WO2017178863A1

WO2017178863A1 - System comprising sun ray collimating central mirror and heliostat

Info

Publication number: WO2017178863A1
Application number: PCT/IB2016/052056
Authority: WO
Inventors: Raj Kumar Singh
Original assignee: India Atomic Energy Department of
Current assignee: India Atomic Energy Department of
Priority date: 2016-04-12
Filing date: 2016-04-12
Publication date: 2017-10-19
Anticipated expiration: 2018-10-12

Abstract

A solar energy system is disclosed.A movement of a small heliostat (4) which sends the collimated light to a fixed receiver is achieved using a linkage arrangement thus avoiding extra two costly motor drives.

Description

SYSTEM COMPRISING SUN RAY COLLIMATING CENTRAL MIRROR AND HELIOSTAT

TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to the conversion of solar radiation to other useful forms of energy, including thermal and chemical energy and electricity. More particularly, to the collection, concentration, and delivery of disperse solar energy to a central location for use in efficient energy generation.

BACKGROUND

[002] Concentrating solar plants use heliostat for directing sun ray on central tower.

The heliostat is a device that includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space. To do this, the reflective surface of the mirror is kept perpendicular to the bisector of the angle between the directions of the sun and the target as seen from the mirror. In almost every case, the target is stationary relative to the heliostat, so the light is reflected in a fixed direction.

[003] Generally, every heliostat is uniquely positioned relative to the central tower.

The heliostat is a reflector that makes precise movements up/down and left/right to reflect sunlight on a fixed spot on the central tower. As the sun moves across the sky, the heliostat adjusts its position so that the spot of reflected light remains stationary on the target. In conventional heliostat design, the mirror is oblique to the direction of sun's incident ray. It results in losses called as cosine losses.

[004] In conventional heliostat design, the normal on each heliostat surface is along the bisector of the angle between incident sun ray on the heliostat and reflected ray from the heliostat towards central tower. Since normal of heliostat having area A makes an angle Θ with incident ray, only A cos Θ area of heliostat is utilized in reflecting the sun ray. This unutilized proportion of area is known as cosine loss. Cosine losses in a big plant can be as high as 18 to 23 % which is big drain on the overall efficiency of the plant. [005] As well known in the prior-art, the parabolic mirror can collimate light coming from point source and can focus the incoming parallel rays to a point. The combination of parabolic disc in heliostat has been tried by many inventors and researchers in the prior-art. The concept of collimating sun rays using set of parabolic mirrors has been already in use for lighting rooms and houses. The parabolic dish can focus incoming parallel rays to point focus and can also collimate light coming from point focus. Based on above, combination of parabolic disc has been tried by inventors to make concentrated parallel rays as shown in the prior-art US6128135 and/or US20110114078, mostly for lighting room and solar application. Conventionally, the parabolic disc is the only possible geometry known that can focus parallel rays.

[006] In tower based solar plants, heliostats with either spherical or flat reflectors are used. Making spherical surface is relatively easy as compared to making parabolic surface. But for large surfaces as of heliostat of 100m area, fabrication leads to deviation from intended surface may not even be axi-symmetric. Avoiding costly sagged parabolic glasses can lead to advantages but it foils the attempt to collimate the rays by secondary reflector as focal point does not exist for surface other than parabolic disc.

[007] Also, in conventional mechanisms, two extra motors are needed so that collimated rays can be sent to fixed receiver which may be located anywhere in field. The prior-art related to the collimation used two extra motors to send collimated light, if there was need to send it at common fixed place.

[008] Further, the convention heliostat usually has spherical curvature to reduce image size (spot size) to get better concentration of the solar radiation. If incident sunlight comes along the axis of spherical surface it leads to reduction in image size but if incident rays make angle with heliostat surface, which leads to relatively large image sizes. If part of the reflected light doesn't fall on receiver surface, it is called spillage losses. Also, the conventional solar tower power plants need tall towers. The tower height is around 100 m for existing plants in MW range. They mainly help in reducing cosine losses and blocking losses. If part of the rays reflected from a heliostat fall on the other heliostat without reaching the receiver, it leads to losses which are known as blocking losses. SUMMARY OF THE INVENTION

[009] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0010] An object of the present invention is to provide system that collects and concentrates sun light economically and efficiently using a collector mirror and collimation of the concentrated rays by means of a central mirror and direct these rays onto the central tower without extra motors drives using a linkage arrangement.

[0011] Another object of the present invention is to provide a system that eliminates the cosine losses by utilizing a collector mirror along with a secondary mirror (central mirror), and thereafter the rays are reflected towards fixed receiver by means of small heliostat.

[0012] Practically, fabrication leads to deviation from intended surface, so another object of the present invention is to provide a system wherein a central mirror is designed for fabricated collector mirror, wherein area of the collector mirror is large so design of small central mirror annihilating errors of collector mirror is economically advantageous.

[0013] To remove two extra motors, another object of the present invention is to provide a system using an arrangement to adjust the direction of third mirror which reflects collimated light to receiver. Hence, the present invention uses only two motors as conventional heliostat. It must be noted that requirement of precise movements in solar tower technology makes motor cost as significant proportion of heliostat cost so use of two extra motors ruins part of advantage gained from collimation arrangement.

[0014] Another object of the present invention is to provide a system having a collector mirror that has similar dimensions and same economy as conventional heliostat. Only a small central mirror for collimating and a small heliostat is added whose combined area is in general less than 4% of collector area [0015] In order to eliminate the losses, another object of the present invention is to provide a system having a central mirror to collimate the concentrated sun ray before it is reflected on the central tower through a small heliostat , thereby eliminating cosine factor leading to better concentration and reduced the spillage losses.

[0016] In order to reduce the blocking losses, yet another object of the present invention is to provide a system wherein a distance between heliostats is decreased which in turn increases the land utilization fraction.

[0017] Still another object of the present invention is to provide a system wherein the collimated beam leaving the small heliostat is of small beam width thus reducing blocking losses significantly. As the cosine losses are also eliminated, the tower height can be reduced. Reduction of blocking losses also permits better land utilization.

[0018] In one implementation, as compared to the prior-art techniques, a solar energy system is disclosed whose performance does not depend on accuracy of primary collector. It is crucial to economics since in the solar tower concepts reflective area heliostat (collector mirror) is large. Moreover, the solar energy system as disclosed in the present invention does not depend on the parabolic disc which is costly to fabricate accurately.

[0019] In one implementation, as compared to the prior-art techniques, a movement of small heliostat which sends the collimated light to fixed receiver is achieved using a linkage arrangement thus avoiding extra two costly motor drives.

[0020] In one implementation, as compared to the prior-art techniques, a design of central mirror surface for general surface relives the effects due to fabrication errors in primary collector. Since central mirror is much smaller than collector mirror, it can be made in desired shape economically.

[0021] Accordingly, in one implementation, a system comprises at least one collector mirror and at least one central mirror having a specific curvature connected to a collector mirror, wherein the mirror is adapted to track the central mirror such that concentrated collimated rays from central mirror, incident from the collector mirror, are reflected towards at least one receiver. [0022] In one implementation, a solar energy reflection and focusing system is disclosed. The solar energy reflection and focusing system comprises one collector mirror and one central mirror having a specific curvature connected to a collector mirror, wherein the mirror is adapted to track the central mirror such that concentrated collimated rays from central mirror, incident from the collector mirror, are reflected towards at least one receiver.

[0023] In one implementation, a collimation system is disclosed. The collimation system comprises at least one mirror and at least one central mirror having a specific curvature connected to a collector mirror, wherein the mirror is adapted to track the central mirror such that concentrated collimated rays from central mirror, incident from the collector mirror, are reflected towards at least one receiver.

[0024] In conventional hehostat design, as the sun moves across the sky, the hehostat adjusts its position so that the spot of reflected light remains stationary on the target. Due to the unique position of each hehostat with respect to the central tower, the normal of the hehostat reflector makes an angle with incident sun rays. The slant incidence of sun rays on the heliostat reflector results in underutilization of reflective area of the mirrors. In contrast to the conventional heliostat design, the present invention enables the incidence of sun ray to be concentrated and collimated by the collector and central mirror respectively and small sun tracking heliostat reflects it on to the receiver. The collimated reflection of sun ray achieved by the innovation in profiling the surface of the central mirror eliminates cosine losses present in the conventional heliostats.

[0025] In conventional heliostat design, a curvature in heliostats is provided for reduction of image size for better concentration. Since, incident rays make slant angle with heliostat surface, it leads to relatively large image sizes. In contrast to the conventional heliostat design, the present invention eliminates cosine factor so that rays hit the collector mirror along its axis leading to better concentration and thus reduction of the spillage losses also.

[0026] As compared to the convention techniques, the present invention collects and concentrates the sun light economically and efficiently using collector mirror, collimate the concentrated rays by innovative central mirror and direct these rays on to the central tower without extra motors drives with innovative linkage arrangement.

[0027] As compared to the convention techniques, the present invention in order to eliminate the losses, central mirror has been introduced whose purpose is to collimate the concentrated sun ray before it is reflected on the central tower through a mini heliostat. Also, the cosine factor is eliminated leading to better concentration and reduced the spillage losses. Further, to reduce the blocking losses, distance between heliostats is increased which in turn reduces the land utilization fraction. Hence, in present invention, the collimated beam leaving the small heliostat is of small beam width thus reducing blocking losses significantly. Since cosine losses are also eliminated, the tower height can be reduced. Reduction of blocking losses also permits better land utilization.

[0028] In view of less number of collector mirrors required, elimination of cosine losses and blockage, high land utilization and low tower height requirement, cost per MW of the plant reduces significantly according to the present invention.

[0029] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0030] The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0031] Figure 1 illustrates a conventional tower based solar plant.

[0032] Figure 2 illustrates a collector mirror and central mirror collimating sun ray, in accordance with the subject matter of the present invention.

[0033] Figure 3 illustrates a collimation system assembly, in accordance with the subject matter of the present invention.

[0034] Figure 4 illustrates a fixed link (component 1), in accordance with the subject matter of the present invention. [0035] Figure 5 illustrates a component 2, in accordance with the subject matter of the present invention.

[0036] Figure 6 illustrates a collector mirror and central mirror (component 3), in accordance with the subject matter of the present invention.

[0037] Figure 7 illustrates a small heliostat (component 4), in accordance with the subject matter of the present invention.

[0038] Figure 8 illustrates a slot (component 5), in accordance with the subject matter of the present invention.

[0039] Figure 9 illustrates a link (component 6), in accordance with the subject matter of the present invention.

[0040] Figure 10 illustrates a component 7, in accordance with the subject matter of the present invention.

[0041] Figure 11 illustrates a component 8, in accordance with the subject matter of the present invention.

[0042] Figure 12 illustrates a component 9, in accordance with the subject matter of the present invention.

[0043] Figure 13 illustrates a detailed view of arrangement, in accordance with the subject matter of the present invention.

[0044] Figure 14 illustrates a detailed view of slot, in accordance with the subject matter of the present invention.

[0045] Figure 15 illustrates a collimating of rays concentrated by any collector mirror, in accordance with the subject matter of the present invention.

[0046] Figure 16 illustrates a profile of the central mirror in the plane OAN for spherical surface, in accordance with the subject matter of the present invention.

[0047] Figure 17 illustrates a proof for linkage system, in accordance with the subject matter of the present invention.

[0048] Figure 18 illustrates a detailed view of linkage arrangement, in accordance with the subject matter of the present invention. [0049] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0050] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0051] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0052] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0053] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0054] By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide. [0055] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0056] It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0057] System comprising sun ray collimating central mirror and heliostat to increase efficiency is disclosed.

[0058] In conventional heliostat design, as the sun moves across the sky, the heliostat adjusts its position so that the spot of reflected light remains stationary on the target. Due to the unique position of each heliostat with respect to the central tower, the normal of the heliostat reflector makes an angle with incident sun rays. The slant incidence of sun rays on the heliostat reflector results in underutilization of reflective area of the mirrors. In contrast to the conventional heliostat design, the present invention enables the incidence of sun ray to be concentrated and collimated by the collector and central mirror respectively and small sun tracking heliostat reflects it on to the receiver. The collimated reflection of sun ray achieved by the innovation in profiling the surface of the central mirror eliminates cosine losses present in the conventional heliostats.

[0059] In conventional heliostat design, a curvature in heliostats may be provided for reduction of image size for better concentration. Since, incident rays make slant angle with heliostat surface, it may lead to relatively large image sizes. In contrast to the conventional heliostat design, the present invention eliminates cosine factor so that rays hit the collector mirror along its axis leading to better concentration and thus reduction of the spillage losses also.

[0060] As compared to the convention techniques, the present invention collects and concentrates the sun light economically and efficiently using collector mirror, collimate the concentrated rays by innovative central mirror and direct these rays on to the central tower without extra motors drives with innovative linkage arrangement. [0061] As compared to the convention techniques, the present invention in order to eliminate the losses, central mirror has been introduced whose purpose is to collimate the concentrated sun ray before it is reflected on the central tower through a mini heliostat. Also, the cosine factor is eliminated leading to better concentration and reduced the spillage losses. Further, to reduce the blocking losses, distance between heliostats is increased which in turn reduces the land utilization fraction. Hence, in present invention, the collimated beam leaving the small heliostat is of small beam width thus reducing blocking losses significantly. Since cosine losses are also eliminated, the tower height can be reduced. Reduction of blocking losses also permits better land utilization.

[0062] In view of less number of collector mirrors required, elimination of cosine losses and blockage, high land utilization and low tower height requirement cost per MW of the plant reduces significantly according to the present invention.

[0063] The conventional tower based concentrating solar plants use Heliostat for directing sun ray on to a central tower. Heliostats are reflectors that track the sun as the sun moves across the sky.

[0064] In one example: typically for 10 MWe solar plant need: According to the conventional techniques, 800 heliostats of size 10 m diameter having spherical curvature positioned surrounding the central tower, 120 m high Central tower, generates an optical efficiency of conventional plant about 65%, cosine losses of 21%, blocking losses of 2%, and spillage losses 3%.

[0065] Whereas, according to the present invention, only 627 No of collector mirror of 10m diameter are required, 30 m high central tower is required. The cosine losses are eliminated, optical efficiency increases to 83%, blocking losses are virtually eliminated, and as the concentrated light is reflected, spillage is eliminated.

[0066] Figure 1 illustrates a conventional tower based solar plant.

[0067] Referring now figure 2, a collector mirror and central mirror collimating sun ray is illustrated, in accordance with the subject matter of the present invention. In one implementation, as shown in figure 2, the collector mirror is supported on conventional structural support as in normal heliostat. It tracks the sun and collects sun energy. The central mirror having curvature is fixed to the collector mirror with truss members. The small heliostat is supported on the support structure of collector mirror and it tracks the central mirror by linkage mechanism so that reflected ray falls on fixed receiver (having spherical curvature same as conventional heliostats).

[0068] In one implementation, the device tracks the sun as the sun moves in the sky to collect the sun energy, concentrates the sun rays by collector mirror, and collimates the concentrated rays by the newly introduced central mirror. The collimated ray is directed on to a small heliostat. Small heliostat moves by linkage arrangement such that reflected ray falls on fixed receiver all the time. It avoids need of two costly motor drives to provide motion to small heliostat. A detail view of the linkage arrangement is provided in figure 13.

[0069] Referring now to figure 3 a collimation system assembly is illustrated, in accordance with the subject matter of the present invention. In one implementation, as shown in figure 3, the arrangement having a collector mirror 3 is shown. The mirror (small heliostat) 4 is rigidly attached with collector mirror 3. The collector mirror 3 and mirror (small heliostat) 4 are always in suns direction but central mirror 30 faces opposite to the sun. The collector mirror 3 is tracked by azimuth elevation arrangement which is common for heliostat tracking. A component 1 is fixed shaft with respect to earth, and a component 2 can rotate about the shaft 1 thus providing azimuth drive. The shaft attached to collector mirror 3 is mounted on the component 2 to provide elevation movement to collector mirror 3.

[0070] Figure 4 illustrates a fixed link (component 1), in accordance with the subject matter of the present invention. The fixed link is a part of collimation assembly as well as linkage arrangement. This fixed link is fixed to the ground. A vertical cylindrical portion of the fixed link acts as a shaft for azimuthal movement of collector mirror. A small inclined rod attached to tip of vertical cylindrical portion, acts as a shaft for small heliostat. The component 5 shown in figure 8 rotates about it as shown in figure 13. Direction of inclined rod attached to tip of vertical cylindrical portion is towards the receiver.

[0071] Figure 5 illustrates a component 2 (a collector), in accordance with the subject matter of the present invention. The component 2 provides support to elevation rotation shaft for collector mirror. The collector mirror is component 3 as shown in figure 6. Vertical hollow cylindrical portion rotates around component 1 to provide azimuthal rotation to collector mirror. There are two cylindrical branches at the top of vertical hollow cylinder which have two bearing housing at the top end. These two bearing support the shaft rigidly connected with collector mirror to provide elevation rotation.

[0072] Figure 6 illustrates a collector mirror and central mirror (component 3), in accordance with the subject matter of the present invention. Central mirror is rigidly connected with central mirror so central mirror rotates with collector mirror. A cylindrical shaft is rigidly attached at bottom of collector mirror which rotates about component 2 to provide elevation rotation. There is a cylindrical link rigidly connected to the bottom of the shaft. It could be seen more clearly in figure 13 than in figure 3. The end of this link is straight collinear with normal of collector mirror at center. This part acts as slide for component 7 shown in figure 10 and component 7 can also rotate about it. The assembly is shown in figure 13 and figure 18.

[0073] Figure 7 illustrates a small heliostat (component 4), in accordance with the subject matter of the present invention. In one implementation, the concentrated collimated rays from the mirror 30 falls on the small heliostat 4 from sun's direction, which is same as collector mirror's 3 directions. As the small heliostat 4 reflects rays to a fixed receiver so the small heliostat 4 may have to move in two directions like conventional heliostat. Heliostat drives are costly and considered one of major contributors in conventional heliostat cost. According to the present invention a special arrangement is made so that two extra drives for small heliostat 4 could be avoided and rays are sent to fixed receiver which may be located anywhere in the field. There is a hollow cylinder connected to bottom of the component, it rotates about horizontal shaft at top of component 5. There is a cylindrical rod connected at the bottom this hollow cylinder. This rod is normal to center of reflective surface of small heliostat. End of this rod acts as shaft for component 8 shown in figure 11. Assembly can be seen in figure 13 and 18.

[0074] Figure 8 illustrates a slot (component 5), in accordance with the subject matter of the present invention. Component 5 carries a special curved slot on its lateral surfaces as shown in figure 14. Equation of the curve in polar coordinates is given as:

Here 'a 'is the length of component 4 from center of small heliostat up to hinge of sleeve 8. b is the length of component 6 between center of two end hinges. Component 9 shown in figure 12 slides inside this slot. Top of the component 5 is cylindrical shaft which provides rotation to component 4. Component 5 also carries a rectangular slot in center as shown in figure 5. This slot allows bottom vertical rod of component 4, component 6 and component 3 to move without interfering with component 5; part of these components passes through this slot. Assembly arrangement can be seen in figure 13 and 18.

[0075] Figure 9 illustrates a link (component 6), in accordance with the subject matter of the present invention. This component has two identical cylindrical rods having perpendicular hollow cylinder at each end. These perpendicular hollow cylinders act as bearing housing. Side cylindrical extensions of component 7 and 8 acts as a shaft for these bearings so component 7 and 8 rotates about component 6 in the plane perpendicular to the rotation axis. Top hollow cylinder of the component 6 also act as bearing housing for component 9 along with component 7 as shown in figure 13 and 18.

[0076] Figure 10 illustrates a component 7, in accordance with the subject matter of the present invention. Component 7 has central hollow cylinder along with two lateral cylindrical extensions at each side perpendicular to central hollow cylinder. These two cylindrical extensions are exactly opposite to each other and act as shaft which is allowed to rotate inside hollow cylinders at the end of component 6. Central hollow cylinder can rotate and slide along cylindrical rod at the bottom of component 3. Top of this cylindrical rod acts as slide for hollow cylindrical part of this component and component 7 can also rotate about it as shown in figure 13 and 18. Axis of rotation of central hollow cylindrical part of component 7 is always towards the normal of collector mirror at center.

[0077] Figure 11 illustrates a component 8, in accordance with the subject matter of the present invention. . Component 8 has central hollow cylinder along with two lateral cylindrical extensions at each side perpendicular to central hollow cylinder. These two cylindrical extensions are exactly opposite to each other and act as shaft which is allowed to rotate inside hollow cylinders at the end of component 6. Central hollow cylinder rotates around cylindrical rod, perpendicular to the reflective surface of small heliostat at center, at the bottom of component 4. Bottom of this cylindrical rod acts as shaft for central hollow cylindrical part of this component as shown in figure 13 and 18. Location of component 8 is fixed with respect to component 4 and it is only allowed to rotate around axis. So axis of rotation of central hollow cylindrical part of component 8 is always towards the normal of small heliostat at center.

[0078] Figure 12 illustrates component 9, in accordance with the subject matter of the present invention. It has two cylinders with coaxial cylindrical extensions of smaller diameter at the end. The component 9 slides in the curved slot of component 5 as shown in figure 13 and 18. The Cylindrical extensions of the component 9 are connected to hollow cylinder at the top end of component 6 and allowed to rotate.

[0079] Figure 13 illustrates a detailed view of linkage arrangement, in accordance with the subject matter of the present invention. As shown in figure 13 and figure 4, in one implementation, component 1 is rigidly fixed to the earth. The receiver location remains fixed at all time, and top inclined cylindrical portion of component 1 shows the direction of receiver from center of collector mirror which remain fixed. The direction of the top of the fixed link will be different for each collector mirror system since many such units are to be used in solar power plant. The component 5 is concentric with the top inclined cylindrical portion of component 1 and may rotate about component 1. The component 4 is mounted on the component 5 and may rotate about it.

[0080] The cylindrical rod at the bottom of component 4 is normal to the reflective surface of the small heliostat (component 4) at the center. The component 5 carries a special curved slot which keeps direction of heliostat in desired direction. Component 3 carries a cylindrical rod connected at bottom of integral shaft of component 3 (collector mirror). Bottom end of the component 4 is connected with the component 8 and it acts as a shaft for the component 8. Position of the component 8 is fixed on component 4 and it is only allowed to rotate. A component 6 is connected on component 8 with a planar hinge joint. The other end of component 6 is connected to the component 9 which slides in the curved slot of the component 5. A component 7 is also connected by planar hinge joint with the component 6. The component 7 can slide along its axis on the component 3 as well as rotate about it.

[0081] It is to be noted that the axis of top inclined cylindrical rod of component 1 and axis of hollow cylindrical portion of component 7 always passes through collector mirrors center if extended. Since, the axis of component 7 is on component 3 so its direction always remains same with respect to collector mirror which is top surface of component 3. Axis of top cylindrical rod of component 1 is fixed towards center of collector mirror. Center about which collector mirror rotates and component 1 both remain fixed in space all the time. Component 4 also rotates about center of rotation of component 3 and bottom cylindrical rod of component 4 is normal to surface of small heliostat which is part of component 4.

[0082] Collector mirror which is part of component is tracked along sun's direction by providing azimuth and elevation rotation using motor drives as in conventional parabolic dishes. As sun moves in the sky the direction of axis of component 7 remains in the direction of sun since it is along normal of collector mirror. Depending on this movement the component 5 rotates about the component 1 and the component 9 slides in curved slot thus direction of component 4 changes. This mechanism acts such a way so that bottom cylindrical rod of component 4(normal of small heliostat) remains bisector of the axis of top inclined cylindrical rod of component 1 (receiver direction) and the axis of component 7(sun direction).

[0083] In one implementation, an equation of the curve in polar coordinates is given as:

Here 'a 'is the length of component 4 from center of rotation of small heliostat up to hinge of component 8. b is the length of component 6 between center of two end hinges located on component 7 and component 8.

[0084] Figure 14 illustrates a detailed view of slot, in accordance with the subject matter of the present invention. [0085] In one implementation, the mathematical details for designing central mirror for general surface of collector mirror are as given below. Figure 15 illustrates a collimating of rays concentrated by any collector mirror, in accordance with the subject matter of the present invention.

be any point of the surface of collector mirror. Reflected ray from

collector mirror meets central mirror at x, y, f(x, y). Since central mirror acts as collimator so normal at x, y, f(x, y) will be parallel to collector mirror normal at

Incident ray is coming parallel to z axis. Reflected ray from x₀, y₀, g(x₀, y₀) meets central mirror at x, y, f(x, y). Law of reflection states

Equating magnitude of both sides gives

Partiall differentiating with respect to x₀ gives

Now using chain rule and using equation 2

From 7

Partially differentiating with respect to x₀ gives

Substituting it gives

Rearranging the terms gives

) by solving it

here Ci(y₀) is arbitrary function of y₀ . Using 12 gives

From equation 7 starting with 8) in place of 8 and following similar steps gives

is arbitrary function of x₀ . Comparison of (y-y₀)

y₀

from 17 and 19 gives

Here c is an arbitrary constant. Finally

Give the final solution in the parametric form, x₀ and y₀ are two independent parameter and coordinates on central mirror (x, y, z) is given in terms of x₀ and y₀.

By this solution central mirror surface (x, y, f) can be found for any collector mirror surface (x₀, y₀, f).

[0086] By above formulation central mirror surface can be found for any collector mirror surface. It is very useful if collector mirror surface deviates from intended shape. Though above formulation gives shape for any collector mirror but it may not be fabricable for any odd intended shape of collector. Intended shape is proposed as spherical since it is easy to fabricate so used in conventional heliostats. Accurate fabrication for intended collector mirror shape is not needed since central mirror, which is smaller in shape can take care of it. It is good from economics point of view since cumulative area of collector mirrors is large. Total reflective area of all collector mirrors is nearly 21% less than total heliostat area in conventional plant for same output power.

[0087] In one implementation, For piecewise construction of collector mirror:

For solar applications large size heliostats up to 100 m are used to reflect light toward receiver. Reflectors in these heliostats are made of several pieces and sometimes transition between two pieces may not be regular in mathematical sense. For such surfaces mollifiers are utilized since second order derivatives are used in above presented derivation.

is standard mollifier.

Mollified function has continuous derivatives up to higher order so equation 21

can be used to find central mirror surface. Furthermore

Now coordinates of the central mirror (x, y, z) is given as

Formulation for surfaces made from pieces which are no more differentiable at joint between pieces locally can be practically useful.

As example for spherical surface of 1 meter radius, shape of the central mirror is shown in figure 16 constant c is taken as -0.92. Central mirror is axisymmetric in case of collector mirror with spherical surface. For collector mirror having deviations from spherical surface, equation of central mirror surface can be found from formulation for designing central mirror as described above. Figure 16 illustrates a profile of the central mirror in cylindrical coordinates for spherical surface.

[0088] Figure 17 illustrates a proof for linkage arrangement, in accordance with the subject matter of the present invention. As shown in the figure 17, origin is at centre of collector mirror denoted as O. AO denotes direction of fixed receiver which is along axis of component 5 AD denotes the slot on component 5. CO is part of the component 4 which is normal to small heliostat. DO denote direction of axis of component 7, this axis is rigid part of collector mirror and is normal to centre of collector mirror. Since normal of collector mirror is kept in direction of sun so DO denotes direction of sun. CI Dl denotes the component 6 between centres of two end hinges. DDI is along axis of component 9 which slides in slot and also connected to component 6.

[0089] CI and Dl are planar hinges on straight component 6 so both hinges will be in same plane thus CCl and DDI will be parallel. Radius of cylindrical component 8 at C and sleeve at D is same so CCl = DDI.

[0090] CCl is perpendicular to CD and CO so CCl and DDI are perpendicular to the plane formed by OCD. Since AO and AD are part of component 5 and DDI is perpendicular to slot. So DDI is perpendicular to the plane formed by AO and OD. So OAD and OCD are coincident planes thus CO, AO and DO are coplanar. It means normal of small heliostat (OC) is in the same plane as incoming ray (OD) and desired reflected ray (AO).

[0091] Now it will be shown that OC bisects the angle between OA and OD.

Equation of curve says that length of OD is r which is given by

Here 'a 'is the length of OC. b is the length of C1D1.

Since CCl and DDI are parallel and of same length so

Taking magnitude of both sides and substituting r from equation of slot.

By simplification it gives it must be noted that Θ is angle between OA and

OD thus OC bisects angle between OA and OD. Thus normal to small heliostat bisects the angle between receiver direction and incoming ray and it is also coplanar with them. Reflected ray will always fall on receiver whatever be the sun's position in the sky.

[0092] In one implementation, a solar energy reflection and focusing system is disclosed. The solar energy reflection and focusing system comprises at least one collector mirror and one central mirror having a specific curvature connected to a collector mirror, wherein the third mirror (component 4) is adapted to track such that concentrated collimated rays from central mirror, incident from the collector mirror 3, are reflected towards at least one receiver.

[0093] In one implementation, a collimation system is disclosed. The collimation system comprises at least one collector mirror and at least one central mirror having a specific curvature connected to a collector mirror, wherein the third mirror 4 is adapted to track such that concentrated collimated rays from central mirror, incident from the collector mirror 3, are reflected towards at least one receiver.

[0094] In one implementation, the central mirror is adapted to receive the concentrated collimated rays from the collector mirror in a direction opposite to a direction of ray's incident on the collector mirror from a direction of sun.

[0095] In one implementation, the central mirror is designed to reflect the concentrated collimated rays towards the mirror 4 in a direction analogous to a direction of at least ray's incident on the collector mirror from a direction of source of energy.

[0096] In one implementation, the small heliostat which is part of component 4 is adapted to move in two directions, by means of a linkage arrangement as shown in figures 3- 7, such that the concentrated collimated rays are reflected towards the receiver.

[0097] In one implementation, the central mirror is connected to the collector mirror preferably by means of at least a truss member.

[0098] In one implementation, the collector mirror is kept in a direction of the source of energy, preferably sun.

[0099] In one implementation, the central mirror faces opposite to the direction of source of energy, preferably sun.

[00100] In one implementation, the small heliostat which is part of component 4is adapted to track preferably by means of linkage arrangement.

[00101] In one implementation, the collector mirror which is part of component 3 is rotatable and coupled to at least a component 2 to provide an elevation movement to the collector mirror. [00102] In one implementation, the component 2 is rotatably coupled to at least a fixed component 1 thereby providing an azimuth drive, the fixed component 1 is preferably a fixed shaft connected to a ground.

[00103] In one implementation, the top end of component 1 is adapted to guide direction of the receiver from a centre of the collector mirror, the direction the component 1 is fixed towards receiver.

[00104] In one implementation, the small heliostat which is part of component 4 is rotatable and coupled component 5, the component 5 comprise at least a curved slot adapted to direct the small heliostat in a desired direction.

[00105] In one implementation, a preferable size of the collector mirror is selected from/between 1 m radius to 10 m radius.

[00106] In one implementation, a preferable combined area of the central mirror and the small heliostat is preferably at least less than 4% of the collector area.

[00107] In one implementation, the collector mirror is preferably a spherical mirror but deviation from preferred surface can be catered by suitable design of central mirror.

[00108] In one implementation, the present invention, characterized in that it comprises the collector mirror, central mirror and small heliostat to eliminate at least the cosine losses, wherein the small heliostat which is part of component 4 is operated by a linkage arrangement to reflect concentrated collimated rays to the receiver.

[00109] Apart the technical benefit as discussed above, the present invention may also include some of the additional advantages as mentioned below:

i. The present invention provides a collimating system for solar energy application, whose performance does not depend on accuracy of primary collector. It is crucial to economics since it is not dependent on parabolic disc which is costly to fabricate accurately. In contrast to the present invention, in prior arts performance depends on accuracy of primary collector.

ii. The present invention provides a central mirror surface, designed such that it relives the small effects due to fabrication errors in primary collector. iii. The present invention provides a mechanism by which collimated light is sent to fixed receiver thus avoiding need of two precise drives.

iv. In conventional concentrated solar plant, heliostat is uniquely positioned relative to the central tower. Heliostat is a mirror that makes precise rotations to reflect sunlight onto a fixed spot on the central tower. As the sun moves across the sky, the heliostat adjusts its position so that the spot of reflected light remains stationary on the target. As the mirror is obliquely placed with respect to direction of sun rays, the mirror surface is not optimally utilized. The resulting optical loss is called cosine loss and it varies from 18 to 23 % in big plants. To eliminate the cosine loss, the present invention provides a central mirror with required profile to collimate the sun rays. v. The present invention provides a collector mirror with innovative central mirror which replaces the conventional heliostat resulting in better and efficient concentration of sunrays on to receiver.

vi. The present invention provides an ability to use any curvature for collector mirror in place of parabolic disc enhances the collector mirror economy close to the heliostat surface, so it can be utilized in solar power technology.

vii. The present invention provides a linkage arrangement to keep the reflected collimated light in fix direction thus avoiding extra motor drives.

viii. The present invention enables deviation from intended surface which can also be catered with design of central mirror, which is helpful in relieving fabrication costs. Furthermore, a big collector mirror can also be fabricated in pieces then joined together.

ix. The present invention solves the problem of collimation with collector using a central mirror design. Since central mirror is of very small size compare to collector mirror, it can be made according to actual fabricated surface of collector mirror.

x. The present invention eliminates the cosine losses taking the optical efficiency to 83 % as against 65 % in conventional plant.

xi. The present invention eliminates blockage and spillage virtually as against 2% blockage in conventional plant. xii. System is proposed to replace conventional heliostat, wherein the size range of the collector mirror will be same as that of conventional heliostats. Size of collector mirror can be 1 m radius to 10 m radius. Combined area of central mirror and a small heliostat is in general less than 4% of collector area. Number of units depends on the power and their coordinates are decided by layout as in conventional heliostats. As example for typical 10 MWe plant, 627 No of collector mirror of 10m diameter are required as against 800 conventional heliostat of size 10m diameter.

[00110] It may be clearly understood by a person skilled in the art that for the purpose of convenient and brief description, for a detailed working process of the foregoing system, devices, and unit, reference may be made to a corresponding process in the foregoing device/apparatus embodiments, and details are not described herein again.

[00111] In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and device may be implemented in other manners. For example, a plurality of units or components or mechanisms may be combined or integrated into another system, or some features may be ignored or not performed.

[00112] Although system comprising sun ray collimating central mirror and heliostat to increase efficiency is disclosed, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices described. Rather, the specific features are disclosed as examples of implementations of the system comprising sun ray collimating central mirror and heliostat to increase efficiency.

Claims

1. A solar energy reflection and focusing system comprising:

at least one central mirror 30 having a specific curvature connected to a collector mirror 3, wherein a third mirror (small heliostat) is adapted to track the sun such that the concentrated collimated rays from the central mirror 30, incident from the collector mirror, are reflected towards at least one receiver, wherein the direction of collector mirror is in the direction of the sun by using at least two computer controlled rotations.

2. The solar energy reflection and focusing system as claimed in claim 1, wherein the central mirror 30 receives the concentrated rays from the collector mirror in a direction opposite to a direction of ray's incident on the collector mirror from the direction of source of energy.

3. The solar energy reflection and focusing system as claimed in claim 1, wherein the central mirror 30 reflects the concentrated collimated rays towards the mirror 4 in a direction analogous to a direction of ray's incident on the collector mirror 3 from a direction of source of energy.

4. The solar energy reflection and focusing system as claimed in claim 1, wherein the small heliostat is adapted to move in at least two directions, by means of a linkage arrangement, such that the concentrated collimated rays are reflected towards the receiver.

5. The solar energy reflection and focusing system as claimed in claim 1, wherein the central mirror 30 is connected to the collector mirror preferably by means of at least a truss member.

6. The solar energy reflection and focusing system as claimed in claim 1, wherein the collector mirror is kept in the direction of the source of energy, using two rotations by motor devices, preferably sun.

7. The solar energy reflection and focusing system as claimed in claim 1, wherein the central mirror 30 faces opposite to a direction of at least a source of energy, preferably sun.

8. The solar energy reflection and focusing system as claimed in claim 1, wherein the third mirror is adapted to track so that reflected ray falls on fixed receiver, preferably by means of linkage arrangement so that two costly motors are avoided.

9. The solar energy reflection and focusing system as claimed in claim 1, wherein the collector mirror is rotatably coupled to at least a component 2 to provide an elevation movement to the collector mirror 3.

10. The solar energy reflection and focusing system as claimed in claim 1, wherein at least a component 2 is rotatably coupled to at least a fixed component 1 thereby providing an azimuth drive, the fixed component 1 is preferably a fixed shaft connected to a ground.

11. The solar energy reflection and focusing system as claimed in claim 10, wherein the component 1 is adapted to guide the direction of the receiver from a center of the collector mirror.

12. The solar energy reflection and focusing system as claimed in claim 1 and 8, wherein the component 4 is rotatably coupled to at least a component 5 and the component 5 comprise at least a curved slot adapted to direct the component 4 in the desired direction.

13. The solar energy reflection and focusing system as claimed in claim 1, wherein a preferable size of the collector mirror 3 is selected from/between 1 m radius to 10 m radius.

14. The solar energy reflection and focusing system as claimed in claim 1, wherein a preferable combined area of the central mirror 30 and the small heliostat is preferably at least less than 4% of the collector area.

15. The solar energy reflection and focusing system as claimed in claim 1, wherein the collector mirror 3 is preferably a spherical mirror.

16. A solar energy reflection and focusing system, comprising: a collector mirror, a central mirror with the small heliostat adapted to eliminate at least the cosine losses, wherein the small heliostat is operated by a linkage arrangement to reflect concentrated collimated rays to the receiver.

17. A collimation system comprising:

at least one mirror (component 4) and at least one central mirror 30 having a specific curvature connected to a collector mirror (component 3), wherein the component 4 is adapted to track such that concentrated collimated rays from central mirror 30, are reflected towards at least one receiver.

18. The collimation system as claimed in claim 17, further comprising: a component 1, a component 2, the component 3 (collector mirror), the small heliostat (component 4), component 5 carrying a special slot, a link component 6, a component 7, a component 8, and a component 9.

19. The collimation system as claimed in claim 17 and 18, wherein the central mirror 30 is rigidly attached with the collector mirror 3 to form a part of the component 3, the collector mirror 3 is in a direction of the sun and the central mirror 30 faces opposite to the sun.

20. The collimation system as claimed in claim 18, wherein the component 1 is a fixed shaft with respect to the earth, and the component 2 is adapted to rotate about the component 1 thereby providing an azimuth drive.

21. The collimation system as claimed in claim 20, wherein collector mirror (component 3) mounted on the component 2 providing an elevation movement to the collector mirror.

22. The collimation system as claimed in claim 18, wherein:

the component 5 is concentric with the inclined cylindrical rod which is part of component 1 and is adapted to rotate about it thereby rotating the component 4 mounted on the component 5;

the component 5 comprises at least one curved slot adapted to maintain at the direction of the component 4 in a desired direction.

23. The collimation system as claimed in claim 18, wherein as sun moves in sky, direction of the collector mirror 3 is kept in the direction of sun with two motor or linear drives, and depending on the movement of the collector mirror (component 3) the component 5 rotates about the component 1 and the component 9 slides in a curved slot of the component 5 changing the direction of the component 4, such that the normal to small heliostat (component 4) remains bisector of the rotation axis of component 5 and the normal to collector mirror .