Abstract:
A solar energy collecting system comprises a manifold defining a closed fluid passage between a condensation point and a heating point. The manifold includes a plurality of heat exchange members configured to be in heat exchange relationship with the fluid passage at the heating point, and a heat sink at the condensation point. A plurality of solar energy collector members extend from and operably connect to the heat exchange members of the manifold. The solar energy collector members collect solar energy and transform it into heat energy. Heat energy is transferred from the solar energy collector members to the heat exchange members and to a fluid in the passage in the manifold at the heating point so as to heat the fluid into a vapor. The fluid is circulated in heat exchange relationship to the condensation point where heat energy is transferred to the heat sink so as to cool the fluid to a liquid. The fluid repeatedly cycles between a vaporized state at the heat exchange members and a liquefied state at the condensation point.

Description:
CROSS-REFERENCES 
     This application is related to U.S. provisional application No. 61/251,568, filed on Oct. 14, 2009, entitled “SOLAR COLLECTOR SYSTEM”, naming Jeffrey Lee as the inventor. The contents of the provisional application are incorporated herein by reference in their entirety, and the benefit of the filing date of the provisional application is hereby claimed for all purposes that are legally served by such claim for the benefit of the filing date. 
    
    
     BACKGROUND 
     This invention relates generally to a solar energy collector system, and more particularly to a system and method for collecting solar radiant energy for converting to heat energy for a practical use. 
     Solar energy collector systems typically comprise a plurality of vacuum jacketed tubular collector elements. Each tubular collector element is sealed at its ends, contains a volatile fluid therein, and is in contact with a solar absorber. The solar absorber converts solar radiant energy to heat energy. The solar absorber transfers the heat energy to the tubular collector elements, which causes fluid in the tubular collector elements to vaporize. A pressure difference between the two ends of the tubular collector elements drives the vapor towards a cooler condenser portion of the collector element. The condenser portion is in contact with a heat sink. In the condenser portion of the collector element, heat is conducted from the vapor of the fluid inside the collector element to the heat sink outside of the collector element. The lower temperature of the vapor due to conduction of the heat from the vapor to the heat sink results in condensation of the fluid in the collector element. The condensed fluid then flows downward from the condenser portion of the collector element wherein solar energy is again absorbed to evaporate the fluid and continue the cycle. 
     In one application, the tubular collector elements are operably connected in a manifold, which serves to distribute and collect a working fluid, functioning as the heat sink. The working fluid is circulated for heating around the condenser portions of the tubular collector elements for removal of thermal energy absorbed by the collector elements. The tubular collector elements transfer the absorbed solar energy to the working fluid for storing the collected thermal energy, or for transferring the energy to a location where it can be put to practical use. 
     Developmental efforts relating to evacuated tubular collector elements has been directed to improving the efficiency of removal of the absorbed thermal energy. For the foregoing reasons, there is a need for an improved system and method for the removal of the thermal energy absorbed by evacuated tubular collector elements. 
     SUMMARY 
     A solar energy collecting system is provided, comprising a manifold defining a closed fluid passage between a condensation point and a heating point. The manifold includes a plurality of heat exchange members configured to be in heat exchange relationship with the fluid passage at the heating point, and a heat sink at the condensation point. A solar energy collecting device includes a plurality of solar energy collector members extending from and operably connected to the heat exchange members of the manifold. The plurality of solar energy collector members are adapted to collect solar energy and transform said solar energy into heat energy. Heat energy is transferred from the solar energy collector members to the heat exchange members and to a fluid in the passage in the manifold at the heating point so as to heat the fluid into a vapor. The fluid is circulated in heat exchange relationship to the condensation point where heat energy is transferred to the heat sink so as to cool the fluid to a liquid. The fluid repeatedly cycles between a vaporized state at the heat exchange members and a liquefied state at the condensation point of the fluid passage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference should now be had to the embodiments shown in the accompanying drawings and described below. In the drawings: 
         FIG. 1  is an elevation view of an embodiment of a solar energy collector system. 
         FIG. 2  is perspective view of a heat exchange manifold with the internal features shown in phantom for use in the solar energy collector system shown in  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the manifold shown in  FIG. 2 . 
         FIG. 4  is a top plan view of the body of the manifold shown in  FIG. 3 . 
         FIG. 5  is a longitudinal cross-section view of the manifold shown in  FIG. 2 . 
         FIG. 6  is a transverse cross-section view of the manifold shown in  FIG. 2 . 
         FIG. 7  is a partial exploded left side perspective view of the solar energy collector system shown in  FIG. 1 . 
         FIG. 8  is a bottom perspective cross-section view of the solar energy collector system shown in  FIG. 1 . 
         FIG. 9  is a top perspective cross-section view of another embodiment of a manifold for use in the solar energy collector system shown in  FIG. 1 . 
         FIG. 10  is a process flow chart of an embodiment of a solar energy collector system. 
     
    
    
     DESCRIPTION 
     Certain terminology is used herein for convenience only and is not to be taken as a limitation on the invention. For example, words such as “upper,” “lower,” “left,” “right,” “horizontal,” “vertical,” “upward,” and “downward” merely describe the configuration shown in the FIGs. Indeed, the components may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise. 
     Referring now to the drawings, wherein like reference numerals designate corresponding or similar elements throughout the several views, an embodiment of a system for collecting and converting solar energy into heat energy is shown in  FIG. 1  and generally designated at  20 . The solar collector  20  comprises a plurality of tubular solar energy collector members  22  operably and detachably connected in parallel and extending from the bottom of an insulated, heat exchange housing  21 . In the embodiment depicted, only four tubular solar energy collector members  22  are shown for illustrative purposes only. It is understood that a large array of spaced collector members  22  in parallel may be used, as is known in the art. 
     The tubular solar energy collector members  22  may comprise conventional glass evacuated tube heat pipe solar collectors, including an outer glass evacuated tube  24  and a closed heat transfer pipe  26  embedded within the glass evacuated tube  24 . The heat transfer pipe  26 , or heat pipe, may be embodied as a copper pipe, including a stem  28  having a bulb  30  extending from one end of the glass tube  24 . The collector members  22  absorb solar radiant energy and transfer the absorbed energy to a working fluid in the heat pipe  26 . 
     As shown in  FIG. 1  and described more fully below, the upper end of each heat pipe  26 , including the bulb  30 , is inserted into the insulated housing  21 . In this arrangement, the heat pipe  26  communicates in a heat exchange relationship with the housing  21  for transferring the heat energy from the heat pipe  26  to a thermal transfer fluid circulating in the housing  21 . In operation, the energy in the form of the working fluid vapor condenses in the pipe bulb  30  for transferring heat energy to the pipe bulb  30 . The heat from the pipe bulb  30  is then transferred in the housing  21  for heating the thermal transfer fluid. While tubular solar energy collector members  22  are depicted, it is understood that any suitable solar energy collecting device having a solar energy collecting surface may be mounted to the heat exchange housing  21  for collecting and transforming solar energy into heat energy to increase the temperature of the thermal transfer fluid in the heat exchange housing  21 . 
     Referring now to  FIGS. 2 and 3 , the heat exchange housing  21  accommodates a manifold assembly  40  comprising a body  42 , a top plate  44  and a bottom plate  46 , and a plurality of receptacles  48  for receiving the pipe bulbs  30  on the ends of the heat pipes  26 . The top plate  44  is a generally flat rectangular piece. The top plate defines a central opening  50  for receiving a heat sink  84 . Similarly, the bottom plate  46  is a generally flat rectangular piece and defines circular openings  52  longitudinally spaced along the bottom plate  46 . 
     The body  42  of the manifold assembly  40  is a generally rectangular box. Longitudinally spaced blind cylindrical bores  54  are formed in the body  42 , which function as receptacle cavities  80  for accommodating the receptacles  48 . As shown in  FIG. 4 , the upper surface  56  of the body  42  has a V-shaped groove  58  formed therein. A four-sided condensation reservoir  60  is centrally located with respect to the groove  58 . The condensation reservoir  60  extends further into body  42  than the V-shaped groove  58 . Three spaced wicking elements  62  extend transversely across the upper surface  56  of the body  42  above the condensation reservoir  60  forming a mesh capillary wick. 
     The receptacles  48  comprise hollow substantially cylindrical copper sleeves open at one end. The receptacles  48  have three longitudinally-spaced circumferential grooves  64 ,  66  in the outer surface of the receptacle adjacent the open end. The upper groove  64  is configured to receive a retaining ring  68 . The lower grooves  66  each receive an o-ring  70 . The o-rings  70  may be made of rubber or suitable plastic material. 
     To assemble the manifold  40 , the receptacles  48  are disposed in the bores  54  of the body  42 . Referring to  FIGS. 5 and 6 , the receptacles  48  are advanced into the bores  54  until the retaining rings  68  seat in a circular groove  72  formed in the bottom surface  74  of the body  42 . The diameter of the receptacles  48  is slightly less than the diameter of the bores  54  such that receptacle cavities  80  are created between the inside surface of the bores  54  and the outside surface of the receptacles  48 . The top plate  44  and bottom plate  46  are then secured to the body  42 . Numerous openings  76  are disposed along the edges of the top plate  44  and bottom plate  46  for passing screws  79  which are threaded into corresponding openings  78  in the body  42 . When assembled, the central opening  50  in the top plate  44  is in registry with the condensation reservoir  60  in the upper surface  56  of the body  42 . The circular openings  52  in the bottom plate  46  are in registry with the receptacle cavities  54  in the body  42 . As shown in  FIGS. 5 and 6 , the open ends of the receptacles  48  extend from the bottom plate  46 . Securing the bottom plate  46  to the body  42  also fixes the retaining rings  68  and their associated receptacles  48  in the body  42 . The o-rings  70  seal the outer surface of the receptacles  48  against the bottom plate  46  to prevent leakage of thermal transfer fluid. 
     Referring to  FIGS. 7 and 8 , the receptacles  48  are sized to receive the bulbs  30  of the heat pipes  26 . The receptacles  48  are sized so that the bulbs  30  fit in close contact with the receptacles  48  such that the bulbs  30  are held securely in the receptacles  48  of the manifold  40  at least partially by friction. It is understood that the pipe bulbs  30  can be secured in the receptacles  48  by any suitable means. For example, the receptacles  48  may have an internal thread and the pipe bulbs  30  may also be provided with a mating externally threaded portion (not shown). It is thus understood that other suitable techniques may be employed for holding the heat pipes  26  in contact at the bulbs  30  with the receptacles  48 . 
     As best seen in  FIGS. 2 and 5 , the manifold  40  defines a fluid passage for circulating the flow of the thermal transfer fluid from the receptacle cavities  80  to the heat sink  84  and from the heat sink  84  back the receptacle cavities  80 . The V-shaped groove  58  in the upper surface  56  of the body  42  of the manifold  40  functions as a vapor chamber in the fluid passage between the receptacle cavities  80  and the heat sink  84 . A small central opening is provided at the top of each receptacle cavity  80  and opens into the vapor chamber  58  ( FIG. 4 ). The fluid passage comprises a distribution passage  82  and a return path  86 . The distribution passage  82  distributes the flow of the thermal transfer fluid to the receptacle cavities  80  and around the peripheral surface of the receptacles  48  for heat transfer from the bulbs  30  to the thermal transfer fluid. As shown by  FIG. 6 , the thermal transfer fluid flows into the receptacle cavities  80  via inlet openings  88  in the distribution passage  82 . The return passage  86  extends between the condensation reservoir  60  and the distribution passage  82 . As best seen in  FIG. 4 , the return path  86  opens into the condensation reservoir  60  at the base of the V-shaped groove  58 . 
     An amount of thermal transfer fluid is placed in the fluid passage of the manifold  40  before it is sealed. It is understood that there are a number of thermal transfer fluids that can be used satisfactorily, including water, ammonia, methanol, ethanol, or other suitable volatile fluid, as well as commercially available heat transfer fluids. For low temperature uses, a fluid with a higher vapor pressure, such as methanol, is preferred, and for higher temperature uses water can be used. 
     Referring to  FIG. 10 , in use the solar collector system  20  is located on top of a house or other building for exposure to sunlight for collecting solar energy. As is known in the art, the collector system  20  is installed preferably in an oblique position, with the heat exchange housing  21  above the collector members  22  and in a generally horizontal position with respect to the ground. The solar collector members  22  are operatively connected with the housing  21  and extend downwardly from the housing such that the distal ends of the heat pipes  26  are in a position somewhat lower than the bulbs  30 . Additionally, parabolic or focusing reflectors can be placed behind the solar collector members for concentrating solar radiation incident upon the collecting surface. 
     The outer surfaces of the collector members  22  define a solar energy collecting surface. As solar radiation impinges on the solar collector members  22 , the solar energy, primarily in the form of light, is absorbed by the collecting surface and the heat generated is transferred to the working fluid within the heat pipes  26 . The energy causes the working fluid in the heat pipes  26  to evaporate so that the vapors are driven to a lower pressure area in the bulb  30  at the upper end of the heat pipe  26 . The bulbs  30  are inside the heat exchange housing  21  in a heat exchange relationship with the receptacles  48 . As described above, the thermal transfer fluid is distributed to each receptacle cavity  80  through the inlet openings  88  in the distribution passage  82 . The thermal transfer fluid in the receptacle cavities  80  provides a cooler environment around the pipe bulbs  30  and absorbs heat from the bulb  30 . The receptacles  48  thus function as a bridge for transferring heat from the pipe bulbs  30  to the interior of the manifold  40 , for heating the thermal transfer fluid in the receptacle cavities  80 . As a result, the heat of the working fluid is exchanged, or given up, to the thermal transfer fluid via the receptacles  48 . As the working fluid cools by such heat transfer, the working fluid becomes more dense and begins to flow downwardly toward the distal ends of the collector members  22  where it is again heated. The working fluid is thus circulated by evaporation and condensation action as is known in the art. 
     The heated receptacles  48  cause the thermal transfer fluid in the receptacle cavities  80  to vaporize. It is understood that several factors are considered in determining the heat transfer between the working fluid and the thermal transfer fluid. For example, physical parameters of the manifold  40 , such as the relative diameter of the receptacles  48  and the receptacle cavities  80 , the thickness of the wall of the receptacle  48  and the thermal conductivity of the material by which the heat absorbing components are made, all determine the heat transfer effectiveness and efficiency between the working fluid and the thermal transfer fluid within the fluid passage. 
     The thermal transfer fluid vapor exits the receptacle cavities  80  via openings  90  at the top of each of the receptacle cavities  80 . The vapor enters the vapor chamber  58  and travels toward the condensation reservoir  60  where the heat sink  84  is located. Once the vaporized thermal transfer fluid reaches the heat sink  84 , the thermal transfer fluid transfers its heat to the heat sink  84 . The heat sink  84  then transfers heat to, for example, a heat engine, such as a Stirling engine or thermoelectric generator, which can convert thermal energy to electricity or other practical use. 
     As a result of heat transfer, the thermal transfer fluid vapor condenses into liquid form. The wick  62  enhances the capillary drive distribution of the thermal transfer fluid along the inside surface of the condensing portion of the heat sink  84 . Conventional mesh or grooved wicks are suitable for efficient capillary drive of the thermal transfer fluid. The wick  62  expedites the flow of condensate away from the surfaces of the heat sink  84  to allow for continual rapid condensation. The condensed thermal transfer fluid is directed into the condensation reservoir  60  and down the return passage  86  located below the heat sink  84 . The return passage  86  feeds the thermal transfer fluid into the distribution passage  82  for distribution to the receptacle cavities  80 . In this manner, the solar collector system  20  facilitates the continuous cycle of vaporization in the receptacle cavities  80  and condensation at the heat sink  84 . 
     Another embodiment of the manifold  40  is shown in  FIG. 9  and comprises a condensate collection system including a plurality of baffles  92  configured in the body  42 . The collection system gathers the condensed thermal transfer fluid by gravity into a common liquid reservoir located below the heat sink  84  and surrounding and shared by all of the receptacle cavities  80 . The receptacle cavities  80  are linked together to allow vapor to flow from the receptacle cavities to a central condenser cavity housing the heat sink  84 . The condenser cavity collects condensation from the heat sink and directs the fluid via the condensate collecting system to the liquid reservoir common to the receptacle cavities  80  where the working fluid can again be heated and turned to vapor. The linkage between the receptacle cavities include the baffles  92 , which are shaped in a manner to allow condensate to drain to the receptacle cavities. 
     The solar collector system  20  as described herein may be fabricated in modular sections and, subsequently, a plurality of modules may be interconnected in series (not shown). Each receptacle  48 , or series of receptacles, is modular and can be linked in series with other receptacles  48  to enlarge the overall size of the manifold  40  and the number of modular receptacle units feeding a central vapor cavity. This modularity also allows for ease of logistics in shipping several modules that can be assembled into a lengthy manifold at the deployment site as opposed to shipping a single lengthy non-modular manifold. 
     The solar collector system  20  described herein is an efficient means for transferring absorbed heat, with minimal loss, to a thermal transfer fluid medium circulating in a manifold. The system provides the advantage of making available a large number of solar energy collector members  22  in parallel to transfer heat to effect the thermal transfer fluid vaporizing-condensing cycle. This arrangement provides for a concentration of heat energy from the collector members to a single point using a closed condensation and evaporation cycle of a heated liquid, allowing for the conversion of heat energy to electricity or other practical use. 
     An additional advantage of the system is unidirectional flow of vapor within the closed vaporizing-condensing cycle. This unidirectional flow provides the benefit of allowing for the conversion of kinetic energy into electrical energy through such means, for example, as a microturbine ( FIG. 10 ). Unidirectional vapor flow is created by designing the condensate collection system in such a way as to allow the thermal transfer fluid to act as a barrier in preventing vapor from flowing in the opposite direction of the intended closed cycle. This barrier is created by both the surface tension of the thermal transfer fluid and the hydrostatic pressure of the condensation reservoir to the return passage. 
     The solar collector system  20  also enables the passive allocation of thermal energy available for conversion to electrical energy based on seasonal variation in sunlight intensity. The manifold allows the user to take advantage of both the efficient operation of heat engines at higher temperature differentials and the inefficient operation of heat engines at lower temperature differentials. The rate of heat energy accumulation in the manifold represented as the ratio between rate of heat loss through the heat engine and rate of heat production from the array of insulated heat pipes will enable passive control in utilizing excess heat production during the summer to generate electricity. Given a certain climate and expected heat demand by dwelling occupants, a target maximal heat production can be used to calculate the number of insulated heat pipes necessary to meet heating demand during the winter. Once the rate of heat production is fixed through the target heat production, the size of the cross-sectional area will be scaled to control the rate at which heat energy is accumulated in the manifold to create a temperature differential needed to drive a heat engine. Given that solar insulation intensity at any given time of the day is roughly twice as intense during the high summer than the low winter, greater temperature differentials will be created in the summer to effectively fuel a heat engine and produce some captured thermal energy ( FIG. 10 ), while lower temperature differentials will be created in the winter to mainly capture thermal energy and generate little fuel for a heat engine. 
     An important passive control component of the manifold is the heat sink. The heat sink is designed in such a way as to facilitate rapid condensation by maximizing the surface area and shedding of condensation. The ability of the heat sink to rapidly condense vapor facilitates the ability of the manifold to create a high temperature differential to fuel a heat engine. The rapid condensation functionality of the manifold is enhanced through the implementation of various methods to the heat sink, for example, various coatings, anodizing, wicks, and the like. 
     The continual closed loop cycle of evaporation-condensation of the thermal transfer fluid is expedited by lowering the internal pressure of the manifold and by removing other unintended fluids from the manifold. Lowering the internal pressure and removing contaminating fluids from the manifold, such as through vacuum sealing, allows the thermal transfer fluid to vaporize at a lower temperature; thus lowering the energy barrier to quickly start the closed loop cycle. Additionally, the thermal transfer fluid is purged of contaminating fluids, such as air, through processes, such as sonication, boiling, and freezing. The process of filling the manifold with thermal transfer fluid can be done by vacuum sealing purified, frozen thermal transfer fluid in an environment with cold ambient temperatures. 
     Although the solar collector system and method has been shown and described in considerable detail with respect to only a few exemplary embodiments thereof, it should be understood by those skilled in the art that I do not intend to limit the invention to the embodiments since various modifications, omissions and additions may be made to the disclosed embodiments without materially departing from the novel teachings and advantages of the invention, particularly in light of the foregoing teachings. For example, a fluid inlet may be adapted for connecting with a fluid source and a fluid outlet may be connected to the manifold for conducting the thermal transfer fluid from the source and out of the manifold. The heated thermal transfer fluid flowing from the outlet can be used for conventional heating applications or other uses. Accordingly, I intend to cover all such modifications, omission, additions and equivalents as may be included within the spirit and scope of the invention as defined by the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures.