JPH03143280A - Method and apparatus for generating power by solar energy - Google Patents

Abstract

PURPOSE:To reduce a manufacturing cost and to improve photoelectric conversion efficiency by employing wavelength converting means for aligning solar light wavelengths in a shorter specific wavelength zone than that of the band gap of the semiconductor material of a solar cell for receiving a solar light. CONSTITUTION:A condensing mirror 1 for condensing a solar light, a wavelength converter 2 for wavelength-converting the condensed solar light, an enlarging mirror 3 for enlarging the wavelength-converted solar light by a predetermined condensing magnification, and an n<+>pp<+> type Si solar cell 4 are provided. For example, after solar light of 1kW/m<2> is condensed to an intensity of approx. 4400kW/m<2> by the mirror 1, it is directed to the converter 2, the condensed light is converted to a wavelength of 650-850nm at an approx. 100% of conversion efficiency by the converter 2. The light is enlarged to a luminous flux of about 40Sun by the mirror 3, directed to the cell 4 to obtain photovoltaic power of high photoelectric conversion efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a solar power generation method and an apparatus thereof that utilize concentrated sunlight to improve proactive conversion efficiency.

"Conventional Technology" Solar power generation has been attracting attention as an alternative energy source to oil, nuclear power, etc.

It is true that the solar energy received by the earth's surface is currently more than 20,000 times the total amount of energy consumed in the world, and is virtually inexhaustible, and solar power generation using this solar energy simply involves receiving sunlight on the surface of solar cells. Because photovoltaic power can be obtained from electricity, it is extremely clean without worrying about environmental pollution like oil or nuclear power, and it has an extremely large advantage over other power generation devices in terms of maintenance and lifespan. Despite this, it is only installed in extremely limited areas such as remote islands and deserts.

The main reason for this is that the photoelectric conversion efficiency remains low, making it impossible to obtain enough photovoltaic power to justify the installation cost.

``Technical Problems to be Solved by the Invention'' In order to eliminate such drawbacks, various measures have been taken in the past.

A. The first is to improve the photoelectric conversion efficiency of the solar cells themselves.

It is true that in recent years, improvements in the structural technology and surface structure of Si solar cells themselves have enabled conversion efficiency of 14 to 15% to be achieved in practical use.
Although improvements have been made to improve the conversion efficiency,
Even if all the technical problems were solved, the theoretical efficiency of Si solar cells is around 20%, so it is impossible to improve it further.

As shown in point 2, there is an upper limit to the theoretical efficiency of Si solar cells.
This is mainly due to the relationship between the wavelength-specific energy distribution of sunlight and the band gap of Si, and the light collection efficiency.

In other words, although the sunlight that reaches the earth's surface has a wide range of energy from 0.3 μm to around several μm, the band gap of Si solar cells is 1.1 eV (112
7nm), so sunlight with a long wavelength of 1127nm or more becomes a transmission loss and cannot be used, and in the sunlight with a short wavelength of 1127nm or less, the Si band gap Eg is (hC Eg) results in a loss.

Furthermore, since the spectral sensitivity of the Si solar cell has the distribution curve shown in Fig. 3, the collection efficiency of sunlight in the wavelength range of 900 to 1l100n and 500r+m or less is significantly increased in a normal Si solar cell. Although the collection efficiency is certainly improved in a solar cell in which an internal electric field is added to improve the collection efficiency, the conversion efficiency of the solar cell is still low.

In order to eliminate such drawbacks, gallium arsenide (GaA1) As/Ga, As solar cells have been proposed without using Si solar cells, and such solar cells have a band gap of 1.4 to 1.5 eV. This improves the photoelectric conversion efficiency to around 20%, but such solar cells are difficult to obtain in large quantities and have high manufacturing costs, making it difficult to use them for general purposes.

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

For example, Japanese Patent Application Laid-Open No. 63-6881 discloses that after wavelength-selecting sunlight using a fluorescent condensing plate, different types of solar cells with corresponding band gaps are arranged to receive light in each of the selected wavelength bands. It is configured to increase photoelectric conversion efficiency.

However, even with such conventional technology, sunlight having a wavelength greater than the corresponding band gap cannot be used as a transmission loss, and the device configuration is complicated and expensive, making it difficult to obtain a photovoltaic power generation amount commensurate with the installation cost. Become.

C2 Now, the photoelectric conversion efficiency of a solar cell is not limited only to the band gap and light collection efficiency, but there is an energy loss (voltage factor) caused by the open circuit voltage being smaller than the band gap.

Therefore, conventionally, a technology has been developed in which sunlight is focused and then made to enter a solar cell.

For example, when using an n+p type (100cm) Si solar cell, the ratio of electrical output to the amount of sunlight received is around 16% (27°C) when the concentration ratio is I Sun; When increasing to 40Sun, the ratio becomes 18-19
% (27℃), but the concentrated sunlight has a wavelength of 1127 nm or more in the infrared region and also contains heat rays that cannot be used for photoelectric conversion. The temperature of the battery itself increases unnecessarily, which may significantly reduce photoelectric conversion efficiency.

In view of the drawbacks of the prior art, the present invention is designed to effectively utilize a wide range of light energy from short wavelengths to long wavelengths,
The purpose of the present invention is to provide a solar power generation method and a device for the same that greatly improves photoelectric conversion efficiency.

Another object of the present invention is to provide solar cells with high versatility, stable quality, and production without using multiple types of solar cells with different band gaps. An object of the present invention is to provide a photovoltaic power generation method and a device thereof, which can greatly increase photoelectric conversion efficiency even when using low-cost Si solar cells.

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

"Technical means to solve problems" First, the progress that led to the present invention will be explained in order.

As described above in the prior art section, the main reason for inhibiting the improvement of the photoelectric conversion efficiency of solar cells is the band gap (forbidden band width) and light collection efficiency, as described above.

Therefore, wavelength conversion is performed on sunlight having a wide range of energy from 0.3 μm to around several μm, and the wavelength of the sunlight is changed to 1127 nm, which corresponds to the band gap of Si.
The photoelectric conversion efficiency can be greatly increased by aligning the specific wavelength smaller than nm and as close as possible to the specific wavelength range where the collection efficiency is highest in the sensitivity distribution curve shown in Fig. 3, for example, 650 to 950 nm. This is extremely important for improving.

Therefore, the first feature of the present invention is to use a wavelength conversion means that aligns the wavelength of sunlight to a specific wavelength range shorter than the bandgap of the semiconductor material of the solar cell that receives sunlight.

However, if energy loss occurs during the process of aligning the wavelengths to the specific wavelength range, the meaning of the wavelength conversion will be lost.

Therefore, the second feature of the present invention is that the wavelength conversion is performed in a high-temperature atmosphere using black body radiation, preferably in a closed vacuum space whose inner wall surface is a black body.

That is, the wavelength conversion can be performed using a dye laser or the like, but what makes wavelength conversion possible with high efficiency is the use of light outside a specific wavelength range in sunlight, for example, as shown in the examples below. It is most preferable to utilize black body radiation, which can be absorbed by a filter member and then repeatedly convert the absorbed energy into radiant energy to perform wavelength conversion.

However, as is well known, black body radiation has a temperature dependence of radiant energy density by wavelength as shown in the PLANK formula, and radiant light from a low-temperature radiator is on the long wavelength side and has a low energy density. Therefore, in order to effectively obtain radiation in the wavelength range of 650 to 950 nm, which is suitable for Si solar cells, the temperature of the radiator must be at least 10 nm.
It is necessary to set it to 00'K or higher.

Therefore, in the present invention, as shown in FIG. 4, the above-mentioned action can be carried out smoothly by setting the ambient temperature to at least 1000' K or more and storing the radiator in a vacuum atmosphere to protect it from oxidation. A possible technique is disclosed in claim 2.

Although it is possible to perform wavelength conversion without condensing sunlight, such a configuration would increase the size of the conversion means itself and reduce energy efficiency, so it is not practical.

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

Therefore, the third feature is that a solar light condensing means is used to prevent a reduction in photoelectric conversion efficiency due to voltage factors, and the wavelength conversion means is arranged downstream of the light concentrating means. In addition, since the sunlight after wavelength conversion is in a condensed state, it can be made to enter the solar cell side either as it is or after being expanded to a predetermined condensing magnification. This also prevents reduction in photoelectric conversion efficiency due to voltage factors.

Now, the more highly the sunlight that is incident on the wavelength conversion means is concentrated, the more the conversion means can save space, improve energy efficiency, and be smaller in size. This is preferable because it becomes easy to maintain the ambient temperature within the conversion means at least 1000'K or higher using thermal energy.

However, the sunlight incident on the solar cell can eliminate the reduction in photoelectric conversion efficiency due to the voltage factor. Even if it is made incident, the photoelectric conversion efficiency will not only decrease due to the temperature increase, but also the photovoltaic force per unit area will become saturated, and the solar cell will be more likely to be damaged.

Therefore, a fourth feature of the present invention as set forth in claim 3 is that the concentration magnification of sunlight incident on the conversion means is different from the concentration magnification of sunlight after wavelength conversion incident on the solar cell. be.

The inventions described in claims 4 and 5 provide a solar power generation device for more effectively embodying the above invention, and the feature thereof is that the wavelength of concentrated sunlight is Although the wavelength conversion means for adjusting the wavelength to the specific wavelength range is used, a concentrating means for concentrating sunlight to a high degree, particularly 1000 Sun or more, is provided on the input side of the conversion means, and a light condensing means for concentrating sunlight to a high degree, particularly 1000 Sun or more, is also provided on the output side of the conversion means. The present invention is characterized in that a diffusion means is provided for diffusing the emitted light to a predetermined condensing magnification of about 10 to 100 Sun and then making it enter the solar cell without making the emitted light directly enter the solar cell.

"Effect" According to this invention, a wide range of light energy from short wavelengths to long wavelengths can be effectively used, and the sunlight can be converted into a wavelength range that is most easily used by solar cells while maintaining an energy conversion efficiency of approximately 100%. Since the wavelength is converted, it is possible to prevent a reduction in photoelectric conversion efficiency caused by the so-called band gap and light collection efficiency.

In addition, since the wavelength conversion is performed on concentrated sunlight, the wavelength converter can be made smaller and the wavelength conversion efficiency can be increased, and since the sunlight after wavelength conversion is also in a condensed state. Furthermore, by directing this light as it is or after expanding it to a predetermined light concentration magnification and making it incident on the solar cell side, it is possible to prevent a reduction in photoelectric conversion efficiency due to voltage factors.

Furthermore, since the sunlight after wavelength conversion does not include sunlight in the infrared region that should become heat rays, the solar cells that receive the sunlight can perform photoelectric conversion at room temperature without unnecessary temperature rise. , conversion efficiency is also improved.

Further, in the present invention, the sunlight incident on the conversion means is highly concentrated, and the solar cell is configured to diffuse the highly concentrated sunlight after wavelength conversion to reduce it to a predetermined concentration magnification. This makes it possible to not only reduce the installation area of the conversion means, improve energy efficiency, and downsize the conversion means, but also to make use of the thermal energy possessed by the sunlight itself. The ambient temperature is at least 1000℃
' K or higher can be easily maintained, and on the solar cell side, it becomes possible to generate sunlight with the most suitable and high conversion efficiency without causing damage to the solar cell.

As a result, it is not only possible to provide a solar power generation device with greatly increased photoelectric conversion efficiency, but also to use multiple types of solar cells with different band gaps (, single type,
More specifically, even when using Si solar cells, which are highly versatile, stable in quality, and inexpensive to manufacture, solar cells can obtain photovoltaic power that is commensurate with the installation cost in terms of high conversion efficiency. It becomes possible to provide power generation equipment.

It has various effects such as

13- "Example" Hereinafter, an example of the present invention will be described in detail based on the drawings. However, unless otherwise specified, the dimensions, materials, shapes, and relative positions of the components described in this example are not intended to limit the scope of this invention, but are merely illustrative examples. Not too much.

First, let's talk about the theoretical configuration necessary to design this example.
The explanation will be based on type solar cells.

As for pn type solar cells, it is known that the collection efficiency can be improved by adding an internal electric field as shown in FIG.

In this case, the wavelength range in which the collection efficiency is highest is 650 to 950 nm.

Therefore, when calculating the photoelectric conversion efficiency of a Si solar cell when the energy conversion efficiency is 100% and the wavelength range is aligned with the above, it is as follows: Q=f-φ860-950 --1) Q: photoelectric conversion efficiency, f: voltage factor Output efficiency by φ850-950:
Basic effect in the wavelength range 650-950 nm 14 - And the above φ650-960 is calculated by the following formula 2) and the following 1st
A value of 0.670 is obtained from the table, and for f, a value of 0.343 is obtained from equation 3) below, so Q is 2.
It will be 3%.

φ850-9508 P: Electrical output of Si solar cell itself (142W/nOEg
:Bandgi+'ybu(1,1eV, 1.7624-"J
, 1,127 nm) η: collection efficiency, λ: wavelength Nλ:
Photon flux (number/n (see) in the wavelength region dλ) However, although the photoelectric conversion efficiency of 23% is several steps higher than the conversion efficiency of the current solar cell itself, it is still not a satisfactory value.

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

One of the countermeasures is the issue of light concentration and temperature.

That is, in the case of an n"PP" type Si solar cell, the temperature at room temperature (27
℃), the output efficiency due to the voltage factor at 40 Sun increases to about 0.516, and therefore the photoelectric conversion efficiency Q increases to about 34%, which is a somewhat satisfactory value.

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

To briefly explain its configuration, 1 is a condenser mirror that condenses sunlight, 2 is a wavelength converter that converts the wavelength of the concentrated sunlight, and 3 is a wavelength converter that condenses the sunlight after wavelength conversion. A magnifying glass that magnifies the magnification, 4 is an n"PP" type Si solar cell, for example], KW/rr! About 440 OK sunlight with condensing mirror 1,
After highly condensing the light around W/rd, it enters the wavelength converter 2, and in the wavelength converter 2, the concentrated sunlight is heated at 650~650% while maintaining the energy conversion efficiency of approximately 100%.
The wavelength is converted to a wavelength range of 950 nm.

Then, by enlarging the wavelength-converted sunlight to a luminous flux of about 40 Sun using a magnifying glass 3, and making it incident on the solar cell 4, it is possible to obtain a photovoltaic force with the above-mentioned photoelectric conversion efficiency.

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

Reference numeral 11 denotes a heat insulating box whose inner wall surface is made of gray heat insulating material, and the inner space is maintained in a vacuum state, and a heater 15 is embedded in the surrounding wall, so that the inner space can be maintained at approximately 1400'K. There is.

In addition, since heat rays are radiated inside the insulation box 11 by black body radiation, by appropriately adjusting the relationship between the amount of highly concentrated sunlight incident and the internal space volume of the insulation box. It is possible to raise the temperature around 1400° and maintain that temperature, so the heater 5 may be used for temperature adjustment.

Reference numerals 12 and 13 denote windows for sunlight input and output, which are fixed on the center axis 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 that transmits sunlight having a wavelength longer than 650 nm, and fine particles 14a such as graphite having good radiation ability are interspersed inside 17- so that absorbed light can be re-radiated.

Reference numeral 16 denotes a selective wavelength reflection plate that reflects light with wavelengths 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 insulating box 11 through the entrance window I2 is filtered by the optical filter member 14 and the reflection member 16 to cut out the wavelength light of 650 nm or less and the wavelength light of 950 nm or more. Light in the wavelength range of ~950 nm is emitted from the exit window 13 to the magnifying glass 3 side.

On the other hand, the light cut by the optical filter member 14 and the reflection member 16 is absorbed by the graphite particle group 14a dispersed within the filter 14, and then becomes radiant light emitted from the particle group 14a. Medium 650~
Light in a wavelength range of 950 nm is emitted from the emitting window section 13 to the magnifying glass 3 side.

At this time, since the inside of the insulation box 11 is maintained at 1400'K, it is possible to obtain radiant energy having a wavelength of about 650 nm or more as shown in FIG. 18 - While repeating radiation-heat conversion, light in the wavelength range of 650 to 950 nm is emitted from the emission window I.
3 to the magnifying glass 3 side, and by repeating this process an infinite number of times, the energy conversion efficiency of the concentrated sunlight is approximately 1.
It is possible to convert the wavelength to a wavelength range of 650 to 950 nm while maintaining the wavelength at 00%.

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

[Brief explanation of the drawing]

FIG. 1 is an overall block diagram schematically showing a solar power generation device 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 a Si solar cell, and FIG. 4 is a spectral characteristic diagram showing the temperature dependence of blackbody radiation. Figure (650-9509k)

Claims (1)

[Claims] 1) A solar light condensing means, and a wavelength conversion that aligns the wavelength to a specific wavelength range shorter than the bandgap of a solar cell that receives the sunlight, which is arranged downstream of the sunlight concentrating means. 2) A solar power generation method characterized in that the wavelength conversion is performed in a high temperature atmosphere while utilizing black body radiation. 2) The high temperature atmosphere is in a vacuum space and at least 100%
3) The solar power generation method according to claim 1, wherein the solar power generation method is set to 0°K or more. 3) The concentration magnification of sunlight incident on the conversion means and the concentration of sunlight after wavelength conversion incident on the solar cell. 4) A solar power generation method according to claim 1, characterized in that the light magnification is made different. 4) A concentrating means for concentrating sunlight to a high degree; 5) A solar power generation device comprising a wavelength conversion means for adjusting the wavelength to a specific wavelength range shorter than the gap, and a diffusion means for diffusing the sunlight outputted from the wavelength conversion means to a predetermined concentration magnification and then making it enter the solar cell. The light means receives at least 1000 Sun of sunlight.
4) The solar power generation device according to claim 4), wherein the means for concentrating the sunlight to approximately 10 to 100 Sun, and the diffusing means is means for diffusing the sunlight outputted from the wavelength converting means to about 10 to 100 Sun.