JP6148131B2 - Solar power system - Google Patents

Description

  The present invention relates to a photovoltaic power generation system including a power generation device having at least one solar cell module and a power conversion device that inputs an output voltage of the power generation device.

  In recent years, in order to improve the power generation efficiency of solar cells, an electrode is not provided on the front surface which is the light receiving surface, and a P-type current collecting layer (electrode) and an N-type current collecting layer (electrode) are provided on the back surface opposite to the light receiving surface. A back electrode type solar cell has been developed in which both are provided to eliminate the shadow loss due to the electrodes (see, for example, Patent Document 1).

JP 2006-128258 A

  However, when generating power by irradiating a solar cell module including a back electrode type solar cell (hereinafter, also referred to as a back electrode type solar cell module) with sunlight, power generation efficiency may decrease with the passage of power generation time. May happen. As a result of analyzing this phenomenon, the present inventors have found that this phenomenon hardly occurs in a solar cell module including a solar cell in which electrodes are also provided on the light receiving surface side that has been used in the past. The larger the potential difference between the potential of the power generation part of the module and the potential of the part that does not contribute to the power generation of the back electrode type solar cell module such as the module frame, the lower the power generation efficiency, and the back electrode type solar cell module due to rainfall, etc. It has been found that the power generation efficiency tends to decrease when a water film is formed on the light receiving surface.

  From the above analysis results, the present inventors have estimated that the power generation efficiency of the back electrode type solar cell module is reduced by the following mechanism. Here, an example of a schematic cross section of the back electrode type solar cell module is shown in FIG. 5, and the mechanism estimated by the present inventors will be described with reference to FIG. 6 which is a partially enlarged view of FIG.

  The back electrode type solar cell module shown in FIG. 5 is opposite to the N-type silicon substrate 1, the passivation film 2 provided on the surface side which is the light-receiving surface of the N-type silicon substrate 1, and the light-receiving surface of the N-type silicon substrate 1. A plurality of back surface electrode type solar cells 5 each having a P type current collecting layer 3 and an N type current collecting layer 4 provided on the back surface on the side, and further adjacent two adjacent back surface electrode type solar cells 5 A connecting member 6 for connecting the P-type current collecting layer 3 and the N-type current collecting layer 4 is also provided. In the N-type silicon substrate 1, a P + layer 1A is formed so as to be in contact with the P-type current collecting layer 3, and an N + layer 1B is formed so as to be in contact with the N-type current collecting layer 4. In the back electrode type solar cell module shown in FIG. 5, the back electrode type solar cell 5 and the connection member 6 are sealed with a sealing material 7 such as ethylene vinyl acetate resin, and glass or the like is formed on the front side of the sealing material 7. The translucent substrate 8 is provided, the back surface protection sheet 9 is provided on the back surface side of the sealing material 7, the side surfaces of the sealing material 7, the translucent substrate 8, and the back surface protection sheet 9, and the translucent substrate 8 is provided with an end surface sealing material 10 such as rubber covering the front surface side periphery of 8 and the back surface side periphery of the back surface protection sheet 9, and a conductive module frame 11 such as aluminum is provided outside the end surface sealing material 10. Yes.

(I) The electric field shown in FIG. 6 is sealed by the potential difference between the power generation unit (N-type silicon substrate 1) in the back electrode type solar cell module and the portion (module frame 11) that does not contribute to the power generation of the back electrode type solar cell module. When applied to the material 7, free electrons 12 contained in the sealing material 7 are collected on the light receiving surface side of the passivation film 2.
(Ii) The holes contained in the N-type silicon substrate 1 are attracted to the passivation film 2 side so as to form a pair with the free electrons 12 contained in the sealing material 7 collected on the light receiving surface side of the passivation film 2. The power to take.
(Iii) When light is irradiated into the N-type silicon substrate 1, a pair of electrons 13 and holes 14 is generated by photoexcitation. These can be extracted to the outside as generated power when the electrons 13 reach the N-type current collecting layer 4 and the holes 14 reach the P-type current collecting layer 3 due to the electric field at the pn junction. Due to the force described in ii), the probability that the holes 14 are directed toward the passivation film 2 increases. As shown in FIG. 6, when the substrate of the solar cell is an N-type silicon substrate, the holes 14 become minority carriers, so the rate at which the holes 14 generated by photoexcitation reach the P-type current collecting layer 3 decreases. If this happens, the generated power that can be taken out, that is, the power generation efficiency, will be reduced.

  In view of the above estimation mechanism, the electric field shown in FIG. 6 is not applied to the encapsulant 7 as a measure for preventing a decrease in power generation efficiency of the back electrode type solar cell module that may occur with the lapse of power generation time. Thus, it can be considered that electrons are not accumulated on the passivation film. However, since the potential difference between the power generation unit in the back electrode type solar cell module and the portion that does not contribute to the power generation of the back electrode type solar cell module is determined by the configuration of the entire solar power generation system, the back electrode type solar cell module itself There was a problem that it was difficult to solve.

  An object of this invention is to provide the solar power generation system which can suppress that power generation efficiency falls with progress of power generation time in view of said condition.

  In order to achieve the above object, a photovoltaic power generation system according to the present invention includes a diode, a power generation device having at least one solar cell module, a positive-side input terminal that inputs a positive side of an output voltage of the power generation device, and the A power conversion device having a negative input terminal for inputting a negative polarity side of the output voltage of the power generation device, and the positive input terminal is grounded via the diode.

  The power generation device may include a plurality of the solar cell modules, and the output voltage of the power generation device may be a solar cell module string voltage obtained by serially adding at least two of the output voltages of the solar cell modules.

  The solar cell module has a back electrode type solar cell in which both a P-type current collecting layer and an N-type current collecting layer are provided on the back surface opposite to the light receiving surface of the N-type silicon substrate. Also good.

  Moreover, you may make it the said solar cell module have an electroconductive module frame which covers the edge part of the said solar cell module.

  The module frame may be grounded.

  According to the present invention, since the positive side potential of the output voltage of the power generation device can be set to a substantially ground potential, it is possible to prevent the power generation unit in the solar cell module from being in a state where the potential is higher than the ground potential. It can suppress that power generation efficiency falls with progress of power generation time.

It is a figure which shows schematic structure of the solar energy power generation system which concerns on 1st embodiment. It is a figure which shows the electric power generating apparatus which concerns on 2nd embodiment. It is a figure which shows the electric power generating apparatus which concerns on 3rd embodiment. It is a figure which shows schematic structure of the solar energy power generation system which concerns on 4th embodiment. It is a figure which shows an example of the schematic cross section of a back electrode type solar cell module. It is the elements on larger scale of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the photovoltaic power generation system according to the first embodiment includes a diode D1, a resistor R1, a power generation device 102 having four solar cell modules 101, and a positive side of an output voltage of the power generation device 102. A power conversion device 103 having a positive input terminal for input and a negative input terminal for inputting a negative input side of the output voltage of the power generation device 102. The positive input terminal of the power conversion device 103 is connected via a diode D1 and a resistor R1. And is grounded. The anode of the diode D1 is connected to the positive input terminal of the power converter 103, and the cathode of the diode D1 is grounded via the resistor R1.

  Although the diode D1 and the resistor R1 are illustrated outside the power conversion device 103 in FIG. 1, it is preferable to provide the diode D1 and the resistor R1 inside the power conversion device 103 so as not to increase time and labor when installing the solar power generation system. .

  Each connection between the solar cell module 101 and the solar cell module 101 and between the solar cell module 101 and the power converter 103 is performed using, for example, a cable.

  The four solar cell modules 101 in the power generation device 102 are connected in series, and the solar cell module string voltage obtained by adding the output voltages of the four solar cell modules 101 in series becomes the output voltage of the power generation device 102.

  As the solar cell module 101, for example, a back electrode type solar cell module shown in FIG. 5 is used, and the module frame 11 is grounded for safety. The structure of the back electrode type solar cell module is not limited to the structure shown in FIG. 5. For example, a passivation film may be provided on the back surface of the N-type silicon substrate 1. Further, in the back electrode type solar cell module, a P-type silicon substrate can be used instead of the N-type silicon substrate.

  Further, the solar cell module 101 is not limited to the illustrated back electrode type solar cell module. If the potential of the power generation unit in the solar cell module is higher than the potential of the portion that does not contribute to power generation, power generation occurs with the passage of power generation time. Any type of solar cell module that may reduce efficiency may be used.

  The power conversion device 103 may be a power conversion device that outputs a DC / AC converted voltage between a positive input terminal and a negative input terminal that is a DC voltage, and is a positive input terminal that is a DC voltage—a negative input side. A power conversion device that performs DC / DC conversion and outputs the voltage between the input terminals may be used. In addition, the power conversion device 103 has a maximum output operating point tracking (MPPT) function, and performs MPPT control so that the power supplied between the positive input terminal and the negative input terminal is maximized. It is preferable that the operation voltage and the operation current of each solar cell module 101 are determined.

  When the power generation device 102 is generating power and no ground fault occurs at the negative input terminal of the power conversion device 103, the anode potential of the diode D1 becomes higher than the cathode potential, the diode D1 is turned on, Since the positive electrode side potential of the output voltage of the device 102 is substantially the ground potential, it is possible to prevent the power generation unit in the solar cell module 101 from being in a high potential state during power generation, and as the power generation time elapses. It can suppress that power generation efficiency falls.

  On the other hand, when a ground fault occurs at the negative input terminal of the power converter 103 while the power generator 102 is generating power, the anode potential of the diode D1 becomes higher than the cathode potential, the diode D1 is turned on, The ground fault current can be limited by the resistor R1. The limitation of the ground fault current by the resistor R1 contributes to prevention of damage to the diode D1 and protection against electric shock when a person touches the negative electrode side.

  Instead of the configuration of the power generation apparatus 102 shown in FIG. 1, a configuration in which a plurality of solar cell module strings in which a plurality of solar cell modules 101 are connected in series as shown in FIG. Good. Moreover, it may replace with the structure of the electric power generating apparatus 102 shown in FIG. 1, and you may make it the structure which has only one solar cell module 101 as shown in FIG. 3 as 3rd embodiment.

  However, in the configuration in which the power generation apparatus 102 has a solar cell module string in which a plurality of solar cell modules 101 are connected in series, when the potential of the module frame 11 is set to the ground potential, the solar cell located on the upper side of the paper in FIG. 1 or FIG. Since the power generation unit in the module 101 has a higher potential than the power generation unit in the solar cell module 101 located on the lower side of the page, it is assumed that the power generation efficiency decreases with the passage of power generation time. Otherwise, the power generation efficiency may be greatly reduced. Therefore, the configuration in which the power generation device 102 has a solar cell module string in which a plurality of solar cell modules 101 are connected in series (first embodiment, second embodiment) has the power generation device 102 connected in series with a plurality of solar cell modules 101. The effect is more conspicuous than the configuration without the connected solar cell module string (third embodiment).

  Next, a solar power generation system according to a fourth embodiment will be described with reference to FIG. In FIG. 4, the same parts as those in FIGS.

  The photovoltaic power generation system according to the fourth embodiment includes a plurality of diodes D1, a single resistor R1, a plurality of power generation devices 102, and a single power conversion device 103. As shown in FIG. 4, the plurality of diodes D <b> 1 and one resistor R <b> 1 are provided inside the power conversion device 103.

  As a structure of the electric power generating apparatus 102, the structure similar to any one of 1st-3rd embodiment (refer FIGS. 1-3) etc. can be mentioned, for example.

  The power conversion device 103 includes a plurality of pairs of positive side input terminals 104 and negative side input terminals 105, a plurality of DC / DC converters 106, and one DC / AC inverter 107.

  Each positive-side input terminal 104 inputs the positive side of the output voltage of each power generator 102, and each negative-side input terminal 105 inputs the negative side of the output voltage of each power generator 102. The output voltage of each power generator 102 is converted into a DC voltage of a predetermined value by each DC / DC converter 106. Each DC / DC converter 106 has a maximum output operating point tracking (MPPT) function and supplies power to itself (positive input terminal 104 connected to itself—negative input terminal connected to itself. It is preferable that the MPPT control be performed so that the electric power supplied between the terminals 105 is maximized.

  The DC voltage of a predetermined value output from each DC / DC converter 106 is collected and then converted into an AC voltage by a DC / AC inverter 107, and the AC voltage is externally output (for example, commercial power) as an output voltage of the power converter 103. System). Note that when the output voltage of the power converter 103 is a DC voltage, the DC / AC inverter 107 may be omitted.

  Each positive input terminal 104 is grounded via each diode D1 and a common resistor R1. More specifically, each positive electrode side input terminal 104 is connected to the anode of each diode D1, and the cathode of each diode D1 is grounded via a common resistor R1.

  When a ground fault does not occur at the negative input terminal 105 to which the arbitrary power generation device 102 is connected when the arbitrary power generation device 102 is generating power, the anode potential of the diode D1 corresponding to the arbitrary power generation device 102 Becomes higher than the cathode potential, the diode D1 corresponding to the arbitrary power generation device 102 is turned on, and the positive potential of the output voltage of the arbitrary power generation device 102 becomes substantially the ground potential. It is possible to prevent the power generation unit in the solar cell module (not shown in FIG. 4) from being in a high potential state during power generation, and to suppress a decrease in power generation efficiency with the lapse of power generation time can do.

  On the other hand, when a ground fault occurs at the negative input terminal to which the arbitrary power generation device 102 is connected when the arbitrary power generation device 102 is generating power, the anode potential of the diode D1 corresponding to the arbitrary power generation device 102 Becomes higher than the cathode potential, the diode D1 corresponding to the arbitrary power generation apparatus 102 is turned on, and the ground fault current can be limited by the resistor R1. The limitation of the ground fault current by the resistor R1 contributes to prevention of breakage of each diode D1 and protection against electric shock when a person touches the negative electrode side.

DESCRIPTION OF SYMBOLS 1 N type silicon substrate 1A P + layer 1B N + layer 2 Passivation film 3 P type current collection layer 4 N type current collection layer 5 Back surface electrode type solar cell 6 Connection member 7 Sealing material 8 Translucent substrate 9 Back surface protection sheet 10 End face sealing material 11 Module frame 12 Free electrons 13 Electrons generated by photoexcitation 14 Holes generated by photoexcitation 101 Solar cell module 102 Power generation device 103 Power conversion device 104 Positive electrode side input terminal 105 Negative electrode side input terminal 106 DC / DC converter 107 DC / AC inverter D1 Diode R1 Resistance

Claims (4)

A diode,
A power generation device having at least one solar cell module;
A power conversion device having a positive side input terminal for inputting a positive side of the output voltage of the power generation device and a negative side input terminal for inputting a negative side of the output voltage of the power generation device;
The solar cell module has a back electrode type solar cell provided with both a P-type current collecting layer and an N-type current collecting layer on the back surface opposite to the light receiving surface of the N-type substrate,
The positive input terminal is grounded via the diode ;
An anode of the diode is connected to the positive electrode side input terminal, and a cathode of the diode is grounded . The power generator comprises a plurality of the solar cell modules,
The photovoltaic power generation system according to claim 1, wherein the output voltage of the power generation device is a solar cell module string voltage obtained by serially adding at least two of the output voltages of the solar cell modules. The solar power generation system according to claim 1 or 2, wherein the solar cell module has a conductive module frame that covers an edge of the solar cell module. The photovoltaic module according to claim 3, wherein the module frame is grounded.