Photovoltaic power generating system

A photovoltaic power generating system of the present invention includes a solar cell module 1, an installation platform 2 for holding a pair of ends of the solar cell module 1, and at least one supporting member 3 disposed on a side of a non-light-receiving surface 1B of the solar cell module 1, wherein the supporting member 3 is disposed at such a distance from the non-light-receiving surface 1B of the solar cell module 1 that the supporting member 3 can abut against the non-light-receiving surface 1B by deformation of the solar cell module 1. A deforming amount of the solar cell module 1 is increased in accordance with an external force applied to the solar cell module 1.

TECHNICAL FIELD

The present invention relates to a photovoltaic power generating system.

BACKGROUND ART

As interest in environmental protection is increased in recent years, photovoltaic power generating systems having lower environment load have come to attention. To get the photovoltaic power generating systems widespread use, cost reduction is considered.

For reducing the cost, it is proposed to provide a solar cell module of frameless (sashless) structure, or to increase an area of a power generator of the solar cell module. However, these proposals may cause deterioration of the strength. For example, since the solar cell module of frameless structure has low rigidity, the module easily bends, and the solar cell module is easily broken. If the area of the solar cell module is increased, a wind pressure and a snow accumulation load applied to one sheet of solar cell module are increased. Therefore, like the case of the solar cell module of frameless structure, a bending amount of a light-receiving surface of the solar cell module is increased, a transparent substrate easily falls off, and a crack is easily produced in the solar cell element.

To solve this problem, it is proposed to dispose a supporting member that supports a central part of the solar cell module (e.g., refer to Japanese Patent Application Laid-Open Nos. 2004-087884 and 2003-105940).

According to the above conventional techniques, however, since the supporting member is provided such that it is in contact with a non-light-receiving surface of the solar cell module, an absolute value of bending moment that is applied to the solar cell module becomes maximum in a central part that is the supporting part. Therefore, when a positive pressure load is applied, stresses are concentrated on the central part. That is, a radius of curvature of the solar cell module surface becomes small and abrupt bending is produced. If the radius of curvature becomes smaller than a certain limit value, the solar cell module is broken due to a fracture of the transparent substrate, a crack of the solar cell element or the like.

Further, since the solar cell module and the supporting member axe in a state where they abut against each other, there is a problem that flow (ventilation) of air along a back surface of the solar cell module is hindered, and heat of the solar cell module cannot be sufficiently radiated.

There is an adverse possibility that water such as rain water is remained in the abutted part. In this case, there is an adverse possibility that the back surface protection material used for the solar cell module is deteriorated due to remain of water for a long time. If water permeates through the back surface protection material, ethylene vinyl acetate (EVA) that is used as filler for sealing the solar cell element absorbs water to generate acetic acid, and there is an adverse possibility that a wiring member is damaged.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a photovoltaic power generating system having excellent heat-radiation performance and improved load-carrying capacity.

A photovoltaic power generating system according to one embodiment of the present invention includes a solar cell module, an installation platform for holding a pair of ends of the solar cell module, and at least one supporting member disposed on a side of a non-light-receiving surface of the solar cell module, wherein the supporting member is disposed at such a distance from the non-light-receiving surface of the solar cell module that the supporting member can abut against the non-light-receiving surface by deformation of the solar cell module.

According to the photovoltaic power generating system, the supporting member is disposed at a position where it can abut against the solar cell module that is bent by a positive pressure load. Therefore, the maximum absolute value of the bending moment of the solar cell module can be reduced as compared with a case where the supporting member is disposed such that it is in contact with the solar cell module, and the load-carrying capacity of the photovoltaic power generating system can be increased.

Further, ventilation can be secured by the gap between the solar cell module and the supporting member. According to this, the solar cell module can be cooled and reduction in power generating efficiency can be suppressed.

BEST MODE FOR CARRYING OUT THE INVENTION

A photovoltaic power generating systems according to the present invention will be described below with reference to the accompanying drawings.

As shown inFIGS. 1A and 1B, a photovoltaic power generating system100generally includes solar cell modules1, an installation platform2, and supporting member3. It is only necessary that the installation platform2holds a pair of ends (ends of opposed sides) of the solar cell modules1and for example, the installation platform2includes a plurality of holding members21, and a plurality of locking members22that sandwich and fix the ends of the solar cell modules1together with holding members21. The supporting member3is provided on the side of a non-light-receiving surface of the solar cell module1.

The solar cell module1can employ various structures such as a superstrate structure, a glass package structure and a substrate structure. Solar cell modules of the superstrate structure will be described as an example. The superstrate structure can be applied to monocrystalline silicon solar cells and polycrystalline silicon solar cells that are manufactured in high quantities, and this structure is preferable because an amount of material used is small.

InFIG. 2, the solar cell module1is formed by laminating a transparent substrate11that also functions as a module substrate, a filler12made of clear thermosetting resin, and a back surface protection film13that protects on the side of the non-light-receiving surface1B, in this order from the side of a light-receiving surface1A. A plurality of solar cell elements14that carry out photoelectric conversion are sealed in the filler12, and the plurality of solar cell elements14are electrically connected to each other through an inner lead15. A terminal box16is provided on the solar cell module1on the side of the non-light-receiving surface1B. Electricity obtained by the photoelectric conversion carried out by the solar cell elements14is outputted to outside through the terminal box16. The solar cell module1is one example of a frameless type solar cell module having no frame that protects an outer periphery of the solar cell module.

A monocrystalline silicon solar cell, a polycrystalline silicon solar cell, a thin film solar cell, a CIGS solar cell, a CdTe solar cell, an HIT type solar cell and the like are suitably employed as the solar cell element14. A solar cell element14of about 15 cm square is generally employed in the case of the monocrystalline silicon solar cell, the polycrystalline silicon solar cell and the HIT type solar cell.

As described above, the installation platform2includes the holding members21and the locking members22. The holding members21have roles to hold the solar cell modules1mainly from below (on the side of the non-light-receiving surface1B). Carbon steel, stainless steel, aluminum or the like can suitably be utilized as material of the holding member21. It is preferable that a supporting surface of the holding member21is protected by galvanization, corrosion-resistant aluminum alloy coating, painting or the like.

The locking members22have roles to fix the solar cell module1held by the holding members21. The locking member22can use the same material as that of the holding member21.

Carbon steel, stainless steel, aluminum, galvanized metal, alumite-coated metal, resin-molded product such as rubber and plastic and corrosion-resistant woods are used as material of the supporting member3for example.

FIG. 1Ashows a case where the supporting members3are rectangular parallelepiped shaped members3aand members3b, but the shapes of the supporting member3are not limited to those. For example, the shape of the member3bmay be columnar. The supporting member3may be of columnar shape having substantially the same length as that of the solar cell module1in a longitudinal direction or a lateral direction. However, to reduce the back surface protection film13from being damaged, it is preferable that the supporting surface (surface that can abut against the non-light-receiving surface1B)3S of the supporting member3is smooth and does not have a projection, and its edge portion is rounded.

As shown inFIG. 3A, the supporting member3is disposed such that it separates from the non-light-receiving surface1B of the solar cell module1. Therefore, when a positive pressure load is not applied from external, a space10R (air layer) through which air flow is formed between the solar cell module1and the supporting member3.

Since the space10R is provided, water such as rain water is less likely to remain as compared with a case where the supporting surface3S and the non-light-receiving surface1B abut against each other.

The space10R makes it easy to grasp both sides of the solar cell module1. Therefore, even if the solar cell module1is increased in size, its construction performance is excellent.

As shown inFIG. 3B, if a positive pressure load is applied to the solar cell module1from the side of the light-receiving surface1A, the solar cell module1is deformed (bent). The supporting member3is disposed at a position where it can abut against the non-light-receiving surface1B by deformation of the solar cell module1, and supports the solar cell module1. A deforming amount of the solar cell module1is increased in accordance with a positive pressure load caused by an external force applied to the solar cell module1, e.g., a wind pressure and a snow accumulation load. A distance between the solar cell module1and the supporting member3is set such that at least destruction such as a fracture does not occur, and the supporting member3abuts against the bent solar cell module1. That is, this distance is set such that before the solar cell module1is destroyed, the supporting member3supports a central part of the solar cell module1.

Next, with reference toFIGS. 4A to 4Dand5, a description will be given of bending moment applied to the solar cell module1when a positive pressure load is applied to the solar cell module1provided in the photovoltaic power generating system100having the above-described configuration. However, the positive pressure load is a uniformly-distributed load. inFIGS. 4A to 4Dand5, positions A and C correspond to positions of both ends of the solar cell module1held by the holding members21. A position B corresponds to a position of a central part of the solar cell module1supported by the supporting member3.

When a positive pressure load is not applied to the solar cell module1from external as shown inFIG. 4A, since a bending degree of the solar cell module1is small, the solar cell module1and the supporting member3are separated from each other. In this case, it can be perceived that the supporting structure of the solar cell module1is a simple supporting beam.

If a distributed load W1is applied to the solar cell module1, the non-light-receiving surface of the solar cell module1and the supporting member3come into contact with (abutment against) each other (FIG. 4B). At this point, it can be perceived that the supporting structure of the solar cell module1is a continuous beam having three fulcrum points as shown inFIG. 4B.

Further, if a distributed load W that is greater than the distributed load W1is applied to the solar cell module1, the solar cell module1is bent as shown inFIG. 4C. This is a state where a distributed load W2(=W-W1) is further applied to the solar cell module1to which the distributed load W1is applied and which starts being supported by the supporting member3(FIG. 4B). That is, it can be considered that the state shown inFIG. 4Cis a state in which a state where only the distributed load W1is applied as shown inFIG. 4Band the state where the distributed load W2is applied to the solar cell module1whose central part is supported by the supporting member3from the beginning as shown inFIG. 4Dare superposed on each other.

FIG. 5is a bending moment diagram of the solar cell module1in each of the states shown inFIGS. 4B,4C and4D. InFIG. 5, a moment diagram51corresponds to bending moment M1of the solar cell module1in the state shown inFIG. 4B. A moment diagram52corresponds to bending moment M2of the solar cell module1in the state shown inFIG. 4D. A moment diagram53in which the bending moment M1and the bending moment M2are synthesized with each other based on a principle of superposition corresponds to the bending moment M generated in the solar cell module1in the state shown inFIG. 4Cwhere the distributed load W is applied. InFIG. 5, a moment diagram54shows bending moment when the distributed load W is applied to a conventional solar cell module that abuts against a supporting member in a state where no load is applied.

Here, the moment diagram53when a positive pressure load is applied to the solar cell module1of the present embodiment and the bending moment diagram54of the conventional case are compared with each other.

In any of the moment diagrams53and54, bending moment becomes the minimum value (negative value) at a position B and becomes the maximum value (positive value) between positions A and B, and between positions B and C.

In this embodiment, since the supporting member3is disposed such that it separates from the solar cell module1, if a distributed load W is applied to the solar cell module1, in the position B, negative bending moment is generated by the distributed load W2as shown with the moment diagram52from a state where positive bending moment is generated by the distributed load W1as shown with the moment diagram51. Therefore, as compared with the conventional configuration, the magnitude of the bending moment at the position B becomes small (V(B)<V0(B)).

A difference (V(AB)−V(B)and V(BC)−V(B)) between an absolute value of the maximum value and an absolute value of the minimum value of the moment diagram53is smaller than a difference (V0(AB)−V0(B)and V0(BC)−V0(B)) between an absolute value of the maximum value and an absolute value of the minimum value of the moment diagram54. That is, by disposing the supporting member3such that it separates from the solar cell module1, the maximum absolute value and the minimum absolute value of the bending moment of the solar cell module1when a positive pressure load is applied can be brought close to each other.

If a stress at a position of one of the maximum value and the minimum value of bending moment that has a greater absolute value exceeds a permissible value, destruction of the solar cell module1is caused at this position. Therefore, in order to suppress a breakage of the solar cell module1to the maximum extent possible, it is preferable that a distance between the solar cell module1and the supporting member3is set such that when a distributed load W0that is assumed to be applied is applied to the solar cell module1, a distance δ in which the absolute value (V(AB)and V(BC)) of the maximum bending moment M and the absolute value (V(B)) of the minimum bending moment M of the solar cell module1become equal to each other is a maximum value.

In order to equalize the absolute value of the maximum value and the absolute value of the minimum value of the bending moment, a value of the distance δ should be set such that a ratio of the distributed loads W1and W2becomes W1:W2=1:15. For example, if a distributed load of 3000 (N/m) is applied as a permissible maximum load when the solar cell module1is approximated to a model shown inFIG. 4A, values of W1and W2become W1:W2=187.5 (N/m):2812.5 (N/m). The permissible maximum load is a maximum load that is assumed to be applied to the solar cell module1, and is a load that is set by a designer and the like of the photovoltaic power generating system100.

A distance δ in which an absolute value of the maximum value and an absolute value of the minimum value of bending moment of the solar cell module1become equal to each other when a distributed load W0(N/M) is applied is expressed by the following equation wherein a width L of the solar cell module1is 2 S (m) and Young's modulus is E (N/m2) and second moment of area is I (m4):
δ=5W1L4/(384EI)=5W0S4/(384EI)  Equation (1)

The photovoltaic power generating system100of the embodiment having the above-described configuration has the following effect.

When the positive pressure load applied to the solar cell module1is small, the solar cell module1is supported by the holding members21. If a positive pressure load of more than a predetermined amount is applied, the solar cell module1is bent, and the non-light-receiving surface1B is abutted against the supporting member3and supported by the supporting member3. According to this, it is possible to reduce the bending moment that is applied at the position of the supporting member3as compared with a case where the supporting member3abuts from the beginning. According to this, the load-carrying capacity of the photovoltaic power generating system100can be enhanced.

When no positive pressure load is applied to the solar cell module1as shown inFIG. 3A, the supporting member3is not in contact with the solar cell module1on the side of the non-light-receiving surface1B, and since air can flow through the space10R of the solar cell module1on the side of the non-light-receiving surface1B, a cooling effect can be obtained. When the sky is clear and there is no wind for example, the solar cell module1can be cooled by convection heat transfer caused by natural convection generated on the side of the non-light-receiving surface1B of the solar cell module1, and high power generating efficiency can be maintained.

The supporting member3can be applied to a solar cell module1ahaving frames4. A configuration of the solar cell module1ahaving the frames4will be described with reference toFIG. 6.

If a periphery of a body part of the solar cell module1ais attached to the frames4as shown inFIG. 6, the body part can be protected and its strength can be increased. It is possible to omit the holding members21and locking members22by mounting the frames4on the installation platform2shown inFIGS. 1A and 1B.

By connecting the supporting member3to the frames4, the solar cell module1aand the supporting member3can integrally be handled. Therefore, the solar cell module1acan be replaced in a state where the supporting member3is mounted thereon. A conventional solar cell module that is used in a heavy-snow region for example can easily be replaced by the solar cell module1ahaving enhanced strength against a positive pressure load.

Next, a configuration of a photovoltaic power generating system100aaccording to a second embodiment of the present invention will be described with reference toFIG. 7. In the description of this embodiment, elements having the same functions as those of the first embodiment are designated with the same symbols, and explanation thereof will be omitted. This also applies to other embodiments.

As shown inFIG. 7, the second embodiment includes a member3aaccording to the first embodiment, and convex hollow supporting members3clocated above the member3a.

Each of the supporting members3chas a pyramidal shape whose cross section in the horizontal direction is gradually reduced toward the non-light-receiving surface1B of the solar cell module1. The supporting member3cis made of elastic member (such as EPDM or natural rubber) so that it can be deformed when it abuts against the solar cell module1.

According to this embodiment, if a positive pressure load applied to the solar cell module1is increased, since a contact area between the solar cell module1and the supporting member3is increased, stresses are dispersed. Therefore, since it is possible to reduce stresses from being applied to a portion of a back surface (non-light-receiving surface1B) of the solar cell module1in a focused manner, destruction of the solar cell module1can be suppressed.

According to a third embodiment of the present invention, as shown inFIG. 8A, supporting members3dare provided on the side of the non-light-receiving surface1B of the solar cell module1. A distance between the supporting member3dand the solar cell module1is set such that the distance becomes gradually smaller from a center portion toward end edges of the solar cell module1. More specifically, a supporting surface3dS of each of the supporting members3dis curved in a concave manner with respect to the non-light-receiving surface1B.

It is preferable that a distance between the supporting member3dand the solar cell module1at each position is set such that the distance is smaller than a limit value of a bending amount of the solar cell module1at each position. It is preferable that the distance between the solar cell module1and the supporting member3dis set such that the distance becomes the maximum at a center part of the solar cell module1when the center part of the solar cell module1is superposed on the supporting member3das viewed from above in a see-through manner.

As shown inFIG. 9A, each of the solar cell modules1is substantially flat when no load is applied from external. If a predetermined positive pressure load is applied to the light-receiving surface1A of the solar cell module1, the solar cell module1is bent and is supported by a portion of the supporting surface3dS of the supporting member3d(not shown). At that time, since the supporting member3dsupports the solar cell module1in accordance with this bent shape, a curved amount of the solar cell module1in the vicinity of the supporting member3dis reduced, and generation of a breakage of the transparent substrate11, a crack of the solar cell element14and the like is reduced.

If a greater load is applied to the solar cell module1, the non-light-receiving surface1B and substantially the entire surface of the supporting member3dcome into contact with each other as shown inFIG. 9B. At that time, since the supporting member3supports the solar cell module1on the side of the non-light-receiving surface113with a relatively large surface, a pressure applied to the solar cell element14can be reduced. Since the supporting member3dsupports a fixed part area of the peripheral edge of the solar cell module1, bending near the fixed part is reduced. This can reduce the generation of a breakage of the transparent substrate11, a crack of the solar cell element14and the like. Therefore, the load-carrying capacity of a photovoltaic power generating system100bcan be enhanced.

For one solar cell module1, a plurality of supporting members3may be disposed in parallel. The supporting surface3dS of the supporting member3may have almost the same width as that of the solar cell module1. The supporting member3dcan also be applied to the solar cell module1ahaving the frames4as shown inFIG. 10. In this case, the supporting member3dis provided into the frames4.

Although the surface of the supporting member3dis curved in shape, the supporting member3dis not limited to this shape. In a fourth embodiment of the present invention, as shown inFIG. 11, supporting members3eare provided on the side of the non-light-receiving surface1B of the solar cell modules1. Each of the supporting members3ehas a supporting surface that is varied such that it includes steps (in a stepwise fashion) in the height direction. By varying the height of the supporting member3ein the stepwise fashion in this manner, its machining operation becomes easy as compared with a case where the supporting surface is formed into the curved surface.

It is also possible to form the supporting member3eby combining members having different heights. In this case, it becomes easy to adjust the height of the supporting member3eand to install the same at the construction site. That is, it is possible to make fine adjustments of the height in accordance with the installation environment.

When the supporting member3esupports a bent solar cell module1, it is preferable that the supporting member3eis disposed such that the step portions and the solar cell element14are not superposed on each other. According to this, it is possible to reduce the generation of a crack in the solar cell element14.

In a fifth embodiment of the present invention, supporting member including a plurality of partial supporting members is used. More specifically, as shown inFIG. 12, each of the supporting members3fincludes partial supporting members31f,32fand33fprovided at predetermined distances from one another between the pair of ends of the solar cell module1on the side of the non-light-receiving surface1B of the solar cell module1. A supporting surface of each of the partial supporting members31f,32fand33fforms a portion of a concave-curved surface like the supporting surface3dS of the supporting member3d.

According to the supporting members3f,material costs and the number of manufacturing steps can be reduced. Further, since a space between the supporting members can be secured below the non-light-receiving surface1B of the solar cell module1, a flow rate of air is increased and the cooling efficiency of the solar cell module1can be enhanced. Further, even when the supporting member3fand the non-light-receiving surface1B abut against each other, since air passes through the space between the partial supporting members, the solar cell module1can be cooled, and reduction of power generating efficiency can be suppressed.

Since a cable and the like for connecting the solar cell modules1with each other can be accommodated in the space between the partial supporting members, even if the solar cell module1and the supporting member3fcome into contact with each other, it is possible to suppress a case where the cable is sandwiched therebetween.

In a sixth embodiment of the present invention, as shown inFIGS. 13A to 13C, a supporting surface of a supporting member3gis concave-curved like the supporting member3d, and the supporting member3gincludes a thin and long shape as viewed from above. As viewed from above in a see-through manner, the supporting member3gis disposed such that both ends thereof in its lateral direction are located between the solar cell elements14(seeFIG. 13B), and both ends of the supporting member3gin its longitudinal direction are not superposed on the solar cell element14(seeFIG. 13C).

When the supporting member3gsupports the solar cell module1, it is possible to reduce a pressure applied directly to the solar cell element14. Therefore, it is possible to reduce generation of a crack in the solar cell element14.

As shown inFIGS. 13A to 13C, the supporting member3gis disposed such that its longitudinal direction becomes equal to a connecting direction of an inner lead15that straightly connects the solar cell elements14with each other. The supporting member3gis disposed such that its side end and the inner lead15are not superposed on each other. According to this, when the supporting member3gsupports the solar cell module1, a pressure applied directly to the inner lead15can be reduced, and it is possible to suppress a case where connected parts between the solar cell element14and the inner lead15come off from each other, and a case where a crack is generated in the solar cell element14in the vicinity of the connected parts.

In a photovoltaic power generating system according to a seventh embodiment of the present invention, as shown inFIGS. 14A to 14C, a straight non-disposition part where the solar cell element14is not disposed is provided substantially at a central part of the solar cell module1. A supporting member3hincludes a plurality of partial supporting members, and is disposed such that the supporting member3his superposed on the non-disposition part, i.e., such that the supporting member3his not superposed on disposition parts as viewed from above in a see-through manner. According to this, when the supporting member3hsupports the solar cell module1, a pressure applied to the solar cell element14is reduced, and generation of a crack in the solar cell element14can be reduced.

The present invention is not limited to the embodiments, and can variously be modified and changed within the scope of the present invention.

For example, the embodiments have been described using the inclined installation platform disposed on a flat roof or the ground, but the shape of the installation platform2is not limited to this. The present invention can preferably be utilized also for an on-roof type photovoltaic power generating system and a roofing type photovoltaic power generating system.

In the embodiments, the supporting structure of the solar cell module1has been described as being analogous to a two-dimensional simple supporting beam. However, even if other supporting structure is employed, a value of positive bending moment and a value of negative bending moment can be adjusted by disposing the supporting member3such that it is separated from the non-light-receiving surface1B of the solar cell module1by an arbitrary distance.

That is, as shown inFIG. 15A, the holding members21may be fixed ends that can neither move nor rotate. The holding members21that fix the pair of ends of the solar cell module1are not limited to a structure that opposed two sides are fixed as in the simple supporting beam, and three or four sides of a rectangular solar cell module may be fixed as shown inFIG. 15B, or the holding member21may be shorter than a length of one side of the solar cell module. As an example of this case, a frameless type solar cell module1may be partially fixed to an installation platform2by a locking member22. In this case, material used for the installation platform2can be reduced. That is, material used for the installation platform2can be reduced by providing the supporting member3. Further, as shown inFIG. 15C, the solar cell module1may be fixed at positions slightly closer to a central part than end sides of the solar cell module1like a projecting beam.