This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2012-250618 Nov. 14, 2012; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a solar power generator.
A problem with a solar cell is that a power generation efficiency decreases with a rise in a cell temperature.
In particular, since the cell temperature rises during the daytime in summer, when an electric power demand is the highest, there have been several proposals made to improve the power generation efficiency by cooling the cell temperature.
Therefore, as a method of decreasing the cell temperature, there has been known a method of absorbing heat of the cell by a latent heat storage material. The cell temperature becomes very high in a region where an amount of solar radiation is high and an outside air temperature is high, and heat storage from the cell to the heat storage material progresses in a short period of time, whereby the heat storage material may be completely melted during the daytime and may reach a temperature equal to or higher than a melting point thereof. In such a case, there was a problem in that latent heat of solidification is released from the heat storage material to the cell over a long period of time during a process where the temperature of the heat storage material decreases from the temperature equal to or higher than the melting point to a temperature equal to or lower than the melting point, and the temperature of the solar cell is kept high in the evening before sunset, whereby the amount of power generation is decreased.
A solar power generator of an embodiment includes: a solar cell module having a solar cell, and a heat storage material filled unit configured to house a heat storage material disposed so as to thermally contact a back surface side of the solar cell, and a nucleating unit configured to release supercooling of the heat storage material; and a controller configured to control the nucleating unit.
Embodiments will be described below with reference to the drawings.
Hereinafter, embodiments will be exemplified with reference to the drawings. Note that detailed descriptions common to the embodiments will be omitted as appropriate. Also note that daytime, evening, and night below are expressions according to an amount of solar radiation under a clear sky, and are not expressions for limiting a period of time.
The glass plate 1 is a plate serving as a protection layer of a surface of the solar cell 2. A low reflectivity glass plate is preferable as the glass plate 1.
The solar cell 2 generates power by converting sunlight, which enters through the glass plate 1, into electricity. The solar cell module 10 is provided with a plurality of solar cells 2, and each of the solar cells 2 is electrically connected with each other. A photoelectric conversion element of the solar cells 2 is net particularly limited. Various photoelectric conversion elements such as a silicon type, a compound type, an organic type, a quantum dot type, and a multi-junction type may be used.
The sealing material 3 seals the solar cells 2 and attaches the solar cells 2 to the glass plate 1. As the sealing material 3, EVA (polyethylene vinyl acetate) and the like may be used, for example. In
The heat exchanger plate 4 is formed on a back surface side of the solar cells 2. The heat exchanger plate 4 is a member that efficiently transmits the heat from the solar cells 2 to the heat storage material 6 inside the heat storage material filled unit 5. As the heat exchanger plate 4, a metal plate or a resin sheet may be used. The hear exchanger plate 4 may function as an adhesive layer for adhering the sealing material 3 and the heat storage material filled unit 5. It is also possible to omit it in a case where it is replaceable by the sealing material 3.
The heat storage material filled unit 5 is formed so as to thermally contact the back surface side of the solar cells 2. The heat storage material filled unit 5 includes a heat storage material 6 and a nucleating unit 7 therein. A housing of the heat storage material filled unit 5 may be a resin container, a metal container, a metal-resin compound container, or a bag having a film made of any of these materials. It is preferable that a member capable of following a volume change of the heat storage material 6 accompanied by solidification and melting thereof be used as the heat storage material filled unit 5.
The heat storage material 6 collects, stores, and releases the heat from the solar cells 2. It is preferable that a latent heat storage material having a melting point thereof in a range between an ordinary temperature (20°C.) and 100°C. and having a supercooling state be used. The latent heat storage material having the supercooling is a material that does not solidify by once heating in a the temperature of equal or higher than the melting point and cooling in a temperature of lower than the melting point and existing in a liquid phase in a room temperature (20°C.) which is lower than the melting point. As the latent heat storage material having the supercooling, a sodium sulfate hydrate, a sodium acetate hydrate, an erythritol, and the like may be used. These heat storage materials have a melting point in a range between 30 and 90°C., and also have a supercooling state in about 20°C. which is a lower temperature than the melting point.
The nucleating unit 7 partially contacts with the heat storage material 6, and functions to solidify (crystallize) the heat storage material 6 in a supercooled state. A specific nucleating method used may be a method of inserting two electrodes and applying a voltage between the electrodes, a method of moving a plate spring by an actuator in a configuration including the plate spring having a recess and a projection and the actuator, and a method of applying a voltage to a thermoelectric element for local rapid cooling, a method of nucleating by inputting a crystal nucleus from a crystal nucleus housing container, and the like.
The controller 8 is connected to the solar cells 2 through a wiring L1 and to the nucleating unit 7 through a wiring L2. The controller 8 has an electronic circuit including an integrated circuit, and is controlled by hardware or software. An operation condition of the nucleating unit 7 is memorized in the controller 8. Electric power generated by the solar cells 2 is transmitted to the controller 8 through the wiring L1. Accordingly, the controller 8 measures an amount of electric power generated by a cell. Furthermore, an operation instruction of the nucleating unit 7 is transmitted from the controller 8 to the nucleating unit 7 through the wiring L2. The controller 8 may be included inside the solar cell module 10 or may be included inside a device outside the solar cell module 10 such as a power conditioner and the like.
Furthermore, by installing the heat exchanger plate 4, the heat storage material filled unit 5, the heat storage material 6, and the nucleating unit 7 according to the embodiment on a back surface of an existing solar cell module, it is possible to modify the existing solar cell module to be a solar cell module or a solar power generator according to the embodiment.
Next, an operation of the solar power generator (solar power generation system) according to the embodiment is described. The operation of the solar power generator according to the embodiment is controlled by the above-described controller 8.
In the flowchart in
During the daytime (from morning to late afternoon), which is a period of time when the amount of solar radiation is large, the solar cell 2 generates power and absorbs solar heat, whereby the temperature thereof rises. Since the heat storage material 6 is thermally in contact with the solar cells 2, the heat from the solar cells 2 is stored in the heat storage material 6 due to a difference in temperatures between the solar cells 2 and the heat storage material 6. Accordingly, a rise in the temperature of the solar cells 2 is suppressed, whereby it is possible to suppress a decrease in the amount of power generation accompanied by the rise in the temperature of the solar cells 2. With the time, absorption of heat from the solar cells 2 to the heat storage material 6 progresses, and when the heat storage material 6 reaches the melting point or above, the heat storage material 6 melts from solid to liquid (in the daytime domain and with a large amount of solar radiation).
Then, the temperature of the solar cells 2 decreases as the amount of solar radiation decreases when it nears the sunset and the like. At this time, even if the temperature of the heat storage material 6 reaches the melting point thereof or below, the heat storage material 6 keeps the supercooling. Therefore, a temperature of the heat storage material 6, without being kept at the melting point, decreases without releasing the latent heat of solidification. Therefore, since there is no release of heat from the heat storage material 6, the temperature of the solar cells 2 decreases, and it is possible to suppress the decrease in the amount of power generation with the temperature (in the evening domain with a low amount of solar radiation).
During nighttime, since there is no solar radiation from the sun, the temperature of the solar cells 2 further decreases, and nears an atmospheric temperature. Therefore, an hour during which the amount of power generation drops below a predetermined set electric power value is determined as the nighttime, whereby the supercooled heat storage material 6 is nucleated, and the heat is radiated at the time when the amount of power generation drops below a lower limit electric power value (in the nighttime domain with no solar radiation). Since there is almost no power generation during the nighttime, the amount of power generation is not decreased even as a result of the rise in the temperature accompanied by radiation of heat. On the other hand, by radiating the latent heat of the heat storage material 6 during the nighttime, even in a case where the heat storage material 6 exceeds the melting point in the evening, the latent heat is not released in a process in which the temperature equal to or lower than the melting point decreases, whereby it is possible to decrease the temperature of the solar cell 2.
In the first embodiment, the amount of power generated by a solar cells 2 is measured, and the nucleating signal is operated based on the value; however, in this embodiment, it is possible to operate the nucleating signal by measuring the nighttime, during which a power generation period (daytime and evening) ends, based on the time. A measured time is the time of a clock incorporated in a controller 8 or the time obtained by the controller 8 from an outside device.
First, the controller 8 measures the time (time detecting: Step S010). Then, the measured time (detected time) and a predetermined set time are compared to perform determination (Step S011). Then, in a case where the measured time is the same as or has passed the predetermined set time, a nucleating signal is given to a nucleating unit through a wiring L2 (from. Step S011 to Step S012). Accordingly, a heat storage material 6, which has stored heat and is kept in a supercooled state, is crystallized, and latent heat is released. In this method, by setting the set time to nighttime, it is possible to cause the heat storage material 6 to nucleate and to radiate heat during the nighttime. In a case where the measured time is before the predetermined set time, the time is measured again (Step S011).
The heat storage material filled unit 50 has a plurality of areas (the heat storage material filled units 50a to 50d) divided by the partition walls 90 (90ab, 90bc, 90cd). In respective areas, the heat storage materials (60a to 60d) are filled, and the nucleating units (70a to 70d) are installed. Respective areas of the heat storage material filled units 50a to 50d are separated such that the heat storage materials (60a to 60d) do not get mixed. The partition wall 90 includes a material same as the heat storage material filled unit 50. Furthermore, each of the areas 50a to 50d may be a separate container housing the heat storage material 60 and may be connected in parallel.
In
The nucleating units 70a to 70d are connected to the controller 8 through a wiring L20. Accordingly, an operation instruction of the nucleating units 70a to 70d is transmitted from the controller 8 to each of the nucleating units 70a to 70d through the wiring L20.
Then, a method of operating the solar power generator 200 is described.
In the flowchart in
The heat storage material 60, when it reaches a melting point thereof or above, changes from solid to liquid; however, since there is a difference in density between the solid and the liquid, the solid tends to precipitate at the bottom in the gravity direction. In a case where the solar cell module 20 tilts at θ, if the heat storage material filled units 50a to 50d are communicated, the solid heat storage material 60 precipitates in a direction from 50d to 50a, and the solid heat storage material 60 is accumulated in the area 50a. In this case, in the area 50a, the heat storage material 60 is melted and becomes a high-temperature liquid, and a cell temperature of an adjacent part rises. Then, the solid heat storage material 60 remains without being melted in the area 50a, whereby the latent heat is released without supercooling. Therefore, in this embodiment, the heat storage material filled unit 50 is divided into 50a to 50d by using the partition wall 90 connecting the under surface and the upper surface of the heat storage material filled unit 50. The partition wall 90 is formed in a direction to prevent the heat storage material 60 from moving in the gravity direction. Since the heat storage materials 60 including 60a to 60d are separated from each other, the heat storage material 60d in the solid state in the above-described area 50d never moves into the area 50a. Therefore, during both daytime and evening, the heat storage material 60 of each area (50a to 50d) can uniformly cool the solar cell 2, whereby the amount of power generation can be improved.
Furthermore, it is also possible to put the heat storage materials 60a to 60d having different melting points in the heat storage material filled units 50a to 50d. The above-described problem can be further suppressed by using a latent heat storage material having a high melting point as the heat storage material 60d and by using a latent heat storage material having a low melting point as 60a.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
Number | Date | Country | Kind |
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2012-250618 | Nov 2012 | JP | national |