Description:FIELD OF THE INVENTION

The present invention relates to a system and a method for utilizing solar energy and particularly relates to a system for harnessing and storing the solar energy as heat for utilizing as and when required.

BACKGROUND

The need for energy is rising with the growth of industrialization, most of which is fulfilled by utilizing non-renewable energy resources. Examples of non-renewable energy resources include fossil fuels such as coal, natural gas, oil, and nuclear energy. These natural resources are limited/finite. Once these resources are used up, they cannot be replaced, which is a major problem for humanity as we are currently dependent on them to supply most of our energy needs.

To cater to the ever-increasing energy demands, the use of non-renewable energy resources such as fossil fuels is also increasing exponentially. This leads to environmental problems such as global warming, pollution due to the emission of greenhouse gases, and the like.

On the other hand, renewable energy comes from renewable resources such as sunlight, wind, the movement of water, geothermal heat, and the like. Renewable energy sources and significantly solar energy has the capability to fulfil the need for energy without impacting the environment. Solar energy is available in abundance. Solar energy is clean, eternal, harmless, reliable, abundant, and free.

Solar thermal collectors collect heat by absorbing the sunlight. The use of solar thermal collectors is a preferred choice to harness the solar energy. The solar collectors are employed to gather the solar energy for various low, medium, and high-temperature applications.

The solar thermal collectors may be an Evacuated Tube Collectors (ETC) or a Flat Plate Collectors (FPC). Recently, Evacuated Tube Collectors (ETC) have replaced Flat Plate Collectors (FPC) due to the associated advantages such as enhanced performance, economical installation, maintenance, use and the like. However, one of the disadvantages of the ETC is the possibility of excessive heating of the vacuum tube. Other disadvantages include dirtying and freezing of working fluid inside the tube, leakage of working fluid due to rapid deterioration of sealings at high working temperatures, glass breakage, and the like.

However, there are some drawbacks with utilizing the solar collectors as a heat source. A major drawback being that the solar energy is an intermittent source of energy. The solar energy is not a continuous and uniform source of energy. It is available only during sunshine hours and that too on clear sky days. This interrupts the consistent operation of a solar energy based heating application. This may be overcome with low-cost ways of storing energy. On a clear sky day, abundant solar energy is available during sunshine hours, which if stored, can be utilized for heating during nighttime or off-sunshine hours.

Thermal batteries can be used to store available solar energy and utilize it when required.

Most common thermal batteries are based on Latent Heat Storage (LHS) using a Phase Change Materials (PCM) as a storage material.
Latent Heat Storage (LHS) may be considered superior to Sensible Heat Storage (SHS) in terms of energy storage capacity per unit mass of the storage material. LHS takes place during a phase change of the storage material at a constant temperature (generally, the melting point of the storage material such as the PCM). On the other hand, SHS provides scope for storing higher amount of energy without increasing the volume or the temperature of the storage material. However, the storage material with SHS at higher temperatures causes substantial heat losses to the surroundings as the rate of heat transfer and thus, heat loss increases with rising temperature. Numerous PCMs are available in market with a range of melting points and latent heat or enthalpy of fusion that can be used in thermal batteries depending on the charging source and end user application requirements.
However, there are problems and issues associated with LHS based systems. A major problem with the LHS based thermal batteries is a low thermal conductivity of the PCM. Due to the low thermal conductivity of the PCM, an inconsistent change of phase takes place. The phase change of the PCM near the heat transfer area occurs rapidly which results in inconsistent storage and dissipation of energy.

Therefore, it is desirable to provide a system for harnessing and utilizing the solar energy which can overcome the above-mentioned problems.

SUMMARY

This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended for determining the scope of the invention.

In one aspect, the invention provides a heat exchanger unit comprising a body comprising an outer wall, an inner wall, and an annular region formed between the inner wall and the outer wall; and a heat storage material disposed in the annular region and adapted to receive and transfer heat via both the inner wall and the outer wall.

In another aspect the invention provides a method for filling the heat exchanger unit with a heat storage material. The method comprises feeding the heat storage material into a body of the heat exchanger using an inlet port; and maintaining, during feeding, the body of the heat exchanger at a temperature above a melting point of the heat storage material.

In another aspect, the invention provides a system comprising a thermal battery for storing the thermal energy. The thermal battery comprises an insulated tank adapted to hold a Heat Transfer Fluid (HTF) and prevent heat loss to surroundings, a heat exchanger unit immersed in the HTF, and a heat storage material. The heat exchanger unit comprises a body comprising an outer wall, an inner wall, and an annular region formed between the outer wall and the inner wall. The heat storage material is disposed in the annular region and adapted to transfer heat between the HTF via the inner wall and the outer wall. In an embodiment, the heat storage material is a Phase Change Material (PCM).

In an embodiment, the annular region is filled with the PCM. Heat transfer between the PCM and the HTF takes place at an outer curved surface of the outer wall and an inner curved surface of the inner wall. This provides maximum surface area for heat transfer between the PCM and the HTF to achieve optimal charging and discharging of the thermal battery.

In an embodiment, the heat exchanger unit comprises an inner pipe and an outer pipe. The inner pipe is joined to the outer pipe to form the annular region.

In an embodiment, at least one of the inner wall and the outer wall comprises a plurality of fins extending out from the respective surface of at least one of the inner wall and the outer wall to transfer heat between the heat storage material and the HTF.

In an embodiment, the heat storage material is a Phase Change Material (PCM) with thermal conductivity less than 1 Watts per Meter-Kelvin, and a melting point in the range of 40-230 degrees Celsius. In an embodiment, a ratio of a radius of the outer wall to a radius of the inner wall is in the range of 1.1:1 to 6:1.

In another aspect, the invention provides a system for utilizing solar energy by harnessing and storing the solar energy as heat energy for utilizing as and when required. The system includes a Solar Thermal Battery (STB) for harnessing and storing the solar energy in the form of heat and using the stored energy on-demand for various applications.

In accordance with an embodiment, the Solar Thermal Battery comprises a solar collector (such as a Heat Pipe Vacuum Tube Solar Collector (HPVT-SC)) for harnessing the heat from the solar energy, a thermal battery for storing the harnessed heat energy, and a circulation pump for circulating an HTF (Heat Transfer Fluid) between the thermal battery and the solar collector.

In an embodiment, the system includes a plurality of heat exchanger units (heat exchangers). Each of the plurality of heat exchanger units is in a tube-in-tube form (including a pair of co-axial pipes: an inner pipe and an outer pipe welded together) and connected to a next corresponding heat exchanger unit in series. The space between the pair of welded coaxial pipes is filled with the PCM. Heat transfer between the PCM and the HTF takes place at the outer curved surface of the outer pipe and the inner curved surface of the inner pipe. This provides maximum surface area for heat transfer between the PCM and the HTF to achieve optimal charging and discharging of the thermal battery.

The STB is charged by utilizing the heat energy from the solar energy via solar collector. The discharging of the STB may be by utilizing the thermal energy stored in the STB for any suitable heating application such as water heating, air heating, cooking, and the like.

The temperature difference between the HTF and the PCM causes heat transfer from the HTF to the PCM. Sensible energy storage occurs in the PCM until the temperature reaches its melting point. Once the PCM is heated to its melting point, phase change occurs at a constant temperature. Once the phase change is complete, the temperature of the PCM rises above its melting point until a thermal equilibrium is maintained with the HTF. Thus, latent heat storage takes place while the phase changes at the constant temperature and sensible heat storage takes place with rise in the temperature of the PCM both before the phase change and after the phase change at the constant temperature (the melting point of the PCM).

Discharging of the STB is achieved by recirculating the hot HTF contained in the thermal battery through a heat exchanger in a closed circuit. Heat transfer occurs as per the heating application. The hot HTF from the top section of the storage tank circulates through the heat exchanger using the second circulation pump, resulting in the heat transfer to the surroundings. The HTF cools down by a certain temperature due to the exchange of heat and is routed to the bottom section of the storage tank. As the HTF temperature decreases, the PCM dissipates energy to the HTF to maintain thermal equilibrium. The temperature of the PCM decreases with the decreasing temperature of the HTF until the temperature of the PCM reaches its melting point. The phase change of the PCM occurs at a constant temperature while dissipating the stored latent heat to the HTF. During the phase change of the PCM, the HTF gains heat from the PCM and discharges it through the heat exchanger. After the phase change is complete, the temperature of the HTF and the PCM decreases gradually while dissipating the energy.

To further clarify the advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 illustrates a schematic view of a system for storing thermal energy, in accordance with an embodiment of the invention;

Figure 2 illustrates a schematic view of a heat exchanger unit, in accordance with an embodiment of the invention;

Figure 3 illustrates a schematic view of the heat exchanger unit with a plurality of fins extending from a plurality of walls of the heat exchanger unit, in accordance with an embodiment of the invention, wherein:

Figure 3A illustrates a schematic view of the heat exchanger unit with the plurality of fins extending from an outer wall, in accordance with an embodiment of the invention;

Figure 3B illustrates a schematic view of the heat exchanger unit with the plurality of fins extending from an inner wall and an outer wall, in accordance with an embodiment of the invention; and

Figure 3C illustrates a schematic view of the heat exchanger unit with the plurality of fins extending from the inner wall, in accordance with an embodiment of the invention;

Figure 4 illustrates a flowchart depicting a method for filling the heat exchanger unit with a heat storage material, in accordance with an embodiment of the invention; and

Figure 5 illustrates a schematic view of a PCM (Phase Change Material) storage unit comprising a plurality of heat exchanger units connected in series, in accordance with an embodiment of the invention.

Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, a plurality of components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION OF FIGURES

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which invention belongs. The system and examples provided herein are illustrative only and not intended to be limiting.

For example, the term “some” as used herein may be understood as “none” or “one” or “more than one” or “all.” Therefore, the terms “none,” “one,” “more than one,” “more than one, but not all” or “all” would fall under the definition of “some.” It should be appreciated by a person skilled in the art that the terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and therefore, should not be construed to limit, restrict or reduce the spirit and scope of the present disclosure in any way.

For example, any terms used herein such as, “includes,” “comprises,” “has,” “consists,” and similar grammatical variants do not specify an exact limitation or restriction, and certainly do not exclude the possible addition of a plurality of features or elements, unless otherwise stated. Further, such terms must not be taken to exclude the possible removal of the plurality of the listed features and elements, unless otherwise stated, for example, by using the limiting language including, but not limited to, “must comprise” or “needs to include.”

Whether or not a certain feature or element was limited to being used only once, it may still be referred to as “plurality of features” or “plurality of elements” or “at least one feature” or “at least one element.” Furthermore, the use of the terms “plurality of” or “at least one” feature or element does not preclude there being none of that feature or element, unless otherwise specified by limiting language including, but not limited to, “there needs to be a plurality of…” or “plurality of elements is required.”

Unless otherwise defined, all terms and especially any technical and/or scientific terms, used herein may be taken to have the same meaning as commonly understood by a person ordinarily skilled in the art.

Reference is made herein to some “embodiments.” It should be understood that an embodiment is an example of a possible implementation of any features and/or elements of the present disclosure. Some embodiments have been described for the purpose of explaining the plurality of the potential ways in which the specific features and/or elements of the proposed disclosure fulfil the requirements of uniqueness, utility, and non-obviousness.

Use of the phrases and/or terms including, but not limited to, “a first embodiment,” “a further embodiment,” “an alternate embodiment,” “one embodiment,” “an embodiment,” “multiple embodiments,” “some embodiments,” “other embodiments,” “further embodiment”, “furthermore embodiment”, “additional embodiment” or other variants thereof do not necessarily refer to the same embodiments. Unless otherwise specified, plurality of particular features and/or elements described in connection with plurality of embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although plurality of features and/or elements may be described herein in the context of only a single embodiment, or in the context of more than one embodiment, or in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

Any particular and all details set forth herein are used in the context of some embodiments and therefore should not necessarily be taken as limiting factors to the proposed disclosure.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

Figure 1 illustrates a schematic view of a system 100 for storing thermal energy comprising a thermal battery 150, in accordance with an embodiment of the invention. The system 100 provides for utilizing the solar energy by harnessing and storing the solar energy as heat for utilizing as and when required, in accordance with an embodiment of the invention. In an embodiment, the system 100 is a Solar Thermal Battery (STB 100).

In accordance with an embodiment, the system 100 comprises a circulation pump and means for harnessing the heat energy. The circulation pump is configured for circulating a HTF (Heat Transfer Fluid) between the thermal battery and the means for harnessing the heat energy.

In accordance with an embodiment, the means for harnessing the heat energy is a solar collector 110. In an embodiment, the STB 100 comprises the solar collector 110 (such as a Heat Pipe Vacuum Tube Solar Collector (HPVT-SC 110)) for harnessing the heat from the sun radiations / solar energy.

In accordance with an embodiment, as shown in Figure 1, the STB 100 comprises a circulation pump 180 (a first circulation pump 180) for recirculating the HTF between the thermal battery 150 and the HPVT-SC 110 in a closed circuit. The circulation pump 180 provides a uniform flow of the HTF throughout the components / elements of the system 100 / STB 100. In accordance with an embodiment, the system 100 includes a second circulation pump 190 for recirculating the HTF between the thermal battery 150 and a heat exchanger of an application 192 (as per the heating application) for heat transfer resulting in discharging of the thermal battery 150.

In an embodiment, the HPVT-SC 110 comprises a plurality of Heat Pipe Vacuum Tubes and a manifold. For example, HPVT-SC 100 may include about 25 HPVTs. The number of HPVTs may vary as per application and keeping in mind the design parameters.

In accordance with an embodiment, each HPVT of the plurality of HPVTs comprises a vacuum tube, an aluminium fin inserted in the vacuum tube, a heat pipe located in the vacuum tube containing a low boiling point fluid, and an end cap for holding and sealing the heat pipe with the vacuum tube.

The vacuum tube comprises a pair of co-axial glass tubes having an inner glass tube fused to an outer glass tube creating a vacuum. Each of the pair of co-axial glass tubes is fused together and the air from the enclosure formed between the pair is pumped out creating a vacuum (of pressure value ranging about P = 5 × 10-2 Pa) which serves as the thermal insulation.

In an embodiment, the outer glass tube is transparent.

In an embodiment, the inner glass tube is coated with a high absorptivity special selective coating and is configured to absorb sunlight and convert the sunlight to heat. Examples of high absorptivity special selective coating may include Aluminium Nitride (Al-N/Al) and the like. The inner glass tube, also called the absorber tube (the absorber tube), absorbs the solar radiation and converts it into heat energy and the vacuum between the glass tubes prevents the heat loss.

The aluminium fin is in direct contact with the inner glass tube and has the means to hold the heat pipe. In an embodiment, the aluminium fin is circular in shape and is inserted in the vacuum tube. The aluminium fin is in direct contact with the absorber tube and has the means to hold the copper heat pipe (the heat pipe). The aluminium fin gains heat from the absorber tube and transfers this heat to the copper heat pipe.

In accordance with an embodiment, the heat pipe comprises an evaporator section and a condenser section. The copper heat pipe is located in the vacuum tube and is in direct contact with the aluminium fin and gains heat from the aluminium fin. The copper heat pipe has a low boiling point fluid with a vacuum. The fluid, due to its low boiling point evaporates by absorbing the latent heat of evaporation. The vapours rise to the condenser section, carrying a lot of energy with it.

In an embodiment, the end cap is a steel cap with a silicone seal and is used to hold the copper heat pipe within the vacuum tube and to prevent convective heat loss.

The manifold comprises a header having means to hold the condenser section. The manifold is configured to circulate a Heat Transfer Fluid (HTF) for transferring heat from the condenser section. The header (such as copper header) has means to hold the condenser section. The Heat Transfer Fluid (HTF) circulates through the header and gains heat from the condenser section. The manifold header is insulated and housed in an Aluminum casing. The HTF circulating through the manifold takes away the heat from the condenser section such that the vapors condense and return to the evaporator section. The cycle of heating is repeated.

In accordance with an embodiment, the system 100 includes connecting pipes for connecting and enabling the transfer of fluids among various system components/elements and guiding the flow of the HTF throughout the system components. As an example, the Galvanized Iron (GI) pipes have been used to connect the system 100 components/elements and guide the flow of the HTF throughout the system 100 components. The GI pipes are capable of withstanding high temperature of up to 250?. The manifold, the tank and the circulation pump are connected in series with the connecting pipes. The connecting pipes are insulated to minimize convective heat loss to the surroundings.

In accordance with an embodiment, the STB 100 comprises the thermal battery 150 for storing the harnessed heat energy.

The thermal battery 150 comprises an insulated tank 152 adapted to hold a Heat Transfer Fluid (HTF) and prevent heat loss to surroundings, a heat exchanger unit 154 immersed in the HTF, and a heat storage material 154m.

The insulated tank 152 (tank 152) houses the heat exchanger unit 154 surrounded by the HTF. The tank 152 is thoroughly insulated to minimize convective heat loss to the surroundings. As an example, the tank 152 is made of mild steel.

Figure 2 illustrates a schematic view of the heat exchanger unit 154, in accordance with an embodiment of the invention. The heat exchanger unit 154 comprises a body 154B comprising an outer wall 154wo, an inner wall 154wi, and an annular region 154ar formed between the outer wall 154wo and the inner wall 154wi; and a heat storage material 154m. The heat storage material 154m is disposed in the annular region 154ar and adapted to transfer heat between the HTF via the inner wall 154wi and the outer wall 154wo.

In an embodiment, a ratio of a radius of the outer wall 154wo and a radius of the inner wall 154wi is in the range of 1.1:1 to 6:1.

In an embodiment, at least one of the inner wall 154wi and the outer wall 154wo of the heat exchanger unit 154 comprises a plurality of fins extending out from the respective surface of the at least one of the inner wall 154wi and the outer wall 154wo to transfer heat between the heat storage material 154m and the HTF.

Figure 3 illustrates a schematic view of the heat exchanger unit 154 with a plurality of fins 154f extending out from the inner wall 154wi and the outer wall 154wo, in accordance with an embodiment of the invention.

Figure 3A illustrates a schematic view of the heat exchanger unit 154A with a plurality of fins extending out from the outer wall 154wo, in accordance with an embodiment of the invention. In an embodiment, the plurality of fins 154f are made of a highly thermal conductive material such as stainless steel and the like. In an embodiment, each of the plurality of fins 154f are attached to the outer wall 154wo using means for attachment such as fastening means and the like.

Figure 3B illustrates a schematic view of the heat exchanger unit 154B with the plurality of fins extending out from the inner wall 154wi and the outer wall 154wo, in accordance with an embodiment of the invention. In an embodiment, the plurality of fins 154f are made of a highly thermal conductive material such as stainless steel and the like. In an embodiment, the plurality of fins 154f are attached to the inner wall 154wi and the outer wall 154wo using means for attachment such as fastening means and the like. The plurality of fins 154f starts from the inner wall 154wi and extends out from the outer wall 154wo.

Figure 3C illustrates a schematic view of the heat exchanger unit 154C with the plurality of fins extending out from the inner wall 154wi, in accordance with an embodiment of the invention. In an embodiment, the plurality of fins 154f are made of a highly thermal conductive material such as stainless steel and the like. In an embodiment, the plurality of fins 154f are attached to the inner wall 154wi using means for attachment such as fastening means and the like. The plurality of fins 154f starts from the inner wall 154wi and extend within the annular region 154ar.

Figure 4 illustrates a flowchart depicting a method 400 for filling the heat exchanger unit 154 with a heat storage material 154m, in accordance with an embodiment of the invention. At step 402, the method 400 comprises feeding the heat storage material 154m into the annular region 154ar of the heat exchanger unit 154 using an inlet port 502 (shown in Figure 5). At step 404, the method 400 comprises maintaining, during feeding, the body 154B of the heat exchanger unit 154 at a temperature above a melting point of the heat storage material 154m.

In an embodiment, the heat storage material 154m is a Phase Change Material (PCM) with thermal conductivity less than 1 Watts per Meter-Kelvin, and a melting point in a range of 40-230 degrees Celsius.

In an embodiment, the heat exchanger unit 154 comprises an inner pipe and an outer pipe. The inner pipe is joined to the outer pipe to form the annular region 154ar. In an embodiment, each of the plurality of heat exchanger unit 154 is in a tube-in-tube form and connected to a next corresponding heat exchanger unit 154 in series and so on.

In an embodiment, the thermal battery 150 comprises a plurality of heat exchanger units 154. The plurality of heat exchanger units 154 are fluidically couped in series forming a PCM storage unit 500.

Figure 5 illustrates a schematic view of the PCM storage unit 500 comprising the plurality of heat exchanger units 154 fluidically couped in series, in accordance with an embodiment of the invention. The PCM storage unit 500 comprises the inlet port 502 adapted to fill the annular region 154ar with the heat storage material 154m and an outlet port 504 adapted to allow an excess of the heat storage material 154m) to egress from the annular region 154ar during the method 400 for filling the heat exchanger unit 154. In an embodiment, the inlet port 502 is provided at a first heat exchanger unit 154 of the plurality of heat exchanger units 154 fluidically couped in series and the outlet port 504 is provided at a last heat exchanger unit 154 of the plurality of heat exchanger units 154.
As an example, the PCM Storage unit 500 is made of a stainless steel (SS-304) and includes the plurality of heat exchanger units 154. As an example, the number of heat exchanger units 154 may be about 10-20 and typically, 12. The plurality of heat exchanger units 154 store the PCM and is configured to enable the transfer of heat from the HTF to the PCM.

In an embodiment, the heat exchanger 154 consists of a pair of coaxial pipes (including an inner pipe and an outer pipe) welded together at both ends. The space between two coaxial pipes form the annular region 154ar and is filled with the PCM. Heat transfer between the PCM and the HTF takes place at the outer surface of the outer pipe and the inner surface of the inner pipe including curved surfaces thereof. This provides maximum surface area for heat transfer between the PCM and the HTF to achieve optimal charging and discharging of the PCM. Heat transfer between the PCM and the HTF takes place at an outer curved surface of the outer pipe and an inner curved surface of the inner pipe. This provides maximum surface area for heat transfer between the PCM and the HTF to achieve optimal charging and discharging of the thermal battery.

It may be apparent that the dimensions and design parameters of the various elements / parts / components of the system 100 may vary depending upon requirements and design constraints. An example of a combination of various parameters / dimensions for various elements of the solar collector 110 of the system 100 may be presented in the form of a table below:

Table 1. Component Details
Component Material Qty. Parameter Value
Heat pipe vacuum tube Vacuum tube Borosilicate glass 25 Vacuum pressure = 5 × 10-2 Pa
Length 2100 mm
Outer diameter of glass tube 58 mm
Outer diameter of absorber tube 47 mm
Fin Aluminum Thickness 0.2 mm
Heat pipe Copper Length of evaporator section 2000 mm
Diameter of evaporator section 12.25 mm
Length of condenser section 63.5 mm
Diameter of condenser section 14 mm
End cap Steel cap, silicone seal

An example of dimensions and design parameters for the thermal battery 150 may be presented below in the table:

Table 2. Component Details
Component Material Parameter Value
Solar thermal battery PCM heat exchanger Stainless steel (SS-304) Weight 20 kg
Length of heat exchanger 450 mm
Diameter of inner pipe 19 mm
Diameter of outer pipe 76 mm
Thickness of pipe 1.2 mm
Storage tank Mild steel Volume 120 L
Sheet thickness 4 mm
PUF Insulation thickness 90 mm

In an embodiment, for sensible heat storage, a synthetic fluid capable of functioning at high temperature applications of up to 290?, such as Hytherm-600 may be used. The properties of the HTF that make it suitable to use for non-pressurized solar thermal heating are presented in Table 3 below.

Table 3. Properties of sensible heat storage (Hytherm-600)
Parameter Unit Value
Temperature °C 50 100 150 200
Density kg/m3 852 818 784 748
Specific heat kJ/kg K 2.31 2.49 2.67 2.84
Pour point °C -25
Flash point °C 220
Auto ignition temperature °C 426
Viscosity index - 100
Appearance - Clear and bright

In an embodiment, for latent heat storage, Acetamide may be used as the PCM. Thermal properties of the PCM are provided in Table 4 below.
Table 4. Properties of latent heat storage (Acetamide)
Parameter Unit Value
Melting point °C 79 – 82
Boiling point °C 222
Latent heat of fusion kJ/kg 263
Density kg/m3 1159 (solid) and 998 (liquid)
Thermal conductivity W/mK 0.43 (solid) and 0.25 (liquid)
Specific heat kJ/kgK 1.98

In accordance with an embodiment, the STB 100 is charged by utilizing the heat energy from the HPVT-SC 110. The discharging of the STB 100 may be by utilizing the thermal energy stored in the STB 100 for any suitable heating application such as water heating, air heating, cooking, and the like.

Now, the process of the charging of the thermal battery 150 using the HPVT-SC 110 will be explained with reference to Figure 1.

In accordance with an embodiment, the HPVT-SC 110 is exposed to sunlight. The high absorptivity special selective coating on the HPVTs absorbs the solar radiation and transfers the heat to the corresponding aluminum fins, which in turn transfer the heat to the corresponding copper heat pipe.

The heat supplied to the copper heat pipes is absorbed by the low boiling point fluid inside leading to heat accumulation in the condenser section of the copper heat pipe. The HTF at a bottom section of the tank 152 is forced to flow through the copper header of the manifold using the first circulation pump 180. The HTF in the manifold gains heat from the condenser section of the copper heat pipe, resulting in the condensation of fluid inside the copper heat pipe. The heated HTF at an outlet of the manifold is routed to a top section of the tank 152. The cycle of heating is repeated and the temperature of the HTF rises.

Subsequently, the temperature difference between the HTF and the PCM causes heat transfer from the HTF to the PCM. Sensible energy storage occurs in the PCM until the temperature reaches the melting point of the PCM, beyond which, phase change occurs at a constant temperature. Once the phase change is complete, the temperature of the PCM rises above its melting point until a thermal equilibrium is maintained with the HTF.

With reference to Figure 1, discharging of the thermal battery 150 is achieved by recirculating the hot HTF contained in the thermal battery 150 through the heat exchanger of the heating application 192 in closed circuit. Heat transfer occurs as per the usage and requirement of the heating application 192. The hot HTF from the top section of the tank 152 circulates through the heat exchanger of the heating application 192 using the second circulation pump 190, resulting in the heat transfer to the application 192. The HTF transfers the heat to the heating application 192 via the heat exchanger of the heating application 192 and is, subsequently, routed to the bottom section of the tank 152.

As the temperature of the HTF decreases, the PCM transfers more energy to the HTF to maintain thermal equilibrium. The temperature of the PCM decreases with the decreasing temperature of the HTF until the temperature of the PCM reaches its melting point. The phase change of the PCM occurs at a constant temperature while dissipating heat to the HTF. During the phase change of the PCM, the HTF gains heat from the PCM and discharges it through the heat exchanger. After the phase change is complete, the temperature of HTF and PCM decreases gradually while dissipating the energy.

In various embodiments, the STB 100 may be configured to work in different modes. As an example, there may be a Mode – I: Consecutive charging and discharging and a Mode – II: Simultaneous charging and discharging.

During the Mode-I, charging of the STB 100 is carried out during sunshine hours and discharging of the STB 100 is carried out by utilizing the stored heat energy during off-sunshine or night hours.

Conversely, in the Mode-II, charging and discharging of STB 100 are carried out simultaneously during sunshine hours. Both the circulation pumps (the first pump 180 and the second pump 190) are operated simultaneously in this mode. The HTF gains heat from the HPVT-SC 110 and heat transfer occurs between HTF and PCM. Simultaneously, the HTF is recirculated through the heat exchanger of the heating application 192 for the heating application. The surplus energy is stored in the thermal battery 150 which can be used for heating during off-sunshine or night hours.

The system of the invention is advantageous in many respects. The invention enables simultaneously harnessing and utilization of solar thermal energy for heating applications during sunshine hours. Moreover, the surplus energy during sunshine hours is stored and used for heating applications during off-sunshine hours by utilizing the solar thermal battery. Therefore, energy is consistently available for useful purposes. Further, because of the construction of the heat exchanger provided by the invention a larger surface area of the heat exchanger unit is available for heat transfer. As a result, the heat transfer rate is also high for both latent heat storage and sensible heat storage. This enables optimum charging and discharging of the thermal batteries. The addition of fins adds to the surface area and makes the heat transfer in the heat exchanger unit faster both for charging and discharging of the thermal battery.

The invention provides for consistent and regular availability of heat from solar energy so that the energy is consistently available for useful purposes as and when required on demand.

While specific language has been used to describe the present subject matter, any limitations arising on account thereto, are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein. The drawings and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment.
, Claims:1. A heat exchanger unit (154) comprising:
a body (154B) comprising an outer wall (154wo), an inner wall (154wi), and an annular region (154ar) formed between the inner wall (154wi) and the outer wall (154wo); and
a heat storage material (154m) disposed in the annular region (154ar) and adapted to receive and transfer heat via both the inner wall (154wi) and the outer wall (154wo).

2. The heat exchanger unit (154) as claimed in claim 1, comprising an inlet port (502) adapted to fill the annular region (154ar) with the heat storage material (154m) and an outlet port (504) adapted to allow an excess of the heat storage material (154m) to egress from the annular region (154ar).

3. A method (400) for filling a heat exchanger unit (154) with a heat storage material (154m), the method (400) comprising:
feeding (402) a heat storage material (154m) into a body (154B) of the heat exchanger unit (154) using an inlet port (502); and
maintaining (404), during feeding (402), the body (154B) at a temperature above a melting point of the heat storage material (154m).

4. A system (100) for storing thermal energy comprising a thermal battery (150), the thermal battery (150) comprising:
an insulated tank (152) adapted to hold a Heat Transfer Fluid (HTF) and prevent heat loss to the surroundings;
a heat exchanger unit (154) immersed in the HTF, the heat exchanger unit (154) comprising: a body (154B), an outer wall (154wo), an inner wall (154wi), and an annular region (154ar) formed between the outer wall (154wo) and the inner wall (154wi); and
a heat storage material (154m) disposed in the annular region (154ar) and adapted to transfer heat between the HTF via the inner wall (154wi) and the outer wall (154wo).

5. The system (100) for storing thermal energy as claimed in claim 4, wherein the heat exchanger unit (154) comprises an inner pipe and an outer pipe, the inner pipe being joined to the outer pipe to form the annular region (154ar).

6. The system (100) for storing thermal energy as claimed in claim 4, wherein at least one of the inner wall (154wi) and the outer wall (154wo) comprises a plurality of fins (154f) extending out from the respective surface of the at least one of the inner wall (154wi) and the outer wall (154wo) to transfer heat between the heat storage material (154m) and the HTF.

7. The system (100) for storing thermal energy as claimed in claim 4, wherein:
the heat storage material (154m) is a Phase Change Material (PCM) with thermal conductivity less than 1 Watts per Meter-Kelvin, and a melting point in range of 40-230 degrees Celsius; and
a ratio of a radius of the outer wall (154wo) and a radius of the inner wall (154wi) is in the range of 1.1:1 to 6:1.

8. The system (100) for storing thermal energy as claimed in claim 4 comprising a circulation pump (180) and means for harnessing heat energy (110), the circulation pump (180) being configured for circulating the HTF between the thermal battery (150) and the means for harnessing heat energy (110).