WO2013024458A2

WO2013024458A2 - Solar receiver

Info

Publication number: WO2013024458A2
Application number: PCT/IB2012/054183
Authority: WO
Inventors: Nir Katzir
Original assignee: Brightsource Industries (Israel) Ltd.
Priority date: 2011-08-18
Filing date: 2012-08-16
Publication date: 2013-02-21
Also published as: WO2013024458A3

Abstract

A solar receiver can include a row of vertically extending tubes, which may receive reflected solar insolation on the outer surface facing the heliostat field. One or more tubes arranged at the end of the row in the receiver can have an additional portion of its outer surface exposed to reflected solar insolation due to its location at the end of the row. This increases the amount of heat being delivered to these endmost tubes. Efficiency of electricity generation using a solar power generation system may be affected by working fluid temperature. The temperature of the working fluid exiting the solar thermal receiver should be uniform at each of the tubes comprising the receiver. As such, a tube can be attached to an inlet header at the edge of the receiver and can be attached to the outlet header at a distance away from the edge. Another tube of the thermal receiver can be attached to the inlet header at a distance away from the edge and then directed toward the edge of the receiver such that it becomes the outermost tube.

Description

SOLAR RECEIVER

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional Application No.

61/525,150, filed August 18, 2011, which is incorporated by reference herein in its entirety.

FIELD

The present application relates generally to the conversion of solar radiation to usable forms of energy, such as heat and/or electricity, and, more particularly, to steam generation at a substantially uniform temperature from a multi-tube solar receiver.

SUMMARY

A solar power generation system can have a thermal-electric power generation component, in which incident solar radiation is concentrated on a solar thermal receiver to heat a heat transfer or working fluid, for example, for use in electricity generation. A field of heliostat-mounted mirrors may reflect and concentrate incident solar radiation onto the solar receiver. The solar receiver can include a row of vertically extending tubes and/or pipes, which may receive reflected solar insolation on a first portion of an outer surface thereof facing the heliostat field. One or more tubes arranged at the end of the row in the receiver can have a second portion of the outer surface exposed to reflected solar insolation due to its location at the end of the row in addition to the first portion.

In embodiments, the solar power generation system can have two separate rows of tubes (i.e., two receivers or receiver panels) that are joined together at their ends forming approximately a ninety degree angle between the respective rows. Alternatively or additionally, four (or more) separate receivers (or receiver panels) can be joined so as to form a box-shaped figure. In embodiments, the heliostat field can encircle the solar thermal receiver such that the thermal receiver can receive reflected insolation from all directions (i.e., 360°). When providing reflected solar radiation to all of the receivers (or receiver panels), the endmost tubes in each row may receive incident solar radiation on both first and second portions of their respective outer surfaces, thereby increasing the amount of heat being delivered to these endmost tubes.

As efficiency of electricity generation using turbines and/or the solar power generation system overall may be affected by working fluid temperature, the temperature of the working fluid exiting the solar thermal receiver should be uniform at each of the tubes comprising the receiver. To this end, one or more embodiments may have tubes at respective row ends in the solar receiver directed away from the row ends. In other words, a tube can be attached to the inlet header at the edge of the receiver (i.e., the end of the row of tubes) and can be attached to the outlet header at a distance away from the edge (i.e., displaced from the end of the row of tubes). Another tube of the thermal receiver can be attached to the inlet header at a distance away from the edge and then directed at one or more points along its length toward the edge of the receiver such that it becomes the outermost tube. Such a modification applied to the tubes at the end of each receiver row may allow for the outlet header to receive working fluid from each tube at a substantially uniform temperature.

Therefore, the system may not require for the working fluid to be further processed before flowing to the next stage in the system (for example, to a turbine, evaporator, or any other equipment).

Embodiments of the disclosed subject matter include systems in which the

arrangement of the endmost tubes of a receiver are configured to accommodate the amount of flux being delivered to thereto such that working fluid delivered to an outlet header is at substantially the same temperature for each tube of the receiver, irrespective of location of the tube within the receiver row. In one or more embodiments, the endmost tubes may switch places with (or cross-over) one or more other tubes at one or more locations such that the second portion of its outer surface is shielded from insolation at least along a part of its length. In one or more embodiments, the thickness of the tube walls can be altered for the endmost tubes with respect to the other tubes in the row. In one or more embodiments, the material for the endmost tubes can be different than the other tubes in the row. In one or more embodiments, the velocity of the flow of the working fluid in the endmost tubes can be different with respect to the velocity of the working fluid in the other tubes of the receiver. In one or more embodiments, the cross-sectional area of the endmost tubes can be different than the other tubes in the row.

Objects and advantages of the present disclosure will be apparent from the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will hereinafter be described with reference to the accompanying drawings, which have not necessarily been drawn to scale. Where applicable, some features may not be illustrated to assist in the illustration and description of underlying features. Throughout the figures, like reference numerals denote like elements.

FIGS. 1A and IB are diagrammatic elevation views of a plurality of helio stats and a central power tower, according to one or more embodiments of the disclosed subject matter.

FIG. 1C is an illustration of a solar tower system including more than one solar receiver, according to one or more embodiments of the disclosed subject matter.

FIG. 2 is an illustration of a hierarchical central heliostat control system, according to one or more embodiments of the disclosed subject matter.

FIG. 3A is a view of a solar thermal receiver showing the arrangement of a row of tubes, according to one or more embodiments of the disclosed subject matter. FIG. 3B is a view of solar thermal receivers showing the arrangement of two rows at an angle, according to one or more embodiments of the disclosed subject matter.

FIG. 4A is an isometric side view illustrating the arrangement of an endmost tube and another tube in a row of a thermal receiver, according to one or more embodiments of the disclosed subject matter.

FIG. 4B is isometric rear view of a solar receiver with an endmost tube switching places with an inner tube in a row, according to one or more embodiments of the disclosed subject matter.

FIG. 4C is a close-up view of a cross-over point between the endmost tube and the inner tube of the receiver shown in FIG. 4B.

FIG. 5A shows a row of tubes with a single cross-over of the pair of tubes at each end of the row, according to one or more embodiments of the disclosed subject matter.

FIG. 5B shows a braided pair of tubes at the end of a row of tubes in a solar receiver, according to one or more embodiments of the disclosed subject matter.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosed subject matter. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures and components may not have been described in detail so as not to obscure aspects of the disclosed subject matter.

Generally, a central receiver system, such as one with a receiver supported on a tower, can include at least one solar receiver and a plurality of heliostats. Each heliostat can track the sun so as to reflect light to a target on a tower or an aiming point on such a target. The heliostats can be arrayed in any suitable manner. For example, heliostat spacing and positioning can be selected to provide optimal financial return over a life cycle according to predictive weather data and at least one optimization goal such as total solar energy utilization, energy storage, electricity production, or revenue generation from sales of electricity.

The solar receiver can receive reflected and optionally concentrated solar radiation and convert the reflected solar radiation to some useful form of energy, such as heat or electricity. The receiver can be located at the top of the receiver tower. Solar receivers may be configured to heat a fluid such as water and/or steam and/or supercritical steam and/or molten salts and/or molten metals using insolation received from the heliostats. In different examples, the solar receiver may be at least 25m, at least 50m, at least 75m or at least 100m or at least 125m or at least 150m or even higher.

As used herein, the term "receiver" refers to the portion (or portions) of a device targeted by the heliostats that captures and converts incident flux to heat and that is actively cooled by a heat transfer or working fluid, as opposed to portions that are primarily reflective or simply used to re -radiate or convect heat (e.g., thermal tiles, refractory shades). The receiver may be the aggregate of concentrated light-receiving portions of a boiler, heat exchanger, superheater, or any other device used for converting sunlight to heat a fluid.

Receivers may be referred to as a "boiler" in the present disclosure, but this reference should be understood, in all embodiments except where noted, to be a convenient notation for all devices that receiver solar energy and convert it to heat for transfer to a working or heat transfer fluid regardless if the boiler is operating below or above the critical point or whether phase change is occurring or has occurred. For example, a boiler may encompass a superheater, a reheater, or a supercritical heater where no gas/liquid phase change occurs. Also, the boiler may be replaced in all embodiments with a non-phase change or phase change material that is intermediate between a boiler, such as a power plant boiler, and the receiver. For example, the receiver may include a boiler having a tangent tube design.

As used herein, a conduit in which the working fluid flows may be called a "tube" or a "pipe," even though in many embodiments the term may be used in a manner not consistent with the usual definition of these words. Both of these terms may be used interchangeably throughout the specification without intending to derogate from the customary meaning of such terms. Moreover, the term "heat transfer fluid" may be used herein to refer a working fluid but should be understood, in all embodiments except where noted, to include a gas or liquid specifically manufactured for the purpose of transmitting heat from one system to another. Examples of a heat transfer fluid include, but are not limited to, water/steam, air, molten salts or molten metals.

Referring now to the figures and, in particular, to FIG. 1A, a solar power system 44 is provided in which heliostats 38 include mirrors 8 that reflect incident solar radiation 28 onto a receiver 1 in which a working fluid (not shown) is heated for later use in an electric power generating plant 45. The heliostat- mounted mirrors 8 are capable of tracking the apparent movement of the sun 25 across the sky each day in order to maintain the reflective focus in the direction of the receiver 1 as the angle of the incident radiation 28 changes. The receiver 1 of solar power system 44' is located atop a tower 43. In an alternative embodiment, shown in FIG. IB, the solar receiver is located on the ground, and the heliostat-mounted mirrors 8 reflect solar radiation onto one or more suspended mirrors 9 which further reflect the radiation onto the receiver 1.

A fluid (not shown) can be heated in the receiver 1 and conveyed via a pipe 47 or other conveyance device (e.g., truck, train, pipeline, etc.) for contemporaneous or later use, for example, to generate power in an electric power generating plant 45. The heated fluid can also be stored in a minimal heat loss storage unit (not shown) for later use by the electric power generating plant 45, for example, when solar insolation levels are below a minimal value. A thermal storage that includes the heat transfer fluid and/or another thermal mass or phase change material may be included in the fluid conveyance device. The heat in the fluid can be used in the generation of electricity by, for example, a turbine employing a Rankine, organic Rankine, or Brayton cycle. The fluid may be a working fluid or intermediate heat transfer fluid (e.g., molten salt) used to heat a working fluid. For example, the fluid in the receiver may be water, steam, a mixture of water and steam, or a molten salt, such as a nitrate salt (e.g., a combination of liquid sodium nitrate and potassium nitrate).

Manually or by using a computerized control system, the solar heat flux reflected onto the exterior surfaces of the receiver can be balanced and/or optimized by selecting and aiming heliostats from the solar fields in the solar power tower system. Optimally, the balancing and optimizing of solar heat flux with respect to a superheating receiver can be assigned higher priority in the system's operating procedures or control programming than the balancing and optimizing of solar heat flux with respect to other receivers in the system.

The balancing and optimizing of solar heat flux with respect to the superheating receiver by selecting and aiming heliostats from at least one of the heliostat fields in a solar power tower system can be performed on the basis of predictive weather data, historical performance parameters, and/or real-time optimization using at least one data feedback mechanism. Such a data feedback mechanism can include temperature measurements, stress and/or strain measurements from receiver pipes, flow measurements and pressure

measurements, which can be taken at or in proximity to the superheating receiver or elsewhere, for example, at a turbine inlet. The selection of heliostats for reflecting insolation at the superheating receiver and the aiming of those heliostats on different parts of the receiver can be performed at least once each day, at least once each hour, or at least three times each hour. More than one solar receiver can be provided on a solar tower. The multiple solar receivers in combination may form a part of the solar energy receiving system. The different solar receivers may have different functionalities. For example, one of the solar receivers may heat water using the reflected solar radiation to generate steam while another of the solar receivers may serve to superheat steam using the reflected solar radiation. The multiple solar receivers can be arranged at different heights on the same tower or at different locations (e.g., different faces, such as a north face, a west face, etc.) on the same tower. Some of the heliostats in the field may be constructed and arranged so as to alternatively direct insolation at the different solar energy receiving systems.

For example, in the embodiment of FIG. 1C, two solar receivers are provided on a single tower 50. The solar energy receiving system 500 thus includes a first solar receiver 810 and a second solar receiver 820. At any given time, a heliostat 70 may be aimed at one or both of the solar receivers, or at none of the receivers. In some use scenarios, the aim of a heliostat 70 may be adjusted so as to move a centroid of the reflected beam projected at the tower 50 from one of the solar receivers (e.g., 810) to the other of the solar receivers (e.g., 820). Although only two solar receivers and a single tower are shown in FIG. 1C, any number of solar towers and solar receivers can be used.

In one or more embodiments, a solar power tower system can include at least one tower and at least one set of heliostats, as described in detail, for example, in International Patent Application No. PCT/US08/58305, filed March 26, 2008, and published as WO 2008/118980 on October 2, 2008, which is hereby incorporated by reference herein in its entirety and is attached to this disclosure as Appendix A. As discussed in PCT/US08/58305, each heliostat can track the sun to reflect light to a designated tower, and the tower designated for each heliostat can change depending on operating requirements and other conditions. A tower can located within the boundaries of a field of heliostats or arranged outside the boundaries of any field of heliostats. The number of towers can be equal to or different from the number of fields or sets of heliostats.

Heliostats 70 in a field of heliostats can be controlled through a central heliostat field control system 130, for example, as shown in FIG. 2. For example, a central heliostat field control system 130 can communicate hierarchically through a data communications network with controllers of individual heliostats. Additionally or alternatively, the heliostat field can be controlled by any combination or variation on centralized control and distributed control, for example, by using a control system that communicates hierarchically through a data communications network with individual or final controllers for each heliostat.

FIG. 2 illustrates a hierarchical control system 130 that includes three levels of control hierarchy, although in other implementations there can be more or fewer levels of hierarchy, and in still other implementations the entire data communications network can be without hierarchy, for example, in a distributed processing arrangement using a peer-to-peer communications protocol. At a lowest level of control hierarchy (i.e., the level provided by heliostat controller) in the illustration there are provided programmable heliostat control systems (HCS) 65, which control the two-axis (azimuth and elevation) movements of heliostats (not shown), for example, as they track the movement of the sun. At a higher level of control hierarchy, heliostat array control systems (HACS) 92, 93 are provided, each of which controls the operation of heliostats 70 (not shown) in heliostat fields 96, 97, by communicating with programmable heliostat control systems 65 associated with those heliostats 70 through a multipoint data network 94 employing a network operating system such as CAN, Devicenet, Ethernet, or the like. At a still higher level of control hierarchy a master control system (MCS) 95 is provided which indirectly controls the operation of heliostats in heliostat fields 96, 97 by communicating with heliostat array control systems 92, 93 through network 94. Master control system 95 further controls the operation of a solar receiver (not shown) by communication through network 94 to a receiver control system (RCS) 99.

In FIG. 2, the portion of network 94 provided in heliostat field 96 can be based on copper wire or fiber optic connections, and each of the programmable heliostat control systems 65 provided in heliostat field 96 can be equipped with a wired communications adapter, as are master control system 95, heliostat array control system 92 and wired network control bus router 100, which is optionally deployed in network 94 to handle communications traffic to and among the programmable heliostat control systems 65 in heliostat field 96 more efficiently. In addition, the programmable heliostat control systems 65 provided in heliostat field 97 communicate with heliostat array control system 93 through network 94 by means of wireless communications. To this end, each of the programmable heliostat control systems 65 in heliostat field 97 is equipped with a wireless communications adapter 102, as is wireless network router 101, which is optionally deployed in network 94 to handle network traffic to and among the programmable heliostat control systems 65 in heliostat field 97 more efficiently. In addition, master control system 95 is optionally equipped with a wireless communications adapter (not shown).

Instead of determining the size of the heliostat field in a solar tower system in accordance with the maximum expected level of solar radiation, the size of the heliostat field for a given rated electrical output can be determined by an optimization of expected financial return projected from the system when taking into account the expected distribution of solar radiation over the course of a year as well as other factors which can include, for example, differential tariffs. The result of this optimization is that there are some hours of peak solar radiation during the year in which the total energy available to the solar field exceeds the rated capacity. During such peak hours, some heliostats can be "defocused" (i.e., the reflected aiming point for the defocused heliostats is moved from the receiver so that the energy is dissipated or employed by another device or system) from the tower to avoid exceeding the rated capacity of the system or one of its components, such as a boiler, turbine or transformer, or to avoid exceeding an output rating mandated by contract or by regulation.

The solar receiver, as a target for solar radiation reflected by heliostats for the purpose of heating a working fluid, can include a plurality of tubes. The fluid can be made to flow through a plurality of tubes in the receiver, for example, by thermosiphon and/or pumping. The receiver can also include conduits, pipelines, headers and/or the like, to provide inlets and outlets to and from the receiver for the fluid.

The tubes can be positioned in a substantially vertical arrangement with multiple tubes conveying the fluid in parallel. Headers, manifolds and other piping arrangements may be provided to facilitate the transport of the fluid within the receiver, to the inlet of the tubes, and/or from the outlet of the tubes. The receiver may be operated in the manner of a once- through boiler or alternatively in the manner of a multiple-pass boiler. Alternatively, the tubes may be arranged so as to provide a serpentine path for the fluid. Solar radiation reflected by the heliostats at the tower can impinge on at least a portion of an exterior surface of the tubes (e.g., the portion of each tube facing the field of heliostats).

As shown in FIG. 3 A, a receiver 301 may include a row of substantially parallel tubes 303. The tubes 303 may be arranged with at least a portion of their respective longitudinal axes arranged substantially vertical. Each tube can have a surface 305 exposed to reflected solar radiation. Portions of the surface facing adjacent tubes or away from the field of heliostats (i.e., toward an internal portion of the receiver) may be shielded from exposure to the solar radiation reflected at the receiver by the heliostats. However, tubes 303 at the end 307 of the row may have an additional portion of the surface exposed to reflected solar radiation since there is no further tube to shield the outermost surface portion from reflected solar radiation. FIG. 3B illustrates an alternative receiver configuration in which multiple rows of tubes are joined at their ends. For example, each receiver 301 (or section or panel thereof) can be arranged such that it faces one of the cardinal directions and thus receives reflected solar radiation from the corresponding quadrant of the solar field of heliostats. Accordingly, the receiver facing west would generally receive reflected solar radiation from heliostats located in a western quadrant of the solar field while the receiver facing north would generally receive reflected solar radiation from heliostats located in the northern quadrant. Similar results would apply for the receivers that face east and south. The heliostats can be arranged such that the field at least partially encircles the tower upon which the receivers are placed. Thus, a receiver having a side facing each of the cardinal directions, for example, in a rectangular configuration, can be used to receive reflected solar radiation from the encircling field of heliostats. Such a configuration may allow for improvement and/or optimization of the system and may provide improved and/or optimal financial return.

As noted above, endmost tubes 307 may receive the reflected solar radiation on a greater portion of its exposed surface 305 than inner tubes (i.e., tubes not at the end of the receiver row). For example, one the endmost tubes of the receiver facing west will receive reflected solar radiation on its front portion (which faces west and the heliostats in the western quadrant of the solar field) as well as a side portion (which faces either north or south, depending on which end of the row the tube is located at, and the heliostats in the corresponding northern or southern quadrant of the solar field). Although the discussion above and elsewhere herein refers to specific cardinal directions, embodiments of the disclosed subject matter may relate to any such cardinal directions or to any other direction as may be dictated by location and orientation of the receiver.

Since the endmost tubes receiving additional energy as compared to the inner tubes due to the solar insolation being reflected onto of the respective side portions, the working fluid exiting these endmost tubes may be substantially hotter than the working fluid exiting the inner tubes of the receiver. For example, the temperature of the working fluid exiting the endmost tubes may be 25°C, 50°C, 75°C, or 100°C than the temperature of the working fluid exiting the inner tubes. As efficiency of the system/receiver may be correlated with uniform temperature, embodiments of the disclosed subject matter may seek to provide working fluid exiting each tube of the receiver at substantially the same temperature.

The use of such an arrangement for the receiver and its components thereof may be used when it is favorable to do. The favorability is a function of optimizing the intensity and distribution of reflected solar radiation on the surface of the receiver, and resulting heat flux, while taking into account variables which may include, but is not limited to, desired thermal output of the receiver, material characteristics including strength, heat transfer parameters and radiation absorptivity and emissivity, predictive weather and solar radiation data, heliostat placement and aiming or tracking accuracy, cost of receiver and heliostat materials and components, land availability, power purchase agreements, and differential electricity tariffs.

In one or more embodiments, one or more tubes at the end or near the end of a row of tubes in a receiver can be constructed and/or arranged to compensate for the increased amount of insolation received at the ends of the row as compared to tubes away from the ends of the row. For example, a first tube that begins at its inlet end as the endmost tube in a row of tubes can switch places (e.g., by crossing-over) at a point along its length with a second tube, which begins at its inlet end as one of the inner tubes in the row of tubes. Thus, the second tube has become the endmost tube while the first tube has become one of the inner tubes at their respective outlet ends. In another example, the first tube and the second tube may repeatedly cross-over each other along their lengths (i.e., in a braided configuration) such that each shares time as the endmost tube. As shown in FIGS. 4A-4C, a first tube 402 of a receiver row can be formed such that its inlet at inlet header 420 and a first part 404 of the tube 402 are positioned at the edge 401 of the receiver row. A second part 406 of the first tube 402 can be formed such that it is displaced from the edge 401 of the receiver row. Thus, the outlet at outlet header 422 of the first tube 402 is no longer at the edge 401 but at a certain distance 408 from the edge 401 of the receiver. A second tube 410, whose inlet at inlet header 420 and first part 412 are initially located at a distance from the edge 401 of the receiver, has a second part 414 that is displaced so as to be at the edge 401 of the receiver. Accordingly, these two tubes 402, 410 switch places with each other at or near the edge of the receiver. The cross-over point may occur at approximately the mid- way point between a top edge of the receiver and a bottom edge of the receiver. In some examples, the solar receiver may be at least 25m, at least 50m, at least 75m, or at least 100m, or at least 125m, or at least 150m high, or even higher.

In an embodiment, the first tube 402, which may initially be in line with the row of parallel tubes, can bend behind the row of tubes at the cross-over point. For purposes of clarity, "behind the row of tubes" refers to behind the surface portions of the inner tubes that do not receive reflected solar radiation, e.g., the surface portions opposed to the surface portions of the inner tubes that receiver reflected solar radiation. In contrast, "the front side" of the row of tubes refers to the surface portions of the inner tubes that receive the reflected solar radiation.

First tube 402 can bend behind the row of parallel tubes as opposed to bending along the front side of the row of tubes. If first tube 402 were to run along the front side of the row of tubes, it may block at least some of the reflected insolation from reaching one or more inner tubes. Further, as the working fluid in first tube 402 is generally hotter than the working fluid in the inner tubes prior to the cross-over point, directing the first tube 402 behind the row of tubes can allow the working fluid to maintain temperature while the working fluid in the other tubes in the row continues to increase in temperature. As a result, the outlet header can receive working fluid at substantially the same temperature from all the tubes of the receiver. However, it is not required that the endmost tubes bend behind the row of tubes. As shown in FIG. 5A, it is also possible for the endmost tubes 502 to bend in front of one or more of the inner tubes 510 according to one or more contemplated embodiments.

The inlet and the first part 412 of the second tube 410 can be located behind the row of tubes. Thus, the second tube 410 may initially not be in line with the row of tubes of the thermal receiver. After the cross-over point with the first tube 402, the second part 414 of the second tube 410 may then be in line with the row of tubes. In other words, before the cross- over point, second tube 410 may be hidden behind the row of inner tubes while first tube 402 is the endmost tube. After the cross-over points, the first and second tubes switch places such that the second tube 410 is now the endmost tube and the first tube 402 is hidden behind the row of inner tubes.

As second tube 410 is located behind the row of tubes prior to the cross-over point, it initially does not receive reflected solar radiation from the heliostats. As such, the working fluid therein has an initial temperature lower than that of the working fluid in the inner tubes and the first tube 402. In some examples, the working fluid in second tube 410 prior to the cross-over point can have a temperature 25° C, 50° C, 75° C, or 100° C less than the working fluid in the first tube 402 at a corresponding point. However, by switching places, the outlet temperature of the working fluid from the first tube 402 is substantially the same as the outlet temperature of the working fluid from the second tube 410, which is also substantially the same as the outlet temperature of the working fluid from the other tubes in the row.

The initial distance between the second tube 410 and the edge of the receiver can be equal to approximately 5-10% of the width of the receiver. For example, the width of the receiver is 5m, 10m, 15m, or 20m. Alternatively or additionally, the second tube 410 can be initially positioned at a distance of at most ten tubes of the row of tubes from first tube 402.

As shown in FIG. 5 A, it is also possible for the second tube 510 to be arranged in line with the inner tubes 520 so as to receive solar insolation prior to the changeover point 524. Thus, the pair 522 of tubes at ends of the row switch places at the changeover point, with tube 502 bending away from the end of the row and tube 510 bending toward the end of the row. Alternatively or additionally, initially-endmost tube 502 can switch places at the cross-over point 524 with one of the inner tubes 520 according to one or more embodiments. In addition, embodiments of the disclosed subject matter are not limited to a single cross-over point 524. Rather, multiple cross-over points may be employed according to one or more contemplated embodiments. For example, the pair of tubes at the end of a row of receiver tubes can have multiple cross-over points so as to appear braided or intertwined, as shown in FIG. 5B.

In some non-limiting examples, the endmost tube may cross multiple tubes such that each of the multiple tubes may individually extend along a portion of the edge of the receiver. The number of multiple tubes may 2, or 3, or 4, or 5 or more tubes. This kind of design may provide enhanced control of the outlet temperature of the working fluid in the endmost tube of the thermal receiver.

A method for of converting solar energy to electricity can include controlling a plurality of heliostats to track the apparent movement of the sun so as to reflect solar radiation onto a thermal receiver. The thermal receiver can be configured to transfer all (or at least a substantial portion of) the reflected solar radiation received thereby as thermal energy to a working fluid. The outermost tube on a receiver panel can receive reflected solar radiation on at least two exposed surface portions thereof. The amount of flux flowing through the outmost tube may be significantly higher than the amount of flux flowing through the other tubes which are part of the receiver. In order to provide working fluid at a uniform temperature to an outlet header attached to the tubes of the thermal receiver, the outlet of the outermost tube can be displaced from the side edge of the thermal receiver, and the outlet of a second tube can be displaced so as to be at the side edge of the receiver. The outermost tube and the second tube can cross-over each other at approximately the mid-point between the top edge of the receiver and the bottom edge of the receiver.

A thermal power generating system can have a solar boiler with a boiler panel having a plurality of tubes. The thermal power generating system can be configured to use steam generated by the solar boiler from solar radiation to drive a turbine. The plurality of tubes can be fluidically connected to an inlet header and an outlet header. A working fluid can be provided to the outlet header at a uniform temperature from the plurality of tubes at least in part by directing the working fluid in an endmost tube located at a side edge of the boiler away from the edge and directing the working fluid in a second tube of the plurality of tubes of the boiler toward the edge of the boiler.

In one or more embodiments of the disclosed subject matter, a method for providing uniform temperature working fluid to an outlet header can include displacing a part of a first tube, whose inlet is positioned at an edge of a solar thermal receiver, away from the edge of the receiver such that the first tube outlet is attached to the outlet header at a distance away from the edge of the solar thermal receiver. The solar thermal receiver can include a plurality of vertical tubes. A second tube can be positioned such that its inlet is at a distance from the first tube (i.e., at a distance from the edge of the receiver). At least a part of the second tube can be displaced such that its outlet is attached to the outlet header at or near the edge of the solar thermal receiver. By having the first tube and the second tube switch places, the temperature of the working fluid entering the outlet header from the first tube can be substantially the same as the temperature of the working fluid entering the outlet header from all other tubes of the receiver.

At its inlet the second tube can be located behind the plurality of tubes. At approximately the mid-point between the top edge of the receiver and the bottom edge of the receiver, the first tube and the second tube can cross each other. After the tubes cross each other, the second tube can straighten out such that it is essentially parallel and in line with the plurality of tubes of the receiver. The endmost tube can be displaced from the edge of the receiver and can bend behind the plurality of tubes. The temperature of the working fluid in the second tube can be lower than the temperature of the working fluid in the endmost tube prior to the crossing point. Since a first part of the second tube is located behind the row of tubes, it does not directly receive any flux from the solar radiation reflected by the heliostats. Therefore, the working fluid flowing through the second tube will not be as hot as the working fluid in the first tube, which receives reflected solar radiation on at least two exposed surface portions. The temperature difference between the two working fluid in the first and second tubes before the crossing point may be at least 25°C, 50°C, 75°C, or even 100°C.

In one or more embodiments, components of the receiver may be constructed, arranged, formed, modified, and/or designed such that the endmost tubes, which can receive a significantly larger amount of flux as compared to the other tubes in the receiver, have a flow of working fluid which exits the endmost tubes at a temperature that is approximately the same as the temperature of the working fluid exiting the other tubes. Such temperature criteria may be satisfied by appropriate selection of exposed surface orientation (as described above and with respect to FIGS. 4A-5B), tube construction (e.g., wall thickness, tube material, etc.), flow characteristics (e.g., working fluid flow rate, flow cross- sectional area, heat transfer coefficients), and/or combinations thereof. For example, the thickness of the tube walls may be increased such that the amount of heat transferred from the external surface portions of the endmost tube to the working fluid flowing within the tube is decreased. Heat flux, q, is directly proportional to the thickness, t, of the tube wall, as indicated by following equation:

where λ is the thermal conductivity of the material, Δ7Ί₂ is the temperature difference across the wall of the tube. As the thickness increases, the rate of heat transfer (heat flux) decreases, thereby compensating for the increased reflected insolation received by the endmost tubes. For example, the wall thickness of the endmost tubes may be increased by 10%, 20%, 30%, 40% or 50%.

Additionally or alternatively, the endmost tubes may be formed from or include a material that has a lower thermal conductivity than the materials used for the other tubes of the receiver. For example, the receiver tubes can be made of stainless steel while the endmost tubes can be made of a material having a thermal conductivity less than that of stainless steel.

Alternatively or additionally, the flow rate of the working fluid flowing in the endmost tubes can be adjusted such that the temperature of the working fluid exiting the endmost tubes is approximately the same as the temperature of the working fluid exiting the other tubes. A mass flow rate equation can be defined as:

m = VAp, (2)

where m is the mass flow rate, V is the velocity of the working fluid, A is the cross-sectional area of the tube, and p is the fluid density. The mass flow rate can thus be modified by either increasing the cross-sectional area of the endmost tubes or by increasing the velocity of the fluid through the endmost tube. A relationship between the mass flow rate, m, of the working fluid and outlet temperature, T_out, of the fluid can be defined by: q = mc_p (T_0Ut - T_in), (3)

where c_p is the heat capacity of the fluid, and Ί_ι-_η is the inlet temperature of the fluid for the tube.

For example, the cross-sectional area of the endmost tube may be increased by 5%, 10%, 20%, 30%, 40% or 50% as compared to the other tubes. Additionally or alternatively, the velocity of the working fluid flowing through the endmost tube may be, for example, 5%, 10%, 20%, 30%, 40%, or 50% greater than the velocity of the fluid in the other tubes. The velocity of the fluid in the endmost tube may be increased by using a device, such as, but not limited to a flow restrictor and a convergent-divergent nozzle.

In one or more embodiments, the configuration and operation of each of the tubes can be based on obtaining a constant value of working fluid mass flow rate per unit exposed surface area. Thus, the ratio of exposed surface area to working fluid mass flow rate should be substantially the same for both endmost tubes as well as the inner and buried tubes. Since the endmost tubes have a higher exposed surface area (i.e., a higher reflected insolation intercept area) than the inner tubes (which are shaded at their sides by adjacent tubes), the endmost tubes may be operated at a higher mass flow rate than the inner tubes. The appropriate mass flow rate for the endmost tubes may be determined based on the

relationship between the inner tube exposed surface area and the endmost tubes exposed surface area. For example, where the mass flow rate is related to the tube cross-sectional area and the endmost tube receives insolation on an exposed surface area twice as large as the inner tube, then an endmost tube with a diameter twice as large as the inner tube diameter would result in the same mass flow to intercept area ratio.

In one or more embodiments of the disclosed subject matter, structures may be provided to compensate for the arrangement of the endmost tubes that results in the additional exposed surface portions as compared to the inner tubes. For example, structures can be provided that shade the second portion of the endmost tubes, such that only the front portion receives reflected insolation. Alternatively or additionally, the amount of reflected solar insolation received by the endmost tubes may be reduced by shading the endmost tubes from at least a portion of the reflected insolation. For example, the endmost tubes may be shaded by isolating a portion of the surface exposed to the reflected solar insolation. Alternatively or additionally, a barrier and/or projection may be placed so as to block reflected solar insolation from striking the endmost tube of the receiver.

Features of the disclosed embodiments can be combined, rearranged, omitted, etc., within the scope of the invention to produce additional embodiments. Furthermore, certain features may sometimes be used to advantage without a corresponding use of other features.

It is, thus, apparent that there is provided, in accordance with the present disclosure, solar energy thermal storage systems and methods for use thereof. Many alternatives, modifications, and variations are enabled by the present disclosure. While specific embodiments have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. Accordingly, Applicants intend to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present invention.

Claims

1. A boiler for a solar receiver comprising:

a boiler panel having a plurality of vertical tubes that convey a working fluid and are fluidically connected to an inlet header of the boiler panel and to an outlet header of the boiler panel, the tubes of the boiler panel spanning the width of the boiler panel from a first side edge of the boiler panel to a second side edge of a boiler panel;

wherein a first tube of the plurality of vertical tubes positioned at the first side edge of the boiler crosses a second tube of the plurality of vertical tubes positioned between the first side edge of the boiler and the second side edge of the boiler such that the outlet of the first tube is displaced from the first side edge and the outlet of the second tube is proximal to the first side edge.

2. The boiler of claim 1, wherein the boiler is a superheater.

3. The boiler of claim 1, wherein the boiler is a reheater.

4. The boiler of claim 1, wherein a distance between the second tube and the first side edge at an inlet header side of the second tube is equal to 5-10% of the width of the boiler.

5. The boiler of claim 1, wherein a temperature of the working fluid at a point in the second tube before the first tube crosses the second tube is lower than a temperature of the working fluid at a corresponding point in the first tube.

6. The boiler of claim 5, wherein a difference between said temperatures is at least

25° C.

7. The boiler of claim 1, wherein a temperature of the working fluid from the first tube at the outlet header is substantially the same as a temperature of the working fluid from the second tube at the outlet header.

8. The boiler of claim 1, wherein the first tube crosses the second tube at a crossing point that is approximately a mid- way point between a top edge of the boiler and a bottom edge of the boiler.

9. The boiler of claim 1, wherein a portion of the second tube at an inlet header side thereof is within ten tubes from a corresponding portion of first tube.

10. The boiler of claim 1, wherein the boiler is a supercritical steam generator.

11. The boiler of claim 1, wherein the boiler is a molten salt boiler.

12. The boiler of claim 1, wherein respective temperatures of the working fluid from the plurality of vertical tubes at the outlet header are substantially the same.

13. The boiler of claim 1, wherein the first tube crosses more than one tube positioned between the first side edge of the boiler and the second side edge of the boiler.

14. A solar energy conversion system comprising:

a receiver having a plurality of pipes that convey a working fluid and that are fluidically connected to an inlet header of the receiver and to an outlet header of the receiver; a plurality of heliostats, each heliostat being configured to direct incident solar radiation at the receiver so as to heat the working fluid flowing through the receiver;

a conveyance device configured to transport the heated working fluid from the receiver to an electric power generating plant, the heated working fluid being used by an electric power generating plant in the generation of electricity;

wherein the working fluid is provided by the plurality of pipes to the outlet header at a substantially the same temperature,

a first pipe has an inlet side portion positioned at a side edge of the receiver and an outlet side portion displaced from the side edge of the receiver, and

a second pipe has an inlet side portion positioned away from the side edge of the receiver and an outlet side portion positioned at the side edge of the receiver.

15. The system of claim 14, wherein a connection between the second pipe and the inlet header is located behind the plurality of pipes such that the inlet side portion of the second pipe does not receive the directed solar radiation.

16. The system of claim 15, wherein the first pipe and the second pipe cross each other at a crossing point approximately mid- way between a top edge of the receiver and a bottom edge of the receiver.

17. The system of claim 16, wherein the outlet side portion of the second pipe is aligned with corresponding outlet side portions of the plurality of pipes, and the outlet side portion of the first pipe is behind the corresponding outlet side portions of the plurality of pipes such that it does not receive the directed solar radiation.

18. The system of claim 14, wherein the inlet side portion of the second pipe is at a distance from the side edge of the receiver that is approximately equal to 5-10% of the width of the receiver.

19. A method of converting solar energy to electricity, the method comprising:

controlling a plurality of heliostats to track the apparent movement of the sun to reflect incident solar radiation on a thermal receiver having a plurality of tubes;

flowing working fluid through a first tube of the plurality of tubes, the first tube having an inlet side portion at a first side edge of the receiver and an outlet side portion displaced from the first side edge of the receiver;

flowing working fluid through a second tube of the plurality of tubes, the second tube having an inlet side portion displaced from the first side edge of the receiver and an outlet side portion at the first side edge of the receiver; and

flowing working fluid through the remaining tubes of the plurality of tubes, wherein temperatures of the working fluids exiting the first tube, the second tube, and the remaining tubes are substantially the same.

20. The method of claim 19, wherein the first tube and the second tube cross each other.

21. The method of claim 20, wherein the first tube and the second tube cross each other at a crossing point approximately half-way between a top edge of the receiver and a bottom edge of the receiver.

22. The method of claim 19, wherein the receiver is a superheater.

23. The method of claim 19, wherein the receiver is a reheater.

24. A method for generating steam for a turbine using solar radiation, comprising: in a solar receiver of a thermal power generating system, the receiver having boiler panel having a plurality of tubes, the plurality of tubes being connected to an inlet header and an outlet header, providing a working fluid to the outlet header at a uniform temperature from the plurality of tubes at least in part by:

directing the working fluid in a first tube located at a side edge of the boiler away from the side edge; and

directing the working fluid in a second tube located at a distance from the side edge of the boiler towards the edge of the boiler.

25. The system of claim 24, wherein the distance from the side edge of the receiver is approximately equal to 5-10% of the width of the receiver.

26. A method of providing uniform temperature to an outlet header from a solar thermal receiver, the solar receiver having a plurality of substantially vertical tubes, the method comprising:

positioning a first of said plurality of tubes such that a first section of said first tube is at a side edge of the receiver and a second section of said first tube is displaced from the side edge of the receiver; and positioning a second of said plurality of tubes such that a first section of said second tube is displaced from the side edge of the receiver and a second section of said second tube is at the side edge of the receiver.

27. The method of claim 26, wherein the first section of the second tube is located behind the others of the plurality of tubes.

28. The method of claim 26, wherein the first tube and the second tube cross.

29. The method of claim 28, wherein second section of the second tube is aligned with the others of the plurality of tubes, and the second section of the first tube is located behind the others of the plurality of pipes.

30. The method of claim 28, wherein a temperature of the working fluid in the first section of the second tube is lower than a temperature of the working fluid in the first section of the first tube.

31. The method of claim 30, wherein the temperature difference is at least 25° C.

32. The method of claim 30, wherein a temperature of the working fluid at the outlet header from the first tube is substantially the same as a temperature of the working fluid at the outlet header from the second tube.

33. A boiler for a solar receiver comprising:

a boiler panel having a plurality of vertical tubes that convey a working fluid, the tubes being fluidically connected to an inlet header and an outlet header of the boiler panel, the tubes being arrayed along a width of the boiler panel from a first side edge to a second side edge thereof,

wherein a first tube of the plurality of vertical tubes is positioned at the first side edge of the boiler so as to receive more flux than other tubes of the plurality of vertical tubes, and working fluid from each of the plurality of tubes is provided to the outlet header at substantially the same temperature.

34. The boiler of claim 33, wherein the first tube has a greater wall thickness than that of the other tubes of the plurality of tubes.

35. The boiler of claim 34, wherein the first tube has a thickness that is at least 10% greater than that of the other tubes.

36. The boiler of claim 33, wherein the first tube is constructed of a material which has lower thermal conductivity than the material in the other tubes.

37. The boiler of claim 33, wherein the first tube is constructed such that the velocity of working fluid flowing therethrough is greater than the velocity of the fluid flowing through the other tubes of the plurality of tubes.

38. The boiler of claim 37, wherein the velocity in the first tube is at least 5% greater than the velocity in at least one other tube of the plurality of tubes.

39. The boiler of claim 33, wherein the cross-sectional area of the first tube is greater than the cross-sectional area of the other tubes of the plurality of tubes.

40. The boiler of claim 39, wherein the cross-sectional area is at least 5% greater than the cross-sectional area in at least one other tube of the plurality of tubes.

41. The boiler of claim 33, wherein the boiler is a supercritical steam generator.

42. The boiler of claim 33, wherein the boiler is a molten salt boiler.

43. The boiler of claim 33, wherein the boiler is a steam superheater.