JP2012256092A - Photovoltaic power generating system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photovoltaic power generating system capable of reducing output loss.SOLUTION: In a photovoltaic power generating system, a plurality of solar cell power generation blocks are parallel connected, and extension cables from the solar cell power generation blocks to a parallel connection point have respective total cable lengths that are partly or entirely different from one another. In the photovoltaic power generating system, the respective electrical resistivity values of power transmission routes from the solar cell power generation blocks to the parallel connection point are made substantially the same, by using a plurality of kinds of extension cables which are different from one another at least in either of their electrical resistivity or conductor cross sectional area.

Description

  The present invention relates to a solar power generation system, and more particularly to a solar power generation system in which a plurality of solar cell power generation units are connected in parallel.

  In a general photovoltaic power generation system, the cable provided in each solar cell power generation unit is connected to each extension cable at the boundary connection point of each solar cell power generation unit, and each extension cable is wired to the parallel connection point in parallel. Connect the parallel connection point and the input terminal of a power conditioner with a maximum power operating point tracking (MPPT) function with a cable to connect the power from each solar cell power generation unit to the power conditioner. Supply to na. The power conditioner performs MPPT control so that the power supplied to the input terminal of the power conditioner is maximized, and determines the operating voltage and operating current of each solar cell power generation unit.

  The solar cell power generation unit is divided for each input unit input to the parallel connection point. The specific configuration of the solar cell power generation unit differs depending on the configuration of the solar power generation system, such as a single solar cell module or a solar cell module string in which a plurality of solar cell modules are connected in series. There are also many photovoltaic power generation systems in which a plurality of parallel connection points exist.

  Here, FIG. 1 shows an example of a solar power generation system in which the solar cell power generation unit is a single solar cell module, and FIG. 2 shows an example of a solar power generation system in which the solar cell power generation unit is a solar cell module string. FIG. 3 shows an example of a photovoltaic power generation system in which a plurality of connection points exist and a plurality of types of solar cell power generation units exist. 1 to 3, reference numeral 1 denotes a solar cell power generation unit, reference numeral 2 denotes a solar cell module, reference numeral 3 denotes a cable provided in the solar battery power generation unit, reference numeral 4 denotes a boundary connection point, and reference numeral 5 denotes a boundary connection point. Reference numeral 6 denotes a parallel connection point, reference numeral 7 denotes a power conditioner having an MPPT function, reference numeral 8 denotes a cable, reference numeral 9 denotes a solar cell module string, reference numeral 10 denotes a boundary connection point and parallel connection point. Each is shown.

US Patent Application Publication No. 2008/0236648 JP 7-45847 A

  In the photovoltaic power generation system having the above-described configuration, the physical distance between each solar cell power generation unit and the power conditioner having the MPPT function determined by the restrictions on the installation location of each solar cell power generation unit and the power conditioner having the MPPT function. Therefore, in most cases, the distance from each solar cell power generation unit to the parallel connection point is different, and when using the same type of extension cable, the resistance value of each extension cable differs depending on the length.

  Even if the current-voltage characteristics in each solar cell power generation unit are the same, the current-voltage characteristics of each solar cell power generation unit at the parallel connection point will be different due to the voltage drop due to the difference in resistance value of the extension cable. The maximum output operating point voltage of each solar cell power generation unit at the connection point is also different.

  When solar power generation units with different maximum output operating point voltages are combined in parallel (the output voltage of solar power generation units with different maximum output operating point voltages is set to the same voltage value, and the output of solar cell power generation units with different maximum output operating point voltages When the currents are added), the maximum output operating point voltage in the current-voltage characteristics after the parallel synthesis does not necessarily match the maximum output operating point voltage of each individual solar cell power generation unit.

  Here, in order to simplify the description, a case where two solar cell power generation units are connected in parallel will be considered.

  FIG. 4 shows an example of the current-voltage characteristics at the parallel connection point when the resistance values of the extension cables from the two solar cell power generation units to the parallel connection point are different. In FIG. 4, symbol T1 indicates the current-voltage characteristics of the solar battery power generation unit 1a with the maximum output Pa and the maximum output operating point voltage Va, and symbol T2 indicates the solar with the maximum output Pb and the maximum output operating point voltage Vb. The current-voltage characteristics of the battery power generation unit 1b, and the symbol T3 indicate the current-voltage characteristics after the parallel synthesis of the solar cell power generation unit 1a and the solar cell power generation unit 1b.

  When the solar cell power generation unit 1a and the solar cell power generation unit 1b are combined in parallel, the maximum output operating point voltage is the maximum output operating point voltage Va of the solar cell power generation unit 1a and the maximum output operating point voltage of the solar cell power generation unit 1b. Vs is also different from Vb.

  FIG. 5 shows an example of the output voltage characteristic at the parallel connection point when the resistance values of the extension cables from the two solar cell power generation units to the parallel connection point are different. In FIG. 5, symbol T4 represents the output voltage characteristic of the solar cell power generation unit 1a, symbol T5 represents the output voltage characteristic of the solar cell power generation unit 1b, and symbol T6 represents a parallel combination of the solar cell power generation unit 1a and the solar cell power generation unit 1b. The output voltage characteristics are respectively shown.

  The power conditioner having the MPPT function of the photovoltaic power generation system performs MPPT control so as to operate at the maximum output operating point voltage Vs after parallel synthesis in order to obtain the maximum output Ps after parallel synthesis. At this time, the output obtained from the solar cell power generation unit 1a is Pa ′, the output obtained from the solar cell power generation unit 1b is Pb ′, and the maximum output Ps after parallel synthesis is the output Pa ′ and the output Pb ′. It is sum.

  As described above, the maximum output operation point voltage Vs after the parallel combination is different from the maximum output operation point voltage Va of the solar cell power generation unit 1a and the maximum output operation point voltage Vb of the solar cell power generation unit 1b. The output Pa ′ of the solar cell power generation unit 1a at the point voltage Vs is smaller than the maximum output Pa of the solar cell power generation unit 1a, and similarly, the output Pb of the solar cell power generation unit 1b at the maximum output operating point voltage Vs after parallel synthesis. 'Becomes smaller than the maximum output Pb of the solar cell power generation unit 1b.

  As described above, in the conventional general photovoltaic power generation system, the mismatch of the optimum operating point occurs, the power generation capability of each solar cell power generation unit cannot be fully exhibited, and the output loss is reduced. It was big.

  As a solar power generation system that can avoid loss due to mismatch of the optimum operating point, for example, MPPT control is performed for each individual solar cell module, and the output of each individual solar cell module is boosted or lowered to stabilize Patent Document 1 proposes a system in which a device (regulator) to be converted is provided. However, the system proposed in Patent Document 1 is disadvantageous in that it is expensive because a regulator is provided, and conversion loss occurs during step-up / step-down.

  An object of this invention is to provide the solar power generation system which can reduce an output loss in view of said situation.

  In order to achieve the above object, a photovoltaic power generation system according to the present invention includes a plurality of solar cell power generation units connected in parallel, and a total cable length of an extension cable from each of the solar cell power generation units to the parallel connection point is partially Or, it is a photovoltaic power generation system that is completely different, using a plurality of types of extension cables having different electrical resistivity and conductor cross-sectional area, and the electric power transmission path from each solar cell power generation unit to the parallel connection point. It is set as the structure (1st structure) which makes resistance value substantially the same.

である構成（第２の構成）にしてもよい。 In the solar power generation system having the first configuration, an electric resistance value of a power transmission path from a certain solar cell power generation unit k to the parallel connection point is R _k, and The number of extension cables used as a power transmission path to the connection point is n (n is a natural number), and the electrical resistivity of the i-th extension cable (i is an arbitrary natural number less than or equal to n) of the n types. _Is ρ _ki , cable length is L _ki , and conductor cross-sectional area is S _ki ,

It is also possible to adopt the configuration (second configuration).

であり、前記総コストＴＣが最小となるように各ケーブル長Ｌ_ｋｉを決定する構成（第３の構成）としてもよい。 In the photovoltaic power generation system of the second configuration, TC is defined as a total cost of an extension cable used as a power transmission path from a certain solar cell power generation unit k to the parallel connection point, and i among the n types If the cost per unit length of the second extension cable is C _ki ,

The cable length L _ki may be determined such that the total cost TC is minimized (third configuration).

In the solar power generation system having the third configuration, as a configuration (fourth configuration) in which the minimum required length of the extension cable is set and each cable length L _ki is determined so that the total cost TC is minimized. Also good.

  In the solar power generation system having any one of the first to fourth configurations, one type of extension cable may be used for the solar cell power generation unit having the shortest distance to the parallel connection point.

  According to the photovoltaic power generation system according to the present invention, since the mismatch of the optimum operating point does not occur, the power generation capability of each solar cell power generation unit can be fully exhibited, and the output loss can be reduced. Can do.

It is a figure which shows an example of the solar power generation system whose solar cell power generation unit is a solar cell module single-piece | unit. It is a figure which shows an example of the solar power generation system whose solar cell power generation unit is a solar cell module string. It is a figure which shows an example of the solar energy power generation system in which multiple parallel connection points exist and multiple types of solar cell power generation units exist. It is a figure which shows an example of the current-voltage characteristic in a parallel connection point in case the resistance value of the extension cable from two solar cell power generation units to a parallel connection point differs. It is a figure which shows an example of the output voltage characteristic in a parallel connection point in case the resistance value of the extension cable from two solar cell power generation units to a parallel connection point differs. It is a figure showing a schematic structure of a photovoltaic power generation system concerning one embodiment of the present invention. It is a figure for demonstrating the effect of the solar energy power generation system which concerns on one Embodiment of this invention.

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

  FIG. 6 shows a schematic configuration of a photovoltaic power generation system according to an embodiment of the present invention. The photovoltaic power generation system according to one embodiment of the present invention shown in FIG. 6 includes three solar cell power generation units, that is, a first solar cell power generation unit 1-1, a second solar cell power generation unit 1-2, and a first solar cell power generation unit 1-2. 3 solar cell power generation units 1-3. Each solar cell power generation unit is divided for each input unit input to the parallel connection point, and is composed of, for example, a single solar cell module or a solar cell module string in which a plurality of solar cell modules are connected in series. .

The first solar cell power generation unit 1-1 is connected to the parallel connection point 6 using one type of extension cable. That is, a cable (not shown) provided in the first solar cell power generation unit 1-1 is connected to one end of the extension cable 5-1 at the boundary connection point 4-1 of the first solar cell power generation unit 1-1. The other end of the extension cable 5-1 is connected to the parallel connection point 6. Incidentally, the electrical resistivity of the extension cable 5-1 and [rho _11, the cable length of the extension cable 5-1 and _{L 11,} the conductor cross-sectional area of the extension cable 5-1 to _{S 11.}

  The second solar cell power generation unit 1-2 is connected to the parallel connection point 6 using two types of extension cables. That is, a cable (not shown) provided in the second solar cell power generation unit 1-2 is connected to one end of the extension cable 5-2-1 at the boundary connection point 4-2 of the second solar cell power generation unit 1-2. The other end of the extension cable 5-2-1 is connected to one end of the extension cable 5-2-2 at the relay point 11-2, and the other end of the extension cable 5-2-2 is connected to the parallel connection point 6. Connected to.

  Examples of a method for connecting the extension cables at the relay point 11-2 include a method of caulking the extension cables with a crimping sleeve and curing with a self-bonding tape or a vinyl tape for electrical work. As another connection method, for example, a connection connector that can correspond to each extension cable diameter is provided at both ends of the relay point, and the extension cables are connected to each other using the connection connector, or waterproof with a terminal block inside. Examples include a method of providing a box at a relay point and connecting extension cables to each other using the terminal block.

Note that the electrical resistivity of the extension cable 5-2-1 is ρ ₂₁ , the cable length of the extension cable 5-2-1 is L _21, and the conductor cross-sectional area of the extension cable 5-2-1 is S ₂₁ . . Further, the electrical resistivity of the extension cable 5-2-2 and [rho _22, the cable length of the extension cable 5-2-2 and _{L 22,} the conductor cross-sectional area of the extension cable 5-2-2 and _{S 22} .

  The third solar cell power generation unit 1-3 is connected to the parallel connection point 6 using three types of extension cables. That is, a cable (not shown) provided in the third solar cell power generation unit 1-3 is connected to one end of the extension cable 5-3-1 at the boundary connection point 4-3 of the third solar cell power generation unit 1-3. The other end of the extension cable 5-3-1 is connected to one end of the extension cable 5-3-2 at the relay point 11-3-1 and the other end of the extension cable 5-3-2 is connected to the relay point. 11-3-2 is connected to one end of the extension cable 5-3-3, and the other end of the extension cable 5-3-3 is connected to the parallel connection point 6.

  The connection method between the extension cables at the relay point 11-3-1 and the connection method between the extension cables at the relay point 11-3-2 are the same as the connection method between the extension cables at the relay point 11-2.

Incidentally, the electrical resistivity of the extension cable 5-3-1 and [rho _31, the cable length of the extension cable 5-3-1 and _{L 31,} the conductor cross-sectional area of the extension cable 5-3-1 and _{S 31} . Further, the electrical resistivity of the extension cable 5-3-2 and [rho _32, the cable length of the extension cable 5-3-2 and _{L 32,} the conductor cross-sectional area of the extension cable 5-3-2 and _{S 32} . Further, the electrical resistivity of the extension cable 5-3-3 and [rho _33, the cable length of the extension cable 5-3-3 and _{L 33,} the conductor cross-sectional area of the extension cable 5-3-3 and _{S 33} .

Hereinafter, the cable length _{L 11} of the extension cable 5-1 is 30 m, the sum of the cable length _{L 21} of the extension cable 5-2-1 cable length _{L 22} of the extension cable 5-2-2 is 45m The total of the cable length L ₃₁ of the extension cable 5-3-1, the cable length L ₃₂ of the extension cable 5-3-2, and the cable length L ₃₃ of the extension cable 5-3-3 is 60 m. A case will be described as an example.

  In the photovoltaic power generation system according to one embodiment of the present invention shown in FIG. 6, each solar cell power generation unit (first solar cell power generation unit 1-1, second solar cell power generation unit 1-2, third solar cell). The electric resistance values from the battery power generation unit 1-3) to the parallel connection point 6 are made to coincide with each other, but it is necessary to determine a reference electric resistance value. As a photovoltaic power generation system, except for the mismatch of the optimum operating point, the lower the electrical resistance value from each solar cell power generation unit to the parallel connection point, the higher the output, but the conductor cross-sectional area of the extension cable is accordingly Since the initial cost is increased, it is necessary to select the conductor cross-sectional area in consideration of the initial cost.

In the photovoltaic power generation system according to one embodiment of the present invention shown in FIG. 6, one type of extension cable used for the solar cell power generation unit having the shortest distance to the parallel connection point 6 is used as a reference. . The reason for such a configuration is that when one type of cable having a small conductor cross-sectional area, that is, a low-cost cable is used, a cable having a small conductor cross-sectional area is connected to the solar cell power generation unit having the shortest distance to the parallel connection point 6 Since the cable length is shorter and the electrical resistance value of the cable with a small conductor cross-sectional area is lower than the use of a cable with a small conductor cross-sectional area for other solar cell power generation units, the minimum value is This is because it is easy to see if the cross-sectional area of the conductor is sufficient. The conductor cross-sectional areas of cables commercialized in Japan are 2 mm ² , 3.5 mm ² , 5.5 mm ² , 8 mm ² , and the like.

As an extension cable 5-1 for connecting the first solar cell power generation units 1-1 distance to the parallel connection point 6 is shortest solar cell power generation units in parallel connection point 6, the conductor cross-sectional area S ₁₁ is 2mm ² and a cable having an electrical resistivity ρ ₁₁ of 0.0171 Ω · mm ² / m (copper is used as the conductor material), the cable length L ₁₁ of the extension cable 5-1 is 30 m. The electrical resistance value of the extension cable 5-1 is 0.2565Ω.

Next, the specifications of two types of extension cables (extension cable 5-2-1 and extension cable 5-2-2) for connecting the second solar battery power generation unit 1-2 to the parallel connection point 6 are determined. Copper is used as the conductor material for the two types of extension cables. Therefore, the electrical resistivity [rho ₂₁ of the extension cable 5-2-1, electrical resistivity [rho ₂₁ of the extension cable 5-2-2 both become 0.0171Ω · ^mm 2 / m. In consideration of cost, in order to reduce the conductor sectional area, the conductor cross-sectional area _{S 21} of the extension cable 5-2-1 and 2 mm ^2, the conductor cross-sectional area _{S 22} of the extension cable 5-2-2 3. Set to 5 mm ² . The total of the cable length L ₂₁ of the extension cable 5-2-1 and the cable length L ₂₂ of the extension cable 5-2-2 is 45 m as described above. Therefore, in order to connect the electrical resistance value of one type of extension cable for connecting the first solar cell power generation unit 1-1 to the parallel connection point 6, and the second solar cell power generation unit 1-2 to the parallel connection point 6. In order to make the total electrical resistance values of the two types of extension cables equal, it is necessary to satisfy the following expression (1).

When the above equation (1) is solved, the cable length L ₂₁ of the extension cable 5-2-1 is 10 m. Thus, the cable length _{L 22} of the extension cable 5-2-2 becomes 35m.

  Next, the specification of the extension cable for connecting the third solar cell power generation unit 1-3 to the parallel connection point 6 is determined.

  First, as in the case of the second solar cell power generation unit 1-2, the electric power of one type of extension cable for connecting the first solar cell power generation unit 1-1 to the parallel connection point 6 using two types of cables. An attempt is made to make the resistance value equal to the total electrical resistance value of the two types of extension cables for connecting the third solar cell power generation unit 1-3 to the parallel connection point 6.

Considering cost, to reduce the conductor sectional area, the conductor cross-sectional area _{S 31} of the extension cable 5-3-1 and 2 mm ^2, the conductor cross-sectional area _{S 32} of the extension cable 5-3-2 3.5 mm ² And Then, the sum of the cable length _{L 31} of the extension cable 5-3-1 cable length _{L 32} of the extension cable 5-3-2 and 60 m. In such a setting, the electrical resistance value of one type of extension cable for connecting the first solar cell power generation unit 1-1 to the parallel connection point 6 and the third solar cell power generation unit 1-3 are connected in parallel. In order to make the total electrical resistance values of the two types of extension cables to be connected to 6 equal, it is necessary to satisfy the following expression (2).

Solving the above equation (2), the cable length _{L 31} of the extension cable 5-3-1 is next -10 m, no solution. Therefore, it is necessary to use a cable having a conductor cross-sectional area of 5.5 mm ² having a lower electrical resistivity.

<First Example of Specification of Extension Cable Corresponding to Third Solar Cell Power Generation Unit>
In the case of relay using a crimping sleeve, relay from a cable having a small conductor cross-sectional area to a cable having a large conductor cross-sectional area, for example, from a cable having a conductor cross-sectional area of 2 mm ² to a cable having a conductor cross-sectional area of 5.5 mm ² May be difficult to relay. For this reason, it is necessary to consider performing relaying by gradually increasing the cross-sectional area of the conductor. Consider the case where conductor cross-sectional area of the extension cable connected directly to the cable that comes with the solar cell power generation unit is 2 mm ^2, the extension extension cable conductor cross-sectional area is 3.5 mm ^2, the conductor cross-sectional area of 5.5 mm ² Cables shall be used in order. That is, in order to connect the third solar cell power generation unit 1-3 to the parallel connection point 6, three types of extension cables (extension cable 5-3-1, extension cable 5-3-2, extension cable 5-3- 3) is used, and two relay points 11-3-1 and 11-3-2 are provided as shown in FIG.

In this case, the sum of the cable length _{L 33} of the cable length _{L 31} of the extension cable 5-3-1 cable length _{L 32} of the extension cable 5-3-2 extension cable 5-3-3 is 60m is there. Further, in order to prevent the deterioration of the connection workability at the relay point, the cable length L ₃₁ of the extension cable 5-3-1, the cable length L ₃₂ of the extension cable 5-3-2, and the extension cable 5-3-3 Each cable length L ₃₃ is 1 m or longer. However, the shortest cable length 1 m set here is merely an example, and an appropriate value may be set as the shortest cable length according to the connection method at the relay point. For example, it can be set to 0.1 m.

The electrical resistance value of one type of extension cable for connecting the first solar cell power generation unit 1-1 to the parallel connection point 6 and 3 for connecting the third solar cell power generation unit 1-3 to the parallel connection point 6 In order to make the total electrical resistance value of the extension cables of the same type equal, it is necessary to satisfy the following expression (3).

Here, in order to investigate the condition that L ₃₁ is 1 m or more, when calculating by substituting L ₃₂ = 60−L ₃₁ −L ₃₃ into the above equation (3),
L ₃₁ = 0.4848 × L ₃₃ −10 ≧ 1
It becomes. As a result, L ₃₃ ≧ 22.7 m.

Subsequently, in order to investigate the condition that L ₃₂ is 1 m or more, when calculating by substituting L ₃₁ = 60−L ₃₂ −L ₃₃ into the above equation (3),
L ₃₂ = 70−1.4848 × L ₃₃ ≧ 1
It becomes. As a result, L ₃₃ ≦ 46.4 m.

Next, consider the cost of the cable. The cable cost is proportional to the cable length, the cost per cable length of an extension cable with a conductor cross-sectional area of 2 mm ² , the cost per cable length of an extension cable with a conductor cross-section area of 3.5 mm ² , Assuming that the cost per length of the extension cable having an area of 5.5 mm ² is 100, 175, and 275, respectively, three types of extension cables for connecting the third solar cell power generation unit 1-3 to the parallel connection point 6 The total cost TC of (extension cable 5-2-1, extension cable 5-2-2, extension cable 5-2-3) is expressed by the following equation (4).
TC = 100 × L ₃₁ + 175 × L ₃₂ + 275 × L ₃₃ (4)

When examining the condition that L ₃₁ = 0.4848 × L ₃₃ −10 obtained when examining the condition that L ₃₁ is 1 m or more and the condition that L ₃₂ is 1 m or more with respect to the above equation (4). Substituting the calculated L ₃₂ = 70-1.4848 × L ₃₃ and calculating,
TC = 63.64 × L ₃₃ +1250
It becomes. In this case, since the cable total cost TC is a monotonically increasing function, the more cable total cost TC is small cable length L ₃₃ of the extension cable 5-2-3 is reduced. Therefore, L ₃₃ = 22.7 m is determined so that the total cable cost TC is minimized while satisfying the condition that L ₃₁ is 1 m or more. From the above, L ₃₁ = 1 m and L ₃₂ = 36.3 m.

<Second Example of Specification Determination of Extension Cable Corresponding to Third Solar Cell Power Generation Unit>
Here, as a modification, in determining the extension cable specification of the third solar cell power generation unit 1-3, the extension cable 5-3-1 has a conductor cross-sectional area of 3.5 mm ² and an electrical resistivity ρ. ₁₁ is 0.0171 Ω · mm ² / m (copper is used as the conductor material), and the extension cable 5-3-2 has a conductor cross-sectional area of 5.5 mm ² and an electrical resistivity ρ. ₁₁ is 0.027Ω · mm ² / m (aluminum is used as the conductor material), and the extension cable 5-3-3 has a conductor cross-sectional area of 8mm ² and an electrical resistivity ρ ₁₁ of Consider a case where a cable of 0.0171 Ω · mm ² / m (copper material is used) is employed.

The electrical resistance value of one type of extension cable for connecting the first solar cell power generation unit 1-1 to the parallel connection point 6 and 3 for connecting the third solar cell power generation unit 1-3 to the parallel connection point 6 In order to make the total electrical resistance value of the extension cables of the same type equal, it is necessary to satisfy the following formula (5).

Here, in order to investigate the condition that L ₃₁ is 1 m or more, calculation is performed by substituting L ₃₃ = 60−L ₃₁ −L ₃₂ into the above equation (5).
L ₃₁ = −1.0085 × L ₃₂ + 46.67 ≧ 1
It becomes. As a result, L ₃₂ ≦ 45 m.

Subsequently, in order to investigate the condition that L ₃₃ is 1 m or more, when calculating by substituting L ₃₁ = 60−L ₃₂ −L ₃₃ into the above equation (5),
L ₃₃ = 0.0085 × L ₃₂ + 13.33 ≧ 1
It becomes. As a result, L ₃₂ ≧ −1450 m, and since actually 1 m or more, L ₃₂ ≧ 1 m.

Next, consider the cost of the cable. If the cable cost is proportional to the cable length, and the aluminum cable cost is about 1/3 of the copper cable cost, the cable length of the extension cable that is a copper cable with a conductor cross-sectional area of 3.5 mm ² Cost per cable length of an extension cable that is an aluminum cable with a conductor cross-sectional area of 5.5 mm ² , and cost per cable length of an extension cable that is a conductor cross-section of 8 mm ² and a copper cable. Assuming that 175, 90, and 400 respectively, three types of extension cables (extension cable 5-2-1, extension cable 5-2-2, and the like) for connecting the third solar cell power generation unit 1-3 to the parallel connection point 6 are used. The total cost TC of the extension cable 5-2-3) is expressed by the following equation (6).
TC = 175 × L ₃₁ + 90 × L ₃₂ + 400 × L ₃₃ (6)

With respect to the above equation (6), L ₃₁ = -1.0085 × L ₃₂ +46.67 obtained when examining the condition that L ₃₁ is 1 m or more, and the condition that L ₃₃ is 1 m or more are examined. Substituting the calculated L ₃₃ = 0.0085 × L ₃₂ +13.33,
TC = −83.09 × L ₃₂ +13499
It becomes. In this case, since the cable total cost TC is a monotonically decreasing function, the cable total cost TC decreases the larger the cable length L ₃₂ of the extension cable 5-2-3. Therefore, L ₃₂ = 45 m is determined so that the total cable cost TC is minimized while satisfying the condition that L ₃₁ is 1 m or more. From the above, L ₃₁ = 1 m and L ₃₃ = 14 m.

<Effect>
The effect of the photovoltaic power generation system according to one embodiment of the present invention shown in FIG. 6 will be described with reference to FIG.

  In FIG. 7, symbol T7 indicates the output voltage characteristic of the first solar cell power generation unit 1-1 at the parallel connection point when the present invention is not applied, and symbol T8 indicates the parallel connection when the present invention is not applied. The output voltage characteristic of the second solar cell power generation unit 1-2 at the point, and the output voltage characteristic of the third solar cell power generation unit 1-3 at the parallel connection point when the present invention is not applied to the reference symbol T9, Symbol T10 indicates the output voltage characteristic after parallel synthesis of each solar cell power generation unit when the present invention is not applied.

  Further, in FIG. 7, reference numeral T11 indicates the output voltage characteristics of each solar cell power generation unit at the parallel connection point when the present invention is applied, and reference numeral T12 indicates after parallel synthesis of each solar cell power generation unit when the present invention is applied. The output voltage characteristics are respectively shown.

When the cable having a conductor cross-sectional area of 2 mm ² is adopted for all the extension cables without applying the present invention, the second solar cell power generation unit 1-2 and the third sun having a long distance from the parallel connection point 6 are used. In the battery power generation unit 1-3, since the electric resistance value of the extension cable is higher than that in the first solar cell power generation unit 1-1, the output decreases due to resistance loss. Thereby, the maximum output operating voltage value of each solar cell power generation unit at the parallel connection point does not match (see output voltage characteristics T7 to T9).

  On the other hand, when the present invention is applied, since the electric resistance value of the extension cable from each solar cell power generation unit to the parallel connection point 6 becomes the same, the current-voltage characteristic of each solar cell power generation unit at the parallel connection point is The output voltage characteristics of each solar cell power generation unit at the parallel connection point coincide with each other, and the maximum output operation voltage value of each solar cell power generation unit at the parallel connection point and the maximum output operation voltage value of the photovoltaic power generation system become the same. (Refer to the output voltage characteristics T11 to T12). Thereby, since the mismatch of an optimal operating point does not generate | occur | produce, the power generation capability which each solar cell power generation unit has can fully be exhibited, and the loss of an output can be made small.

  When the present invention is applied, the electrical resistance value of the extension cable is lowered with respect to the second solar cell power generation unit 1-2 and the third solar cell power generation unit 1-3 as compared with the case where the present invention is not applied. Therefore, since a cable having a large conductor cross-sectional area must be selected, the initial cost increases.

  However, for example, in a solar power generation system that generates 10000 kWh per year, it is assumed that the amount of power generation increased by 1% and the annual power generation increased by 100 kWh by the application of the present invention. Then, if electricity can be sold for 40 yen per kWh, 4000 yen can be obtained annually, and if the interest rate and price increase are not taken into consideration, the initial increase cost can be recovered in 12.5 years. Further, if the value per kWh increases, the collection period is further shortened, and the merit of the present invention is further utilized.

  The absolute value of the maximum output value varies depending on the electric resistance value of the extension cable corresponding to the first solar cell power generation unit 1-1, but the second solar cell power generation unit 1-2 and the third solar cell power generation unit. The loss due to the electrical resistance value of the extension cable is reduced by matching each electrical resistance value of 1-3 to the first solar cell power generation unit 1-1 that has the lowest electrical resistance value when the same cable is used. Is done.

In order to increase the absolute value of the maximum output value, for example, by using a cable having a high conductor cross-sectional area of 5.5 mm ² for all extension cables, the absolute value can certainly be increased. Then, since the mismatch of the optimum operating point occurs, the power generation merit with respect to the initial increase cost is larger when the present invention is applied than the method.

<Others>
In the above description, a copper cable having a conductor cross-sectional area of 2 mm ² is used as one type of extension cable for connecting the first solar cell power generation unit 1-1 to the parallel connection point 6. When the electric resistance value from the battery power generation unit to the parallel connection point is desired to be lower than the above-described example, one type of extension cable for connecting the first solar cell power generation unit 1-1 to the parallel connection point 6 is used. It is also possible to use a copper cable having a conductor cross-sectional area of 3.5 mm ² . In this case, the reference electric resistance value is 0.1466Ω. What is necessary is just to recalculate the cable length of each extension cable corresponding to each solar cell power generation unit with the calculation method similar to the example mentioned above.

  In the above description, the total cable length of the extension cable corresponding to the first solar cell power generation unit 1-1, the total cable length of the extension cable corresponding to the second solar cell power generation unit 1-2, and the third The total cable lengths of the extension cables corresponding to the solar cell power generation unit 1-3 are all different. For example, the total cable length of the extension cable corresponding to the second solar cell power generation unit 1-2 and the third cable length The total cable length of the extension cable corresponding to the solar cell power generation unit 1-3 may be equal, and the total cable length of the extension cable corresponding to each solar cell power generation unit may be partially different.

DESCRIPTION OF SYMBOLS 1 Solar cell power generation unit 1-1 1st solar cell power generation unit 1-2 2nd solar cell power generation unit 1-3 3rd solar cell power generation unit 2 Solar cell module 3 Cable provided in the solar cell power generation unit 4 4-1, 4-2, 4-3 Boundary connection point 5,5-1, 5-2-1, 5-2-2, 5-3-1, 5-2-2, 5-3-3 Extension cable 6 Parallel connection point 7 Power conditioner having MPPT function 8 Cable 9 Solar cell module string 10 Boundary connection point and parallel connection point 11-2, 11-3-1, 11-3-2 Relay point

Claims (5)

Connect multiple solar power generation units in parallel,
A photovoltaic power generation system in which the total cable length of the extension cables from each of the solar cell power generation units to the parallel connection point is partially or entirely different,
A plurality of types of extension cables having at least one of electrical resistivity and conductor cross-sectional area are used, and the electrical resistance values of the power transmission paths from the solar cell power generation units to the parallel connection points are made substantially the same. Solar power generation system. An extension cable used as a power transmission path from a certain solar cell power generation unit k to the parallel connection point, where R _k is an electric resistance value of a power transmission path from the certain solar cell power generation unit k to the parallel connection point The electrical resistivity of the i-th (i is an arbitrary natural number less than or equal to n) extension cable is ρ _ki , the cable length is L _ki , and the conductor length is n (n is a natural number) When the area is S _ki ,

The photovoltaic power generation system according to claim 1, wherein: The total cost of an extension cable used as a power transmission path from a certain solar cell power generation unit k to the parallel connection point is TC,
When the cost per unit length of the i-th extension cable among the n types is C _ki ,

The solar power generation system according to claim 2, wherein each cable length L _ki is determined so that the total cost TC is minimized. 4. The photovoltaic power generation system according to claim 3, wherein a minimum required length of an extension cable is set, and each cable length _Lki is determined so that the total cost TC is minimized.   The photovoltaic power generation system according to any one of claims 2 to 4, wherein one type of extension cable is used for the solar cell power generation unit having the shortest distance to the parallel connection point.

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