Mixed heliostat field

Abstract

Mixed heliostat field combining, in the same field, heliostats of different sizes and/or with different types of facets, all of them having at least one facet and being canted or not, and either having spherical, cylindrical, flat or quasi-flat (spherical with a high curvature radius) facets, such that the solar field is optimised in order to minimise shadows and blockages between heliostats, as a result of correct positioning of the heliostats in the field.

Claims

1. A mixed heliostat field for a solar concentration plant having a central receiver, wherein the mixed heliostat field minimizes losses due to astigmatism and a cosine effect, and maximizes visibility of each heliostat, the mixed heliostat field comprising a plurality of heliostats installed in a single field, wherein: each of the heliostats has at least one facet; the plurality of heliostats comprises heliostats of at least two different sizes and the plurality of heliostats comprises a first heliostat comprising facets of a first facet type and a second heliostat comprising facets of a second facet type, the first and second facet types being selected from the group of facet types consisting of spherical, cylindrical, and flat; the plurality of heliostats are actively controlled; the plurality of heliostats comprises heliostats having different canted profiles; and the heliostat field comprises at least a first area and a second area, the heliostats in the first area being on average farther from the central receiver than the heliostats in the second area, and the heliostats in the first area having larger surface areas than the heliostats in the second area.

2. The mixed heliostat field of claim 1, wherein the plurality of heliostats comprises large heliostats, with a surface area of at least 120 m.sup.2.

3. The mixed heliostat field of claim 2, wherein the large heliostats have canted spherical facets.

4. The mixed heliostat field of claim 2, wherein the large heliostats have parabolic or spherical canted cylindrical facets in a direction of the larger dimension.

5. The mixed heliostat field of claim 2, wherein the large heliostats have flat or spherical facets.

6. The mixed heliostat field of claim 2, wherein the field is established with groups of heliostats with a similar theoretical curvature radius, all of them with a real curvature radius equivalent to the theoretical curvature radius of the heliostat of the group furthest from the receiver or closest to an average of all the theoretical curvature radiuses for that group.

7. The mixed heliostat field of claim 2, wherein the plurality of heliostats are distributed in four areas as follows: Area 1: Made up of a first portion of the large heliostats with a spherical or parabolic canted structure and flat or spherical facets and which are located in that area of the field in which an average annual angle of incidence is greater than 45% of a maximum annual angle of incidence of the field and a visibility of the heliostat is medium or high, wherein a medium visibility means having an angle of visibility greater than 25 and less than 35, and a high visibility means having an angle of visibility greater than 15 and less than 25; Area 2: Made up of a second portion of the large heliostats with a spherical or parabolic canted structure and flat facets located in that area of the field, in which an average annual angle of incidence is less than 45% of the field's maximum annual angle of incidence and the angle of visibility of the receiver is less than 15 and the heliostat distance to a base of a tower onto which the heliostats direct solar energy is greater than ten times an optical height of the tower; Area 3: Made up of medium size heliostats having a surface area of at least 20 m.sup.2 and less than 120 m.sup.2 with a spherical or parabolic canted structure and cylindrical facets which are located in that area of the field in which an average annual angle of incidence is greater than 45% of the field's maximum annual angle of incidence and the visibility of the receiver is low, and wherein a low visibility means having an angle of visibility greater than 35; and Area 4: Made up of small heliostats having a surface area of less than 20 m.sup.2 located in that area of the field in which an average annual angle of incidence is less than 45% of the field's maximum annual angle of incidence and the visibility of the receiver is medium or low.

8. The mixed heliostat field of claim 7, wherein the field has a latitude of 37.34 and north field, angle of incidence less than 45 or average annual cosine effect lower than 0.78.

9. The mixed heliostat field of claim 7, wherein the heliostats of areas 1 and 2 each have a surface area of 120 m.sup.2 with 28 facets distributed in 4 columns and 7 rows and the heliostats of area 4 have a surface area of 4 m.sup.2 each.

10. The mixed heliostat field of claim 9, wherein the heliostats of area 3 have a surface area of 20 m.sup.2 each.

11. The mixed heliostat field of claim 9, wherein the heliostats of area 3 includes small heliostats having a surface area of less than 20 m.sup.2 for carrying out an active control that directs a reduced solar spot where required.

12. The mixed heliostat field of claim 11, wherein in said area 3 heliostats with a 4 m.sup.2 facet are used.

13. The mixed heliostat field of claim 2, wherein the field has an atmospheric transmission coefficient above 0.95 and the heliostats are distributed in two areas: Area 5: receiver angle of visibility greater than 15 and less than 25, large heliostats having a surface area of greater than 120 m.sup.2 with cylindrical or flat facets; and Area 6: angle of visibility greater than 25, reserved for small heliostats having a surface area of less than 20 m.sup.2 with no astigmatism with reduced spot.

14. The mixed heliostat field of claim 2, wherein the field has an atmospheric transmission coefficient above 0.95 and the heliostats are distributed in three areas: Area 7: angles of incidence less than 45% of a maximum annual angle of incidence and receiver angle of visibility less than 25, heliostats with cylindrical or flat facets; Area 8: angle of visibility greater than 25, small heliostats having a surface area of less than 20 m.sup.2 with no astigmatism with a reduced spot; and Area 9: angles of incidence greater than 45% of the maximum annual angle of incidence, reserved for heliostats with no astigmatism with reduced spot and spherical or cylindrical facet.

15. The mixed heliostat field of claim 2, wherein the heliostats are distributed in four areas as follows: Area 10: angles of incidence less than 45% of a maximum annual angle of incidence and receiver angles of visibility less than 25, with heliostats with cylindrical or flat facets; Area 11: angles of visibility greater than 25, small heliostats having a surface area of less than 20 m.sup.2 with no astigmatism with a reduced spot; Area 12: angles of incidence less than 45% of the maximum annual angle of incidence, reserved for heliostats with no astigmatism with reduced spot and spherical or cylindrical facet; and Area 13: angles of incidence less than 30% of the maximum annual angle of incidence, reserved for heliostats with no astigmatism with reduced spot.

16. The mixed heliostat field of claim 1, wherein the plurality of heliostats comprises medium size heliostats, with a surface area of at least 20 m.sup.2 and less than 120 m.sup.2.

17. The mixed heliostat field of claim 16, wherein the medium size heliostats have spherical canted facets.

18. The mixed heliostat field of claim 16, wherein the medium size heliostats have cylindrical canted facets in a direction of the larger dimension.

19. The mixed heliostat field of claim 16, wherein the medium size heliostats have flat or spherical facets.

20. The mixed heliostat field of claim 16, wherein in areas of the field in which a receiver angle of visibility is greater than 35, medium sized or small heliostats are used, wherein a small heliostat is defined as having a surface area less than 20 m.sup.2.

21. The mixed heliostat field of claim 1, wherein the plurality of heliostats comprises small heliostats with at least one single facet with surface area less than 20 m.sup.2.

22. The mixed heliostat field of claim 21, wherein the facet is cylindrical.

23. The mixed heliostat field of claim 21, wherein the facet is flat or spherical.

24. The mixed heliostat field of claim 21, wherein the facet is spherical.

Description

DRAWING DESCRIPTION

(1) In addition to the description, a series of drawings have been included to aid in understanding the invention, which include, but are not limited to, the following:

(2) FIG. 1: Flat mirror with a half-angle of acceptance

(3) FIG. 2: Flat heliostat facet from the state of the art

(4) FIG. 3: Non-imaging focusing heliostat from the state of the art

(5) FIG. 4: Spherically canted heliostats with flat facets

(6) FIG. 5: Heliostat with cylindrical facets

(7) FIG. 6: Example of cosine effect in heliostat field North

(8) FIG. 7: Angle of visibility of the receiver in the heliostat field

(9) FIG. 8: First preferred embodiment in mixed solar field

(10) FIG. 9: Second preferred embodiment in mixed solar field

(11) FIG. 10: Third preferred embodiment in mixed solar field

(12) FIG. 11: Fourth preferred embodiment in mixed solar field

(13) The references that appear in the figures represent: 1. Area of mixed heliostat field where <35 and cos >0.78 2. Area of mixed heliostat field where <15 and cos <0.78 3. Area of mixed heliostat field where <35 and cos >0.78 4. Area of mixed heliostat field where <15 and cos <0.78 5. Area of mixed heliostat field with <25 6. Area of mixed heliostat field with <25 7. Area of mixed heliostat field with angles of incidence <45% from the maximum annual angle of incidence and <25 8. Area of mixed heliostat field with <25 9. Area of mixed heliostat field with angles of incidence <45% from the maximum annual angle of incidence 10. Area of mixed heliostat field with angles of incidence <45% from the maximum annual angle of incidence and <25 11. Area of mixed heliostat field with <25 12. Area of mixed heliostat field with angles of incidence <45% from the maximum annual angle of incidence. 13. Area of mixed heliostat field with angles of incidence <30% from the maximum annual angle of incidence 18. Area of heliostat field with very high receiver visibility <10 19. Area of heliostat field with very high receiver visibility 10<<15 20. Area of heliostat field with high receiver visibility 15<<20 21. Area of heliostat field with high receiver visibility 20<<25 22. Area of heliostat field with medium receiver visibility 25<<30 23. Area of heliostat field with medium receiver visibility 30<<35 24. Area of heliostat field with low receiver visibility 35<<40 25. Area of heliostat field with low receiver visibility >40 30. Area of the heliostat field with cosine effect between 0.911 and 0.811 31. Area of the heliostat field with cosine effect between 0.811 and 0.761 32. Area of the heliostat field with cosine effect between 0.761 and 0.711 33. Area of the heliostat field with cosine effect between 0.711 and 0.661 34. Area of the heliostat field with cosine effect between 0.661 and 0.55

PREFERRED EMBODIMENT OF THE INVENTION

(14) In view of the figures, below is a preferred embodiment of the system described in this invention.

(15) Before beginning the description of a specific mixed field, attached are a series of drawings that show some of the different types of heliostats that can be combined.

(16) FIG. 1 shows a flat mirror with a half-angle of acceptance

(17) FIG. 2 shows an example of a flat heliostat facet.

(18) FIG. 3 shows a non-imaging focusing heliostat

(19) FIG. 4 represents a spherically canted heliostat with flat facets, i.e. each of the flat facets is orientated in such a way that the entire heliostat acquires a spherical curvature.

(20) FIG. 5 shows a heliostat made up of cylindrical facets.

(21) The heliostat field proposed in this invention can be combined in a single central receiver plant: Very large heliostats, typically 120 m2 or 140 m2, with spherical or parabolic canted profiles, with 28 or 32 flat facets respectively, Very large heliostats, 120 or 140 m2 with spherical or parabolic canted profiles with 28 or 32 facets shaped spherically or cylindrically. Medium size heliostats, typically 20 m2 with spherical or parabolic canted profiles with only a few (4 or 5) flat facets, spherically or cylindrically shaped and small heliostats typically 4 m2 with a flat or cylindrical facet.

(22) The choice of one or another type of heliostat in the different field positions, is mainly based on the cost minimisation criteria of the plant; on the average annual angle of incidence (which translates into annual cosine effect and astigmatic effects), the visibility of the heliostat receiver and on the possible need for the plant to have part of the solar field able to generate minimum size sun spots in order to help with the possible control of the receiver's finer transfer of heat.

(23) In the specific case of FIG. 6, it shows an example of the cosine effect in a North heliostat field, specifically it is a circular field at latitude 37.24. It schematically displays different ranges of cosine effect distributed as follows: Interval of 0.911 to 0.811 (30), of 0.811 to 0.761 (31), of 0.761 to 0.711 (32), of 0.711 to 0.661 (33) and of 0.661 to 0.55 (34).

(24) FIG. 7 shows the receiver visibility of the heliostats calculated for a circular field in North latitude and external cylindrical receiver. The heliostat field is schematically divided into eight areas (18, 25) in which the heliostat view of the receiver varies, with the areas with greater visibility or very high visibility being areas (18) and (19) with <15, areas (20) and (21) area areas of high visibility with a visibility angle of 15<<25, the areas with medium visibility (22) and (23) are visibility angles of 25<<35, and areas with low visibility (24) and (25) are for >35.

(25) FIG. 8 shows the first preferred case for a heliostat field, in North latitude, in which the distribution of the different types of heliostats is outlined as follows: Area 1: Made up of type 1.3 heliostats, i.e. very big heliostats with a spherical or parabolic canted structure and flat facets as represented in FIG. 3, which are located in that area of the field, in which the average annual angle of incidence is greater than 45% of the field's maximum annual angle of incidence (for a latitude of 37.34 and north field, angle of incidence greater than 45 or average annual cosine effect greater than 0.78) and the visibility of the heliostat is medium or high.
cos >0.78

(26) 15<<35 Area 2: Made up of type 1.3 heliostats, i.e. very big heliostats with a spherical or parabolic canted structure and flat facets which are located in the area of the field in which the average annual angle of incidence is less than 45 of the field's maximum annual angle of incidence (for a latitude of 37.34 and north field, angle of incidence less than 45 or average annual cosine effect less than 0.78) and the visibility of the receiver is very high.
cos <0.78

(27) <15 Area 3: Made up of 2.1 or 2.2 type heliostats, i.e. medium size heliostats with a spherical or parabolic canted structure and cylindrical facets as represented in FIG. 4, which are located in the area of the field in which the average annual angle of incidence is greater than 45% of the field's maximum annual angle of incidence (for a latitude of 37.34 and north field, angle of incidence greater than 45 or average annual cosine effect greater than 0.78) and the visibility of the receiver is low.
cos >0.78

(28) >35

(29) If part of the solar field needs to be able to generate a minimum size sunspot in order to carry out an active control and thus help with the eventual control of a finer transfer of heat to the receiver, small parabolic or spherical canted heliostats can be included here with a low number of facets (typically 4 or 5), or small heliostats with a flat plane, 3.2 and 3.3 type heliostats.

(30) Area 4: Made up of smaller heliostats than the rest of the field heliostats with spherical facets (preferably small type 3.1 or 3.2 heliostats), which are located in the area of the field in which the average annual angle of incidence is greater than 45% of the field's maximum annual angle of incidence (for a latitude of 37.34 and north field, angle of incidence lower than 45 or average annual cosine effect lower than 0.78) and the visibility of the receiver is medium or low.
cos <0.78

(31) >25

(32) Preferably the heliostats in areas 1, 2 are 120m2 with 28 facets distributed in 4 columns and 7 rows and the heliostats in area 3 are 20 m2. For heliostats in area 3, 4 m2 heliostats with 1 facet can also be used. For area 4 the preferred embodiment is 4 m2 heliostats.

(33) FIG. 9 shows the second case of preferred embodiment of the invention, with high atmospheric transmission coefficient in excess of 0.95: Area 5: high or very high receiver visibility (<25), heliostats 1.2 or 1.3 Area 6: medium or low visibility (angles of visibility of the receiver >25), reserved for heliostats with no astigmatism with reduced spot: Heliostat 3.2 or 3.3 around 4 m2

(34) FIG. 10 shows the third case of preferred embodiment of the invention, with high atmospheric transmission coefficient in excess of 0.95: Area 7: low angles of incidence (less than 45% of the maximum annual angle of incidence) and high or very high receiver visibility ( less than 25), heliostats 1.2 or 1.3 Area 8: medium or low visibility (>25), heliostats with no astigmatism with reduced spot type 3.1 or 3.2 Area 9: high angles of incidence (greater than 45% of the maximum annual angle of incidence), reserved for heliostats with no astigmatism with reduced spot, 2.1 or 2.2 20 m2 heliostat with 5 facets.

(35) FIG. 11 shows the fourth case of preferred embodiment of the invention, with low atmospheric transmission coefficient lower than 0.95: Area 10: low angles of incidence (less than 45% of the maximum annual angle of incidence) and high or very high receiver visibility a less than 25 heliostat 1.2 or 1.3 Area 11: medium or low visibility (>25), heliostats with no astigmatism with reduced spot type 3.2 or 3.3. Area 12: low angles of incidence (lower than 45% of the maximum annual angle of incidence), reserved for heliostats with no astigmatism with reduced spot: heliostat 2.1 or 2.2 Area 13: low angles of incidence (lower than 30% of the maximum annual angle of incidence), reserved for heliostats with no astigmatism with reduced spot type 3.2 or 3.3.