JP4253191B2 - Concentrating solar power generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a concentrating solar power generation device that condenses sunlight onto a solar cell surface by a condensing lens, and in particular, the illuminance of the solar cell surface without being affected by tracking errors or lens assembly errors. The present invention relates to a concentrating solar power generation apparatus that can maintain power uniformly and perform stable power generation.
[0002]
[Prior art]
A concentrating solar power generation device always efficiently generates power by concentrating sunlight on a relatively small-diameter solar cell surface with a condensing lens directed toward the sun. Fresnel lenses are often used as condenser lenses. In such a concentrating solar power generation device, if the orientation of the condensing lens slightly deviates from the solar direction due to tracking error, Fresnel lens assembly error, etc., the illuminance on the light-receiving surface of the solar cell rapidly decreases. Power generation is greatly impaired. Therefore, conventionally, a secondary condenser is provided between the condenser lens and the solar cell so that the light beam emitted from the condenser lens is reflected inside the secondary condenser even if the light beam is slightly deviated from the normal direction. This ensures that the light flux is always incident on the light receiving surface of the solar cell (Patent Document 1).
[0003]
On the other hand, as the Fresnel lens, a flat Fresnel lens is frequently used because of easy manufacturing and maintenance. An example of the flat Fresnel lens 1 is shown in FIG. In FIG. 4, a large number of concentric annular ridges 11 having a substantially triangular prism cross section are formed on the surface side of the flat plate 12, and the apex angle θt of the triangular prism of each ridge 11 is usually perpendicular to the flat plate 12 surface. The parallel sunlight L1 incident from the surface side of the flat plate 12 at the incident angle θi with respect to the prism inclined surface is set to be refracted at the minimum deviation angle θd. Since chromatic aberration can be minimized by this, when a multi-junction solar cell in which a large number of PN junction elements having different power generation wavelength regions are joined in series is used, sunlight in a wide wavelength region (0.45 μm to 1.7 μm) is used. Can be efficiently incident on the solar cell.
[0004]
[Patent Document 1]
JP 2001-36120 A
[0005]
[Problems to be solved by the invention]
However, in the flat Fresnel lens 1 in which the substantially triangular prism section of the ridge 11 is set so as to be refracted at the minimum deflection angle θd, the lens focal point located near the light incident end face 2a of the secondary condenser 2 shown in FIG. In the region, the focal position F1 of the light L21 reaching from the ridge 11 in the low light ray region (lens inner periphery) is the focal point of the light L22 reaching the ridge 11 in the high light ray region (lens outer periphery). It is closer to the end face 2a than the position F2. That is, the focal length of the protrusion 11 on the inner peripheral portion of the lens is longer than the focal length of the protrusion on the outer peripheral portion of the lens. This is because the apex angle θt of the triangular prism is usually made as small as possible at the inner peripheral portion of the lens in order to minimize the decrease in optical efficiency (transmittance) due to the occurrence of the light shielding portion. As a result, the light L21 refracted by the protrusion 11 on the inner peripheral portion of the lens is compared with the light L22 refracted by the protrusion 11 on the outer peripheral portion of the lens, and the light incident end face 2a of the secondary condenser 2. The incident angle θ becomes smaller and the reflection inside the secondary concentrator 2 is not sufficiently performed. For this reason, the incidence of sunlight on the light-receiving surface of the solar cell becomes uneven and unevenness may occur. there were.
[0006]
Therefore, the present invention solves such a problem, and in a concentrating solar power generation device that combines a flat Fresnel lens and a secondary concentrator, the incidence unevenness of sunlight on the light receiving surface of the solar cell is reduced. It aims at providing the concentrating solar power generation device which can be suppressed.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, Fresnel lens (1) that condenses sunlight (L1) and light (L2) collected by Fresnel lens (1) are incident to repeat internal reflection. In a concentrating solar power generation apparatus including a secondary concentrator (2) that guides light while the light is output from the secondary concentrator (2), a flat plate ( A large number of concentric annular ridges (11) having a substantially triangular prism cross section are formed on the surface side of 12) to form the Fresnel lens (1), and the light (L21) from the ridge (11) on the inner periphery of the lens. ) Is farther from the light incident end face (2a) of the secondary condenser (2) than the focal position (F2) of the light (L22) reaching the ridge (11) on the outer periphery of the lens. The cross-sectional shape of these protrusions (11) is set so that it may become . In this case, the setting of the cross-sectional shape of the ridge is performed, for example, by setting the apex angle of the substantially triangular prism section of the ridge to an appropriate angle.
[0008]
In the present invention, the focal position of the light reaching the protrusion on the inner peripheral portion of the lens in the flat plate Fresnel lens is more from the light incident end face of the secondary condenser than the focal position of the light reaching the protrusion on the outer peripheral portion of the lens. Since the focal length of the protrusion on the inner periphery of the lens is shorter than the focal distance of the protrusion on the outer periphery of the lens, the light refracted by the protrusion on the inner periphery of the lens The angle of incidence on the light incident end face of the secondary condenser is increased, and reflection within the secondary condenser is sufficiently performed. As a result, the light incident on the light incident end face of the secondary condenser from either the lens inner peripheral part or the lens outer peripheral part of the flat Fresnel lens is sufficiently reflected inside the secondary condenser, and is received by the solar cell. The incidence of sunlight on the surface is uniform, and uneven illumination is prevented. In addition, even if it remove | excludes the conditions which refract the incident parallel sunlight with the minimum deflection angle about the protrusion of an inner peripheral part, since the refraction angle is small in the said inner peripheral part, the breadth of light by a chromatic aberration does not become so large. In addition, since the area of the inner periphery of the lens is smaller than the total area of the lens, even if the apex angle of the triangular prism is increased to increase the light incident angle to the secondary condenser, the light shielding is increased thereby. Since the area of the portion is still small when viewed from the total area of the lens, the loss is small and the effect of improving the illuminance unevenness is greater.
[0009]
In addition, the code | symbol in the said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An example of the configuration of a concentrating solar power generation device (hereinafter simply referred to as a power generation device) of the present invention is shown in FIG. In FIG. 1, the power generating apparatus is provided with a concentrating flat plate Fresnel lens 1, and the structure thereof has many concentric annular ridges 11 on the surface (upper surface) side as already described in the section of the prior art. The cross-sectional shape of each protrusion 11 formed is a substantially triangular prism cross section (see FIG. 4). Below the flat Fresnel lens 1, a quadrangular pyramid-shaped secondary concentrator 2 having a small diameter toward the rear end (lower end) and having four tapered side surfaces 2c is disposed, and its rear end surface (light emission end surface). A solar cell 3 having a square substrate in contact with 2b is provided.
[0011]
When the parallel sunlight L1 enters the flat Fresnel lens 1, it converges into a circular light beam L2 and is emitted toward the secondary condenser 2, and near the front end face (light incident end face) 2a of the secondary condenser 2. After being condensed (FIG. 2), the light is diffused to the light incident end face (for example, 11 mm square) 2a and enters this. The circular light beam L2 incident on the light incident end surface 2a of the secondary condenser 2 is directed to the light output end surface 2b while being totally reflected by the four tapered side surfaces 2c, and the light receiving surface of the solar cell 3 provided in contact therewith. Incident (for example, 7 mm square). A large number of kaleidoscopic virtual images of solar cells are formed in the secondary concentrator 2, and light incident on the secondary concentrator 2 is repeatedly reflected in various directions on the side surface 2 c to each virtual image. As a result, the incident light uniformly enters the light receiving surface of the solar cell 3.
[0012]
Here, in this embodiment, with respect to the ridge 11 on the inner peripheral portion of the flat Fresnel lens 1, the apex angle θt (FIG. 4) of the substantially triangular prism section is refracted, and the incident parallel sunlight L1 is refracted with the minimum deviation angle θd. It is set larger than the angle that satisfies the condition to be satisfied. Thereby, the sunlight L1 collected by the flat Fresnel lens 1 is a focal position F1 of the light L21 that has reached the ridge 11 on the inner periphery of the lens, as shown in FIG. However, it is farther from the light incident end face 2a of the secondary condenser 2 than the focal position F2 of the sunlight L22 that reaches the protrusion 11 on the outer periphery of the lens. That is, the focal length of the protrusion 11 on the inner periphery of the lens is shorter than the focal length of the protrusion 11 on the outer periphery of the lens.
[0013]
As a result, the angle θ at which the light L21 refracted by the protrusion 11 on the inner periphery of the lens is incident on the light incident end surface 2a of the secondary condenser 2 becomes larger than before, and the secondary condenser described above. 2 is sufficiently reflected inside. As a result, the light L21 and L22 incident on the light incident end surface 2a of the secondary condenser 2 from either the lens inner peripheral part or the lens outer peripheral part of the flat Fresnel lens 1 is also sufficiently reflected inside the secondary condenser 2. As a result, the incidence of sunlight on the light receiving surface of the solar cell 3 becomes uniform and the occurrence of unevenness is prevented. As described above, even if the condition for refracting the incident parallel sunlight L1 at the minimum deviation angle θd is removed, the inner peripheral portion has a small refraction angle, and thus light caused by chromatic aberration. The spread of the light is not so large, and the illuminance unevenness of the incident light to the solar cell due to the light wavelength does not occur.
[0014]
In the above embodiment, the example in which the focal length of the protrusion on the inner peripheral portion is shortened with respect to the focal length of the protrusion on the outer peripheral portion of the flat plate Fresnel lens has been described, but the inner peripheral portion is further made into a plurality of inner and outer annular portions. It is also possible to divide and set the focal lengths of the ridges of each annular portion so as to be sequentially shorter than the focal lengths of the ridges of the outer peripheral portion.
[0015]
【The invention's effect】
As described above, according to the present invention, in a concentrating solar power generation device that combines a flat Fresnel lens and a secondary concentrator, it is possible to reduce the uneven incidence of sunlight on the light receiving surface of the solar cell. .
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of a concentrating solar power generation device according to an embodiment of the present invention.
FIG. 2 is an optical path diagram of the concentrating solar power generation device.
3 is an enlarged view of a condensing region in the optical path, and is an enlarged view of a part A in FIG.
FIG. 4 is a partially enlarged cross-sectional view of a flat Fresnel lens.
FIG. 5 is an enlarged view of a condensing region in an optical path in a conventional concentrating solar power generation device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Flat Fresnel lens, 11 ... Projection, 12 ... Flat plate, 2 ... Secondary concentrator, 3 ... Solar cell, L1 ... Sunlight, L2 ... Condensed light.

Claims (1)

Output from the secondary concentrator, the secondary concentrator that guides the light collected by the Fresnel lens that collects the sunlight, the light that is collected by the Fresnel lens is incident , and the internal reflection is repeated on its side surface. In a concentrating solar power generation device including a solar cell on which light is incident, a large number of concentric annular ridges having a substantially triangular prism cross section are formed on the surface side of a flat plate to form the Fresnel lens, and the inner periphery of the lens The cross-sectional shape of these ridges is such that the focal position of light reaching the ridge is farther from the light incident end face of the secondary condenser than the focal position of light reaching the ridge on the outer periphery of the lens. A concentrating solar power generation device characterized by being set.

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