JPH07177652A - Solar beam power generation system and protective system therefor - Google Patents

Abstract

PURPOSE:To obtain a solar beam power generating system in which high generation efficiency can be sustained stably while facilitating maintenance and management. CONSTITUTION:The solar beam power generation system comprises a first switch 3 for switching the output lines 12 connected in parallel with the positive and negative power supply output terminals of a solar cell string 1, a switch 2 for short-circuiting or open-circuiting the power supply output terminals, a comparator 7 for comparing the voltage between the detecting terminals at a predetermined position of the solar cell string and delivering a comparison signal, and a controller 8 for controlling the first and second switches based on the the comparison signal. A decision is made that a solar cell string 1 is abnormal when the voltage between the detecting terminals is lower than a predetermined level and the power supply output terminal thereof is interrupted from the output line and then the power supply output terminals are short-circuited. Identification code of abnormal string is presented on a display 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar power generation system and a protection system for the solar power generation system. More specifically, the present invention relates to a solar cell string used in a solar power generation system, and a system configuration and a protection method for maintaining / repairing the system.

[0002]

2. Description of the Related Art In recent years, there has been an increasing interest in environmental protection and stable energy supply / supply on a global scale.
In such a situation, the solar cell has a feature that it uses an inexhaustible clean energy source and does not consume other energy to acquire this energy. There is great expectation that it has the advantage of low loss for so-called operation.

A photovoltaic power generation system using a solar cell is
It is usually composed of multiple solar cell modules. With this solar cell module as a basic unit, various names are given at various stages in order to identify the configuration state. For example, from the bottom to the top, it is a division of solar cell modules, strings, solar cell arrays, solar power generation systems, and the like.

Solar power generation systems are connected in series to obtain a desired voltage. The series body of the solar cell modules is generally called a string. Some of these strings are connected in parallel to form a solar cell array with a desired power generation scale. Peripheral control to the solar cell array,
A photovoltaic power generation system is configured by adding components for protection and connection. Therefore, the larger the power generation scale required for the solar power generation system, the larger the solar cell array, and the greater the number of solar cell modules that compose it.

A specific example will be illustrated. Now operating voltage 200V
The 10 kW solar power generation system is configured using a solar cell module having an optimum voltage of 16 V and a maximum output of 50 W.
If one string is composed of 13 solar cell modules connected in series, the operating voltage in this case is 208 V (208
[V] = 16 [V / sheet] × 13 [sheet]). Output 1
The number of strings connected in parallel to obtain 0 kW is 16
({10 [kW] ÷ (50 [W / sheet] × 13 [sheet]))}
= 15.3≈16). In this way, 2 in total
Operating voltage of 208V using 08 solar cell modules
The 10.4 kW solar power generation system is configured.

In the above solar power generation system, as the power generation capacity is increased, the number of solar cell modules used increases, the system expands, and the incidence of defective solar cell modules in the entire system increases. Become.

[0007]

However, when a defect occurs in the solar cell module, the defective module does not normally generate power, and the harmful effects that accompany the expansion of the photovoltaic power generation system also increase. For example, the power generation capacity of the string in which the defective module is generated is lower than that of the string only in the normal module. These strings are connected in parallel, and if the power generation operation is continued while the defective modules are mixed, the strings in which the defective modules exist cause a decrease in the power generation capacity of the normal strings. In other words, a string including a defective module that cannot generate power at all cannot contribute to power generation and reduces the power generation capacity of the system.
Further, even if the string in which the defective module exists contributes to the power generation, if the performance at the time of the initial design cannot be exerted, the power generation cannot be performed at the optimum operating point for all the modules, which lowers the power generation capacity of the system. Therefore,
In either case, the power generation efficiency of the entire array is reduced. From this, in order to maintain efficient power generation, it is necessary to detect a defective module early and promptly perform repair such as replacement with a normal module.

However, when such a large number of solar cell modules are used, even if a solar cell module that cannot generate power is generated, the rate of decrease in power generation capacity is small at the early stage of the failure, and the occurrence of failures occurs. Easy to miss. In addition, even if the symptoms progress and the defects expand, it is necessary to manually investigate each solar cell module to know whether the solar cell is normal. It is very time consuming and requires a great deal of effort. The risk of electric shock increases as the power generation capacity increases. In addition, it is difficult to investigate during operation, and it is not unusual for the existence of a defective module to become known only after a considerable amount of time has elapsed since the occurrence of the defective module. Further, depending on the installation method or the installation site, it may be very difficult to conduct the periodic survey itself.

It is an object of the present invention to provide a solar power generation system and a protection system for the solar power generation system, which facilitates maintenance and can stably maintain high power generation efficiency.

[0010]

In order to achieve the above object, in the solar power generation system of the present invention, a plurality of solar cell modules are connected in series to form a solar cell string, and two or more solar cell strings are formed. It is a photovoltaic power generation system configured to be connected in parallel, and a first switching unit that connects or disconnects between the positive and negative power supply output terminals of the solar cell string and the output line that outputs in parallel, Second switching means for short-circuiting or opening the power supply output terminals, and comparison means for outputting a comparison signal obtained by comparing and comparing the voltage value between the detection terminals at predetermined locations in the solar cell string with a predetermined value. It has a signal input and a control means for controlling the opening and closing of the first switching means and the second switching means based on the input signal, and the voltage value between the detection terminals is equal to or less than a predetermined value. Determines cell strings abnormal, cut off the power supply output terminal of the solar cell string from the output line, is characterized by and a short circuit between the power output terminal.

The comparison of the voltage value between the detection terminals with a predetermined value is performed at least twice, and the solar cell string is determined to be abnormal based on the comparison signal, and the comparison means and the control means are connected. It is preferable that the comparison signal is transmitted and received by an electrically insulated circuit. The above-mentioned solar power generation system further has load means for applying a predetermined load between the power supply output terminals, and the comparison of the voltage value between the detection terminals with the predetermined value indicates that the load has been applied. It is good to do it in the state.

Further, the comparison between the voltage value between the detection terminals and a predetermined value is performed by disconnecting the connection with the output line by the first switching means and electrically isolating the solar cell string from the solar power generation system. It is better to make a determination in this isolated solar cell string. This comparison may be automatically performed when a sudden abnormality occurs and at a regular time. Incidentally, the interruption and short circuit of the solar cell string determined to be abnormal in this comparison may be held until a predetermined operation is performed from the outside.

The above photovoltaic power generation system further includes display means for displaying the operating state of opening / closing of the first switching means and / or the second switching means, and the solar cell string determined to be abnormal can be identified. It should be configured so that it can be done easily.

According to the protection method of the solar power generation system of the present invention, a plurality of solar cell modules are connected in series to form a solar cell string.
A first switching step, which is a protection method for a photovoltaic power generation system configured by connecting more than one in parallel, and which opens and closes the connection between the positive and negative power supply terminals of the solar cell string and the connection line connected in parallel. , A comparison step of comparing the voltage value between the detection terminals at predetermined locations of the solar cell string with a predetermined value, and a second switching step of short-circuiting the power output terminals, and the voltage value in the comparison step is preset. When the value is equal to or less than the predetermined value, the open state of the connection with the connection line in the first switching step and the short-circuit state between the power supply terminals in the second switching step are maintained.

[0015]

Therefore, in the solar power generation system of the present invention, the solar cell string in which the voltage value between the detection terminals becomes equal to or less than the predetermined value is determined to be abnormal, and the power output terminal of this solar cell string is output from the output line. Since the power is cut off and the power output terminals are short-circuited, it is possible to quickly disconnect and invalidate the defective solar cell string from the solar power generation system.

In the solar power generation system protection method of the present invention, the voltage value between the detection terminals is compared with a predetermined value, and if the voltage value in this comparison is less than or equal to the predetermined value, the connection with the connecting line is made. Since the open state and the short-circuit state between the power supply terminals are maintained, it is possible to quickly disconnect and invalidate the defective solar cell string from the solar power generation system.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the solar power generation system and the protection system for the solar power generation system of the present invention will be described below in detail based on the embodiments shown in the drawings.

<First Embodiment> FIG. 1 shows a first embodiment of the solar power generation system of the present invention. The solar power generation system of this embodiment is a power generation system called a grid-connected solar power generation system. This system includes a solar cell array 1 that performs solar power generation, two switches 2 and 3 that connect and disconnect between circuits, and a power control device.

The solar cell array 1 is formed by connecting four solar cell modules in series to form a string and connecting 16 strings in parallel. Some solar cells use amorphous silicon, crystalline silicon, compound semiconductors, or the like. In the embodiment, the product name U
PM880 Amorphous solar cell module (USSC
Company) is used.

The switch 2 is a switch for short-circuiting the output terminals of the string, and is for setting the output voltage from the string to 0V. The switch 3 is for connecting / disconnecting the connection between the string and the inverter 5, and opens / closes the output of the DC power generated by the solar cell array 1.

The power control device 4 has an inverter 5, a detection unit 7, a control unit 8 and a display unit 9. The inverter 5 is a device that converts the DC power generated by the solar cell array 1 into AC power and outputs the AC power. This device is configured in a full bridge circuit using a power MOSFET as a switching element. As the switching element, there are an IGBT, a power transistor, a GTO, etc. in addition to the power MOSFET, and the power MOSFET is a high-speed switching element among them. This inverter 5
By changing the ON / OFF duty ratio of the gate pulse, the power flow, input / output voltage, output frequency, etc. are controlled and the DC input power is converted to AC current and output. This AC output is converted to 100V by using a transformer (not shown) and output to the commercial AC system 6 which is a load. The detection unit 7 is a circuit unit that inputs the voltage of each solar cell module of the solar cell array 1 and outputs an insulated detection signal. The control unit 8
It is a circuit unit having an arithmetic element (CPU) and controls the opening / closing operations of the switches 2 and 3. High and low H / L detection signals from the detection unit 7 are connected to the signal input terminal of the control unit 8, and the control unit 8 causes the switch 2 to operate based on this input signal.
Opening and closing operations 3 and 3 are performed. Further, the display 9 is an LED
Is a circuit unit configured to have display elements such as, and performs a display operation based on an output signal from the control unit 8.

FIG. 2 shows a concrete circuit example for one string of the solar cell string 1a. The strings are solar cell modules 1a1 to 1a4, protective diodes 10a1 to 10a4, and photocouplers 7a1a to 7a.
a4a, current adjusting resistors 7a1b to 7a4b and resistor 7
a1c to 7a4c and NOT circuits 7a1d to 7a4d
It is composed of

The positive electrode of each of the solar cell modules 1a1 to 1a4 forming the above string is the photocoupler 7a1.
a to 7a4a connected to the anodes of the LEDs, and the negative electrodes of the photocouplers 7a1a to 7a1a to 7a4b via resistors 7a1b to 7a4b.
7a4a connected to the cathode of the LED. As shown in the figure, the cathode of the solar cell is connected to the cathode and the anode of the solar cell is connected to the diodes 10a1 to 10a4 for bypass protection so that the anode serves as the anode. On the output side of the photocouplers 7a1a to 7a4a, the collector of the phototransistor is connected to the power supply V _CC, and the emitter of the phototransistor is connected to the ground via the resistors 7a1c to 7a4c. Further, the voltage between the emitter and the ground, that is, the voltage between both ends of the resistors 7a1c to 7a4c is the NOT circuit 7a1d to 7a which is a logic circuit.
4d, and H / of the NOT circuits 7a1d to 7a4d.
The binary output of L becomes the detection signal.

In the solar power generation system having the above structure, the output voltage of the solar cell module when the module is normal is about 15 to 16 V, and the photocoupler 7a1a is used.
Resistance values of the resistors 7a1b to 7a4b are selected so that a sufficient forward current flows for light emission of the LEDs of ~ 7a4a.
In this state, the phototransistors of the photocouplers 7a1a to 7a4a become conductive, and the resistors 7a1c to 7a4 are turned on.
The voltage of the power supply V _CC is applied to c. As a result, the outputs from the NOT circuits 7a1d to 7a4d become "L" level signals.

When there is an abnormality, for example, when the module 1a1 cannot generate electricity, the voltage between the output terminals of the module 1a1 is the bypass diode 10a1 and the photocoupler 7.
The load of a1a and the resistor 7a1b has a voltage drop value. Generally, when an abnormality occurs in the solar cell, the internal impedance of the solar cell becomes higher than the electromotive force, and it becomes impossible to supply sufficient electric power to the load. If this load cannot be fully carried, no current flows in the input of the photocoupler 7a1a, and its output end becomes non-conductive. Therefore, the resistor 7a
No voltage is generated at 1c, and the output of the NOT circuit 7a1d becomes an "H" level signal. It should be noted that this symptom is easier to identify the characteristics of individual strings when the strings 1a to 1p are carried out independently. Therefore, the inspection can be performed more accurately by opening the switch 3 and sequentially shutting off the string to be inspected from the parallel connection line 12.

The detection signal of each of the solar cell modules 1a1 to 1a4 is input to the control unit 8, and the control unit 8 determines whether each module is normal or abnormal based on the input detection signal. If the input detection signal is low level "L", it is normal, and if high level "H" is detected, it is abnormal. When an abnormality is detected in the string 1a, the switch 2a of the string 1a is opened and
The string output switch 3a is closed, and the output terminals of the solar cell string 1a are short-circuited. Thereby, the input terminal of the inverter 5 and the other solar cell strings 1b to 1p are electrically insulated. Moreover, the output voltage of the module of the solar cell string in which the abnormality is detected is set to zero, and the risk of electric shock is reduced.

The display unit 9 receives a signal from the control unit 8 to display the abnormality detection location, so that the location where the abnormality is detected can be seen at a glance and the labor for investigating the abnormality location can be saved.
The replacement work can be started immediately. If the string output end switch 2a is opened after the abnormality detection and replacement with a normal solar cell module, normality / abnormality of each module of the solar cell string 1a is judged at that time, and the solar cell is immediately detected. It can be determined whether or not the string 1a has returned to normal. When an abnormality is detected, it is recommended that the switch 3 is opened, the switch 2 is cut off, and the display on the display 9 is held, the maintenance worker confirms the content of the abnormality, and then performs the restoration after a predetermined treatment. .

The above-mentioned self-diagnosis of the so-called photovoltaic power generation system is executed at the time of occurrence of a sudden accident and at a regular time with a predetermined time interval. When a sudden accident occurs, it is a predetermined symptom, for example, a sharp change in the output voltage level. The predetermined regular time is, for example, a preset time of day.
The power generation characteristics of the individual strings 1a to 1p are inspected, and the quality is determined by comparing the balance with a specified value or less or with others.

<Second Embodiment> FIG. 3 shows a second embodiment of the solar cell string of the present invention. In FIG. 3, the DC power generated by the solar cell string 1a is the switch 3a.
Is supplied to the load via. Further, the string output end switch 2a is provided between the output end of the solar cell string 1a and the switch 3a, and the output ends can be short-circuited.

Solar cell string 1a, two switches 2
The configurations a and 3a and the bypass diode 10a1 may be the same as those in the first embodiment. The detection unit 7 includes bypass diodes 10a1, 10b2, 10c3, 10d of the solar cell modules 1a1 to 1a4 of the solar cell string 1a.
The voltage across 4 is detected, and an insulated detection signal is output. Below, one of the specific examples of the detection part 7 is demonstrated.

The positive electrodes of the respective solar cell modules 1a1 to 1a4 are connected to the cathodes of the LEDs 7a1d to 7a4d,
The negative electrode of each solar cell module 1a1 to 1a4 is a resistor 7a.
Diodes 7a1f to 7a4f through 1e to 7a4e
Connected to the anode of. Diodes 7a1f to 7a4
The cathode of f is connected to the anodes of LEDs 7a1d to 7a4d.

The photovoltaic elements 7a1g to 7a4g are LEDs.
Only the light emitted from 7a1d to 7a4d is received, and the light from the outside is blocked. Photovoltaic device 7a1g-7
The negative electrode of a4g is connected to the ground, and the positive electrode is connected to the input side of the NOT circuits 7a1h to 7a4h.
The binary output of L / H of a1h to 7a4h becomes the detection signal.

The control section 8 receives the detection signal from the detection section 7 and judges whether the solar cell modules 1a1 to 1a4 are normal or abnormal, and accordingly outputs the control signal to the string output end switch 2a, the switch 3a and the display. Output to the container 9. If the solar cell module is normal, the LED is in the reverse bias state, so that no forward current flows through the LED and no light is emitted. Therefore, no light is incident on the photovoltaic element, the terminal voltage of the photovoltaic element is zero, and the output of the NOT circuit, that is, the detection signal is "H".
Becomes

When an abnormality occurs in the solar cell, a current flows through the bypass diode and a current also flows through the LED, so that the LED emits light. In the photovoltaic element, a voltage is generated across the photovoltaic element in response to the light from the LED. As a result, the output of the NOT circuit, that is, the detection signal becomes "L".

The control unit 8 determines that the detection signal input from the detection unit is "H" level, and that the detection signal is "L" level is abnormal. When an abnormality is detected, the switch 2a of the string 1a is opened, the string output switch 3a is closed, and the solar cell string 1a is closed.
Short the output terminal of.

Also in this second embodiment, the same effect as in the first embodiment can be obtained.

<Third Embodiment> A third embodiment of the present invention will be described. The third embodiment has a configuration as shown in FIG. 1 similarly to the first embodiment. The control method of the control unit 8 different from that of the first embodiment will be described below.

The control unit 8 receives the detection signal from the detection unit 7 and determines whether each module is normal or abnormal. However, even if the detection signal is abnormal, it is not immediately determined to be abnormal, and the detection signal is determined to be abnormal. Power is generated as it is by simply displaying on the display 9 that the solar cell module has stopped generating power. The detection unit 7 and the control unit 8 continue to detect abnormality. Then, if the abnormality detection of the same module continues for a predetermined time, it is determined that the module is abnormal, and the opening operation of the switch 3 of the string having the abnormal module and the string output end switch 2 are performed.
To instruct the closing operation of. Further, the display 9 displays the abnormality of the solar cell module.

As a result, even when the solar power generation system is installed in a place where the solar cell array partial shade is likely to occur, it is possible to efficiently generate power without disconnecting the solar cell strings unnecessarily, and the solar cell module is abnormal. Can also be detected.

The above-described embodiment is one example of the preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention.

[0041]

As is apparent from the above description, the solar power generation system of the present invention determines that a solar cell string in which the voltage value between the detection terminals is equal to or lower than a predetermined value is abnormal, and the solar cell string is abnormal. The power supply output terminal of the string is cut off from the output line, and the power supply output terminals are short-circuited. For this reason,
The defective solar cell strings can be cut off and invalidated from the solar power generation system quickly, and the following effects are achieved. (1) It is possible to constantly diagnose an abnormality and detect an abnormality in the solar power generation system at an early stage. (2) By promptly disconnecting the defective solar cell string from the solar power generation system, it is possible to prevent the deterioration of the power generation efficiency of the solar power generation system from being accelerated. (3) When an abnormality is detected, the abnormality is detected by the display unit, so that it is possible to omit a human investigation of a large number of solar cell modules and reduce the number of steps. (4) The automation of inspection and invalidation of defective solar cell strings reduce the risk of electric shock during repairs and investigations. (5) When replacing a defective solar cell string or solar cell module, the solar power generation system has already been cut off, and the replacement / repair work can be immediately started. It is possible to recover in a short time. (6) Remote detection is possible by insulating the detection unit. (7) By disconnecting the solar cell string from the system and checking it, it is possible to accurately determine whether the solar cell string is good or bad without being affected by other solar cell strings. (8) By applying a predetermined load to determine the quality of the solar cell string, it is possible to make a more accurate determination.

[Brief description of drawings]

FIG. 1 is an example of a solar power generation system of the present invention and a protection system for the solar power generation system.

FIG. 2 is an example of a detection unit of the solar power generation system of the present invention.

FIG. 3 is an example of a solar cell string of the present invention.

[Explanation of symbols]

 1 solar cell array, 2 string output end switch, 3 switch, 4 power control device, 5 inverter, 6 commercial AC system, 7 detection unit, 8 control unit, 9 indicator.

Claims (15)

[Claims] 1. A photovoltaic system in which a plurality of solar cell modules are connected in series to form a solar cell string, and two or more solar cell strings are connected in parallel, wherein a positive electrode of the solar cell string. A first switching means for connecting or disconnecting between a negative power source output terminal and the output line connected in parallel and outputting; a second switching means for shorting or opening the power source output terminals; and a solar cell Comparing means for comparing the voltage value between the detection terminals at a predetermined location in the string with a predetermined value and outputting the compared comparison signal; and the first switching means for inputting the comparison signal and based on the input signal. A control means for controlling opening / closing of the second switching means, and a power output terminal of the solar cell string having a voltage value between the detection terminals equal to or lower than the predetermined value. Photovoltaic systems, characterized in that shut off from the serial output line, and a short circuit between the power output terminal. 2. The comparison between the voltage value between the detection terminals and the predetermined value is performed at least twice, and the solar cell string is determined to be abnormal based on the comparison signal. The described solar power generation system. 3. The photovoltaic power generation system according to claim 1, wherein the comparison signal is exchanged between the comparison unit and the control unit in an electrically insulated circuit. 4. The solar power generation system further includes load means for applying a predetermined load between the power supply output terminals, and comparing the voltage value between the detection terminals with the predetermined value, The solar power generation system according to any one of claims 1 to 3, wherein the solar power generation system is performed in a state where the load is applied. 5. The comparison of the voltage value between the detection terminals with the predetermined value cuts off the connection with the output line by the first switching means to connect the solar cell string to the solar power generation system. 5. The solar power generation system according to claim 1, wherein the solar cell string is electrically isolated from the solar cell string, and the determination is performed in the isolated solar cell string. 6. The method according to claim 1, wherein the comparison of the voltage value between the detection terminals and the predetermined value is automatically performed when a sudden abnormality occurs and at a regular time. 5. The solar power generation system according to any one of 5. 7. The cutoff and the short circuit of the solar cell string determined to be abnormal in the comparison of the voltage value between the detection terminals and the predetermined value are held until a release operation is performed. 7. The method according to claim 1, wherein
The solar power generation system according to any one of 1. 8. The solar power generation system further includes a display unit for displaying an operating state and / or a detection position of opening / closing of the first switching unit or / and the second switching unit, and the abnormality detection The photovoltaic power generation system according to any one of claims 1 to 7, wherein the determined solar cell string can be easily identified. 9. A protection method for a photovoltaic power generation system, which is configured by connecting a plurality of solar cell modules in series to form a solar cell string, and connecting two or more solar cell strings in parallel, wherein the solar cell A first switching step of opening and closing the connection between the positive and negative power supply terminals of the string and the connection lines connected in parallel; and a predetermined voltage value between the detection terminals at predetermined locations of the solar cell string. A comparison step of comparing and a second switching step of short-circuiting between the power supply output terminals, and when the voltage value in the comparison step is less than or equal to the predetermined value, the first switching step is performed. A protection system for a photovoltaic power generation system, characterized in that an open state of connection with a connection line and a short-circuit state between the power supply terminals in the second switching step are maintained. 10. The step of comparing the voltage value between the detection terminals with the predetermined value is executed at least twice, and the connection with the connection line by the first switching step is performed based on the comparison result by the execution. 10. The protection system for a photovoltaic power generation system according to claim 9, wherein the open state and the short-circuit state between the power supply terminals are held in the second switching step. 11. The protection method for the photovoltaic power generation system further includes a load applying step of applying a predetermined load between the power supply terminals, and the comparing step is performed by executing the load applying step. 11. The method according to claim 9 or 10, wherein the processing is executed in a state where a load is applied.
The protection method for the described solar power system. 12. The comparison step disconnects the connection with the output line by executing the first switching step, electrically isolates the solar cell string from the solar power generation system, and the isolated said 12. The method according to claim 9, wherein the operation is performed in a solar cell string.
The solar power generation system protection method described in the item. 13. The photovoltaic power generation system according to claim 9, wherein the comparing step is automatically performed when a sudden abnormality occurs and at a regular time. Protection method. 14. The holding state of the connection open state with the connection line in the first switching step and the short-circuit state between the power supply terminals in the second switching step is maintained until a release operation is performed. 9. The method according to claim 9, characterized in that it is sustained.
The method for protecting the photovoltaic power generation system according to any one of 3 above. 15. The method for protecting the photovoltaic power generation system further includes a display step of displaying an operating state of opening and closing and / or a detection location in the first switching step and / or the second switching step, 15. The display of the open state of the connection with the connection line in the first switching step and / or the holding state of the short-circuited state between the power supply terminals in the second switching step is displayed. Either one
The protection method of the solar power generation system described in the item.