JP2530927B2 - Optical wavelength converter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a wavelength conversion device that aligns the wavelength of sunlight in a specific wavelength range, and more particularly to a wavelength conversion device incorporated in a solar power generation device.

“Prior Art” Solar power generation has been attracting attention as an alternative energy source such as oil or nuclear power.

Certainly, solar power generation using solar energy can obtain photovoltaic power simply by receiving sunlight on the surface of the solar cell, so it is extremely clean without worrying about environmental pollution like oil and nuclear power. Even though it has an extremely great advantage in terms of maintenance and life compared to other power generators, it is installed only in a very limited area such as a remote island or a desert.

It is considered that there are the following two main reasons for the low photoelectric conversion efficiency.

That is, the first is that the sunlight has a peak of energy distribution by wavelength in the vicinity of 500 nm, while the spectral sensitivity of the solar cell has a distribution characteristic as shown in FIG.
Low utilization of solar energy with wavelengths below m.

In order to improve this point, in a Si solar cell to which an internal electric field is applied, the collection efficiency of light with a short wavelength of 500 nm or less is significantly improved, but the collection efficiency of light with a wavelength longer than 950 nm is still low.

The second is that the energy of sunlight is mainly distributed in the region of wavelength much shorter than the light wavelength of 1127 nm, which corresponds to the band gap 1.1 electron volt (eV) of Si crystal, so the absorbed photon energy is converted into electron energy. It is not used at all because the proportion of light emitted is low and sunlight with wavelengths longer than 1127 nm is not absorbed by Si solar cells.

Therefore, the present inventor has previously described, for example, as shown in FIG.
The sunlight collected by the condenser 1 is converted into Si by the wavelength converter 2.
After adjusting the wavelength to a wavelength region shorter than the band gap of the solar cell, more specifically, 650 nm to 950 nm, the wavelength-converted sunlight is magnified by the magnifying glass 3 to a predetermined condensing magnification, and then the solar cell 4 is provided. We have proposed a device that makes it incident (Japanese Patent Application No. 1-278481, hereinafter referred to as basic technology), and in particular, in this basic technology, in order to align sunlight with a specific wavelength range, a short wavelength of the specific wavelength range is used. An optical screen member having a structure in which fine particles composed of a black body are evenly dispersed in a filter glass whose end has a transmission limit wavelength, and transmits short-wave light from the long-wavelength end of the specific wavelength range, and has a long-wavelength from the end. A reflecting plate having a function of reflecting light and causing the black glass fine particle-containing filter glass to circulate is disposed so as to be opposed and held in a high-temperature sealed container, and sunlight in a condensed state is an optical screen member. Irradiate the While transmitting long-wave light from the short-wavelength end of the wavelength range, the energy that is absorbed by the filter glass and converted into heat is transmitted to the blackbody fine particle group because the wavelength is shorter than this end, We propose a light wavelength conversion technology by the combination of the process of re-emitting as black body radiation and the transmitted light wavelength selection capability of the reflectors arranged oppositely.

However, in the case of using such a wavelength conversion technique, a) the temperature of the filter glass containing the black body particles, which is a radiator, cannot be raised too much because of the restriction due to the heat resistance of the filter glass.

On the other hand, the temperature dependence of blackbody radiation has the characteristics shown in Fig. 4 as is well known, and in consideration of the above restrictions, when the maximum possible temperature is set to 1400 ° K, The radiation amount in the desired specific wavelength range of 650 nm to 950 nm is 1400
There is a problem that the volume efficiency of the wavelength converter is poor because it is only 0.5% of the total amount of black body radiation at K.

b) Since the concentration of the black body particles dispersed in the filter glass must be increased to a considerably high level, the radiation emitted from each particle is blocked by another particle group, resulting in a total surface area of the particle group. There is also a problem that the deviation from the effective radiation surface area becomes large and the surface area efficiency decreases.

An object of the present invention is to provide an optical wavelength conversion device that can overcome the drawbacks of the prior application technique.

"Technical means for solving the problem" In order to achieve the technical problem, the present invention is, for example, a device for converting sunlight into light in the wavelength range of 600 nm to 1100 nm, in which incident sunlight is approximately 600 nm or more. Specifically 6
Instead of the black body fine particle-containing filter glass described in the basic technology, which transmits light having a wavelength of 50 nm or more and absorbs light having a wavelength of 650 nm or less and converts it into heat radiation, incident sunlight Is characterized by the fact that a blackbody radiator made of a material having both high heat resistance and high thermal emissivity that absorbs almost all of the above and converts it into heat radiation is adopted.
(Claims 1) and 2)) In this case, in order to increase the one-pass acquisition ratio of the radiant light in the desired wavelength range of 650 nm to 1100 nm, the temperature of the black body radiator is set to 1500 ° K or more. Is good.

Furthermore, in order to improve the energy efficiency of the present invention,
The black body radiator and the optical filter according to claim 3, wherein among the black body radiator, the sunlight incident surface and the side surface which do not face the optical filter are covered with a thin layer body made of a material having a low thermal emissivity. A means for reducing the radiant heat flux radiated from the black body radiator toward the inner wall surface of the high temperature chamber that houses the black body radiator and the black body radiator and the light. We propose a technique to cover the inner wall surface of a high temperature chamber that houses a filter and forms a high temperature atmosphere with a thin layer made of a material having high heat resistance and high heat ray reflectance. (Claim 4) "Action" Blackbody radiation has a temperature dependence of the radiation energy density for each wavelength, and is a wavelength range suitable for, for example, a Si solar cell.
In order to effectively obtain radiation in the wavelength range of 650 nm to 1100 nm, it is necessary to set the temperature of the radiator to at least 1400 ° K.

Furthermore, by setting the radiation temperature to 1400 ° K, the lower limit wavelength can be specified to 650 nm. In other words, since the lower limit wavelength of the specific wavelength can be set by the temperature, it is sufficient to directly irradiate the black body radiator with sunlight without using the screen member to cut the lower limit wavelength.

Then, the energy of the sunlight absorbed by the blackbody radiator is radiated as radiant energy at the blackbody holding temperature and reaches the facing optical filter, where light with a wavelength shorter than 1100 nm is transmitted and 1100 nm. Light of longer wavelengths is reflected back towards the blackbody radiator and reabsorbed. This reflux energy again becomes radiation corresponding to the holding temperature and is radiated from the black body to reach the optical filter.

Through such circulation, the energy of the incident sunlight is in the desired wavelength range with high energy efficiency.
Converts light energy from 0nm to 1100nm.

That is, by arranging a black body radiator and an optical filter having a selective action of light transmission and reflection at a wavelength of 1100 nm by facing each other.
650nm to 11 sunlight with energy efficiency close to 100%
Get converted to 00nm light.

It is preferable that the radiator and the reflector are housed in a vacuum atmosphere in order to protect them from oxidation.

[Examples] Examples of the present invention will be exemplarily described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention to this, but are merely illustrative examples. Not too much.

In order to achieve the present invention smoothly, the selection of the material of its main constituents is a very important factor.

 Therefore, the material of each member will be first examined.

(1) Material Selection of Reflector If the free electron density in the conductive material is N m ^-3 and the corresponding characteristic frequency is ν _ρ s ^-1 , the light frequency is ν s ^-1.
, The light of ν> ν _ρ transmits through the substance, and ν _ρ >ν>
It is known that the light of ν _τ is reflected by the substance. Where ν _τ is the relaxation frequency. According to the free electron theory, it is calculated by [nu _[rho following equation.

Where ε _o : dielectric constant in vacuum 8.854 × 10 ^-12 Fm ^-1 e: electronic charge 1.6021892 × 10 ^-19 CM _e : static mass of electron 9.109534 × 10 ^-31 kg λ _ρ = C / ν _ρ : Wavelength corresponding to the characteristic frequency m C: Light speed, 2.99792458 × 10 ⁸ ms ⁻¹ in vacuum To make the characteristic frequency correspond to the light wavelength of 1100 nm, ν _ρ = C / ( 11000 × 10 ^-9 ) ＝ 2.725 × 10 ¹⁴ s ^{-1 In} addition, the corresponding free electron density is N ₍₁₁₀₀₎ = 9.213 × 10 ²⁶ Z m ^-3 The value of Z differs depending on the substance, for example, in graphite, Z = 0.
GaP, which is 03-0.04 and is a III-V compound semiconductor,
It is 0.25.

a) In the case of metal, the free electron density is 10 ²⁸ m ⁻³ , and 10 ²⁵ to 10 ²⁶ m ⁻³ cannot be obtained.

b) In the case of a semiconductor, a free electron density of the order of 10 ²⁶ m ⁻³ can be obtained by doping an n-type dopant in a high concentration and raising electrons from the donor level to the conduction band by thermal excitation.

However, in the case of semiconductors, the light that should be transmitted is 650n.
It must be a substance with a bandgap of 2 eV or more so as not to absorb m light (corresponding to 1.91 eV).

 Table 1 is a comparison of some substances.

From Table 1, graphite or GaP with an n-type dopant added is selected as the preferred material.

c) Further, the dielectric reflector made by alternately vapor depositing a high refractive index material such as TiO ₂ and a low refractive index material such as SiO ₂ on the substrate with a thickness of λ / 4, is also the structure of the present invention. Can be used as an optical filter (hereinafter referred to as a reflector). In this case, the characteristic of the dielectric reflector is that a high reflectance is realized only in a narrow wavelength range of about ± 10% of the center wavelength, so the thickness λ / 4 of each layer is set so that the center wavelength of the reflected light is 1200 nm. For reflection of light having a wavelength longer than 1300 nm, it is preferable to use the above-mentioned graphite or the like as the substrate of the dielectric multilayer film.

(2) Selection of material for blackbody radiator The role of the blackbody radiator is to absorb incident sunlight, convert the received energy into blackbody radiation energy at the temperature at which the blackbody is held, and to the downstream side. It is to eject. Therefore, this radiator must meet the following requirements.

B. To absorb incident sunlight with a reflectance as low as possible. Otherwise, the reflected sunlight will be converted into heat on the inner wall surface of the high temperature room, and the loss rate will increase.

That is, in order to improve the absorption of incident sunlight, the substance must have a high thermal emissivity ε.

Since SiC has high heat resistance and large ε, it is a good material for this purpose.

B. Of course, thermal radiation is radiated from the radiator even toward the upstream side and the side surface. These radiant flows are reflected by the material having a high reflectance constituting the inner wall surface of the high temperature chamber by about 99% and are returned to the radiator, but about 1% results in heat loss. This 1% heat loss is that number for incident sunlight.
Since it is a large proportion equivalent to 10%, it is necessary to reduce it, but from the process where the radiant energy Q from the radiator is given by the formula of Q = 5.67 × 10 ^-8 εT ⁴ Watt m ^-2 , If it is possible to reduce the heat loss rate by selecting a radiator with a small thermal emissivity ε, this is because in order to effectively absorb the incident sunlight,
The radiator is inconsistent with the requirement that it must have a high ε.

In order to solve this contradiction, the present inventors have thought and found that, as shown in FIG. 1, the front surface and the side surface of the radiator are surrounded by a material having a low thermal emissivity, but the front surface is coated. Is not to cover the entire surface, but to open only the passage of incident sunlight.

Next, an embodiment of the present invention constituted by using the above material will be described with reference to FIG.

Reference numeral 11 denotes a capsule that forms a vacuum closed space, and faces a black body radiator 12 made of SiC and a cylindrical cylindrical covering body 14 containing n-type dopant and surrounding the black body radiator 12 at a central position inside the capsule. The reflector 13 is installed in the shape.

Further, the inner wall surface of the capsule 11 is constituted by a polished surface of a metal having a high heat ray reflectance and a high melting point, for example, tungsten, and the outside thereof has a heat insulating structure.

The sunlight enters the radiating body 12 through the optical fiber 17 in a condensed state and heats it. The temperature of the radiator 17 approaches 1600 ° K which is the desired temperature only by sunlight, but it is still heated by the heater 16 and kept at 1600 ° K.

It is not necessary for the reflector 13 to match its temperature to 1600 ° K, and it is necessary to keep the temperature below 600 ° K by keeping the temperature as low as possible in order to reduce the heat radiation loss from the reflector 13. Also, it is desirable to suppress unnecessary supply of heat rays to the Si solar cells located on the downstream side. Such cooling means may be formed by winding a cooling pipe around the reflection plate 13, or a heat pipe or the like may be used, and is not particularly limited.

The reflection plate 13 reflects all heat rays on the wavelength side longer than 1100 nm and is configured not to absorb them, so that heat is not supplied by the conduction mechanism from the capsule 11 held at a high temperature, It should not heat up. In the present embodiment, the a-axis direction of graphite doped with ammonium graphite as an n-type dopant at a ratio of 30 × 10 ⁻⁴ molecule / one carbon atom was used as the material of the reflector, and the temperature was kept at 550 ° K. .

With the above configuration and conditions, operate a device corresponding to 1kW of incident sunlight, and output 0.80k as 650nm ~ 1100nm light output.
W, its energy density of 16kWm ^-2 was obtained. This 650nm ~ 110
After further concentrating 0 nm light and raising the energy density to 40 kWm ^-2 , it was led to an n + pp + type Si solar cell to obtain a power generation of 0.28 kW.

As described above, it was confirmed that the effects of the present invention can be achieved smoothly by the examples.

“Effect” As described above, according to the present invention, particularly 600 nm to 1100 n
It is possible to obtain extremely high wavelength conversion efficiency even in the temperature range of 1400 ° K to 1600 ° K, where the proportion of energy distributed to specific wavelength ranges such as m is small, and simply place the reflector and radiator in opposition. Since there is only one, the structure is simple and there is no room for failure.

Further, since the member is arranged in a closed space, particularly a vacuum closed space, it can be used semipermanently without deterioration such as oxidation or contamination.

Further, in claim 8), even when wavelength conversion is performed in a high temperature atmosphere, the wavelength converted light can be incident on the solar cell after being lowered to near room temperature, so that there is room for damage or deterioration of the solar cell. Thus, it is possible to form a semi-permanent solar power generation device.

It has various remarkable effects.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the internal configuration of a wavelength converter according to an embodiment of the present invention, FIG. 2 is a sensitivity distribution diagram showing the collection efficiency of Si solar cells, and FIG. 3 is a photovoltaic power generation device of the prior application. FIG. 4 is an overall block diagram showing the outline of FIG. 4, and FIG. 4 is a spectral characteristic diagram showing the temperature dependence of black body radiation.

Claims (9)

(57) [Claims] 1. In a wavelength conversion device for aligning the wavelength of sunlight in a specific wavelength range, a black body radiator and an optical filter are arranged to face each other in a high temperature atmosphere, and light in the specific wavelength range can be taken out from the optical filter. An optical wavelength conversion device characterized by being configured. 2. The black body radiator is a highly heat-resistant radiator that absorbs incident sunlight and converts it into heat radiation, while the optical filter has a wavelength shorter than a long wavelength end of a specific wavelength range. The optical wavelength conversion device according to claim 1, which is a filter plate that transmits the light of (1) and reflects the light of a wavelength longer than the wavelength end. 3. The incident surface and side surface of the black body radiator excluding the passage of incident sunlight, which does not face the optical filter, are covered with a thin layer having a low thermal emissivity. The optical wavelength conversion device described. 4. An optical wavelength conversion device according to claim 1, wherein an inner wall surface of a high temperature chamber for accommodating the black body radiator and the optical filter is coated with a thin layer having high heat resistance and high heat ray reflectance. . 5. The optical wavelength conversion device according to claim 1, wherein in the optical conversion device in which the specific wavelength region is a wavelength region of 600 nm to 1100 nm, the optical filter is formed of graphite in which an n-type dopant is highly doped. apparatus 6. The optical conversion device, wherein the specific wavelength range is a wavelength range of 600 nm to 1100 nm, wherein the optical filter is a filter member having an n-type GaP film formed on a quartz glass substrate. Optical wavelength converter 7. The optical conversion device, wherein the specific wavelength range is a wavelength range of 600 nm to 1100 nm, wherein the optical filter is 1200
2. A filter member comprising a multilayer dielectric film designed to have a central wavelength of nm and a reflective film formed on a graphite substrate highly doped with an n-type dopant. Optical wavelength converter described 8. The temperature of the black body radiator in the optical conversion device, wherein the specific wavelength range is a wavelength range of 600 nm to 1100 nm.
More than 1500 ° K and the temperature of the optical filter is 600 ° K
The optical wavelength conversion device according to claim 1), characterized in that: 9. The light conversion device, wherein the specific wavelength range is a wavelength range of 600 nm to 1100 nm, wherein the black body radiator is made of a SiC material, and the black body radiator except for the passage of incident sunlight is incident. The optical wavelength conversion device according to claim 3), wherein the surface and the side surface are coated with a graphite thin layer body in which an n-type dopant is highly doped.