MODULAR FRESNEL SOLAR ENERGY COLLECTION SYSTEM
A modular linear Fresnel solar energy collection system comprises one or more reflector units having a number of spaced, elongated solar panels that extend between a pair of opposed, light-weight aluminum beams. A first drive mechanism rotates the solar panels at angles progressively increasing from the center of the two beams to their ends so that each panel reflects incident sunlight to a secondary reflector located above the panels. The secondary reflector, in turn, reflects the sunlight it receives from the solar panels onto a receiver tube mounted in a fixed position substantially concentric to a central axis extending between the two aluminum beams. A second drive mechanism is coupled to one of the beams which is operative to pivot the assembly of beams, solar panels and secondary reflector between a generally easterly direction and westerly direction in order to track the apparent movement of the sun during the course of a day.
This invention relates to the generation of electrical energy through solar thermal power collection, and, more particularly, to a modular Fresnel solar energy collection system that employs a secondary reflector, light-weight solar panels and a fixed linear receiver through which a heat transfer fluid is circulated.
BACKGROUND OF THE INVENTIONSystems for the generation of electricity by collecting solar thermal radiation were first introduced in 1914, and have become increasingly popular with the rise in fossil fuel costs and concerns over global warming. A majority of solar energy collection systems currently in use employ parabolic, trough-shaped reflectors that focus the sun's energy on a receiver such as an engine. Recently, a new type of system has emerged known as a linear Fresnel reflector that includes a series of long, narrow mirrors having a shallow curvature, or none at all, which focus light onto one or more linear receivers positioned above the mirrors. The concept of large reflectors being broken down into many Fresnel sub-elements to improve manageability was advanced by Baum et al. (1957), and in the 1960's, important development work was undertaken by the solar pioneer Giovanni Francia (Francia, 1968) of the University of Genoa, who developed both linear Fresnel reflector systems and Fresnel point focus systems. Typically, a linear Fresnel reflector focuses sunlight at 80 to 100 times its normal intensity on the receiver. The concentrated energy heats a heat transfer fluid flowing through the receiver, which, in turn, is used to generate steam to power a turbine that drives an electric generator.
Instead of a large parabolic surface, Fresnel reflectors use many smaller mirrors which are more manageable, easier to install, less expensive to maintain and aim to reduce overall costs by sharing a receiver between several mirrors while still using simple line-focus geometry with one axis of tracking, i.e., the individual mirrors can pivot in a generally easterly and westerly direction. Despite these advantages, there is more heat loss due to the larger width dimension of the receiver which is needed to compensate for the lack of curvature in the mirrors. Another disadvantage of current linear Fresnel reflectors is that although they work well when the sun is nearly vertical in the sky, e.g. between about 10:00 a.m. to 2:00 p.m., rapid performance degradation occurs at other times during the day. As the sun incident angle increases, the solar collection efficiency drops quickly because while the mirrors are pivotal, the framework supporting them is stationary.
The goal of any solar collection system is to reduce the cost of electricity generated. There are fundamentally two ways to do this, namely, reduce the cost of the solar field and annual operating expenses, and, to increase system efficiency. Solar field optical efficiency is dependent upon a number of factors, including, without limitation, sunlight incident angle effects, collector tracking error, the geometric accuracy of the mirrors to focus light on the receiver tubes, mirror reflectivity, cleanliness of the mirrors, the creation of shadows across the mirrors, transmittance of solar energy into the receiver tubes, cleanliness of the receiver tubes, absorption of solar energy by the receiver tubes, end losses and the creation of shadows between rows of mirrors. While current systems produce electricity at a cost in the range of $0.12 to $0.18 per kilowatt-hour, it is desirable to achieve a cost level of about $0.05 per kilowatt-hour to be more competitive with present fossil-fuel based systems.
SUMMARY OF THE INVENTIONThis invention is directed to a linear Fresnel solar energy collection system that improves solar field efficiency, lowers operational and maintenance costs, and therefore reduces the overall cost of generating electricity per kilowatt-hour.
One aspect of this invention is predicated on the concept providing a simple, modular linear Fresnel solar energy collection system comprising one or more reflector units each fabricated using light-weight materials arranged in a construction that is highly accessible, easily maintained, and lower in initial cost. In one embodiment, each reflector unit comprises a number of spaced, elongated solar panels, having a slightly curved or flat reflective surface, that extend between a pair of opposed, light-weight aluminum beams. A first drive mechanism rotates the solar panels at angles progressively increasing from the center of the two beams to their ends so that each panel reflects incident sunlight to a secondary reflector located above the panels. The secondary reflector, in turn, reflects the sunlight it receives from the solar panels onto a receiver tube mounted in a fixed position substantially concentric to a central axis extending between the two aluminum beams. A second drive mechanism is coupled to one of the beams which is operative to pivot the assembly of beams, solar panels and secondary reflector between a generally easterly direction and westerly direction in order to track the apparent movement of the sun during the course of a day.
Preferably, each solar panel comprises a honeycomb aluminum section and a highly reflective silver-metallized surface connected together by an adhesive layer. The solar panels are strong, durable, light-weight and efficiently reflect incident sunlight many times its normal intensity onto the secondary reflector. The reflective surface of such panels may be washed to maintain cleanliness which enhances the efficiency with which they reflect incident sunlight to the secondary reflector.
A heat transfer fluid is circulated through the receiver tube for heating by the sunlight directed thereto from the secondary reflector. Because the receiver tube is fixed relative to the pivoting beams, it may be connected to a fixed transfer conduit that communicates with a steam generator and turbine. Since both the receiver tube and transfer conduit are mounted in a fixed position, heat losses resulting from the transfer of fluid out of the receiver tube are minimized and maintenance problems are reduced.
In an alternative embodiment, a reflector unit includes solar panels that are formed in smaller segments and mounted to a number of shafts extending between the opposed beams described above. The shafts are operative to tilt the segmented solar panels at a desired latitude angle, e.g. in a generally northerly or southerly direction, dependent upon the geographic location of the system. This allows the system of this invention to account for the varying incidence angle of the sun with the earth as the seasons change so that the solar panels more directly face the sun throughout the year. An improvement in solar collection efficiency of at least 5% may be realized by this enhancement of the present invention.
The several embodiments of this invention are modular in construction in the sense that several reflector units may be mounted side-by-side, and their receiver tubes connected, to form a linear Fresnel solar collection system with increased capacity and overall efficiency.
The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings, wherein:
Referring now to the drawings, one embodiment of a reflector unit 10 for the solar energy collection system 12 of this invention is illustrated with reference to
With reference initially to
The reflector unit 10 may be supported above ground level by pylons 28 secured on a foundation such as concrete footers (not shown) that can support the weight of the unit 10 and wind loading applied to it. As described in detail below, in one embodiment the beams 14, 16, solar panels 20 and secondary reflector 22 may be collectively tilted by operation of a first drive mechanism in a generally easterly and westerly direction.
Referring now to
The receiver tube 24 is a component employed in prior art solar collection systems and is readily commercially available. As shown in
As noted above, the solar panels 20 and secondary reflector 22 collectively function to direct incident sunlight onto the receiver tube 24 to elevate the temperature of heat transfer fluid circulating within the receiver tube 24 to a level sufficient to operate a steam generator (not shown) for the production of electricity. The positioning of the solar panels 20 with respect to the secondary reflector 22, and the configuration of the solar panels 20 and secondary reflector 22, are both important in maximizing the efficiency of the reflector unit 10. The discussion that follows concerns this aspect of the present invention.
A parabola is a geometric shape defined by the locus of points that are equidistant from a point (the focus) and a line (directrix) that lie in the same plane. Reflective surfaces having the shape of a parabola have been commonly used in solar power collection systems because incident sunlight may be reflected to a collection device located at the focus or directrix of the parabola. The unit 10 of the present invention is designed to tale advantage of this property of a parabola, but in a much more efficient, less expensive and practical manner than taught in the prior art.
The standard mathematical equation defining a parabola is as follows:
Where:
y=x2/4f
f=the focal point
x=horizontal distance from the center
y=vertical distance
In the presently preferred embodiment of reflector unit 10, each of the solar panels 20 is formed with a curvature according to the above equation. The parabolic effect of focusing rays of light to a focus or directrix of the parabola, discussed above, can be used in a linear arrangement. As viewed in
The manner in which the solar panels 20 may be oriented at the appropriate angles depicted in
An alternative embodiment of the first drive mechanism of this invention is shown in
As noted above with reference to
Referring now to
In the presently preferred embodiment, the receiver tube 24 remains in a fixed position with respect to the beams 14, 16 and drive wheel 82 throughout the pivotal motion of the beams 14, 16, solar panels 20 and secondary reflector 22. As described above, the receiver tube 24 may extend through an openings 46 formed in each beam 14, 16. A protruding end of receiver tube 24 enters a bore 90 formed in the plate 88, and a central bore 92 formed in the drive wheel 82 where it is received and supported by a bearing 94 that allows the receiver tube 24 to remain in a fixed position during rotation of the drive wheel 82. This construction has the advantage of allowing the receiver tube 24 to be connected to a fixed transfer conduit coupled to a steam generator (not shown). Consequently, the expensive and leak-prone connections between the moving receiver tubes and transfer conduits employed in some prior art systems are eliminated in this invention.
The solar energy collection system 12 of this invention is modular in construction. As shown in
As discussed above with reference to
A still further embodiment of a solar energy collection system according to this invention having one or more reflector units 100 is illustrated in
The same beams 14, 16 described above are employed in unit 100, but instead of elongated solar panels 20 extending between the two beams 14, 16, a plurality of shorter, segmented solar panels 102 are provided. The solar panels 102 are divided into groups, and each group of panels 102 essentially takes the place of a single solar panel 20 in the embodiment of
In one embodiment, as shown in
While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof.
For example, the receiver tube 24 is depicted in
Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims
1. A solar energy collection system, comprising:
- a first beam and a second beam;
- a number of solar panels each having a reflective surface, said solar panels extending between said first and second beams;
- at least one drive mechanism coupled to said solar panels and being operative to tilt respective solar panels into a position to reflect sunlight on said reflective surface thereof;
- a receiver tube within which a heat transfer fluid is circulated;
- a secondary reflector positioned so as to receive sunlight reflective from said solar panels and to reflect said sunlight onto said receiver tube to heat the heat transfer fluid therein.
2. The system of claim 1 in which said at least one drive mechanism comprises a number of drive mechanisms each including a motor having an output coupled to one end of a solar panel, said motors being operative to pivot a respective solar panel at an angle relative to said secondary reflector.
3. The system of claim 2 in which each of said drive mechanisms operates independent of the other.
4. The system of claim 1 in which said at least one drive mechanism comprises a worm gear drivingly connected to a number of follower gears each coupled to one of said solar panels, said worm gear being operative to rotate said follower gears to tilt respective solar panels relative to said secondary reflector.
5. A solar energy collector system, comprising:
- a first beam and a second beam;
- a number of solar panels, each of said solar panels including a first section formed of a light-weight honeycomb structure, a second section having a reflective surface and a third section connecting said first and second layers, said solar panels extending between said first and second beams;
- at least one drive mechanism coupled to said solar panels and being operative to tilt respective solar panels into a position to reflect sunlight on said reflective surface thereof;
- a receiver tube within which a heat transfer fluid is circulated;
- a secondary reflector positioned so as to receive sunlight reflected from said solar panels and to reflect said sunlight onto said receiver tube to heat the heat transfer fluid therein.
6. The system of claim 5 in which said light-weight honeycomb structure is honeycomb aluminum.
7. The system of claim 5 in which said first section has opposed sides, said first section being formed in a concave shape between said opposed sides.
8. A solar energy collection system, comprising:
- a first beam and a second beam;
- a number of solar panels each having a reflective surface, said solar panels extending between said first and second beams;
- a first drive mechanism coupled to said solar panels and being operative to tilt respective solar panels into a position to reflect sunlight on said reflective surface thereof;
- a second drive mechanism operative to pivot said first and second beams between a first position in which said solar panels face a generally easterly direction, and second position in which said solar panels face a generally westerly direction;
- a receiver tube within which a heat transfer fluid is circulated;
- a secondary reflector positioned so as to receive sunlight reflected from said solar panels and to reflect said sunlight onto said receiver tube to heat the heat transfer fluid therein.
9. The system of claim 8 in which said at least one first drive mechanism comprises a number of drive mechanisms each including a motor having an output coupled to one end of a solar panel, said motors being operative to pivot a respective solar panel at an angle relative to said secondary reflector.
10. The system of claim 8 in which said at least one first drive mechanism comprises a worm gear drivingly connected to a number of follower gears each coupled to one of said solar panels, said worm gear being operative to rotate said follower gears to tilt respective solar panels relative to said secondary reflector.
11. A solar energy collection system, comprising:
- a first beam and a second beam;
- a number of solar panels each having a reflective surface, said solar panels extending between said first and second beams;
- a first drive mechanism operative to pivot said first and second beams between a first position in which said solar panels face a generally easterly direction, and second position in which said solar panels face a generally westerly direction;
- a number of second drive mechanisms coupled to at least one of said first and second beams, each of said second drive mechanisms mounting a group of said solar panels and being operative to tilt said solar panels within a respective group in a generally northerly direction and in a generally southerly direction to reflect sunlight incident on said reflective surface thereof;
- a receiver tube within which a heat transfer fluid is circulated;
- a secondary reflector positioned so as to receive sunlight reflective from said solar panels and to reflect said sunlight onto said receiver tube to heat the heat transfer fluid therein.
12. The system of claim 11 in which each of said solar panels comprises a first section formed of a light-weight honeycomb structure, a second section having a reflective surface and a third section connecting said first and second layers.
13. The system of claim 11 in which said light-weight honeycomb structure is honeycomb aluminum.
14. The system of claim 11 in which said first section has opposed sides, said first section being formed in a concave shape between said opposed sides.
15. A solar energy collector system, comprising:
- a number of reflector units oriented side-by-side, each of said reflector units comprising: (i) a first beam and a second beam; (ii) a number of solar panels each having a reflective surface, said solar panels extending between said first and second beams; (iii) at least one first drive mechanism coupled to said solar panels and being operative to tilt respective solar panels into a position to reflect sunlight on said reflective surface thereof; (iv) a receiver tube within which a heat transfer fluid is circulated; (v) a secondary reflector positioned so as to receive sunlight reflected from said solar panels and to reflect said sunlight onto said receiver tube to heat the heat transfer fluid therein.
16. The system of claim 15 in which said at least one first drive mechanism of each reflector units comprises a number of drive mechanisms each including a motor having an output coupled to one end of a solar panel, said motors being operative to pivot a respective solar panel at an angle relative to said secondary reflector.
17. The system of claim 15 in which said at least one first drive mechanism of each of said reflector units is operative to tilt each of said solar panels individually, each of said reflector units further including a second drive mechanism operative to pivot said first and second beams in an easterly direction and in a westerly direction.
18. The system of claim 15 in which said solar panels of each reflector unit comprises a first section formed of a light-weight honeycomb structure, a second section having a reflective surface and a third section connecting said first and second layers.
19. The system of claim 18 in which said light-weight honeycomb structure is honeycomb aluminum.
20. The system of claim 18 in which said first section has opposed sides, said first section being formed in a concave shape between said opposed sides.
21. A solar energy collector system, comprising:
- a number of reflector units oriented side-by-side, each of said reflect units comprising: (i) a first beam and a second beam; (ii) a number of solar panels each having a reflective surface, said solar panels extending between said first and second beams; (iii) a first drive mechanism operative to pivot said first and second beams between a first position in which said solar panels face a generally easterly direction, and second position in which said solar panels face a generally westerly direction; (iv) a number of second drive mechanisms each mounting a group of said solar panels and being operative to tilt said solar panels within a respective group in a generally northerly direction and in a generally southerly direction to reflect sunlight incident on said reflective surface thereof; (v) a receiver tube within which a heat transfer fluid is circulated; (vi) a secondary reflector positioned so as to receive sunlight reflected from said solar panels and to reflect said sunlight onto said receiver tube to heat the heat transfer fluid therein.
22. The system of claim 21 in which said solar panels of each reflector unit comprises a first section formed of a light-weight honeycomb structure, a second section having a reflective surface and a third section connecting said first and second layers.
23. The system of claim 22 in which said light-weight honeycomb structure is honeycomb aluminum.
24. The system of claim 22 in which said first section has opposed sides, said first section being formed in a concave shape between said opposed sides.
Type: Application
Filed: Aug 27, 2008
Publication Date: Mar 4, 2010
Inventor: Danny F. Ammar (Windermere, FL)
Application Number: 12/198,970
International Classification: F24J 2/38 (20060101);