Patent Publication Number: US-2011070635-A1

Title: Systems and methods of generating energy and fresh water from solar radiation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 12/849,761, filed Aug. 3, 2010, which is incorporated by reference herein in its entirety and which claims priority to U.S. Patent Application Ser. Nos. 61/231,081, filed Aug. 4, 2009, 61/233,667, filed Aug. 13, 2009, and 61/244,349, filed Sep. 21, 2009, each of which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to solar energy systems. 
     BACKGROUND OF THE DISCLOSURE 
     There has been a long-standing need to provide energy generation from renewable sources. Various renewable energy sources have been pursued, such as solar energy, wind, geothermal, and biomass for biofuels as well as others. There also exists an ever-increasing need for cost effective fresh water production systems to keep pace with the fresh water needs of an ever-increasing population. Various approaches have been tried such as flash-distillation, reverse osmosis membranes, solar stills, among others, but none has produced water at high volumes and low cost. 
     Solar radiation has long been a prime candidate for fulfilling the need for low cost renewable energy. Various approaches have been taken to achieve energy generation from solar radiation. To that end, much focus has been directed to creating a low cost solar energy conversion system that functions with high efficiency and requires little maintenance. 
     For example, solar panels formed of photovoltaic cells (solar cells) are used to transform light to electricity. Such systems have been implemented in various applications. Solar panels have been generally effective for small-scale electrical generation, such as powering small electronics, electrical generation for residential applications, and electrical generation for space-based systems. However, current solar panel technology has been ineffective for large-scale uses, such as electrical generation sufficient for municipal applications. The costs associated with such large-scale usages have been prohibitive. Current solar panels are relatively expensive and do not allow cost-effective energy storage. 
     Other approaches include concentrating solar radiation on solar collectors for energy generation, commonly referred to as concentrated solar power (CSP). CSP systems typically use reflective surfaces to concentrate the sun&#39;s energy from a large surface area on to a solar collector. For example, the concentrated solar energy can be used to heat a working fluid. The heated fluid is then used to power a turbine to generate electricity. Alternatively, photovoltaic cells can be used at the solar collector, eliminating the need for numerous, expensive cells. In an effort to maximize efficiency, the reflective surfaces of CSP systems can be coupled to a device that tracks the sun&#39;s movement, maintaining a focus on a receiver target throughout the day. Using this approach, the CSP system can optimize the level of solar radiation directed towards the solar collector. 
     Although such CSP systems are better than traditional flat-panel photovoltaic cells for large-scale applications, shortfalls exist. For example, glass and metal reflector assemblies are expensive to manufacture, ship and install. Further, current tracking devices used with CSP can be relatively expensive and complicated. As a result, current approaches have yet to achieve significant market penetration because of cost issues. 
     Biomass production, such as algae and other microorganisms, has increasingly been of interest. The potential usage of such material is found across a wide range of applications, including biofuel feedstock production, fertilizer, nutritional supplements, pollution control, and other uses. 
     Current approaches for biomass production include “closed-air” systems that contain biomass production within a controlled environment, limiting exposure to outside air. Examples of such systems include closed photo-bioreactor structures forming a closed container for housing a culture medium for generating biomass. Having a controlled environment helps maximize the generation of algal material by limiting exposure to invasive species as well as controlling other environmental factors that promote algal growth. Closed-air systems significantly reduce evaporation and therefore significantly reduce demands on water resources. In addition, closed-air systems facilitate the sequestration of carbon dioxide gas, which promotes algal growth, facilities compliance with environmental regulations, and, according to a large number of scientists, benefits the environment generally. However, such systems can be expensive and, in many instances, cost prohibitive. 
     Current approaches for desalination include multi-stage flash distillation, which accounts for the majority of desalinated water production worldwide, and reverse osmosis which accounts for a significant minority of desalinated water production. Multi-stage flash distillation involves boiling salt water in successive stages to collect fresh water, and reverse osmosis systems involve high pressure pumping of salt water across expensive membrane systems that prevent salt from passing through. Both methods are energy and capital intensive, prohibiting wide spread adoption. Another method for low-cost, low volume applications is use of a solar still. In a solar still, impure water is contained outside a collector, where it is evaporated by sunlight shining through clear plastic. The pure water vapor condenses on the cool inside plastic surface and drips down off of the weighted low point, where it is collected and removed. 
     It should be appreciated that there remains a need for a system and method of generating energy from solar radiation in a low-cost, large-scale manner. There also exists a need for a closed-air photo-bioreactor to promote algal growth in a low-cost, large-scale manner. There further exists a need for a large-scale, low-cost method to desalinate saline water. The present disclosure fulfills these needs and others. 
     SUMMARY OF THE DISCLOSURE 
     In general terms, the present disclosure provides a solar reflector assembly useable for generating energy from solar radiation. Embodiments of the solar reflector assemblies are inflatable elongated tubes of flexible material with each tube including a reflective sheet to reflect solar radiation to a solar collector. This structure and the materials employed provide significant cost savings for manufacture, shipping and deployment of the solar reflector assemblies. The solar reflector assembly is configured to be deployed on a supporting body of liquid. This provides both liquid ballasting capability and structural support. Beneficially, the solar reflector assemblies are inexpensive to manufacture, deploy and operate, providing a cost effective solution for energy generation. 
     Exemplary embodiments of a solar reflector assembly includes an inflatable elongated tube having an upper portion formed at least partially of a flexible material and a lower ballast portion formed at least partially of a flexible material. The lower ballast portion may define a reservoir containing fluid facilitating ballast. The elongated tube has an axis of rotation oriented generally parallel to a surface of a supporting body of liquid and a reflective sheet coupled to a wall of the tube to reflect solar radiation towards the solar collector. The reflective sheet may be coupled to either an interior wall or an exterior wall of the elongated tube. The fluid facilitating ballast has a top surface that is generally parallel to a surface of a supporting body of liquid. 
     In exemplary embodiments, the reflective sheet can be configured to reflect substantially all solar radiation towards the solar collector. In another exemplary embodiment, the reflective sheet can be configured to substantially reflect a first prescribed wavelength range towards a solar collector and to substantially transmit a second prescribed wavelength range therethrough. In the case of an interior reflective sheet, the reflective sheet may also facilitate equilibrium of pressure on its opposing sides. One end cap assembly may be coupled to the elongated tube, or a pair of end cap assemblies can be coupled to the elongated tube, in which at least one of the end cap assemblies is configured to facilitate the flow of gas and/or liquid into and out of the elongated tube to maintain pressure within the tube. The upper portion formed of thin-gauge, flexible material allows solar radiation to pass through for reflection by the reflective sheet. 
     Inflatable supports can be disposed on the exterior wall of the tube to maintain the reflective sheet in a prescribed orientation. For example, the reflective sheet can be disposed to have various cross sectional shapes, including flat, v-shaped, u-shaped, or parabolic, among others, as desired. A pair of supports can be used, coupled to longitudinal sides of the reflective sheet. 
     In a detailed aspect of an exemplary embodiment, the reflective sheet is formed as a hot mirror, configured to reflect infrared (IR) radiation (e.g., heat reflective) while allowing visible light to pass through (e.g., visibly transparent), across wide angles of incidence. For example, the reflective sheet allows transmittance of at least 50 percent of incident energy in the wavelength band between about 400 nm and 700 nm at normal incidence. In a detailed aspect of an exemplary embodiment, the reflective sheet allows transmittance of at least 90 percent of incident energy in the wavelength band between about 400 nm and 700 nm at normal incidence. 
     In another detailed aspect of selected exemplary embodiments, the reflective sheet can have a high percentage of reflection for substantially all incident solar IR radiation above about 700 nm or, in other embodiments, above about 750 nm. In yet other embodiments, the reflective sheet can be configured to have a high percentage of reflection within a bounded range of IR wavelengths. Exemplary ranges include 700-1200 nm, 700-2000 nm, 750-1200 nm, and 750-2000 nm, among others. It should be appreciated that other ranges can be used. 
     More particularly, by example and not limitation, a system for generating energy from solar radiation is provided, comprising a pool housing a supporting body of liquid and one or more solar reflector assemblies disposed on the supporting body of liquid. Each solar reflector assembly includes an inflatable elongated tube having an upper portion formed at least partially of flexible material, a lower ballast portion formed at least partially of flexible material and an axis of rotation oriented generally parallel to a surface of the supporting body of liquid, and a reflective sheet coupled to a wall of the tube to reflect solar radiation towards a solar collector. The reflective sheet may be coupled to an interior wall of the elongated tube such that the upper portion and the lower ballast portion are separated by the reflective sheet. Alternatively, the reflective sheet may be coupled to an exterior wall of the elongated tube. 
     The reflective sheet may be coupled to the elongated tube in a manner to provide a pressure differential between opposing sides of the reflective sheet such that the reflective sheet can be given a prescribed shape to facilitate reflection of solar radiation towards the solar collector. The solar reflector assembly may facilitate equilibrium of pressure on opposing sides of the reflective, sheet. The lower ballast portion of the elongated tube contains liquid facilitating ballast. The liquid facilitating ballast has a top surface that is generally parallel to the surface of the supporting body of liquid. The system further includes a solar collector positioned to receive reflected solar radiation from the reflective sheet. 
     Embodiments of the system for generating energy from solar radiation may further comprise an electrical generator assembly operatively coupled to the solar collector to convert the reflected solar radiation to electricity. At least one end cap assembly can be coupled to an elongated tube, and a pair of end cap assemblies can be coupled to opposing ends of the one or more elongated tubes, in which at least one of the end cap assemblies is configured to facilitate the flow of gas and/or liquid into and out of the elongated tube to maintain pressure within the tube. A rotation assembly may be coupled to an elongated tube at any location on the tube. In exemplary embodiments, a rotation assembly is coupled to at least one of the end cap assemblies to induce controlled rotation of the elongated tubes to direct the reflected solar radiation to the solar collector. 
     In an exemplary embodiment, the reflective sheet is coupled to the elongated tube in a manner to provide a pressure differential between opposing sides of the reflective sheet such that the reflective sheet can be given a prescribed shape to facilitate reflection of solar radiation towards the solar collector. Alternatively, the reflective sheet can be configured to be taut when the elongated tube is inflated to form a generally planar shape. In yet another embodiment, the reflective sheet can be configured to hang between spaced-apart portions of the internal wall of the tube to form a generally catenary shape. 
     In an exemplary embodiment, the elongated tube defines an elongated reservoir extending the length of the tube for passing a heat-transfer fluid therethrough, the elongated reservoir positioned above the reflective sheet such that solar radiation reflected by the reflective sheet is directed towards the elongated reservoir. The elongated tube can further define a plurality of elongated reservoirs positioned above the reflective sheet, defining multiple focal areas of reflected radiation present at different angles of incident solar radiation. In this manner, the solar collector can be coupled to the tube, through which a heat-transfer fluid can pass to absorb the reflected radiation, and then be used to power electricity generation. 
     In exemplary embodiments, the solar reflector assembly may comprise one or more pass-through fittings coupled to the elongated tube to facilitate the flow of gas and liquid into and out of the elongated tube. 
     In a detailed example of an exemplary embodiment, the solar reflector assembly or system can include a rotation assembly coupled to at least one end of the elongate tube and configured to rotate the elongated tube such that the reflective sheet directs solar radiation towards the solar collector throughout the day. In one approach, the rotation assembly can include a plurality of gas bladders coupled to the elongated tube, in which the rotation assembly is configured to adjust the content of gas bladders to rotate the elongated tube. In another approach, the rotation assembly is coupled to at least one end of the elongated tube to induce controlled rotation of the elongated tube to direct the reflected solar radiation towards the solar collector. 
     In another exemplary embodiment, a plurality of elongated tubes are coupled together along longitudinal sides, forming a raft, in which a reflective sheet is disposed either within or atop each tube. The tubes can further include one or more reservoirs for passing heat-transfer fluid through. Alternatively, an external solar collector can be disposed in a prescribed location, spaced apart from an elongated tube or from the raft of elongated tubes to receive reflected solar radiation from the reflective sheets. 
     The elongated tube may further comprise a culture medium for photosynthetic biomass, thus forming a combined solar reflector and photobioreactor assembly (“CSP/PBR”). The culture medium housed in the tube can be used, e.g., to facilitate photosynthetic biomass growth, such as algal biomass. The reflective sheet may be configured to substantially reflect a first prescribed wavelength range towards a solar collector and to substantially transmit a second prescribed wavelength range therethrough to the culture medium within the elongated tube. In this manner, a portion of solar energy is directed towards the solar collector, while another portion is utilized by the culture medium, e.g., to facilitate photosynthetic biomass growth, such as algal biomass. The CSP/PBR assemblies may be disposed on a supporting body of liquid and include a solar collector positioned to receive reflected solar radiation from the reflective sheet. Beneficially, this embodiment serves to reduce the heat input, and therefore the cooling load for the biomass production component of such an embodiment 
     Exemplary embodiments include a combined solar reflector and desalination assembly comprising an inflatable elongated tube having an upper portion formed at least partially of flexible material and a lower ballast portion formed at least partially of flexible material, a reflective sheet coupled to a wall of the tube to reflect solar radiation, and at least one catchment device coupled to a wall of the tube. The elongated tube has an axis of rotation oriented generally parallel to a surface of a supporting body of liquid. The assembly may further comprise at least one end cap assembly coupled to the elongated tube to facilitate flow of gas and/or liquid into and out of the elongated tube. Exemplary embodiments of a combined solar reflector and desalination assembly may further comprise a pool housing a supporting body of liquid, and the assembly floats on the supporting body of liquid. 
     The at least one catchment device may comprise at least one catchment sheet coupled to a wall of the tube, and may define one or more apertures. In exemplary embodiments each aperture comprises an adjacent lip to guide collected water away from the aperture. Alternatively, the at least one catchment device may comprise a porous membrane mounted to a bottom side of the reflective sheet. A support tab may be coupled to a wall of the tube and be located beneath and to the side of the porous membrane. In exemplary embodiments, the at least one catchment sheet comprises a top sheet and a bottom sheet. A support tab may be coupled to a wall of the tube and may be located beneath and laterally to a side of the bottom sheet. 
     Exemplary embodiments of a combined solar reflector and desalination assembly further comprise a collection assembly mounted to an end of the tube. The at least one catchment sheet may be slidably coupled to the collection assembly. Exemplary embodiments of a collection assembly comprise a pulley mechanism mounted to the end of the tube. The pulley mechanism may slidably engage the at least one catchment sheet. A catchment cup may be mounted to the end of the tube, located beneath the pulley mechanism. A squeegee mechanism may be coupled to the catchment cup to direct water from the at least one catchment sheet into the catchment cup. In exemplary embodiments, the collection assembly further comprises a fresh water pass-through fitting. Exemplary embodiments of a combined solar reflector and desalination assembly may further comprise a culture medium for photosynthetic biomass so algae and other biomass may be grown in the elongated tube. The combined solar reflector and desalination assembly may also be part of a CSP system and may comprise a solar collector spaced apart from the elongated tube and positioned to receive reflected solar radiation from the reflective sheet. 
     Exemplary embodiments may include methods of desalinating water comprising the steps of inflating an elongated tube to form an upper portion made at least partially of flexible material and a lower ballast portion made at least partially of flexible material, coupling a reflective sheet to a wall of the tube to reflect solar radiation, coupling at least one catchment device to a wall of the tube, filling the lower ballast portion with water and directing cold air through the upper portion of the tube to create conditions for condensation of the water. The methods may further comprise the step of collecting condensed water from the at least one catchment device. 
     Exemplary embodiments may also include a desalination apparatus comprising an inflatable elongated tube having an upper portion formed at least partially of flexible material and a lower ballast portion formed at least partially of flexible material, at least one catchment device coupled to a wall of the tube and a collection assembly mounted to an end of the tube. The elongated tube has an axis of rotation oriented generally parallel to a surface of a supporting body of liquid. In exemplary embodiments, the at least one catchment device comprises at least one catchment sheet. The at least one catchment device may comprise a porous membrane mounted to a bottom side of the reflective sheet. A support tab may be coupled to a wall of the tube and may be located beneath and to the side of the porous membrane. In exemplary embodiments, the at least one catchment device comprises a top catchment sheet and a bottom catchment sheet. A support tab may be coupled to a wall of the tube and may be located beneath and laterally to a side of the bottom catchment sheet. In exemplary embodiments, the desalination apparatus may further comprise a culture medium for photosynthetic biomass. 
     In exemplary embodiments, the collection assembly comprises a pulley mechanism mounted to the end of the tube, a catchment cup mounted to the end of the tube and located beneath the pulley mechanism and a squeegee mechanism coupled to the catchment cup. The pulley mechanism slidably engages the at least one catchment device. The squeegee mechanism directs water from the at least one catchment device into the catchment cup. 
     For purposes of summarizing the disclosure and the advantages achieved over the prior art, certain advantages of the disclosure have been described herein. Of course, it is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the disclosure. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     All of these embodiments are intended to be within the scope of the disclosure herein disclosed. These and other embodiments of the present disclosure will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the disclosure not being limited to any particular preferred embodiment disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure will now be described, by way of example only, with reference to the following drawings in which: 
         FIG. 1  is cross-sectional view of an embodiment of a solar energy collection system in accordance with the present disclosure; 
         FIG. 2  is a perspective view of an embodiment of an array of solar reflector assemblies of a solar energy collection system in accordance with the present disclosure; 
         FIG. 3  is a perspective view of an embodiment of an end cap assembly coupled to a solar reflector assembly in accordance with the present disclosure; 
         FIG. 4  is a cross-sectional view of an embodiment of a solar energy collection system in accordance with the present disclosure; 
         FIG. 5  is a cross-sectional, perspective view of an embodiment of an array of solar reflector assemblies in accordance with the present disclosure; 
         FIG. 6  is a cross-sectional view of an embodiment of an array of solar reflector assemblies in accordance with the present disclosure; 
         FIGS. 7   a - c  are cross-sectional views of an embodiment of a solar reflector assembly in accordance the present disclosure; 
         FIGS. 8   a - c  are cross-sectional views of embodiments of solar reflector assemblies in accordance with the present disclosure; 
         FIGS. 9   a - b  are cross-sectional views of embodiments of solar reflector assemblies in accordance with the present disclosure; 
         FIG. 10  is a cross-sectional view of an embodiment of a solar reflector assembly in accordance with the present disclosure; 
         FIG. 11  is a perspective view of an embodiment of a solar reflector assembly in accordance with the present disclosure; 
         FIG. 12  is a cross-sectional view of an embodiment of a solar reflector assembly having an external reflector in accordance with the present disclosure; 
         FIG. 13  is a cross-sectional view of an embodiment of a solar reflector assembly having an external reflector in accordance with the present disclosure; 
         FIG. 14  is a cross-sectional view of an embodiment of a solar reflector assembly having an external reflector in accordance with the present disclosure; 
         FIG. 15  is an embodiment of a solar energy collection system in accordance with the present disclosure; 
         FIG. 16  is a cross-sectional view of a solar energy collection system in accordance with the present disclosure; 
         FIG. 17  is a cross-sectional view of an embodiment of a concentrated solar power/photobioreactor assembly in accordance with the present disclosure; 
         FIG. 18  is a perspective view of an embodiment of an array of concentrated solar power/photobioreactor assemblies in accordance with the present disclosure; 
         FIG. 19   a  is a perspective view of an embodiment of an end cap assembly coupled to a concentrated solar power/photobioreactor assembly in accordance with the present disclosure; 
         FIG. 19   b  is a perspective view of an embodiment of an end cap assembly having pass-throughs and coupled to a concentrated solar power/photobioreactor assembly in accordance with the present disclosure; 
         FIG. 20  is a graph depicting percent transmittance at zero degrees incidence, as a function of wavelength, for an exemplary embodiment of a reflective sheet for a reflector/photobioreactor assembly in accordance with the present disclosure; 
         FIG. 21  is a cross-sectional view of an embodiment of a solar reflector assembly in accordance with the present disclosure; 
         FIG. 22  is a cross-sectional view of an embodiment of a solar reflector assembly in accordance with the present disclosure; 
         FIG. 23  is a perspective view of an embodiment of an array of solar reflector assemblies of a solar energy collection system in accordance with the present disclosure; 
         FIG. 24  is a perspective view of an embodiment of an array of solar reflector assemblies of a solar energy collection system in accordance with the present disclosure; 
         FIG. 25  is a cross-sectional view of an embodiment of a solar reflector assembly in accordance with the present disclosure; 
         FIG. 26  is a perspective view of an embodiment of an array of solar reflector assemblies of a solar energy collection system in accordance with the present disclosure; 
         FIG. 27   a  is a perspective view of an embodiment of a solar reflector assembly in accordance with the present disclosure; 
         FIG. 27   b  is a perspective view of an embodiment of a solar reflector assembly having pass-throughs in accordance with the present disclosure; 
         FIG. 28  is a perspective view of an embodiment of a combined solar reflector and desalination assembly in accordance with the present disclosure; 
         FIG. 29  is a perspective view of an embodiment of a combined solar reflector and desalination assembly in accordance with the present disclosure; 
         FIG. 30  is a perspective view of an embodiment of a combined solar reflector and desalination assembly in accordance with the present disclosure; 
         FIG. 31A  is a cross-sectional view of an embodiment of a combined solar reflector and desalination assembly in accordance with the present disclosure; 
         FIG. 31B  is a cross-sectional view of an embodiment of a combined solar reflector and desalination assembly in accordance with the present disclosure; 
         FIG. 32  is a perspective view of an embodiment of a combined solar reflector and desalination assembly in accordance with the present disclosure; 
         FIG. 33  is a side view and detail view of a collection assembly in accordance with the present disclosure; 
         FIG. 34A  is a perspective view of an embodiment of a desalination apparatus in accordance with the present disclosure; 
         FIG. 34B  is a perspective view of an embodiment of a desalination apparatus in accordance with the present disclosure; 
         FIG. 35  is a perspective view of an embodiment of a desalination apparatus in accordance with the present disclosure; 
         FIG. 36  is a cross-sectional view of an embodiment of a desalination apparatus in accordance with the present disclosure; 
         FIG. 37  is a perspective view of an array of combined solar reflector and desalination assemblies shown with a solar collector, in accordance with the present disclosure; and 
         FIG. 38  is a cross-sectional view of an array of combined solar reflector, desalination and photobioreactor assemblies in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     With reference now to the drawings, and particularly  FIGS. 1 and 2 , there is shown an array  1  of solar reflector assemblies  10 . Each solar reflector includes an inflated elongated tube  12  having a reflective sheet  14  coupled along opposed sides of the sheet to a wall of the tube. In exemplary embodiments, reflective sheet  14  is coupled to an interior wall  15  of the elongated tube  12  so that the reflective sheet  14  divides the elongated tube  12  into two portions, an upper portion or chamber  21  and a lower ballast portion or chamber  23 . 
     More particularly, in exemplary embodiments the elongated tube  12  is a unitary structure that includes lower ballast portion  23 , which provides ballast for the solar reflector assembly  10 . In other words, lower ballast portion  23  is the lower section of the elongated tube itself and, as such, is integrally formed with the elongated tube  12 . This structure is advantageous because it obviates the need for additional components or structural elements to facilitate ballast. It also enables pressure differential or pressure equilibrium between the chambers  21 ,  23  on either side of the reflective sheet  14 , as described in more detail herein. The elongated tubes may include a gas in the upper chamber  21  and a reservoir liquid  20  in the lower chamber  23  to facilitate ballast. As discussed in more detail herein, the reflective sheet could also be coupled to an exterior wall of the tube. 
     The solar reflectors are supported by a body of liquid  16  and are configured to rotate to direct reflected solar radiation towards a solar collector  18 . The solar reflectors are used to reflect solar radiation towards a solar collector  18  configured to transform the solar energy to electricity or process heat. Beneficially, the solar reflector assemblies are inexpensive to manufacture and operate, providing a cost effective solution for electrical generation or process heat from solar energy. 
     Each tube  12  is formed of transparent, lightweight flexible plastic optionally coupled at each end to rigid end cap assemblies  24 , which facilitate the flow of liquid and gas into and out of the tubes. Positive pressure within the tube keeps them rigid and maintains the tube in a generally cylindrical configuration having a substantially constant cross section along the length of the tube. The tube is set on an expanse of liquid  16  in a pool  19  and includes a reservoir of fluid  20  to facilitate ballast of the tube and maintain buoyancy in a prescribed manner to best track the sun, as described herein. The tubes  12  will float at a level such that the liquid level within the tube is generally even or parallel with the level of liquid  16  on which the tube is floating. More specifically, in operation the top surface of the ballast liquid is substantially parallel to the top surface of the supporting body of liquid. However, the level of liquid within the tube can vary, from empty to full with liquid, as desired. 
     The tubes  12  are configured in an elongated cylindrical configuration. In exemplary embodiments, the tubes are formed of a single sheet of a thin gauge, flexible material, which can be various plastics such as polyethylene, having a thickness between about 50 microns (2 mil) and 300 microns (12 mil). In other embodiments, tubes can be formed of multiple layers and multiple sections of material. In addition, other lightweight, flexible materials or combinations of materials can be used. Tubes of various sizes can be used, to include tube diameter and tube length, without departing from the disclosure. In the present embodiment, the entire tube is formed of transparent material; however, it is sufficient if an upper portion of the tube is transparent to enable solar radiation to be directed towards the reflective sheet. 
     The tubes can be susceptible to deterioration over time as result of exposure to solar radiation. For example, polyethylene can be susceptible to UV-B radiation, and other materials may be susceptible to other ranges of radiation. The tubes can be protected from premature deterioration using systems and methods as disclosed in the present inventor&#39;s co-pending application, U.S. application Ser. No. 12/253,962, filed Oct. 18, 2008, entitled “System and Method for Protecting Enclosure from Solar Radiation,” which is incorporated by reference herein for all purposes. 
     With reference now to  FIG. 2 , the reflective sheet  14  is disposed within the elongated tube  12 , having opposing longitudinal sides attached to the interior wall of the tube. The reflective sheet is formed of lightweight flexible reflective material, such as PET polyester film sold under the brand name Mylar®, available from E. I. Du Pont De Nemours &amp; Co. Other examples of usable materials include reflective polyester film, metalized polymer film, metallic film, or other material having sufficient reflective traits while being sufficiently lightweight. In the exemplary embodiment, the reflective sheet is formed of one layer of material configured to reflect a broad wavelength spectrum. In other embodiments, the substrate film is also a polymer sheet with a reflective sheet laminated, adhesively applied, or otherwise disposed on top. In addition, multiple layers can be used, and the reflective sheet can be configured to allow prescribed wavelengths of solar radiation to pass through, while reflecting other wavelengths of solar radiation towards the solar collector. 
     The reflective sheet  14  can be coupled to the elongated tube  12  to enable a pressure differential to be maintained on opposing sides of the sheet. The pressure differential can be used to form the reflective sheet to a prescribed shape. For example, a higher pressure can be maintained on the upper surface of the reflective sheet such that the reflective sheet has a curved or, more preferably, a generally parabolic shape. Alternatively, the solar reflector assembly can be configured to maintain pressure equilibrium on both sides of the reflective sheet to facilitate other desired shapes for the reflective sheet. For example, the one or more end caps can be configured to allow gas to move between the upper portion and lower ballast portion of the tubes by coupling a pass-through to the upper chamber with a pass-through to the lower chamber. As discussed in more detail below, the reflective sheet can be configured to assume any number of different shapes without departing from the disclosure. 
     In an exemplary method of manufacture, a sheet of reflective material is attached along longitudinal side edges to a first side of a sheet of tube material at a prescribed distance from each other. Opposing longitudinal side edges of the tube material are attached to each other forming a cylinder with the reflective material disposed within the interior of the tube. The distance between the edges of the reflective material is selected to form a prescribed shape for the reflective sheet, when in use. 
     With reference again to  FIGS. 2 and 3 , end cap assemblies  24  are disposed at opposing ends of the tube  12 , and a rotation assembly  26  is configured to enable rotation of the tubes about a longitudinal axis oriented generally parallel to the surface of the supporting body of liquid  16 . Rotation assembly  26  includes a motor  28  and a transmission system  30 . The motor  28  is connected to at least one end cap assembly  24  by the transmission system  30 . The motor  28  provides power to turn the tube  12  either way. It is possible to drive both ends of the tube  12  by installing motors and transmission systems at both ends. The tubes can be turned to track the sun to optimize reflection of solar radiation onto the solar collector. In other embodiments, longitudinal bladders can be built into the tubing material or otherwise used to support the tubes. Air pressure varied within said bladders can be used to change the buoyancy of one side of the tube, causing rotation until equilibrium is reached. 
     Each end cap assembly  24  is configured to facilitate flow of gas and liquid to and from the interior of the elongated tube  12 . To that end, end cap assembly  26  may include liquid transfer tubes  32  and gas transfer tubes  34  that extend from the end caps. Liquid can be injected or withdrawn through liquid transfer tubes to regulate how high the elongated tubes  12  float in the support liquid  16 . Similarly, gas can be injected or withdrawn through gas transfer tubes. The inlets and outlets pass through pipes  36 , which also serve as axles on which end-caps rotate. By passing through the axis of rotation of the end-caps, the liquid and gas transfer tubes can thus be permanently interfaced to the elongated tube  12  and can allow fluid and gas transfer while the elongated tube is turning. However, other inlets and outlets passing through both, eccentrically mounted control valves on the end-cap, or valves mounted on the plastic tubing itself are possible in other embodiments without departing from this disclosure. 
     In exemplary embodiments, the liquid transfer tubes  32  are submerged within the liquid  20  within the tube. Gas transfer tubes  34  are disposed above the liquid. In other embodiments, various other configurations can be used. One liquid and one gas transfer tube passing through each end-cap are used. It is also possible to have more than two transfer tubes passing through each end-cap. In exemplary embodiments, the rotation element includes sealed ball bearings, which enable long life of the assembly despite potential prolonged exposure to moisture. There are multiple methods possible for sealing the ends of the tubes. 
     The solar energy collection system can include an array of solar reflector assemblies configured to reflect solar radiation towards multiple solar collectors. For example, the system can include groupings of solar reflectors disposed on opposing sides of linear solar collectors, and the solar reflectors can be directed to the closest solar collector. It should also be noted that any embodiment of a solar energy collection system could include additional components providing water desalination capability, as described herein with reference to  FIGS. 28-38 . 
     With reference now to  FIGS. 4 and 5 , a solar reflector assembly  110  is shown having a heat-transfer reservoir  142  positioned above a reflective sheet  114  such that solar radiation reflected by the sheet is directed towards the reservoir. More particularly, the reservoir is in an upper portion of the elongated tube  112 , extending the entire length of the tube. Heat-transfer fluid enters a heat-transfer reservoir  142  at a first end cap, and it absorbs the reflected solar radiation from the reflective sheet  114  of the solar reflector assembly  110  as it passes through the heat-transfer reservoir  142  to a second end cap assembly. The heated fluid is then directed to power an electrical generator (not shown) or is used for process heat. Reflective sheet  114  is coupled to an interior wall of the elongated tube  112  so that the reflective sheet  114  divides the elongated tube  112  into two portions, an upper portion or chamber  121  and a lower ballast portion or chamber  123 . An array of solar reflectors  110  can be configured to rotate to track the sun to ensure that the reflective solar radiation is directed towards the reservoir, as in  FIG. 5 . The solar reflector assemblies  110  are supported by a body of liquid  116  in a pool  119 . 
     In exemplary embodiments, the heat-transfer reservoir  142  is attached to or formed in the wall of the elongated tube from the same polymer material. For example, an exterior and an interior sheet of polymer material can be used together by spaced apart, generally parallel seams to form the heat-transfer reservoir. The material for the heat-transfer reservoir should have sufficient strength and durability characteristics to handle the anticipated pressure, heat, and so on, when the heat-transfer fluid is heated. 
     In other embodiments, the heat-transfer reservoir can include additional structure and/or other materials, to facilitate the use of selected heat-transfer fluids that achieve high pressures and high temperatures. For example, the heat-transfer reservoir as discussed above can further include a rigid tube installed at tube deployment, sandwiched between the exterior and interior sheets and extending between the end cap assemblies. 
     With reference now to  FIGS. 6 and 7   a - c , an array  200  of solar reflector assemblies  210  is shown. Each solar reflector assembly  210  includes a tube  212  having a plurality of heat-transfer reservoirs  242   a - c , similar to the heat-transfer reservoir depicted in  FIG. 4 . A reflective sheet  214  is disposed within each tube  212 . The elongated tubes  212  are coupled together along longitudinal sides  270 , forming a raft. A raft configuration can be used in other embodiments, such as with an external solar collector that can be disposed in a prescribed location, spaced apart from the raft to receive reflected solar radiation from the reflective sheets. 
     Use of a plurality of heat transfer reservoirs can be effective in embodiments in which the solar reflector assembly does not rotate to track the sun. Rather, as the sun progresses across the sky, the reflected focal area of the reflective sheet will track across the plurality of heat transfer reservoirs. The system can be configured to pass the heat-transfer fluid through the appropriate reservoir at prescribed times to coincide with the location of the reflected focal area. 
     For example, as shown in  FIG. 7   a , the system passes heat-transfer fluid through the first reservoir  242   a  in the morning. During midday, the system passes heat transfer fluid through the center reservoir  242   b  ( FIG. 7   b ). In the afternoon, the system passes heat transfer fluid through the third reservoir  242   c  ( FIG. 7   c ). In other embodiments, the system can be designed with any number of heat-transfer reservoirs, and the size and configuration of each reservoir of the plurality of reservoirs can vary from each other, as requirements dictate. 
     With reference now to  FIGS. 8   a - c , the reflective sheet  14  can be configured to achieve various different shapes. For example, as in  FIG. 8   a , the reflective sheet  14  can be configured to be held taut when the tube is inflated, forming a generally planar shape. Alternatively, as in  FIGS. 8   b, c , a curved shape for the reflective sheet  14   a ,  14   b  can also be used. The reflective sheet  14   a  can be configured to drape between the attachment seams of the opposing longitudinal edges of the reflective sheet, forming a generally catenary shape ( FIG. 8   b ). Alternatively, as in  FIG. 8   c , the curved shape can be formed by maintaining a pressure differential on opposing sides of the sheet  14   b , forming a generally parabolic shape. Nonetheless, other shapes for the reflective sheet can be used without departing from the disclosure. 
     With reference now to  FIGS. 9   a - b , the elongated tube  312  of the solar reflector assembly  310  can be configured to achieve various different cross-sectional shapes. In each example depicted, the tube  312  has a generally constant cross-section profile. In other embodiments, the cross-section profile can vary across the length of the tube.  FIG. 9   a  depicts an elongated tube  312  having an oval shaped cross section, used with a curved reflective sheet  314   a .  FIG. 9   b  depicts an elongated tube  312  having an oval shaped cross section, used with a planar reflective sheet  314   b . It should be appreciated that variations of these shapes and others having different parameters can be used. In addition, other cross-sectional shapes for the tube can be used, such as an ellipse, superellipse, vesica piscis, lens, and polygon, to name a few, without departing from the disclosure. 
     Various approaches for manufacture can be used. For example, the tube can be formed by an upper panel and a lower panel, along opposing seams, and the reflective material is disposed therebetween attached at the seam. The tube can also be formed by a single sheet of material to which the reflective sheet is attached. The opposing ends of the sheet can be coupled together forming the tube, having the reflective sheet disposed in the interior. Due to the flexibility of the material it can be rolled up into a compact format for shipping and deployment. 
     With reference now to  FIGS. 10 and 11 , a solar reflector assembly  410  is shown having gas bladders  482  that extend the length of the tube  412 . Each gas bladder is independently controlled with a regulator valve manifold assembly  486 , to optimize the stability of the system. An array of solar reflectors  410  can be used together, in which a subset of the tubes can be inflated with the other tubes partially or completely deflated to control the angle at which the tubes float in the supporting body of liquid (not shown). The assembly can incorporate similar features as discussed with reference to other embodiments, including end cap assemblies  424 , reflective sheet  414 , gas and liquid pass-through tubes  432 ,  434 , a rotation assembly  426  including a motor (not shown) and a transmission system  430  and so on. 
     Turning to  FIGS. 12-14 , exemplary embodiments of a solar reflector assembly with an externally mounted reflector will be described. With reference now to the drawings, and particularly  FIG. 12 , there is shown a solar reflector assembly  510  including an inflated elongated tube  512  and a reflective sheet  514  coupled to an exterior wall  517  of the tube, usable as a solar reflector and/or a photobioreactor, in which the tube is disposed on a supporting body of liquid (not shown). The reflective sheet  514  is disposed along the top of the tube  512 . 
     Supports  525  are disposed on an exterior side  517  of the tube  512 . The longitudinal sides of the reflective sheet  514  are coupled to the supports  525  and an intermediate section of the reflector sheet  514  can be coupled to the tube  512 , such that the reflective sheet  514  is generally flat. The elongated tube  512  has an upper portion  521  and a lower ballast portion  523  containing reservoir liquid  520 , though the upper and lower ballast portions are not physically separated because of the external location of the reflective sheet  514 . In exemplary embodiments, the elongated tube  512  is a unitary structure that includes lower ballast portion  523 , which provides ballast for the solar reflector assembly  510 . In other words, lower ballast portion  523  is the lower section of the elongated tube itself and, as such, is integrally formed with the elongated tube  512 . This structure is advantageous because it obviates the need for additional components or structural elements to facilitate ballast. The elongated tube  512  is made of a thin-gauge, flexible material, as described in more detail above, and, in contrast to other embodiments, need not be transparent because the reflective sheet  514  is externally mounted. 
     With reference now to  FIG. 13 , a second embodiment is shown in which the reflector sheet  514  is positioned and attached in a similar manner as in  FIG. 12 . However, the longitudinal sides  527   a ,  527   b  of the reflector sheet  514  are raised relative to the intermediate section  529  of the sheet  514 , such that the reflected solar radiation can be focused. More particularly, the reflective sheet  514  is mounted to have a generally v-shaped cross section. In other embodiments, the reflective sheet  514  can be mounted to have various other cross-sectional shapes such as u-shaped or parabolic, among others. 
     In the exemplary embodiments of  FIGS. 12 and 13 , the supports  525  are formed as inflatable tubes similar to the primary tube  512 . The supports  525  are formed of a single sheet of plastic such as polyethylene, having a thickness between about 50 microns (2 mil) and 300 microns (12 mil). In other embodiments, the supports  525  can be formed of multiple layers and multiple sections of material. In addition, other lightweight, flexible materials or combinations of materials can be used for the supports. 
     The supports  525  of the exemplary embodiments are independently inflatable relative to each other and the primary tube  512 . Alternatively, the supports  525  can be operatively coupled to each other and/or to primary tube  512  to enable air to pass between the components to maintain air pressure therein. 
     In the exemplary embodiments of  FIGS. 12 and 13 , the supports  525  have a generally circular cross section. In other embodiments, the supports  525  can have other cross-sectional shapes, to facilitate other shapes for the reflective sheet  514  such as a parabolic shape. In addition, the supports  525  run substantially the entire length of the tube  512 . In other embodiments, multiple supports  525  can be used and can be intermittently spaced along the length of the tube  512 . Moreover, the supports  525  need not be inflatable. Rather, other structure can be used to maintain the reflective sheet  514  in the proper position. 
     With reference now to  FIG. 14 , a rigid reflector sheet  514  is disposed tangentially along the top of the tube  512 . The rigid reflector  514  is supported by its connection to the tube  512  and its rigidity. The reflector  514  can be formed of reflective material mounted on a rigid base sheet. In the present embodiment, the base sheet is formed of rigid polyvinyl chloride (RPVC) having a thickness between about 200 and 300 microns. Other exemplary materials that can be used include thermoplastic polymers and other materials having rigidity sufficient to maintain a prescribed cross-sectional geometry independent of lateral supports  525 . The rigid reflector  514  can be rolled up for storage or transport, and yet configured to remain relative flat when deployed. 
     An externally mounted reflector sheet can also be used in embodiments described above in which a plurality of elongated tubes are coupled together along longitudinal sides, forming a raft, as well as with embodiments having gas bladders that extend the length of the tube(s). 
     Turning to  FIGS. 15 and 16 , a system  5  of generating energy from solar radiation is shown, having a solar collector  92  that includes solar PV cells  94  disposed below heat-transfer pipes  96 . The PV cells are configured to receive energy from reflected radiation within a prescribed wavelength, such as the visible light spectrum. The solar reflectors concentrate reflected radiation on the PV cells, thereby optimizing efficiency. The heat-transfer pipes are used to pass heat-transfer fluid as discussed above. Beneficially, the pipes are positioned to absorb reflected radiation from the solar reflectors as well as serving as a heat sink for the PV cells, cooling the PV cells and keeping them in an optimal heat range to minimize risk of overheating. In an alternate embodiment, thermoelectric modules (using, e.g., the Seebek effect) could be substituted for the PV cells. The heat-transfer fluid can capture the IR portion of the reflected radiation, thereby collecting heat for use in a generator. Once heated, the heat-transfer fluid can be used to generate energy as known in the art, such as electricity or process heat (as discussed above). As in previously discussed embodiments, the solar reflector assemblies  10  includes an elongated tube  12  having an upper portion  21  and a lower ballast portion  23  containing a reservoir liquid  20 , a reflective sheet  14 , end cap assemblies  24  and rotation assembly  26 . The solar reflector assemblies  10  are supported by a body of liquid  16  in a pool  19  and rotate to direct reflected solar radiation to solar collector  92 . 
     In each of the forgoing configurations, the reflective sheet can be fully reflective, such as when used for embodiments configured only as a solar reflector. Alternatively, the reflective sheet can be configured as a hot mirror, as disclosed in the U.S. Patent Application Ser. No. 61/233,667, filed Aug. 13, 2009, which is incorporated by reference herein in its entirety, and described herein, for embodiments configured for biomass generation or for a combined solar reflector and photobioreactor assembly (“CSP/PBR assembly”). It should be noted that in exemplary embodiments employing both internal and exterior mounting of the reflective sheet, the tube material is at least partially translucent such that biomass may grow in the ballast fluid in the lower ballast portion of the tube. In addition, biomass may grow in the pools of support liquid. This biomass could be harvested and processed into a useful product 
     In exemplary embodiments the reservoir of liquid within the tubes can also be used to grow biomass using systems and methods as disclosed in U.S. Patent Application Ser. No. 61/152,949, filed Feb. 16, 2009 (“&#39;949 Application”), which is incorporated by reference herein in its entirety. With reference now to the drawings, and particularly  FIGS. 17 and 18 , there is shown an array  601  of concentrated solar power/photobioreactor assemblies  610  (“CSP/PBR assemblies”). Each CSP/PBR assembly  610  includes an inflated elongated tube  612  having a reflective sheet  614  coupled along opposed sides of the sheet to an interior wall  615  of the tube. Thus, the tube  612  is divided into an upper portion  621  and a lower ballast portion  623 . 
     The reflective sheet is configured to reflect IR radiation towards a solar collector  618 , while allowing visible light to pass through to a culture medium  620  within the lower ballast portion  623  of the tube  612 . The array is supported by a body of liquid  616  in a pool  619 . 
     The reflective sheet  614  is formed of lightweight flexible reflective material configured to allow prescribed wavelengths of solar radiation to pass through, while reflecting other wavelengths of solar radiation towards the solar collector  618 . In exemplary embodiments, the reflective sheet is formed as a hot mirror, configured to reflect IR radiation (e.g., heat reflective) while allowing visible light to pass through (e.g., visibly transparent), across wide angles of incidence. Thus, IR radiation is reflected towards the solar collector, while the visible light passes through to the culture medium  620  to facilitate growth of the biomass, e.g., algal biomass. Moreover, minimizing penetration of IR radiation into the culture medium reduces the heat load of culture, allowing the culture to be maintained at a temperature conducive to optimal biomass growth. It should be noted that in this and other exemplary embodiments some tubes could be deployed with hot mirrors and some with full spectrum reflectors, in order to finely tune the percentage of insulation that makes it into culture to generate biomass, and how much insulation is reflected to the receiver for power generation. 
     The term “visibly transparent,” unless otherwise specified, is intended to refer to an attribute of the reflective sheet of transmitting a large fraction (e.g., an average of at least 50%) of visible radiation (e.g., at least between about 400 nm to about 700 nm) therethrough. The term “heat reflective,” unless otherwise specified, is an attribute of the reflective sheet of reflecting a large fraction (e.g., an average of at least 50%) of IR radiation (e.g., above 750 nm). 
     In exemplary embodiments, the reflective sheet  614  comprises a dielectric thin film disposed on a flexible substrate, such as a flexible polymeric sheet. For example, the reflective sheet  614  can include flexible films such as IR reflective films sold under the brand name Prestige™ Series, available from 3M Company. The reflective sheet  614  is further configured to endure a high moisture environment, without significant deterioration. The dielectric film can comprise one or more layers (or stacks) disposed on the substrate. In multi-layer configurations, the thickness of each of the layers can be selected to optimize the properties of the reflective sheet. Moreover, intervening layers having varying properties can be used to optimize performance of the reflective sheet. In other embodiments, the reflective sheet can comprise other materials, known in the art, having sufficient characteristics for use in the intended purposes, such as metal oxides disposed on a substrate. Suitable substrates can include standard contractor-grade low-density polyethylene (LDPE), polyethylene terephthalate (PET) (e.g., uniaxial, biaxial), polyester, polyterephthalate esters, polyethylene naphthalate, polypropylene, and others. 
     In exemplary embodiments, the reflective sheet  614  is configured to be visibly transparent and heat reflective across a wide range for the angle of incidence of solar radiation, (e.g., 0 degrees to at least 60 degrees). At very high angles of incidence, the reflective sheet may behave more like a full spectrum reflector. As discussed below, the assembly can be configured to rotate to track the sun such that the reflective sheet  614  can be optimized for operation with a tight range for the angle of incidence of solar radiation (e.g., ±20 degrees). It should be understood that disclosed CSP/PBR assemblies may further incorporate features directed to desalinating water, as described herein with reference to  FIGS. 28-38 . 
     As shown in  FIG. 19   a , end cap assembly  624  may include liquid transfer tubes  632  and gas transfer tubes  634  that extend from the end caps. Liquid can be injected or withdrawn through liquid transfer tubes to regulate how high the elongated tubes  612  float in the support liquid  616 . Similarly, gas can be injected or withdrawn through gas transfer tubes. The inlets and outlets pass through pipes  636 , which also serve as axles on which end-caps rotate. 
     The end cap assembly  624  may also comprise eccentrically mounted pass-through fittings  639  instead of transfer tubes, as shown in  FIG. 19   b . Pass-through fittings  639  provide access to the inside of the tube  612  to facilitate flow of gas and/or liquid into and out of the tubes through fluid lines  637 . 
     With reference now to  FIG. 20 , a chart is shown, depicting the transmission percentage across a wavelength spectrum for an exemplary embodiment of a reflective sheet at a normal angle of incidence. In this chart, the x-axis shows wavelength in nanometers (nm), and the y-axis shows percent of incident energy reflected or transmitted. The solid line represents the percent transmission, while the dashed line represents the percent reflection. In this exemplary configuration, the reflective sheet is configured to allow substantial transmission of wavelengths between about 400 nm and 700 nm and to substantially reflect wavelengths between above 750 nm. More particularly, the reflective sheet allows transmittance of at least 50 percent of incident energy in the wavelength band between about 400 nm and 700 nm at normal incidence. Moreover, over 80 percent of the solar radiation between 500 nm and 600 nm passes through the reflective sheet to radiate the culture medium. Meanwhile, above 700 nm, the reflective sheet becomes highly reflective, even at normal incidence. 
     In other embodiments, the reflective sheet can be configured to varied parameters for reflection and transmission performance. For example, the reflective sheet can be configured to achieve higher levels of transmittance within the visible spectrum, particularly within wavelengths to optimize photosynthesis (e.g., between about 380 nm-420 nm, at the lower end, and about 690 nm-750 nm, at the upper end). In yet other embodiments, the reflective sheet can be configured for high transmission (e.g., above 50 percent) for a range (or ranges) within the visible spectrum, such as, between about 400-500 nm and/or about 600-700 nm. Such ranges can be selected based on the needs of an algal culture of a prescribed embodiment. 
     The reflective sheet&#39;s performance parameters as a heat reflector can also be varied across embodiments without departing from the disclosure. For example, it is contemplated to configure the reflective sheet to have a high percentage of reflection for substantially all incident solar IR radiation above about 700 nm or, in other embodiments, above about 750 nm. More particularly, the reflective sheet reflects at least 50 percent of incident energy at wavelengths above about 750 nm at normal incidence, and in some instances reflects at least 90 percent of incident energy at wavelengths above about 750 nm at normal incidence. In yet other embodiments, the reflective sheet can be configured to have high percentage of reflection within a bounded range of IR wavelengths. Exemplary ranges include 700-1200 nm, 700-2000 nm, 750-1200 nm, and 750-2000 nm, among others. It should be appreciated that other ranges can be used, to account for performance, location, cost, and other considerations. 
     With reference again to  FIGS. 17-19 , each tube  612  is formed of transparent, lightweight flexible plastic coupled at each end to rigid end cap assemblies  624 , which facilitate the flow of liquid and gas into and out of the tubes. More particularly, each CSP/PBR assembly  610  may comprise an end cap assembly  624  coupled to an end of the elongated tube  612 , or two end cap assemblies  624 , with one coupled to each end. End cap assemblies  624  include liquid transfer tube  632  and gas transfer tube  634 . Liquid transfer tube  632  provides access to the culture medium  620  and may facilitate addition of nutrients and harvesting of biomass. The CSP/PBR array  601  may further include a rotation assembly  626  operatively connected to one or both ends of the elongated tubes  612 . In particular, the rotation assembly may include a motor  628  coupled to end caps  624  by a transmission system  630  to turn the tubes  612  to track the sun. 
     Positive pressure within the tube maintains the tube in a substantially rigid, cylindrical configuration. In addition to growing biomass, the culture medium within the tube facilitates ballast of the tube on the supporting liquid  616  in pool  619 . The tube will float such that the top surface of the liquid within the tube is generally parallel with the surface of liquid on which the tube is floating. The level of liquid within the tube can vary, from empty to fully filled with liquid, as desired. The system may be further configured to extract biomass from within the CSP/PBR assemblies for processing. Various approaches can be used for this purpose. For example, the present inventor&#39;s co-pending &#39;949 application, entitled “System for Concentrating Biological Culture and Circulating Biological Culture and Process Fluid,” which is incorporated by reference herein for all purposes, discloses effective approaches towards that end. 
     It should be noted that any of the above-described solar reflector assembly and system embodiments could be modified to incorporate a culture medium to provide different embodiments of a CSP/PBR assembly. For instance, the elongated tube of the CSP/PBR assembly can be configured to achieve various different cross-sectional shapes, as depicted in  FIGS. 9   a - b  with reference to the solar reflector assembly. A CSP/PBR assembly could also have gas bladders to optimize the stability of the system, like the solar reflector assembly depicted in  FIGS. 10-11 . 
     In addition, as with the solar reflector assemblies discussed above with reference to  FIGS. 1 and 2 , the system can include an array of CSP/PBR assemblies configured to reflect solar radiation towards multiple solar collectors. For example, the system can include groupings of CSP/PBR assemblies disposed on opposing sides of linear solar collectors, and the CSP/PBR assemblies can be directed to the closest solar collector. As with the solar reflector assemblies discussed above with reference to  FIGS. 2 ,  4  and  5 , an array of CSP/PBR assemblies can be configured to rotate to track the sun to ensure that the reflective solar radiation is directed towards the reservoir. Systems of generating energy from solar radiation including PV cells, such as those discussed above with reference to  FIGS. 15 and 16 , could also incorporate a culture medium for growing biomass to provide CSP/PBR assemblies. As discussed above, such CSP/PBR systems optimize efficiency by reflecting radiation on the PV cells, and heat-transfer pipes both absorb radiation and serve as a heat sink for the PV cell. Thermo-electric modules employing, e.g., the Seebek effect could also be used, as discussed above. 
     Turning to  FIGS. 21-26 , exemplary embodiments of a solar reflector assembly having additional shapes and cross-sections are illustrated.  FIG. 21  shows an embodiment of a solar reflector assembly  710  comprising an elongated flexible tube  712  having an upper portion  721 , a lower ballast portion  723  and an “egg shaped” cross section. The tube  712  contains ballast liquid  720  and sits on an expanse of liquid  716 . This configuration is made by coupling the reflective panel or sheet  714  to the inner walls  715  of the tube  712  in two places that would normally form a chord of the circular cross section of a certain length. The reflective sheet  714 , however, is slightly shorter than the characteristic chord length, thus pulling in the sides of the circles at the attachment points A. In the case of modest internal pressure that is equal on both sides of the panel, this advantageously guarantees that the panel is flat, even in the case of modest irregularities introduced in manufacturing. The lower ballast portion  723  remains largely (but not exactly) cylindrical, and the upper portion&#39;s protruding “egg” shaped dome  735  does not materially impact the performance of the system. It should be noted in this regard that various exaggerated geometries are possible, with very large egg domes having no adverse impact on performance. 
       FIGS. 22-23  illustrate exemplary embodiments of solar reflector assemblies  810  with each assembly comprising an elongated flexible tube  812  having an upper portion  821 , lower ballast portions  823   a ,  823   b  and a “triple panel” cross section. This configuration is made by attaching a second sheet or panel  845  to the reflective sheet or panel  814  either in the middle B or at some other point between the two ends of the reflective sheet  814  and connecting the bottom of the second panel  845  to the bottom of the tube  812  at some middle point C or at some other point. This allows the reflective sheet  814  to be pulled into a “V” formation. There are other ways to create a “V” formation, for example, with a weight attached at the middle of reflective sheet  814 . The “V” formation provides the advantage of a tighter focus on the target. The tube  812  contains ballast liquid  820  and sits on an expanse of liquid  816 . 
     The “triple panel” solar reflector assemblies can be arranged in an array configuration, as shown in  FIG. 23 . This view shows that there are holes  847  defined in the second panel  845 . This facilitates the passage of liquid between the two lower ballast portions  823   a ,  823   b  created by the second panel  845 . Holes  847  facilitate the equalization of the level of ballast within the tube during rotation. 
       FIG. 24  illustrates an array of CSP/PBR assemblies  910  having a triple-panel configuration. Each CSP/PBR assembly includes an inflated elongated tube  912  having a reflective sheet  914  coupled along opposed sides of the sheet to an interior wall  915  of the tube. A second sheet or panel  945  is attached to the reflective sheet or panel  914  either in the middle or at some other point between the two ends of the reflective sheet  914  and connecting the bottom of the second panel  945  to the bottom of the tube  912  at some point in the middle or at some other point. Thus, the tube  912  is divided into an upper portion  921  and two lower ballast portions  923   a ,  923   b . The reflective sheet is configured to reflect IR radiation towards a solar collector (not shown), while allowing visible light to pass through to a culture medium  920  within the lower ballast portions  923   a ,  923   b  of the tube  912 . The array is supported by a body of liquid  916  in a pool  919 . Holes  947  defined in the second panel  945  facilitate the equalization of the level of ballast within the tube during rotation. 
     Turning to  FIGS. 25-26 , an embodiment of a solar reflector assembly having an “Egg shaped, triple panel” cross section will be described. Each solar reflector assembly  1010  comprises an elongated flexible tube  1012  having an upper portion  1021 , lower ballast portions  1023   a ,  1023   b  and an “egg shaped, triple panel” cross section. This configuration is made by attaching a second sheet or panel  1045  to the reflective sheet or panel  1014  either at a middle point B or at some other point between the two ends of the reflective sheet  1014  and connecting the bottom of the second panel  1045  to the bottom of the tube  1012  at some middle point C or at some other point. This allows the reflective sheet  1014  to be pulled into a “V” formation. The second panel  1045 , is shorter than otherwise necessary which leads to the deformation at C. Laying this reflector assembly on an expanse of liquid  1016  and using internal ballast provides a stable, level reflector array that is easily turned by actuators at each end. 
     The reflective sheet  1014  is slightly shorter than the characteristic chord length, thus pulling in the sides of the circles at the attachment points A. In the case of modest internal pressure that is equal on both sides of the panel, this advantageously guarantees that the panel is flat, even in the case of modest irregularities introduced in manufacturing. The lower ballast portions  1023   a ,  1023   b  together remain largely cylindrical. Holes  1047  defined in the second panel  1045  facilitate the equalization of the level of ballast within the tube during rotation. As shown in  FIG. 26 , the “egg shaped, triple panel” solar reflector assemblies can be arranged in an array configuration. The array of solar reflector assemblies is supported by a body of liquid  1016  in a pool  1019 . 
       FIGS. 27   a - 27   b  illustrate further exemplary embodiments of solar reflector assemblies having simplified end designs.  FIG. 27   a  shows an embodiment of a solar reflector assembly utilizing direct coupling to a rotation axle. Solar reflector assembly  1110  comprises an elongated flexible tube  1112  having an upper portion  1121  and a lower ballast portion  1123 . The elongated tube  1112  is directly coupled to a rotation axle  1136  without an end cap component. It can be seen that the tube  1112  develops folds  1157  where it is bunched up and locked onto the axle  1136 . A retaining ring  1153  facilitates locking of the tube  1112  onto the axle  1136 . Axle  1136  includes liquid transfer tube  1132  and gas transfer tube  1134 . The axle  1136  may also be coupled to a transmission system  1130  that serves to turn the tube  1112  to track the sun. 
       FIG. 27   b  shows an embodiment of a solar reflector assembly without an end cap or a rotation axle, but instead is heat-sealed at its ends and employs pass-through fittings for ingress and egress of fluids. Solar reflector assembly  1110  comprises an elongated flexible tube  1112  having an upper portion  1121  and a lower ballast portion  1123 . In this exemplary embodiment, solar reflector assembly  1110  employs a heat-seal  1159  at the end. Pass-through fittings  1139  provide access to the inside of the tube  1112  to facilitate flow of gas and/or liquid into and out of the tubes through fluid lines  1137 . 
     Rotation of the tube  1112  is accomplished by a rotation assembly that includes a strap  1149  and a stabilizer  1151 . In this embodiment, the strap is coupled to the tube  1112  by being wrapped  1147  around the tube, but other means of coupling a rotation assembly to the tube are possible. The tube  1112  is rotated by pulling the strap  1149  in the direction corresponding to the desired turning direction for the tube  1112 . Stabilizer  1151  with stabilizer rods  1143  prevents lateral movement of the tube when strap  1149  is pulled, thereby inducing rotation as opposed to translation. It will be appreciated that a rotation assembly can be placed anywhere along the length of the tube, and that multiple different means, including end-caps, axles, straps and other means can be employed simultaneously to impart rotation on the tube. 
     It should be noted that exemplary embodiments described herein can be controlled by a computer. Either an open loop system that is pre-programmed with the position of the sun in the sky or a closed loop system that has a sensor or sensors that detect the position of the sun in the sky or a combination of these two strategies can be used to control the position of the tubes. 
     With reference to  FIGS. 28-38 , exemplary embodiments of desalination apparatus and combined solar reflector and desalination assemblies will now be described. As shown in  FIGS. 28-30 , an embodiment of a combined solar reflector and desalination assembly  1210  comprises an inflated elongated tube  1212  having a reflective sheet  1214  coupled along opposed sides of the reflective sheet  1214  to a wall of the tube. The reflective sheet  1214  may be internally mounted by being coupled to an interior wall  1215  of the elongated tube  1212 , as illustrated in  FIG. 28 . As such, the reflective sheet  1214  divides the elongated tube into two portions, an upper portion or chamber  1221  and a lower ballast portion or chamber  1223  containing ballast fluid  1220 , which is water in exemplary embodiments. In exemplary embodiments the elongated tube  1212  is a unitary structure that includes integrally formed lower ballast portion  1223 . Alternatively, as shown in  FIG. 29 , the reflective sheet  1214  may be externally mounted along the top of tube  1212 . As discussed in detail above, the tube  1212  can be used to reflect solar radiation to a solar collector or otherwise harness solar radiation to generate energy, and the assembly may sit in a supporting body of liquid  1216 . 
     Also coupled to a wall of the elongated tube  1212  is a catchment device  1260  or other internal structures to absorb, catch, collect and convey or transmit fresh condensed water  1270 . In exemplary embodiments, the catchment device  1260  is a catchment sheet coupled to an inner wall  1215  of the elongated tube  1212 . The catchment sheet  1260  may be located below reflective sheet  1214  and thereby create a condensation chamber  1261  between it and the reflective sheet. In exemplary embodiments, a temperature differential is created between the upper chamber  1221 , on the one hand, and the lower chamber  1223  and condensation chamber  1261 , on the other hand, to induce condensation. The catchment sheet  1260  may define one or more apertures  1262  to allow air laden with water vapor to pass from the lower ballast portion  1223  of the elongated tube  1212  into the condensation chamber  1261 . The apertures  1262  may vary in number and may be regularly or unevenly spaced along the catchment sheet  1260 . The apertures  1262  may also vary in size. 
     Each aperture  1262  may include an adjacent lip  1264  formed along the edge of the aperture and extending around at least a part or all of the aperture. As water vapor condenses out of the air onto the side walls of the tube and the bottom surface of the reflective sheet  1214 , it drips onto the catchment sheet  1260 . The lips  1264  serve to guide the condensed water that has collected on the catchment sheet  1260  away from the apertures  1262 , thereby preventing the condensed water from falling back down into the lower ballast chamber  1223 . The catchment sheet  1260  conveys condensed water to a fresh water pass-through fitting  1278  (best seen in  FIG. 33 ) located at an end of the tube  1212 . 
     Turning to  FIG. 30 , another exemplary embodiment of a combined solar reflector and desalination assembly utilizing a porous membrane as a catchment device can be seen. Similar to assemblies discussed above, an embodiment of a combined solar reflector and desalination assembly  1210  comprises an inflated elongated tube  1212  having a reflective sheet  1214  coupled along opposed sides of the sheet to an interior wall  1215  of the tube  1212 . The reflective sheet  1214  divides the elongated tube into two portions, an upper portion or chamber  1221  and a lower ballast portion or chamber  1223 . The elongated tube  1212  is a unitary structure that includes integrally formed lower ballast portion  1223  containing water as a ballast liquid  1220 . 
     The assembly  1210  further comprises a catchment device  1266  coupled to an inner wall  1215  of the tube  1212  to catch and retain condensed water. In this exemplary embodiment, the catchment device is a porous membrane  1266  mounted to a bottom side  1267  of the reflective sheet  1214 . The porous membrane  1266  soaks up water that condenses from the ballast liquid and forms droplets  1270  in the membrane  1266 . A support tab  1273  may be coupled to the inner wall  1215  of the tube  1212 . In exemplary embodiments, two support tabs  1273   a ,  1273   b  are mounted to a respective wall of the tube and are located beneath the porous membrane  1266  and to the sides of the membrane. This configuration allows the support tabs  1273   a ,  1273   b  to catch water runoff from the side walls of the tube  1212  and prevent it from falling back into the pool of ballast liquid in the lower chamber  1223  of the tube  1212 . The porous membrane  1266  soaks up the condensed water from the air and from the bottom of the reflective sheet  1214  and conveys it to a fresh water pass-through fitting  1278  (best seen in  FIG. 33 ) located at an end of the tube  1212 . 
       FIGS. 31A-32  show another exemplary embodiment of a combined solar reflector and desalination assembly that employs a dual catchment sheet configuration. Exemplary embodiments comprise an elongated flexible tube  1212  having an upper portion  1221  and a lower ballast portion  1223 . As best seen in  FIG. 31B , exemplary embodiments include two lower ballast portions  1223   a ,  1223   b  and a “triple panel” cross section. This configuration is made by attaching a second sheet or panel  1245  to the reflective sheet or panel  1214  either in the middle B or at some other point between the two ends of the reflective sheet  1214  and connecting the bottom of the second panel  1245  to the bottom of the tube  1212  at some middle point C or at some other point. A reflective sheet  1214  is coupled along opposed sides of the sheet to a wall of the tube  1212 . The reflective sheet  1214  may be internally mounted by being coupled to an interior wall  1215  of the elongated tube  1212  or externally mounted. When internally mounted, the reflective sheet  1214  and the second panel  1245  divide the elongated tube into three portions, an upper portion or chamber  1221  and a lower ballast portion  1123  or two lower ballast portions or chambers  1223   a ,  1223   b  containing water as ballast fluid. 
     A catchment device comprises a top catchment sheet  1271  and a bottom catchment sheet  1272 . The top and bottom catchment sheets  1271 ,  1272  may be coupled to the elongated tube by being mounted either to an interior wall  1215  and/or to the second panel  1245  of the tube  1212 . When cold air is directed through the upper portion  1221  of the tube  1212 , air containing water vapor in the air in the lower portions condenses on the underside of the reflective sheet  1214  and drips onto the top catchment sheet  1271 . A support tab  1273  may be coupled to the inner wall  1215  of the tube  1212 . In exemplary embodiments, two support tabs  1273   a ,  1273   b  are mounted to a respective wall of the tube and are located beneath the bottom catchment sheet  1272  and to the sides of the dual catchment sheets. This configuration allows the support tabs  1273   a ,  1273   b  to catch water runoff from the catchment sheets  1271 ,  1272  and prevent it from falling back into the pool of ballast liquid  1220  in the lower chambers  1223   a ,  1223   b  of the tube  1212 . 
     The collected water is conveyed via the catchment sheets  1271 ,  1272  to a collection assembly  1280  to collect the fresh condensed water. With reference to  FIG. 33 , an exemplary embodiment of a collection assembly comprises a motor-driven pulley mechanism  1274 , a fresh water catchment cup  1277  and a squeegee mechanism  1276 . The collection assembly  1280  and accompanying fresh water pass through fittings  1278  may be located at one or more ends of the elongated tube  1212  and/or at one or more locations at intermediate points along the length of the tube  1212 . This assembly allows the condensed water to be used beneficially as potable water. The pulley mechanism  1274  may be mounted to an end of the tube or to an end cap assembly  1224  via a pulley mount  1275 . The catchment cup  1277  is mounted to an end of the tube or to the end cap assembly  1224  beneath the pulley mechanism  1274 . The squeegee mechanism  1276  is coupled to the catchment cup  1277 . The pulley mechanism  1274  may slidably engage one or more of the catchment sheets  1271 ,  1272 . In exemplary embodiments, the bottom catchment sheet  1272  is engaged by the pulley mechanism. 
     In operation, cold air may be directed through upper portion  1221  of the tube  1212  to create a temperature differential between the upper portion  1221  and lower portions  1223   a ,  1223   b  and facilitate condensation of the water from the lower chambers  1223   a ,  1223   b . The pulley mechanism  1274  pulls the bottom catchment sheet  1272  around and slides it through the pulley mechanism, turning it upside down so the collected condensed water drips into the catchment cup  1277 . The top catchment sheet  1271  is urged past the squeegee mechanism  1276  and contacts it so the squeegee mechanism  1276  forces the remainder of collected water into the catchment cup  1276 . As best seen in  FIG. 33 , in exemplary embodiments the top and bottom catchment sheets  1271 ,  1272  are a continuous sheet that cycle through the pulley mechanism  1276  of the collection assembly  1280 . The fresh water collected in the catchment cup  1276  then exits the tube  1212  through a fresh water pass through fitting  1278 . It will be readily apparent to those skilled in the art that the various embodiments of catchment devices and collection mechanisms described herein can be used with any type of tube design, including the triple panel configuration, the upper and lower two chamber configuration or other types of internal geometry. 
     Turning to  FIG. 37 , in exemplary embodiments a solar collector  1218  may be located near a combined solar reflector and desalination assembly  1210  or an array  1201  of assemblies, and the tubes  1212  are configured to rotate to direct reflected solar radiation towards the solar collector  1218 . The solar collector transforms the reflected solar radiation to electricity or process heat. In exemplary embodiments, the reservoir of liquid in the tubes  1212  can also be used to grow biomass as discussed in detail above in connection with  FIGS. 17 and 18 . As shown in  FIG. 38 , in such embodiments the reflective sheet  1214  is configured to reflect IR radiation while allowing visible light to pass through to a culture medium  1220  within the lower ballast portion  1223  of the tube  1212 , thereby forming a combined concentrating solar power/desalination/photobioreactor assembly  1210 . 
     It should be noted that embodiments of a desalination apparatus without a solar reflector or other solar reflection or concentration features are provided herein using the system described above.  FIGS. 34A-36  show exemplary embodiments of a desalination apparatus  1310  comprising an inflated elongated tube  1312  having at least one catchment device  1360  coupled along opposed sides of the sheet to an inner wall  1315  of the tube  1312 . The catchment device  1360  may divide the elongated tube into two portions, an upper portion or chamber  1321  and a lower ballast portion or chamber  1323 . In exemplary embodiments the elongated tube  1312  is a unitary structure that includes integrally formed lower ballast portion  1323 . The lower portion  1323  may contain culture medium and may be used to grow photosynthetic biomass. 
     The catchment device  1360  is an internal structure configured to absorb, catch, collect and convey or transmit fresh condensed water. Referring to  FIG. 34A , in exemplary embodiments, the catchment device  1360  is a catchment sheet coupled to an inner wall  1315  of the elongated tube  1312 . The catchment sheet  1360  may define one or more apertures  1362  to allow air laden with water vapor to pass from the lower ballast portion  1323  of the elongated tube  1312  into the upper chamber  1321 . The apertures  1362  may vary in number and may be regularly or unevenly spaced along the catchment sheet  1360 . The apertures  1362  may also vary in size. Each aperture  1362  may include an adjacent lip  1364  formed along the edge of the aperture and extending around at least a part or all of the aperture. In an alternative embodiment shown in  FIG. 34B , a non-reflective sheet  1313  may be used instead of a reflective sheet to create a condensation chamber  1361  between the catchment sheet  1360  and the non-reflective sheet  1313 . 
     As shown in  FIG. 35 , the catchment device may comprise a porous membrane  1366  and be accompanied by one or more support tabs  1373   a ,  1373   b . The porous membrane  1366  soaks up water that condenses from the ballast liquid and forms droplets  1368  in the membrane  1366 . A support tab  1373  may be coupled to the inner wall  1315  of the tube  1312 . In exemplary embodiments, two support tabs  1373   a ,  1373   b  are mounted to a respective wall of the tube and are located beneath the porous membrane  1366  and to the sides of the membrane. This configuration allows the support tabs  1373   a ,  1373   b  to catch water runoff from the tube sidewalls  1315  and prevent it from falling back into the pool of ballast liquid in the lower chamber  1323  of the tube  1312 . The porous membrane soaks up the condensed water and conveys it to a fresh water pass-through fitting  1378  (best seen in  FIG. 33 ) located at an end of the tube  1312 . 
     The catchment device may also comprise a dual sheet structure having a top and bottom catchment sheet  1371 ,  1372  and one or more support tabs  1373   a ,  1373   b , as shown in  FIG. 36 . Exemplary embodiments comprise an elongated flexible tube  1312  having an upper portion  1321 , lower ballast portions  1323   a ,  1323   b  and a “triple panel” cross section. The triple panel configuration is made by attaching a first sheet or panel  1313  to interior walls  1315  of the tube  1312  and a second sheet or panel  1345  to the reflective sheet or panel  1314  either in the middle B or at some other point between the two ends of the first panel  1313  and connecting the bottom of the second panel  1345  to the bottom of the tube  1312  at some middle point C or at some other point. Thus, the first panel  1313  and the second panel  1345  divide the elongated tube into three portions, an upper portion or chamber  1321  and two lower ballast portions or chambers  1323   a ,  1323   b  containing water as ballast fluid. The top and bottom catchment sheets  1371 ,  1372  may be coupled to the elongated tube by being mounted either to an interior wall  1315  and/or to the second panel  1345  of the tube  1312 . 
     When cold air is directed through the upper portion  1321  of the tube  1312 , water vapor in the air in the lower portion condenses on the underside of the reflective sheet  1314  and drips onto the top catchment sheet  1371 . A support tab  1373  may be coupled to the inner wall  1315  of the tube  1312 . In exemplary embodiments, two support tabs  1373   a ,  1373   b  are mounted to a respective wall of the tube and are located beneath the bottom catchment sheet  1372  and to the sides of the dual catchment sheets. This configuration allows the support tabs  1373   a ,  1373   b  to catch water runoff from the catchment sheets  1371 ,  1372  and prevent it from falling back into the pool of ballast liquid in the lower chambers  1323   a ,  1323   b  of the tube  1312 . Exemplary embodiments of a desalination apparatus may include a collection assembly to collected fresh condensed water, as described in connection with  FIG. 33 . 
     Thus, it is seen that systems and methods of generating energy and fresh water from solar radiation are provided. It should be understood that any of the foregoing configurations and specialized components or chemical compounds may be interchangeably used with any of the systems of the preceding embodiments. Although exemplary embodiments of the present disclosure are described hereinabove, it will be evident to one skilled in the art that various changes and modifications may be made therein without departing from the disclosure. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the disclosure.