HK1166650A1 - Solar thermal collector - Google Patents

Description

Solar heat collector

Technical Field

The present invention relates to solar thermal technology, in particular to a plant designed for converting solar energy into thermal energy and which can be used for heating water, in particular residential or industrial water.

Background

A solar collector is known which consists of a body in the form of a water tank with light-transmitting (transparent) glass and a light-absorbing coating (see for example document RU 2 '108' 520).

Such collectors have the following disadvantages: the water is heated by the sunlight passing through the light absorbing coating, but lacks heat storage capacity.

Also known in the prior art are solar collectors constituted by an insulating body with a cover comprising a light-transmitting glass and a corrugated inner wall. The region between the bottom of the body and the corrugated inner wall is filled with a heat storage material in the form of a phase change material (e.g. paraffin). Water is supplied to the thermal energy collector by a flow heat exchanger, e.g. a heating coil, in order to exchange thermal energy with the thermal storage material (see e.g. documents RU 2 '230' 263 and CN 101285622).

Referring to fig. 7, a heat collector according to the prior art includes the following important features: the heat-insulating and heat-absorbing heat-preserving solar water heater comprises a heat-insulating main body 1, a flow type heat exchanger 5 (used for heating water), light-transmitting glass 2, a selective light-absorbing material 4, a heat accumulator 3 in the form of a phase-change material, a liquid supply pipeline 6 for water flow circulation and a heat-conducting element.

However, in the above-described conventional solar collector, the thermal energy R is first absorbed by the water. When there is excessive sunlight, the excess energy heats and melts the phase change material (regenerator 3), i.e. thermal energy is accumulated. When there is no sunlight, water is heated by the thermal energy radiated when the phase change material is crystallized.

According to another embodiment, the solar energy R is first absorbed by the selectively light absorbing material, which then transfers the thermal energy to the phase change material. The metal ribs inside the collector can transition the heat energy from the phase change material to water, which enhances heat transfer.

In addition, thermal storage materials (e.g., paraffin wax) do not have the ability to retain thermal energy over time and lose thermal energy through heat transfer, convection, and dissipation.

It must also be noted that the volume of the water tank is calculated on the basis of the condition that the water collected in the water tank is not allowed to overheat, i.e. the water cannot be heated to 100 ℃ or above. In other words, the volume of the water tank is calculated with the maximum value (introduction intensity index) of the energy received by the heater from the heat source in consideration of the actual specific heat of water and the maximum allowable temperature of 100 ℃.

One example of solar collector calculations follows. For maximum daily solar energy insulation 17MJ/m²The capacity (capacity) of the collector is equal to: 17,000,000J/4190J/kg/K/80g x K ═ 50.75l/m²。

This means that if the efficiency of the solar collector is 100%, one square meter will be sufficient to heat 50.75l of water to 80 ℃. Thus, the water tank must hold at least 50.75l of water for each square meter of absorption surface of the solar collector. In practice, however, the efficiency of the solar collector is not more than 40-70%. Thus, having 2m²The absorption surface area of the solar collector of (2) requires at least 71.5l of thermal storage tank.

To attract buyers, the volume is typically increased to 100-. The results are obvious: a larger volume of water in the tank requires more heat; thus, either the water is not heated to the desired temperature or an additional heat source (e.g., a gas heater or an electric heater) is required. On the other hand, even under the highest conditions (hot sunny days), when the water is heated only by the sunlight to reach the required temperature, the user cannot use this volume of heated water efficiently, because the hot water is discharged from the collecting heater by displacing an equal volume of cold water, i.e. the hot water is mixed with the cold water. Thus, discharging only 30l of water heated to 58 ℃ from a 100l collector and replacing it with tap water at 20 ℃ results in a temperature drop to 46.6 ℃. The next 30l use resulted in a temperature drop to 42 ℃.

To eliminate this drawback, manufacturers have adopted various structural arrangements, such as filling layer by layer, installing additional tanks inside the main tank (to achieve convective heat transfer), and so on.

However, they all have common disadvantages: during the heating process, heat is accumulated as the internal energy of the material increases (heating the water). In other words, the energy accumulation is linearly dependent on the temperature of the material.

In addition to this major drawback, the collectors according to the prior art also suffer from the precipitation of insoluble salts from water, since the conditions inside the water heater favour the growth of crystals, creating serious bacterial problems: colonies of harmful bacteria develop in warm places, porous deposits on the walls thereof, and the like.

Moreover, these precipitates are responsible for a significant decrease in heat exchange efficiency: as energy consumption increases, efficiency decreases. The water in the tank may overheat if the tank is not drained regularly. This can lead to increased pressure in the water tank and the main heat carrier supply line, which often causes malfunctions. These general problems of storage heaters are eliminated only by changing their structure primarily.

Disclosure of Invention

Technical problem

The object of the present invention is to provide a novel solar collector which avoids the above-mentioned disadvantages.

More particularly, the present invention aims to improve the design of flow solar collectors to reduce heat loss during heat storage and water heating, thereby improving the utilization of solar energy.

Solution to the problem

This object is achieved by a solar collector according to the appended claim 1.

Advantageously but optionally, the invention comprises at least one of the following features:

at least one surface of the regenerator is coated with a selectively light-absorbing material,

the thermal storage material comprises a solution of sodium acetate (acetate trihydrate) in distilled water with a gelling agent,

-the gelling agent comprises a solution of carboxymethylcellulose (CMC) and/or a solution of polyvinylpyrrolidone (PVP) and/or a solution of sodium laureth sulfate and/or carrageenan,

the thermal storage material comprises a coating of a high coefficient of thermal expansion material,

the high coefficient of thermal expansion material comprises paraffin.

Advantageous effects of the invention

The invention is essentially based on the combination of a salt solution based on hydrogel and gelling agents as phase change material with stacked, thermally conductive, stamped metal sheets in order to construct a heat exchanger device.

The solar collector according to the invention ensures the following characteristics:

firstly, the surface of the regenerator absorbs sunlight with high efficiency, which results in more thermal energy being transferred to the phase change material;

secondly, it improves the convective heat transfer between the regenerator and the flow heat exchanger element.

As a result, heat loss is reduced, and a high-efficiency heat collector can be realized.

Drawings

Fig. 1a shows a schematic overview of a solar collector according to an embodiment of the invention;

fig. 1b shows a lateral cross-section of the solar collector of fig. 1 a;

fig. 2a and 2b show the internal structure of a solar collector according to a particular embodiment of the invention;

figures 3a, 3b and 3c show the internal structure of a solar collector according to a particular embodiment of the invention;

fig. 4a and 4b show a solar collector according to another embodiment of the invention;

FIG. 5 shows a solar collector designed to be placed in a window according to a particular embodiment of the invention;

figure 6 shows a solar collector designed to be placed on a roof according to a particular embodiment of the invention;

fig. 7 shows a solar collector according to the prior art.

Detailed Description

Referring to fig. 1a and 1b, a solar thermal collector C according to a particular embodiment of the invention comprises an insulating body 1 with a light-transmitting glazing 2.

The main body 1 comprises a liquid supply duct 6, more particularly an inlet duct 60 and an outlet duct 62, for supplying a liquid for heating, such as water, to the solar collector C. More particularly, the liquid for heating enters the solar collector body 1 through the conduit 60, is heated inside the body 1 and then exits through the conduit 62. It can be used in the domestic or industrial field.

The heat accumulator block 3 is provided inside the main body 1. The heat storage block 3 is filled with a heat storage material 30.

The regenerator 3 comprises a selectively light-absorbing coating 4. The heat accumulator works in conjunction with a flow heat exchanger 5 through which the liquid to be heated flows.

The coating 4 is made of a material having a high absorption coefficient and a low reflection coefficient (for example, black copper or black copper may be used).

The regenerator 3 is hydraulically connected to the liquid supply conduit 6 (inlet conduit 60 and outlet conduit 62).

The heat exchanger 5 is designed to provide a thermal energy exchange between the phase change material 30 and a liquid 600 to be heated (e.g. water) flowing inside the heat exchanger 5.

With reference to fig. 2a and 2b, the heat exchanger 5 comprises a core structure 54 for the exchange of thermal energy between the liquid 600 to be heated and the thermal storage material 30, according to a particular embodiment of the present invention.

The heat exchanger core structure 54 is formed with a stack of stamped metal sheets 540.

All of the sheets 540 of the heat exchanger core structure 54 are identical. Each sheet 540 includes deformations obtained during swaging.

When the sheets 540 of the heat exchanger core 54 are stacked, the deformation of the sheets forms the enclosed spaces 560 of the global channel 56, the enclosed spaces 560 containing the liquid to be heated (e.g., water) and being sealed by the sealing channel 58. When the sheet 540 is stacked, it also forms a cavity 57 designed to receive the thermal storage material 30. In this embodiment, the channels 56 form straight longitudinal channels along the stacked sheets. Each sheet 540 includes an aperture 542 located along the channel 56.

Referring to fig. 2b, the holes 542 of a given plate and the holes of the following plate are located at opposite ends of the channel 56.

For example, the apertures of sheets 540a and 540c (apertures 542a and 542c) are located to the left of channel 56, and the apertures of sheets 540b and 540d (apertures 542b and 542d) are located to the right of channel 56.

Thus, water begins to flow through the holes 542a, into the channel spaces 560 between the sheets 540a and 540b, then along the channel spaces up to the holes 540b, and then through the holes to the interior of the channel spaces between the sheets 540b and 540 c.

And so on until the water circulates in each channel interval until it exits behind the hole 542 d.

Referring to fig. 3a, 3b and 3c, according to another embodiment of the invention, the heat exchanger 5 comprises an inlet 50 connected to an inlet conduit 60 of the solar collector and an outlet 52 connected to an outlet conduit 62 of the solar collector.

A channel 56 inside the heat exchanger 5 connects the inlet 50 with the outlet 52, along which a thermal energy exchange takes place between the liquid 600 to be heated and the thermal storage material 30.

The heat exchanger 5 comprises at least one channel 56 for the flow of a liquid 600 to be heated, for example water, and a cavity 57, which is heated by the heat release of the heat accumulating material 30 inside the heat accumulator 3 through the cavity 57.

The heat exchanger 5 comprises a core structure 54 for the exchange of thermal energy between the liquid 600 to be heated and the thermal storage material 30.

The heat exchanger core structure 54 is formed with a stack of stamped metal sheets 540.

All of the sheets 540 of the heat exchanger core structure are identical. Each sheet 540 includes a deformation 5401, preferably in the form of a half-pipe groove. The groove follows a path that follows the trajectory 5042 of the channel 56.

When the sheets 540 of the heat exchanger core structure 54 are stacked, the deformations 5401 form enclosed spaces 560 of the channels 56, the enclosed spaces 560 containing the liquid to be heated (e.g., water) and being sealed by the sealing channels 58.

The area outside the liquid channel 56 (and the sealed channel 58) forms a cavity 57 that will be filled with the thermal storage material 30. Thus, the cavity 57 and the channel 56 are separated from each other by a sealing channel 58.

The sheets 540 of the heat exchanger 5 represent a heat transfer medium between the heat accumulating material and the liquid to be heated.

The heat exchanger core structure 54 can be built as any type of uniflow or multi-flow heat exchanger: liquid-solid, liquid-liquid, liquid-gas, gas-solid, and the like.

In addition, the heat exchanger core structure 54 comprises a single standard component (sheet 540) and does not contain welds or electrical welded seams. And is therefore highly suitable for computerized/automated manufacturing.

Furthermore, maintenance and repair of such a heat exchanger core structure 54 is easy, as the sheets 540 can be disassembled and reassembled multiple times without having to resort to welding or electric welding equipment.

All of the channel spaces 560 formed between each sheet 540 of the heat exchanger core structure are secured by a securing means such as a single threaded bushing (not shown) that gathers all of the sheets into a single block.

A bypass valve (not shown) rotating around the axis of rotation of the bushing or sliding longitudinally along the axis may be mounted within the bushing, enabling switching of the channel (there is also room for a small turbine oscillator for exciting sound waves in the liquid to be heated).

In addition to the bushings, all of the tabs 540 are also gathered together by pins (pins) 59. The required capacity of at least one channel 56 can be obtained by designing the channel 56 in such a way: the gap between the sheets is controlled by spacers (not shown).

In addition, the passage spacer 560 has a rounded portion that imparts additional elasticity to the passage spacer 560 in both the longitudinal and transverse directions. Thus, the assembly of the sheets 540 pulls them very tightly together.

Sealing of the channel spacing 560 may be enhanced by using a coating of viton, butyl, latex or silicon compound that is placed in a groove of the sealing channel 58 extending along the fluid channel 56.

In the first embodiment, water flowing from the inlet 50 and into the first compartment 560 circulates along the tortuous passage 56 and, once it reaches the opposite aperture, flows into the following passage compartment in the same manner as described above (except that the passage 56 has a tortuous form).

Alternatively, the flow of water from the inlet 50 to the outlet 52 may be parallel throughout the channel spacing 560.

To form the heat exchanger 3, the assembled heat exchanger block 5 is placed in the sealing body 1 filled with the heat storage material 30.

The Z-shaped channels form a hydraulic seal to eliminate the possibility of air intrusion into the heat exchanger when liquid is being drained from the heat exchanger ("complete gas seal").

With regard to the duct 6, the airtight principle has been applied:

the height difference in the flow heater must be ensured, the heater being mounted at an angle to the horizon in order to let the air out when the heat exchanger is full of water,

a bypass valve for cutting off the water and forcing the remaining water out of the heat exchanger, and

-a flush ramp: a pipe with a sprayer for cleaning the glass of the solar heat accumulator. Water is admitted to the heat exchanger only when the user opens the supply valve. When the valve is closed, water is discharged to the user. The length and cross section of the discharge are chosen to ensure that the remaining liquid is sucked out of the heat exchanger by gravity when the valve at the highest point in the system is opened. Either through an outlet in the supply manifold-the simplest case-or through a special slide valve.

In addition to being influenced by gravity, the remaining liquid in the heat exchanger expands during heating, i.e. water is "squeezed out" through the gaps in the heat exchanger. Having the smallest possible space within the channel is a necessary requirement to speed up heat transfer and minimize heat loss.

The thermal storage material 30 is basically a hydrogel and a gelling agent as a phase change material.

In particular, the accumulation of thermal energy takes place in the form of the dissolution of the salt in the crystallization water and the fixing (encapsulation) of the residual water by the gelling agent.

Preferably, the heat storage material 30 is a eutectic mixture, and preferably, hydrated sodium acetate gel may be used as the phase change material.

When heated, such a heat storage material quickly reaches its melting point. The use of this type of material has the following advantages over continuous linear heating: when a material undergoes a liquid crystal phase change, it receives and releases energy while the temperature remains constant.

The molten crystalline material releases, for example, 60-80% of its useful heat without its temperature dropping. In other words, with this heat storage material, the first 60-80% of the total volume of the liquid to be heated by the heat storage material is heated at a constant temperature.

Only after the crystallization is completed does the temperature start to drop. Therefore, the amount of thermal energy used does not affect the efficiency of the regenerator.

The release of thermal energy (due to salt crystallization) is triggered by an external request, either mechanical or electronic, on the gel.

In contrast to prior art embodiments using paraffin wax, the present invention uses a dissolution process of salt in a solvent such as crystal water. Therefore, the heat storage material does not "melt" but dissolves (becomes ions in the electrolyte) during the temperature rise.

The gelling agent stabilizes the thermal dissolution of the salt crystals when the hydrogel is formed.

The gelling agent thus has the following functions:

-encapsulating the entire additional element(s),

-the avoidance of the phenomenon of convection,

-absorbing the mechanical oscillations by means of a vibration absorber,

therefore, the possibility of occurrence of crystal centers is reduced.

In case the gel is subjected to a shock (ultrasound, cavitation, electricity, etc.) then the salt starts to precipitate in a saturated solution. This phenomenon is exothermic.

In a particular embodiment, the hydrogel is covered with a coating of a high coefficient thermal expansion material (e.g., paraffin wax) having a melting temperature above the dissolution temperature. When the temperature is lowered, the volume of this type of material decreases, thereby compensating for the volume increase due to crystallization. Thus, the mechanical tension inside the regenerator is reduced. Preferably, the volume of the high coefficient thermal expansion material represents 5 to 10% of the total volume.

In a preferred embodiment, a supersaturated aqueous solution of sodium acetate is used as the thermal storage material.

Compared with solids, saturated solutions have the following advantages: as its temperature decreases, the solubility decreases, meaning that it is capable of forming "super-cooled" ("frozen") molten salts dissolved in the liquid that will release its heat of fusion during recrystallization.

Sodium acetate solution can be "super cooled" in the range from 50 ℃ to 60 ℃ (typically at 52 ℃) without releasing the accumulated thermal energy. Thus, the sodium acetate solution can provide a thermal energy storage material that is able to store energy not because of strong insulation (like a thermos bottle), but because of phase changes, thus releasing the stored thermal energy when needed.

Commercial sodium acetate trihydrate has a dissolution point in the range of 50 ℃ to 60 ℃, typically 58 ℃.

Sodium acetate trihydrate is not as corrosive as other salts. Thus, a compact regenerator can be constructed using such salts while maintaining good capacity.

In order to ensure stable thermophysical properties, special hydrogels (also called "hydrogels") may be used: sodium acetate solution in distilled water with gelling agent (acetate trihydrate): a dilute solution of carboxymethylcellulose (CMC) and/or polyvinylpyrrolidone (PVP) and/or sodium laureth sulfate and/or carrageenan.

In a preferred embodiment, the following ratios are used:

hydrogel components (mass percent):

96 percent of sodium acetate trihydrate

CMC 700 3.0％

PVP 1.0％

The gel has a heat of dissolution/crystallization of 282,000J/kg and a heat capacity of from 2,650J/kg/deg.C to 2,800J/kg/deg.C.

The mixing process was verified using a dilute phenolphthalein solution (0.001% by mass) as an acidic indicator. When the regenerator is reloaded, the regenerator material itself will not overheat. It neither boils nor causes an explosion, since the boiling temperature of the hydrogel is much higher than 100 ℃, while the equilibrium point between heat inflow and heat loss due to radiation in the solar collector lies in the interval from 90 ℃ to 96 ℃.

To allow the gel to expand due to the heat build-up, the regenerator is designed with spare capacity.

In a preferred embodiment of the present invention, 10% of the space occupied by the thermal storage material is provided as a spare capacity.

Using a eutectic mixture such as hydrated sodium acetate gel as the phase change material reduces the amount of energy required to melt the phase change material because the melting temperature of the eutectic mixture is lower than the melting temperature of the mixture of any other component; this also results in reduced heat loss.

The heat accumulation-removal of the heat accumulator follows a specific sequence: rapid temperature rise and stabilization during the heat storage phase and vice versa, long plateaus of the heat rejection temperature, which do not require any additional control or stabilization.

The heat extraction of the heat accumulator 3 comprises two phases:

-heat accumulation when the salt is dissolved and supercooling of the mixture;

-heat rejection due to recrystallization of the eutectic mixture at any moment of user selection using the mechanical or electronic trigger described above.

The solar collector with direct heat absorption according to the invention enables the most efficient use of solar energy. The direct coating of the solar radiation absorbing layer on the surface of the heat storage block sets ideal conditions for the storage of solar energy:

first, the present invention eliminates various auxiliary devices, primary conduits, used in other designs, so that heat energy is directly transferred to the thermal storage material 30.

Second, heat transfer has two stages:

in the first phase, the thermal storage material is simply heated until it begins to melt (salt dissolution). Since the mass of the thermal storage material is less than that of a similar capacity water heater, and its thermal capacity is about half that of the water heater, the thermal storage material 30 heats up three times faster than a similar water heater, and it is also more thermally insulating.

In a second phase, the thermal storage material melts while its temperature remains virtually unchanged. This makes the solar collector more efficient, since its losses through radiation are lower, and since it can operate in variable cloudy conditions, i.e. the inflow of thermal energy is not affected by temperature variations due to direct heat transfer from the selective absorption layer.

Third, the heat transfer is performed without using any auxiliary electronic or mechanical devices, such as circulation pumps, thermosiphons, etc., making its operation extremely reliable throughout the process.

Advantageously, the absorbing layer is protected by a protective means made of ultratransparent borosilicate glass. The protective device can be manufactured in the form of a glass in a single-or multi-chamber package.

The thickness of the assembled heat exchanger block has been set based on the following conditions: the heat storage material 30 needs to be melted. Thus, the hydrogel layer (thermal storage material 30) must be thick enough to enable a large amount of solar energy sufficient to melt the entire volume of the thermal storage material 30 into a given specific surface area on an average sunny day. Therefore, the mass of the heat storage material 30 needs to be 30 to 70kg/m of the absorption surface²Depending on the average annual insulation of the site where the solar collector is to be used.

Three different heat accumulators have been tested, relating to the weight per unit surface: 60. 45 and 30mm thick.

Furthermore, in order to improve the range of suitable levels of thermal insulation in average size solar thermal storage, the authors decided to assemble three different thickness thermal storage blocks connected in series: the thickest one is closest to the water supply, then the average thickness, then the thinnest one.

The advantage of this distribution over a thermal accumulator consisting of three identical blocks is that even when the solar energy is very low and not sufficient to heat by the thick heavy blocks, the thin blocks will still store some energy, sufficient to heat a small amount of water. On the other hand, even the thickest mass with a large capacity will still transfer a portion of its energy to the water, albeit at a lower temperature, while the thin hotter mass will further heat the water.

The thermal insulation of the solar collector comprises the thermal insulation of the heat accumulator block and the thermal insulation from the atmosphere at the side of the absorption surface.

The thermal insulation protection of the solar heat accumulator can be of any type, such as a vacuum chamber.

In a preferred embodiment of the invention, the insulation consists of glass in the distance control frame made of pure glass and silica gel.

To reduce heat loss by radiation in the infrared band, the transparent shield has an inner layer with an infrared reflector. In addition, the transparent shield is designed with a double-glazed glass package to reduce convection losses.

For example, the infrared mirror can be manufactured by gluing a special TC-88 film of some kind manufactured by 3M company onto the inner surface of the glass, or by depositing a thin layer of indium oxide using a vacuum ion apparatus.

It is also possible to use a filler between the heat accumulator block and the glass distance control frame, made of a composite material capable of insulating the glass from the heat absorbing surface.

According to a particular embodiment of the invention, this material is manufactured by thermal insulating impregnation of very thin pieces (diameter not greater than 2 μm) of basalt fibres with liquid ceramic. A free area is left between the distance control frame and the body extending along the periphery of the glass. The interior of this area is coated with an absorbent black paint (primer).

The heat collector according to a particular embodiment of the invention further comprises a heat conducting element to conduct heat from the selectively light absorbing coating to the phase change material and optionally to the water in the heat exchanger. For example, the heat conducting elements are in the form of ribs. To eliminate heat loss due to thermal radiation through the bottom surface of the ribs, the ribs are isolated from the special composite coating on the interior. Furthermore, the ribs may be installed into a network of glass fibers soaked in liquid ceramic insulating material, as described above.

As another measure designed to reduce convection losses: the heated end of the glass absorbs less heat from the internal air layer, thus preventing convection.

The thermal insulation of the heat accumulator comprises three phases:

first of all, the body of the thermal storage block itself is made of polished metal, acting as a mirror for infrared thermal radiation.

Secondly, the "liquid ceramic" layer deposited on the regenerator block represents a special high-temperature insulation (for example"Astratech" can be used "Or similar products of the household industry). The thermal resistance of these materials is very high.

The third stage is constituted by a polyurethane foam, similar to the sandwich structure, also acting as a structural element, holding together the outer shell and the inner block.

The body of the solar collector is subjected to considerable stresses: thermal deformation, atmospheric settling, transport stress. Thus, according to a preferred embodiment of the invention, the body is made of polyvinyl fluoride.

Alternatively, a housing vacuum formed from a thermoplastic material or an acrylic or epoxy based glass reinforced plastic may be selected. Indeed, this feature is common in the industry.

Furthermore, the sandwich structure, with a shell of polyurethane filling, has high mechanical and impact strength, is heat and freeze resistant, cheap and not bulky. Advantageously, by using polyurethane glues for special notches of the glass (for example "Teroson") And gluing to fix the transparent protection on the main body. The distance control frame is glued between the heat accumulator block and the glass through butyl ester heat-resistant glue. This allows for some movement and vibration of the glass and protects the glass from breakage.

With reference to fig. 4a and 4b, according to another particular embodiment of the invention, the regenerator further comprises a heat-conducting element 7, the heat-conducting element 7 being for example in the form of a metal rod 70 comprising ribs 72 (preferably in the form of louvers) thermally connected to the metal rod 70. The heat conducting element 7 is thermally connected and preferably incorporated into a package made of a heat conducting material such as metal.

The solar collector operates as follows. The solar rays reach the absorbing louvers 72 and heat them. Thermal energy is transferred from the louvers 72 to the metal rod 70, and the metal rod 70 carries further thermal energy to the heat collector.

In particular embodiments, the metal bar 70 may be filled with any liquid that is capable of efficiently transporting thermal energy. In a particular embodiment of the invention, the liquid is a volatile liquid. Thus, when the volatile liquid is heated by the absorption of solar energy (the metal louvers are also able to absorb and conduct thermal energy to the metal rod 70), the volatile liquid begins to evaporate, rises inside the metal rod, and then reaches the end 700 of the rod 70 that is thermally connected to the collector.

Compared to solar collectors according to the prior art, the solar collector has the following advantages:

it can be installed in an existing sash W (as shown in fig. 5). Such a window can let a part of the reflected and scattered light into the room, and is used not only as a heater but also as a general window.

According to fig. 6, the solar collector according to the invention can also be mounted at a corner box, for example incorporated in a roof. It can also be used as a skylight.

Claims (9)

1. A solar collector for heating a liquid (600) to be heated, comprising:

-an insulating body (1),

-a light-transmitting barrier (2),

-a heat accumulator (3) comprising a heat accumulating material (30), and

-a heat exchanger (5) designed for transferring thermal energy from a phase change material to the liquid (600) to be heated,

wherein the heat exchanger (5) is formed by die forging a stack of metal sheets, and wherein the heat storage material comprises a salt solution based on a hydrogel and a gelling agent.

2. A solar collector according to claim 1, wherein at least one surface of the heat accumulator (3) is coated with a selectively light absorbing material (4).

3. A solar thermal collector according to claim 1 or 2, wherein the thermal storage material comprises a solution of sodium acetate (acetate trihydrate) in distilled water with a gelling agent.

4. A solar collector according to any of claims 1-3, wherein the gelling agent comprises a solution of carboxymethylcellulose (CMC) and/or a solution of polyvinylpyrrolidone (PVP) and/or a solution of sodium laureth sulfate and/or carrageenan.

5. A solar thermal collector according to any one of claims 1 to 4, wherein the thermal storage material comprises a coating of a high coefficient of thermal expansion material.

6. A solar thermal collector according to claim 5, wherein the high coefficient of thermal expansion material comprises paraffin wax.

7. A solar collector according to any of claims 1 to 6, wherein the solar collector further comprises a metal bar (70) thermally connected to the insulating body (1).

8. A solar collector according to claim 7, wherein the solar collector further comprises a metal rib (72) thermally connected to the metal bar (70).

9. A window comprising at least one solar collector according to claim 8, wherein the metal rib (72) is in the form of a louver.