Solar energy collection system

In one aspect of the present invention, a solar energy collection system that includes multiple longitudinally adjacent collectors is described. The collectors are coupled end to end to form a collector row. The collector row extends along a longitudinal axis and is arranged to rotate about a pivot axis to track the sun in at least one dimension. Each collector includes a reflector, one or more solar receivers and a support structure. The support structure includes a tube assembly that underlies the reflector. The tube assemblies of the collector row are arranged end to end along the longitudinal axis. There is a space between the tube assemblies of adjacent collectors in the collector row, where the reflectors of the adjacent collectors extend beyond the underlying tube assemblies to form a substantially continuous reflective surface over the space. A coupling device is positioned in the space between the tube assemblies. The coupling device connects and helps to rotate the tube assemblies of the adjacent collectors. Some embodiments relate to various types of coupling devices and collector arrangements.

FIELD OF THE INVENTION

Generally, the present invention relates generally to solar energy collection systems. More specifically, the present application relates to solar collectors and solar collector arrangements for use in concentrating photovoltaic systems.

BACKGROUND OF THE INVENTION

Typically, the most expensive component of a photovoltaic (PV) solar collection system is the photovoltaic cell. To help conserve photovoltaic material, concentrating photovoltaic (CPV) systems use minors or lenses to concentrate solar radiation on a smaller cell area. Since the material used to make the optical concentrator is less expensive than the material used to make the cells, CPV systems are thought to be more cost-effective than conventional PV systems.

One of the design challenges for any CPV system is the need to balance multiple priorities. For one, a CPV system requires a support structure that arranges the optical concentrators and the photovoltaic cells such that incoming sunlight is properly received and focused. This support structure should also accommodate a tracking system and provide for the adequate dissipation of heat. Another consideration is the cost of manufacturing, installing and repairing the CPV system. Existing CPV designs address these issues in a wide variety of ways. Although existing CPV systems work well, there are continuing efforts to improve the performance, efficiency and reliability of CPV systems.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a solar energy collection system that includes multiple longitudinally adjacent collectors is described. The collectors are coupled end to end to form a collector row. The collector row extends along a longitudinal axis and is arranged to rotate about a pivot axis to track the sun in at least one dimension. Each collector includes a reflector, one or more solar receivers and a support structure. The support structure includes a tube assembly that underlies the reflector. The tube assemblies of the collector row are arranged end to end along the longitudinal axis. There is a space between the tube assemblies of adjacent collectors in the collector row, where the reflectors of the adjacent collectors extend beyond the underlying tube assemblies to form a substantially continuous reflective surface over the space. A coupling device is positioned in the space between the tube assemblies. The coupling device connects and helps to rotate the tube assemblies of the adjacent collectors.

In some implementations, the gap between adjacent reflectors is minimal e.g., less than approximately 10 or 15 millimeters. A minimal gap helps the adjacent reflectors cooperate to form a substantially continuous flux line on the receivers of the associated collectors. In some designs, the gap is covered at least in part by a reflective splice that helps further reduce or eliminate discontinuity in the flux line.

In another embodiment of the present invention, a solar energy collection system that includes at least two longitudinally adjacent collectors and a drive coupling device will be described. The two adjacent collectors are connected with one another using the drive coupling device to form at least a portion of a collector row. The drive coupling device includes a motor that applies rotational torque to help rotate the reflectors of the adjacent collectors. The motor is attached in manner such that it rotates together with the reflectors of the adjacent collectors.

Various designs involve a collector row that includes additional collectors that extend the collector row in a longitudinal direction. In particular embodiments, these additional collectors may be coupled together using non-drive coupling devices. The non-drive coupling devices are arranged to transfer rotational torque between adjacent collectors. In some implementations, the motive force for tilting the entire collector row originates from a single drive coupling device at the center of the collector row. The rotational torque is then transferred throughout the collector row via the non-drive coupling devices.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates generally to solar energy collection. Some aspects of the invention relate to solar collectors, arrangements of multiple solar collectors, and devices for tracking the sun. It should be appreciated that additional embodiments, features and drawings related to the present application are described in Provisional Application No. 61/229,905, filed Jul. 30, 2009, entitled “Manufacturable Dual Trough Solar Collector,” which is incorporated herein in its entirety for all purposes.

Referring now toFIG. 1, a solar energy collection system100according to one embodiment of the present invention will be described. Solar energy collection system100includes multiple solar collectors102a-102dthat are coupled end to end along a longitudinal axis107to form a solar collector row106. Each solar collector includes a reflector110that is arranged to direct incident sunlight towards the solar receivers116. The solar energy collection system100is arranged to pivot the solar collector row106around a pivot axis in order to track the movements of the sun. Multiple mounting posts104support the solar collector row106.

The collectors102a-102dare arranged side by side along the longitudinal axis107such that there is a minimal gap between the reflectors110of adjacent collectors. Light reflected from the reflectors110thus forms a substantially continuous flux line on the photovoltaic (PV) cells of the solar receivers116. This results in a more uniform distribution of light across the PV cells and helps increase their efficiency.

The solar energy collection system100also includes a tracking system that helps the collector row106track movements of the sun throughout the day. In the illustrated embodiment ofFIG. 1, the collector row106rotates (as shown by arrow114) around a pivot axis that extends parallel to the longitudinal axis107. This rotation is powered by a motor in a drive coupling device300. The rotational torque generated by the drive coupling device is transferred to the outer collectors102aand102dvia additional non-drive coupling devices400. The coupling devices300and400are positioned in spaces between the support structures of adjacent collectors. The reflectors110of the adjacent collectors extend over these spaces to form a substantially continuous reflective surface.

Referring now toFIGS. 2A and 2B, perspective and cross-sectional views of the collector102baccording to particular embodiment of the present invention will be described. The collector102bincludes a reflector110, one or more solar receivers116, and a support structure118, which includes a tube assembly120. The solar receivers116include one or more strings of photovoltaic cells. It should be appreciated that the present invention is not intended to be limited to the collectors illustrated in this application. By way of example, any of the solar collector designs, receiver designs and features described in U.S. Pat. No. 7,709,730, entitled “Dual Trough Concentrating Solar Photovoltaic Module,” filed on Apr. 10, 2008, and Provisional Patent Application No. 61/362,591, entitled “Optimized Solar Collector,” filed on Jul. 8, 2010, which are both incorporated herein by reference for all purposes, may be used with the present invention.

The tube assembly120is any structure that is arranged to help support and rotate the reflectors110(e.g., a cylinder, a beam, a rod, associated braces, brackets, etc.). In some implementations, the tube assembly120is arranged to rotate around a pivot axis122, which in turn causes the attached reflectors110and receivers116to tilt. When the reflectors110are appropriately oriented towards the incident sunlight124, the reflectors110reflect the sunlight to form a flux line on the receivers116. A diagrammatic illustration of how the sunlight may be reflected is provided inFIG. 2B.

Referring now toFIGS. 2C and 2D, a side view of collectors102b-102cofFIG. 1according to a particular embodiment of the present invention will be described.FIG. 2Cillustrates a side view of a single collector102b, whileFIG. 2Dillustrates a region where the collectors102b-102care adjacent to one another. As discussed previously, the collectors102b-102care arranged such that only a minimal gap202exists between their respective reflectors110. (It should be noted that the size of the gap202inFIG. 2Dhas been enlarged for the sake of clarity and is not to scale.) That is, the reflectors110of the adjacent collectors102b-102cform a substantially continuous reflective surface. Incident sunlight that is reflected off of this surface forms a substantially continuous flux line on the solar receivers116ofFIG. 1.

The support structures underlying the reflectors110are arranged to accommodate a coupling device that helps connect the collectors102b-102ctogether. More specifically, the end of the tube assembly108of each collector102b-102cdoes not extend as far as the end of its overlying reflector110. As a result, an indentation111is formed at the end of each collector. When the ends of the collectors102band102care positioned adjacent to one another, their respective indentations111cooperate to form a space204between the tube assemblies108. The reflectors110form a substantially continuous reflective surface over this space204between the tube assemblies108. In various implementations, a coupling device (e.g., drive coupling device300ofFIG. 3A, non-drive coupling device400ofFIG. 4A, etc.) is positioned within this space to help connect the tube assemblies, as will be discussed in greater detail below.

The small gap202between the reflectors of adjacent collectors may vary in size. In some embodiments, for example, the width of the gap202is less than approximately 10 or 15 millimeters. A gap size of between approximately 5 and 15 millimeters works well for various applications. Preferably, the size of the gap202should be quite small relative to the width of the photovoltaic cells used in the receivers of the collector row. This helps ensure that there are no large disparities in exposure between photovoltaic cells in a string of serially connected cells. Such disparities can reduce the efficiency of the cell string. Accordingly, some designs involve a gap202whose width is no more than approximately 10, 20 or 30% of the width of a photovoltaic cell in the solar receiver.

In particular implementations, the gap202is covered with a splice (not shown) that is made of a reflective material. The splice, together with the reflectors110of the adjacent collectors102b-102c, is arranged to reflect light to form a substantially continuous flux line on the cells of the receivers. To make room for thermal expansion along the length of the collector row, the splice is preferably coupled with the adjacent reflectors in a manner that allows them to move in the longitudinal direction205.

Referring now toFIGS. 3A and 3B, perspective views of a drive coupling device300according to a particular embodiment of the present invention will be described.FIG. 3Aprovides an exploded view of the drive coupling device300, whileFIG. 3Bprovides a view of an assembled drive coupling device300. Generally, the drive coupling device300is arranged to apply rotational torque to the adjacent solar collectors so that they properly track the movements of the sun. The drive coupling device300can include a wide variety of components. In the illustrated embodiment, for example, the drive coupling device300includes a slew drive308, a planetary drive312and a motor314. The drive coupling device300is positioned between tube assemblies316a-316bof two adjacent collectors (e.g., of collectors102band102cofFIGS. 1 and 2C). A mounting post104physically supports the drive coupling device300.

Preferably, the drive coupling device300is arranged such that the motor314rotates in tandem with the reflectors110. That is, the motor314substantially maintains its position relative to the reflectors110even when the reflectors are in motion. In the illustrated embodiment, for example, the motor314and the planetary drive312are attached to a rotatable portion of the slew drive308and thus rotate together with any other structures that are attached therewith (e.g., the tube assembly108, the reflectors110, etc.) This feature conserves space underneath the reflectors and helps eliminate the need for flexible connectors to extend between the motor314and the slew drive308, the reflectors110and/or their associated support structure.

The slew drive308can be any device suitable for applying rotational torque to tilt the reflectors of the adjacent collectors. In the illustrated embodiment, for example, the slew drive308includes a rotatable portion, which is a part of the slew drive that is capable of rotating independently from other parts of the slew drive, and a stationary portion, which is a part of the slew drive that is fixed and incapable of rotating independently from other parts of the slew drive. The rotatable portion of the slew drive308is coupled with the tube assemblies316a-316b. When activated, the slew drive308rotates the tube assemblies and their corresponding reflectors using the motive force provided by the motor314.

The optional planetary drive312, which is coupled with the motor314and the slew drive308, may be used to reduce the rotational speed of the motor to a speed that is appropriate for driving the collector row. By way of example, the amount of gear reduction may be approximately 10,000:01 to 20,000:1, although smaller and larger reductions are also possible. The gear reduction can increase the torque that is applied to the tube assemblies316aand316bso that a relatively small motor314can be used.

The tube assemblies316aand316b, the mounting post104and the slew drive308can be coupled with one another using a wide variety of structures. In the illustrated embodiment, for example, the stationary portion of the slew drive308is attached to a mounting support306. The mounting post104underlies and supports the mounting support306. The end of the tube assembly316ais connected to a bracket302, which is coupled with a coupler304. The coupler304extends through an aperture in the mounting support306and is coupled to the rotatable portion on one side of the slew drive308. A mounting plate310is coupled to the rotatable portion on the opposite side of the slew drive. The mounting plate310is connected to another bracket302, which is in turn connected to the other tube assembly316b.

The drive coupling device300may include various features to facilitate assembly and repair. In some embodiments, for example, some or all of the aforementioned parts of the drive coupling device300and the tube assemblies316aand316bare connected using fasteners and without welding. Additionally, some or all of these parts may include alignment features. Each alignment feature can include an alignment hole and a precision dowel that is used to hold adjacent parts in place.

The drive coupling device300can be positioned in any suitable location within the collector row. By way of example, the drive coupling device300ofFIG. 1is positioned in the center of the collector row106i.e., between collectors102band102c. Some designs involve only one drive coupling device300per collector row106. Accordingly, inFIG. 1, the rotational torque used to rotate the collector row106comes entirely from the single drive coupling device300, although this is not a requirement. Additional collectors102aand102dare coupled to the collectors102band102c, respectively, using a non-drive coupling device, which will be described in greater detail below.

Referring now toFIGS. 4A and 4B, a non-drive coupling device400according to one embodiment of the present invention will be described.FIG. 4Aprovides an exploded view of the non-drive coupling device400, whileFIG. 4Bshows a view of an assembled device400. The non-drive coupling device400may be any device suitable for transferring rotational torque between adjacent collectors in a collector row. In the illustrated embodiment, the non-drive coupling device400, which includes transfer arms404, interconnects406and bushing blocks408, connects with two tube assemblies420a-420bthat underlie two adjacent collectors (e.g., collectors102c-102din the collector row106ofFIG. 1.)

The non-drive coupling device400may connect the tube assemblies420a-420bin a wide variety of ways. By way of example, inFIGS. 4A and 4Bthe bushing blocks408are mounted on a top end of a mounting post600. Each tube assembly420a-420bis attached with a bracket412, which in turn is attached to an interconnect406with a protruding shaft410. The shaft410is received by a hole in the bushing block408, where the shaft410is generally free to rotate.

The transfer arms404are coupled with their respective tube assemblies420a-420band are attached to one another in a manner that allows for the transfer of rotational torque between the tube assemblies420-420b. In various designs, each transfer arm404includes one or more flexible portions that allow the transfer arm to move along the longitudinal axis414, while maintaining rigidity for rotation about the longitudinal axis. This allows the transfer arm404to help compensate for differential thermal expansion along the collector row. In the illustrated embodiment, most of the weight of the tube assemblies420a-420bis not carried by the transfer arms404. Instead, the weight of the tube assemblies420a-420bis carried more by the bushing blocks408than by the transfer arms404.

It should be appreciated that the various components illustrated inFIGS. 4A and 4Bmay be connected and supported in a wide variety of ways. For example, some or all of these components may be coupled with one another using fasteners and/or without the use of any welding. Some or all of the components may have one or more alignment features (e.g., alignment holes with precision dowels, etc.) to facilitate rapid assembly of the non-drive coupling device400.

Referring next toFIG. 5, a free end coupling device500according to a particular embodiment of the present invention will be described. Generally, the free end coupling device may be any coupling device that is arranged to facilitate the rotation of a reflector that is positioned at the end of a collector row (e.g, collector102aor102dofFIG. 1.) In the illustrated embodiment, for example, the free end coupling device includes a bushing block502and an interconnect506. The bushing block502is mounted on the top end of a mounting post (not shown). A shaft504extends out of an interconnect506, which is attached to a tube assembly510via a bracket508. The shaft504rests in a hole in the bushing block502and is generally arranged to rotate freely therein.

Referring now toFIG. 6, a mounting post600according to a particular embodiment of the present invention will be described. The mounting post600is arranged to help increase the range of motion of an overlying solar collector. In the illustrated embodiment, the mounting post600includes a lower portion604, an upper portion606and a dogleg602. Mounted on the top end of the upper portion606is an attachment support608, which is arranged to support one of the aforementioned coupling devices. By way of example,FIG. 4Aillustrates a mounting post600that supports a non-drive coupling device400.

The mounting post600is arranged to increase the tilt range of the reflectors, which can allow the reflectors to track the sun for longer periods. That is, the sharp bend in the mounting post600helps create additional space below the reflectors so that a bottom portion of the reflectors is not blocked by the mounting post when the reflectors are tilted far to one side. In some embodiments, the mounting post600is arranged to allow the reflectors of the collector row to tilt up to at least ±75° (i.e., for a total range of motion of 170°) around a pivot axis without coming in contact with the mounting post, although larger and smaller tilt angles are also possible. By way of example, a range of tilt angles of up to at least ±70°, ±80° or ±85° around the pivot axis works well for various applications. It should also be appreciated that the range of motion need not be symmetric. Some implementations involve reflectors whose maximum tilt angle in one direction around the pivot axis is approximately 5° to 20° greater than in the opposing direction (e.g., a reflector whose tilt range is up to at least +85° and −70°.) In still other embodiments, the aforementioned ranges are achievable at least in part by appropriately arranging the support structure underneath the reflectors. For example, some implementations involve lowering the tube assembly120and/or the pivot axis122relative to the overlying reflectors110ofFIG. 2Bso that the reflectors110have more room to tilt without being blocked by the underlying mounting post.

Although only a few embodiments of the invention have been described in detail, it should be appreciated that the invention may be implemented in many other forms without departing from the spirit or scope of the invention. By way of example, some of the figures relate to a collector design involving dual trough reflectors and receivers in a particular arrangement. However, it should be appreciated that the collector rows, coupling devices, coupling arrangements, mounting posts and any other feature described in this application may also be applied to a wide assortment of collector designs i.e., almost any suitable collector design that tracks the sun in at least one dimension, almost any suitable collector that can be arranged side by side with other collectors along a longitudinal axis, etc. Although various drawings and descriptions in this application are quite detailed in explaining how various components interface and interact, it should be noted that the present invention contemplates modifying these embodiments to suit a variety of applications. For example, it should be appreciated that the present invention contemplates non-drive coupling devices400ofFIG. 4Awithout the illustrated transfer arms404, and also contemplates drive coupling devices300ofFIG. 3Awithout a coupler304or a mounting plate310. It should be further noted that any component of one figure may be replaced or modified using a corresponding component that is described herein. For example, any of the mounting posts104ofFIG. 1may be replaced or modified using the mounting post600ofFIG. 6. Additionally, any of the coupling devices used to connect the tube assemblies of collectors102a-102dinFIG. 1may be replaced with any of the coupling devices described herein. The foregoing description sometimes refers to forming a substantially continuous flux line. It is noted that the present application contemplates various definitions of the term, “flux line,” and various ways of forming a substantially continuous flux line on the photovoltaic cells of a solar receiver. Some of these definitions and approaches are described, for example, in patent application Ser. No. 12/728,149, entitled “Reflective Surface for Solar Energy Collector,” filed Mar. 19, 2010, which is incorporated herein in its entirety for all purposes. Therefore, the present embodiments should be considered as illustrative and not restrictive and the invention is not limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.