Solar light heat collection system

Abstract

A solar light heat collection system 1 comprises: a solar light heat collection panel 2 which has a non-heat insulation part 2c for performing convection heat transfer with ambient air, and transmits radiation heat from solar light and convection heat from the ambient air to a heat medium M; a heat medium circulation line 4 which sends the heat medium M from a heat medium tank 3 for storing the heat medium M to the solar light heat collection panel 2, and sends the heat medium M from the solar light heat collection panel 2 to the heat medium tank 3; a heat medium circulation control mechanism 5 which performs at least one of switching of the circulation availability of the heat medium M along the heat medium circulation line 4 and adjustment of the flow rate of the heat medium M; and a control device 9. The control device 9 measures the quantity Q1 of radiation heat input to the solar light heat collection panel 2, measures the quantity Q2 of convection heat transfer between the solar light heat collection panel 2 and the ambient air, and controls the heat medium circulation control mechanism 5 on the basis of the radiation heat input quantity Q1 and the convection heat transfer quantity Q2.

Description

Solar heat collection system

[0001] The present disclosure relates to solar thermal collection systems.

[0002] Patent Literature 1 discloses a solar heat collection control device that supplies a heat medium from a heat storage tank to a heat collection unit, heats the heat medium with solar heat in the heat collection unit, and returns the heat medium from the heat collection unit to the heat storage tank. The device switches on or off a pump that circulates the heat medium according to temperature conditions inside the device, such as the heat collection unit and the heat storage tank. For example, the pump operates when the temperature of the heat collection unit is higher than the temperature of the heat storage tank by a predetermined temperature or more, and when the temperature of the heat medium return pipe is higher than the temperature of the heat storage tank by a predetermined temperature or more.

[0003] Japanese Unexamined Patent Publication No. 58-102062

[0004] In conventional solar heat collection systems such as those described above, emphasis is placed on transferring radiant heat from sunlight to a heat medium in the panel-shaped heat collection unit, and it is believed that there is room for improvement in the amount of heat acquired in the heat collection unit.

[0005] The present disclosure addresses the problem of improving the amount of heat captured by solar thermal collection panels.

[0006] One aspect of the present disclosure provides a solar thermal collection system comprising: a solar thermal collection panel having a hollow section for circulating a heat medium, a light-receiving section for receiving sunlight, and a non-insulated section for performing convective heat transfer between the solar thermal collection panel and the ambient air, and transferring radiant heat from the sunlight and convective heat from the ambient air to the heat medium; a heat medium tank for storing the heat medium; a heat medium circulation line for sending the heat medium from the heat medium tank to the solar thermal collection panel and from the solar thermal collection panel to the heat medium tank; a heat medium circulation control mechanism for at least one of switching whether or not the heat medium is allowed to flow along the heat medium circulation line and adjusting the flow rate of the heat medium; and a control device, wherein the control device measures the amount of radiant heat input to the solar thermal collection panel, measures the amount of convective heat transfer between the solar thermal collection panel and the ambient air, and controls the heat medium circulation control mechanism based on the amount of radiant heat input and the amount of convective heat transfer.

[0007] Generally, solar thermal collection panels have been designed with an insulated structure to prevent convective heat transfer between the panel and the surrounding air. In contrast, the above-described configuration actively includes non-insulated sections that are expected to allow convective heat transfer between the panel and the surrounding air. This allows the solar thermal collection panel to transfer not only radiant heat from sunlight but also convective heat from the surrounding air to the heat medium, increasing the amount of heat captured by the solar thermal collection panel. Furthermore, the switching between allowing and not allowing the heat medium to flow and the amount of heat medium flow are adjusted based on the amount of radiant heat input and the amount of convective heat transfer. This optimizes heat recovery using the heat medium.

[0008] When the convective heat is transferred from the solar thermal collection panel to the surrounding air, the convective heat transfer amount becomes negative, and the control device may control the heat medium flow control mechanism to stop the supply of the heat medium to the solar thermal collection panel when the convective heat transfer amount is negative and the radiant heat input amount is less than the absolute value of the convective heat transfer amount.

[0009] Here, if a non-insulated section is provided in the solar thermal collection panel to capture convective heat from the ambient air, it is conceivable that the convective heat may escape from the solar thermal collection panel into the ambient air depending on the situation. In contrast, with the above configuration, the supply of the heat medium is stopped when the amount of convective heat transferred from the solar thermal collection panel to the ambient air exceeds the amount of radiant heat input received by the solar thermal collection panel. This prevents the temperature of the heat medium from dropping, and optimizes heat recovery by the heat medium.

[0010] The control device may control the heat medium flow control mechanism so that the heat medium is supplied to the solar thermal collection panel when the convective heat transfer amount is negative and the radiant heat input amount is greater than or equal to the absolute value of the convective heat transfer amount.

[0011] According to the above configuration, when the amount of convective heat transferred from the solar thermal collection panel to the surrounding air is less than the amount of radiant heat input to the solar thermal collection panel, the heat medium circulates. Therefore, the heat medium can be heated by the amount of heat acquired by the solar thermal collection panel.

[0012] The control device may control the heat medium flow control mechanism so that the heat medium is supplied to the solar thermal collecting panel when the amount of convective heat transfer is positive.

[0013] According to the above configuration, when convection heat enters the solar heat collecting panel from the surrounding air, the heat medium circulates, and therefore the heat medium can be heated by the amount of heat acquired by the solar heat collecting panel.

[0014] The solar heat collecting system may further include a pyranometer that measures global solar radiation, and the control device may measure the radiant heat input as heat quantity per unit time based on the global solar radiation measured by the pyranometer and the surface area of ​​the light receiving unit.

[0015] According to the above configuration, the amount of radiant heat input can be successively measured as the amount of heat per unit time based on the measurement results of the amount of global solar radiation, which can change from moment to moment. This allows the flow of the heat transfer medium to be switched on or off or the flow rate of the heat transfer medium to be adjusted based on the amount of radiant heat input. This improves the ability to follow environmental changes such as fluctuations in cloud cover, and makes it easier to optimize heat recovery using the heat transfer medium.

[0016] The solar thermal collection system may further include an outside air temperature sensor that measures the temperature of the air surrounding the solar thermal collection panel, and a panel temperature sensor that measures the temperature on the solar thermal collection panel side, and the control device may measure the convective heat transfer amount as heat quantity per unit time based on the difference between the temperatures measured by the outside air temperature sensor and the panel temperature sensor, the outer surface area of ​​the non-insulated portion, and the convective heat transfer coefficient of the non-insulated portion.

[0017] With this configuration, the convective heat transfer rate can be measured sequentially as the heat quantity per unit time based on the measurement results of the temperature difference, which can change from moment to moment. This convective heat transfer rate is used to switch whether the heat transfer medium is allowed to flow or to adjust the flow rate of the heat transfer medium. This improves the ability to follow environmental changes such as temperature fluctuations, making it easier to optimize heat recovery using the heat transfer medium.

[0018] The panel temperature sensor may be composed of at least one of a surface temperature sensor that measures the surface temperature of the non-insulated portion, an inlet temperature sensor that measures the temperature near the entrance of the hollow portion, and an outlet temperature sensor that measures the temperature near the exit of the hollow portion.

[0019] According to the above configuration, the panel temperature can be measured with high accuracy.

[0020] The heat medium tank may include a first heat medium tank and a second heat medium tank separate from the first heat medium tank, and the heat medium circulation line may include an inlet line that sends the heat medium from the first heat medium tank to the hollow portion, and an outlet line that sends the heat medium from the hollow portion to the second heat medium tank.

[0021] According to the above configuration, the temperature of the heat medium supplied to the solar heat collecting panel during the heat collection time can be kept lower than the temperature of the solar heat collecting panel, and a large temperature difference can be maintained, so the amount of heat transferred from the solar heat collecting panel to the heat medium can be kept high, and as a result, the amount of heat stored in the second tank obtained by the solar heat collecting panel can be increased.

[0022] The heat medium circulation line may further include a return line branching from the outflow line and returning the heat medium to the first heat medium tank, and the heat medium flow control mechanism may include a direction switching mechanism that switches between a state in which the heat medium is sent to the second heat medium tank via the outflow line and a state in which the heat medium is returned to the first heat medium tank via the return line.

[0023] In the above configuration, when the heat medium returns from the first heat medium tank via the solar thermal collection panel to the first heat medium tank, the heat medium temperature in the first heat medium tank can be increased, and a high-temperature heat medium can be obtained. Also, when the heat medium is sent from the first heat medium tank via the solar thermal collection panel to the second heat medium tank, the heat medium temperature cannot be made higher than when the heat medium is returned to the first heat medium tank, but the amount of heat collected can be maximized.

[0024] The heat transfer medium tank may be a stratified type having an outlet at the bottom and an inlet at the top, and the heat transfer medium circulation line may include an inlet line connecting the outlet of the heat transfer medium tank to the hollow portion, and an outlet line connecting the hollow portion to the inlet of the heat transfer medium tank.

[0025] According to the above configuration, the amount of heat collected can be maintained high without increasing the number of heat medium tanks.

[0026] According to the present disclosure, the amount of heat captured by a solar thermal collection panel can be improved.

[0027] 1 is a schematic diagram showing the overall configuration of a solar thermal collecting system according to a first embodiment. A perspective view of a solar thermal collecting panel. An exploded perspective view of a solar thermal collecting panel. A cross-sectional view of a solar thermal collecting panel. A schematic diagram showing a main part of a solar thermal collecting system according to a first embodiment. A flowchart showing processing executed by a control device. A graph showing changes over time in the amount of radiant heat input, outside air temperature, and panel temperature. A schematic diagram of a solar thermal collecting system according to a second embodiment. A schematic diagram of a solar thermal collecting system according to a third embodiment. A schematic diagram of a solar thermal collecting system according to a fourth embodiment.

[0028] Hereinafter, embodiments will be described with reference to the drawings. Note that the same or corresponding elements are designated by the same reference numerals throughout the drawings, and detailed descriptions thereof will be omitted.

[0029] First Embodiment Referring to FIG. 1 , a solar heat collecting system 1 according to a first embodiment includes a solar heat collecting panel 2 , a heat medium tank 3 , a heat medium circulation line 4 , and a heat medium flow control mechanism 5 .

[0030] The solar thermal collecting panel 2 is in the form of a flat plate and forms a flow path through which a liquid-phase heat medium M flows. The heat medium tank 3 stores the heat medium M. The heat medium M is, for example, water. However, a liquid other than water may be used as the heat medium M, such as an antifreeze solution containing ethylene glycol as a main component.

[0031] In this embodiment, there is only one heat medium tank 3. The heat medium circulation line 4 includes an inflow line 4a that sends the heat medium M from the heat medium tank 3 to the solar thermal collection panel 2, and an outflow line 4b that sends the heat medium M from the solar thermal collection panel 2 to the heat medium tank 3.

[0032] The heat medium tank 3 has a thermal insulation structure, and can control the temperature of the heat medium M in the heat medium tank 3 at a required temperature regardless of the ambient temperature. The inlet line 4a and the outlet line 4b are made of piping members such as metal or resin pipes. The piping members may also have a thermal insulation structure.

[0033] The heat medium flow control mechanism 5 at least performs one of switching whether or not the heat medium M flows along the heat medium circulation line 4, and adjusting the flow rate of the heat medium M along the heat medium circulation line 4. In this embodiment, the heat medium flow control mechanism 5 is configured to be able to perform both switching and adjustment.

[0034] The heat medium flow control mechanism 5 may include a pump 5a that pumps the heat medium M along the heat medium circulation line 4, and a valve 5b that is disposed on the heat medium circulation line 4. In the illustrated example, the pump 5a and the valve 5b are disposed on the inlet line 4a, but the pump 5a may be provided inside the heat medium tank 3, and the valve 5b may be disposed on the outlet line 4b.

[0035] In this embodiment, as an example, the pump 5a is a fixed displacement type, and the valve 5b is a flow control valve. Switching between allowing and not allowing the heat medium M to flow is achieved by switching the pump 5a between an operating state and a stopped state. Adjustment of the flow rate of the heat medium M is achieved by adjusting the opening degree of the valve 5b. However, this is just one example, and if the valve 5b is an on-off valve, switching between the open state and the closed state of the valve 5b can switch between allowing and not allowing the heat medium M to flow. If the pump 5a is a variable displacement type, adjusting the capacity of the pump 5a can adjust the discharge rate of the heat medium M, and therefore the flow rate.

[0036] The heat medium M is pressure-fed by a pump 5a from the heat medium tank 3 through the inflow line 4a to the solar thermal collection panel 2. As the heat medium M flows through the inside of the solar thermal collection panel 2, it is heated by the heat collected in the solar thermal collection panel 2. When the heat medium M flows out of the solar thermal collection panel 2, it is sent to the heat medium tank 3 through the outflow line 4b. As a result, hot water is stored in the heat medium tank 3.

[0037] 2A to 2C, the structure of the solar thermal collection panel 2 will be described. The solar thermal collection panel 2 has a panel body 11, a first header 12, a second header 13, an inlet 14, and an outlet 15.

[0038] The panel body 11 is made of an extruded aluminum alloy material. As the aluminum alloy, 1000 series aluminum alloys having excellent thermal conductivity or 6000 series aluminum alloys having excellent thermal conductivity and strength are suitable.

[0039] The panel body 11 has a first main wall 11a, a second main wall 11b, and a pair of side walls 11c. The first main wall 11a, the second main wall 11b, and the pair of side walls 11c form a long, wide, and low-profile rectangular tube with both longitudinal ends open. This longitudinal direction corresponds to the extrusion direction. The first main wall 11a is a rectangular flat plate. The long side extends in the longitudinal direction of the panel body 11, the short side extends in the width direction of the panel body 11, and the thickness direction corresponds to the height direction of the panel body 11. The pair of side walls 11c are erected from both side edges of the first main wall 11a. The second main wall 11b is a flat plate of the same shape as the first main wall 11a, is arranged parallel to the first main wall 11a, and completely overlaps the first main wall 11a when viewed in the thickness direction, connecting the ends of the pair of side walls 11c. These four walls define a wide, low rectangular opening at each longitudinal end.

[0040] The panel body 11 has a plurality of partition walls 11d. The partition walls 11d extend between and parallel to the pair of side walls 11c and connect the inner surfaces of the first main wall 11a and the second main wall 11b. The partition walls 11d divide the space surrounded by the four walls into a plurality of hollow portions 2a aligned in the width direction.

[0041] In the illustrated example, there are six partition walls 11d and seven hollow portions 2a, one more than the six, but the number of hollow portions 2a can be changed as needed. Each hollow portion 2a has a rectangular cross-section. Using extrusion molding, such a structure having multiple closed cross-sections or multiple hollow portions 2a can be manufactured continuously and integrally. In the illustrated example, the first main wall 11a, the second main wall 11b, and the pair of side walls 11c are flat. However, as long as they have hollow portions inside, they may not be flat and may have irregularities. Multiple protrusions (fins) may be provided on at least one surface of the first main wall 11a, the second main wall 11b, and the pair of side walls 11c. Providing irregularities or fins increases the light-receiving area and the contact area with air, thereby increasing the amount of radiant heat input and convective heat transfer.

[0042] Each hollow portion 2a is open at both ends in the longitudinal direction. The first header 12 closes the opening at one end of the hollow portion 2a. The second header 13 closes the opening at the other end of the hollow portion 2a. Both the first header 12 and the second header 13 close the openings of multiple hollow portions 2a together.

[0043] The first header 12 has a cover plate 12a, a peripheral wall 12b extending from the periphery of the cover plate 12a, and an internal space 12c surrounded by the cover plate 12a and the peripheral wall 12b. The internal space 12c is open on the side opposite the cover plate 12a. The cross section of the internal space 12c (the cross section of the inner peripheral surface of the peripheral wall 12b) has the same shape (rectangular in this embodiment) as the cross section of the outer peripheral surface of the panel body 11. The first header 12 abuts against one end of the panel body 11 and is joined to the panel body 11 in a liquid-tight manner.

[0044] The second header 13 has a cover plate 13 a, a peripheral wall 13 b, and an internal space 13 c, similar to the first header 12, and is attached to the other end of the panel body 11 in the longitudinal direction, similar to the first header 12.

[0045] The inlet 14 and the outlet 15 are provided in the first header 12 or the second header 13. The inlet 14 is connected to the inlet line 4a (see FIGS. 1 and 3), and the outlet 15 is connected to the outlet line 4b (see FIGS. 1 and 3). The inlet 14 is cylindrical or nipple-shaped, and the inlet line 4a, which serves as a piping member, is attached to the inlet 14 in a liquid-tight manner. The same applies to the outlet 15 and the outlet line 4b.

[0046] In this embodiment, a single inlet 14 is provided in the first header 12, and a single outlet 15 is provided in the second header 13. The inlet 14 and the outlet 15 penetrate the corresponding cover plates 12a, 13a. The heat transfer medium M flows into the internal space 12c of the first header 12 via the inlet 14 and then branches off from the internal space 12c into each of the multiple hollow portions 2a. The heat transfer medium M flows from each of the multiple hollow portions 2a to join together in the internal space 13c of the second header 13 and then flows out of the internal space 13c via the outlet 15.

[0047] In this way, the heat medium M flows in one direction, from one side to the other in the longitudinal direction, through the solar thermal collecting panel 2. The heat medium M flows through the hollow portion 2a while filling the hollow portion 2a, that is, while being in contact with the wall and its inner surface of the panel body 11 that defines the hollow portion 2a.

[0048] 3, the solar thermal collection panel 2 has a light-receiving portion 2b that receives sunlight. The solar thermal collection panel 2 transfers radiant heat from sunlight to a heat medium M. The solar thermal collection panel 2 also positively has a non-insulated portion 2c that is expected to allow convective heat transfer to occur between the solar thermal collection panel 2 and the ambient air. When convective heat is transferred from the ambient air to the solar thermal collection panel 2, the solar thermal collection panel 2 transfers the convective heat to the heat medium M. The radiant heat and convective heat are transferred to the heat medium M by solid-state heat transfer in the panel body 11, thereby warming the heat medium M.

[0049] The amount of heat Q acquired by the solar thermal collecting panel 2 per unit time can be defined as the sum of the amount of radiant heat input Q1 and the amount of convective heat transfer Q2 (Q = Q1 + Q2). The temperature of the heat medium M rises from the inlet 14 to the outlet 15 by an amount corresponding to the amount of heat acquired Q and the flow rate of the heat medium M.

[0050] The "amount of radiant heat input Q1" can be defined as the amount of radiant heat (W) input by sunlight to the solar heat collecting panel 2 (particularly its light receiving portion 2b) per unit time. The amount of radiant heat input Q1 is expressed by the following formula (1).

[0051] Q1 = αWsunAsun (1) where α is the emissivity (dimensionless) of the surface of the solar heat collecting panel 2, more specifically, the emissivity of the light receiving part 2b. Wsun is the global solar radiation (W / m 2 ) A sun is the light receiving area of ​​the solar heat collecting panel 2 (m 2 ), more specifically, the surface area of ​​the light receiving portion 2b (hereinafter simply referred to as the light receiving area Asun).

[0052] The light receiving portion 2b is all or part of the outer surfaces of the first main wall 11a, the second main wall 11b, the pair of side walls 11c, the first header 12, and the second header 13. The surface of the light receiving portion 2b is painted black. This makes the emissivity α of the light receiving portion 2b close to 1, improving the heat collection ratio of the solar thermal collecting panel 2. The emissivity of aluminum alloy is 10 -2 From 10 -1 Since this is an order of magnitude, the effect of painting is significant when the panel body 11 is made of an aluminum alloy. The heat collection ratio is a dimensionless value obtained by dividing the heat energy per unit area acquired through sunlight by the total solar radiation Wsun, and the closer the ratio is to 1, the higher the heat collection efficiency.

[0053] The "amount of convective heat transfer Q2" can be defined as the amount (W) of convective heat exchanged between the ambient air and the solar thermal collecting panel 2 (particularly, the non-insulated portion 2c thereof) per unit time. The amount of convective heat transfer Q2 is expressed by the following formula (2).

[0054] Q2 = μ (Tair - Tp) Ap (2) where μ is the convection heat transfer coefficient of the solar heat collecting panel 2 (W / K m 2 ), more specifically, the convection heat transfer coefficient of the non-insulated portion 2c. Tair is the temperature (K) of the air around the solar thermal collecting panel 2 (hereinafter referred to as the outside air temperature Tair). Tp is the temperature (K) on the solar thermal collecting panel 2 side (hereinafter referred to as the panel temperature Tp). Ap is the outer surface area (m2 ), more specifically, the outer surface area of ​​the non-insulated portion 2c (hereinafter simply referred to as the outer surface area Ap).

[0055] The heat medium M contacts the inner surfaces of the walls that define the hollow portion 2a. Substantially the entire inner surfaces of the first main wall 11a, the second main wall 11b, the pair of side walls 11c, the first header 12, and the second header 13 contact the heat medium M, and substantially the entire outer surfaces thereof contact the ambient air. In this embodiment, no heat insulating material is provided on these inner surfaces, nor on their outer surfaces. Therefore, substantially the entire four walls and headers 12 and 13 that constitute the panel body 11 can serve as the non-insulated portion 2c.

[0056] As shown in the above formula (2), the convective heat transfer amount Q2 is proportional to the temperature difference between the outside air temperature Tair and the panel temperature Tp. When the outside air temperature Tair exceeds the panel temperature Tp, the convective heat transfer amount Q2 is positive. Convective heat is transferred from the ambient air to the solar thermal collecting panel 2 (particularly, its non-insulated portion 2c). Conversely, when the panel temperature Tp exceeds the outside air temperature Tair, the convective heat transfer amount Q2 is negative. Convective heat is transferred from the solar thermal collecting panel 2 (particularly, its non-insulated portion 2c) to the ambient air.

[0057] The emissivity α, light-receiving area A sun, convective heat transfer coefficient μ, and outer surface area A p are determined according to the design specifications of the solar thermal collecting panel 2. These parameters can be treated as constants during the design and practical stages of the solar thermal collecting panel 2. On the other hand, the global solar radiation W sun, outside air temperature T air, and panel temperature T p change from moment to moment. When calculating the amount of radiant heat input Q1 and the amount of convective heat transfer Q2, it is necessary to measure these parameters in real time.

[0058] Returning to Fig. 1, the solar heat collecting system 1 further includes a pyranometer 6, an outside air temperature sensor 7, and a panel temperature sensor 8. The pyranometer 6 is installed near the light receiving unit 2b and measures the global solar radiation Wsun. The outside air temperature sensor 7 is installed outside the solar heat collecting panel 2 and near the solar heat collecting panel 2 and measures or detects the outside air temperature Tair. The panel temperature sensor 8 is installed on the surface of or inside the solar heat collecting panel 2 and measures or detects the panel temperature Tp.

[0059] The panel temperature sensor 8 is composed of at least one of a surface temperature sensor 8a, an inlet temperature sensor 8b, and an outlet temperature sensor 8c. The surface temperature sensor 8a measures the surface temperature of the solar thermal collecting panel 2 (hereinafter referred to as the surface temperature Tsf), in particular the temperature of the outer surface of the non-insulated portion 2c. The inlet temperature sensor 8b measures the temperature near the inlet 14 of the heat medium M of the solar thermal collecting panel 2 (hereinafter referred to as the inlet temperature Tin). The outlet temperature sensor 8c measures the temperature near the outlet 15 of the heat medium M of the solar thermal collecting panel 2 (hereinafter referred to as the outlet temperature Tout). The inlet temperature Tin may be the temperature of the inner surface of the solar thermal collecting panel 2 near the inlet 14, or may be the temperature of the heat medium M flowing near the inlet 14. The same applies to the outlet temperature Tout.

[0060] Any one of the surface temperature Tsf, the inlet temperature Tin, and the outlet temperature Tout may be treated as the panel temperature Tp. The panel temperature Tp may also be an average value of two or more temperatures among the surface temperature Tsf, the inlet temperature Tin, and the outlet temperature Tout. The surface temperature Tsf may be measured at multiple measurement points on one solar collecting panel 2. In this case, the average value of the measurement results of the multiple surface temperatures Tsf may be treated as a single measurement result of the surface temperature Tsf.

[0061] The solar heat collecting system 1 further includes a control device 9. The control device 9 is connected to the pyranometer 6, the outside air temperature sensor 7, and the panel temperature sensor 8, and sequentially acquires the measurement results of these measurement elements at a predetermined sampling period. The control device 9 is connected to the heat medium flow control mechanism 5, and controls the heat medium flow control mechanism 5 based on the measurement results. In other words, the control device 9 controls whether the heat medium M flows along the heat medium circulation line 4, or controls the flow rate of the heat medium M along the heat medium circulation line 4, based on the measurement results.

[0062] The control device 9 includes, for example, a central processing unit (CPU) or a microprocessing unit (MPU) that cooperates with software to implement predetermined functions. The control device 9 may be configured with hardware circuits, such as dedicated electronic circuits or reconfigurable electronic circuits, designed to implement the predetermined functions, or may be configured with various semiconductor integrated circuits. Examples of various semiconductor integrated circuits include a CPU, an MPU, a microcomputer, a digital signal processor (DSP), a field programmable gate array (FPGA), and an application specific integrated circuit (ASIC). The control device 9 may also include storage devices such as random access memory (RAM) and read-only memory (ROM). Specifically, the control device 9 may be configured with, for example, an information processing device such as a desktop personal computer, a laptop computer, a workstation, or a tablet terminal, or a printed circuit board with equivalent functions.

[0063] The storage device of the control device 9 stores programs and information for executing the processes described below. Examples of information pre-stored in the storage device include the emissivity α, the light-receiving area A, the convective heat transfer coefficient μ, and the outer surface area A.

[0064] 4 shows a flow of processing executed by the control device 9. The control device 9 repeatedly executes processing according to the flow shown in the figure at predetermined control intervals.

[0065] The control device 9 acquires the measurement results of the global solar radiation Wsun output from the pyranometer 6, the outside air temperature Tair output from the outside air temperature sensor 7, and the panel temperature Tp output from the panel temperature sensor 8 (step S1). As described above, the panel temperature Tp may be the surface temperature Tsf itself, the inlet temperature Tin itself, or the outlet temperature Tout itself, or may be calculated based on a plurality of these temperatures. The control device 9 may set the acquired measurement result as the panel temperature Tp, or may arithmetically use the panel temperature Tp as the measurement result from the acquired plurality of measurement results.

[0066] Next, the control device 9 calculates the amount of radiant heat input Q1 according to the above formula (1) (step S2). The factors in formula (1), ie, the emissivity α and the light receiving area A sun , can be read from the storage device.

[0067] The control device 9 also calculates the convective heat transfer quantity Q2 based on the temperature difference between the measured outside air temperature Tair and the panel temperature Tp according to the above formula (2) (step S2). The convective heat transfer coefficient μ and the outer surface area Ap, which are factors in formula (2), can be read from the storage device.

[0068] Next, the control device 9 determines whether the measured convective heat transfer quantity Q2 is 0 or positive (step S3a). If the convective heat transfer quantity Q2 is negative (S3a: NO), the control device 9 determines whether the absolute value of the radiant heat input quantity Q1 is equal to or greater than the absolute value of the convective heat transfer quantity Q2 (step S3b).

[0069] If the convective heat transfer quantity Q2 is 0 or positive (S3a: YES), the control device 9 controls the heat medium flow control mechanism 5 to continue the flow of the heat medium M (step S4). If the convective heat transfer quantity Q2 is negative (S3a: NO) and the absolute value of the radiant heat input quantity Q1 is equal to or greater than the absolute value of the convective heat transfer quantity Q2 (S3b: YES), the process also proceeds to step S4. To continue the flow of the heat medium M, the control device 9, for example, continues the operation of the pump 5a and maintains the opening of the valve 5b at a predetermined opening or greater.

[0070] If the convective heat transfer quantity Q2 is negative (S3a: NO) and the absolute value of the radiant heat input quantity Q1 is less than the absolute value of the convective heat transfer quantity Q2 (S3b: NO), the control device 9 controls the heat medium flow control mechanism 5 to stop the flow of the heat medium M (step S5). To stop the flow of the heat medium M, the control device 9, for example, stops the pump 5a and fully closes the valve 5b.

[0071] Here, the radiant heat input Q1 is proportional to the global solar radiation Wsun. Since the global solar radiation Wsun cannot be negative, the radiant heat input Q1 is also zero or positive. If the convective heat transfer Q2 is zero or positive (S3a: YES), the acquired heat Q is zero or positive. Even if the convective heat transfer Q2 is negative, if the absolute value of the convective heat transfer Q2 is lower than the radiant heat input Q1 (or its absolute value) (S3b: YES), the acquired heat Q is positive. Thus, if the acquired heat Q is zero or positive, the flow of the heat medium M continues (step S4).

[0072] On the other hand, if the convection heat transfer quantity Q2 is negative and the absolute value of the convection heat transfer quantity Q2 exceeds the radiant heat input quantity Q1 (or its absolute value) (S3b: NO), the acquired heat quantity Q is negative. In this case, if the heat medium M passes through the solar thermal collecting panel 2, there is a risk that the temperature of the heat medium M will drop. If the acquired heat quantity Q is negative, the flow of the heat medium M is stopped (step S5), thereby preventing the temperature of the heat medium M from dropping.

[0073] Figure 5 shows the changes over time in the amount of radiant heat input Q1, the outside air temperature Tair, and the panel temperature Tp on a clear, sunny day from before sunrise to after sunset. The horizontal axis represents time, and the vertical axis represents the amount of heat (W) or temperature (K) per unit time on an arbitrary scale.

[0074] The amount of radiant heat input Q1 is proportional to the amount of global solar radiation Wsun. Therefore, although not shown in the figure, the amount of global solar radiation Wsun changes over time in the same manner as the amount of radiant heat input Q1. The amount of convective heat transfer Q2 depends on the temperature difference between the outside air temperature Tair and the panel temperature Tp. Therefore, the greater the temperature difference (the difference in the vertical axis coordinate between the outside air temperature Tair and the panel temperature Tp at the same time), the greater the absolute value of the amount of convective heat transfer Q2. When the outside air temperature Tair is higher than the panel temperature Tp (see the hatched area hatched downward to the right), the amount of convective heat transfer Q2 is positive. When the outside air temperature Tair is lower than the panel temperature Tp (see the hatched area hatched upward to the right), the amount of convective heat transfer Q2 is negative.

[0075] The radiant heat input Q1 and the global solar radiation Wsun reach their maximum values ​​at the time of meridian and change linearly symmetrically around the time of meridian. This is because the example is based on a day with clear skies all day, and the radiant heat input Q1 and the global solar radiation Wsun can change in a complex manner depending on the amount of cloud cover.

[0076] The outdoor air temperature Tair also fluctuates in the same way as the global solar radiation Wsun, reaching a maximum value near the time of meridian. In contrast, the panel temperature Tp reaches a maximum value at a time later than the time of meridian. After sunrise, the panel temperature Tp rises toward the maximum value, but continues to fluctuate at a temperature lower than the outdoor air temperature Tair. At time t1 during the rise toward the maximum value, the panel temperature Tp exceeds the outdoor air temperature Tair. Time t1 is around the time of meridian. After reaching the maximum value, the panel temperature Tp decreases while remaining higher than the outdoor air temperature Tair.

[0077] In the time period before time t1, the convective heat transfer quantity Q2 is positive, so the heat medium M flows and the temperature of the heat medium M in the heat medium tank 3 rises. At time t1, the convective heat transfer quantity Q2 changes from positive to negative. Immediately after time t1, the temperature difference is small and the absolute value of the convective heat transfer quantity Q2 is small. On the other hand, since time t1 is near noon, sufficient solar radiation is obtained. The radiant heat input quantity Q1 greatly exceeds the absolute value of the convective heat transfer quantity Q2, and the acquired heat quantity Q becomes positive. Therefore, even if the convective heat transfer quantity Q2 changes to negative, the heat medium M continues to flow and the acquired heat quantity Q continues to be recovered by the heat medium M.

[0078] After that, the temperature difference continues to widen until near the time when the panel temperature Tp reaches its maximum value. As sunset approaches, the temperature difference does not narrow, and the global solar radiation Wsun and therefore the radiant heat input Q1 decrease significantly. At time t2, when the radiant heat input Q1 reaches the absolute value of the convective heat transfer Q2, the heat gain Q changes from positive to negative. At time t2, the flow of the heat medium M stops, preventing a drop in the temperature of the heat medium M from time t2 onwards.

[0079] According to the solar thermal collecting system 1 of this embodiment, the solar thermal collecting panel 2 actively has a non-insulated portion 2c that is expected to cause convective heat transfer with the surrounding air. Therefore, in the solar thermal collecting panel 2, not only radiant heat from sunlight but also convective heat from the surrounding air can be transferred to the heat medium M, and the amount of heat acquired Q in the solar thermal collecting panel 2 increases. Furthermore, switching whether or not to allow the heat medium M to circulate or adjusting the flow rate of the heat medium M is performed based on the amount of radiant heat input Q1 and the amount of convective heat transfer Q2. Therefore, heat recovery by the heat medium M is optimized.

[0080] Specifically, when the convective heat transfer amount Q2 is negative and the radiant heat input amount Q1 is less than the absolute value of the convective heat transfer amount Q2, the control device 9 controls the heat medium flow control mechanism 5 to stop the supply of the heat medium M to the solar thermal collection panel 2. As a result, the supply of the heat medium is stopped when the convective heat transfer amount Q2 going out from the solar thermal collection panel 2 to the ambient air exceeds the radiant heat input amount Q1 received by the solar thermal collection panel 2. In other words, when the acquired heat amount Q is negative, the supply of the heat medium M is stopped, and therefore it is possible to prevent the temperature of the heat medium M from decreasing in the solar thermal collection panel 2.

[0081] Conversely, even if the convection heat transfer quantity Q2 is negative, if the radiant heat input quantity Q1 is equal to or greater than the absolute value of the convection heat transfer quantity Q2, the control device 9 controls the heat medium flow control mechanism 5 so that the heat medium M is supplied to the solar thermal collecting panel 2. As a result, if the acquired heat quantity Q is positive, the acquired heat quantity can be recovered by the heat medium M.

[0082] The amount of radiant heat input Q1 is measured sequentially as the amount of heat per unit time based on the measurement results of the global solar radiation Wsun, which can change from moment to moment. The amount of convective heat transfer Q2 is also measured sequentially as the amount of heat per unit time based on the measurement results of the temperature difference between the outside air temperature Tair and the panel temperature Tp, which can change from moment to moment. Based on the amount of radiant heat input Q1 and the amount of convective heat transfer Q2, the amount of heat acquired Q is also evaluated as the amount of heat per unit time. This improves the ability of the control to follow environmental changes, and optimizes heat recovery by the heat transfer medium M. For example, the pump 5a can be immediately stopped in response to a sudden increase in cloud cover or a rise in outside temperature to prevent heat loss from the heat transfer medium M.

[0083] Returning to Fig. 1 , the heat thus recovered by the heat medium M may be used in an agricultural greenhouse 90. The agricultural greenhouse 90 is a suitable application example of the solar heat collecting system 1 according to this embodiment.

[0084] The agricultural greenhouse 90 is constructed on a substantially horizontal rectangular site. The agricultural greenhouse 90 has a framework 91 formed from steel or extruded aluminum. The entire framework 91 is covered with an exterior skin (not shown) formed from a light-transmitting material (e.g., polyvinyl chloride). This protects the interior of the agricultural greenhouse 90 from wind and rain. The framework 91 includes columns 91a erected at the four corners and the center of the site, girders and beams 91b horizontally extending from the upper ends of the columns 91a, and a roof 91c provided on the girders and beams 91b. The roof shape is not particularly limited and may be, for example, gabled or arched. Within the agricultural greenhouse 90, plants 99 are planted in a medium 98. The plants 99 are preferably agricultural crops. The medium 98 is a growth medium for the plants 99 and is appropriately selected from soil, rock wool, nutrient solution, etc., taking into consideration compatibility with the plants 99 to be cultivated.

[0085] The solar heat collection system 1 is used to assist the growth of plants 99. The temperature of the culture medium 98 and the plants 99 may be adjusted using heat recovered by the heat medium M. In this case, the solar heat collection panel 2 is preferably installed directly below the roof 91c of the agricultural greenhouse 90 (inside the agricultural greenhouse 90) with the light receiving portion 2b facing south. Since the roof is transparent and the air inside the agricultural greenhouse 90 is heated by sunlight, the solar heat collection panel 2 can collect not only radiant heat input from sunlight passing through the transparent roof but also convective heat transfer from the heated air inside the agricultural greenhouse 90. By placing the heat medium tank 3 inside the agricultural greenhouse 90, an insulating effect can be expected from the air inside the agricultural greenhouse 90. Note that the heat medium tank 3 may be placed outside the agricultural greenhouse 90, but in that case, the tank structure must have higher insulating properties than when it is placed inside the agricultural greenhouse 90. A similar effect can be obtained by installing the solar heat collecting panel 2 on the roof or wall of a building such as a building, and it is expected that radiant heat and convective heat from the building structure heated by sunlight can be collected.

[0086] Second Embodiment Next, a solar heat collecting system 1 according to a second embodiment will be described with reference to FIG. 6, focusing on the differences from the first embodiment.

[0087] In this embodiment, the heat medium tank 3 includes a first heat medium tank 3a and a second heat medium tank 3b that is separate from the first heat medium tank 3a. The inflow line 4a connects the first heat medium tank 3a to the inlet of the solar thermal collection panel 2, and sends the heat medium M from the first heat medium tank 3a to the hollow portion 2a. The outflow line 4b connects the outlet of the solar thermal collection panel 2 to the second heat medium tank 3b, and sends the heat medium M from the hollow portion 2a to the second heat medium tank 3b.

[0088] In this case, the heat medium M after heat recovery is stored in the second heat medium tank 3b, so the heat medium M in the first heat medium tank 3a is maintained at a low temperature. This allows the panel temperature Tp to be maintained at a low temperature, and the amount of convective heat transfer Q2 to be maintained at a high positive value. Therefore, the amount of heat Q acquired by the solar thermal collecting panel 2 can be increased.

[0089] Third Embodiment Next, a solar heat collecting system 1 according to a third embodiment will be described with reference to FIG. 7, focusing on the differences from the second embodiment.

[0090] In this embodiment, the heat medium tank 3 also includes a first heat medium tank 3a and a second heat medium tank 3b that is separate from the first heat medium tank 3a. The heat medium circulation line 4 includes an inlet line 4a and an outlet line 4b, as in the second embodiment. The heat medium circulation line 4 further includes a return line 4c that branches off from the outlet line 4b and returns the heat medium M to the first heat medium tank 3a.

[0091] The heat medium flow control mechanism 5 includes a three-way valve 5c provided at the branch point of the return line 4c from the outflow line 4b. The three-way valve 5c is an example of a direction switching mechanism that switches the direction in which the heat medium M is sent. The three-way valve 5c switches between a state in which the heat medium M flowing out from the solar thermal collecting panel 2 is sent to the second heat medium tank 3b via the outflow line 4b, and a state in which the heat medium M flowing out from the solar thermal collecting panel 2 is returned to the first heat medium tank 3a via the return line 4c. The three-way valve 5c is an electromagnetic valve, and is connected to the control device 9. The switching of the state of the three-way valve 5c is controlled by the control device 9. Here, if the value of the heat acquisition Q (= Q1 + Q2) calculated by the control device 9 is greater than a reference value set by the user, the heat medium M is returned to the first heat medium tank 3a to become a high-temperature heat medium, and if it is smaller than the reference value, the heat medium M is sent to the second heat medium tank 3b to maximize the amount of heat collected, and the control device 9 controls the switching of the three-way valve 5c.

[0092] According to this embodiment, it is possible to switch between a state in which the temperature of the heat medium M supplied to the solar heat collecting panel 2 is kept low and a state in which the heat medium M is kept warm, depending on the situation.

[0093] Fourth Embodiment Next, with reference to FIG. 8 , a solar heat collecting system 1 according to a fourth embodiment will be described, focusing on the differences from the first embodiment.

[0094] In this embodiment, the heat medium tank 3 is single, as in the first embodiment. However, the heat medium tank 3 is a stratified type. That is, the heat medium tank 3 has an outlet at the bottom and an inlet at the top. A relatively low-temperature heat medium M is stored at the bottom, and a relatively high-temperature heat medium after heat recovery is stored at the top. No active convection occurs within the heat medium tank 3, so the same heat medium M with different temperatures is stored in two layers. An inflow line 4a connects the outlet of the heat medium tank 3 to the inlet of the solar thermal collection panel. An outflow line 4b connects the outlet of the solar thermal collection panel 2 to the inlet of the heat medium tank 3.

[0095] According to this embodiment, the convective heat transfer amount Q2 can be maintained at a high positive value in the same way as in the second embodiment without increasing the number of tanks, and the heat acquisition amount Q of the solar heat collecting panel 2 can be increased.

[0096] (Modifications) Although the embodiments have been described above, the above configurations can be modified as appropriate within the scope of the present invention.

[0097] The panel body 11 of the solar thermal collecting panel 2 is not limited to an extruded aluminum alloy material, and may be manufactured using other materials and manufacturing methods. For example, the panel body 11 may be formed by overlapping two aluminum plates. In this case, a groove is formed in at least one of the plates. The groove is closed by the other plate, thereby forming a hollow portion. Steel or copper may also be used as a material other than aluminum.

[0098] There may be provided a plurality of solar thermal collecting panels 2. In this case, the inflow line 4a connects the heat medium tank 3 to a plurality of inlets in parallel, and the outflow line 4b connects the heat medium tank 3 to a plurality of outlets in parallel.

[0099] The control device 80 may control the heat medium flow control mechanism 5 to adjust the flow rate of the heat medium M based on the acquired heat amount Q.

[0100] The solar heat collecting system 1 can be applied to uses other than the agricultural greenhouse 90. For example, it may be installed in a structure such as a building or a house, and used to generate hot water to be used in the structure.

[0101] The present disclosure may include the following aspects: (Aspect 1) A solar thermal collection system comprising: a solar thermal collection panel having a hollow section for circulating a heat medium, a light receiving section for receiving sunlight, and a non-insulated section for convective heat transfer between the solar thermal collection panel and ambient air, and transferring radiant heat from the sunlight and convective heat from the ambient air to the heat medium, a heat medium tank for storing the heat medium, a heat medium circulation line for sending the heat medium from the heat medium tank to the solar thermal collection panel and from the solar thermal collection panel to the heat medium tank, a heat medium circulation control mechanism for at least one of switching whether or not the heat medium is allowed to flow along the heat medium circulation line and adjusting a flow rate of the heat medium, and a control device, wherein the control device measures an amount of radiant heat input to the solar thermal collection panel, measures an amount of convective heat transfer between the solar thermal collection panel and the ambient air, and controls the heat medium circulation control mechanism based on the amount of radiant heat input and the amount of convective heat transfer. (Aspect 2) The solar thermal collecting system according to Aspect 1, wherein the amount of convective heat transfer becomes negative when the convective heat is transferred from the solar thermal collecting panel to the ambient air, and the control device controls the heat medium flow control mechanism to stop the supply of the heat medium to the solar thermal collecting panel when the amount of convective heat transfer is negative and the amount of radiant heat input is less than the absolute value of the amount of convective heat transfer. (Aspect 3) The solar thermal collecting system according to Aspect 1 or 2, wherein the control device controls the heat medium flow control mechanism to supply the heat medium to the solar thermal collecting panel when the amount of convective heat transfer is negative and the amount of radiant heat input is equal to or greater than the absolute value of the amount of convective heat transfer. (Aspect 4) The solar thermal collecting system according to any of Aspects 1 to 3, wherein the control device controls the heat medium flow control mechanism to supply the heat medium to the solar thermal collecting panel when the amount of convective heat transfer is positive. (Aspect 5) The solar heat collecting system according to any one of Aspects 1 to 4, further comprising a pyranometer that measures global solar radiation, wherein the control device measures the amount of radiant heat input as heat quantity per unit time based on the global solar radiation measured by the pyranometer and a surface area of ​​the light receiving portion.(Aspect 6) The solar thermal collecting system according to any one of Aspects 1 to 5, further comprising: an outside air temperature sensor that measures the temperature of the air surrounding the solar thermal collecting panel; and a panel temperature sensor that measures the temperature on the solar thermal collecting panel side, wherein the control device measures the amount of convective heat transfer as a heat quantity per unit time based on a difference between the temperatures measured by the outside air temperature sensor and the panel temperature sensor, an outer surface area of ​​the non-insulated portion, and a convective heat transfer coefficient of the non-insulated portion. (Aspect 7) The solar thermal collecting system according to Aspect 6, wherein the panel temperature sensor is constituted by at least one of a surface temperature sensor that measures a surface temperature of the non-insulated portion, an inlet temperature sensor that measures a temperature near an inlet of the hollow portion, and an outlet temperature sensor that measures a temperature near an outlet of the hollow portion. (Aspect 8) The solar thermal collecting system according to any one of Aspects 1 to 7, wherein the heat medium tank includes a first heat medium tank and a second heat medium tank separate from the first heat medium tank, and the heat medium circulation line includes an inlet line that sends the heat medium from the first heat medium tank to the hollow portion, and an outlet line that sends the heat medium from the hollow portion to the second heat medium tank. (Aspect 9) The solar thermal collecting system according to Aspect 8, wherein the heat medium circulation line further includes a return line that branches off from the outflow line and returns the heat medium to the first heat medium tank, and the heat medium flow control mechanism includes a direction switching mechanism that switches between a state in which the heat medium is sent to the second heat medium tank via the outflow line and a state in which the heat medium is returned to the first heat medium tank via the return line. (Aspect 10) The solar heat collecting system according to any one of Aspects 1 to 7, wherein the heat medium tank is a stratified type having an outlet provided at the bottom and an inlet provided at the top, and the heat medium circulation line includes an inlet line connecting the outlet of the heat medium tank to the hollow portion, and an outlet line connecting the hollow portion to the inlet of the heat medium tank.

[0102] This application claims priority from Japanese Patent Application No. 2023-188416, filed November 2, 2023. Japanese Patent Application No. 2023-188416 is incorporated herein by reference.

[0103] REFERENCE SIGNS LIST 1 Solar heat collecting system 2 Solar heat collecting panel 2a Hollow portion 2b Light receiving portion 2c Non-insulated portion 3 Heat medium tank 3a First heat medium tank 3b Second heat medium tank 4 Heat medium circulation line 4a Inlet line 4b Outlet line 4c Return line 5 Heat medium flow control mechanism 5a Pump 5b Valve 5c Three-way valve 6 Pyranometer 7 Outdoor air temperature sensor 8 Panel temperature sensor 8a Surface temperature sensor 8b Inlet temperature sensor 8c Outlet temperature sensor 9 Control device 11 Panel body 11a First main wall 11b Second main wall 11c Side wall 11d Partition wall 12 First header 13 Second header 12a, 13a Cover plate 12b, 13b Peripheral wall 12c, 13c Internal space 14 Inlet 15 Outlet 90 Agricultural house 91 Frame 91a Column 91b Beam 91c Roof 98 Culture medium 99 Plant Ap External surface area Asun Light-receiving area M Heat medium Q1 Radiant heat input Q2 Convective heat transfer Tair Outside air temperature Tp Panel temperature Tin Inlet temperature Tout Outlet temperature Tsf Surface temperature Wsun Total solar radiation α Emissivity μ Convective heat transfer coefficient

Claims

1. A solar thermal collection system comprising: a solar thermal collection panel having a hollow section for circulating a heat medium, a light receiving section for receiving sunlight, and a non-insulated section for performing convective heat transfer between the solar thermal collection panel and the surrounding air, and which transfers radiant heat from the sunlight and convective heat from the surrounding air to the heat medium; a heat medium tank for storing the heat medium; a heat medium circulation line for sending the heat medium from the heat medium tank to the solar thermal collection panel and from the solar thermal collection panel to the heat medium tank; a heat medium circulation control mechanism for at least one of switching whether or not the heat medium can flow along the heat medium circulation line and adjusting the flow rate of the heat medium; and a control device, wherein the control device measures the amount of radiant heat input to the solar thermal collection panel, measures the amount of convective heat transfer between the solar thermal collection panel and the surrounding air, and controls the heat medium circulation control mechanism based on the amount of radiant heat input and the amount of convective heat transfer.

2. The solar thermal collection system of claim 1, wherein the amount of convective heat transfer becomes negative when the convective heat is transferred from the solar thermal collection panel to the surrounding air, and the control device controls the heat medium flow control mechanism to stop the supply of the heat medium to the solar thermal collection panel when the amount of convective heat transfer is negative and the amount of radiant heat input is less than the absolute value of the amount of convective heat transfer.

3. The solar thermal collection system described in claim 2, wherein the control device controls the heat medium flow control mechanism so that the heat medium is supplied to the solar thermal collection panel when the convective heat transfer amount is negative and the radiant heat input amount is equal to or greater than the absolute value of the convective heat transfer amount.

4. The solar heat collecting system according to claim 2, wherein the control device controls the heat medium flow control mechanism so that the heat medium is supplied to the solar heat collecting panel when the amount of convective heat transfer is positive.

5. A solar heat collecting system as described in any one of claims 1 to 4, further comprising a pyranometer for measuring total solar radiation, wherein the control device measures the amount of radiant heat input as heat quantity per unit time based on the total solar radiation measured by the pyranometer and the surface area of ​​the light receiving part.

6. A solar thermal collection system as described in any one of claims 1 to 4, further comprising an outside air temperature sensor that measures the temperature of the air surrounding the solar thermal collection panel, and a panel temperature sensor that measures the temperature on the solar thermal collection panel side, wherein the control device measures the convective heat transfer amount as heat quantity per unit time based on the difference in the temperatures measured by the outside air temperature sensor and the panel temperature sensor, respectively, the outer surface area of ​​the non-insulated part, and the convective heat transfer coefficient of the non-insulated part.

7. The solar heat collecting system described in claim 6, wherein the panel temperature sensor is composed of at least one of a surface temperature sensor that measures the surface temperature of the non-insulated portion, an inlet temperature sensor that measures the temperature near the inlet of the hollow portion, and an outlet temperature sensor that measures the temperature near the outlet of the hollow portion.

8. A solar thermal collection system as described in any one of claims 1 to 4, wherein the heat medium tank includes a first heat medium tank and a second heat medium tank separate from the first heat medium tank, and the heat medium circulation line includes an inlet line for transporting the heat medium from the first heat medium tank to the hollow portion, and an outlet line for transporting the heat medium from the hollow portion to the second heat medium tank.

9. The solar thermal collecting system described in claim 8, wherein the heat medium circulation line further includes a return line branching off from the outflow line and returning the heat medium to the first heat medium tank, and the heat medium flow control mechanism includes a direction switching mechanism that switches between a state in which the heat medium is sent to the second heat medium tank via the outflow line and a state in which the heat medium is returned to the first heat medium tank via the return line.

10. A solar thermal collecting system as described in any one of claims 1 to 4, wherein the heat medium tank is a stratified type having an outlet at the bottom and an inlet at the top, and the heat medium circulation line includes an inlet line connecting the outlet of the heat medium tank to the hollow portion, and an outlet line connecting the hollow portion to the inlet of the heat medium tank.

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