In  FIG. 2 , a safe mode for installation or maintenance is achieved when the blade  104  is inserted between the two contactors  102  and  103 . The blade  104  is manufactured from a dielectric material and when inserted between the two contactors  102  and  103  there is no electrical continuity between the contactors  102  and  103 . 
     As illustrated in  FIG. 2 , the blade  104  may also have a flag  105  attached. The flag  105  could be red or some other highly visible color, to provide a visual indicator of the state of the panel. 
     In one embodiment, the panels and/or panel with integral modules would come shipped from the factory with the blade  104  and the flag  105 , where the blade  104  is inserted between the two contactors  102  and  103 . The panels would be installed and integrated with the blade  104  present and flag  105  visible. The installer would mount, secure, and plug in all of the connections in the system, including the grounding. 
     As illustrated in  FIG. 3 , once the installation is completed the installer would remove the blades  104  at all those places indicated by the flags  105 . Once the blade  104  is removed, the spring loaded contactors  102  and  103  contact each other to provide an electric path from the photovoltaic cells to the output connectors of the photovoltaic panel. 
     If additional work or troubleshooting were needed, the blade(s)  104  and flag(s)  105  could be reinserted, aided by the tapered section  207  of the blade  104 , thereby breaking the electrical continuity between the contactors  102  and  103  at point  206 . 
     In some embodiments, there is symmetry in contactors  102  and  103 . In other embodiments, the contactors  102  and  103  are not identical or even similar. The contactors  102  and  103  are made of electrically conductive material and configured to be in physical contact with each so that an electrically conductive path  206  is maintained, after the blade  104  is removed. In at least some embodiments, the electrical conductive path  206  is maintained without the blade  104  being inserted between the contactors  102  and  103 , then disrupted by the blade  104  inserted between the contactors  102  and  103 , and then reestablished by the reinsertions of a dielectric device such as the blade  104 . 
     In addition to the visual indication of the modes of the panels provided by the flag(s)  105 , the flags could also provide information in the form of text, such as, for example, “Remove before operation” or a warning of potentially lethal voltage. 
       FIG. 4  illustrates a configuration of a spring loaded switch integrated with a junction box  308  of a photovoltaic panel. The junction box  308  includes a connector to connect the solar power generated by the photovoltaic panel to a load (e.g., an inverter, a voltage bus, etc.) via a cable  307 . Thus, when the blade  104  is inserted into the switch, with the flag  105  visible, the voltage generated by the solar cells is isolated from the connector for the cable  307 ; and thus it is safe to install the photovoltaic panel or to perform maintenance operations on the photovoltaic panel. 
       FIG. 5  shows the components of the spring loaded switch and the junction box of a photovoltaic panel. As illustrated in  FIG. 5 , the junction box  308  has an opening  409 , which provides access to remove the blade  104  and/or to re-insert the blade  104 . The contactors  103  of the switch can be attached to the junction box  308  via fastening the portion  401  to a supporting member of the junction box  308 , such as a printed circuit board (PCB). 
       FIGS. 6-7  illustrate a junction box with a reed switch for a photovoltaic panel according to one embodiment.  FIG. 6  shows an assembly of a reed switch  510  and magnets for integrated into the photovoltaic junction box  308 .  FIG. 7  shows a cut-away section illustrating the reed switch  510  and the magnets  511  and  512  installed within the portion  509  of the junction box  308 . 
     In  FIG. 7 , a reed switch  510  is made normally closed by integrating a stationary biasing magnet  511  into the junction box  308  in close proximity to the normally open reed switch, so that the switch  510  is closed in absence of the magnet  512 . 
     In one embodiment, the magnet  512  is inserted into the junction box well  509  so that the reversed polarity cancels the magnetic lines of force and the reed switch  510  opens. 
     In one embodiment, the magnet  512  is installed in the junction box well  509  at the factory; and a flag  105  (not shown in  FIGS. 6 and 7 ) is attached to the magnet  512 . The magnet  512  is removable and/or re-insertable via the junction box well  509 . 
     In other embodiments, normally closed (NC) reed contacts can be used to replace the normally open (NO) reed contacts  510  and the magnet  511 , avoiding the need for the additional stationary magnet. 
     Once the installation and integrations are complete the magnet  512  is removed and may be discarded. The power leads of the junction box  308  can then be energized via the semiconductor switch or relay (not shown), when the reed switch  512  is in the closed state. 
     In some cases, a semiconductor switch (not shown in  FIG. 7 ) can be used to energize the power leads of the junction box  308 . The panel junction box  308  or inverter (not shown in  FIG. 7 ) may include a controller unit with a watchdog circuit configured to send a signal periodically (e.g., every time interval t) to maintain the connection of the panel outputs to the string. When this signal is timed-out or is absent, the panel outputs of the panel are disconnected via a semiconductor switch device (not shown). 
       FIG. 8  illustrates an optical sensor to control a safety switch for a photovoltaic panel according to one embodiment. In  FIG. 8 , an optical sensor unit  700  with an optical sensor  701  is mounted on a printed circuit board (PCB)  711 . Additionally, springs  702  and  712  hold a separator  703  in place that can be removed in direction of arrow  704  using a pull-tab similar to the flag  105  discussed earlier. Not shown in  FIG. 8  is the exterior enclosure that would contain the mechanical elements such as the cable connections and the guide elements for guiding separator  703  in and out of the unit. 
     In one embodiment, additional circuitry (not shown in  FIG. 8 ) will be on the side of the PCB  711 , such as a control circuit to affect an on/off switching either in some cases by FET (Field-Effect Transistor) transistors or using, in other cases, a relay, such as a bi-stable relay or another suitable circuit. The operational power may be drawn from the solar system itself, or it may be brought up by auxiliary wiring. 
     In yet some other embodiments, a relay can be simply remote controlled by an auxiliary wire to close or open the circuit. The advantage of this approach is that no pull-tabs (flags or blades) can be forgotten on the roof. 
     In one embodiment, a mechanism and/or circuitry is integrated in the panel to identify the load from the inverter and connect the panel to the panel outputs when the load is detected. When no load is present the panel outputs is disconnected. This functionality would also be implemented using a semiconductor switch device or other suitable device (such as a relay), and some sensor circuitry, allowing an automatic reconnect when the loop appears to be closed and a load connected. 
       FIG. 9  illustrates a solar panel having a safety switch controlled via auxiliary wiring according to one embodiment. In  FIG. 9 , a separate wire is connected to control the switch  16  from a remote location. For example, the switch may be controlled via a signal from a watchdog circuit, from a remote switch or controller, etc. 
     In the foregoing specification, the disclosure has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.