WO2012076949A1

WO2012076949A1 - A solar parabolic trough collector or reflector system

Info

Publication number: WO2012076949A1
Application number: PCT/IB2011/002805
Authority: WO
Inventors: Ravikumar Valjibhai Karoria; Shailesh Virendrabhai Pandya; Siddarth Mukesh Bhandari; Sachin Rameshchandra Shah
Original assignee: Electrotherm Renewables
Priority date: 2010-12-07
Filing date: 2011-11-24
Publication date: 2012-06-14

Abstract

The present invention relates to a solar parabolic trough collector or reflector system. More particularly, the present parabolic trough collector / reflector system is installed inclined, with all glass evacuated tube absorber and passive heat collection. More particularly, the said solar parabolic trough type collector system, having an inclined setup with reference to the horizontal plane.

Description

A SOLAR PARABOLIC TROUGH COLLECTOR OR REFLECTOR SYSTEM"

FIELD OF THE INVENTION

The present invention relates to a solar parabolic trough collector or reflector system.

More particularly, the present invention relates to a parabolic trough collector / reflector system, which is installed inclined with reference to the horizontal plane, with all glass evacuated tube absorber and passive heat collection. BACKGROUND AND PRIOR ART OF THE INVENTION

It is known that solar energy can be the replacement of fossil fuels in future as latter tends to diminish. The enormous amount of solar energy falling on the earth surface can be utilized with properly designed solar products as per the requirement.

Solar energy can be collected by a collector which can be of concentrating or non- concentrating type as per the temperature requirement of the application for which it has been designed. Concentrating type solar collectors are used to achieve higher temperatures. In a concentrating type solar thermal collector, the absorber collects the heat which is concentrated using reflectors / optical mirrors or lenses having suitable geometry. A suitable tracking system is also incorporated to keep the focus of collected sunlight on absorber throughout the day. The heat is transferred to the working fluid from the absorber which is taken to the usage point. Solar concentrating products having temperatures in the range of 90 °C to 1200 °C are already in commercial use and can be designed depending upon application requirement, systems for different temperatures.

Solar parabolic trough has been proven and widely used product in the area of solar concentrating collectors due to its ease in engineering design as compared to other solar concentrating collector designs.

The parabolic troughs which are used in power plants possess a huge structural element which is a drawback for tracking. Another drawback is high absorber prices due to its complex technology. This kind of absorbers are generally metal tubes having solar selective coating which are shielded with glass tube and space between them is evacuated for minimizing heat losses. To maintain the evacuation when in operating mode, while the temperature is high and thermal expansion of both the metal tube and glass tube is different, a bellow shaped design is in practice to adjust against differential expansions. To reduce the absorber length for a particular field, trough width is increased. Increased trough width has to undergo higher wind facing due to higher area.

In general, absorber tubes shown in figures 1 (photographic view) and 2 (schematic view) are the glass evacuated tube Images which are presently in commercial use. This kind of absorber tubes are normally used for solar power generation plants and are very costly to use for other puiposes like solar air-conditioning, process heating, etc.

The Purpose of such tubes:

1 . Inner tube is made of SS/metal with solar selective coating and outer tube is made of transparent glass; the space between both the tubes is evacuated to suitable level so as to reduce overall heat loss. The design is such that it allows sustaining vacuum in spite of different thermal expansion of inner and outer tube material. This kind of absorber tubes are both side open which facilitates joining of two consecutive tubes by orbital welding or similar technique (as shown in figure 2a).

Following are the disadvantages of such absorber tubes:

1. Extremely costly;

2. The use of such tubes almost makes restriction to install the parabolic troughs horizontally only which is disadvantageous because it gives less effective collection of solar energy per unit of collector area;

3. Horizontal installation also limits the system for single axis tracking only for daily east to west movements, while in case of inclined installation system can be facilitated with dual axis tracking in which second axis will take care of seasonal elevation changes of sun hence further improving collection efficiency. Such system with dual axis tracking deployed in it will collect solar radiation almost normal to its collector/aperture area;

4. The use of rotating/pivoting type piping end connections (at the end of each row) make it very costly due to moving absorber tube in most of the conventional parabolic trough designs (as shown in figure 4); and 5. No mass balancing practices due to costly reflective surface.

Further, there are non-moving absorber type parabolic trough design (as shown in figure 6 and 7), however the said system having disadvantages of 1 ) non-mass balancing increases higher tracking power consumption 2) Use of non-evacuated absorbers makes it less efficient and 3) Horizontal trough design makes solar energy collection less efficient. The aperture area of such trough is not near normal to the sun direction.

Another reason for huge structural elements is the use of glass mirrors. Due to its fragile nature, the thickness of glass is kept enough to sustain against wind and other loads. The high thickness glass mirror elements results in high handling weight for structure due to its high density.

Such huge structures are difficult to process and assemble at site with glass mirrors. They require high power consumption and complex tracking mechanism also.

The parabolic troughs are usually having its installation in horizontal condition for ease in flow of working fluid inside the absorber tube. This has a drawback of less effective solar radiation collection per unit of collector area especially with installation in higher geographic latitude region in either hemisphere.

OBJECTIVES OF THE INVENTIONS

The primary objective of the present invention is to provide a solar parabolic trough collector or reflector system, which overcome the above-said drawbacks.

Another objective of the present invention is to provide a solar parabolic trough system whereby the said system capable to install inclined with reference to the horizontal plane and according to geographical location.

Yet another objective of the present invention is to provide a solar parabolic trough system whereby dual axis tracking is possible to collect the radiation normal to its collector area so as to gain maximum possible collection efficiency. Yet another objective of the present invention is to provide a solar parabolic trough system having a parabolic profile and structure designed to achieve mass balancing with reference to tracking axis. Yet another objective of the present invention is to provide a solar parabolic trough system whereby the evacuated all glass absorber tube is incorporated.

SUMMARY OF THE INVENTION

The present invention relates to a solar parabolic trough collector or reflector system, whereby to collect solar energy, the said system comprising a solar energy concentrator on a line focus which is kept inclined. The major components of the present invention are concentrator (collector), absorber tube, heat transfer system, structure, bearing blocks, tracking system including mechanism, electronics and software. The present parabolic trough system having:

1. Inclined main tracking axis as per the geographic location

2. Concept of dual axis tracking in a parabolic trough system

3. Mass balancing of rotating segment for minimizing tracking torque requirement

4. Non-moving absorber

5. Use of evacuated all glass absorber tube

BRIEF DESCRIPTION OF FIGURES /DRAWINGS

Further aspects and advantages of the present invention will be readily understood from the following detailed description with reference to the accompanying figures.

The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention wherein: Figure 1 , 2 and 2a show an individual absorber tube which is known in the parabolic trough system.

Figure 3 and 4 shows an absorber tube (3a) is kept in horizontal plane in a parabolic trough collector/ reflector.

Figure 5 shows a typical non-mass balanced axial assembly having focus of parabola and center of mass apart from each other. Figure 6 and 7 shows non-moving absorber type parabolic trough design presently in use. Figure 8 shows a mass balanced axial assembly having focus of parabola and center of mass coincides according to the present invention.

Figure 9 shows that by using hanging support (9a) an absorber tube is placed at focal line of parabolic trough, in case parabolic profile is constructed shallow according to an embodiment of the present invention.

Figure 10 shows that an absorber tube (fixed component) is placed at focal line of parabolic trough (rotating component) by using bearing block assembly ( 10a) according to an embodiment of the present invention.

Figure 1 1 shows another novel and inventive aspect of the present invention, wherein the parabolic trough comprising absorber tubes (1 l a) in inclined condition as compare to land / ground ( l i b) according to an embodiment of the present invention.

Figure 12 shows typical setup for two axis tracking system which can be facilitated by manual or automatic according to an embodiment of the present invention.

Figure 13 shows the typical isometric view of the present solar parabolic trough assembly with fixed (non-moving) absorber tube according to an embodiment of the present invention.

Figure 14 exhibit absorber tube and heat pipe assembly according to an embodiment of the present invention.

Figure 15 and 16 shows one or more parabolic trough collector / reflector (25, 26 and 27), which are being connected to a common header (28) in a solar field according to an embodiment of the present invention.

Figure 17 shows typical parabolic rib installed in the rotating frame at defined interval to provide support to the flexible mirror / metal reflectors according to an embodiment of the present invention.

Figure 18 denotes a typical main frame which is assembled to the bearing blocks at both ends of present system to form rotating joint according to an embodiment of the present invention.

Figure 19 shows a typical mass balanced axial assembly having focus of parabola and center of mass coinciding according to an embodiment of the present invention. Figure 19 denotes typical axial assembly in which center of mass of the rotating body coincides with the parabolic profile focus to get benefit of less energy consumption while tracking. Figure 20 shows a typical cross-section of bearing block for the present invention. Skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

DETAIL DESCRIPTION OF THE FIGURES/DRAWINGS

While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figures and will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the invention as defined by the appended claims.

Before describing in detail embodiments it may be observed that the novelty and inventive step that are in accordance with the present invention resides in solar parabolic trough system. It is to be noted that a person skilled in the art can be motivated from the present invention and modify the various constructions of assembly. However, such modification should be construed within the scope and spirit of the invention.

Accordingly, the drawings are showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such setup or device. In other words, one or more elements in a system or apparatus proceeded by "comprises... a" does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus. The following paragraphs explain present invention with respect to a solar parabolic trough system with all glass evacuated tube absorber and passive heat collection. The invention in respect of the same may be deduced accordingly. Accordingly the present invention relates to a solar parabolic trough collector system comprising:

individual absorber tubes (22, 24a, 24b) connected to a common header (28) and aligned parallel with each other so that heat is transferred to the fluid flowing in the common header (28), the said individual absorber tubes are glass evacuated tube and open from one side, whereby the heat tube (23) along with heat pipe condenser (24) extends through the open end (22f) of absorber tube and connected to the said common header,

individual parabolic reflectors ( 15, 25, 26, 27) being mounted with inclination on mounting stand ( 14) in such a manner that tracking axis and focal line of parabolic reflectors remain coincide with each other and the said individual absorber tube (22, 24a, 24b) is installed on the said focal line, so that the radiation reflected by the reflector surfaces ( 16) of parabolic reflectors focuses on to the glass absorber tubes.

assembly for dual axis tracking (12a) for the said parabolic trough reflectors, the said assembly being mounted on the mounting stand along with driving mechanism ( 19) and operationally configured with a controller (21 ).

First aspect of the present invention relates to a solar parabolic trough collector system, wherein the said absorber tube (22) having two ends, one is close end (22e) and another one is open end (22f), whereby at close end (22e) the ends of inner tubes are fused each other and ends of outer tube are also being fused from each other, whereas at open end the outer glass tube ends and inner glass tubes ends are fused and created an open end (22f).

Second aspect of the present invention relates to a solar parabolic trough collector system, wherein vacuum is created between outer tube and inner tube of absorber tube and solar selective material coating (22g) is provided on the outer surface of inner tube (22b) to sustain against medium and high temperatures.

One more aspect of the present invention relates to a solar parabolic trough collector system, wherein the solar selective coating material (22g) is selected which sustain at high temperature with improved optical parameters. Another aspect of the present invention relates to a solar parabolic trough collector system, wherein the solar selective coating material is selected from Titanium, Aluminium Nitride (A1N), black Chrome, black Nitride or combination thereof or other conventional known solar selective coatings.

Still another aspect of the present invention relates to a solar parabolic trough collector system, wherein the absorber tube comprising metal fins (22c), heat pipe (23) along with heat pipe condenser (24), so that absorbed energy on the coated surface of inner tube is transferred to the metal fin inside the tube, and subsequently to the heat pipe located at the centre of the absorber tube whereas the absorbed energy on the coated surface of inner tube is transferred to the working fluid inside the header by using suitable gadget using conduction or convection or radiation or a combination thereof, e.g. heat pipe can be replaced by "U" shaped pipe in combination of suitable fins and both the ends of "U" pipe is brazed to individual headers to form a parallel connection or brazed back to back (for successive troughs) to form a series connection.

Yet another aspect of the present invention relates to a solar parabolic trough collector system, wherein the header (28) is located horizontally and perpendicular to the heat pipe and heat pipe condenser extend through the glass evacuated tubes/ absorber tube.

Further aspect of the present invention relates to a solar parabolic trough collector system, wherein the header (28) comprising sockets / cavities (30a, 30b) at suitable distances to assemble the consecutive heat pipe condensers of successive parabolic troughs with heat sink material / conductive compound.

Another aspect of the present invention relates to a solar parabolic trough collector system, wherein the header (28) usually carrying fluid or thermic oil of suitable grade.

Still another aspect of the present invention relates to a solar parabolic trough collector system, wherein the header (28) is selected from the any shape and size.

Yet another aspect of the present invention relates to a solar parabolic trough collector system, wherein the parabolic reflector ( 15) is in the shape of parabola and reflector surface ( 16) is made of either glass sheet or flexible aluminum sheet or silver sheet or by using suitable coatings on any metallic or non-metallic base substrate or combination thereof.

Another aspect of the present invention relates to a solar parabolic trough collector system, wherein if the parabolic reflectors are made of flexible aluminum sheet or silver sheet, the edges of the sheet is supported by side ribs (17a, 17b) of stainless steel and back portion is supported by support ribs ( 15a, 15b, 15c) of stainless steel either for entire length of reflector or intermittently in the said length and provided with protective cover. Still another aspect of the present invention relates to a solar parabolic trough collector system, wherein the side ribs (17a, 17b) or support ribs ( 15a, 15b, 15c) having profile in conformity with the profile of parabolic reflectors.

Yet another aspect of the present invention relates to a solar parabolic trough collector system, wherein the side ribs ( 17a, 17b) of parabolic reflector is operationally configured with gear train ( 19) of driving mechanism for adjusting the tracking axis of solar motion.

Further aspect of the present invention relates to a solar parabolic trough collector system, wherein the parabolic trough reflectors /collector (15, 25, 26, 27) are placed at a predetermined inclination, preferably in the range of 10° to 80° from the horizontal plane in order to achieve high effective energy collection as the radiation collection is almost normal to aperture area of collector for fixed elevation axis configuration.

Another aspect of the present invention relates to a solar parabolic trough collector system, wherein the parabolic trough reflectors /collector (15, 25, 2, 27) are placed at a predetermined inclination and tracked for elevation changes either by manually or automation driving mechanism so as to receive radiation nonnal to aperture area of collector for two axis tracking configuration. Still another aspect of the present invention relates to a solar parabolic trough collector system, wherein the driving mechanism ( 19) of dual axis tracking assembly ( 12a) comprising gear train which is being operated with stepper motor or servo motor (20) in accordance with the pre fixed data in the controller. The elevation axis tracking can be easily disabled in the controller for only single axis tracking or manual elevation axis configurations.

Yet another aspect of the present, invention relates to a solar parabolic trough collector system, in series or parallel or combination and having application in process industries, solar power generation, solar air conditioning, solar desalination, solar drying and any application where thermal energy is required.

Accordingly, the present invention relates to solar parabolic trough type collector system, the said system comprises of tilted axis solar parabolic trough development with support gadgets. The absorber is all glass evacuated tube which is open at one end having physical shape similar to the evacuated tubes used for solar water heating application. The inner glass tube of the absorber is coated with solar selective coating to sustain against medium and high temperatures more than 100°C or more. The absorbed energy on the coated surface is transferred to the metal fins inside the tube which successively transfers the collected heat to a heat pipe placed at center of the tube which in turn absorbs the energy and the material inside the heat pipe changes its phase to absorb latent heat and delivers it to the condenser at top of the heat pipe. A header is placed in the horizontal condition and perpendicular to the heat pipe in which the condenser of heat pipe is inserted for good heat transfer.

For such assembly, cavities are created in headers at suitable distances to assemble the consecutive condensers of successive troughs for good thermal contacts. Fluid flow from header absorbs the heat from condenser and becomes heated which can be thennic oil of suitable grade or high pressure water or any fluid found suitable for such purposes. The solar field is designed for suitable series/parallel configuration to meet the requirements of temperature and flow rate. The heated fluid is then taken for utility.

The system is facilitated with suitable main east to west tracking system to keep the focus of sunlight on the absorber throughout the day. The system facilitates for secondary elevation tracking also for higher heat gain which is less feasible in regular horizontal systems.

Referring to figure 1 , an individual absorber tube is shows, which is known in the parabolic trough system. Inner tube (l a) is made of SS/metal with solar selective coating ( l b) and outer tube ( l c) is made of transparent glass; the space ( l e) between both the tubes is evacuated to suitable level so as to reduce overall heat loss. The design is such that it allows sustaining vacuum in spite of different thermal expansion of inner and outer tube material. This kind of absorber tubes are both side open which facilitates joining of two consecutive tubes by orbital welding or similar technique.

Referring to Figure 2, the conventionally known absorber tubes comprises a inner metal tube (l a) which is basically coated by a suitable absorber coating ( l b) so that maximum solar energy can be collected and further said tube is enclosed by a glass tube (lc) in order to reduce the convection loss of collected solar energy by wind. The ends of such glass tube ( l c) and metal tube ( l a) are sealed by means ( I d) which can adjust/allow the thermal expansion of metal and glass material and keep the ends of both tubes in a sealed condition. The vacuum condition is obtained between the metal tube and glass tube in order to reduce the conduction and convection loss of collected solar energy at metal tube.

As shown in figures 2 and 2a, there is one or more absorber tubes are connected end-to- end and are placed in horizontal plane in parabolic trough reflectors/ collectors. The said parabolic trough collectors /reflectors are assembled in a series, which is known in the art.

As shown in figure 3, an absorber tube (3a) is kept in horizontal plane in a parabolic trough collector/ reflector. The said parabolic trough collectors /reflectors are assembled in a series and parallel arrangement, which is known in the art. The use of such tubes almost makes restriction to install the parabolic troughs horizontally only, which is disadvantageous because it collects less amount of radiation (3c) because sun rays are not normal to its aperture area (3d). It gives less effective collection of solar energy. Horizontal installation also limits the system to operate for single axis tracking only for daily east to west movements. Also, the use of rotating/pivoting type piping end connections (at the end of each row) make it very costly due to moving absorber tube in most of the conventional parabolic trough designs (as shown in figure 4) in the known technology.

As shown in figure 5, the assembly as disclosed in figure 3 and 4, does not comprises mass balancing practices due to costly reflective surface. Also, non-mass balancing increases tracking power consumption. The reason of non-mass balancing is that the conventional parabolic troughs are having shallow parabolic profile (5d) to save cost of reflective material. Therefore, the tracking axis remain behind the parabolic profile, which makes majority of mass accumulated on one side (5b), and in such way the tracking axis (5b) and focal axis (5a) of parabolic trough remain distant apart from each other and does not coincide with each other. Therefore, it demands high tracking torques to move the parabolic trough in accordance with solar trajectory, which result high power consumption by motor and cost of the whole system is increased. Further in such arrangement flexible end connections for piping are required which makes the system costly.

As shown in figure 8, the first aspect of the present invention is that the parabolic trough profile are kept more deep (8a) as compare to shallow, so that it increases reflective material usage and facilitates mass balancing as well as static absorber concept. By keeping such design the tracking axis (8b and 8c) coincided with focal axis. The parabolic profile calculation and structure design (8d) is optimized and selected in such a way that center of gravity of parabolic trough of the present invention falls on the tracking axis which results in negligible torque requirement for tracking and hence reduced power consumption of motor. However, it is within the purview of a person skilled in the art that by various ways tracking axis and focal line can be coincided to each other (as shown in figure 9 and 10).

Referring to figure 9, an absorber tube is placed at focal line of parabolic trough by using hanging support (9a).

Referring to figure 10, an absorber tube (fixed component) is placed at focal line of parabolic trough (rotating component) by using suitable bearing block assembly (10a) at both the ends of absorber tube. The parabolic profile calculation and structure design (8d) is optimized and selected in such a way that center of gravity of parabolic trough of the present invention falls on the tracking axis which results in negligible torque requirement for tracking and hence reduced power consumption of motor.

Referring to figure 1 1 , the parabolic trough comprises absorber tubes ( 1 1a) in inclined condition as compare to land / ground ( l ib) and combined with each other in a series or parallel combinations according to an embodiment of the present invention. The use of all glass absorber tube almost makes no restriction to install the parabolic troughs inclined which is advantageous because it collects radiation ( 1 1 c) almost normal to aperture area ( l i d) to collect maximum effective solar energy. Inclined installation also does not limit the system for single axis tracking only for daily east to west movements. Also, there are non- moving or static absorber tube placements and no rotating or pivoting type piping end connections (at the end of each row) make the whole assembly very economic.

Referring to figure 12, parabolic trough collector or reflector is positioned at some inclination from the horizontal plane, facilitated with dual axis tracking in which second axis will take care of seasonal elevation changes of sun hence further improving collection efficiency. As shown in figure 12, two axis tracking can be facilitated by manual or automatic movement of seasonal axis as per the sun elevation of geographic location. A slot ( 12a) in vertical pillars or suitable structure can be used for manual movement i.e. upward and downward direction of trough for seasonal angular variations for maximum radiation collection. Assembly deployed with dual axis tracking collect solar radiation almost normal to its aperture area. Such movement can be automated by using motorized rack and pinion gear train or similar devices for individual parabolic trough or for the whole system. Further, the angle of inclination of parabolic trough collector / reflector can be set out in accordance with geographical location of place.

Generally, preferred inclination of parabolic trough is kept equal to latitude of the place which varies country to country and city to city.

Referring to figure 13, the typical isometric view of the present solar parabolic trough assembly with fixed (non-moving) absorber tube is shown which provides basic design of the construction according to an embodiment of the present invention. The trough is installed in inclined condition having both ends pivoting. The dual axis tracking by adding suitable elevation tilt mechanism is shown in figure 13. Further, as shown in figure 13, the solar parabolic trough assembly comprises a mounting stand ( 14), wherein the parabolic trough collector / reflector ( 15 ) can be installed inclined with the support of two vertical pillars ( 14a and 14b) of different height. The said two pillars are connected at two separate ends of a horizontal beam ( 14c). The height of two pillars can be varied for changing the inclination angle of parabolic trough reflector/ collector. The said parabolic trough collector /reflector having absorber tube (22), wherein the said absorber tube consist a heat pipe (23) and heat pipe condenser (24).

The solar parabolic trough collector /reflector (15) are in the shape of parabola and reflecting surfaces ( 16) are made of either glass sheet or flexible aluminum sheet or silver sheet or combination thereof or by using suitable coatings on any metallic or non-metallic base substrate. Such reflector surfaces are treated for weather protection to increase its life. Wherein if the parabolic reflectors are made of flexible sheet, the edges of the sheet is supported by side ribs ( 17a and 17b) of stainless steel and back, portion is supported by support ribs ( 15a, 15b, 15c,) of stainless steel either for entire length of reflector or intermittently in the said length and provided with protective cover ( 18) at the backside of collector. The side ribs and support ribs having profile in conformity with the profile of parabolic reflectors and wherein the side ribs of parabolic reflector is operationally configured with gear train (19) of driving mechanism for adjusting the tracking axis of solar motion. As shown in figure 13, the driving mechanism of dual axis tracking assembly comprising gear train (driving gear 19a, driven gear 19b) which is being operated with stepper motor or servo motor (20) in accordance with the pre fixed data in the controller (21 ). The Controller (21 ) is having prefixed data of geographical locations, and also means to sense the conditions of environment and adjust the parabolic trough reflectors/ collectors in a minimum resistance conditions.

For example, if there is heavy wind flow or snow falls and the environmental conditions reaches to its threshold level, then in such situation the controller adjust the parabolic trough collector / reflector in a position which provide minimum damage to the reflecting surface ( 16) / collector ( 15) of parabolic trough and thereby increase the life of whole assembly and system made thereof. Similarly, if there is non-sunny condition (radiation below threshold value) during daytime or night, the controller changes the position of parabolic trough completely reverse, i.e. facing towards the ground (i.e. parking mode or stop mode) condition.

Referring to figure 14, the details of absorber tube (22) installed in a solar parabolic trough collector are depicted according to an embodiment of the present invention. As shown in figure 14, the said absorber tube (22) having two ends, one is close end (22e) and another one is open end (22f). An enlarged view of open end (22f) is shown in the figure 14, which depict an outer glass tube (22a) and inner glass tube (22b). At close end (22e) the ends of inner tubes are fused each other and ends of outer tube are also being fused from each other, however at open end the outer glass tube ends and inner glass tubes ends are fused and created an open end (22f)- Further, vacuum (22d) is created between outer tube (22a) and inner tube (22b) of absorber tube and solar selective material coating (22g) is provided on the outer surface of inner tube (22b) to sustain against medium and high temperatures. There are various solar selective materials for coating is commercially known, and they are differing from each other depending on base substrate/material, sustainability at high temperature and optical properties. The optical properties of coating are defined in terms of its absorption, emission and transmittance capacity. In the present invention, for getting best results, solar selective material is preferred which have absorption value more than 96 %, emissivity less than 5.0%. Transmittance of outer tube is more than 93 % (taken by applying anti refection coating on outer tube). The solar selective coating on the outer surface on inner tube (22b) may be comprised of one or more layer of similar or different material or in a suitable combination thereof. In the present invention, the solar selective coating material is selected from Titanium, Aluminum Nitride (AIN), black Chrome, black Nitride or combination thereof or other conventional known solar selective coatings. Further, as shown in figure 14, each absorber tube (22) comprising metal fins (22c), heat pipe (23) along with heat pipe condenser (24), so that absorbed energy on the coated surface of inner tube (22b) is transferred to the metal fin inside the tube (22c), and subsequently to the heat pipe (23) and heat pipe condenser (24) located at the centre of the absorber tube. The heat pipe (23) along with heat pipe condenser (26) extends through the open end of absorber tube and connected to a common header (28) (as shown in figure

15). The shape of heat pipe (23) is cylindrical and having circular cross-section, whereas the shape of heat pipe condenser is cylindrical with hemispherical ends. However, the shape and size of heat pipe (23) and heat pipe condenser (24) should be selected in such a way that both having maximum surface area, in order to collect maximum heat from the inner tube of absorber tube and transfer to the header (28), which is carrying heat transfer fluid. A person skilled in the art can select any shape of heat pipe and heat pipe condenser having cross-section circular or square or triangular or oval or any combination thereof. Referring to figure 15 and 16, one or more parabolic trough collector / reflector (25, 26, 27) are shown which are being connected to a common header (28) according to an embodiment of the present invention. The said common header (28) comprising one or more sockets / cavities (30a, 30b) at suitable distances to assemble the consecutive parabolic trough collector / reflector through heat pipe condensers (24a, 24b) of successive parabolic troughs (25, 26, 27) with heat sink material (22h) (i.e. conductive compound). The first advantage of the heat sink material is that it provides maximum heat transfer from the heat pipe condenser to the heat transfer fluid flowing in the header. Secondly, the roughness in the surface of sockets / slots of header and roughness on the surface of the heat pipe condenser is reduced by filling the heat sink material (conductive material), so that maximum heat can be transferred. The header usually carries heat transfer fluid such as pressurized water or thermic oil of suitable grade. The header is insulated by suitable material (29) and may be constructed in any shape and size. It is within the purview of a person skilled in the art to select any shape of header such as circular or square or triangular or oval or any combination thereof and making an assembly with heat pipe and heat pipe condensers.

As shown in figure 15 shows interconnection diagram for the solar field installation. More particularly, the solar field comprising the parabolic trough collector system in series or parallel (25, 26, 27) or combination and having application in process industries, solar power generation, solar air conditioning, solar desalination, solar drying or any application where thermal energy is required. It is also demonstrated in the figure that each parabolic trough consisting independent tracking unit, which can be connected with adjacent troughs with rack and pinion or chain drive or linkages, or belt drive or any other method to facilitate tracking in multiple trough units with single tracking device.

ADVANTAGES OF THE INVENTIONS

The advantage of the present invention is to provide a solar parabolic trough type collector system.

Another advantage of the present invention is to provide a solar parabolic trough type collector system having economic viability of absorber tube. The present invention incorporates the use of all glass evacuated absorber tube for which production facilities are already well established and manufacturing is very economical. The heat extraction is indirect with metal fins and heat pipe which is transferred to header due to phase changing of material inside the heat pipe. The indirect heat extraction method adopted in the present system is due to the one side open absorber tube.

Still another advantage of the present invention is to provide a solar parabolic trough type collector system with lesser collector/aperture area required for same thermal output. Inclined trough- ensures high efficiency for solar energy collection resulting in less collector/aperture area required for same thermal output as compared to horizontal trough systems.

Yet another advantage of the present invention is to provide a solar parabolic trough type collector system exhibiting dual axis tracking feasible in parabolic trough system. The present invention facilitates the use of dual axis tracking in the system by which the system gets ability to collect the radiation normal to its collector area. The system can also be installed with fixed inclination as per the geographic location.

Another advantage of the present invention is to provide a solar parabolic trough type collector system with mass balancing around tracking axis for minimizing tracking energy requirement. The invention disclosed is a mass balanced structure in which the center of mass of the rotating segment falls on bearing axis which is absorber axis also.

Another advantage of the present invention is to provide a solar parabolic trough type collector system comprising fixed absorber concept. In the present invention, the absorber tube is a static component. It doesn't move along with the rotating segment of parabolic trough. This eliminates complex flexible joints at the ends of absorber line.

The advantages of the disclosed invention are thus attained in an economical, practical, and facile manner. While preferred aspects and example configurations have been under trial, further it is to be understood that various further modifications and additional configurations will be apparent to those skilled in the art. It is intended that the specific embodiments and configurations herein disclosed are illustrative and there is further experimentation is going on for best practicing the invention, and hence, it should not be interpreted as limitations on the scope of the invention.

Claims

AIM

A solar parabolic trough collector or reflector system comprising

a. individual absorber tubes (22, 24a, 24b) connected to a common header (28) and aligned parallel with each other so that heat is transferred to the fluid flowing in the common header (28), the said individual absorber tubes are glass evacuated tube and open from one side, whereby the heat tube (23) along with heat pipe condenser (24) extends through the open end (22f) of absorber tube and connected to the said common header,

b. individual parabolic reflectors ( 1 5, 25, 26, 27) being mounted with inclination on mounting stand ( 14) in such a manner that tracking axis and focal line of parabolic reflectors remain coincide with each other and the said individual absorber tube (22, 24a, 24b) is installed on the said focal line, so that the radiation reflected by the reflector surfaces ( 16) of parabolic reflectors focuses on to the glass absorber tubes.

c. assembly for dual axis tracking ( 12a) for the said parabolic trough reflectors, the said assembly being mounted on the mounting stand along with driving mechanism ( 19) and operationally configured with a controller (21 ).

The solar parabolic trough collector system as claimed in claim 1 , wherein the said absorber tube (22) having two ends, one is close end (22e) and another one is open end (22f), whereby at close end (22e) the ends of inner tubes are fused each other and ends of outer tube are also being fused from each other, whereas at open end the outer glass tube ends and inner glass tubes ends are fused and created an open end (22f).

The solar parabolic trough collector system as claimed in claim 2, wherein vacuum is created between outer tube and inner tube of absorber tube and solar selective material coating (22g) is provided on the outer surface of inner tube (22b) to sustain against medium and high temperatures.

4. The solar parabolic trough collector system as claimed in claim 3, wherein the solar selective coating material (22g) is selected which sustain at high temperature with improved optical parameters.

5. The solar parabolic trough collector system as claimed in claim 4, wherein the solar selective coating material is selected from Titanium, Aluminium Nitride (AIN), black Chrome, black Nitride or combination thereof or other conventional known solar selective coatings.

6. The solar parabolic trough collector system as claimed in claim 1 , wherein the absorber tube comprising metal fins (22c), heat pipe (23) along with heat pipe condenser (24), so that absorbed energy on the coated surface of inner tube is transferred to the metal fin inside the tube, and subsequently to the heat pipe located at the centre of the absorber tube.

7. The solar parabolic trough collector system as claimed in claim 1 , wherein the header (28) is located horizontally and perpendicular to the heat pipe and heat pipe condenser extend through the glass evacuated tubes/ absorber tube.

8. The solar parabolic trough collector system as claimed in claim 1 , wherein the header (28) comprising sockets / cavities (30a, 30b) at suitable distances to assemble the consecutive heat pipe condensers of successive parabolic troughs with heat sink material / conductive compound.

9. The solar parabolic trough collector system as claimed in claim 1 , wherein the header (28) usually carrying fluid or thermic oil of suitable grade.

10. The solar parabolic trough collector system as claimed in claim 1 , wherein the header (28) is selected from the any shape and size.

1 1 . The solar parabolic trough collector system as claimed in claim 1 , wherein the parabolic reflector ( 15) is in the shape of parabola and reflector surface ( 16) is made of either glass sheet or flexible aluminum sheet or silver sheet or by using suitable coatings on any metallic or non-metallic base substrate or combination thereof.

12. The solar parabolic trough collector system as claimed in claim 1 , wherein if the parabolic reflectors are made of flexible aluminum sheet or silver sheet, the edges of the sheet is supported by side ribs ( 17a, 17b) of stainless steel and back portion is supported by support ribs (15a, 15b, 15c) of stainless steel either for entire length of reflector or intermittently in the said length and provided with protective cover.

1 3. The solar parabolic trough collector system as claimed in claim 12, wherein the side ribs (17a, 17b) or support ribs (15a, 15b, 15c) having profile in conformity with the profile of parabolic reflectors.

14. The solar parabolic trough collector system as claimed in claim 1 , wherein the side ribs ( 17a, 17b) of parabolic reflector is operationally configured with gear train ( 19) of driving mechanism for adjusting the tracking axis of solar motion.

15. The solar parabolic trough collector system as claimed in claim 1 , wherein the parabolic trough reflectors /collector (15, 25, 26. 27) are placed at a predetermined inclination, preferably in the range of 10° to 80° from the horizontal plane in order to achieve high effective energy collection as the radiation collection is almost normal to aperture area of collector for fixed elevation axis configuration.

16. The solar parabolic trough collector system as claimed in claim 1 , wherein the parabolic trough reflectors /collector ( 15, 25, 2, 27) are placed at a predetermined inclination and tracked for elevation changes either by manually or automation driving mechanism so as to receive radiation normal to aperture area of collector for two axis tracking configuration.

17. The solar parabolic trough collector system as claimed in claim 1 , wherein the driving mechanism (19) of dual axis tracking assembly ( 12a) comprising gear train which is being operated with stepper motor or servo motor (20) in accordance with the pre fixed data in the controller.

18. The solar field comprising the parabolic trough collector system as claimed in claim 1 , in series or parallel or combination and having application in process industries, solar power generation, solar air conditioning, solar desalination, solar drying and any application where thermal energy is required.