WO2016051233A1

WO2016051233A1 - System and method for harvesting solar thermal energy

Info

Publication number: WO2016051233A1
Application number: PCT/IB2014/064962
Authority: WO
Inventors: Basel Alsayyed
Original assignee: United Arab Emirates University
Priority date: 2014-09-30
Filing date: 2014-09-30
Publication date: 2016-04-07
Also published as: US20170241671A1

Abstract

A system and method for harvesting solar thermal energy is disclosed. The system includes an absorption module, a storage module, and a flow control module. The absorption module retains a working fluid in a substantially constant volume and facilitates absorption of solar thermal energy in the working fluid. The storage module is fluidically coupled to the absorption module and is spatially positioned such that working fluid stored therein has higher gravitational potential energy relative to that stored in the absorption module. The flow control module permits passage of the working fluid from the absorption module to the storage module based on pressure of the working fluid in the absorption module exceeding a predefined threshold. When the working fluid transfers from the absorption module to the storage module, the thermal kinetic energy of the working fluid is transformed into gravitational potential energy thereof.

Description

SYSTEM AND METHOD FOR HARVESTING SOLAR THERMAL ENERGY BACKGROUND OF THE PRESENT INVENTION TECHNICAL FIELD

[0001] The present invention generally relates to harvesting solar thermal energy. More specifically, the present

invention relates to a system and a method for harvesting solar thermal energy to facilitate electrical power

generation .

DESCRIPTION OF THE RELATED ART

[0002] In view of ever increasing demands for electrical power and drawbacks of conventional power generation

techniques, there has been a growing impetus on use of renewable sources of energy.

[0003] Solar energy is an important source of renewable energy. Solar power systems are usually based on photovoltaic principle wherein electricity is directly generated from sunlight. The photovoltaic principle is based on absorption of radiation energy typically in the visible spectrum.

However, such systems suffer from several inherent drawbacks, cost and efficiency being the key inhibitors.

[0004] An alternative technique that has been proposed harnesses solar energy through concentrating solar thermal energy and in turn, using such concentrated solar thermal energy to generate electrical energy. While such techniques appear to be better aligned with conventional power

generation systems and accordingly, more conducive for retro^¬ fitting in the existing power generation systems, such techniques have not been commercially viable so far owing to complex architecture, high cost of maintenance, relatively low efficiency, and overall, low return on investments. [0005] In light of the foregoing, there is a need for simple, low-cost, and efficient system and method for

electrical power generation using solar thermal energy.

SUMMARY OF THE PRESENT INVENTION

[0006] It is an object of the present invention to provide a system for harvesting solar thermal energy in an efficient and cost-effective manner.

[0007] It is another object of the present invention to provide a method for harvesting solar thermal energy in an efficient and cost-effective manner.

[0008] It is yet another object of the present invention to provide a system and a method for generating electrical energy using harvested solar thermal energy.

[0009] The underlying concept of the present invention is to provide means for absorbing solar thermal energy in a working fluid which is retained in a substantially constant volume in an absorption module. Owing to increase in temperature at constant volume, the pressure of working fluid increases. Depending upon its nature, the working fluid may undergo phase transformation and become supercritical. Upon reaching a predefined state, the working fluid is permitted to escape from the confined volume to a storage module, which is at a relatively elevated position in relation to the absorption module. Thus, the working fluid gains gravitational potential energy, which is subsequently used for generating electrical energy. When the working fluid transfers from the absorption module to the storage module, only a part of thermal energy is transformed into gravitational potential energy. The remaining thermal energy still resident in the working fluid is transformed into electrical energy through use of

thermoelectric principle.

[0010] In a first aspect of the present invention, a system for harvesting solar thermal energy is provided. The system comprises an absorption module, a storage module, and a flow control module. The absorption module retains a working fluid in a substantially constant volume. The absorption module is further configured for absorbing solar thermal energy in the working fluid such that thermal kinetic energy of the working fluid is relatively increased resulting in relatively higher pressure thereof. The storage module is fluidically coupled to the absorption module and is spatially positioned such that when stored therein, the working fluid has higher gravitational potential energy relative to when stored in the absorption module. The flow control module regulates passage of the working fluid from the absorption module to the storage module. The flow control module permits passage of the working fluid from the absorption module to the storage module based on pressure of the working fluid in the

absorption module exceeding a predefined threshold. When the working fluid transfers from the absorption module to the storage module, the thermal kinetic energy of the working fluid is transformed into gravitational potential energy thereof .

[0011] In a second aspect of the present invention, a method for harvesting solar thermal energy is provided. At a first step, means for absorbing solar thermal energy are provided such that solar thermal energy is absorbed in a working fluid retained in a substantially constant volume. The thermal kinetic energy of the working fluid is relatively increased resulting in relatively higher pressure thereof.

Subsequently, means for storing the working fluid are provided. Such means are spatially positioned such that when stored therein, the working fluid has higher gravitational potential energy relative to when stored in the means for absorbing solar thermal energy. Finally, passage of the working fluid from the means for absorbing solar thermal energy to the means for storing the working fluid is

permitted based on pressure of the working fluid exceeding a predefined threshold. Thus, thermal kinetic energy of the working fluid is transformed into gravitational potential energy thereof.

[0012] Accordingly, the present invention advantageously provides a system and a method for harvesting solar thermal energy in a simple, efficient, and cost effective manner.

[0013] The present invention transforms the solar thermal energy into gravitational potential energy, which may be subsequently used for generating electrical energy, as may be desired. Accordingly, the techniques of the present invention obviate the need for developing expensive thermal storage systems, as currently being envisaged in the state of the art .

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention is further described

hereinafter with reference to illustrated embodiments shown in the accompanying drawings, in which: illustrates a schematic view of a system for harvesting solar thermal energy in accordance with various exemplary embodiments of the present invention, illustrates a schematic view of a system for harvesting solar thermal energy in accordance with an exemplary embodiment of the present invention,

FIGS 3A-3B illustrate a schematic view of an absorption

module in accordance with an exemplary embodiment of the present invention,

FIG 4 illustrates a schematic view of an absorption

module in accordance with another exemplary embodiment of the present invention, and FIG 5 illustrates a flow chart of a method for

harvesting solar energy in accordance with various exemplary embodiments of the present invention .

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0015] Various embodiments are described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following

description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough

understanding of one or more embodiments. It may be evident that such embodiments may be practised without these specific details .

[0016] Referring to FIG 1, a schematic view of a thermal energy harvesting system 100 for harvesting solar thermal energy is illustrated in accordance with various exemplary embodiments of the present invention.

[0017] The thermal energy harvesting system 100 includes an absorption module 102, a storage module 104, a conversion module 106, and flow control modules 108a, 108b, and 108c. The absorption module 102, the storage module 104, and the conversion module 106 are fluidically coupled through fluid channels 110. The passage of working fluid between individual modules being regulated through the flow control modules 108.

[0018] It should be noted that the term "fluidically

coupled", as used herein, is intended to refer to an

interconnection between any two components such that a fluid channel (regulated or unregulated) exists there between permitting passage of fluid between such components.

[0019] The absorption module 102 retains a working fluid in a substantially constant volume. The absorption module 102 is also configured for absorbing solar thermal energy in the working fluid. [0020] The storage module 104 is fluidically coupled to the absorption module 102 and is spatially positioned such that when stored therein, the working fluid has higher

gravitational potential energy relative to when stored in the absorption module 102.

[0021] Such relative positioning may be achieved in numerous different manners. As one example, it is contemplated that the absorption module 102 is installed relatively closer to ground level, and the storage module 104 is installed at the top of a support tower.

[0022] As the thermal kinetic energy of the working fluid increases, such increase is manifested in an increase in temperature of the working fluid. As stated, the absorption module 102 is configured to retain the working fluid at a substantially constant volume. This could be achieved through use of solid materials with relatively low coefficients of thermal expansion. As the temperature increases at

substantially constant volume, the working fluid attains a higher pressure.

[0023] The working fluid may undergo phase transformation. The working fluid may also become supercritical. The

temperature and/or pressure may be suitably monitored through use of pressure and/or temperature sensors (not shown) .

[0024] The flow control module 108a permits passage of the working fluid from the absorption module 102 to the storage module 104 when pressure of the working fluid in the

absorption module 102 exceeds a predefined threshold. As the working fluid flows from the absorption module 102 to the storage module 104, the thermal kinetic energy of the working fluid is transformed into gravitational potential energy thereof .

[0025] The conversion module 106 is fluidically coupled to the storage module 104. When required, the flow control module 108b is actuated to permit passage of working fluid from the storage module 104 to the conversion module 106. The conversion module 106 is configured to generate electrical energy through converting kinetic energy using techniques generally well understood in the art.

[0026] The working fluid is, subsequently, guided back to the absorption module 102.

[0027] Referring now to FIG 2, a schematic view of a thermal energy harvesting system 200 for harvesting solar thermal energy is illustrated in accordance with an exemplary embodiment of the present invention.

[0028] The thermal energy harvesting system 200 includes an absorption module 202, a storage module 204, a conversion module 206, and flow control modules 208a, 208b, 208c, and 208d. The absorption module 202, the storage module 204, and the conversion module 206 are fluidically coupled through fluid channels 210. The passage of working fluid between individual modules is regulated through the flow control modules 208. The components are analogous to those explained in conjunction with FIG 1 with further details being provided herein .

[0029] As explained previously, the working fluid is

retained at a substantially constant volume in the absorption module 202. The absorption module 202 is configured for absorbing solar thermal energy in solar radiation incident thereon. One exemplary implementation of absorption module 202 is shown in FIG 3.

[0030] Referring now to FIGS 3A and 3B, a schematic diagram of an absorption module 202 is illustrated in accordance with an exemplary embodiment of the present invention.

[0031] The absorption module 202 includes a collector assembly 302 and a reflector assembly 304. The reflector assembly 304 is configured for tracking direction of incident solar radiation and concentrating the incident solar

radiation onto the collector assembly.

[0032] It should be noted that although in the adjoining figure the reflector assembly 304 is shown to be implemented using a conventional solar dish, the present invention is not limited to any specific implementation as such. In various exemplary embodiments of the present invention, the reflector assembly 304 may be implemented using any suitable techniques known in the art, such as use parabolic mirror assemblies, solar tower arrangements, and so on. The reflector assembly 304 typically has a large surface area and is configured to concentrate solar radiation incident over such large surface area on to the collector assembly 302.

[0033] The collector assembly 302 is configured for carrying the working fluid and absorbing therein thermal energy of incident solar radiation. The collector assembly 302 is made of material with high thermal conductivity and low

coefficient of thermal expansion. In one exemplary

implementation, as can be best seen in FIG 3B, the collector assembly 302 is arranged in a spiral-like manner surrounding a loci of focal points of the reflector assembly 304.

[0034] Referring back to FIG 2, the absorption module 202 is fluidically coupled to the storage module 204 through the flow control module 208a. In one embodiment of the present invention, the flow control module 208a is a pressure- actuated valve.

[0035] As explained previously, as temperature of the working fluid rises at substantially constant volume, the pressure of the working fluid increases.

[0036] As the pressure of the working fluid exceeds a predefined threshold, the flow control module 208a permits passage of the working fluid from the absorption module 202 to the storage module 204 through the fluid channel 210. [0037] In an alternative embodiment of the present invention, the flow control modules 208 are electrically- actuated valves. In this embodiment, the absorption module 202 is provided with pressure and/or temperature sensors. The sensors transmit respective sensed values to an integrated control system (not shown) . The integrated control system, in turn, provides actuation signals to a desired flow control module 208 to permit passage of working fluid there through. In particular, when the pressure of the working fluid exceeds a predefined value, the integrated control system actuates flow control module 208a to permit passage of the working fluid from the absorption module 202 to the storage module 204 through the fluid channel 210.

[0038] Regardless of mechanism of actuation flow control module 208, as the working fluid passes from the absorption module 202 to the storage module 204, the thermal kinetic energy of the working fluid is transformed into gravitational potential energy.

[0039] As shown in the adjoining figure, the conversion module 206 is fluidically coupled to the storage module 204. The conversion module 206 is configured for transforming gravitational potential energy of the working fluid stored therein into electrical energy.

[0040] In one embodiment of the present invention, the conversion module 206 includes a turbine assembly 216 and a generator assembly 218 operatively coupled through a drive assemb1y 220.

[0041] The flow control module 208b is operated to permit the working fluid to flow through the fluid channel 210 from the storage module 204 to the conversion module 206. While flowing from the storage module 204 to the conversion module 206, the working fluid gains kinetic energy. In other words, the gravitational potential energy of the working fluid is transformed into kinetic energy. The turbine assembly 216 is, thus, driven by the working fluid. As mentioned previously, the turbine assembly 216 is operatively coupled to the generator assembly 218. The driving force is transmitted from the turbine assembly 216 to the generator assembly 218 through the drive assembly 220. Thus, electrical energy is produced .

[0042] In another exemplary embodiment of the present invention, the conversion module 206 includes a hydraulic motor assembly 216. As in case of the above embodiment, the flow control module 208b is operated to permit the working fluid to flow through the fluid channel 210 from the storage module 204 to the conversion module 206. The working fluid operates the hydraulic motor assembly 216. The hydraulic motor assembly 216 is operatively coupled to the generator assembly 218. The driving force is transmitted from the hydraulic motor assembly 216 to the generator assembly 218 through the drive assembly 220. Thus, electrical energy is produced .

[0043] The electrical energy, thus generated, is output through electrical supply line 224. The electrical supply line 224, in turn, may be connected to an electrical energy storage module 226. In addition, the electrical supply line 224 may feed an electrical grid and/or drive local or remote electrical loads. The electrical energy storage module 226, in turn, is configured for storing electrical energy and may be implemented through capacitor banks or the like. The electrical energy storage module 226 provides a power supply to at least one electrically operated component of the thermal energy harvesting system 200, for example circulating pumps, which will now be explained.

[0044] Still referring to FIG 2, the thermal energy

harvesting system 200 includes a circulating pump 212 fluidically coupling the conversion module 206 and the absorption module 202. The circulating pump 212 is configured for guiding the working fluid from the conversion module 206 to the absorption module 202. [0045] As will be appreciated, when the working fluid flows from the absorption module 202 to the storage module 204, only a part of the thermal kinetic energy is transformed into gravitational potential energy. Accordingly, in one

embodiment of the present invention, it is contemplated that the thermal energy harvesting system 200 includes a

thermoelectric generation module 222 thermally coupled to the storage module 204 and configured to convert thermal energy resident in said working fluid to electrical energy. It is further contemplated that the electrical energy, thus

produced is also output to electrical supply line 224.

[0046] The absorption module 202 may further include a reservoir module 214. The reservoir module 214 maintains volume of the working fluid in circulation. As will be evident from the foregoing description, the working fluid is circulated through a closed loop between three main modules, namely, the absorption module 202, the storage module 204, and the conversion module 206. Hence, as such the volume of the working fluid is envisaged to remain constant. However, in practice certain loss of working fluid may happen. To ensure that the volume of the working fluid remains constant, the reservoir module 214 is provided. As can be seen in the adjoining figure, the reservoir module 214 is fluidically coupled to the absorption module 202 through the flow control module 208d and the circulating pump 212. The flow control module 208d is operated, as may be required, to replenish volume of the working fluid in circulation in the thermal energy harvesting system 200.

[0047] As will now be well understood, thermal energy harvesting system 200 may be provided with multiple flow control modules 208 to regulate passage of fluid there through between any two parts of thermal energy harvesting system 200.

[0048] Referring now to FIG 4, a schematic view of an absorption module 202 is provided in accordance with an exemplary embodiment of the present invention. [0049] The absorption module 202 includes a reflector and collector assembly 402, a heat exchanger 404, a circulating pump 406, and a reservoir module 408.

[0050] As can be understood from the adjoining figure, two independent fluid flow paths A and B are established. The thermal energy of incident solar radiation is absorbed using a first working fluid circulating through fluid flow path A. The heat in the first working fluid is transferred to a second working fluid in the heat exchanger 404.

[0051] Advantageously, in the current embodiment, the two working fluids may be selected to exhibit different thermal properties. In particular, the first working fluid is characterized by higher specific heat relative to the second working fluid, while the second working fluid is

characterized by higher coefficient of thermal expansion relative to the first working fluid.

[0052] It will be readily apparent that the first working fluid should preferably exhibit good heat carrying capacity. This may be achieved through using a fluid with relatively high specific heat such as molten salt. On the other hand, the second working fluid should preferably exhibit high coefficient of thermal expansion such that relatively greater increase in pressure is achieved for a given rise in

temperature .

[0053] It should be noted that the reservoir module 408 is additional to the reservoir module 214. Similarly, the circulating pump 406 is additional to the circulating pump 212.

[0054] Referring now to FIG 5, a flow chart for a method for harvesting solar thermal energy is illustrated in accordance with various exemplary embodiments of the present invention. [0055] At step 502, means for absorbing solar thermal energy are provided such that solar thermal energy is absorbed in a working fluid retained in a substantially constant volume. The thermal kinetic energy of the working fluid is relatively increased resulting in relatively higher pressure thereof.

[0056] At step 504, means for storing the working fluid are provided. Such means are spatially positioned such that when stored therein, the working fluid has higher gravitational potential energy relative to when stored in the means for absorbing solar thermal energy.

[0057] At step 506, passage of the working fluid from the means for absorbing solar thermal energy to the means for storing the working fluid is permitted based on pressure of the working fluid exceeding a predefined threshold. Thus, thermal kinetic energy of the working fluid is transformed into gravitational potential energy thereof.

[0058] In an embodiment of the present invention, at this step, means for thermoelectric generation thermally coupled to said means for absorbing solar thermal energy are also provided to convert thermal energy resident in said working fluid to electrical energy.

[0059] At step 508, means for converting gravitational potential energy of the working fluid into electrical energy are provided.

[0060] At step 510, means for guiding the working fluid from the means for converting gravitational potential energy to said means for absorbing solar thermal energy.

[0061] In various embodiments, the method of the present invention, as mentioned in the preceding steps, also includes providing means for flow control for regulating passage of fluid there through. [0062] While the present invention has been described in detail with reference to certain embodiments, it should be appreciated that the present invention is not limited to those embodiments. In view of the present disclosure, many modifications and variations would present themselves, to those of skill in the art without departing from the scope of various embodiments of the present invention, as described herein. The scope of the present invention is, therefore, indicated by the following claims rather than by the

foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.

Claims

What is claimed is:

1. A system for harvesting solar thermal energy, said system comprising :

- an absorption module, said absorption module configured for retaining a working fluid in a substantially constant volume and further configured for absorbing solar thermal energy in said working fluid such that thermal kinetic energy of said working fluid is relatively increased resulting in relatively higher pressure thereof;

- a storage module, said storage module being fluidically coupled to said absorption module and spatially

positioned such that when stored therein, said working fluid has higher gravitational potential energy relative to when stored in said absorption module, and

- a flow control module, said flow control module

regulating passage of said working fluid from said absorption module to said storage module, wherein said flow control module is configured for permitting passage of said working fluid from said absorption module to said storage module based on pressure of said working fluid in said absorption module exceeding a predefined threshold, whereby thermal kinetic energy of said working fluid is transformed into gravitational potential energy thereof.

2. The system according to claim 1 further comprising a

conversion module, said conversion module being

fluidically coupled to said storage module and configured for transforming gravitational potential energy of said working fluid stored therein into electrical energy.

3. The system according to claim 2, wherein said conversion module comprises a turbine assembly configured to be driven by said working fluid, said turbine assembly operatively coupled to a generator assembly and

configured for providing a driving force thereto, whereby electrical energy is produced.

4. The system according to claim 2, wherein said conversion module comprises a hydraulic motor assembly configured to be operated by said working fluid, said hydraulic motor assembly operatively coupled to a generator assembly and configured for providing a driving force thereto, whereby electrical energy is produced.

5. The system according to claim 2 further comprising a

circulating pump fluidically coupling said conversion module and said absorption module and configured for guiding said working fluid from said conversion module to said absorption module.

6. The system according to any of the preceding claims,

wherein said absorption module comprises a collector assembly configured for carrying said working fluid and absorbing therein thermal energy of incident solar radiation, a reflector assembly configured for tracking direction of incident solar radiation and concentrating said incident solar radiation onto said collector

assembly .

7. The system according to any of the preceding claims

wherein said absorption module further comprises a heat exchanger such that thermal energy of incident solar radiation is absorbed using a first working fluid, and transferred to a second working fluid in said heat exchanger .

8. The system according to any of the preceding claims

wherein, said first working fluid is characterized by higher specific heat relative to said second working fluid .

9. The system according to any of the preceding claims

wherein, said second working fluid is characterized by higher coefficient of thermal expansion relative to said first working fluid.

10. The system according to any of the preceding claims wherein said absorption module comprises a reservoir module, said reservoir module configured for maintaining volume of said working fluid in circulation.

11. The system according to any of the preceding claims

further comprising a plurality of flow control modules to regulate passage of fluid there through between at least a first part and at least a second part of said system.

12. The system according to any of the preceding claims,

wherein said flow control module is a pressure-actuated valve .

13. The system according to any of the preceding claims,

wherein said flow control module is an electrically- actuated valve.

14. The system according to any of the preceding claims

further comprising a thermoelectric generation module thermally coupled to said storage module and configured to convert thermal energy resident in said working fluid to electrical energy.

15. The system according to any of the preceding claims

further comprising an electrical energy storage module configured for storing electrical energy and providing a power supply to at least one electrically operated component of said system.

16. A method for harvesting solar thermal energy, said method comprising :

- providing means for absorbing solar thermal energy in a working fluid retained in a substantially constant volume such that thermal kinetic energy of said working fluid is relatively increased resulting in relatively higher pressure thereof;

- providing means for storing said working fluid

spatially positioned such that when stored therein, said working fluid has higher gravitational potential energy relative to when stored in said means for absorbing solar thermal energy, and

- permitting passage of said working fluid from said means for absorbing solar thermal energy to said means for storing said working fluid based on pressure of said working fluid exceeding a predefined threshold, whereby thermal kinetic energy of said working fluid is

transformed into gravitational potential energy thereof.

17. The method according to claim 16 further providing means for converting gravitational potential energy of said working fluid into electrical energy.

18. The method according to claim 17 further comprising

providing means for guiding said working fluid from said means for converting gravitational potential energy to said means for absorbing solar thermal energy.

19. The method according to any of the preceding claims

further comprising providing means for flow control for regulating passage of fluid there through.

20. The method according to any of the preceding claims

further comprising providing means for thermoelectric generation thermally coupled to said means for absorbing solar thermal energy to convert thermal energy resident in said working fluid to electrical energy.