Non-contact optical power feeding method using a multi-junction solar cell, and light-projecting device for optical power feeding

Abstract

There are provided a method and a device for feeding electric power to a vehicle, etc. installed with a solar photovoltaic power generation panel employing a multi-junction solar cell in a non-contact manner by irradiating light to the solar photovoltaic power generation panel. In the method, light containing a wavelength component absorbed by each of all solar cell layers laminated in a multi-junction solar cell of the vehicle, etc. is projected from a light-projecting device to the light receiving surface of the multi-junction solar cell; and electric power generated by the irradiation of light from the multi-junction solar cell is taken out. The device includes structures for emitting light containing a wavelength component absorbed by each solar cell layer laminated in the multi-junction solar cell, and for irradiating the light to a light receiving surface of the multi-junction solar cell.

Claims

1. A method of non-contact electric power feeding to an apparatus, which is any one of a vehicle, a mobile body, a machinery, and an appliance, installed with a solar photovoltaic power generation panel having a multi-junction solar cell, comprising steps of: (a) preparing a light-projecting device which emits light containing a wavelength component absorbed by each of all solar cell layers laminated in the multi-junction solar cell and projects the light; (b) irradiating the light projected from the light-projecting device onto a light receiving surface of the multi-junction solar cell of the solar photovoltaic power generation panel of the apparatus; and (c) taking out electric power generated from the multi-junction solar cell by the irradiation of the light, wherein a light intensity of the wavelength component absorbed by each of the solar cell layers contained in the light projected from the light-projecting device is adjusted such that a difference in a number of photoelectrons generated by absorption of photons in the respective solar cell layers becomes within a predetermined allowable range.

2. The method of claim 1, wherein the light projected from the light-projecting device contains, as the wavelength component absorbed by each of the solar cell layers, photons having energy which exceeds beyond a band gap of the corresponding solar cell layer.

3. The method of claim 2, wherein the light projected from the light-projecting device contains, as the wavelength component absorbed by each of the solar cell layers, a component of a wavelength band having a peak wavelength in a range from an upper limit wavelength [nm] given by:
h.Math.c/(e.Math.Eg) with the band gap of the corresponding solar cell layer Eg[eV], the Planck constant h[Js], the speed of light c[m/s] and the electron charge e[C], to a lower limit wavelength [nm] which is shorter than the upper limit wavelength by a predetermined width.

4. The method of claim 3, wherein the lower limit wavelength [nm] is h.Math.c/(e.Math.Eg) [nm]−100 [nm].

5. The method of 1, wherein the light intensity of each of the wavelength components is adjusted such that a difference in a number of photons absorbed in each of the said solar cell layers given by: Pi.Math.Ti/(h.Math.c/λi) with a light intensity Pi of each of the wavelength components, a transmissivity Ti at which each of the wavelength components reaches the corresponding solar cell layer, the Planck constant h [Js], the speed of light c[m/s] and a wavelength of each of the wavelength components becomes within a predetermined allowable range.

6. The method of claim 1, wherein the light intensity of the wavelength component absorbed by each of the solar cell layers contained in the light projected from the light-projecting device is adjusted such that a difference of electric currents generated in the respective solar cell layers becomes within a preset allowable range.

7. The method of claim 1, wherein the light projected by the light-projecting device is laser light.

8. The method of claim 1, wherein the light projected by the light-projecting device is LED light.

9. The method of claim 1, wherein the apparatus is a vehicle or a mobile body, and the light-projecting device is a device which projects light to the solar photovoltaic power generation panel of the vehicle or the mobile body, the vehicle or the mobile body existing on a ground surface or a water surface.

Description

BRIEF DESCRIPTIONS OF DRAWINGS

(1) FIG. 1A is a schematic drawing illustrating one embodiment of the non-contact electric power feeding method to a vehicle, etc. installed with a solar photovoltaic power generation panel according to the present disclosure.

(2) FIG. 1B is a schematic drawing explaining a condition that the non-contact electric power feeding method according to the present disclosure is applied to vehicles running or stopping on a road.

(3) FIG. 2 is a drawing showing schematically a structure of a light-projecting device used in one embodiment of the non-contact electric power feeding method according to the present disclosure.

(4) FIG. 3A shows a schematic drawing of a structure of 2 junction solar cell, and a schematic drawing of wavelength characteristic of the light to be irradiated to the 2 junction solar cell in the non-contact electric power feeding method according to the present disclosure.

(5) FIG. 3B shows a schematic drawing of a structure of 3 junction solar cell, and a schematic drawing of wavelength characteristic of the light to be irradiated to the 3 junction solar cell in the non-contact electric power feeding method according to the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) The Structure of Non-Contact Optical Power Feeding Method

(7) Referring to FIG. 1A, in a the non-contact optical power feeding method of the preferable present embodiment, a light-projecting device 20 which projects light L to a certain region is prepared. For instance, as illustrated, the light projecting device 20 may be formed like a streetlamp, having a light-emitter which generates light L in the upper portion of a pole 22, on which a light projector 21 projecting the light to a certain region, e.g., a lower region is mounted. The energy for generating the light L in the light projector 21 may be supplied to the light projector 21, for instance, through a power line (not shown) in an arbitrary manner. Then, on the region to which the light L is projected, a solar photovoltaic power generation panel 12, typically installed on a vehicle body upper surface of a vehicles 10, such as automobile, on a road surface R, is positioned, and in this condition, the solar photovoltaic power generation panel 12 is irradiated with the light L. In this regard, the solar photovoltaic power generation panel 12 may be of a type ordinarily used in this field. Thus, by the irradiation of the solar photovoltaic power generation panel 12 with the light L, as explained later, the light L is absorbed into a photoelectric conversion element (multi-junction solar cell) of the solar photovoltaic power generation panel 12, and then, the energy of the absorbed light is converted into electrical energy, which is outputted from the solar photovoltaic power generation panel 12 (P in the drawing) and accumulated in a storage battery or an electric storage device 14 carried in the vehicle 10. And, the electric energy accumulated in the storage battery or electric storage device 14 is used as energy for driving or operating machines and apparatus, such as an electric motor 16 (The output of the solar photovoltaic power generation panel 12 may be directly used for the operation of machines and apparatus, such as the electric motor 16). According to this structure, when the light L is absorbed by the multi-junction solar cell of the solar photovoltaic power generation panel 12 and a significant generated current flows out of the multi-junction solar cell, the non-contact electric power feeding by the light L is achieved through the solar photovoltaic power generation panel 12. Therefore, even when there is no sunlight or little sunlight, such as during night time (from the evening to the early morning), in a cloudy weather, in a rainy weather, or under a shade, or even when the energy demanded in a vehicle is not fully obtained only from the sunlight, the vehicle 10 will be fed with electricity and capable of obtaining energy.

(8) The non-contact optical power feeding method according to the above-mentioned present embodiment may be performed in an arbitrary manner. For instance, as illustrated schematically in FIG. 1B, the electric power feeding with light (optical power feeding) to vehicles 10 may be performed by arranging light-projecting devices 20 along the road R on which the vehicles are running, and, irradiating the light L to the upper surfaces of the vehicles 10 passing through thereunder (the vehicles may be stopped during the feeding of electric power.). Further, although not shown, also in cases of other mobile bodies, such as two-wheeled vehicles placed on a ground surface or a road surface, aircraft, vessels floating on a water surface, etc., the optical power feeding may be achieved similarly to the above by irradiating a solar photovoltaic power generation panel installed therein with the light from the light-projecting device 20. Furthermore, the non-contact optical power feeding method according to the present embodiment may be used for not only a mobile body but also electric feeding of arbitrary machines and apparatus installed with a solar photovoltaic power generation panel and it should be understood that such cases belong to the scope of the present embodiment, also.

(9) The Structure of Light Projector

(10) As schematically drawn in FIG. 2, the light projector 21 in the light-projecting device 20 illustrated in FIG. 1 has at least two light-emitters S1˜ (In the drawing, the number of light-emitters is 3), which generate lights λ1˜ of mutually different wavelengths, and optical instruments (reflective mirrors M1˜, a light condenser op, etc.), which condense the lights λ1˜ emitted from the respective light-emitters S1˜, emits them as the light L from a light projecting opening 21a and irradiates it to the solar photovoltaic power generation panel 12. While an arbitrary light source may be used as the light-emitters S1˜, considering that the photoelectric conversion efficiency in the solar photovoltaic power generation panel 12, a laser device or an LED with high monochromaticity of each light emitted therefrom can be used, as explained later. In this regard, it is sufficient that the light sources just satisfy the conditions of the characteristics of the wavelengths of the light irradiated from the light projector explained below, and the number of the light sources may be more than the number of the solar cell layers of the multi-junction solar cell in the solar photovoltaic power generation panel. Further, with respect to the light L emitted from the light projecting opening 21a, its divergence angle may be appropriately adjusted using optical instruments so that the light L will be more certainly irradiated to the solar photovoltaic power generation panel 12.

(11) The Conditions of Characteristics of Wavelengths of Light Irradiated From a Light Projector

(12) As noted, in most cases of the solar photovoltaic power generation panel 12 designed to be installed on a vehicle, etc. for using the solar energy by converting it to electric energy, the multi-junction solar cell is employed as a photoelectric conversion element. In this multi-junction solar cell, as schematically drawn in FIGS. 3A and 3B left, a plurality of solar cell layers PCL1˜, having mutually different energy band gaps Eg1˜, are laminated, and thereby the respective solar cell layers PCL1˜ absorb the lights of different wavelength bands and convert them into electric power, and therefore, the light energy of more wavelength components in the sunlight whose wavelength band extends over a broad range can be converted into electric energy so that more solar energy can be taken in. However, since the solar cell layers PCL1˜ laminated in the multi-junction solar cell are electrically connected in series, electric current cannot flow through all the solar cell layers PCL1˜ when no light absorption occurs and no electric current is generated in at least one of the solar cell layers PCL1˜, and in that case, it becomes difficult to take electric power out of the multi-junction solar cell. Thus, in the optical power feeding method of this embodiment, the light L irradiated from the light projector 21 to the solar photovoltaic power generation panel 12 is prepared to contain all of the wavelength components absorbed by the respective solar cell layers PCL1˜ such that light absorption will occur in all the solar cell layers PCL1˜. Namely, in the case of 2 junction photovoltaic cell as in FIG. 3, the light L is prepared so that the wavelength component absorbed by PCL1 and the wavelength component absorbed by PCL2 will be contained, and in the case of 3 junction photovoltaic cell as in FIG. 3 B, the light L is prepared so that the wavelength component absorbed by PCL1, the wavelength component absorbed by PCL2 and the wavelength component absorbed by PCL3 will be contained.

(13) Moreover, in each solar cell layer PCL1˜, photons having the photon energy exceeding the band gap Eg1˜ of each solar cell layer PCL1˜ are absorbed, and photons which is not absorbed cannot be taken out as electric power, resulting in the loss of energy (refer to Note 1 below). Thus, in order to suppress energy loss as low as possible and to increase the photoelectric conversion efficiency, it is preferable that photons to be absorbed by each solar cell layer PCL1˜ in the light L are prepared to be those having the photon energy exceeding the corresponding band gap Eg1˜. In this respect, the wavelength λ.sub.ULi [nm] of a photon having the energy of the band gap Egi [eV] of each solar cell layer PCLi (i=1˜)(the upper limit wavelength) is given by:
λ.sub.ULi [nm]=h.Math.c/(e.Math.Egi)≈1240/Egi  (3)

(14) (Here, h [Js] is the Planck constant; c [m/s] is the speed of light; and e [C] is the electronic charge.),

(15) and therefore, it is preferable that the wavelength component that each solar cell layer PCLi is made to absorb in the light L is prepared to be λ.sub.ULi [nm] given by Expression (3) or below.

(16) [Note 1] As already noted, in a multi-junction solar cell, usually, a solar cell layer having a larger band gap (a shorter absorption wavelength) is laid to be closer to the light receiving side. Thus, photons which were not absorbed in each solar cell layer will be absorbed by solar cell layers laid under it (photons having energy smaller than the minimum band gap Eg are not absorbed, resulting in the energy loss.). However, as explained below, in photons absorbed in each solar cell layer, since the energy loss in taking out energy as electric power becomes larger as the photon energy exceeding the band gap Eg becomes larger, it is preferable that photons in a wavelength component prepared to be absorbed by each solar cell layer PCLi are made absorbed surely in the corresponding solar cell layer PCLi as noted above, and thus, it becomes preferable to make the wavelength of the photons below λ.sub.ULi [nm] given by Expression (3).)

(17) On the other hand, with respect to photons to be absorbed in each solar cell layer PCLi, when the photon energy is larger than the band gap Eg, in taking out their energy as electric power, the portion exceeding the band gap Eg in the photon energy becomes energy loss. So, in order to suppress energy loss as low as possible and to increase the photoelectric conversion efficiency, it is preferable that the wavelength component prepared to be absorbed by each solar cell layer PCLi in the light L is prepared so that its wavelength will be within a range not greatly shorter than λ.sub.ULi [nm] given by Expression (3).

(18) By the way, when each wavelength component λi of the light L is given by laser light or LED light, the wavelength spectrum of each wavelength component λi has an upwardly convex shape. Thus, in order to satisfy the above-mentioned preferable conditions with respect to the wavelength of each wavelength component λi, preferably, each wavelength component λi may be prepared such that the peak wavelength λ.sub.pi of its wavelength spectrum satisfies λ.sub.LLi<λ.sub.pi<λ.sub.ULi as schematically drawn in FIGS. 3A and 3B right, respectively. Here, λ.sub.LLi is the lower limit wavelength of the range in which the peak wavelength λ.sub.pi is to be encompassed, and the width (a predetermined width) Δi between λ.sub.ULi and λ.sub.LLi may be appropriately set while taking the photoelectric conversion efficiency into account. In a typical light source employed in this embodiment, the predetermined width Ai may be e.g. 100 nm.

(19) Light Intensity of Each Wavelength Component Irradiated from Light Projector

(20) As noted above, when the light absorption occurs and an electric current is generated in each solar cell layer of a multi-junction solar cell, it will become possible to take out electric power to the exterior of the multi-junction solar cell. In this condition, if the electric currents generated in the respective solar cell layer differ mutually, the electric current flowing through the whole solar cell layers will be restricted to the minimum amount in the electric currents generated in all the solar cell layers, and thus, in each solar cell layer, the energy equivalent to the difference between the electric current to be generated corresponding to the number of the absorbed photons and the actually flowing electric current becomes lost as heat, resulting in the reduction of the photoelectric conversion efficiency corresponding to the difference. Then, the electric current to be generated in each solar cell layer corresponds to the number of the photons absorbed in each solar cell layer, which is determined based on the light intensity of the wavelength component which reaches each solar cell layer and is absorbed therein. Therefore, in the non-contact optical power feeding method of the present embodiment, for suppressing the reduction of the photoelectric conversion efficiency, preferably, the light intensity of each wavelength component to be absorbed in each solar cell layer may be adjusted so that almost no difference will be generated in the electric currents generated in the respective solar cell layers, for example, so that such a difference will be within an allowable range which may be set appropriately. In this regard, for instance, the allowable range may be set so that the difference will be within 10%, preferably within 5% and more preferably within 3%, etc. (the photoelectric conversion efficiency becomes better as the range becomes narrower.). The adjustment of the light intensity of each wavelength component can be achieved by adjusting the output of each light source or using an optical filter.

(21) In one manner of the adjustment of the light intensity of each wavelength component in the light L, through measuring in an arbitrary way or estimating experimentally the electric current or the number of photoelectrons to be generated in each solar cell layer in a multi-junction solar cell to which the non-contact optical power feeding method of this embodiment will be applied, the light intensity of each wavelength component in the light L may be adjusted so that the difference of the electric currents generated in the respective solar cell layers will be within the allowable range as mentioned above.

(22) Further, in another manner of the adjustment of the light intensity of each wavelength component in the light L, the number of photons Ni absorbed in each solar cell layer PCLi is estimated by
Ni=Pi.Math.Ti/(h.Math.c/λi)  (4),
using the light intensity Pi[J/s] of the wavelength component λi absorbed in each solar cell layer (at the output from a light projector or on the light receiving surface of a multi-junction solar cell), the transmissivity Ti at which each wavelength component reaches the corresponding solar cell layer which absorbs it, the Planck constant h [Js], the speed of light c [m/s] and the wavelength λi [nm] of each wavelength component (it may be the peak wavelength.). (Here, h.Math.c/λi is the energy of a single photon.) Thus, for each solar cell layer in the multi-junction solar cell to which the non-contact optical power feeding method of this embodiment will be applied, while measuring experimentally the above-mentioned transmissivity Ti beforehand, the light intensity Pi of each wavelength component of the light L may be adjusted so that the number of photons Ni estimated by the Expression (4) will be within the above-mentioned allowable range.

EXAMPLE

(23) (i) When the multi-junction solar cell of the solar photovoltaic power generation panel to which the non-contact optical power feeding is applied is a 3 junction solar cell which consists of InGaP/GaAs/Ge, the band gap [eV] of each layer and the upper limit wavelength [nm] of each wavelength component according to Expression (3) are as follows:

(24) TABLE-US-00001 Band gap Upper limit Layer No. Composition [eV] wavelength [nm] 1 InGaP 1.9 652 2 GaAs 1.4 886 3 Ge 0.7 1771

(25) Thus, the light source which generates the light of the wavelength component to be absorbed in each layer as mentioned above may be, for instance, as follows, respectively:

(26) 1 AlInGaP Series Semiconductor Laser (Oscillation wavelength: 600 nm)

(27) 2 AlGaAs Series Semiconductor Laser (Oscillation wavelength: 850 nm)

(28) 3 InGaAs/InGaAsP Distorted MQM (MultiQuantumWell) Type Semiconductor Laser (Oscillation wavelength: 1700 nm)

(29) (ii) When the multi-junction solar cell of the solar photovoltaic power generation panel to which the non-contact optical power feeding is applied is a 2 junction solar cell which consists of perovskite (MAPbI3)/Si, the band gap [eV] of each layer and the upper limit wavelength [nm] of each wavelength component according to Expression (3) are as follows:

(30) TABLE-US-00002 Band gap Upper limit Layer No. Composition [eV] wavelength [nm] 1 Perovskite 1.8 689 2 Si 1.1 1033

(31) Thus, the light source which generates the light of the wavelength component to be absorbed in each layer as mentioned above may be, for instance, as follows, respectively:

(32) 1 AlInGaP Series Semiconductor Laser (Oscillation wavelength: 650 nm)

(33) 2 InGaAs Series Semiconductor Laser (Oscillation wavelength: 1000 nm)

(34) The full width at half maximum of each laser mentioned above may be 10 nm or less, and its power may be about 1 kW. In this regard, the light source may be LED and, in that case, its full width at half maximum may be 50 nm or less and its power may be about 1 kW.

(35) Although the above explanation has been described with respect to embodiments of the present disclosure, it will be apparent for those skilled in the art that various modifications and changes are possible, and that the present disclosure is not limited to the above-illustrated embodiments and may be applied to various devices and apparatus without deviating from the concepts of the present disclosure.