Stacked solar cell device

This stacked solar battery device includes a plurality of solar battery units 4, an enclosure case made of a metal plate to house these solar battery units 4 therein, a cover glass having a partial cylindrical lens formed. The plurality of solar battery units 4 are housed in a plurality of recesses of the enclosure case, and are sealed with a sealing material of synthetic resin. The solar battery unit 4 has a planar light receiving solar battery module 10, and rod light receiving solar battery modules 30 and 50 stacked so that the module having a shorter center wavelength of the sensitivity wavelength band is positioned closer to the incident side of the sunlight. The solar battery module 10 is configured so that five planar light receiving solar-battery cells 11 are connected in parallel with four connection rods 20a and 20b, and the sunlight modules 30 and 50 are configured so that five sub modules 31 and 51 are connected in parallel respectively with the connection rods 40a, 40b, 60a and 60b. The sub modules 31 and 51 are configured so that a plurality of rod-shaped solar battery cells 32 and 52 respectively are connected in series.

TECHNICAL FIELD

The present invention relates to a stacked solar battery device in which a plurality of solar battery modules having different sensitivity wavelength bands are stacked in order to effectively utilize wavelength components in a wide range of sunlight spectrum. Particularly, the invention relates to the stacked solar battery device in which the solar battery module is stacked so that the larger the forbidden band of a semiconductor the solar battery module has, that is, the shorter center wavelength of the sensitivity wavelength band the solar battery module has, the closer to an incident side of sunlight the solar battery module is positioned.

BACKGROUND TECHNOLOGY

For the spread of the solar battery device, there are important elements such as convenience, photoelectric conversion efficiency, production cost, quality stability, lifetime of the device, energy consumption required for manufacturing the solar battery, disposal after use and the like of the solar battery or the solar battery module.

As examples of the solar battery, there are known (A) a planar light receiving solar battery, (B) a solar battery in which granular solar battery cells are arranged in a panel shape of a plurality of rows and columns, (C) a solar battery in which a plurality of fiber solar battery cells are arranged in a panel shape, (D) a tandem solar battery, (E) a stacked solar battery, etc.

The solar battery of above (B) is proposed in, patent application publications WO02/35613, WO03/017383, WO03/036731, WO2004/001858, etc. The solar battery of above (C) is proposed in patent publications of U.S. Pat. Nos. 3,984,256, 5,437,736, etc. The tandem solar battery of above (D) is manufactured in order to enhance the photoelectric conversion efficiency of a single solar battery cell. In this solar battery, the sensitivity wavelength band of the sunlight spectrum is divided into plural bands, and semiconductors having the forbidden band optimal to each of the sensitivity wavelength bands are used to make pn junctions, which are crystal-grown continuously on a common semiconductor substrate.

The stacked solar battery of above (E) is manufactured in order to enhance the use efficiency and the photoelectric conversion efficiency of the sunlight spectrum. In this solar battery, plural kinds of solar battery modules of planar type are manufactured respectively with the solar battery cell made of a semiconductor having the forbidden band optimal to respective sensitivity wavelength band of the sunlight spectrum, and plural kinds of solar battery modules are vertically stacked.

In the solar batteries of (A) to (E), technologies are employed in which the sunlight is collected by a lens and a reflector to increase the energy density. In this case, not only the photoelectric conversion efficiency is improved, but also a high output is obtained with a relatively small light receiving area; therefore, the cost of the solar battery can be reduced. These technologies have been already disclosed in many academic documents and patent publications.

For example, the technology for collecting light in the solar battery is disclosed in patent publications of U.S. Pat. Nos. 4,834,805, 4,638,110, etc. Since with the light collection, the temperature of the solar battery cell rises and the photoelectric conversion efficiency is reduced to be liable to deteriorate the solar battery module; it is important how efficiently to radiate the generated heat due to the light collection. Patent publications of U.S. Pat. Nos. 5,482,568, 6,252,155, 6,653,551 and 6,440,769 disclose a solar battery employing a configuration where the solar battery cell is housed in a bottom portion of a plurality of cone-like reflection surfaces, which the reflection surface collects the light and radiates the generated heat.

However, the tandem solar battery and the stacked solar battery have a flat receiving surface, and receive the light from the receiving surface only; thus, they cannot convert effectively photoelectrically with respect to reflected and scattered lights coming from plural directions around. Moreover, a plurality of planar pn junctions formed in the solar battery are each a single pn junction having the same area, and connected in series. Therefore, among the plurality of pn junctions constituting the tandem solar battery or the stacked solar battery, the pn junction with the smallest output current restricts the output current. Accordingly, there is a problem in which the pn junction which intrinsically can output the high output current singularly cannot exhibit the output to a maximum extent.

In addition, the tandem solar battery must have a configuration where semiconductor crystals different in the forbidden band and a lattice constant are grown into a thin film on a common semiconductor substrate, and a tunnel junction different from the pn junction is formed in each layer. In order to grow continuously the different kinds of semiconductors, the lattice constants have to be matched, the selectable semiconductor is limited, and it is necessary to control the precise composition in the thin film crystal growth, leading to an increased cost for a manufacturing device and works.

In the stacked solar battery of a wavelength dividing type in which plural kinds of solar battery modules are mechanically stacked, it is necessary to neither form the tunnel junction nor match the lattice constants. However, when stacking the solar batteries each having a planar single pn junction, unless a precise setting is performed for arrangement of the electrodes of the solar battery module, and an interval and a parallelism of the solar battery module, the output may passively be reduced by the electrode shielding and the reflection at the surface.

In order to solve the problems of the stacked solar battery described above, the present inventor, as shown in a publication of WO2005/088733, has proposed a stacked solar battery where independently manufactured are the planar light receiving solar battery modules and plural kinds of the solar battery modules made of a large number of spherical solar battery cells disposed in plural rows and plural columns, which are made of the semiconductor different in the forbidden bands. And these solar battery modules are stacked so that the module with the larger forbidden band is closer to the incident side of the sunlight.

In the stacked solar battery, when connecting in series the independent solar battery modules made of the semiconductors different in the forbidden band, the series connection number and the parallel connection number of the solar battery cells are selected so that the currents flowing in the respective solar battery modules are equal to one another, thereby the entire output can be maximized.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, in the stacked solar battery, increase of the number of the spherical solar battery cells results in the inevitable increase of the points to be electrically connected between the cells, leading to a high assembling cost including a wire connection cost, thereby, reliability of the device tends to decrease. Moreover, since there are generated gaps which cannot be filled even if a large number of spherical solar battery cells are arranged densely to a maximum extent, particularly in a case of receiving the light collected by a lens, the light passing through the gaps cannot be used sufficiently.

Objects of the invention is to provide a stacked solar battery device which is provided with at least one kind of solar battery module including a plurality of rod-shaped solar battery cells having a partial cylindrical pn junction and a pair of strap-shaped electrodes, to provide a stacked solar battery device in which the number of the solar battery cells and the number of connection points can be reduced by use of a rod-shaped solar battery cell to lower the cost, to provide a stacked solar battery device in which the photoelectric conversion efficiency can be improved by collecting light with a lens and a reflection surface and the production cost can be reduced, and to provide a stacked solar battery device in which heat radiation can be enhanced by the enclosure case made of metal, and so on.

Means to Solve the Problem

The present invention relates to a stacked solar battery device in which a plurality of solar battery modules are stacked in plural layers, characterized by comprising: plural kinds of solar battery modules with different sensitivity wavelength bands, the plural kinds of solar battery modules being stacked so that the solar battery module having a shorter center wavelength of the sensitivity wavelength band is positioned closer to an incident side of sunlight; wherein at least one kind of the solar battery module is constituted by a plurality of rod light receiving solar battery sub modules each of which is provided with a plurality of rod-shaped solar battery cells; and the rod-shaped solar battery cell comprises: a substrate made of a rod-shaped semiconductor crystal of a p-type or n-type semiconductor having a circular or partial circular cross-section; an another conductive layer formed at a portion of a surface layer of the substrate except for a strap-shaped portion parallel to an axial center of the substrate, and having a conductivity type different from the substrate; a pn junction formed with the substrate and the another conductive layer and having a partial cylindrical shape; a first strap-shaped electrode ohmic-connected to a surface of the strap-shaped portion of the substrate; and a second strap-shaped electrode ohmic-connected to a surface of the another conductive layer on an opposite side from the first electrode with respect to the axial center of the substrate.

Advantages of the Invention

The rod-shaped solar battery cell includes the rod-shaped substrate, the another (separate) conductive layer of a conductivity type different from the substrate, the partial cylindrical pn junction, and the first and second strap-shaped electrodes which are provided to both ends of the cell with respect to the axial center of the substrate being sandwiched therebetween and are connected to the pn junction. Thus, a distance from each point on the pn junction to the first and second electrodes is maintained at an almost constant small value. Therefore, the entire pn junction generates uniformly photovoltaic power, enabling keeping the photoelectric conversion efficiency of the rod-shaped solar battery cell high.

In a case of configuring the rod light receiving solar battery sub module by arranging a plurality of rod-shaped solar battery cells in parallel to be connected in series via the first and second electrodes, the voltage generated in the sub module can be varied by changing the diameter of the substrate to change the number of the plurality of rod-shaped solar battery cells.

In the solar battery module including a plurality of rod light receiving solar battery sub modules, such a configuration is adopted so that a plurality of rod light receiving solar battery sub modules are connected in parallel, and the current generated in the solar battery module can be varied by changing the number of the sub modules connected in parallel.

In the rod-shaped solar battery cell, since the length thereof in a direction of the axial center can be set several to a dozen times the diameter of the substrate, the light receiving area can be significantly increased compared with the granular solar battery cell. Additionally, a plurality of rod-shaped solar battery cells can be arranged densely in parallel to constitute the rod light receiving solar battery sub module, and a ratio of the light receiving area to a projected area of the sunlight can be set larger to increase light receiving efficiency for receiving the sunlight.

Moreover, the rod light receiving solar battery sub module can have a much smaller number of the electric connection points to connect the solar battery cells compared with the sub module having a plurality of granular solar battery cells. Therefore, assembling cost of the sub module including the electric connection cost can be significantly reduced.

The solar battery device includes plural kinds of solar battery modules whose sensitivity wavelength bands are each different from one another, and which solar battery modules are stacked so that the solar battery module having a shorter center wavelength of the sensitivity wavelength band is positioned closer to the incident side of sunlight; therefore, the sunlight in a wide wavelength range of the sunlight spectrum can be photoelectric-converted.

The shorter wavelength the light has, the less transmission the light has; thus, as described above, the plural kinds of solar battery modules are stacked so that the solar battery module having a shorter center wavelength of the sensitivity wavelength band is positioned closer to the incident side of the sunlight; therefore, the photoelectric conversion efficiency of each solar battery module can be enhanced.

In the solar battery device, plural kinds of vertically stacked solar battery modules are connected in series, and the output currents thereof are set substantially to the same current, allowing respective electric-generating capacities of the plural kinds of the solar battery modules to be exhibited to a maximum extent.

Since at least one kind of solar battery module is constituted by a plurality of rod light receiving solar battery sub modules, in respective sub modules the output voltage of the rod light receiving solar battery sub modules can be adjusted by varying the series connection number of the rod-shaped solar battery cell. Further, since the output current of the solar battery module thereof can be adjusted by varying the parallel connection number where a plurality of rod light receiving solar battery sub modules are connected in parallel, it becomes easy to uniform the output currents of plural kinds of solar battery modules vertically stacked.

As constitutions of dependent claims, following various constitutions may be adopted.

(1) At least one kind of solar battery module is constituted by a plurality of planar light receiving sub modules each of which is constituted by a planar light receiving solar battery cell having a planar pn junction.

(2) Three kinds of solar battery modules are provided in which two kinds of solar battery modules are each constituted by a plurality of rod light receiving solar battery sub modules, one kind of solar battery module is constituted by a plurality of planar light receiving sub modules. The solar battery module constituted by the plurality of planar light receiving sub modules is arranged on the uppermost position.

(3) Each rod light receiving solar battery sub module and each planar light receiving sub module are configured so that the light receiving area thereof is equal to each other.

(4) A plurality of rod-shaped solar battery cells in the rod light receiving solar battery sub module are arranged in parallel so that the conductive direction defined by the first and second electrodes is aligned in a horizontal direction, and are electrically connected in series via the first and second electrodes.

(5) A pair of first connection rods are provided which connect in parallel and couple integrally a plurality of rod light receiving solar battery sub modules constituting the solar battery module, and two pairs of second connection rods are provided which connect in parallel and couple integrally a plurality of planar light receiving sub modules constituting the solar battery module.

(6) An enclosure case made of a metal plate is provided which has one or more recess protruding downward; the recess of the enclosure case houses plural kinds of solar battery modules in a stacked state.

(7) The enclosure case has a plurality of recesses arranged in parallel and horizontally in the width direction of the recess, and plural kinds of solar battery modules are housed in a stacked state in each of the plurality of recesses.

(8) The recess of the enclosure case has substantially an inverted trapezoidal cross-section of which the width gradually increases upward, and a pair of side walls and the bottom wall of the recess have inner surfaces made to be light reflecting surfaces.

(9) A lens member having a lens portion which has a light collecting function to collect the sunlight toward the plurality of solar battery modules is provided closer to the incident side of sunlight than the plurality of solar battery modules.

(10) Spaces in the plurality of recesses of the enclosure case are filled with transparent synthetic resin sealing materials, and they are packaged by the enclosure case and the lens member.

(11) A trapezoidal protruding pedestal which protrudes upward by a slight predetermined height is formed at a bottom wall of the enclosure case.

(12) A plurality of end stopping blocks are provided each of which closes an end of the recess of the enclosure case to which the stopping block provided are a plurality of connection pipes made of metal for inserting ends of the first and second connection rods so as to be electrically connected, and the connection pipes being projected an outside of the end stopping block as external terminals.

DESCRIPTION OF NUMERALS

BEST MODE FOR IMPLEMENTING THE INVENTION

A solar battery device according to the present invention is a stacked solar battery device in which a plurality of solar battery modules are stacked in plural layers, characterized by comprising: plural kinds of solar battery modules with different sensitivity wavelength bands, the plural kinds of solar battery modules being stacked so that the solar battery module having a shorter center wavelength of the sensitivity wavelength band is positioned closer to the incident side of sunlight; wherein at least one kind of the solar battery module is constituted by a plurality of rod light receiving solar battery sub modules each of which is provided with a plurality of rod-shaped solar battery cells. The rod-shaped solar battery cell includes a specific constitution as follows.

EMBODIMENT

As shown inFIGS. 11 to 15, a light collecting type stacked solar battery device1comprises an enclosure case2made of a metal plate, stacked solar battery units4respectively housed in three recesses3of the enclosure case2, a sealing material63(not shown inFIG. 13) filled in each of the recesses3, a cover glass5arranged on an incident side of sunlight, end stopping blocks6arranged at both ends of each of the recesses3of the enclosure case2.

The stacked solar battery unit4comprises three kinds of solar battery modules10,30and50which are different from one another in the sensitivity wavelength band, and the shorter center wavelength of the sensitivity wavelength band the solar battery module has, the closer to the incident side of the sunlight of the solar battery module is positioned. The first solar battery module10has five planar light receiving sub modules11connected in parallel as planar light receiving solar battery cells, and are arranged on an uppermost position.

The second solar battery module30has five rod light receiving solar battery sub modules31connected in parallel, each of which has four rod-shaped solar battery cells32connected in series, is arranged on the middle position next to the uppermost one. The third solar battery module50has five rod light receiving solar battery sub modules51connected in parallel, each of which has eight rod-shaped solar battery cells52connected in series, is arranged on a lowermost position. In the solar battery unit4, the three kinds of solar battery modules10,30and50are arranged in parallel at a predetermined interval.

First, the planar light receiving sub module11is explained with reference toFIGS. 1 to 3. The planar light receiving sub module11includes a planar light receiving GaAsP/GaP solar battery cell. The GaAsP/GaP solar battery cell can be manufactured by a similar method to that of a well-known light-emitting diode emitting an orange color light.

The GaAsP/GaP solar battery cell (sub module11) uses a n-type GaP single crystal wafer as a substrate12, on which a n-type GaAsP layer13is grown by, for example, the vapor-phase epitaxial method (VPE). In this case, while a graded layer is formed where a ration of As to P increases gradually from a surface of the n-type GaP substrate12, finally the n-type GaAs0.4P0.6 layer13having a constant composition is grown. Next, on a lower surface of the n-type GaP substrate12, a silicon nitride film (Si3N4) is deposited as a diffusion mask for diffusing impurities, followed by diffusing zinc as p-type impurities on all over the surface of the GaAsP layer13so as to make a p-type GaAs0.4P0.6 layer14of 0.5 to 1.0 μm depth to form a planar pn junction15.

Next, in a state of the silicon nitride film on the lower surface of the n-type GaP substrate12being removed, the lower surface is deposited with Au—Ge, and the surface of the p-type GaAs0.4P0.6 layer14is deposited with Au—Zn, followed by photo-etching. Thereby, as shown inFIGS. 1 and 3, both upper and lower surfaces of GaAsP/GaP solar battery cell11are formed thereon with a plurality of elongated rectangular slit windows16and17so as to be opposed relative to the both surfaces, and next, provided with positive electrodes18and negative electrodes19which are ohmic-connected to both surfaces respectively by sintering. Note that the entire surfaces except for the positive and negative electrodes18and19are covered with an antireflective film (not shown) of SiO2 and the like, of which drawings are omitted.

As shown inFIG. 11, the first solar battery module10is configured such that, for example, five sub modules11are aligned in one plane with the positive electrodes18being directed upward and orientations of the slit windows16and17corresponding to each other, and connected in parallel. In a case of assembling the first solar battery module10, prepared are four connection rods20aand20beach formed of a rod material made of copper or an alloy of nickel and iron with a diameter of 0.5 to 1.0 mm, and the five sub modules11have at one end upper and lower pair of connection rods20aand20barranged, and at the other end upper and lower pair of connection rods20aand20barranged.

The positive electrodes18on the upper surface side of the five sub modules11are electrically connected at both ends thereof to a pair of connection rods20aas a positive electrode lead by soldering or an electrically conductive adhesive, and the negative electrodes19on the lower surface side of the five sub modules11are electrically connected at both ends thereof to a pair of connection rods20bas a negative electrode lead by soldering or an electrically conductive adhesive.

The GaAsP layer13and the pn junction15in the sub module11are formed by not only the vaporphase epitaxial method but also the metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxial growth (MBE). Moreover, a thin p-type window layer with a increased ratio of P is additionally provided on the p-type GaAs0.4P0.6 layer14as needed, thereby a recombination rate of a carrier generated on the surface is effectively decreased to enhance photoelectric conversion efficiency.

The planar light receiving sub module11including the GaAsP/GaP solar battery cell performs a photoelectric conversion by absorbing sunlight in a range of spectral sensitivity (wavelength sensitivity band) shown by a curve A inFIG. 20, however sunlight of a wavelength longer than the range travels through the slit windows16and17of the GaAsP/GaP solar battery cell11downwards. The sub module11has a size of about 7 mm in length, 6 mm in width and 0.4 mm in thickness, for example.

Note that, it is possible to increase productivity of the cell by that many solar battery cells are formed on the common GaP substrate12of a larger size at the same time, and thereafter, the substrate is divided into the solar battery cells having a size described above. In this case, a portion having a locally inferior property can be eliminated compared with the case where the GaP substrate12of a larger size is used to make a single solar battery cell of a larger size. Therefore, deterioration of the entire solar battery cells does not occur due to cracks of the substrate12, allowing an expensive compound semiconductor to be effectively used.

Next, for explaining a configuration of rod-shaped solar battery cells32and52adopted to the rod light receiving solar battery sub modules31and51of the second and third solar battery modules30and50, a rod-shaped solar battery cell70having a similar configuration to those will be described.

As shown inFIG. 4, the rod-shaped solar battery cell70is manufactured using a substrate71(base material) of a rod which has a circular cross-section and is made of semiconductor crystal of a single elements such as Si, Ge, etc., or a compound semiconductor crystal of a III-V group elements and a II-VI group elements.

The rod-shaped semiconductor crystal is manufactured by a method where, for example, with Ge and Si, a rod-shaped seed crystal is passed through a thin diameter nozzle of a crucible to be contacted with a melt, and is cooled with being pulled upward or downward to continuously grow a rod of a single crystal in an elongated shape. With a semiconductor of Si, Ge, GaAs, GaSb, etc., this method can be used to manufacture a single crystal rod having a diameter of 0.5 to 2.5 mm.

However, with a material difficult to be grown into such a thin diameter rod, it may be that the material is mechanically cut out from a bulk crystal to be formed into a rod shape. The elongated rod-shaped semiconductor crystal is divided such that each divided portion has a length of about three to ten times the diameter thereof to form the substrate of a semiconductor crystal to be formed into the rod-shaped solar battery cell70. Note that the length of the substrate is not limited to that of about three to ten times the diameter, but the division may be performed so that the length be ten times or more, or several tens times the diameter of the substrate71. When this division is performed, the rod-shaped semiconductor crystal is cut perpendicularly to the axial center of the rod. The rod-shaped solar battery cell70is manufactured as follows using, as the substrate, the rod-shaped semiconductor crystal of a circular cross-section described above.

First, for example, as shown inFIG. 4, the substrate71of the n-type semiconductor crystal is prepared, and next, a part of a surface portion of the substrate71is cut out parallel to the axial center to form a strap-shaped flat surface72(strap-shaped portion) parallel to the axial center. Note that a width of the flat surface72is set about 0.4 to 0.6 times the diameter of the substrate71. Subsequently, a partial cylindrical p-type layer73(another conductive layer) is provided on a surface layer of the substrate71except for the flat surface72and the vicinity of both sides thereof, and a partial cylindrical pn junction74is formed along the entire length of the substrate71. The flat surface72of the substrate71has a strap-shaped negative electrode75formed thereon which is ohmic-connected to a n-type semiconductor crystal (substrate71) and in parallel to the axial center of the substrate71. On the opposite side from the negative electrode75with respect to the axial center of the substrate71, a surface of the p-type layer73has a strap-shaped positive electrode76formed thereon which is ohmic-connected thereto and parallel to the axial center of the substrate71. Then, the entire surface except for the positive and negative electrodes76and75is covered by a transparent insulating antireflective film77.

Almost all the surface of the rod-shaped solar battery cell70except for the positive and negative electrodes76and75as well as the flat surface72and the vicinity thereof is a surface capable of receiving sunlight. Moreover, a projected cross-sectional area of the substrate71viewed in a direction perpendicular to the axial center78is approximately constant except for the flat surface72, therefore, a light receiving area with respect to an directly incident sunlight is approximately constant independently of an incident light angle. A total of distances from each of points P, Q and R in the pn junction74to the positive and negative electrodes76and75, that is (a+b), (a′+b′) and (a″+b″), is almost constant. Therefore, a distribution of current flowing in the pn junction74is excellent in symmetry and uniformity, and directionality to an incident sunlight is small, allowing photoelectric conversion with a high efficiency.

However, it may be possible that the substrate is constituted by the p-type semiconductor and the surface layer thereof is formed with the partial cylindrical n-type semiconductor layer (another conductive layer). As for forming method for forming the pn junction74of the rod-shaped solar battery cell70, it may be possible to use known methods such as selective impurity diffusion, ion implantation, and vapor phase or liquid phase epitaxial growth. As for forming of electrode and forming of antireflective film, it may be possible to use known methods, and the detailed description thereof is omitted.

Next, the rod-shaped solar battery cell32adopted to the rod light receiving solar battery sub module31of the second solar battery module30is explained with reference toFIGS. 5 to 7.

As a substrate33of the GaAs rod-shaped solar battery cell32, the n-type GaAs single crystal having a circular cross-section is prepared to have thereon formed with a strap-shaped flat surface34parallel to the axial center of the substrate33. In a state where the flat surface34and the vicinity of both sides thereof on a surface of the substrate33are masked with a Si3N4 film, the surface of the substrate33is brought into contact with a melt of GaAs with a solution of Ga at a high temperature, and then the temperature is decreased, thereby an n-type GaAs layer (not shown) is epitaxial-grown with a uniform thickness on the partial cylindrical surface not masked of the substrate33.

Next, the GaAs melt is replaced, and while the surface of the substrate33is contacted with a Ga0.8Al0.2As melt doped with zinc, the temperature is further decreased, and then, a p-type Ga0.8Al0.2As layer36is continuously grown. While the p-type Ga0.8Al0.2As layer36is grown, zinc is heat-diffused from the Ga0.8Al0.2As melt to a middle depth of the partial cylindrical n-type GaAs layer to form a p-type GaAs layer35(separate conductive layer). At a boundary between the p-type GaAs layer35and the adjacent n-type GaAs layer, a pn junction37is formed.

In this way, for example, on the surface of the substrate33of a thin n-type GaAs single crystal having a diameter of about 1.7 mm, the n-type GaAs layer (not shown) of 20 to 50 μm thickness and the p-type GaAlAs layer36of 1 to 2 μm thickness are continuously grown in the partial cylindrical area not masked, and at the same time, from growing interfaces of both layers to a position of 0.5 to 1.0 μm toward the n-type GaAs layer side, the p-type GaAs layer35is formed, then a boundary between the epitaxial grown n-type GaAs layer (not shown) and the p-type GaAs layer35is formed into the pn junction37of the partial cylindrical shape. The p-type GaAlAs layer36functions as a light transmissive window layer, and owing to a hetero junction of the boundary face between the p-type GaAs layer35and the GaAlAs layer36, a recombination rate of a small number carriers on the surface of the solar battery cell32is decreased, and, thus, a photoelectric conversion of the GaAs solar battery cell is improved.

Next, the Si3N4 film mask is removed by chemical etching, the surface of the n-type GaAs layer of the substrate33is exposed on the flat surface34, and on the flat surface34with the n-type GaAs layer exposed, formed is a strap-shaped negative electrode38which is parallel to the axial center of the substrate33and is electrically connected to the n-type GaAs layer. On the opposite side from the negative electrode38with respect to the axial center of the substrate33, a surface of the p-type GaAlAs layer36has a strap-shaped positive electrode39formed thereon which is parallel to the negative electrode38. When forming the positive and negative electrodes39and38, gold doped with Zn is deposited and sintered on the surface of the p-type GaAlAs layer36to form the positive electrode39ohmic-contacted to the p-type GaAlAs layer36, and gold doped with Ge is deposited and sintered on the surface of the n-type GaAs layer exposed on the flat surface34to form the negative electrode38ohmic-contacted to the substrate33. Note that the positive and negative electrodes39and38are the electrodes of several μm thickness. In this way, a continuous body of the rod-shaped solar battery cell32can be manufactured.

Then, the continuous body of the rod-shaped solar battery cell32is cut by use of a cutoff device such as a wire saw, at an interval of about 8 mm, for example, to form the rod-shaped solar battery cell32. A plurality of rod-shaped solar battery cells32are bundled with an acid resistant wax, and thereafter, the cut surfaces are exposed, followed by being etched with chemicals to form an oxide film such that leakage current on the surface of the pn junction37at end faces is decreased. Incidentally, the entire surface other than the positive and negative electrodes39and38is covered by an antireflective film (not shown) of SiO2 or the like, to complete the rod-shaped solar battery cell32.FIG. 20shows a spectral sensitivity characteristic of the rod-shaped GaAs solar battery cell32with a curve B.

However, although in the above example, the Si3N4 film mask is adopted when forming the pn junction37, it may be possible that the substrate of the n-type GaAs single crystal of a circular cross-section is adopted, and similarly to the above, the entire surface of the substrate is formed with the n-type GaAs layer and the p-type GaAlAs layer doped with Zn, to form the cylindrical pn junction, and thereafter, the strap-shaped portion parallel to the axial center of the substrate is removed by cutting work to form the flat surface34, the strap-shaped n-type GaAs layer parallel to the axial center is exposed, and the flat surface34thereof is provided with the strap-shaped negative electrode38.

As shown inFIG. 11, when the rod light receiving solar battery sub module31is manufactured, four rod-shaped solar battery cells32are arranged such that conductive directions from the positive electrodes39toward the negative electrodes38are aligned to a horizontal direction, and those solar battery cells32are arranged adjacent to one another in one plane in parallel. Subsequently, the positive and negative electrodes39and38of the solar battery cells32adjacent to each other are brought into contact and adhered by soldering or the electrically conductive adhesive to manufacture the sub module31.

The second solar battery module30is configured such that, for example, five sub modules31are arranged in one plane in a line with the conductive directions and the axial center direction being aligned, and connected in parallel. In a case of assembling the second solar battery module30, prepared are two connection rods40aand40beach formed of a rod material made of copper or an alloy of nickel and iron with a diameter of 0.5 to 1.0 mm, and at both end side of the five sub modules31a pair of connection rods40aand40bare arranged, and the positive electrode39of the sub module31at one end side is electrically connected with the connection rod40aas the positive electrode lead by soldering or the electrically conductive adhesive, as well as the negative electrode38of the sub module31at the other end side is electrically connected with the connection rod40bas the negative electrode lead by soldering or the electrically conductive adhesive.

Next, the rod-shaped solar battery cell52adopted to the rod light receiving solar battery sub module51of the third solar battery module50is explained with reference toFIGS. 8 to 10.

First, as the substrate53of the Ge rod-shaped solar battery cell52, the rod-shaped p-type Ge single crystal having a diameter of about 0.9 mm and a circular cross-section is prepared to have thereon formed with the strap-shaped flat surface54parallel to the axial center of the substrate53. The rod-shaped Ge single crystal described above is formed such that, for example, a seed crystal of a thin diameter is brought into contact with a germanium melt by a nozzle at the bottom of a crucible made of graphite containing melt germanium and is pulled out downward. The resulting substance is polished so as to become a cylindrical column of a constant diameter and have no unevenness on the surface, and is etched with chemicals.

After that, in a state where the flat surface54and the vicinity of both sides thereof on the substrate53are masked with a Si3N4 film, a rod-shaped p-type germanium is heated in a gaseous atmosphere containing antimony to provide an n-type diffusion layer55(separate conductive layer) of 0.5 to 1.0 μm depth from the surface to form the partial cylindrical pn junction56. Then, the mask of the Si3N4 film is removed by etching; silver containing tin is deposited on the flat surface54at a center portion thereof with the p-type Ge being exposed; on the opposite side therefrom with respect to the axial center, silver containing antimony is deposited on the surface of the diffusion layer55including the n-type Ge; and then, sintering is performed; and provided are a strap-shaped positive electrode57ohmic-contacted to the flat surface54with the p-type Ge layer being exposed and a strap-shaped negative electrode58ohmic-contacted to the n-type diffusion layer55. Note that the positive and negative electrodes57and58are electrodes of several μm thickness. In this way, the continuous body of the rod-shaped solar battery cell52is manufactured.

Subsequently, the continuous body of the rod-shaped solar battery cell52is cut by use of a cutoff device such as a wire saw, at an interval of about 8 mm, for example, to form the rod-shaped solar battery cell52. The solar battery cells52in plural numbers are bundled with an acid resistant wax to mask the peripheral surfaces thereof, and each of the cut surfaces of the solar battery cells52is etched with chemicals by a known method to form an oxide film such that leakage current from the pn junction56at the cut face is decreased.FIG. 20shows a spectral sensitivity characteristic of the Ge rod-shaped solar battery cell52with a curve C.

Incidentally, in the above example, the Si3N4 film mask is adopted when forming the pn junction56. However, it may be possible that the cylindrical the pn junction is formed on the entire surface of the p-type Ge rod of a circular cross-section, thereafter, a strap-shaped portion parallel to the axial center on the surface portion of the rod-shaped Ge single crystal is removed by cutting work to form the strap-shaped flat surface54parallel to the axial center, on which the flat surface54the p-type Ge base is exposed and the strap-shaped positive electrode57is provided, on the opposite side from which positive electrode57provided is the strap-shaped negative electrode58connected to the n-type Ge layer.

As shown inFIG. 11, when manufacturing the rod light receiving solar battery sub module51, eight rod-shaped solar battery cells52are arranged such that conductive directions from the positive electrodes57toward the negative electrodes58are aligned to a horizontal direction, and those solar battery cells52are arranged adjacent to one another in one plane in parallel. Subsequently, the positive and negative electrodes57and58of the solar battery cells52adjacent to each other are brought into contact and adhered by soldering or the electrically conductive adhesive to manufacture the sub module51. Note that the sub modules11,31and51are configured so as to have the same or almost the same length and width, that is, the light receiving area.

The third solar battery module50is configured such that, for example, five sub modules51are arranged in one plane in a line with the conductive direction and the axial center direction being aligned, and connected in parallel. In a case of assembling the third solar battery module50, prepared are two connection rods60aand60beach formed of a rod material made of copper or an alloy of nickel and iron with a diameter of 0.5 to 1.0 mm, and at both end sides of the five sub modules51a pair of connection rods60aand60bare arranged, and the positive electrode57of the sub module51at one end side is electrically connected with the connection rod60aas the positive electrode lead by soldering or the electrically conductive adhesive, as well as the negative electrode58of the sub module51at the other end side is electrically connected with the connection rod60bas the negative electrode lead by soldering or the electrically conductive adhesive.

Next, description will be given of a configuration of the light collecting stacked solar battery device1having the above-described sub modules11,31and51installed therein.

As shown inFIGS. 12 to 18, the stacked solar battery device1includes, for example, three sets of solar battery units4, which are packaged by an enclosure case2, six end stopping blocks6and a cover glass5.

The enclosure case2is manufactured by press forming a thin stainless steel plate (thickness of 0.5 to 1.5 mm) to be formed in a rectangular shape in a plan view. The enclosure case2has three gutter-shaped recesses3arranged in a width direction thereof and in parallel. Each of the recesses3has substantially an inverted trapezoidal cross-section of which width gradually increases upward and has a pair of side walls2aand a bottom wall2binner surfaces of which are made to be light reflecting surfaces in order to collect sunlight to the solar battery unit4, and a portion of the bottom wall2bother than both ends thereof is formed to be a protruding pedestal2cprotruding upward by a slight predetermined height and having a trapezoidal cross-section.

The surfaces of the side wall2aand the bottom wall2bof the recess3are mirror-like finished, formed with a metal film such as silver, or attached with magnesium oxide powder in order to improve a light reflecting effect. A pair of side walls2aof the adjacent recesses3have a common support portion2dformed horizontally at upper ends thereof. The enclosure case2has flat flange portions2eformed at left and right ends thereof, and enclosing walls2fformed so as to stand vertically from ends of the flange portions2ewith a predetermined height.

The end stopping block6is made of a white insulating ceramic material, and fitted to the both ends of the recess3of the enclosure case2. As shown inFIGS. 16 and 17, the end stopping block6is provided with a plurality of metal connection pipes20A,20B,40A,40B,60A and60B in advance into which inserted respectively are the ends of the connection rods20a,20b,40a,40b,60aand60bof the solar battery modules10,30and50. These connection pipes20A,20B,40A,40B,60A and60B are projected to an inside of the end stopping block6by a predetermined length and projected to an outside of the end stopping block6by a predetermined length. The above connection pipes are made of Fe58%-Ni42% alloy or the like, air-tightly penetrating through the end stopping block6.

In order to connect in series the solar battery modules10,30and50in the respective solar battery units4, the end stopping block6provided with in an outer surface side thereof a connector61connecting in series between the connection pipes20B and40A inserted with the connection rods20band40a, as well as a connector62connecting in series between the connection pipes40B and60A inserted with the connection rods40band60a.

As shown inFIGS. 12 to 14, andFIG. 18, the cover glass5is made of a transparent glass material. The cover glass5includes three partial cylindrical lens portions5arespectively collecting sunlight toward the three recesses3, a pair of left and right flat plate portions5bto be fixed to the left and right flange portions2eof the enclosure case2, inverted-trapezoid fitted portions5cof a small height to be fitted each to an upper end of the recess3, and two engaged grooves5dto be engaged to the two support portions2dof the enclosure case2, and a lower face of the cover glass5is formed to be almost flat.

Next, description will be given of a method for assembling the stacked solar battery device1.

With a state that the end stopping block6is adhered to a rear end portion of each of the recesses3, rear end side portions of the connection rods60aand60bof the solar battery module50are inserted to the connection pipes60A and60B of the relevant end stopping block6, respectively, rear end side portions of the connection rods40aand40bof the solar battery module30are inserted to the connection pipes40A and40B of the relevant end stopping block6, respectively, and rear end side portions of the connection rods20aand20bof the solar battery module10are inserted to the connection pipes20A and20B of the relevant end stopping block6, respectively, and then, the solar battery modules10,30and50are kept horizontally in parallel with one another.

Next, front end side portions of the connection rods20a,20b,40a,40b,60aand60bof the solar battery modules10,30and50are inserted to the connection pipes20A,20B,40A,40B,60A and60B of the end stopping block6on a front side, and thereafter, the end stopping block6is positioned and adhered to a front end portion of the recess3. In this way, the solar battery modules10,30and50in the respective solar battery units4are stacked (layered) vertically in the recess.3of the enclosure case2at a predetermined small interval therebetween.

Thereafter, these connection pipes20A,20B,40A,40B,60A and60B are electrically connected with the connection rods20a,20b,40a,40b,60aand60bby calking the connection pipes20A,20B,40A,40B,60A and60B. However, the electrical connection may be performed by adhering with the electrically conductive adhesive. Note that the connection pipes20A,20B,40A,40B,60A and60B are also utilized as external terminals.

Next, the recess3having the solar battery modules10,30and50housed therein are filled with a transparent synthetic resin (e.g., silicon rubber), followed by being defoamed and subjected to heat-curing to polymerize the synthetic resin, and then all of the sub modules11,31and51are brought into a state of being buried in the synthetic resin sealing material63. Thereafter, the cover glass5with a transparent silicon resin or the like being applied to a lower surface thereof is covered over the recesses3, the support portion2dis engaged with the engaged groove5dto be adhered, and the flat plate portion5bis adhered to the flange portion2e. Gaps between the cover glass5and the enclosure case2and between the cover glass5and the synthetic resin sealing material63are sealed with a transparent silicon resin64.

Next, as shown inFIGS. 12 to 14, the flat plate portions5bof the cover glass5and the flange portions2eof the enclosure case2are clamped by four bolts65and nuts66, respectively on the left and right both ends thereof. The clamping is performed via a packing67made of a butyl rubber and a washer68at this bolt-clamping portion.

Next, operations of the solar battery device1described above are explained.

FIG. 19is a diagram showing an equivalent circuit of the stacked solar battery unit4, in which the solar battery cells11,32and52are shown by diodes11A,32A and52A. The solar battery modules10and30are connected in series at both the front and rear end sides thereof by a connector61electrically connecting the connection pipes20B and40A.

The solar battery modules30and50are connected in series at both the front and rear end sides thereof by a connector62electrically connecting the connection pipes40B and60A. Note that with respect to the center one set of the solar battery unit4, the solar battery units4on the left and right sides inFIGS. 13 and 14are connected in parallel via the connection pipes20A,20B,40A,40B,60A and60B, and lead wires. A positive electrode terminal80is formed at a center portion of the lead wire connected to the connection pipe20A, and a negative electrode terminal81is formed at a center portion of the lead wire connected to the connection pipe60B.

As the spectral sensitivity characteristics of the solar battery cells11,32and52shown inFIG. 20, the sensitivity wavelength band where the photoelectric conversions is possible and an energy density are varied depending on the kinds of the solar battery cells11,32and52. The energy density of the sunlight on the ground is 100 mW/cm2, whereas an open voltage of only the solar battery cell with the sunlight is about 1.2 volts in the GaAsP/GaP solar battery cell11(sub module), about 0.9 volt in the GaAs solar battery cell32, and about 0.4 volts in the Ge solar battery cell52.

In a situation where the solar battery modules10,30and50are connected in series, if output currents of the solar battery modules10,30and50are largely varied, the output currents thereof are restricted by an output current of a solar battery module having the smallest output current, and other solar battery modules cannot generate the output current larger than that as well. Consequently, since the GaAsP/GaP solar battery cell11has the smallest output current per light receiving area in the solar battery device1, the output currents of other sub modules31and51are set to be substantially equal to the output current of the GaAsP/GaP solar battery cell11such that the output currents of the solar battery modules10,30and50are approximately the same value. Therefore, the solar battery cells11,32and52can exhibit respective electric-generating capacities to a maximum extent.

The solar battery module10can increase or decrease the output current by increasing or decreasing the number of the sub modules11(the number of the connection in parallel), and can increase or decrease the output current by increasing or decreasing the light receiving area of the sub module11. The solar battery modules30and50can increase or decrease the output current by increasing or decreasing the number of the sub modules31and51(the number of the connection in parallel), and can increase or decrease the output voltages of the sub modules31and51by increasing or decreasing the number of the solar battery cells32and52to be installed in the sub modules31and51(the number of the connection in series).

The light collecting solar battery device1utilizes a light collecting effect owing to refraction by the lens portions5aof the cover glass5and light reflection and collection of the enclosure case2to obtain a large output with the small-sized solar battery modules10,30and50.FIG. 18is a drawing illustrating the light collecting effect using the center one set of solar battery unit4as an example. If the direct sunlight is incident on the cover glass5perpendicularly, the sunlight is refracted by the lens portion5ato be collected. Many direct sunlights are incident on the surface of the upper most GaAsP/GaP solar battery cell11(sub module11), the light in the sensitivity wavelength band of the curve A inFIG. 20is absorbed, and the light longer in the wavelength than that is incident on the surface of the sub module31including the GaAs solar battery cell32thereunder.

The sub module31absorbs the light in the sensitivity wavelength band of the curve B inFIG. 20, the light longer in the wavelength than that is incident on the surface of the sub module51including the Ge solar battery cell52thereunder. The sub module51absorbs the light in the sensitivity wavelength band of the curve C inFIG. 20, the light longer in the wavelength than that is incident on the surface of the protruding pedestal2cthereunder, occurring reflection and absorption. The lights absorbed by the respective solar battery cells11,32and52are converted into the electrical energy to obtain the electrical outputs from the external terminals80and81of the respective solar battery modules10,30and50.

Of the sunlights passing through the lens portions5a, the sunlight which is not directly incident on the surface of the GaAsP/GaP solar battery cell11(sub module11) and is incident on the tilted side wall2ais reflected there to be incident on the surface of the sub modules31and51. In the relevant sunlights, some are absorbed by that surface, others are reflected to go in other directions. The latter lights are reflected in multiple among the enclosure case2, the end stopping block6, the cover glass5, and the respective sub modules11,31and51, and the lights to reach the surfaces of the sub modules11,31and51are absorbed to be photoelectric-converted.

There are small intervals among the sub modules11,31and51as well as between the Ge sub module51and the protruding pedestal2c, where the light can enter. The sunlight is absorbed in a higher ratio by the surfaces of the rod-shaped solar battery cells32and52which surfaces have a cylindrical shape compared with the solar battery cell11whose light receiving surface is flat, achieving the improved output of the solar battery device1.

Incidentally, inFIG. 18, for example, the side wall2aof the recess3is drawn in a flat surface, but it may be designed in a curved surface so as to collect many reflection lights effectively to the solar battery cells11,31and51. Moreover, the GaAs sub module31and the Ge sub module51have a function to collect the light which has the wavelength passing through the modules31and51(the light which has the wavelength can not be absorbed) like the lens portion5a. Therefore, arrangement of the solar battery cells can be devised from an optical point of view such that the collected light enters a solar battery sub module placed ahead thereof.

Light energy which is not photoelectric-converted by the solar battery modules10,30and50is converted into thermal energy. As temperatures of the solar battery cells11,32and52rise with the thermal energy, the photoelectric conversion efficiency decreases. Therefore, it is important that heat radiation capability of the enclosure case2is increased to lower the temperature rise. Thus, in this embodiment, the enclosure case2is formed into a gutter shape to enlarge its surface area such that heat generated from the solar battery cells11,32and52is easily radiated to the external. Incidentally, it may be configured that the surface surrounding the outside of the enclosure case2is provided with a cover member (not shown) to form a duct, through which a cooling medium is circulated between the enclosure case2and the cover member, allowing improvement of a cooling effect.

Here, as a spectral distribution of the incident light varies depending on a place and a weather condition, the output current of the solar battery cell constituting the stacked solar battery device1varies. Correspondingly to this, it may be also configured such that the parallel connection number and the series connection number of the sub modules11,31and51is changed to maintain the maximization of the entire output. Since the solar battery modules10,30and50have respectively independent external terminals (connection pipes), it may be that a plurality of electronic switch devices are provided which change the parallel connection number and the series connection number, and the electronic switch devices are controlled to be on and off to automatically maximize the output depending on the spectrum variation.

Moreover, the solar battery modules10,30and50are provided with the connection pipes as the external terminals, and thus, with respect to the sunlight whose condition varies, it is possible to individually measure output characteristics of each solar battery module and evaluate the performance. Then, based on the measured data, it becomes possible to optimally design a reflection structure of the lens portion5aof each solar battery module of the solar battery device1and the inner surface of the enclosure case2, and the arrangement, the parallel connection number and the series connection number of the solar battery cell.

In the sub module31, a plurality of rod-shaped solar battery cells32are arrange in parallel and connected in series via the positive and negative electrodes39and38to form the rod light receiving solar battery sub module31. Therefore, the number of the rod-shaped solar battery cells32can be varied by varying the diameter of the substrate33to vary a voltage generated in the sub module31. This similarly applies to the sub module51. Moreover, in the solar battery module30, since a plurality of sub modules31are connected in parallel, the current generated in the solar battery module30can be varied by varying the number of the sub module31connected in parallel. This similarly applies to the solar battery module50.

In the rod-shaped solar battery cell32, since a length in the axial center thereof can be set to from several to a dozen times the diameter of the substrate33, the light receiving area can be significantly increased compared with the granular solar battery cell. In addition, a plurality of rod-shaped solar battery cells32can be arranged densely in parallel to configure the rod light receiving solar battery sub module31, and therefore, a ratio of the light receiving area to a projected area of the sunlight can be set larger, increasing a light receiving efficiency for receiving the sunlight. This similarly applies to the rod-shaped solar battery cell52.

Moreover, in the rod light receiving solar battery sub modules31and51, the number of wire connecting positions to electrically connect the solar battery cells can be significantly less compared with the sub module provided with a plurality of granular solar battery cells, reducing significantly the cost for assembling the sub module including the wire connection cost.

The solar battery device1includes plural kinds of the solar battery modules10,30and50which are different from one another in a sensitivity wavelength band, and the shorter center wavelength of the sensitivity wavelength band the solar battery module has, the closer to the incident side of the sunlight the solar battery module is positioned, therefore the sunlight in a wide wavelength range of the sunlight spectrum can be photoelectric-converted. The shorter wavelength the light has, the less transmissive the light is, thus, as described above, the plural kinds of solar battery modules10,30and50are stacked such that the shorter center wavelength of the sensitivity wavelength band the solar battery module has, the closer to the incident side of the sunlight the solar battery module is positioned, thereby allowing increase of the photoelectric conversion efficiency of the respective solar battery modules.

In the solar battery device1, the plural kinds of solar battery modules10,30and50vertically stacked are connected in series, the output currents of which are set substantially equal to one another, and thereby allowing the solar battery modules to exhibit respective electric-generating capacities to a maximum extent.

Of three kinds of solar battery modules, two kinds of solar battery modules30and50are configured respectively with a plurality of rod light receiving solar battery sub modules31and51. Therefore, the output voltages of the rod light receiving solar battery sub modules31and51can be adjusted by varying the number of the connections in series of the rod-shaped solar battery cells32and52in the respective sub modules31and51, and the output currents of the solar battery modules30and50can be adjusted by varying the number of the connections in parallel for connecting in parallel a plurality of rod light receiving solar battery sub modules31and51. Thereby, it becomes easy to set the output currents to be substantially the same among the plural kinds of solar battery modules10,30and50vertically stacked.

The substrate of the rod-shaped solar battery cells32and52can be manufactured more easily with a lower cost compared with manufacturing of a semiconductor single crystal for the substrate of a planar and spherical solar battery cells because a thin cylindrical single crystal can be easily grown by pulling upward or downward the seed crystal from the semiconductor melt.

The rod-shaped solar battery cells32and52, when being manufactured, after forming the pn junction and the electrodes, can be cut into a desired length to be used, thus, suitable for mass production.

The rod-shaped solar battery cells32and52each are provided with the partial cylindrical pn junction and a pair of strap-shaped electrodes which are respectively parallel to the axis direction and connected to the surface at a center portion of the p-type region and the n-type region. There is little directivity of sunlight at the surface perpendicular to the axial center of the substrate, thus, not only the direct incident light but also the light in directions reflected or scattered can be used.

The rod-shaped solar battery cells32and52have the strap-shaped elongated electrodes38,39,57and58formed, allowing the connection points with the external lead to be reduced. Moreover, the electrodes of the solar battery cells32and52can directly join to each other by soldering or the conductive synthetic resin without a dynamic stress. In the sub modules31and51, the number of solar battery cells32and52connected in series respectively can be set freely, therefore, a high voltage output can be attained readily.

In the rod-shaped solar battery cells32and52, a ratio occupied by the electrodes in the light receiving area is small compared with the planar light receiving solar battery cell11, a shadow loss is small, and the current flows in a direction perpendicular to the electrode thickness to lower a resistance. In the sub modules31and51, the rod-shaped solar battery cells are arranged densely in parallel to one another and directly connected with one another to be modularized, enabling free extension of the light receiving area. The sub module can have the light receiving surface area a ratio of which to the projected area is large, allowing manufacture of the sub module with a compact size.

In the module where the spherical solar battery cells are arranged and wire-connected, a gap is generated between the cells. However, the rod-shaped solar battery cells32and52can be arranged and connected with almost no gap, and thereby, the output per unit area can be increased with respect to the direct incident light in a vertical direction. This is advantageous in a case of manufacturing the solar battery module to collect sunlight by the lens. As the sub modules31and51, it is possible to manufacture the sub modules the same in the area and different in the number of the connection in series using rod-shaped cells different in the diameter.

In the recess3of the enclosure case2, the sub modules11,31and51different in the sensitivity wavelength band with one another are arranged via the transparent synthetic resin at a constant interval, thus, the heat which the respective solar battery cells generate by absorbing the light is dispersed in terms of the position. Accordingly, there is no partial temperature rising intensively, thereby, the solar battery cells11,32and52rise in temperature a little.

The enclosure case2is configured such that the inner surface is a light reflection surface and the outer surface is a heat radiation surface, which serves as light collection and restraining of the temperature rising, and is useful for improving a conflicting relation. The end stopping block6is made of the white ceramic which is light-reflectable or light-scatterable to trap the sunlight in the recess3. This makes the light incident indirectly on the rod-shaped solar battery cells32and52to increase a light use efficiency.

Since a plurality of solar battery units4can be connected in parallel via the connection pipes20A,20B,40A,40B,60A and60B (external terminals), the solar battery modules10,30and50are connected in series and connected in parallel to enable constitution of an electrical power supply with required output voltage and current.

A position adjustment of the center of the lens portion5aof the cover glass5and the center of the recess3can be done easily by engaging the engaged groove5dof the cover glass5with the support portion2dof the enclosure case2. Since the protruding pedestal2cis formed at the bottom wall2bof the recess3of the enclosure case2, rigidity of the enclosure case2can be enhanced and the heat radiation area can be increased. Further, the end stopping block6and the lens portion5aof the cover glass5also improve the mechanical strength of the entire solar battery device1.

The sub modules11,31and51are buried in the flexible transparent silicon resin, and the enclosure case2and the cover glass5are clamped and sealed via the packing67by the bolts65and the nuts66, securing the mechanical strength, the airtightness relative to the atmosphere and weather resistance to the sunlight.

In a case that the stacked solar battery device1becomes unnecessary, the clamping between the bolts65and the nuts66is released to disassemble into the cover glass5and the enclosure case2, and further, the sub modules11,31and51can be easily separated and retrieved from the sealing material63made of the transparent resin by adding an organic solvent or a high temperature steam.

Next, description will be given of examples in which the above embodiment is partially modified.

1) The embodiment was described in which three recesses3are formed in the enclosure case2and three sets of solar battery units4are installed therein. However, this is only an example, and four or more recesses3may be formed and four or more sets of solar battery units4may be installed in some cases, as needed.

Moreover, the embodiment was described in which five sub modules11,31and51respectively are installed in the solar battery modules10,30and50. However, the number of the sub modules installed in the solar battery modules10,30and50may be set appropriately, and six or more sub modules11,31and51may be installed in some cases. In this way, the output voltage and the output current of the solar battery device1can be set freely.

2) The number of solar battery cells32installed in the sub module31is not limited to four, but five or more cells32may be installed in some cases. This similarly applies to the sub module51. Nine or more solar battery cells52may be installed in the sub module51.

3) In place of the uppermost GaAsP/GaP solar battery cell11, the planar light receiving solar battery cell may be employed with a semiconductor crystal of GaP, InGaP, SiC, GaN, InGaN and ZnO used as the substrate, and the rod light receiving solar battery sub module may be adopted which includes the solar battery cell using the substrate constituted by any of the semiconductor crystals.

4) In place of the rod-shaped Ge cell52of the lowermost sub module51, the solar battery cell may be adopted which includes the substrate of a crystal of GaSb, InGaAs, and InGaAsSb.

5) In place of the rod-shaped solar battery cell32of the middle sub module31, adopted may be the planar light receiving solar battery cell including the substrate of a crystal of GaAlAs, Si and InP, or the rod-shaped solar battery cell using the substrate constituted by any of the semiconductor crystals.

6) In the solar battery device1of the embodiment described above, the example was described in which three kinds of the solar battery modules10,30and50different in the sensitivity wavelength band are installed in a stacked manner. However, it may be possible that the solar battery device in which two kinds of solar battery modules different in the sensitivity wavelength band are installed in a stacked manner. In this case, at least one kind of solar battery module should be constituted by the rod light receiving solar battery sub module. Incidentally, the solar battery device can also be manufactured in which four or more kinds of solar battery modules different in the sensitivity wavelength band are installed in a stacked manner.

7) In place of the cover glass5, a cover member made of a synthetic resin material such as transparent polycarbonate or acrylic may be adopted, on which cover member formed is a lens portion similar to the lens portion5a.

8) As for the materials for the enclosure case2, there may be adopted an Fe58%-Ni42% alloy plate in which an inner side surface is plated with a metal of high reflection ratio such as silver, nickel or the like, or an aluminum plate, an aluminum alloy plate or a magnesium alloy plate the surfaces of which are subjected to anticorrosion treatment.

9) In the rod-shaped solar battery cells32and52, the strap-shaped flat surfaces34and54are formed on the substrate, whose flat surface is provided with a single electrode (38,57). However, as a rod-shaped solar battery cell70A shown inFIG. 21, the flat surface may be omitted, and a single electrode (75A) of strap-shape ohmic-contacted to the substrate71A may be formed on a surface of the substrate71A of a circular cross-section. However, in this case, it is preferable to configure such that materials, colors, and shapes of the positive and negative electrodes are made different to enable to identify the positive and negative electrodes. Also, those similar to the solar battery cell70inFIG. 4are attached the same numerals, and the description is omitted.

INDUSTRIAL APPLICABILITY

The stacked solar battery device can be utilized for various power generation devices generating electricity by use of the sunlight.