US20100154788A1

US20100154788A1 - Solar receiver

Info

Publication number: US20100154788A1
Application number: US12/340,379
Authority: US
Inventors: Jason R. Wells; Khiem B. Do
Original assignee: Skyline Solar Inc
Current assignee: Skyline Solar Inc
Priority date: 2008-12-19
Filing date: 2008-12-19
Publication date: 2010-06-24
Also published as: WO2010080204A3; WO2010080204A2

Abstract

In one embodiment, a solar receiver has a base plate having a first surface and a second surface, a plurality of solar cells positioned over and supported by the first surface of the base plate, and a multiplicity of fins extending outwardly from the second surface of the base plate. Each of the multiplicity of fins has a fin height axis extending generally perpendicular relative to the base plate, a fin length axis extending generally in parallel with the base plate, and a bottom end attached to the second surface of the base plate, wherein each of the multiplicity of fins are formed from a single, continuous sheet of metal arranged in a serpentine configuration, and wherein each of the multiplicity of fins have a plurality of undulations along the length axis of the fin.

Description

FIELD OF THE INVENTION

The present disclosure relates generally to solar receivers. More particularly, the present disclosure relates generally to solar receivers having a heat sink.

BACKGROUND OF THE INVENTION

The highest cost components of a solar photovoltaic (PV) system are the solar cells that convert sunlight to electricity by the photoelectric effect. To use these cells more effectively, concentrating photovoltaic (CPV) systems focus sunlight from a larger aperture onto a smaller cell area. The waste heat generated in the solar receivers used in CPV systems may raise the cell temperature subjecting the solar cells to thermal stresses causing malfunction, inefficiencies, and increased costs.
Heat sinks may be used to absorb and dissipate the heat from the solar receivers. However, current solar receivers are not sufficiently efficient from a thermal energy transfer standpoint while at the same time sufficiently simple, rugged, compact, and lightweight to be transportable, susceptible to on-site assembly, or efficiently stored.

Overview

A solar receiver is described having a base plate having a first surface and a second surface, a plurality of solar cells positioned over and supported by the first surface of the base plate, each solar cell having a cell face suitable for receiving solar radiation that faces away from the base plate, and a multiplicity of fins extending outwardly from the second surface of the base plate. Each of the multiplicity of fins has a fin height axis extending generally perpendicular relative to the base plate, a fin length axis extending generally in parallel with the base plate, and a bottom end attached to the second surface of the base plate, wherein each of the multiplicity of fins are formed from a single, continuous sheet of metal arranged in a serpentine configuration, and wherein each of the multiplicity of fins have a plurality of undulations along the length axis of the fin.
In another embodiment, the solar receiver may have a base plate having a first surface and a second surface, a plurality of solar cells positioned over and supported by the first surface of the base plate, each solar cell having a cell face suitable for receiving solar radiation that faces away from the base plate, and a multiplicity of fins extending outwardly from the second surface of the base plate. Each of multiplicity of fins has a bottom end opposite a top end, the bottom end attached to the first surface of the base plate, wherein the top end has a width less than a width of the bottom end, wherein each of the multiplicity of fins are formed from a single, continuous sheet of metal arranged in a serpentine configuration, and wherein each of the multiplicity of fins have a plurality of undulations along a length axis of the fin.
Stackable solar receivers are also described with a first solar receiver having a first base plate having a first surface and a second surface, a first plurality of solar cells positioned over the first surface of the first base plate, each solar cell having a cell face suitable for receiving solar radiation that faces away from the first base plate, and a first multiplicity of fins extending outwardly from the second surface of the first base plate, each of the first multiplicity of fins are formed from a single, continuous sheet of metal arranged in a serpentine configuration having a bottom end opposite a top end, the bottom end attached directly to the second surface of the first base plate, wherein the top end has a width less than a width of the bottom end.
The stackable solar receiver also has a second solar receiver having a second base plate having a first surface and a second surface, a second plurality of solar cells positioned over the first surface of the second base plate, each solar cell having a cell face suitable for receiving solar radiation that faces away from the second base plate, and a second multiplicity of fins extending outwardly from the second surface of the second base plate, each of the second multiplicity of fins are formed from a single, continuous sheet of metal arranged in a serpentine configuration having a bottom end opposite a top end, the bottom end attached directly to the second surface of the second base plate, wherein the top end has a width less than a width of the bottom end, wherein the first multiplicity of fins is interleaved with the second multiplicity of fins to stack the first solar receiver with the second solar receiver during transport or storage.
These and other features will be presented in more detail in the following detailed description of the invention and the associated figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more example embodiments and, together with the description of example embodiments, serve to explain the principles and implementations.

In the drawings:

FIGS. 1A-1D illustrate one embodiment of a heat sink.

FIGS. 2A-2D illustrates a heat sink fin in accordance with one embodiment of the invention.

FIGS. 3A-3C illustrate example solar receivers.

FIGS. 4A and 4B illustrates an embodiment of a stackable solar receiver.

FIGS. 5A and 5B illustrate other embodiments of a stackable solar receiver.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments are described herein in the context of a solar receiver. The following detailed description is illustrative only and is not intended to be in any way limiting. Other embodiments will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts.
In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.
Heat sinks can be used to absorb and dissipate heat from solar receivers. Heat sinks have a plurality of fins whereby heat generated by the solar cells dissipates by natural free convection through the plurality of fins. This minimizes the temperature rise experienced by the solar cells to improve efficiency and prevent warping, electrical shorts, or any other malfunctions due to high temperatures.
FIGS. 1A-1D illustrate one embodiment of a heat sink. FIG. 1A illustrates a side view of a plurality of heat sink fins and FIG. 1B illustrates a perspective view of the plurality of heat sink fins of FIG. 1A. As illustrated in FIGS. 1A and 1B, the plurality or multiplicity of fins 102 are formed or fabricated from one continuous roll or sheet of material and bent to form a serpentine configuration. This eliminates the need to assemble a heat sink using individual fins and is low cost and easy to manufacture. The sheet of material can be any material that has good thermal conductivity such as aluminum, copper, or the like.
However, forming the plurality of fins illustrated in FIGS. 1A and 1B has some drawbacks. FIG. 1C illustrates a side view of various imperfect formations of a bottom end of the plurality of heat sink fins of FIGS. 1A and 1B. The plurality of fins can be attached to a base plate 106 of a solar receiver 100 in multiple bonding areas, such as at the bottom end 104 a,b of each of the plurality of fins 102. Each of the plurality of fins may be attached to the base plate 106 through any known means, such as with the use of adhesives.
Forming a flat and/or squared bottom end 104 a, 104 b is a challenging task when forming the serpentine configuration. The end result may be a rounded bottom end 104 a, a skewed bottom end 104 b, or any other non-flat or non-planar configuration.
The various shapes and configurations of the bottom end 104 a, b result in a non-uniform gap 108 between the base plate 106 and each of the plurality of fins 102. Thus, more adhesive is necessary to bond the fins 102 to the base plate 106, which increases thermal resistance to the fins 102. Adhesives have less thermal conductivity than the material used to form the base plate and/or the plurality of fins. Thus, the amount of adhesive should be minimized to form a very thin layer of adhesive between the base plate and the heat sink fin to minimize thermal resistance of the bonding layer. Although the use of a adhesive has been used to describe the bond or attachment between the heat sink fin and the base plate, it is not meant to be limiting as any suitable means that enables good thermal conductivity contact between the heat sink fin and the base plate may be used, such as the use of bolts, screws, mechanical fasteners, soldering, brazing, welding or the like.
The thermal conductivity of most adhesives is only approximately 1% that of aluminum. Thus, a larger gap 108 between the base plate 106 and the bottom end 104 a, b requires more adhesive to bond the fins 102 to the base plate 106. The use of more adhesive forms a thicker bonding layer 103, which then impedes heat transfer from the base plate 106 to the fins 102. Furthermore, since only a small portion or a small surface area of the bottom end 104 a, 104 b of the fin 102 is in close contact with the base plate 106, the heat flow or transfer from the base plate 106 to the fin 102 is not symmetric or uniform. More heat flows from the area where the fin 102 is closer to the base plate 106 than the areas where the fin 102 is further away from the base plate 106. As such, there is a higher thermal resistance in the areas where there is more adhesive, such as the areas where the fin 102 is furthest away from the base plate 106. This undesirably reduces the effectiveness of the heat sink and solar receiver 100.
FIG. 1D illustrates a side view of the plurality of heat sink fins being attached to the base plate. To bond the plurality of fins 102 to the base plate 106, the plurality of fins 102 may to be pressed against the base plate 106 by a force in the direction illustrated by arrows A. As illustrated in FIG. 1D, the plurality of fins 102 easily bow when the pressed against the base plate 106. Although FIG. 1D illustrates a symmetric outwardly bowing of each of the plurality of fins 102, in practice, uneven bowing occurs with each of the plurality of fins 102 such that some fins 102 may bow inward and others bow outward. Additionally, some of the fins 102 may also break or crack as a result of the force or pressure applied when pressed against the base plate 106.
As such, there is a limit to the amount of force that may be applied to the plurality of fins 102. This makes it difficult to obtain a thin adhesive bonding layer between the base plate 106 and the plurality of fins 102 to obtain high thermal conductivity between the base plate 106 and each of the fins 102.
FIGS. 2A-2D illustrates a heat sink fin in accordance with one embodiment of the invention. FIG. 2A illustrates a top view of the heat sink fin and FIG. 2B illustrates a perspective view of the heat sink fin of FIG. 2A. The heat sink fins 200 are formed or fabricated from one continuous roll or sheet of material and bent to form a serpentine configuration similar to the fins illustrated in FIG. 1A. This eliminates the need to assemble a heat sink using individual fins and is low cost and easy to manufacture. The sheet of material can be any material that has good thermal conductivity such as aluminum, copper, or the like.
Each fin 202 may also be bent to form a plurality of undulations 204 along a length axis 206 of each of the fins 202. The length axis 206 can extend generally in parallel with the base plate 106. The plurality of undulations 204 creates a wave-like or ruffled configuration to each of the fins 202. Each fin 202 may also have a fin height axis 208 that extends generally perpendicular relative to the base plate. For example, the fin height and fin height axis may be within 100 of the perpendicular to the base plate. In another embodiment, the fin height axis 208 need not be generally perpendicular to the base plate. For example, the fin height axis 208 may vary from a perpendicular axis to the base plate by about 0°-45°.
In one embodiment, each fin 202 may have between about 2 to 10 undulations along the length axis 206. In another embodiment, each fin 202 may have between about 3-6 undulations, and in a specific embodiment, each fin 202 may have between about 4-5 undulations along the length axis 206.
In another embodiment, each fin 202 has between about 2 to 15 peaks 220 and valleys 222 along the length axis 206 of each of the fin 202. In another embodiment, each fin 202 may have between about 3 to 8 peaks 220 and valleys 222 along the length axis 206, and in a specific embodiment, each fin 202 may have at least 4 peaks 220 and valleys 222 along the length axis 206 of each fin 202.
Each of the plurality of undulations 204 may have an undulation pitch 212, which is the distance between each undulation. In one embodiment, the undulation pitch is no greater than approximately one undulation per inch. An undulation amplitude 216 is the depth of the undulation parallel to the base plate 106 and an undulation radius 218 is the radius of the curvature associated with the undulation 204. The heat sink fin 200 may have a fin pitch 214, which is the distance between similar structures on an adjacent fin.
The plurality of undulations 204 forms a heat sink fin 200 having an overall higher stiffness or rigidity that is able to withstand additional pressure during bonding or attachment to the base plate without bowing or breaking of the fins 202. The resulting heat sink fin 200 is more stabilized and able to withstand bending and distortions.
FIG. 2C illustrates the bottom ends of the heat sink fin of FIGS. 2A and 2B and FIG. 2D illustrates the top ends of the heat sink fin of FIGS. 2A and 2B. The formation of the fins with the plurality of undulations 204 results in each fin 202 having a bottom end 206 that is substantially planar or flat which facilities an efficient bond with the base plate 106. The bottom ends 206 of each of the fins 202 are substantially perpendicular to the fin height 208 and parallel to the base plate 106. As illustrated in FIG. 2D, a top end 226 of each fins 202 may also be substantially planar or flat and substantially perpendicular to the fin height 208 and parallel to the base plate 106.
This results in little to no gap between the base plate 106 and the fin 202, which in turn increases thermal conductivity between the base plate 106 and the heat sink fins 200. Furthermore, substantially the entire surface area of the bottom end 206 of each fin 202 is in close contact with the base plate 106.
Since the heat sink fin 200 has an overall higher stiffness or rigidity, it may be bonded or attached to the base plate 106 using a greater force or pressure between the heat sink fin 200 and the base plate 106. This results in a thinner bonding layer 210. Additionally, since each of the bottom ends 206 are substantially planar, the heat sink fin 200 may be bonded to the base plate 106 with a uniform bonding layer 210. Both the thinner and more uniform bonding layer 210 results in decreased thermal resistance at the bonding layer 210 between the heat sink fin 200 and the base plate 106.
The formation of the plurality of undulations along the fin length axis also allows for the use of thinner material to form the heat sink fin since the heat sink fin has an overall higher stiffness or rigidity. This enables the formation of a lighter and less expensive heat sink and solar receiver. Moreover, it has been unexpectedly determined that the fin height may be increased without compromising the mechanical integrity of the heat sink fin. Thus, the fin height 208 to fin length 206 ratio may increase which results in high thermal conductivity since there is more surface area for heat transfer. In one embodiment, the fin height to fin length ratio may be greater than 0.5.
FIGS. 3A-3C illustrate example solar receivers. Referring to FIGS. 3A and 3B, FIG. 3A is a perspective view of the back of one example solar receiver and FIG. 3B is a perspective view of the front of the example solar receiver using an embodiment of the heat sink fin. The solar receiver 300 may have a base plate 106 having a first surface 304 and a second surface 320 opposite the first surface 304. The solar receiver 300 may have a plurality of solar cells 306 positioned over and supported by the first surface 304 of the base plate 106. Each solar cell 306 has a cell face, facing away from the base plate 106, which is suitable for receiving solar radiation.
The solar receiver 300 has a multiplicity of fins 308 extending outwardly from the second surface 320 of the base plate 106. Each of the multiplicity of fins 308 has a fin height axis 208 and a length axis 206. The fin height axis 208 can extend generally perpendicular relative to the base plate 106 and the fin length axis 206 can extend generally parallel with the base plate 106. A bottom end of each of the fins 308 can be attached to the second surface of the base plate 106.
The solar cells 306 and multiplicity of fins 308 may be attached or assembled to the base plate by any known means such as those described in co-pending application Ser. No. 12/124,121, entitled “Photovoltaic Receiver”, filed May 20, 2008, which is incorporated herein by reference in its entirety.
In use, the solar cells 306 produce waste heat that must be removed from the solar receiver. The heat may be transferred or transmitted to the base plate 106, through the bonding layer 210 (FIG. 2C), and to the heat sink fins 308 via conduction. In one embodiment, the heat can then be dissipated into the surrounding environment or air via natural convection along the length axis 206 of the multiplicity of fins 308.
FIG. 3C illustrates a perspective view of another example solar receiver. A portion of the top end 226 (FIG. 2D) of the heat sink fins 308 may be removed thereby forming an opening 322 on the top end of the fin 308. The entire surface of the top end 226 is not removed to retain the serpentine shape of the heat sink and to allow the heat sink to be formed from one continuous sheet of material. This embodiment allows for additional air flow paths in the region below the top end 226, for example, the area enclosed by the heat sink fin and the base plate as illustrated by arrow 326. These additional air flow paths may improve thermal conductance of the heat, reduce photovoltaic cell temperature, and improve solar cell efficiency.

EXAMPLE

Examples are described herein for exemplary purposes only and not intended to be limiting. An example heat sink fin may be made from a continuous sheet of material, such as aluminum. The sheet of material may have a thickness of about 0.020 inches. Each fin may have a fin length of about 5.50 inches and a fin height of about 3 inches. Thus, the ratio of fin height to fin length may be 3 inches/5.5 inches=0.55.
Each fin may have a fin pitch of about 0.25 inches and about 5.5 undulations along the fin length axis. Each fin may have an undulation amplitude of about 0.050 inches, an undulation period of about 1 inch, and an undulation radius of about 1.262 inches. The heat sink may be formed to any desired length. In one embodiment, the heat sink may have a length of about 52 inches, which results in the formation of about 208 fins.
FIGS. 4A and 4B illustrates an embodiment of a stackable solar receiver. FIG. 4A illustrates a cross-sectional side view of a solar receiver. The solar receiver 400 may have a plurality of fins 402 having a bottom end 404 and a top end 406 opposite the bottom end 404. The bottom end 404 may be attached to the base plate 106 via a bonding layer 408 as discussed above. Each fin 402 may have a top end width 410 and a bottom end width 412. Current heat sinks have a top end width 410 that is equal to the bottom end width 412. This does not allow for the ability of heat sink fins of two opposing heat sinks to nest or stack within each other for efficient transport or storage because the spacing between each fin is equal to the bottom end width. The fins would simply interfere with each other and not be able to nest or stack within each other.
FIG. 4A illustrates a solar receiver 400 having a plurality of fins 402 with a top end width 410 less than the bottom end width 412 thereby forming fins 402 with a trapezoidal or tapered cross-section. This allows for the fins of two opposing solar receivers to nest, stack, or be interleaved within each other as illustrated in FIG. 4B. FIG. 4B illustrates a perspective view of the nested, stacked, or interleaved solar receivers. Although the figure illustrates nested heat sinks, this is not intended to be limiting as the heat sinks may be attached to the base plate forming a complete receiver the base plates are not illustrated for clarity to illustrate how the fins stack or nest within each other. A first solar receiver 414 having a first multiplicity of fins 418 may be flipped and nested or stacked within a second solar receiver 416 having a second multiplicity of fins 420. The undulation pitch and undulation phase of each fin, as discussed above, should be matched and/or substantially similar in order for the solar receivers 414, 416 to nest within each other.
The first multiplicity of fins 418 may extend substantially the entire fin height 208 of the second multiplicity of fins 420 when the first multiplicity of fins 418 are nested within the second multiplicity of fins 420. The combined height of the first solar receiver 414 and the second solar receiver 416 is only slightly greater than the height of one of the solar receivers.
The ability to nest solar receivers increases the packing density of the solar receivers during transportation or storage. In fact, the shipping and storage volume of the solar receivers may be reduced by a factor of two as compared to current shipping and storage volumes where nesting of solar receivers are not possible. As such, concomitant shipping and storage costs may be reduced which can influence the commercial viability of CPV systems.
Furthermore, nesting the solar receivers reduces the probability of fin damage during transportation or storage. The fins form a mechanical protection layer for each opposing fin thereby increasing the mechanical robustness of the structure.
FIGS. 5A and 5B illustrate other embodiments of a stackable solar receiver. FIGS. 5A and 5B illustrate side views of alternative embodiments of a stackable solar receiver. Referring to FIG. 5A, the solar receiver 500 has a plurality of tapered heat sink fins 510. Each fin 510 has a top end width 504 that is less than a bottom end width 506. The tapered angle 508 of each fin 510 may be between about 2° to about 30°.
FIG. 5B illustrates another embodiment of a stackable solar receiver. The solar receiver 502 may have a plurality of heat sink fins 512. Each fin 512 may have a rounded taper at the top end 514 such that the bottom end width 516 is greater than a width of the tapered top end 514. The difference in width between the bottom end 518 and the top end 514 of the fins 512 allows two solar receivers to nest within each other for transport or storage.
Although FIGS. 5A and 5B are illustrated with the top end width less than the bottom end width, this is not limiting as the opposite may be possible. The top end width may be greater than the bottom end width. In this embodiment, one heat sink may slideably engage another heat sink in order to nest or stack the heat sink fins.
While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts herein.

Claims

1. A solar receiver, comprising:

a base plate having a first surface and a second surface;

a plurality of solar cells positioned over and supported by the first surface of the base plate, each solar cell having a cell face suitable for receiving solar radiation that faces away from the base plate; and

a multiplicity of fins extending outwardly from the second surface of the base plate, each of the multiplicity of fins having a fin height axis extending generally perpendicular relative to the base plate, a fin length axis extending generally in parallel with the base plate, and a bottom end attached to the second surface of the base plate, wherein each of the multiplicity of fins are formed from a single, continuous sheet of metal arranged in a serpentine configuration, and wherein each of the multiplicity of fins have a plurality of undulations along the length axis of the fin.

2. The solar receiver of claim 1, wherein there are at least four undulations along the length axis of each fin.

3. The solar receiver of claim 1, wherein the plurality of undulations have at least four peaks and four valleys along the length axis of each of the multiplicity of fins.

4. The solar receiver of claim 1, wherein a pitch of each of the plurality of undulations is no greater than approximately one undulation per inch.

5. The solar receiver of claim 1, wherein the multiplicity of fins are made from a metal.

6. The solar receiver of claim 5, wherein the multiplicity of fins are made from aluminum.

7. The solar receiver of claim 1, wherein the bottom end is substantially flat whereby substantially all of a surface area of the bottom end is attached with the second surface of the base plate.

8. The solar receiver of claim 7, wherein the bottom end is attached to the second surface of the base plate with an adhesive.

9. The solar receiver of claim 1, wherein each of the plurality of fins has a top end opposite the bottom end and wherein a width of the top end is less than a width of the bottom end.

10. The solar receiver of claim 1, wherein the top end further comprises an opening to facilitate convective air flow.

11. A solar receiver, comprising:

a base plate having a first surface and a second surface;

a multiplicity of fins extending outwardly from the second surface of the base plate, each of multiplicity of fins having a bottom end opposite a top end, the bottom end attached to the second surface of the base plate, wherein the top end has a width less than a width of the bottom end, wherein each of the multiplicity of fins are formed from a single, continuous sheet of metal arranged in a serpentine configuration, and wherein each of the multiplicity of fins have a plurality of undulations along a length axis of the fin.

12. The solar receiver of claim 11, wherein the bottom end is substantially flat whereby substantially all of a surface area of the bottom end is attached with the second surface of the base plate.

13. The solar receiver of claim 11, wherein there are at least four undulations along the length axis of each fin.

14. The solar receiver of claim 11, wherein the plurality of undulations have at least four peaks and four valleys along the length axis of each of the multiplicity of fins.

15. The solar receiver of claim 11, wherein the bottom end is attached to the base plate with an adhesive.

16. The solar receiver of claim 11, wherein the multiplicity of fins are made from a metal.

17. The solar receiver of claim 11, wherein the top end further comprises an opening to facilitate convective air flow.

18. Stackable solar receivers, comprising:

a first solar receiver, having:

a first base plate having a first surface and a second surface;

a first plurality of solar cells positioned over the first surface of the first base plate, each solar cell having a cell face suitable for receiving solar radiation that faces away from the first base plate; and

a first multiplicity of fins extending outwardly from the second surface of the first base plate, each of the first multiplicity of fins are formed from a single, continuous sheet of metal arranged in a serpentine configuration having a bottom end opposite a top end, the bottom end attached directly to the second surface of the first base plate, wherein the top end has a width less than a width of the bottom end;

a second solar receiver, having:

a second base plate having a first surface and a second surface;

a second plurality of solar cells positioned over the first surface of the second base plate, each solar cell having a cell face suitable for receiving solar radiation that faces away from the second base plate; and

a second multiplicity of fins extending outwardly from the second surface of the second base plate, each of the second multiplicity of fins are formed from a single, continuous sheet of metal arranged in a serpentine configuration having a bottom end opposite a top end, the bottom end attached directly to the second surface of the second base plate, wherein the top end has a width less than a width of the bottom end,

wherein the first multiplicity of fins is interleaved with the second multiplicity of fins to stack the first solar receiver with the second solar receiver during transport or storage.

19. The solar receivers of claim 18, wherein each of the first and second multiplicity of fins have a plurality of undulations along a length axis of the fin.

20. The solar receivers of claim 19, wherein an undulating pitch and an undulating phase of each of the plurality of undulations are substantially similar.

21. The solar receivers of claim 18, wherein each of the first multiplicity of fins having a first fin height axis extending generally perpendicular relative to the first base plate and wherein each of the second multiplicity of fins having a second fin height axis extending generally perpendicular relative to the second base plate.

22. The solar receivers of claim 21, wherein the first multiplicity of fins extend substantially the entire second fin height of the second multiplicity of fins when the first multiplicity of fins are interleaved within the second multiplicity of fins.