Solar cell module

According to one embodiment, a solar cell module includes a solar cell panel and a concentrator. The solar cell panel includes a solar cell. The concentrator reflects light incident from the outside and irradiates the light onto the solar cell. The concentrator has a first surface and a second surface. The first surface reflects light incident at a first incident angle and irradiates the light incident at the first incident angle onto a first portion within the area of the solar cell. The second surface reflects light incident at a second incident angle and irradiates the light incident at the second incident angle onto a second portion within the area of the solar cell. The second incident angle is different from the first incident angle. The second portion is different from the first portion. The first surface and the second surface are asymmetric as viewed from the solar cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-192254, filed on Sep. 22, 2014; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a solar cell module.

BACKGROUND

Research and development of solar cell modules are being performed. When light is directly incident on a solar cell panel of a solar cell module, that is, when concentration of the light is not performed, the solar cell panel can absorb light from a relatively wide range of angles; but the solar cell panel must have a relatively wide surface area. Therefore, the solar cell module is expensive.

There is a possibility that the cost per surface area of the solar cell module can be reduced by combining the solar cell panel with an inexpensive concentrator. A condensing lens, a concentrator called a CPC (Compound Parabolic Concentrator), etc., may be used as technology for combining the concentrator and the solar cell panel. However, when the condensing lens or the CPC is used in the solar cell module, a drive device becomes necessary to drive the solar cell panel to follow the sun because the orientation of the light of the sun changes according to the season, the time, etc. Therefore, the solar cell module is expensive.

There is a possibility that the cost per surface area of the solar cell module can be reduced by reducing the surface area of the solar cell panel. To reduce the surface area of the solar cell panel, it is desirable to improve the concentration ratio of the solar cell module.

DETAILED DESCRIPTION

According to one embodiment, a solar cell module includes a solar cell panel and a concentrator. The solar cell panel includes a solar cell. The concentrator reflects light incident from the outside and irradiates the light onto the solar cell. The concentrator has a first surface and a second surface. The first surface reflects light incident at a first incident angle and irradiates the light incident at the first incident angle onto a first portion within the area of the solar cell. The second surface reflects light incident at a second incident angle and irradiates the light incident at the second incident angle onto a second portion within the area of the solar cell. The second incident angle is different from the first incident angle. The second portion is different from the first portion. The first surface and the second surface are asymmetric as viewed from the solar cell.

The drawings are schematic or conceptual; and the relationships between the thicknesses and widths of portions, the proportions of sizes between portions, etc., are not necessarily the same as the actual values thereof. The dimensions and/or the proportions may be illustrated differently between the drawings, even in the case where the same portion is illustrated.

In the drawings and the specification of the application, components similar to those described in regard to a drawing thereinabove are marked with like reference numerals, and a detailed description is omitted as appropriate.

FIG. 1is a schematic conceptual view showing a solar cell module according to an embodiment.

FIG. 2is a schematic perspective view showing the solar cell module according to the embodiment.

The solar cell module100according to the embodiment includes a solar cell panel110and a concentrator120and is mounted, for example, on a roof221facing south, etc.

The solar cell panel110includes a solar cell111. For example, the solar cell111is disposed in the interior of the solar cell panel110. The solar cell panel110(the solar cell111) converts incident light into electrical power.

Two solar cell panels110and two concentrators120are provided in the solar cell module100shown inFIG. 1andFIG. 2. However, the number of solar cell panels110and the number of concentrators120is not limited thereto.

As shown inFIG. 2, the concentrator120includes a first light concentration plate121and a second light concentration plate122. The solar cell panel110is provided between the first light concentration plate121and the second light concentration plate122. The first light concentration plate121has a first surface123. In other words, the first light concentration plate121has a parabolic surface configuration. The second light concentration plate122has a second surface124. In other words, the second light concentration plate122has a parabolic surface configuration. The concave surface of the first surface123of the first light concentration plate121opposes the concave surface of the second surface124of the second light concentration plate122. The configuration of the first surface123of the first light concentration plate121is different from the configuration of the second surface124of the second light concentration plate122. That is, the second light concentration plate122and the first light concentration plate121are asymmetric as viewed from the solar cell panel110. InFIG. 2, the east and west directions (EN-direction) and the south and north directions (SN-direction) are illustrated.

As shown inFIG. 1, for example, the concentrator120reflects light211of the sun210and guides the light211toward the solar cell panel110. In the embodiment, a minimum solar elevation A11of the sun210is taken to be 30 degrees; and a maximum solar elevation A13of the sun210is taken to be 80 degrees. For example, the minimum solar elevation A11is the elevation of the sun210in winter. For example, the maximum solar elevation A13is the elevation of the sun210in summer. When the elevation of the sun210is the minimum solar elevation A11, an incident angle A12(a first incident angle) of the light211is 60 degrees. On the other hand, when the elevation of the sun210is the maximum solar elevation A13, an incident angle A14(a second incident angle) of the light211is 10 degrees. The incident angle A12is the maximum incident angle of the sunlight for a time period of one year. The incident angle A14is the minimum incident angle of the sunlight for a time period of one year. For the east and west directions, the concentration of light can be performed for only a limited amount of time because the angle of sunlight changes 180° from sunrise to sunset. For a limited amount of time, the concentration of light can be performed even for the east and west directions.

As described above, the first light concentration plate121and the second light concentration plate122have parabolic surfaces. For example, when the formula expressing a parabola is y=x2/(4p), the light that is incident parallel to the y-axis concentrates at the focal point (0, p) of the parabola. The concentration of light is possible by using this property of the parabola. Specifically, the first light concentration plate121and the second light concentration plate122are mounted so that the focal point (0, p) is included within the area of the solar cell panel110(or the solar cell111).

The focal point of the first surface123of the first light concentration plate121exists in a first portion within the area of the solar cell panel110(or the solar cell111). The focal point of the second surface124of the second light concentration plate122exists in a second portion within the area of the solar cell panel110(or the solar cell111). The second portion is different from the first portion. More favorably, the focal point of the first surface123of the first light concentration plate121is positioned at a first edge portion of the solar cell panel110(or the solar cell111). More favorably, the focal point of the second surface124of the second light concentration plate122is positioned at a second edge portion of the solar cell panel110(or the solar cell111).

This will now be described further with reference to the drawings.

In the specification of the application, the “edge portion” includes not only the edge of some object, but also a portion that is inside the object in an area from the edge such that the ratio of the distance from the edge to the length in a prescribed direction of the object is within 10%, and/or a portion that is outside the object in an area from the edge such that the ratio of the distance from the edge to the length in the prescribed direction of the object is within 5%.

FIG. 3is a schematic plan view showing the solar cell module according to the embodiment.

FIGS. 4A to 4Dare schematic plan views showing light that is incident on the solar cell module according to the embodiment.

FIG. 5is a schematic plan view showing the light that is reflected for the parabolas.

FIG. 4Ais a schematic plan view showing the state in which the light211of the sun210at the minimum solar elevation A11is incident on the solar cell module100.FIG. 4Bis a schematic plan view showing the state in which the light211of the sun210at the maximum solar elevation A13is incident on the solar cell module100.FIG. 4Cis a schematic plan view showing the state in which the light211of the sun210is incident on the solar cell module100when a solar elevation A15is 45 degrees.FIG. 4Dis a schematic plan view showing the state in which the light211of the sun210is incident on the solar cell module100when a solar elevation A16is 60 degrees.

As shown inFIG. 3, the first light concentration plate121and the second light concentration plate122have parabolic surface configurations. The second light concentration plate122and the first light concentration plate121are asymmetric as viewed from the solar cell panel110.

As shown inFIG. 4AtoFIG. 4D, the first light concentration plate121is formed along a first parabola161. The second light concentration plate122is formed along a second parabola162. In the example shown inFIG. 4AtoFIG. 4D, a first axis171is parallel to the travel direction of the light211of the sun210at the minimum solar elevation A11and corresponds to the y-axis of the first parabola161. A second axis172is parallel to the travel direction of the light211of the sun210at the maximum solar elevation A13and corresponds to the y-axis of the second parabola162.

As shown inFIG. 4A, a portion of the light211that is incident parallel to the first axis171(the y-axis of the first parabola161) is reflected at the first light concentration plate121and concentrates at a focal point166of the first parabola161. The light211that is incident parallel to the first axis171but is not reflected at the first light concentration plate121is incident directly on the solar cell panel110.

As shown inFIG. 4B, a portion of the light211that is incident parallel to the second axis172(the y-axis of the second parabola162) is reflected at the second light concentration plate122and concentrates at a focal point167of the second parabola162. The light211that is incident parallel to the second axis172but is not reflected at the second light concentration plate122is incident directly on the solar cell panel110.

As shown inFIG. 4C, for example, when the solar elevation A15is 45 degrees, a portion of the light211of the sun210is reflected at the first light concentration plate121and is incident on the solar cell panel110on the focal point167side of the second parabola162as viewed from the focal point166of the first parabola161. For example, when the solar elevation A15is 45 degrees, the light211of the sun210that is not reflected at the first light concentration plate121is incident directly on the solar cell panel110.

As shown inFIG. 4D, for example, when the solar elevation A16is 60 degrees, a portion of the light211of the sun210is reflected at the second light concentration plate122and is incident on the solar cell panel110on the focal point166side of the first parabola161as viewed from the focal point167of the second parabola162. For example, when the solar elevation A16is 60 degrees, the light211of the sun210that is not reflected at the second light concentration plate122is incident directly on the solar cell panel110.

The light211that is reflected at the parabolas will now be described further.

As shown inFIG. 5, when the formula expressing the first parabola161is y=x2/(4p), the light that travels parallel to the first axis171concentrates at the focal point166(0, p) of the first parabola161. When the formula expressing the second parabola162is y=x2/(4q), the light that travels parallel to the second axis172concentrates at the focal point167(0, q) of the second parabola162.

Here, the rotation matrix for rotating x counterclockwise by an angle θ to obtain X and rotating y counterclockwise by the angle θ to obtain Y is expressed by the following formula.

When the first axis171is taken to be the y-axis, the formula expressing the first parabola161is as follows.

When the second axis172is taken to be the y-axis, the formula expressing the second parabola162is as follows.

In Formula (2) and Formula (3), a is the width of the solar cell111. In Formula (2), the angle θ is the incident angle A12of the light of the sun210at the minimum solar elevation A11. In Formula (3), an angle φ is the incident angle A14of the light of the sun210at the maximum solar elevation A13.

Then, the first axis171is converted to a first y-axis176by rotating in the clockwise direction by the angle θ and by adjusting the origin position. The first axis171is converted to the first y-axis176and the origin position is adjusted as follows.

When the second axis172is converted to a second y-axis177, the second axis172is rotated in the clockwise direction by the angle φ; and the origin position is adjusted. The second axis172is converted to the second y-axis177and the origin position is adjusted as follows.

In the case where a refractive index layer having a refractive index n is provided, the formula θ′=sin−1(sin(θ)/n) holds. In such a case, the refractive index (nambient air) of the ambient air is taken to be 1. Details of the refractive index layer are described below.

In the solar cell module100according to the embodiment as shown inFIG. 4AtoFIG. 4D, the focal point166of the first parabola161is included within the area of the solar cell panel110(or the solar cell111). The focal point167of the second parabola162is included within the area of the solar cell panel110(or the solar cell111).

The focal point166of the first parabola161exists in a first portion113within the area of the solar cell panel110(or the solar cell111). The focal point167of the second parabola162exists in a second portion114within the area of the solar cell panel110(or the solar cell111). The second portion114is different from the first portion113. More favorably, the focal point166of the first parabola161is positioned at a first edge portion115of the solar cell panel110(or the solar cell111). More favorably, the focal point167of the second parabola162is positioned at a second edge portion116of the solar cell panel110(or the solar cell111). The “edge portion” is as described above in regard toFIG. 1andFIG. 2.

According to the embodiment, all of the light211of the sun210between the minimum solar elevation A11and the maximum solar elevation A13is incident on the solar cell panel110. By using the first light concentration plate121and the second light concentration plate122that are asymmetric to each other as viewed from the solar cell panel110, for example, the solar cell module100can be mounted on a roof facing north, which is relatively unsuitable for utilizing sunlight. The solar cell module100according to the embodiment includes the first light concentration plate121described above and the second light concentration plate122described above. Thereby, compared to the case where the solar cell module100does not include the first light concentration plate121and the second light concentration plate122, the concentration ratio is improved; and the surface area of the solar cell panel110can be reduced.

The concentration ratio is expressed by d/a using the width a of the solar cell111and the pitch d of the solar cell111(referring toFIG. 2). The concentration ratio (d/a) is regulated by a height h of the concentrator120(referring toFIG. 2). In the case where the height h of the concentrator120is relatively high, the concentration ratio is relatively high. As described above, because the solar cell module100according to the embodiment can improve the concentration ratio, the concentration ratio can be ensured even in the case where the height h of the concentrator120is suppressed. Thereby, the thickness of the solar cell module100can be reduced. Generally, the reflection of the light at the light concentration plate121is not 100%. Therefore, d/a is lower than that of the case where the light reflectance at the light concentration plate121is 100%. Therefore, in the embodiment, the concentration ratio d/a is used as the ideal concentration ratio for convenience.

The maximum concentration ratio is obtained when the focal point166of the first parabola161is positioned at the first edge portion115, and the focal point167of the second parabola162is positioned at the second edge portion116. Thereby, the solar cell111and the solar cell panel110can be minimized.

The parabolic surface configuration of the concentrator120is a basic geometrical configuration. Therefore, the fabrication of the concentrator120is relatively easy.

According to the embodiment, the solar cell module100can perform similar operations year round. Thereby, it is unnecessary for the solar cell panel110to follow the sun210according to the season. Therefore, a drive device to drive the solar cell panel110or the like is unnecessary.

The solar cell module100according to the embodiment includes the solar cell panel110and the concentrator120. The solar cell panel110has a first cell surface111f1. The first cell surface111f1includes the first portion113and the second portion114.

The concentrator120has the first surface123, and the second surface124that is separated from the first surface123. A first light211athat is incident on the first surface123at a first incident angle A11is incident on the first portion113. A second light211bthat is incident on the second surface124at the second incident angle A14is incident on the second portion114.

The first surface123includes the first parabola161where the first surface123intersects a first perpendicular plane111f1vperpendicular to the first cell surface111f1. The first perpendicular plane111f1vincludes a direction from the first portion113toward the second portion114. The second surface124includes the second parabola162where the second surface124intersects the first perpendicular plane111f1v.

A first point161aon the first parabola161and a second point162aon the second parabola162are asymmetric with respect to a second perpendicular plane111f2vperpendicular to the first cell surface111f1and the first perpendicular plane111f1v.

The first portion113includes a first focal point161pof the first parabola161. The second portion114includes a second focal point162pof the second parabola162. The solar cell111includes the first edge portion115and the second edge portion116. The first edge portion115includes the first focal point161pof the first parabola161. The second edge portion116includes the second focal point162pof the second parabola162.

The first surface123has a first concave surface123u. The second surface124has a second concave surface124u. The first concave surface123uopposes the second concave surface124u.

The first incident angle A11is the one-year maximum value of the angle between the sunlight and a direction perpendicular to the ground surface. The second incident angle A14is the one-year minimum value of the angle between the sunlight and the direction perpendicular to the ground surface.

The concentrator120includes the first light concentration plate121that has the first surface123, and the second light concentration plate122that has the second surface124.

FIGS. 6A and 6Bare schematic views showing another example of the concentrator of the embodiment.

FIG. 6Ais a schematic plan view showing the light reflected by the concentrator of the example.FIG. 6Bis a graph of the reflection state of the light when the angle of the second light concentration plate is changed.

In the example shown inFIG. 6AandFIG. 6B, a first light concentration plate125has a planar surface. In other words, the first light concentration plate125has a planar configuration. A second light concentration plate126has a planar surface. In other words, the second light concentration plate126has a planar configuration.

In the example, the height h is expressed by h=a·sin(θm−θmin) for the first light concentration plate125and for the second light concentration plate126. The concentration ratio is expressed by 1+cos(θmax−θmin)−h/a/tan(θmax).

The angle θmin, the angle θmax, and the width a of the solar cell111are set respectively so that θmin=30 degrees, θmax=80 degrees, and a=4 centimeters (cm).

In such a case, the height h is h=3.06 cm. The concentration ratio is about 1.508.

In the case where a second concentrator126ais employed as shown inFIG. 6B, the amount of the light211that is reflected by the second concentrator126aand incident on the solar cell panel110is relatively low. Therefore, the second concentrator126ahas room for improvement.

When employing a second concentrator126c, a relatively large portion of the light211reflected by the second concentrator126cis radiated outside the solar cell panel110without being incident on the solar cell panel110. Therefore, the second concentrator126chas room for improvement.

When employing a second concentrator126b, a relatively large portion of the light211reflected by the second concentrator126bis incident on the solar cell panel110. Therefore, for the second concentrator126b, there is room for improvement for increasing the concentration ratio.

In the example, there is a limiting formula for the width a of the solar cell111, the height h of the first light concentration plate125and the second light concentration plate126, and the angles θminand θmax.

In the case where the first light concentration plate125and the second light concentration plate126have planar configurations, focal points such as those of parabolas do not exist. Therefore, compared to the case where the first light concentration plate125and the second light concentration plate126have parabolic surface configurations, the light211can be dispersed.

Another embodiment will now be described with reference to the drawings.

FIG. 7is a schematic perspective view showing a solar cell module according to the embodiment.

The solar cell module100aaccording to the embodiment includes the solar cell panel110and a concentrator130.

The solar cell panel110is as described above in regard toFIG. 1toFIG. 6B.

Two solar cell panels110and two concentrators130are provided in the solar cell module100ashown inFIG. 7. However, the number of solar cell panels110and the number of concentrators130is not limited thereto.

In the embodiment described above in regard toFIG. 1toFIG. 6B, the concentrator120reflects the light211. Loss (reflection loss) occurs when the light211is reflected by any object surface.

By reducing the reflecting surface area in the embodiment, the reflection loss is reduced; and the concentration ratio is improved further.

The refractive index of the concentrator130is higher than the refractive index of the ambient air. That is, the concentrator130includes a so-called high refractive index material. For example, a polymethylmethacrylate resin (an acrylic resin (PMMA)) or the like is used as the material of the concentrator130. For example, the concentrator130is formed by injection molding, etc. As shown inFIG. 7, the concentrator130has a first surface131and a second surface132and has a convex configuration on the solar cell panel110side. When viewed from the solar cell panel110, the second surface132may be asymmetric to the first surface131or symmetric to the first surface131.

It is favorable for the light211to undergo total internal reflection for at least a portion of the surfaces (the first surface131and the second surface132) of the concentrator130. It is unnecessary to provide a mirror coating on the surface of the concentrator130in the region where the light211undergoes total internal reflection. Thereby, in the region where the light211undergoes total internal reflection, the reflection loss can be reduced.

In the embodiment, the mirror coating is not eliminated for the entire first surface131and the entire second surface132. As described above in regard toFIG. 1toFIG. 6B, even in the case where the entire first surface131and the entire second surface132reflect the light211, the concentration ratio can be improved.

As described above, the concentrator130includes the high refractive index material. Thereby, the incident angle of the light211can be relaxed.

This will now be described further with reference to the drawings.

FIG. 8is a schematic conceptual view showing the solar cell module according to the embodiment.

Because the refractive index of the concentrator130is higher than the refractive index of the ambient air, a refraction angle A22is smaller than an incident angle A21as shown inFIG. 8. Therefore, the substantial incident angle in the interior of the concentrator130can be increased. That is, the incident angle of the light211can be relaxed. Thereby, the thickness of the solar cell module100acan be reduced for the same range of incident angles.

To further increase the range of the incident angles of the light211, it is more favorable to increase the clarity of the concentrator130. Also, to further increase the range of the incident angles of the light211, it is more favorable to use a material having a higher refractive index as the material of the concentrator130. The trapping effect of the light211can be increased by gradually reducing the refractive index from the interior of the concentrator130toward the outside.

The solar cell module100aon the right side ofFIG. 8is an example in which a mirror coating135is provided on the entire first surface131and the entire second surface132.

The solar cell module100aon the left side ofFIG. 8is an example in which the mirror coating135is provided on a portion of the first surface131and a portion of the second surface132. More specifically, the mirror coating135is provided in a first region F1of the first surface131and a second region F2of the second surface132.

For example, silver (Ag), aluminum (Al), etc., may be used as the material of the mirror coating135.

FIGS. 9A and 9Bare schematic views showing the total internal reflection of the light.

FIG. 9Ais a schematic plan view showing the light incident on the solar cell module according to the embodiment.FIG. 9Bis a schematic plan view showing the area where the mirror coating is unnecessary.

For the parabolic surface of the concentrator130, the light for which it is most difficult to undergo total internal reflection is the light that is parallel to the axis of the parabola. As shown inFIG. 9A, for example, the light211that is parallel to an axis173of the parabola of the second surface132is the light211that is parallel to the axis173of the parabola. Therefore, in the embodiment, the conditions at which the light211that is parallel to the axis173of the parabola undergoes total internal reflection are considered.

FIG. 9AandFIG. 9Bshow an example in which the second surface132and the first surface131are symmetric as viewed from the solar cell panel110.

The conditions at which the light211parallel to the axis173of the parabola undergoes total internal reflection is expressed by the following formula, where n is the refractive index of the concentrator130, and the formula of the parabola is y=x2/(4p).

In Formula (6), p is the value of the focal point of the parabola. In the case where the second surface132is asymmetric to the first surface131as viewed from the solar cell panel110, the value p of the focal point of the first surface131is different from the value p of the focal point of the second surface132.

In the case where the tilt of the solar cell panel110is steep, the conditions of the solar cell panel110change. This will now be described with reference to the drawings.

FIGS. 10A and 10Bare schematic plan views showing different tilts of the solar cell panel.

FIGS. 11A and 11Bare schematic plan views showing the method for mounting the solar cell panel.

FIG. 10Ais a schematic plan view showing an example in which the tilt of the solar cell panel is gradual compared to that of the example ofFIG. 10B.FIG. 10Bis a schematic plan view showing an example in which the tilt of the solar cell panel is steep compared to that of the example ofFIG. 10A.

FIG. 11Ais a schematic plan view showing an example in which the placement location is horizontal.FIG. 11Bis a schematic plan view showing an example in which the placement location is tilted.

The solar elevation of the sun210ashown inFIG. 10Ais the same as the solar elevation of the sun210ashown in FIG.10B. The solar elevation of the sun210cshown inFIG. 10Ais the same as the solar elevation of the sun210cshown inFIG. 10B. The solar elevation of the sun210bshown inFIG. 10Bis a solar elevation between the sun210cand the sun210a.

InFIG. 10B, the solar cell panel110is mounted on a location (e.g., a roof facing north, etc.) tilted toward the side opposite the sun. In such a case, as shown inFIG. 10B, the light211of the sun210cof the minimum solar elevation is not incident on the concentrator130and is not incident on the solar cell panel110. Other conditions of the example ofFIG. 10Bmay include the arctic, the antarctic, the northern side of a hill, etc., where the solar elevation is low compared to that of other regions.

Therefore, in such a case, the angle of the first surface131and the like are modified appropriately according to the tilt angle of the location (e.g., the land, the roof, etc.) where the solar cell panel110is mounted.

For example, as shown inFIG. 11A, in the case where the solar cell panel110is mounted at a location tilted at an angle A18from a horizontal plane225, the incident angle is reduced by the amount of the angle A18of the placement location. That is, the incident angle of the light of the sun at the maximum solar elevation A13and the incident angle of the light of the sun at the minimum solar elevation A11are modified appropriately according to the angle A18of the placement location.

In the example, it is assumed that the solar cell panel110is mounted at a flat location.

Returning now toFIG. 9B, the mirror coating135is necessary according to the configuration of the concentrator130in the region at the vicinity of the solar cell111. On the other hand, the light211that is incident on the concentrator130undergoes total internal reflection in regions more than a prescribed distance away from the solar cell111. Therefore, it is unnecessary to provide the mirror coating135in the region where the light211undergoes total internal reflection; and the reflection loss can be reduced.FIG. 9Bshows the case where the refractive index n of the concentrator130is 1.493.

FIGS. 12A to 12Care schematic plan views showing examples in which three solar cell modules are connected.

FIG. 12Ais a schematic plan view showing an example in which the mirror coating135is not provided on the concentrator130.FIG. 12Bis a schematic plan view showing an example in which the mirror coating135is provided on a portion of the concentrator130.FIG. 12Cis a schematic plan view showing an example in which an anti-reflection film (a reflection suppression film)141is provided.

Three solar cell modules100aare connected in the example shown inFIG. 12A. The first surface131may not be connected directly to the second surface132in a region F3where the two solar cell modules100aare adjacent to each other. Even in such a case, total internal reflection is possible for the entire first surface131and the entire second surface132. Thereby, in the example shown inFIG. 12A, the mirror coating135is not provided.

PMMA, etc., may be used as the material of the concentrator130. The refractive index of PMMA is 1.493. The concentrator130includes a plate unit133. The plate unit133suppresses the mutual-separation of the multiple concentrators130that would cause the multiple concentrators130to become separate bodies. A thickness D1of the plate unit133is, for example, about 0.5 cm.

In the example shown inFIG. 12B, compared to the example shown inFIG. 12A, the mirror coating135is provided on a portion of the first surface131. For example, silver (Ag), aluminum (Al), etc., may be used as the material of the mirror coating135. However, the material of the mirror coating135is not limited thereto; and a material having a reflectance similar to those of silver (Ag), aluminum (Al), etc., may be used.

For example, the minimum solar elevation A11of the sun210is taken to be 30 degrees; and the maximum solar elevation A13of the sun210is taken to be 80 degrees. In such a case, the incident angle of the light211of the sun210at the maximum solar elevation A13is 10 degrees. The incident angle of the light211of the sun210at the minimum solar elevation A11is 60 degrees. In the case where the material of the concentrator130is PMMA, the refractive index of the PMMA is 1.493; and therefore, the substantial incident angle in the interior of the concentrator130is not less than 6.68 degrees and not more than 35.45 degrees.

The width a of the solar cell111is set to 4 cm. The thickness D1of the plate unit133is set to 0.5 cm; and a dimension D2between the solar cell panel110and the lower portion of the plate unit133is set to 3.5 cm. 100 nanometers (nm) of MgF2is deposited on the upper surface of the plate unit133.

From calculations based on such conditions, total internal reflection does not occur in the region where the height of the first surface131is 2.83 cm or less. On the other hand, total internal reflection occurs in the region where the height of the first surface131is higher than 2.83 cm. Therefore, in the example shown inFIG. 12B, a height D3of the mirror coating135is 2.83 cm. In other words, the mirror coating135is unnecessary in the region where the height of the first surface131is higher than 2.83 cm. The ideal concentration ratio is about 1.78.

In the example shown inFIG. 12C, compared to the example shown inFIG. 12B, the anti-reflection film141is provided on the side opposite to the concentrator130as viewed from the solar cell panel110. The anti-reflection film141suppresses reflections at the surface of the concentrator130of the light211passing through the interior of the concentrator130and traveling toward the solar cell panel110.

The anti-reflection film will now be described further with reference to the drawings.

FIGS. 13A and 13Bare schematic plan views showing the anti-reflection film of the embodiment.

FIG. 13Ais a schematic plan view showing an example in which three solar cell modules100aare connected.FIG. 13Bis a schematic plan view showing the light211traveling through the interior of the concentrator130of the embodiment.

In the examples shown inFIG. 13AandFIG. 13B, a first anti-reflection film (reflection suppression film)143is provided on the upper surface of the plate unit133of the concentrator130. The refractive index of the first anti-reflection film143is higher than the refractive index of the ambient air and lower than the refractive index of the concentrator130. It is more favorable for the refractive index of the first anti-reflection film143to be about 1.22. Or, the material of the first anti-reflection film143may be MgF2(having a refractive index of about 1.38).

It is unfavorable for the light211passing through the interior of the concentrator130and traveling toward the solar cell panel110to be reflected at the interface between the concentrator130and the solar cell panel110as illustrated by arrow A31shown inFIG. 13B. It is favorable for the light211passing through the interior of the concentrator130and traveling toward the solar cell panel110to pass through the interface between the concentrator130and the solar cell panel110to be incident on the solar cell panel110as illustrated by arrow A32shown inFIG. 13B.

Therefore, in the example shown inFIG. 13AandFIG. 13B, a second anti-reflection film (a reflection suppression film)145is provided between the concentrator130and the solar cell panel110. It is favorable for the refractive index of the second anti-reflection film145to have a value between the refractive index of the solar cell111and the refractive index of the concentrator130. That is, it is favorable for formula np<nm<ncto hold, where ncis the refractive index of the solar cell111, npis the refractive index of the concentrator130, and nmis the refractive index of the second anti-reflection film145. Or, the refractive index of the second anti-reflection film145may decrease gradually (be graded) from the concentrator130side toward the solar cell panel110side.

It is more favorable for the refractive index of the second anti-reflection film145to satisfy the following formula.
nm=(nc·np)1/2Formula (7)

It is more favorable for a thickness tmof the second anti-reflection film145to satisfy the following formula.
tm=λ/(4·(nc·np)1/2)  Formula (8)

In Formula (8), λ is the wavelength of the light211. The unit of the thickness tmis nanometers (nm).

For example, in the case where the refractive index ncof the solar cell111is 3.7 (silicon (Si)) and the refractive index npof the concentrator130is 1.5, it is more favorable for the refractive index nmof the second anti-reflection film145to be about 2.35 (TiO2, SrTiO3, etc.). Or, in the case where, for example, the refractive index ncof the solar cell111is 3.7 (silicon (Si)) and, for example, the refractive index npof the concentrator130using a reflection plate is 1, it is more favorable for the refractive index nmof the second anti-reflection film145to be about 1.9 (Si3N4, etc.).

Thereby, the reflections of the light211at the surface of the concentrator130are suppressed; and the light211can be guided efficiently toward the solar cell panel110.

FIG. 14is a schematic plan view showing an example of the solar cell module according to the embodiment.

Two solar cell modules100aare connected in the example shown inFIG. 14.

The minimum solar elevation A11of the sun210is taken to be 30 degrees; and the maximum solar elevation A13of the sun210is taken to be 80 degrees. In such a case, the incident angle of the light211of the sun210at the maximum solar elevation A13is 10 degrees. The incident angle of the light211of the sun210at the minimum solar elevation A11is 60 degrees.

The refractive index npof the concentrator130is set to 1.493 (PMMA). Here, the light211is refracted when incident on the concentrator130. Therefore, the substantial incident angle of the interior of the concentrator130is not less than 6.68 degrees and not more than 35.45 degrees. That is, a minimum substantial incident angle A23shown inFIG. 14is 6.68 degrees. A maximum substantial incident angle A24shown inFIG. 14is 35.45 degrees.

The width a of the solar cell111is set to 4 cm. The thickness D1of the plate unit133of the concentrator130is set to 0.5 cm. The dimension D2between the solar cell panel110and the lower portion of the plate unit133is set to 3.5 cm. In such a case, the ideal concentration ratio (d/a) is about 2.06.

The mirror coating135is provided on the first surface131of the solar cell module100aon the left side ofFIG. 14. In other words, in the example shown inFIG. 14, it is necessary to provide the mirror coating135on the first surface131of the solar cell module100aon the left side; but it is unnecessary to provide the mirror coating135in the relatively wide region of the other parabolic surface.

The first surface123includes a third portion123cand a fourth portion123d. The second surface124includes a fifth portion124eand a sixth portion124f. The distance between the third portion123cand the solar cell111is shorter than the distance between the fourth portion123dand the solar cell111. The distance between the fifth portion124eand the solar cell111is shorter than the distance between the sixth portion124fand the solar cell111. A distance D12between the fourth portion123dand the sixth portion124fis longer than a distance D11between the third portion123cand the fifth portion124e.

The first surface123includes the third region F3. The second surface124includes a fourth region F4. The first light211athat is incident on the first surface123undergoes total internal reflection in the third region F3. The second light211bthat is incident on the second surface124undergoes total internal reflection in the fourth region F4.

The solar cell module100according to the embodiment further includes a first mirror coating layer135aand a second mirror coating layer135b. The first surface123further includes the first region F1. The second surface124further includes the second region F2. The first mirror coating layer135ais provided in the first region F1. The second mirror coating layer135bis provided in the second region F2.

The solar cell module100according to the embodiment further includes the first reflection suppression film143. The first light211apasses through the first reflection suppression film143to be incident on the first surface123. The second light211bpasses through the first reflection suppression film143to be incident on the second surface124.

The refractive index of the first reflection suppression film143is lower than the refractive index of the concentrator130.

The solar cell module100according to the embodiment further includes the second anti-reflection film145. The second anti-reflection film145is provided between the first reflection suppression film143and the solar cell panel110. The first light211apasses through the second reflection suppression film145to be incident on the first portion113. The second light211bpasses through the second reflection suppression film145to be incident on the second portion114.

The refractive index of the second reflection suppression film145is higher than the refractive index of the concentrator130and lower than the refractive index of the solar cell111.

One of the first mirror coating layer135aor the second mirror coating layer135bincludes one of silver or aluminum.

FIG. 15is a schematic plan view showing another example of the solar cell module according to the embodiment.

In the example shown inFIG. 15, the width a of the solar cell111of the solar cell module100ashown inFIG. 14is set to 1 cm. Thereby, the first axis171intersects the second surface132in the solar cell module100aon the left side as shown inFIG. 15. The first axis171corresponds to the y-axis of the first surface131. Otherwise, the structure is the same as the structure of the solar cell module100adescribed above in regard toFIG. 14.

As described above in regard toFIG. 4AtoFIG. 4D, the first axis171is parallel to the travel direction of the light211of the sun210at the minimum solar elevation A11. The second axis172is parallel to the travel direction of the light211of the sun210at the maximum solar elevation A13. Therefore, the light211of the sun210travels in the area between the first axis171and the second axis172toward the concentrator130.

However, the light211of the sun210of a prescribed elevation from the minimum solar elevation A11(e.g., the light211substantially parallel to the first axis171) is shielded by the second surface132of the solar cell module100aon the left side. Therefore, the light of the sun210of an elevation relatively proximal to the minimum solar elevation A11that can be incident on the concentrator130is light213shown inFIG. 15.

Even in such a case, the mirror coating135is provided on the first surface131of the solar cell module100aon the left side. As illustrated by arrow A33shown inFIG. 15, the light211that is incident on the concentrator130and reaches the first surface131of the solar cell module100aon the right side undergoes total internal reflection at the first surface131. In the example shown inFIG. 15, the ideal concentration ratio (d/a) is about 3.4.

FIG. 16is a schematic plan view showing another example of the solar cell module according to the embodiment.

In the example shown inFIG. 16, the height of the plate unit133of the concentrator130of the solar cell module100ashown inFIG. 15is set to be high. That is, the dimension D2between the solar cell panel110and the lower portion of the plate unit133is longer than 3.5 cm.

In such a case, light215of the maximum incident angle may not be able to reach the region where the mirror coating135is provided. The light215of the maximum incident angle is parallel to the first axis171. In other words, the light215of the maximum incident angle is the light of the sun210at the minimum solar elevation A11. Therefore, in the example shown inFIG. 16, it is necessary to redesign the solar cell module100ato match the light213of the sun210of an elevation relatively proximal to the minimum solar elevation A11that can reach the region where the mirror coating135is provided. In the example shown inFIG. 16, the ideal concentration ratio (d/a) is about 4.1.

FIGS. 17A and 17Bare schematic views showing another example of the solar cell module according to the embodiment.

FIG. 17Ais a schematic plan view showing another example of the solar cell module according to the embodiment.FIG. 17Bis a graph of an example of the relationship between an incident angle An and a light amount Lg. In the graph shown inFIG. 17B, the light amount Lg is taken to be 100% when the incident angle An is 0 degrees for no light concentration (the case where the concentrator130is not provided). InFIG. 17B, data SPL1correspond to “partial vapor-deposition”. Data SPL2correspond to “entire vapor-deposition”. Data SPL3correspond to “without partial vapor-deposition”. Data SPL4correspond to “no light concentration”.

The solar cell module100ashown inFIG. 17Aincludes the solar cell panel110, the concentrator130, the first anti-reflection film143, and the second anti-reflection film145. The structure of the solar cell module100ashown inFIG. 17Ais similar to the structure of the solar cell module100adescribed above in regard toFIG. 13A.

The first anti-reflection film143is provided on the upper surface of the plate unit133of the concentrator130. The material of the first anti-reflection film143is MgF2. The first anti-reflection film143has a rectangular configuration. A length D4of one side of the first anti-reflection film143is 4 cm. A length D5of another side of the first anti-reflection film143intersecting the one side is 8.3 cm. The thickness of the first anti-reflection film143is 100 nm.

The second anti-reflection film145is provided between the concentrator130and the solar cell panel110. The material of the second anti-reflection film145is TiO2. The thickness of the second anti-reflection film145is 60 nm.

As the mirror coating135, a portion in which aluminum is vapor-deposited is provided in the first surface131. In the example, the relationship between the incident angle An and the light amount Lg is investigated for the case where the aluminum is vapor-deposited on the entire first surface131, the case where the aluminum is vapor-deposited on a portion of the first surface131, and the case where the aluminum is not vapor-deposited on the first surface131. Similarly, the case where the concentrator130is not provided is investigated.

The solar cell111has a square configuration. The length of one side of the solar cell111is 4 cm.

The ideal concentration ratio of the solar cell module100ashown inFIG. 17Ais 2.06.

The investigation results are as shown inFIG. 17B.

In other words, the light amount Lg is higher for the case where the concentrator130is provided than for the case where the concentrator130is not provided.

In the case where the aluminum is vapor-deposited on the entire first surface131, the total internal reflection of the light cannot be utilized; and reflection loss occurs. Therefore, the light amount Lg is lower for the case where the aluminum is vapor-deposited on the entire first surface131than for the case where the aluminum is vapor-deposited on a portion of the first surface131. However, the light amount Lg of the case where the aluminum is vapor-deposited on the entire first surface131is higher than the light amount Lg of the case where the aluminum is not vapor-deposited on the first surface131. In the embodiment, the case where the aluminum is vapor-deposited on the entire first surface131is not eliminated.

Even in the case where the aluminum is not vapor-deposited on the first surface131, there is a light concentration effect when the concentrator130is provided.

Embodiments include following Clauses:

A solar cell module, comprising:a solar cell panel having a first cell surface including a first portion and a second portion; anda concentrator,the concentrator havinga first surface, anda second surface separated from the first surface,a first light incident on the first surface at a first incident angle being incident on the first portion,a second light incident on the second surface at a second incident angle being incident on the second portion,the first surface including a first parabola where the first surface intersects a first perpendicular plane, the first perpendicular plane including a direction from the first portion toward the second portion, the first perpendicular plane being perpendicular to the first cell surface,the second surface including a second parabola where the second surface intersects the first perpendicular plane,a first point on the first parabola and a second point on the second parabola being asymmetric with respect to a second perpendicular plane, the second perpendicular plane being perpendicular to the first cell surface and the first perpendicular plane.
Clause 2

The module according to Clause 1, whereinthe first portion includes a first focal point of the first parabola, andthe second portion includes a second focal point of the second parabola.
Clause 3

The module according to Clause 1, whereinthe solar cell panel includes a first edge portion and a second edge portion,the first edge portion includes the first focal point of the first parabola, andthe second edge portion includes the second focal point of the second parabola.
Clause 4

The module according to Clause 1, whereinthe first surface has a first concave surface,the second surface has a second concave surface, andthe first concave surface opposes the second concave surface.
Clause 5

The module according to Clause 1, whereinthe first incident angle is a one-year maximum value of an angle between sunlight and a direction perpendicular to a ground surface, andthe second incident angle is a one-year minimum value of the angle between the sunlight and the direction perpendicular to the ground surface.
Clause 6

The module according to Clause 1, wherein the concentrator includes:a first light concentration plate having the first surface; anda second light concentration plate having the second surface.
Clause 7

The I module according to Clause 1, whereinthe first surface includes a third portion and a fourth portion,the second surface includes a fifth portion and a sixth portion,a distance between the third portion and the solar cell is shorter than a distance between the fourth portion and the solar cell,a distance between the fifth portion and the solar cell is shorter than a distance between the sixth portion and the solar cell, anda distance between the fourth portion and the sixth portion is longer than a distance between the third portion and the fifth portion.
Clause 8

The module according to Clause 7, whereinthe concentrator includes a light concentrating material, anda refractive index of the concentrator is higher than a refractive index of ambient air.
Clause 9

The module according to Clause 8, whereinthe first surface includes a third region,the second surface includes a fourth region,the first light incident on the first surface undergoes total internal reflection in the third region, andthe second light incident on the second surface undergoes total internal reflection in the fourth region.
Clause 10

The module according to Clause 9, further comprising:a first mirror coating layer; anda second mirror coating layer,the first surface further including a first region,the second surface further including a second region,the first mirror coating layer being provided in the first region,the second mirror coating layer being provided in the second region.
Clause 11

The module according to Clause 8, further comprising a first reflection suppression film,the first light passing through the first reflection suppression film to be incident on the first surface,the second light passing through the first reflection suppression film to be incident on the second surface.
Clause 12

The module according to Clause 11, wherein a refractive index of the first reflection suppression film is lower than the refractive index of the concentrator.

The module according to Clause 12, further comprising a second reflection suppression film provided between the first reflection suppression film and the solar cell panel,the first light passing through the second reflection suppression film to be incident on the first portion,the second light passing through the second reflection suppression film to be incident on the second portion.
Clause 14

The module according to Clause 13, wherein a refractive index of the second reflection suppression film is higher than the refractive index of the concentrator and lower than a refractive index of the solar cell.

The module according to Clause 8, wherein the concentrator includes a polymethylmethacrylate resin.

The module according to Clause 10, wherein one of the first mirror coating layer or the second mirror coating layer includes one of silver or aluminum.