Patent Application
20170025992
The present invention is related to mirrors that are transparent to specific regions of the electromagnetic spectrum, and their implementation in Space-based Solar Power (SBSP) Systems.
Space-based Solar Power (SBSP) describes the collection of solar power in space by a Solar-Power Satellite or a Satellite Power System (SPS) and then the conversion and transmission of the power to a remote receiver for conversion back to electrical power. In an SBSP System, solar energy is collected as electrical energy on board, powering some manner of wireless power transmission to a receiver located remotely from the SBSP System. The wireless power transmission application might include a microwave transmitter or laser emitter, which would direct its beam toward a collector, such as a power receiving rectenna at the remote location, such as, on the Earth's surface.
SBSP differs from ground-based solar collection methods in that the means used to collect energy resides on an orbiting satellite instead of on the Earth's surface. Basing such a system in space results in a higher collection rate for the solar energy due to the lack of a diffusing atmosphere. In a conventional ground-based system a large percentage (55-60%) of the solar energy is lost on its way through the atmosphere by the effects of reflection and absorption. Space-based solar power systems convert solar energy to a far-field emission such as microwaves outside the atmosphere, avoiding these losses. In addition, SBSP Systems have a longer collection period and the ability to collect solar energy continuously without the downtime (and cosine losses, for fixed flat-plate collectors) that result from the Earth's rotation away from the sun.
A general limitation for conventional SBSP Systems is the size of SPS required to generate sufficient electrical power from solar energy. For example, for a 500 MW system a 5 km2 platform may be required. Such a platform would conventionally be formed of large satellites on the order of tens to hundreds of tonnes/satellite. The launch costs associated with placing such large structures into orbit reduces the economic viability of conventional SBSP Systems.
Systems and methods in accordance with various embodiments of the invention implement mirrors that are more transparent to specific regions of the electromagnetic spectrum (e.g. the microwave region of the electromagnetic spectrum) relative to conventional metallic mirrors (e.g. mirrors made form aluminum or silver). In one embodiment, a space-based solar power system includes: a photovoltaic material; and a mirror that is—relative to a 10 μm thick sheet of aluminum—more transparent to at least one of a substantial portion of the microwave region of the electromagnetic spectrum and a substantial portion of the radio wave region of the electromagnetic spectrum; where the mirror is configured to focus incident visible light onto the photovoltaic material.
In another embodiment, the mirror includes alternating layers of high refraction index materials and low refraction index materials.
In yet another embodiment, the alternating layers of high refraction index and low refraction index materials are disposed on a polymer membrane.
In still another embodiment, a plurality of the high refraction index materials include the same material, and a plurality of the low refraction index materials include the same material.
In still yet another embodiment, the alternating layers of high refraction index and low refraction index materials are configured such that incident light reflects off of the constituent interfaces and thereby constructively interferes to achieve reflection.
In a further embodiment, adjacent high refraction index and low refraction index materials define a pair, and the mirror includes at least 72 pairs.
In a still further embodiment, adjacent high refraction index and low refraction index materials define a pair, and the mirror includes at least 144 pairs.
In a yet further embodiment, adjacent high refraction index and low refraction index materials define a pair, and at least two of the pairs include different materials.
In a still yet further embodiment, the different pairs each give rise to different reflectivity profiles.
In another embodiment, at least two reflectivity profiles are characterized by a reflectance % of greater than 90% for at least some region within the visible light portion of the electromagnetic spectrum.
In still another embodiment, at least one layer that includes a low index refraction material includes one of: MgF2 and SiO2.
In yet another embodiment, at least one layer that includes a high index refraction material includes one of: Diamond, AlN, and Ta2O5.
In still yet another embodiment, adjacent high refraction index and low refraction index materials define a pair, and at least one pair includes Diamond and MgF2 adjacently disposed.
In a further embodiment, adjacent high refraction index and low refraction index materials define a pair, the mirror includes at least 72 pairs, and each of the pairs includes Diamond and MgF2 adjacently disposed.
In a still further embodiment, adjacent high refraction index and low refraction index materials define a pair, the mirror includes at least 144 pairs, and each of the pairs includes Diamond and MgF2 adjacently disposed.
In a yet further embodiment, the thickness of the mirror is between approximately 1 μm and approximately 10 μm.
In a still yet further embodiment, adjacent high refraction index and low refraction index materials define a pair, and at least one pair includes AlN and SiO2 adjacently disposed.
In another embodiment, adjacent high refraction index and low refraction index materials define a pair, and at least one pair includes Diamond and SiO2 adjacently disposed.
In still another embodiment, adjacent high refraction index and low refraction index materials define a pair, and at least one pair includes AlN and MgF2 adjacently disposed.
In yet another embodiment, adjacent high refraction index and low refraction index materials define a pair, and at least one pair includes Ta2O5 and MgF2 adjacently disposed.
The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims.
The description will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiments of the disclosure and should not be construed as a complete recitation of the scope of the disclosure, wherein:
Turning now to the drawings, mirrors that are more transparent to predetermined regions of the electromagnetic spectrum relative to conventional mirrors (e.g. those fabricated from aluminum or silver) in accordance with many embodiments of the invention are illustrated. Many systems, including many systems configured for extraterrestrial operation, can benefit from such structures. For example, many SBSP Systems implement concentrators, e.g. in the form of mirrors, to focus solar radiation onto constituent photovoltaic materials, which then generate electrical current based on the incident solar radiation. As can be appreciated, a photovoltaic material's ability to generate electrical current is related to the amount of incident solar radiation/flux. For instance, U.S. patent application Ser. No. 14/728,985, entitled “Large-Scale Space-Based Solar Power Station: Efficient Power Generation Tiles,” discloses SBSP Systems that incorporate mirrors to focus solar radiation onto constituent photovoltaic materials, and the respective generation of electrical current. U.S. patent application Ser. No. 14/728,985 is hereby incorporated by reference in its entirety, especially as it pertains to the disclosure of SBSP Systems that incorporate mirrors to focus solar radiation onto photovoltaic materials. As explained in U.S. patent application Ser. No. 14/728,985, using concentrators to increase the solar flux experienced by a photovoltaic material can be advantageous relative to simply increasing the surface area of a photovoltaic material to increase electric current generation in a number of respects. For example, configurations that utilize concentrators in the aforementioned manner can be less massive than those that implement relatively more photovoltaic material (e.g. as measured by surface area). This is because photovoltaic materials are typically implemented in conjunction with cover glass, which can be relatively massive. Hence, the more photovoltaic material that is used, the more—relatively massive—attendant cover glass is used (generally speaking). As can be appreciated, it is often desirable to implement SBSP Systems having a reduced payload, e.g. to reduce launch costs and to improve maneuverability. SBSP Systems that utilize concentrators, e.g. in the form of mirrors, can be advantageous insofar as they can provide for greater power generation per unit mass.
While the implementation of mirrors in this manner can enable improved efficacy and efficiency for SBSP Systems, the utilization of conventional metallic mirrors, such as aluminum films or silver surfaces, can introduce some problems. For example, such metallic mirrors can interfere with the wireless transmission of the generated power.
Importantly, conventionally implemented metallic mirrors (e.g. made from aluminum or silver) are typically not transparent to RF electromagnetic waves. Rather, such metallic materials can substantially interfere with the transmission of RF waves. As a result, the RF Subsystem cannot simply wirelessly transmit power through the PV Subsystem. Thus, many embodiments of the invention are directed to implementing mirrors that are much more transparent to targeted portions of the electromagnetic spectrum, e.g. the RF region. This can allow for a more flexible operation for a respective SBSP System. For example,
Mirrors that are more transparent to specified regions of the electromagnetic spectrum, and their incorporation in SBSP Systems, are now discussed in greater detail below.
Mirrors that are Transparent to Specified Regions of the Electromagnetic Spectrum
In many embodiments of the invention, mirrors are implemented that are relatively more transparent to predetermined portions of the electromagnetic spectrum as compared to conventional mirrors (e.g. made from aluminum or silver). In a number of embodiments, the mirrors are configured such that they are optically reflective, but are more transparent to at least certain of those portions of the electromagnetic spectrum that are commonly used for wireless power transmission (e.g. the microwave region and the radio wave region). In many embodiments, the mirrors are more transparent to at least a substantial portion (e.g. the majority of) of one of the microwave region and the radio wave region. In numerous embodiments, the mirrors are more transparent in one of the following ranges: between approximately 300 GHz and approximately 30 GHz; between approximately 30 GHz and approximately 3 GHz; between approximately 3 GHz and approximately 300 MHz; between approximately 300 MHz and approximately 30 MHz; between approximately 30 MHz and approximately 3 MHz; between approximately 3 MHz and approximately 300 kHz; between approximately 300 kHz and approximately 30 kHz; between approximately 30 kHz and approximately 3 kHz; and portions and combinations thereof. In this way, the mirrors can be implemented in SBSP Systems such as those described above, so as to allow for power generation and transmission for virtually the entire orbit.
In many embodiments the mirrors take the form of alternating layers of high and low refraction index materials; the reflective characteristic of the mirror can be achieved via constructive interference. Note that in many instances, the reflectance of the mirror can be a function of the number of pairs of high and low refraction index materials implemented. In many instances, the alternating layers are disposed on a polymer membrane. As an example,
In many instances, the number of pairs of constituent layers can impact the reflectance profile (relative to wavelength) of the mirror. For instance,
Notably, while conventional materials—such as those based entirely on TiO2 and/or SiO2—may be sufficient to provide a reflective surface, they might have characteristics that would hinder their performance as concentrators in in SBSP Systems. For example, in many SBSP systems, such as those described in U.S. patent application Ser. No. 14/728,985, incorporated by reference above, the concentrators also serve as ‘fins’ insofar as they help radiate heat away from the structures, and thereby facilitate the maintenance of suitable operating temperatures. Conventional reflective surfaces may not have optimal thermal conductivity characteristics. Accordingly, in many embodiments, material combinations are implemented that have favorable thermal conductivity characteristics (e.g. high thermal conductivities). For example, in numerous embodiments, the mirror is constructed from combinations of: AlN, Diamond, and/or Ta2O5, MgF2, SiO2.
Furthermore, in many instances it can be desirable to implement mirrors that are characterized by relatively light weights. For instance, as alluded to previously, it is often desirable to reduce the overall payload for SBSP Systems; reducing the weight can provide for reduced launch costs and greater maneuverability in orbit. Table 1 below lists sample weight values for various combinations of alternating materials that can be implemented in accordance with embodiments of the invention. In particular, Table 1 lists mass per unit area values for 72 layer configurations and 144 layer configurations for each of the listed material combinations. Any of the configurations listed in Table 1 can be implemented to construct mirrors in accordance with embodiments of the invention.
Notably, the reflectivity of the mirror can be dependent on the respective angle of incidence, and this dependency can be a function of specific material combinations. Hence, in many embodiments, particular materials combinations are implemented that result in mirrors characterized by reflectivity profiles that are relatively resilient against incident angle variation. For example,
As can be appreciated, the overall optical efficiency of the mirror is also an important consideration. Table 2 lists sample optical efficiencies for the listed mirror configurations and conventional mirrors.
In many embodiments, mirrors are implemented that include constituent materials that allow the mirror to have relatively high optical efficiency values.
Note that while the above data has in part regarded 72 layer and 144 layer mirror configurations, mirrors having any suitable number of constituent layers can be implemented in accordance with many embodiments of the invention. Embodiments of the invention are not limited to specific numbers of constituent layers.
Importantly, while examples of suitable combinations of high refraction index and low refraction index materials have been given, it should be clear that any of a variety of suitable such combinations can be implemented in accordance with many embodiments of the invention. More generally, any suitable structure that can function as a mirror, but that is relatively more transparent (as compared to conventional mirrors such as a 10 μm sheet of Aluminum or a 10 μm sheet of silver) to at least some portion of the radio wave portion of the electromagnetic spectrum or the microwave portion of the electromagnetic spectrum, can be implemented in accordance with embodiments of the invention.
Note that any suitable techniques can be used to fabricate the above-described mirrors. For instance, in many embodiments, sputtering techniques are used to deposit the constituent layers of the described mirrors. For instance, SiO2, Mg F2, AlN, and Ta2O5, may be amenable to sputtering deposition. In many instances, chemical vapor deposition can be used to deposit the constituent layers. For instance, the deposition of diamond may be amenable to chemical vapor deposition techniques. To be clear, the described mirrors can be fabricated using any suitable techniques in accordance with embodiments of the invention, including any suitable deposition techniques. Additionally, the described mirrors can be manufactured to conform to any suitable thickness in accordance with many embodiments of the invention. In many embodiments, the thickness of the mirror is based on the specific requirements of the context that it is to be implemented in. For example, in many embodiments, the thickness of the mirror is between approximately 1 μm and approximately 10 μm. In a number of embodiments where the mirror is to be used in an SBSP System, the thickness of the implemented mirror is approximately 2.5 μm. Additionally, the particular regions of the electromagnetic spectrum that the implemented mirrors are transparent to can be based on the structure of the mirror. Accordingly, in many instances, structures are implemented that enable the mirror to be transparent to predetermined targeted regions of the electromagnetic spectrum. In many instances, configurations are implemented that allow the mirror to be transparent to that region of the electromagnetic spectrum conventionally used to wirelessly transmit power (e.g. the microwave region and/or the radio wave region). Of course, mirrors can be made to be transparent to any appropriate region of the electromagnetic spectrum in accordance with embodiments of the invention.
While the mirrors described above have largely been presented in the context of SBSP Systems, such as those described in U.S. patent application Ser. No. 14/728,985, it should be clear that the described mirrors can be implemented in conjunction with any of a variety of structures, including any of a variety of SBSP Systems. For example, the disclosed structures can be used in conjunction with the systems and methods described in: U.S. provisional patent application Ser. No. 61/993,016 entitled “Large-Scale Space-Based Array: Packaging, Deployment and Stabilization of Lightweight Structures,” filed on May 14, 2014; U.S. provisional patent application Ser. No. 61/993,025 entitled “Large-Scale Space-Based Array: Multi-Scale Modular Space Power System,” filed on May 14, 2014; U.S. provisional patent application Ser. No. 61/993,957 entitled “Large-Scale Space-Based Array: Modular Phased Array Power Transmission,” filed May 15, 2014; U.S. provisional patent application Ser. No. 61/993,037 entitled “Large-Scale Space-Based Array: Space-Based Dynamic Power Distribution System,” filed May 14, 2014; U.S. provisional patent application Ser. No. 62/006,604 entitled “Large-Scale Space-Based Array: Efficient Photovoltaic Structures for Space,” filed Jun. 2, 2014; U.S. provisional patent application Ser. No. 62/120,650 entitled “Large-Scale Space-Based Array: Packaging, Deployment and Stabilization of Lightweight Structures,” filed Feb. 25, 2015; U.S. patent application Ser. No. 14/712,812 entitled “Large-Scale Space-Based Solar Power Station: Packaging, Deployment and Stabilization of Lightweight Structures,” filed May 14, 2015; U.S. patent application Ser. No. 14/712,783 entitled “Large-Scale Space-Based Solar Power Station: Multi-Scale Modular Space Power,” filed May 14, 2015; U.S. patent application Ser. No. 14/712,856 entitled “Large-Scale Space-Based Solar Power Station: Power transmission Using Steerable Beams,” filed May 14, 2015; and U.S. patent application Ser. No. 14/728,985 entitled “Large-Scale Space-Based Solar Power Station: Efficient Generation Tiles,” filed Jun. 2, 2015, all of which are incorporated by reference herein in their entirety.
To be clear, although the implementation of the mirrors that are relatively more transparent to specified regions of the electromagnetic spectrum have been discussed above largely in the context of SBSP Systems, it should be clear that the described mirrors can be implemented on any of a variety of structures, including any of a variety of structures configured for extraterrestrial operation, in accordance with many embodiments of the invention. For instance, they can be implemented in any of a variety of structures, where it may be beneficial to be able to transmit electromagnetic signals through the structure. Nevertheless, suitable space-based solar power generation apparatus that can benefit from the described mirrors are described below.
Suitable Space-Based Solar Power Stations that Can Benefit from the Described Mirrors
A large-scale space-based solar power station that can benefit from the incorporation mirrors that are more transparent to specified regions of the electromagnetic spectrum in accordance with many embodiments can be a modular space-based construct that can be formed from a plurality of independent satellite modules placed into orbit within an orbital formation such that the position of each satellite module relative to each other is known. Each of the satellite modules can include a plurality of power generation tiles that capture solar radiation as electrical current and use the current to transmit the energy to one or more remote receivers using power transmitters. In many instances, the transmissions are generated using microwave power transmitters that are coordinated to act as a phased- and/or amplitude array capable of generating a steerable beam and/or focused beam that can be directed toward one or more remote receivers. In other instances, any of a variety of appropriate power transmission technologies can be utilized including (but not limited to) optical transmitters such as lasers.
In many instances, lightweight space structures used to construct the modular elements of the solar power station can benefit from the incorporation of the described mirrors. Some such lightweight space structures are used in the construction of the power generation tiles and/or satellite modules and may incorporate movable elements that allow the lightweight space structure to be compacted prior to deployment to reduce the area or dimensional length, height and/or width of the power generation tiles and/or satellite modules prior to deployment. The space structures may be made of any number, size and configuration of movable elements, and the elements may be configured to compact according to any suitable compacting mechanism or configuration, including one or two-dimensional compacting using, among others, z-folding, wrapping, rolling, fan-folding, double z-folding, Miura-ori, slip folding, wrapping, and combinations thereof. Some such movable elements are interrelated by hinges, such as, frictionless, latchable, ligament, and slippage hinges, among others. Some structures are pre-stressed and/or provided with supportive frameworks to reduce out-of-plane macro- and micro-deformation of the lightweight structures. Structures and modules may include dynamic stabilizing movement (e.g., spinning) during deployment and/or operation. Deployment mechanisms to deploy the compactible lightweight structures into a deployed operational state may be incorporated into or associated with instances of the lightweight structures. Some deployment mechanisms may include (but are not limited to) expansive boom arms, centrifugal force mechanisms such as tip masses or module self-mass, among others.
Large-scale space-based solar power stations that can benefit from the described mirrors according to many embodiments can utilize a distributed approach to capture solar radiation, and use the energy thus captured to operate power transmitters, which transmit power to one or more remote receivers (e.g., using laser or microwave emissions). The satellite modules of the solar power station can be physically independent structures, each comprising an independent array of power generation tiles. The satellite modules can each be placed into a specified flying formation within an array of such satellite modules in a suitable orbit about the Earth. The position of each of the independent satellite modules in space within the orbital array formation can be controllable via a combination of station-keeping thrusters and controlled forces from absorption, reflection, and emission of electromagnetic radiation, as well as guidance controls. Using such controllers, each of the independent satellite modules may be positioned and maintained within the controlled orbital array formation relative to each of the other satellite modules so that each satellite module forms an independent modular element of the large-scale space-based solar power station. The solar radiation received by each of the power generation tiles of each of the independent satellite module can be utilized to generate electricity, which can power one or more power transmitters on each of the power generation tiles. Collectively, the power transmitters on each of the power generation tiles can be configured as independent elements of a phased and/or amplitude-array.
The power generation tiles and/or satellite modules may also include separate electronics to process and exchange timing and control information with other power generation tiles and/or satellite modules within the large-scale space-based solar power station. In many implementations, the separate electronics form part of an integrated circuit that possesses the ability to independently determine a phase offset to apply to a reference signal based upon the position of an individual tile and/or transmitter element. In this way, coordination of a phased array of antennas can be achieved in a distributed manner.
In some instances of the distributive approach, different array elements of the phased array may be directed to transmit power with different transmission characteristics (e.g., phase) to one or more different remote power receiving collectors (e.g., ground based rectenna). Each satellite module of power generation tiles, or combinations of power generating tiles across one or more satellite modules, may thus be controlled to transmit energy to a different power receiving collector using the independent control circuitry and associated power transmitters.
A photovoltaic cell (PV) refers to an individual solar power collecting element on a power generation tile in a satellite module. The PV includes any electrical device that converts the energy of light directly into electricity by the photovoltaic effect including elements made from polysilicon and monocrystalline silicon, thin film solar cells that include amorphous silicon, CdTe and CIGS cells, multijunction cells, perovskite cells, organic/polymer cells, and various alternatives thereof.
A power transmitter or radiator refers to an individual radiative element on a power generation tile in a satellite module and its associated control circuitry. A power transmitter can include any device capable of converting power in the electrical current generated by the PV to a wireless signal, such as microwave radiation or light, including (but not limited to) a laser, a klystron, a traveling-wave tube, a gyrotron, or suitable transistor and/or diode. A power transmitter may also include suitable transmissive antennas, such as, dipole, patch, helical or spherical antennas, among others.
A phased array refers to an array of power transmitters in which the relative phases of the respective signals feeding the power transmitters are configured such that the effective radiation pattern of the power emission of the array is reinforced in a desired emission direction and suppressed in undesired directions. Phased arrays may be dynamic or fixed, active or passive.
An orbital array formation refers to any size, number or configuration of independent satellite modules being flown in formation at a desired orbit in space such that the position of the satellite modules relative to each other is known such that power generation tiles on each of the satellite modules within the formation serves as an array element in the phased array of the solar power station.
A power generation tile refers to an individual solar power collecting and transmitting element in the phased array of the large-scale space-based solar power station. In many instances a power generation tile is a modular solar radiation collector, converter and transmitter that collects solar radiation through at least one photovoltaic cell disposed on the tile, and uses the electrical current to provide power to at least one power transmitter collocated on the same tile that transmits the converted power to one or more remote power receiving collectors. Many of the power generation tiles incorporated within a space-based solar power station include separate control electronics independently control the operation of the at least one power transmitter located on the power generation tile based upon timing, position, and/or control information that may be received from other tiles and/or other modules within the large-scale space-based solar power station. In this way, the separate control electronics can coordinate (in a distributed manner) the transmission characteristics of each of the power generation tiles form a phased array. Each power generation tile may also include other structures such as radiation collectors for focusing solar radiation on the photovoltaic, thermal radiators for regulating the temperature of the power generation tile, and radiation shielding, among other structures.
A satellite module refers to an array of power generation tiles collocated on a single integral space structure. The space structure of the satellite module may be a compactable structure such that the area occupied by the structure may be expanded or contracted depending on the configuration assumed. The satellite modules may include two or more power generation tiles. Each power generation tile may include at least one solar radiation collector and power transmitter. As discussed above, each of the power generation tiles may transmit power and may be independently controlled to form an array element of one or more phased arrays formed across the individual satellite module or several such satellite modules collectively. Alternatively, each of the power generation tiles collocated on a satellite module may be controlled centrally.
A lightweight space structure refers to integral structures of movably interrelated elements used in the construction of the power generation tiles and/or satellite modules that may be configurable between at least packaged and deployed positions wherein the area and or dimensions of the power generation tiles and/or satellite modules may be reduced or enlarged in at least one direction. The lightweight space structures may incorporate or be used in conjunction with deployment mechanisms providing a deploying force for urging the movable elements between deployed and compacted configurations.
A large-scale space-based solar power station or simply solar power station refers to a collection of satellite modules being flown in an orbital array formation designed to function as one or more phased arrays. The one or more phased arrays may be operated to direct the collected solar radiation to one or more power receiving collectors.
Transmission characteristics of a power generation tile refer to any characteristics or parameters of the power transmitter of the power generation tile associated with transmitting the collected solar radiation to a power receiving collector via a far-field emission. The transmission characteristics may include, among others, the phase and operational timing of the power transmitter and the amount of power transmitted.
Structure of Large-Scale Space-Based Solar Power Station that Can Benefit from the Incorporation of the Described Mirrors
A large-scale space-based solar power station including a plurality of satellite modules positioned in an orbital array formation in a geosynchronous orbit about the Earth that can benefit from the incorporation of the described mirrors in accordance with certain embodiments of the invention is illustrated in
In some instances, the satellite modules in the solar power station are spatially separated from each other by a predetermined distance. By increasing the spatial separation, the maneuverability of the modules in relation to each other is simplified. As discussed further below, the separation and relative orientation of the satellite modules can impact the ability of the power generation tile on each of the satellite modules to operate as elements within a phased array. In one instance, each satellite module 1A through NM may include its own station keeping and/or maneuvering propulsion system, guidance control, and related circuitry. Specifically, as illustrated in
In many instances, as illustrated in
Power generation tiles 112 in many instances include a multicomponent structure including a photovoltaic cell 113, a power transmitter 114, and accompanying control electronics 115 electrically interconnected as required to suit the needs of the power transmission application. As illustrated in
In some instances, the PV 113 is a multi-layer cell, as illustrated in
In a number of instances, the power transmitters that are components of power generation tiles are implemented using a combination of control circuitry and one or more antennas. The control circuitry can provide the power generation tile with the computational capacity to determine the location of the power generation tile antenna(s) relative to other antennas within the satellite module and/or the solar power station. As can readily be appreciated, the relative phase of each element within a phased array is determined based upon the location of the element and a desired beam direction and/or focal point location. The control circuitry on each power generation tile can determine an appropriate phased offset to apply to a reference signal using a determined location of the power generation tile antenna(s) and beam-steering information. In certain instances, the control circuitry receives position information for the satellite module and utilizes the position information to determine the location of the power generation tile antenna(s) and determine a phase offset to apply to a reference signal. In other instances, a central processor within a satellite module can determine the locations of antennas on power generation tiles and/or phase offsets to apply and provides the location and/or phase offset information to individual power generation tiles.
In many instances, the positional information of each tile is received from partially redundant systems, such as, but not limited to, gyroscopes, accelerometers, electronic ranging radar, electronic positioning systems, phase and/or timing information from beacons, as well as employing a priori knowledge from system steering and flight control commands. In several instances, electronic systems are located on the ground, and/or in space on satellites deployed for this purpose (and, possibly, other purposes, e.g. in the case of using GPS satellites).
In a number of instances, position information may be relayed in a hierarchical fashion between modules, panels and/or tiles within the space-based solar power station, such that a central processing unit relays positional information such as location and orientation of the entire space-based solar power station with respect to a ground station and/or other suitable known locations to modules within the system. The relayed information can be expressed as an absolute and/or differential location(s), and/or orientation(s) as appropriate to the requirements of specific applications. In a similar fashion, the location and/or orientation of each module with respect to the center of the space-based solar power station or other suitable reference point can be determined at each module using processes similar to those outlined above. Furthermore, going down a hierarchical level, the position and orientation information of individual panels and tiles can be determined in a similar fashion. The entirety or any useful part of this information can be used at the tile-level, the panel-level, the module-level, the system-level and/or any combination thereof to control the phase and/or amplitude of each tile radiator to form a beam or focal spot on the ground. The aggregate computational power of the computational resources of each tile, panel and/or module can be utilized since each tile (and/or panel or module) can utilize its local computational power available from a DSP, microcontroller or other suitable computational resource to control its operation such that the system in aggregate generates the desired or close-to desired beam and/or focused transmission.
In various instances, as illustrated conceptually in
Although specific integrated circuit implementations are described above with reference to
In many instances, as illustrated conceptually in
In one instance, the power generation tiles and/or satellite modules may include other related circuitry. The other circuitry may include, among others, circuitry to control transmission characteristics of the power generation tiles, thermal management, inter or intra-module communications, and sensors to sense physical parameters, such as orientation, position, etc. The control circuitry may control transmission parameters such as phase and timing information such that the arrays of power generation tiles across each module and across the solar power station may be operated as independent array elements of one or more phased arrays. The sensors may include gyroscopes, GPS or IGS devices to estimate position and orientation, and thermocouples to estimate the temperature on the power generation tiles.
In one instance, the circuits for controlling transmission characteristic parameters may be collocated on the several power generation tiles or satellite modules and may control each transmitter of each power generation tile independently or in a synchronized manner such that the tiles operate as one or more element of one or more phased arrays. Reference signals (e.g., phase and timing) that can be used to synchronize the operation of the power generation tiles as a phased array may be generated locally on each power generation tile or satellite module and propagated via wired or wireless intra and inter-module communications links, or may be generated centrally from a single source on a single satellite module and propagated via wired or wireless intra and/or inter-module communications links across each of the satellite modules and power generation tiles. In addition, one or multiple timing reference signals may be generated from outside the space-based solar power station system such as one or more satellites flying in close proximity or even in different orbits; as well as from one or more ground stations.
Each power generation tile or satellite module may be operated independently or collectively as an element in a phased array. Entire or most operations associated with each individual power generation tile may be collocated on each of the power generation tiles or collectivized within the satellite module on which the power generation tiles are collocated, or across multiple satellite modules. In one instance, a central reference signal is generated and deviation (e.g., phase) from such reference signal is determined for each power generation tile array element of the phased array. By propagating a central reference signal from the reference signal, higher levels of control abstraction can be achieved to facilitate simpler programming for many operations of the phased array.
In some instances, each power generation tile of each satellite module may be the same or different. The number of distinct combinations of photovoltaic cells, transmission modules and control electronics may be as large as the number of power generation tiles in the satellite modules. Further, even where each of the power generation tiles on a satellite module are the same, each of the satellite modules 1A through NM or a group of satellite modules may have different solar radiation collection or transmission characteristics or may have arrays of power generation tiles of different sizes, shapes and configurations.
In certain instances, the solar power station is designed as a modular phased array where the plurality of satellite modules and power generating tiles located thereon form the array elements of the phased array. For this purpose, each of the satellite modules may be designed to be physically compatible with conventional launch vehicles although the achieved power generation of the phased array of the solar power station may exceed conventional space-based solar power satellites in many respects. Taking advantage of the increased performance, the solar power station phased array in this case may include smaller payload size and overall array size to obtain equal or better power generation compared to conventional space-based solar power satellites. Alternatively, the size of the overall solar power station may be reduced compared to solar platforms in conventional solar power satellites while achieving comparable results.
In order to match the power generation of a conventional solar power satellite without increasing platform size or weight, the power collection, transmission and control logic for the individual power generation tiles is preferably collocated within each of the power generation tiles or within the satellite module on which the power generation tiles are collocated thus eliminating the need for intra- or inter-module communications, wiring or structural interconnection. In one instance, much of the power transmission control logic is a single collection of functions common to all or most of the power generating tiles. In this instance, the conventional external intra- and inter-power generation tile infrastructure for the solar power station may be entirely eliminated thus reducing the power generated per weight unit (W/kg).
In one instance, the phased array of the solar power station including the satellite modules and power generation tiles replaces a conventional monolithic solar power satellite. The solar power stations includes N×N satellite modules, each module including power generation tiles of
Table 3 lists example configurations of solar power stations.
The Conventional SPS performance in Table 3 are taken from published literature. The Exemplary Phased Array System Performance in Table 3 are estimates and may differ based on the actual design parameters implemented.
The number of power generation tile array elements in each satellite module, and the number of satellite modules in the solar power station may be determined based on, among other factors, power requirements, payload restrictions, etc. A first factor for the size of an overall solar power station is the power to be generated at the power receiving rectenna. As illustrated in
In certain instances this limitation many also be overcome by dividing the power transmission output 176 of the solar power station 174 between different rectenna power receivers 178, as illustrated conceptually in
A second factor that may constrain the number of array elements in any satellite module is the issue of payload size and weight. Current payload delivery technologies for geosynchronous orbits range from 2,000 to 20,000 kg. Accordingly, the limit to the size of any single satellite module is the actual lift capacity of available payload delivery vehicles. Based on an assumption of 100 g/m2 for the phased array satellite modules, a 60×60m satellite module would have a weight of 360 kg, well within the limits of current delivery technologies. Larger modules could be produced provided they are within the lift capacity of available lift vehicles.
In some instances, satellite modules are compactable such that the size of the satellite module in one or more dimensions may be reduced during delivery to overcome payload space constraints and then expanded into its final operating configuration. As illustrated in
In many instances the power generation tiles may have further compactible and expandable features and structures disposed thereon. In some instances of power generation tiles the photovoltaic cell and power transmitter may be movably interrelated through a compactable structure, such that when in a compacted or packaged configuration the elements of the power generating cell are compressed together to occupy a total volume lower than when in a deployed configuration. In some deployed configurations the photovoltaic cell and power transmitter are separated by a gap (e.g., to create a vertical offset therebetween). Certain instances having a compactable structure include motorized interconnections and resilient members such as spring or tension arms that are bent or under compression, among others. Such compactable structures may also incorporate packaging techniques such as one or a combination of z-folding, wrapping, rolling, fan-folding, double z-folding, Miura-ori, slip folding and symmetric wrapping may be used, among others.
The power generation tiles and/or satellite modules may include other structures to enhance the collection of solar radiation or transmission of power from the power generation tiles and/or satellite modules. Structures that may be incorporated into power generation tiles and/or satellite modules may include, among others, thermal radiators for controlling the thermal profile of the power generation tiles, light-collecting structures (e.g., radiators, reflectors and collectors) to enhance the efficiency of solar radiation collection to the photovoltaic cell, and radiation shielding to protect the photovoltaic cells, power transmitters and/or control electronics from space radiation. Such structures may also be independently compactible, between packaged and deployed configurations, as described above in relation to other elements of the power generation tiles.
A design for a satellite module or power generation tile may be applied to different satellite modules or power generation tiles. Other variables in the solar power station such as spatial distances, photovoltaics, power transmitter, control electronics and combinations with may be modified to produce a phased array with differing power collection and transmission characteristics. In this way, a diverse mix of solar power stations may be produced while maintaining the benefits of the modular solar power station described.
Compactable Space Structures that Can Benefit from the Incorporation of the Described Mirrors
In many instances, the satellite modules of the solar power station employ compactible structures which can benefit from the incorporation of mirrors in accordance with certain embodiments of the invention. Compactable structures allow for the satellite modules and/or power generation tiles to be packaged in a compacted form such that the volume occupied by the satellite module and/or power generation tiles can be reduced along at least dimension to allow for the satellite modules to fit within an assigned payload envelope within a delivery vehicle. Several exemplary instances of possible packaging schemes are provided, however, it should be understood that the packaging procedure and compactible structures may involve, among other procedures, using one and two-dimensional compaction techniques, including, one or a combination of z-folding, wrapping, rolling, fan-folding, double z-folding, Miura-ori, star folding, slip folding and wrapping.
In many instances a two-dimensional compacting technique may be utilized to package and deploy the satellite modules and/or power generation tiles.
In many instances a slip-wrapping compacting technique may be utilized to package and deploy the satellite modules and/or power generation tiles.
Some instances of a slip-wrap packing technique as applied to a compactible satellite module 350 are shown in a perspective view in
Using such techniques it is possible to significantly reduce the packaging volume of the satellite modules. In one exemplary instance where the compactible structures of a satellite module have a tile/panel thickness of 1 cm and a minimum bend radius of 10 cm, a satellite module with a deployed area of 60 m×60 m and being comprised of 30 such compactible structures would be compactible using the slip-wrap packaging technique into cylindrical package with a diameter of 5 m and a height of 2 m.
In many instances, the number of compactible elements in each of the satellite modules in a solar space station may be the same or different and may contain one or more power generation tiles collocated thereon. One or more compacting techniques may be used in packaging the compactible elements of each of the satellite modules and the techniques use may also the same or different. In many instances the compacting techniques utilized to package the satellite modules prior to deployment reduce the packaging volume of the satellite module in at least one dimension such that the satellite module fits within the allowed payload volume of the selected delivery vehicle.
In many instances, the power generation tiles may have further compactible and expandable features and structures disposed thereon. In some instances, power generation tiles, the photovoltaic cell, and power transmitter may be movably interrelated through a compactable structure, such that when in a compacted or packaged configuration the elements of the power generation tile are compressed together to occupy a total volume lower than when in a deployed configuration. In some deployed configurations the photovoltaic cell and power transmitter are separated by a gap (e.g., to create a vertical offset therebetween). Some instances of compactable structure include motorized interconnections and resilient members such as spring or tension arms that are bent or under compression, among others. Such compactable structures may also incorporate packaging techniques such as one or a combination of z-folding, wrapping, rolling, fan-folding, double z-folding, Miura-ori, slip folding and symmetric wrapping may be used, among others.
In many instances, deployment mechanisms are provided to deploy the compacted satellite modules (e.g., move the compactible elements of the satellite module from a compacted to a deployed configuration). In many instances, an active or passive mechanism is interconnected with one or more portions of the compactible structures of the satellite module such that when activated the compacted structures of the satellite modules may be expanded into a deployed operational configuration.
In some instances, a mechanically expandable member may be incorporated into the satellite module. An illustration of such a satellite module is provided in
In many instances the compactible structures of the satellite module may be configured such that motion of the satellite module provides the expansive deployable force. An illustration of one such instance is provided in
Regardless of the mechanism chosen, in many instances, the satellite module may be divided into any number and configuration of separate compactible structures with any number of hubs and deployment mechanisms (e.g., expandable members, weighted elements, etc.). In many instances, the compactible structures are attached along at least two edges to more than one deployment mechanism such that more even expansion of the compactible structures may be obtained. In many instances, for example, multiple weights or expandable members may be attached to each of the compactible structures along multiple points or edges of the compactible structures. Some expandable members or weighted elements may be incorporated into the structure of the compactible structures. Many instances of deployment mechanisms may include deployment controls to controllably operate the compactible structures of the satellite modules so that the satellite modules are expanded into a deployed configuration when desired. Some instances of such deployment controls may be automated, such that the positioning or motion of the satellite hub automatically engages the deployment mechanism, such as, for example, by spinning the satellite module at a specified rate. Other instances may incorporate control circuits such that an external signal or command is required to activate the deployment mechanism. Such deployment controls may operate across an entire satellite module, may be disposed individually in each power generation tile, or a combination thereof.
In many instances, particularly efficient power generation tiles are implemented within Space-based Solar Power Stations that can benefit from incorporating the above-described mirrors. The implementation of such power generation tiles within the described SBSP systems can make them more practicable insofar as they can offer greater power generation per unit mass. As can be appreciated, power generation tiles having a reduced mass can be advantageous for at least two reasons: (1) they can allow for reduced launch costs—i.e. a reduced payload can be cheaper to send into outer space; and (2) they can enable easier maneuverability of corresponding satellite modules. Against this backdrop, in many instances, thin film, pliable, photovoltaic materials that create an electrical current from solar radiation are implemented; the thin film photovoltaic materials can be used in conjunction with lightweight substrates for structural support. As can be appreciated, a photovoltaic material can be understood to be a contiguous material having a structure whereby the receipt of incident light (photons) excites electrons to a conduction band to a useful extent, and thereby allows for the creation of a useful electrical current. In a number of instances, concentrators are implemented that redirect solar radiation toward an associated photovoltaic material, such that the photovoltaic material can experience greater solar flux relative to the case where no concentrators are used. As can be appreciated, the amount of electrical current that a corresponding PV cell is able to produce is directly related to the incident solar radiation (accounting for its concentration/flux). In this way, for a given target power generation value, the utilization of concentrators can allow the amount of photovoltaic materials used, along with respective attendant radiative shielding (which can be relatively massive), to be reduced. In several instances, configurations are implemented that facilitate the radiative cooling of the photovoltaic materials, which can allow them to generate power more efficiently. For example, in many embodiments, structures that are sized approximately on the order of wavelengths of thermally radiated light and are otherwise configured to effectively increase the emissivity of the of power generation tiles, and thereby contribute to the radiative cooling of the photovoltaic materials, are implemented.
In many instances, a thin film photovoltaic material is implemented, such as those used in a typical III-V solar cell, to produce electrical current from incident solar radiation. Thus, for instance, in many instances, a Gallium Arsenide thin film photovoltaic material is implemented, such as those developed by ALTADEVICES.
Notably, in many instances when photovoltaic materials are implemented in outer space, they are typically accompanied by radiation shields that protect them from deleterious radiation. The radiation shields are typically in the form of cover glass, which can be relatively massive. To provide context,
Moreover, in many instances power generation tile configurations are implemented that facilitate the cooling of the photovoltaic materials, e.g. by using microstructures. The use of microstructures to facilitate the cooling of photovoltaic materials is discussed in U.S. Pat. App. No. 62/269,901, the disclosure of which is hereby incorporated by reference in its entirety. As can be appreciated, photovoltaic materials can heat up extensively during operation, and heat can adversely impact a photovoltaic material's ability to produce electrical current. To provide context, an energy balance for a sample solar cell in operation is depicted in
In many instances, configurations are implemented that provide improved power generation per unit mass. For instance, in many instances concentrators are implemented that concentrate solar radiation onto a corresponding photovoltaic material such that the photovoltaic material experiences greater solar flux relative to if the photovoltaic material were subjected to unaltered solar radiation. As can be appreciated a photovoltaic material's ability to generate electrical current is related to the amount of incident solar radiation/flux. Note that concentrators can be made to be less massive than the combined mass of conventional PV Cells including radiation shielding. Accordingly, the incorporation of concentrators can reduce the amount of photovoltaic material for a given desired power generation value, and can correspondingly reduce the amount of radiation shielding implemented.
As already alluded to above, the concentrators can take any suitable form in accordance with many instances. For example, in many instances, concentrators are implemented in the form of mirrors, as already discussed above.
Importantly, concentrators can be implemented in any of a variety of geometric configurations. For example, in many instances, Cassegrain configurations are implemented; Cassegrain configurations are typically characterized by primary and secondary reflectors that redirect solar radiation onto a photovoltaic material (typically disposed on the primary reflector). Typically, a primary reflector redirects incident solar radiation onto a secondary reflector, which subsequently redirects incident solar radiation onto a photovoltaic material. Note that a reflector can be understood to be that portion of a concentrator which directly reflects incident solar radiation. For example,
Note that the reflectors implemented in Cassegrain structures can incorporate any of a variety of complementary shapes to redirect—and focus—solar radiation onto a photovoltaic material. For example, in many instances, a primary reflector conforming to a parabolic shape is implemented, while a corresponding secondary reflector that conforms to a hyperbolic shape is implemented. Moreover, the particular characteristics of the parabolic and hyperbolic shapes can be adjusted based on the requirements of a particular application. For instance, the parabolic and hyperbolic shapes can be made to be wider or narrower based on desired design criteria. To be clear though, any suitable pairing of reflector shapes that redirect solar radiation onto a photovoltaic material can be implemented, and not just those conforming to parabolic/hyperbolic shapes.
Cassegrain structures, such as those illustrated in
While Cassegrain structures can exhibit advantageous thermal properties, they can be sensitive to solar radiation angle of incidence. For example, the secondary reflector can cast a shadow and thereby hinder solar flux received by the primary reflector, and eventually the photovoltaic material. Additionally, because of the somewhat sophisticated geometry, some angles at which solar radiation reaches the corresponding power generation tile may not be received. Moreover, because Cassegrain structures employ two reflectors, they are subject to more reflection loss relative to configurations that employ only a single reflector.
While Cassegrain structures have been discussed, it should be clear that any of a variety of concentrator configurations can be implemented. For example, in many instances, ‘Parabolic Trough’ configurations are implemented. Parabolic Trough configurations are similar to the Cassegrain structures discussed above, except that they do not include a secondary reflector; rather the primary reflector is used to redirect solar radiation onto an opposingly disposed photovoltaic material. For example,
While the reflector can conform to any shape that redirects solar radiation to a photovoltaic material, it can be advantageous if it conforms to a parabolic shape so as to efficiently focus solar radiation onto the opposingly disposed photovoltaic material. Additionally, as can be appreciated from the discussion above, the configurations can be implemented using any of a variety of materials. For example, in many instances, the concentrator is implemented using a reflective surface, in conjunction with a lightweight substrate. Additionally, the photovoltaic material can be any suitable material, such as—but not limited to—thin film photovoltaics produced by ALTADEVICES.
Parabolic Trough configurations can be advantageous relative to Cassegrain structures in that, since they only employ a single reflector (as opposed to two reflectors), they are subject to less reflective loss relative to Cassegrain structures that implement two reflectors. However, as the photovoltaic material is not typically directly coupled to a large surface area such as the primary reflector (as in the case of a Cassegrain structure), Parabolic Trough configurations may not be as efficient at radiative heat transfer.
In many instances, a ‘Venetian Blinds’ configuration is implemented, whereby concentrators redirect solar radiation towards photovoltaic materials that are disposed on the backside of adjacently disposed concentrators.
Venetian Blinds configurations can be constructed using any of a variety of materials and techniques. For example, in several instances, Venetian Blinds configurations are implemented using polyimide films in conjunction with carbon springs, and reflectors.
To provide context,
Venetian Blinds configurations can be advantageous insofar as each of the concentrators can act as a heat sink for a coupled photovoltaic material, thereby facilitating conductive and radiative cooling, and consequently a more efficient operation. Additionally, in contrast to the Cassegrain configuration, only a single reflector is used in redirecting solar radiation onto a photovoltaic material. As alluded to above, using a single reflector can reduce the potential energy loss relative to configurations that incorporate a plurality of reflectors. In many instances, optical efficiencies of greater than 90% can be realized using Venetian Blind configurations. Moreover, such configurations can result in concentrations of between approximately 10× to approximately 40× or more.
As noted above, the number of junctions within a photovoltaic material also influences the power generation efficiency. Interestingly,
In many instances, the contacts used by PV Cells are integrated so as to facilitate the efficiency of the power generation tile. For instance, in many instances, conductive structures that already exist within a power generation tile are used as the conductive contacts of constituent PV Cells. In this way, the conductive structures are made to be dual purpose. For example, in many instances, a Venetian Blinds configuration is implemented that includes a conductive reflector as well as carbon springs for structural support, and the conductive reflector and/or the carbon springs are used as the electrical contacts for the PV Cell. This can be achieved in any of a variety of ways.
For instance,
In many instances, a reflector is used to implement the contacts for a PV cell. For example,
In numerous instances, carbon springs within a power generation tile act as the contacts for a PV cell. For example,
To provide context,
While the above descriptions have largely regarded suitable Space-based Solar Power Systems that can benefit from the incorporation of the described mirrors, it should be clear that the previously described mirrors can be implemented in any of a variety of apparatus. Additionally, while specific mirror structures have been discussed, mirrors can be incorporated in any of a variety of ways in accordance w/many embodiments of the invention. More generally, while particular embodiments and applications of the present invention have been illustrated and described herein, it is to be understood that the invention is not limited to the precise construction and components disclosed herein and that various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatuses of the present invention without departing from the spirit and scope of the invention as it is defined in the appended claims.
The current application claims priority to: U.S. Provisional Application No. 62/195,605, filed Jul. 22, 2015; U.S. Provisional Application No. 62/203,159, filed Aug. 10, 2015; U.S. Provisional Application No. 62/220,017, filed Sep. 17, 2015; U.S. Provisional Application No. 62/239,706, filed Oct. 9, 2015; and U.S. Provisional Application No. 62/290,145, filed Feb. 2, 2016, the disclosures of which are hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62195605 | Jul 2015 | US | |
| 62203159 | Aug 2015 | US | |
| 62220017 | Sep 2015 | US | |
| 62239706 | Oct 2015 | US | |
| 62290145 | Feb 2016 | US |
