JP2609163B2 - Photovoltaic power generation method and device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photovoltaic power generation method and a photovoltaic power generation method that improve photoelectric conversion efficiency by using collected sunlight.

[Prior Art] Conventionally, solar power generation has attracted attention as an alternative energy such as oil or nuclear power.

Certainly, the solar energy received by the earth's surface is virtually inexhaustible, currently over 20,000 times the total amount of energy consumed in the world, and solar power generation using this solar energy simply receives sunlight on the solar cell surface. Oil is very clean without the risk of environmental pollution like nuclear power, and has an extremely large advantage compared to other power generators in terms of maintenance and life. Despite the fact, it is still installed only in very limited areas of remote islands and deserts.

The biggest reason was that the photoelectric conversion efficiency was still low, and it was not possible to obtain a sufficient amount of photovoltaic power for the installation cost.

"Technical problems to be solved by the invention" Various measures have been taken in the past to solve such a drawback.

A, The first is to improve the photoelectric conversion efficiency of the solar cell itself.

Certainly, in recent years, 14-15% conversion efficiency has been obtained in practical use by improving the structural technology and surface structure of Si solar cells themselves.
Improvements have been made to improve the conversion efficiency, but even if all the technical problems were solved, the theoretical efficiency of the Si solar cell was around 20%, so it was impossible to further improve it. is there.

There is an upper limit to the theoretical efficiency of a Si solar cell,
This is mainly due to the relationship between the energy distribution by wavelength of sunlight and the band gap of Si, and the light collection efficiency.

That is, despite the fact that sunlight reaching the surface of the earth has a wide energy range of 0.3 μm to several μm, the band gap of the Si solar cell is 1.1 eV (wavelength conversion: 1127 nm), so that the long-wavelength The light cannot be used as a transmission loss, and in the short-wavelength sunlight of 1127 nm or less, only the bandgap Eg of Si is used in the energy hν held by the photon (hν−Eg). Would. Furthermore, since the spectral sensitivity of the Si solar cell has a distribution curve shown in FIG. 3, the collection efficiency of sunlight in a wavelength range of 900 to 1100 nm and 500 nm or less in a normal Si solar cell is significantly increased. Although the collection efficiency is certainly improved in the solar cell to which the internal electric field is added to improve the collection efficiency, the conversion efficiency of the solar cell is still low.

In order to solve such a drawback, a gallium arsenide (GaAl) As / GaAs solar cell without using a Si solar cell has also been proposed.
Although the photoelectric conversion efficiency is improved to about 20% because of 1.5 eV, it is difficult to obtain such a solar cell in large quantities and its production cost is large, so that it is difficult to use it for general purposes.

B. In order to enhance the photoelectric conversion efficiency, a wavelength selection technique for sunlight has been proposed.

For example, Japanese Patent Application Laid-Open No. 63-6881 discloses that after sunlight is wavelength-selected using a fluorescent light-collecting plate, the wavelength is selected in each of the selected wavelength bands.
By arranging and receiving different types of solar cells having corresponding band gaps, the photoelectric conversion efficiency is increased.

However, even in such a conventional technique, sunlight having a wavelength equal to or larger than the corresponding band gap cannot be used as a transmission loss, and the device configuration is complicated and expensive. Become.

C. By the way, the photoelectric conversion efficiency of the solar cell is not limited only to the band gap and the light collection efficiency, but there is an energy loss (voltage factor) due to the open voltage being smaller than the band gap.

Therefore, a technique has been conventionally developed in which sunlight is condensed and then incident on a solar cell.

For example, when using an n ⁺ p type (10Ωcm) Si solar cell,
When the light-collecting ratio is 1 Sun, the ratio of the electrical output to the amount of solar light received is around 16% (27 ° C), whereas when the light-collecting ratio is increased to 40Sun, the ratio improves to 18-19% (27 ° C) However, the condensed sunlight also includes heat rays that are in the infrared region having a wavelength of 1127 nm or more and cannot be used for photoelectric conversion, and when this directly enters the solar cell, the solar cell itself heats up unnecessarily. As a result, the photoelectric conversion efficiency may be significantly reduced.

In view of the drawbacks of the related art, the present invention provides a photovoltaic power generation method and a photovoltaic power generation method that is configured to effectively use a wide range of light energy from short wavelength to long wavelength, thereby greatly improving photoelectric conversion efficiency. For the purpose.

Another object of the present invention is to use a single type, more specifically, high versatility, stable quality and low production cost without using a plurality of types of solar cells having different band gaps. It is an object of the present invention to provide a photovoltaic power generation method and a photovoltaic power generation method capable of greatly increasing the photoelectric conversion efficiency even when a simple Si solar cell is used.

Another object of the present invention is to provide a photovoltaic power generation method and a photovoltaic power generation method capable of obtaining a photovoltaic power commensurate with the installation cost.

"Technical Means for Solving the Problem" First, the process leading to the present invention will be described step by step.

As described in the section of the related art, the main reason that the improvement in the photoelectric conversion efficiency of the solar cell is hindered by the band gap (forbidden band width) and the light collection efficiency is as described above.

Therefore, wavelength conversion is performed on sunlight having a wide energy range from about 0.3 μm to about several μm, and the wavelength of the sunlight is, for example, a specific wavelength smaller than 1127 nm corresponding to the band gap of Si and as close as possible to this. hand,
Further, a region having the highest collection efficiency in the sensitivity distribution curve shown in FIG. 3, for example, in the case of a junction having a uniform impurity concentration (i)
600 to 800 nm, 400 to 100 when built-in electric field exists (ii)
It is extremely important to make the specific wavelength range of 0 nm, preferably 650 to 950 nm, in order to greatly improve the photoelectric conversion efficiency.

Therefore, the first feature of the present invention is to use wavelength conversion means for adjusting the wavelength of sunlight to a specific wavelength region shorter than the band gap of a semiconductor material of a solar cell that receives sunlight.

However, if an energy loss occurs in the process of aligning the wavelength to the specific wavelength range, the effect of performing the wavelength conversion is lost as a result.

Therefore, a second feature of the present invention resides in that the wavelength conversion is performed using a blackbody radiation in a high-temperature atmosphere, and more preferably in a closed vacuum space where the inner wall surface is blackened.

That is, the wavelength conversion can be performed by using a dye laser or the like, but it is possible to perform wavelength conversion with high efficiency.
As shown in the examples below, for example, light other than a specific wavelength range in sunlight is absorbed by a filter member, and black body radiation capable of performing wavelength conversion while repeatedly converting the absorbed energy into radiant energy. Most preferably, it is used.

More specifically, as described in claim 5, a solar light concentrating means, and a specification shorter than the band gap of a solar cell disposed downstream of the solar light condensing means and receiving the sunlight. Wavelength conversion means for aligning the wavelength in the wavelength range, the wavelength conversion means comprising a filter member that absorbs light having a wavelength shorter than the specific wavelength range and a reflection member that reflects light having a wavelength longer than the specific wavelength range. It is preferable that the filter has a function and re-radiates the energy absorbed and reflected by the filter member and the reflection member as black body radiation at a set temperature, thereby repeatedly selecting the wavelength.

However, as is well known, blackbody radiation has a temperature dependence of radiation energy density at each wavelength as shown in the PLANCK formula, and radiation from a low-temperature radiator is on the long wavelength side and its energy density is low. Therefore, in order to effectively obtain radiation having a wavelength range suitable for the Si solar cell, for example, 650 to 950 nm, the temperature of the radiator must be at least 1000 ° C.
Must be set to K or more.

Therefore, according to the present invention, as shown in FIG. 4, the above-mentioned operation can be performed smoothly by setting the ambient temperature to at least 1000 ° K or more and storing the radiator in a vacuum atmosphere to protect the radiator from oxidation. A possible technique is disclosed in claim 1 .

By the way, the wavelength conversion can also convert the wavelength without condensing sunlight, but such a configuration increases the size of the conversion unit itself and lowers energy efficiency.
Not practical.

Further, as described above, the photoelectric conversion efficiency of the solar cell is not limited to only the band gap factor and the light collection efficiency, but also depends on the voltage factor.

Therefore, the third feature is to use a sunlight condensing means to prevent a decrease in photoelectric conversion efficiency based on a voltage factor,
By arranging the wavelength conversion means on the downstream side of the light collection means, the installation area of the conversion means is reduced, the energy efficiency is improved and the size is reduced, and further, the sunlight after the wavelength conversion is in a light collection state. The point is that this is incident on the solar cell side as it is or after being enlarged to a predetermined light-condensing magnification, thereby preventing a reduction in photoelectric conversion efficiency due to a voltage factor.

Now, the more highly the sunlight that is incident on the wavelength conversion means is condensed, the more it is possible not only to achieve a reduction in the installation area and an improvement in energy efficiency and miniaturization of the conversion means, but also to possess the sunlight itself. It is preferable because it is easy to maintain the atmosphere temperature in the conversion means at least 1000 ° K or more by utilizing thermal energy.

However, since the sunlight incident on the solar cell needs only a light concentration sufficient to eliminate the reduction in the photoelectric conversion efficiency due to the voltage factor, such highly concentrated sunlight is directly incident on the solar cell. In addition, not only does the photoelectric conversion efficiency decrease due to the temperature rise or the like, but also the photovoltaic power per unit area is saturated, and the solar cell is more likely to be damaged.

Therefore, a fourth feature of the present invention described in claim 2 is that the light-collecting magnification of sunlight incident on the converting means and the light-condensing magnification of wavelength-converted sunlight incident on the solar cell are different. is there.

The inventions described in claims 3 and 4 provide a solar power generation device for more effectively embodying the invention, and the feature of the invention is the wavelength of collected sunlight. The wavelength conversion means for adjusting the wavelength to the specific wavelength range is also used.
After the light condensing means for condensing the light, and diffusing the light emitted from the wavelength conversion means to a predetermined light condensing magnification of approximately 10 to 100 Sun without directly making the light emitted from the wavelength conversion means directly incident on the solar cell, The point is that diffusion means for making the light incident on the solar cell is provided.

[Effect] According to the invention, a wide range of light energy from a short wavelength to a long wavelength is effectively used, and the sunlight is converted into a wavelength region most easily used for a solar cell while maintaining the energy conversion efficiency at approximately 100%. In order to perform wavelength conversion, it is possible to prevent a decrease in photoelectric conversion efficiency due to a so-called band gap or light collection efficiency.

In addition, since the wavelength conversion is performed on the collected sunlight, downsizing of the wavelength converter, high efficiency of the wavelength conversion efficiency is achieved, and the sunlight after the wavelength conversion is also in the light collection state. In addition, by injecting the light into the solar cell side as it is or after expanding it to a predetermined light-collecting magnification, it is possible to prevent a decrease in photoelectric conversion efficiency due to a voltage factor.

In addition, since the sunlight after the wavelength conversion does not include infrared sunlight that should be a heat ray, the solar cell that has received the sunlight can perform photoelectric conversion at room temperature as it is without needlessly raising the temperature, Conversion efficiency also improves.

Further, the present invention highly concentrates the sunlight incident on the conversion means, while diffusing the highly focused wavelength-converted sunlight into the solar cell and reducing the sunlight to a predetermined concentration. Not only can achieve a positive installation area of the conversion means, improve energy efficiency and reduce the size of the conversion means, but also use the thermal energy held by the sunlight itself to allow the conversion means to be installed in the conversion means. Ambient temperature at least 1000 ゜
It becomes easy to maintain the temperature at K or more, and on the other hand, on the solar cell side, it is possible to generate solar light with the most suitable and high conversion efficiency without causing damage to the solar cell.

As a result, it is possible not only to provide a photovoltaic power generation device with greatly improved photoelectric conversion efficiency, but also to use a single type, more specifically a general-purpose type, without using a plurality of types of solar cells having different band gaps. To provide a photovoltaic power generation device that can obtain photovoltaic power that is commensurate with the installation cost even when using a Si solar cell that is highly efficient, has stable quality, and is inexpensive to manufacture. Becomes possible.

And so on.

"Example" Hereinafter, an example of the present invention will be illustratively described in detail with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just.

First, the theoretical configuration required to design this embodiment
A description will be given based on a solar cell.

It is known that the collection efficiency of a pn solar cell is improved by adding an internal electric field as shown in FIG.

The wavelength range in which the collection efficiency is highest in this case is 400 to 1000 nm, preferably 650 to 950 nm.

Therefore, when calculating the photoelectric conversion efficiency of the Si solar cell in the case where the energy conversion efficiency is set to the above-mentioned wavelength region at the energy conversion efficiency of 100%, Q = f · _φ650-950 1) Q: photoelectric conversion efficiency, f: voltage output by factor efficiency φ _650-950: basic efficiency and the phi _650-950 in the wavelength band 650~950nm is below 2) and the following numbers in table 1 than 0.670 is obtained, the addition f is below 3) Since a value of 0.343 is obtained, Q is 23%.

P: Electric power of the Si solar cell itself (142 W / m ² ) Eg: Band gap (1.1 eV, 1.7624 ^-19 J, 1,127 nm) η: Collection efficiency, λ: wavelength Nλ: wavelength range, photon flux in dλ ( pieces / m ² sec), however 23% photoelectric conversion efficiency because the number stages higher than the conversion efficiency of the current solar cell itself still not numeric satisfactory.

Therefore, it can be understood from the first equation that if the output efficiency is increased by the voltage factor, the efficiency is further improved.

 One of the measures is the problem of light concentration and temperature.

That is, in the case of the n ⁺ PP ⁺ type Si solar cell, at room temperature (27 ° C.), the output efficiency due to the voltage factor at 40 Sun is 0.516.
The photoelectric conversion efficiency Q increases to about 34%, and a satisfactory numerical value is obtained.

FIG. 1 is an overall block diagram schematically showing a photovoltaic power generation device created based on such a theoretical configuration.

To briefly explain the configuration, 1 is a condensing mirror for condensing sunlight, 2 is a wavelength converter for converting the wavelength of the condensed sunlight, and 3 is a predetermined condenser for the sunlight after the wavelength conversion. Magnifying glass magnifying to magnification, 4 is an n ⁺ PP ⁺ type Si solar cell, for example, 1KW / m
The ^second sunlight condensing mirror 1 is incident on the wavelength converter 2 after highly focused substantially 4400KW / m ^2, and in the wavelength converter 2,
The collected sunlight is wavelength-converted to a wavelength range of 650 to 950 nm while maintaining the energy conversion efficiency at approximately 100%.

After the sunlight after the wavelength conversion is expanded into a light flux of about 40 Sun by the magnifying mirror 3 and then incident on the solar cell 4, the photovoltaic power of the above-described photoelectric conversion efficiency can be obtained.

 FIG. 2 shows a wavelength converter 2 used in the device.

Numeral 11 is a heat insulating box having an inner wall made of a gray heat insulating material.The inner space is maintained in a vacuum state, and a heater 15 is buried in the peripheral wall so that the inner space can be maintained at about 1400 ° K. I have.

In addition, since heat rays are radiated from the inside of the heat insulation box 11 by black body radiation, by appropriately adjusting the relationship between the incident amount of highly concentrated sunlight and the internal space volume of the heat insulation box.
The temperature can be raised to and maintained at about 1400 ° K. Therefore, the heater 15 may be used for temperature adjustment.

Reference numerals 12 and 13 denote windows for incident and outgoing sunlight, fixed on the central axes of both end walls of the heat insulating box 11, and are made of high-purity quartz glass.

Reference numeral 14 denotes an optical filter member for transmitting sunlight having a wavelength longer than 650 nm, and fine particles 14a such as graphite having good radiating ability are scattered therein so that the absorbed light can be re-emitted.

Reference numeral 16 denotes a selective wavelength reflector that reflects light having a wavelength longer than 950 nm, and is made of, for example, graphite doped with an n-type dopant at a high concentration.

According to this embodiment, the sunlight introduced into the heat insulation box 11 from the entrance window 12 cuts light having a wavelength of 650 nm or less and light having a wavelength of 950 nm or more by the optical filter member 14 and the reflection member 16, Light in the wavelength range of 950950 nm is emitted from the emission window 13 toward the magnifying mirror 3.

On the other hand, the light cut by the optical filter member 14 and the reflecting member 16 is absorbed by the graphite particles 14a dispersed and incorporated in the filter 14, and then becomes radiation emitted from the particles 14a. The light in the wavelength range of 650 to 950 nm is emitted from the emission window 13 toward the magnifying glass 3.

At this time, since the inside of the heat insulating box 11 is maintained at 1400 ° K, radiant energy having a wavelength of about 650 nm or more can be obtained as shown in FIG. -Heat conversion While returning, the light in the wavelength range of 650 to 950 nm is emitted from the emission window 13 to the magnifying mirror 3 side, and this operation is repeated an infinite number of times to maintain the energy conversion efficiency of the collected sunlight at approximately 100%. The wavelength can be converted to a wavelength range of 650 to 950 nm.

Therefore, according to this embodiment, the effects of the present invention described above can be smoothly achieved.

[Brief description of the drawings]

FIG. 1 is an overall block diagram schematically showing a photovoltaic power generator according to an embodiment of the present invention. FIG. 2 shows a wavelength converter used in the device. FIG. 3 is a sensitivity distribution diagram showing the collection efficiency of Si solar cells, and FIG.
The figure is a spectral characteristic diagram showing the temperature dependence of blackbody radiation.

Claims (5)

(57) [Claims] 1. A solar light collecting means, comprising: a solar light collecting means; and a wavelength converting means arranged downstream of the solar light collecting means for adjusting a wavelength to a specific wavelength region shorter than a band gap of a solar cell that receives the solar light. A photovoltaic power generation method, wherein the wavelength conversion is performed in a high-temperature atmosphere using blackbody radiation, and the high-temperature atmosphere is set in a vacuum space and at least 1000 ° K or more. 2. A solar light collecting means, comprising: a solar light collecting means; and a wavelength converting means arranged downstream of the solar light collecting means for adjusting a wavelength to a specific wavelength region shorter than a band gap of a solar cell receiving the sunlight. Along with the condensing magnification of the sunlight to be incident on the conversion means and the condensing magnification of the sunlight after the wavelength conversion to be incident on the solar cell, the wavelength conversion is performed under a high-temperature atmosphere using blackbody radiation. Solar power generation method characterized by doing 3. A condensing means for highly condensing sunlight, a wavelength converting means for adjusting the wavelength of the condensed sunlight to a specific wavelength region shorter than a band gap of a solar cell, and the wavelength converting means. And a diffusing unit for diffusing the output solar light to a predetermined light-condensing magnification and then incident the solar light on a solar cell. 4. The condensing means according to claim 1, wherein said light condenses at least 1000Su
4. The photovoltaic power generator according to claim 3, wherein the photovoltaic power generation device is a device for converging light to n or more, and wherein the diffusion device is a device for diffusing sunlight output from the wavelength conversion device to approximately 10 to 100 Sun. 5. A solar light collecting means, comprising: a solar light collecting means; and a wavelength converting means disposed downstream of the solar light collecting means and for adjusting a wavelength to a specific wavelength region shorter than a band gap of a solar cell for receiving the solar light. The wavelength converting means has a wavelength selecting function of a filter member that absorbs light having a wavelength shorter than a specific wavelength region and a reflecting member that reflects light having a longer wavelength than the specific wavelength region, and the filter member and the reflecting member Photovoltaic power generation method characterized by re-radiating the absorbed and reflected energy as black body radiation at a set temperature and repeatedly selecting wavelengths