JP6327940B2 - Power generator - Google Patents

Description

  The present invention relates to a power generation apparatus that includes a photothermal power generation element having an emitter that emits electrons upon receiving light and heat, and a collector that captures electrons emitted from the emitter, and that generates power between the emitter and the collector.

Non-Patent Document 1 below discloses a power generation device that generates power by photon-excited thermionic emission (PETE) that combines photoelectric conversion and thermoelectric power generation.
This power generation device is configured to irradiate condensed sunlight to an emitter made of a semiconductor, and light in a short wavelength region of sunlight is used for photoexcitation in the semiconductor, and light in a long wavelength region is heated for the semiconductor. By using this, a photothermal power generation element (PETE element) having a collector for capturing electrons emitted from the emitter and a collector for capturing the emitted electrons by a synergistic effect of photoexcitation and heating is provided. Further, in the power generation device described in this document, only sunlight is used as an energy source for power generation, and a predetermined power is obtained by increasing the concentration ratio of sunlight irradiated to the emitter, for example, 1000 times or more. ing.

JWSchwede, I.Bargatin, DCRiley, BEHardin, SJRosenthal, Y.Sun, F.Schmitt, P.Pianetta, RTHowe, Z.-X.Shen, NAMelosh, "Photon Enhanced Thermionic Emission for Solar Concentrator Systems , "Nature Materials 9, 762-767, (2010)

  However, in the power generation device of Non-Patent Document 1, in order to obtain predetermined power, it is necessary to increase the sunlight condensing rate to 1000 times or more. Therefore, there is a problem that a large condensing device that realizes such a condensing rate is required, and the power generation device becomes large. Furthermore, when sufficient sunlight cannot be obtained due to bad weather or the like, there is a problem that power generation output cannot be stably obtained.

  The present invention has been made paying attention to this point, and an object of the present invention is to provide a power generator capable of obtaining a predetermined power while reducing the size of the apparatus.

To achieve this object, the power generator according to the present invention comprises:
A power generation device that includes a photothermal power generation element having an emitter that emits electrons upon receiving light and heat, and a collector that captures electrons emitted from the emitter, and that generates power between the emitter and the collector, the first feature thereof The configuration is
Condensing irradiation means for condensing sunlight at a concentration ratio of 10 to 100 times and irradiating the emitter;
Heating means for heating the temperature of the emitter to 650 K or higher,
The band gap of the semiconductor constituting the emitter is selected from 0.8 eV to 1.6 eV ,
The heat source of the heating means is exhaust gas generated by burning fuel .

  According to the 1st characteristic structure of the said electric power generating apparatus, both a condensing irradiation means and a heating means are provided. Then, both solar energy and thermal energy are applied to the emitter on the electron (thermal electron) generation side from both means. Therefore, the power generation apparatus according to the present application also generates power using the energy given to the emitter by both means based on the principle of photothermal power generation. However, according to the study by the inventors, as described in the present application, solar energy is provided to the emitter at a low concentration rate (10 to 100 times) and relatively small (much less than the conventional 1000 times). In addition, when heat energy is separately supplied to the emitter, as will be described later in detail with reference to FIGS. 2 and 3, it is relatively limited as compared to the case where the same sunlight concentration state (rate) is maintained. It has been found that a predetermined power generation output (power generation efficiency) can be obtained only within the range of the band gap.

  More specifically, in the configuration of the present application, since the concentration ratio of sunlight is relatively low between 10 times and 100 times, it is possible to first reduce the size of the focused irradiation means and thus the apparatus.

  Further, according to this characteristic configuration, the band gap of the semiconductor constituting the emitter is selected to be 0.8 eV or more and 1.6 eV or less.

  The reason for selecting such a band gap material as the emitter material in the present application will be described with reference to FIGS.

FIG. 2 is a diagram showing the relationship between the band gap and the power generation output when the light collection rate of sunlight is 50 times, where the energy source depends only on sunlight (sunlight L (comparative example)). ) And the description) and the case of heat donation from the heating means (described as sunlight L + exhaust gas E). Here, as the former example, the power generation output when the heating means is not used is shown, and as the latter example, the power generation output when the environmental temperature of the emitter is set to 700K using the heating means is shown. The ambient temperature of the emitter is the ambient temperature where the emitter is located. And as mentioned above, since the energy of sunlight is given to the emitter by the focused irradiation means, in the latter example, the temperature of the emitter is 700 K or more. Therefore, the higher the environmental temperature, the higher the emitter temperature and the power generation output.
Here, as in the latter example, the reason for assuming that the ambient temperature of the emitter is 700K is that the heat source of the heating means for raising the ambient temperature of the emitter is, for example, about 650K to 750K discharged from an engine, a boiler, or the like. This is because combustion exhaust gas having a temperature is relatively easily available and the emitter can be heated using such exhaust heat.
Moreover, the temperature of an emitter can be heated to 650K or more by using such combustion exhaust gas of about 650K to 750K.

  FIG. 3 is a diagram showing the relationship between the band gap and the power generation output when the concentration ratio of sunlight is 10 times, and depends on only sunlight (described as sunlight L (comparative example)). And a case where heat is supplied from the heating means (described as sunlight L + exhaust gas E). Similarly to FIG. 2, the power generation output when the heating unit is not used is shown as the former example, and the power generation output when the environmental temperature of the emitter is 700 K using the heating unit is shown as the latter example.

  Referring to these results, in the case where the concentration ratio of sunlight is 10 times (FIG. 3), in any band gap to be studied, by receiving heat supply from the heating means, the sunlight alone It is possible to obtain a higher power output than when power is generated at Furthermore, in the case of sunlight alone, a relatively low power output of approximately the same level is obtained over a relatively wide band gap (0.75 eV to 2.0 eV).

  On the other hand, when heat is supplied from the heating means, there is a strong correlation between the power generation output and the band gap. Compared to the case of sunlight alone, the band gap near the middle of the wide band gap shown above. The region where the power generation output becomes high appears. The band gap region where the power generation output can be increased is approximately 0.8 eV to 1.6 eV.

In the case where the concentration ratio of sunlight is 50 times (FIG. 2), a specific bandgap that can obtain a higher power output than when performing power generation alone with sunlight by receiving heat supply from the heating means. Appears. Such a band gap is from 0.8 eV to 1.6 eV described so far.
Furthermore, in the study by the inventors, this tendency was maintained even when the concentration ratio of sunlight was increased to about 100 times.

Therefore, in a power generation apparatus equipped with a photothermal power generation element, the band gap range of the emitter constituent material is selected from 0.8 eV to 1.6 eV, so that the energy supply source is sunlight with a relatively low concentration rate. And a higher power output (power generation efficiency) than a configuration using only sunlight as an energy source as both an available heating source capable of heating the emitter temperature to 650 K or higher (heating means as referred to herein). Can do.
In addition, the heat source of the heating means is exhaust gas generated by burning fuel. Since the exhaust gas generated by the combustion of the fuel is usually at a temperature of 650K or higher, for example, the emitter can be heated to an appropriate temperature of 650K or higher using the exhaust gas generated by the operation of the engine or boiler as a heat source. .

In addition to the first feature configuration, the second feature configuration of the power generation device according to the present invention is:
The said condensing irradiation means condenses the said sunlight with the condensing rate in the range of 40 times or more and 60 times or less,
The heating means is that the temperature of the emitter is heated to 780K or more and 880K or less.

  According to the 2nd characteristic structure of the said power generator, since the condensing rate of sunlight is made into 40 times or more and 60 times or less (approximately 50 times), size reduction of a condensing irradiation means can be achieved. Moreover, since the heating means heats the temperature of the emitter to 750 K or more and 900 K or less, it is possible to give the emitter sufficient thermal energy and promote the emission of thermionic electrons from the emitter. As a result, the power generation output can be further increased. On the other hand, the temperature range from 750 K to 900 K is sufficiently lower than the melting point of a general semiconductor, so that it is possible to prevent the emitter from being overheated and improve the lifetime and operational stability of the emitter. .

The third characteristic configuration of the power generator according to the present invention is in addition to the first and second characteristic configurations described above,
The emitter is at least one selected from silicon Si, gallium arsenide GaAs, and indium phosphide InP.

According to the third characteristic configuration of the power generation device, silicon Si, gallium arsenide GaAs, and gallium antimony GaSb are all materials within the band gap range suitable for the present application. These materials can be used for the emitter.
Further, since silicon is inexpensive and strong, the emitter can be configured inexpensively and with high strength by using silicon as the emitter material. In addition, it can be used safely without toxicity. Since gallium arsenide is excellent in workability, an emitter can be easily formed. And since indium phosphide has high electron mobility, electron saturation speed, and electron concentration, it is possible to improve power generation output (power generation efficiency).

Schematic elevation showing a power generator according to the present invention The figure which shows the relationship between the band gap and power generation output when the light collection rate is 50 times The figure which shows the relationship between the band gap and the power generation output when the light collection rate is 10 times The figure which shows the relationship between the band gap and the emitter temperature when the light collection rate is 50 times

Hereinafter, an embodiment of a power generator according to the present invention will be described with reference to FIG.
As shown in FIG. 1, the power generation device S converts light energy and heat energy into electrical energy using thermoelectrons that move between an emitter 1 and a collector 2 that are opposed electrodes, and loads 5 Is provided with a photothermal power generation element 3 for supplying electric power.
And on the emitter side of the photothermal power generation element 3, a condensing lens 4 as a condensing irradiation means for condensing and irradiating the sunlight L on the emitter 1, and a high temperature toward the solar light receiving surface side of the emitter 1 A high-temperature exhaust gas discharge pipe 7 as a heating means for supplying the exhaust gas E is provided. Further, on the collector side of the photothermal power generation element 3, a cooling water passage 8 is provided as a heat exchanging portion capable of cooling the collector 2.

Hereinafter, each structure of the electric power generating apparatus S is demonstrated.
The condensing lens 4 as the condensing irradiation means is a convex lens made of resin or glass. The condensing lens 4 is capable of condensing the sunlight L at a condensing rate of 50 times, and is fixed to the sunlight incident side of the photothermal power generation element 3 by a fixing means (not shown).

  The photothermal power generation element 3 includes an emitter 1 that is photoexcited by light energy and is heated by heat energy, and a collector that captures the thermoelectrons that are spaced apart from the emitter 1 and are emitted from the emitter 1. 2. The emitter 1 and the collector 2 are disposed in the vacuum space V. Specifically, the emitter 1 is composed of one or more selected from silicon Si, gallium arsenide GaAs, and indium phosphide InP, and the collector 2 is composed of phosphorous-doped diamond, both of which are plate-shaped. Is formed. The emitter 1 includes a thermoelectron emission surface 1a that emits thermoelectrons, and the collector 2 includes a thermoelectron capture surface 2a that captures thermoelectrons emitted from the emitter 1, and the thermoelectron emission surface 1a and the thermoelectrons. It arrange | positions in the vacuum space V so that the capture surface 2a may become mutually parallel.

  Therefore, in this embodiment, in addition to the irradiation of the sunlight L to the emitter 1 by the condenser lens 4, the emitter 1 is heated by the high-temperature exhaust gas E discharged from the high-temperature exhaust gas discharge pipe 7 described later, thereby generating light energy and heat. In a state where energy is applied to the emitter 1, the thermal energy provided by the exhaust gas E effectively promotes the emission of thermoelectrons from the emitter 1, and a high output current can be obtained. In this regard, as described above with reference to FIGS. 2 and 3, for example, higher generated power is obtained than when only the sunlight L is collected by the condenser lens 4 and irradiated to the emitter 1. be able to.

  A load 5 is provided on the conducting wire portion 6 connected between the emitter 1 and the collector 2. The electric power output from the photothermal power generation element 3 is supplied to the load 5 through the conductor portion 6.

  Hereinafter, the thermal configuration of the power generation apparatus S will be described in more detail. A high-temperature exhaust gas discharge pipe 7 serving as a heating unit for heating the emitter 1 is provided on the sunlight receiving surface side of the emitter 1 of the photothermal power generation element 3. ing. Thereby, the exhaust gas E of 650 K or more is brought into contact with the emitter 1 to give thermal energy to the emitter 1, and the thermal electrons emitted from the emitter 1 can be increased. The high-temperature exhaust gas discharge pipe 7 discharges, for example, high-temperature exhaust gas E discharged from a gas engine (not shown) that uses city gas or the like as fuel toward the emitter 1.

  On the collector 2 side of the photothermal power generation element 3, a cooling water passage 8 is provided as a heat exchanging portion capable of cooling the collector 2. The cooling water passage 8 is provided on the non-emitter side of the collector 2, and the collector 2 is cooled by the cooling water W flowing through the cooling water passage 8. The cooling water W heated by cooling the collector 2 is supplied to a hot water supply means (not shown) and used effectively.

[Study of suitable band gap range]
Hereinafter, FIGS. 2 and 3 used in the description of the present application will be described.
These drawings are diagrams showing the relationship between the band gap [eV] of the constituent material constituting the emitter 1 and the power generation output P [W / m ² ]. 2 is assumed to be 50 times and FIG. 3 is assumed to be 10 times. Furthermore, the environmental temperature (actually the temperature of the exhaust gas E) on the sunlight receiving surface side of the emitter 1 is assumed to be 700K. On the other hand, the collector temperature was 500K.

  The equation used to determine the relationship between the band gap and the power generation output P (the power generation output P is obtained from the maximum output Pmax obtained according to the following procedure) is a so-called emitter energy balance equation shown below. (Formula (21) described in Non-Patent Document 1).

[Equation 1]
Pnet, c = Psun
-ΣT _C ⁴
-Exp ((E _{F, n} -E _{F, p} ) / KT _C -1) P _BB
+ J _A (φ _C +2 kT _A )
-J _C (φ _C +2 kT _C )
+ Q

  In this equation, each term represents the following contents. The following radiation from the emitter and radiation from the high-temperature radiation generator were regarded as black body radiation (black body radiation). The input energy from the collector to the emitter is energy that changes to heat when electrons emitted from the collector are collected by the emitter. The amount of waste heat is the amount of heat given to the emitter by the exhaust gas E.

[Equation 2]
Pnet, c: energy balance of the emitter pSUN: photon energy of sunlight oT _C ^4: black body radiation energy from emitter _{exp ((E F, n -E} F, p) / KT C -1) P BB
: Energy of electrons emitted by black body radiation J _A (φ _C +2 kT _A ): Input energy from collector to emitter J _C (φ _C +2 kT _C ): Output energy of emitter
E _{F, n} : Pseudo Fermi energy of electron E _{F, p} : Pseudo Fermi energy of hole P _BB : Energy of electron emitted by black body radiation J _A , J _C : Current density of collector and emitter φ _A , φ _C : work function of collector and emitter T _A : collector temperature T _C : emitter temperature Q: amount of waste heat

Hereinafter, a procedure for obtaining the maximum output Pmax of the power generation output using the above formula and using the band gap as a parameter by the inventor of the present application will be described.
Step 1 Assume a band gap Eg to be examined.
Step 2 Assume an electron affinity E_A to be examined.
Step 3 Using the band gap Eg and the electron affinity E_A assumed in Step 1 and Step 2, the number of photons (electrons) incident on the emitter, the number of emitted photons (electrons) + recombined photons Under the condition that the sum with the number of (electrons) becomes 0, the emitter energy balance Pnet, c is obtained using the emitter energy balance equation.

In this study, the concentration factor of sunlight energy is fixed because it is assumed to be 10 times, 50 times, and 100 times. Further, the pseudo-Fermi energy E _{F, n of} the electron, the emitter temperature T _C , the emitter current density J _C , and the pseudo-Fermi energy E _{F, p} of the hole are variable, the collector current density J _A , and the collector temperature T _A. Fixed.

Then,
Step 4 The emitter temperature T _C is changed within the set range, and the step 3 is repeated to obtain the emitter temperature T _{C at} which Pnet, c is minimized.
By executing step 4, the band gap Eg, the electron affinity E_A, and the emitter temperature T _{C in the} state under consideration are determined.

In this system, the photon energy Psun of sunlight input to the system, the current densities J _A and J _C of the collector and the emitter, and the work functions φ _A and φ _{C of the} collector and the emitter can be specified. Based on the following formula, the maximum output Pmax in the state under consideration is obtained by the following formula.

[Equation 3]
Pmax = (J _C −J _A ) × (φ _C −φ _A )

Less than,
Step 5 The electron affinity E_A is varied within the set range, and Steps 2 to 4 are repeated to obtain parameters (electron affinity E_A, emitter temperature T _C ) at which the power generation output indicates the maximum output.
The maximum output Pmax with the obtained parameters (electron affinity E_A, emitter temperature T _C ) was set as the power generation output P of the element in the band gap Eg to be studied.

  As a result of the examination under the above conditions with a light collection magnification of 50 times, within the band gap range (0.5 eV to 2 eV) to be studied, the temperature of the emitter 1 increases as the band gap increases as shown in FIG. It rose to about 770K-930K. Further, in the present application, within the range of 0.8 eV to 1.6 eV, which is a preferable band gap range of the emitter 1, the voltage rises from about 780K to 880K. On the other hand, the electron affinity E_A was 0.8 eV when the band gap was less than 0.75 eV, and 0.7 eV when the band gap was 0.75 eV or more.

  In this application, silicon Si in the range of 0.8 eV to 1.6 eV, which is a preferable emitter 1 band gap range, has an emitter temperature of 806 K and an electron affinity because the band gap is 1.12 eV. Was optimized at 0.7 eV.

In this case, an example of numerical values of the terms and parameters in the above equation is as follows. The energy balance Pnet, c of the emitter is −47 W / m ² , the photon energy Psun of sunlight is 45,099 W / m ² , and the black from the emitter. The body radiation energy σT _C ⁴ is 23929 W / m ² , the electron energy exp ((E _{F, n} −E _{F, p} ) / KT _C −1) P _BB is 2264 W / m ² , the collector from the input energy to the emitter _{J a (φ C + 2kT a} ) is 461W / m ^2, the emitter of the output energy _{J C (φ C + 2kT C} ) is 32938W / m ^2, the amount of heat Q of the exhaust heat from the 13614 W / m ² Become.
Furthermore, the pseudo-Fermi energy E _{F, n} of electrons is 0.5973 eV, the pseudo-Fermi energy E _{F, p} of holes is 0.1049 eV, and the energy P _BB of electrons emitted by black body radiation is 1.9786 W / m ^2. The collector current density J _A is 265.3457 _A / m ² , the emitter current density J _C is 1.7799 A / m ² , the collector work function φ _A is 0.9 eV, and the emitter work function φ _C is 1.71 eV.

Further, when GaAs is used for the emitter 1, the band gap is 1.42 eV, so that the emitter temperature is 849K and the electron affinity is optimized at 0.7 eV.
Therefore, power can be generated efficiently in this state.

[Another embodiment]
Finally, another embodiment of the present invention will be described. Note that the configuration of each embodiment described below is not limited to being applied independently, and can be applied in combination with the configuration of other embodiments as long as no contradiction occurs.

(A) In the above embodiment, the high-temperature exhaust gas E discharged from the gas engine is discharged toward the emitter 1 from the high-temperature exhaust gas discharge pipe 7, but not limited to this, the high-temperature exhaust gas E discharged from the boiler is discharged. You may comprise so that it may discharge toward the emitter 1. FIG. Furthermore, it is good also as a structure which heats the emitter 1 using the combustion exhaust heat of gas in a gas burner, a gas water heater, or a gas stove, and the exhaust heat of a fuel cell.

(B) In the said embodiment, although the sunlight L was condensed by using the condensing lens 4 as the convex condensing lens 4, not only this but the condensing lens 4 is comprised by the planar or concave mirror surface body. The reflecting plate may be configured to reflect the sunlight L and collect it on the emitter 1.

  As described above, it is possible to provide a power generation device that can obtain predetermined power while reducing the size of the device.

DESCRIPTION OF SYMBOLS 1 Emitter 2 Collector 3 Photothermal power generation element 4 Condensing lens (Condensing irradiation means)
7 High-temperature exhaust gas discharge pipe (heating means)
8 Cooling water passage L Solar S Power generator

Claims (3)

A power generation device that includes a photothermal power generation element having an emitter that emits electrons upon receiving light and heat, and a collector that captures electrons emitted from the emitter, and generates power between the emitter and the collector,
Condensing irradiation means for condensing sunlight at a concentration ratio of 10 to 100 times and irradiating the emitter;
Heating means for heating the temperature of the emitter to 650 K or higher,
The band gap of the semiconductor constituting the emitter is selected from 0.8 eV to 1.6 eV ,
A power generation apparatus in which a heat source of the heating means is exhaust gas generated by burning fuel . The said condensing irradiation means condenses the said sunlight with the condensing rate in the range of 40 times or more and 60 times or less,
The power generation device according to claim 1, wherein the heating unit heats the temperature of the emitter to 780 K or more and 880 K or less.   The power generator according to claim 1 or 2, wherein the emitter is at least one selected from silicon Si, gallium arsenide GaAs, and indium phosphide InP.

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