Patent Abstract:
Solar generators have Fresnel lenses and spaced heat absorbers or photovoltaic cells for receiving focused solar rays. Heat is removed from their backs by boiling liquid in conical receivers. Pins or fins extend rearward into the receivers from the heat absorbers or photovoltaic cells. Liquid supply to the receivers is controlled by valves and floats or sensors. Tubes remove steam or vapor from the receivers for driving generators or for cooling photovoltaic cells. Hinged tubes which form the foldable support conduct the steam to generators and condense the vapor. Liquid is returned to a holding tank, is pumped to a distribution tank and is conducted by some of the structural tubes back to the valved receivers.

Full Description:
This application claims the benefit of U.S. Provisional Application No. 60/749,050 filed Dec. 12, 2005, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     In several previous terrestrial systems, very high levels of solar concentration (hundreds of suns) have been achieved with reflective optics to generate steam for powering turbines and direct conversion of heat to electricity via Sterling engines or photovoltaic (PV) cell for direct electrical conversion. Refractive optics in many forms, mainly Fresnel lenses, has been used for moderate levels of concentration (e.g., 20 suns) using flat or curved lenses to focus on a linear PV receiver. Flat or domed Fresnel lenses can achieve hundreds of suns of concentration using spot PV receivers. 
     MIDWAY Corporation, Chicago, Ill., for example, marketed a flat aperture configuration, with multiple Fresnel lenses concentrating light on small PV cells (1-2 cm 2 ) distributed on the back plane of the structure with a focal length less than a foot. The heat was dissipated in the sheet metal back plane, and was adequate as long as the small receivers were adequately spread apart. 
     ENTECH Corporation, Keller, Tex., has developed both trough (curve lens) line concentrators and domed lenses for spot concentrators, and has flown a domed Fresnel lens in space using dual-junction cells. In the case of the line array, the terrestrial system uses passive cooling (aluminum back plane with extruded aluminum fins) for 20× concentration. In space application, ENTECH uses high thermal conductivity graphite for heat spreading for both domed and trough concentrators. In each case, however, the size of the PV receiver is relatively small, with a short focal length lens. 
     As long as the lenses and receivers are small, the thermal management problem can be solved through passive cooling techniques. But, if the size of the system (larger lenses, receivers, and focal lengths) is increased to achieve “economies of scale,” the thermal management of waste heat (that not converted to electrical energy by the PV conversion) becomes technically challenging. 
     Traditionally, the cooling of high power electronics requires active cooling to remove kilowatts of heat. This often entails pumping of water or other working fluids through cold plates, or in the extreme, the use of refrigeration units to chill the working fluid. In traditional two-phase systems, the use of compressors and heat exchangers is required to remove the heat. These often entail large investment of equipment, require additional kilowatt of electrical energy to operate refrigeration equipment, all of which adds considerably to the cost, and weighs against “scaling up” the high concentration (hundreds of suns) PV systems. 
     Needs continue to exist for improved solar power methods and apparatus, and for assembly methods that allow rapid deployment of arrays of any kind. 
     SUMMARY OF THE INVENTION 
     The method and apparatus of the invention, called SOLFIRE, takes advantage of a new two-phase Subambient Cooling System (SACS) designed and patented by Raytheon (McKinney, Tex.), which can efficiently remove tens, even hundreds kilowatts of waste heat without the need for expensive refrigeration units, requiring only a moderate-sized liquid pump, a reservoir for the working fluid, and a vapor-to-air heat exchanger. In order to reduce costs, ZENTEK is proposing a large aperture structure consisting of a continuous path piping system that can act as the heat exchanger for the SACS system, thus eliminating some of the costs associated with SACS, eliminating a separate heat exchanger and the fan-motor required to move air thought the heat exchanger. 
     SOLFIRE can also be used as a large collector of thermal energy for generation of steam that can power small, distributed turbine generators at the focal points of the concentrator lenses. The system can use commercial parts to maintain the goal of low cost. For example, automobile air conditioning compressors which are mass produced and can be bought in quantity, can be run in reverse by injecting steam in the output port and act as a steam turbine to power small kW generators. Rotary tools that run on compressed air can also be converted to run on moderate pressure steam. 
     In order to keep costs at a minimum, SOLFIRE incorporates modular parts that can be mass produced in a clean, all weather, all season factory environment, then transported to the deployment site and built up into the completed system. Many embodiments can be devised for how SOLFIRE can be manufactured and deployed. One, however, which will be illustrated below, maximizes the amount of work done in the factory, and minimizes the amount of work required at the deployment site. In one embodiment illustrated below, the array is built up with 8 ft high×40 ft long sections, pre-joined at the factory, then folded up and sealed into a transportable package 40 feet long, 8 ft wide and 3 to 4 feet deep, with one or two packages transportable on a flat bed truck. At the site, the package is “unfolded” onto a platform consisting of the substructure of the pointing and tracking system, then elevated and put into service. 
     SOLFIRE is a new solar concentrator system that brings together a number of established technologies with some innovative new concepts in order to radically lower the cost of electric power generation. SOLFIRE could be used for electric power generation via collection of solar thermal energy to generate steam to power turbo-generators, or to covert solar energy directly into electric power using photovoltaic device technology. Although many variants are possible, the SOLFIRE system, for purposes of illustration, is described as a point design, capable of producing 36 kW of electric power based on a built up of 1 kW modular cells each containing a 4 square meter aperture, a 2.5 meter focal length, illuminating a 100 cm 2  PV receiver for a concentration of up to 400 suns. The system, of course, is scalable to other apertures, focal lengths and receiver apertures. The 36 kW array is chosen as the nominal size that in turn can serve as a building block to a much larger system, capable of producing megawatts of electric power for the grid. The SOLFIRE point embodiment is for the purposes of illustration only relies on the following technologies, which can be applied to larger or smaller system. 
     The unit cell contains a square meter silicone lens, e.g. manufactured by 3M on a transparent acrylic support structure. The lens can be flat, curved or domed. A preferred photovoltaic receiver of 27.5% efficient multi-junction (MJ) cells (e.g. manufactured by EMCORE, Albuquerque, N. Mex.) with grid lines appropriate for high levels of solar concentration (e.g. 300-400 suns). An alternative 1 kW turbine generator is powered by the heat from the concentrator lens. A secondary lens system affixed to the PV cell itself directs light around the grid lines (by ENTECH, Keller, Tex.) for increased efficiency. 
     The new optical subsystem for redirecting stray light illumination back onto the PV cells called SLR (Stray Light Recovery) is applicable to the PV or steam turbine systems. 
     A two-phase Subambient Cooling System abbreviated SACS (RAYTHEON-McKinney Division) uses a water/glycol or methanol working fluid to efficiently remove the heat from the PV receiver nodes. For example, 36×1 kW PV nodes would require over 100 kW of thermal heat removal. 
     A multifunctional truss structure for keeping the PV cells aligned, is composed of continuous piping that also serves as the vapor—phase heat exchanger for the SACS system as well as the liquid-phase manifold for injecting the working fluid into each PV receiver subsystem. The system is also capable of re-condensing steam from the turbo-generator. Various new pointing and tracking maintain 1-2 degree pointing accuracy. 
     SOLFIRE uses on a combination of technical innovations to achieve a low cost system that may not be able to achieve the goal of “one dollar per watt” of capitol investment, but is intended to compete with oil, gas, nuclear. Current market conditions may allow for a system in the $2-3/watt category. This means that a 36 kW SOLFIRE system with have to meet challenging manufacturing goals of $75,000-$100,000 per unit cost. SOLFIRE is designed primarily as a subsystem capable of being replicated and deployed as a multi-megawatt electric power generation system. 
     The SOLFIRE modular system is aimed at systematically assessing the contributions of several demonstrated solar concentrator technologies, coupled with some new thermal management and structural concepts in order to achieve a low cost, and ultimately competitive renewable energy system design for large, grid-compatible solar electricity generation. The use of high efficiency, but also very expensive, MJ cells for terrestrial use requires solar concentration in order to achieve low enough costs to compete with non renewable power sources (oil, coal, nuclear). 
     The use of solar concentration is mandated not only by cost, but also by the limited manufacturing capacity of the two principal US vendors, SPECTROLAB and EMCORE. Terrestrial applications of MJ technology must compete with the primary market for MJ cells, which is space power for satellites, where performance, not cost, is the principal driver. SOLFIRE target of 300-400 sun concentration is thus driven by both cost and availability. A SOLFIRE array will use only 1/300 to 1/400 of the area of PV cells required for a comparable planar array system. 
     The invention provides a scalable array structure containing Fresnel lenses that concentrates sun illumination on a receiver body that generates steam to drive a turbine generator for production of electrical power. 
     It is an object of the invention to provide a receiver body at the focal point of the concentrating optics that contains PV cells to generate electricity, and a two phase Sub-Ambient Cooling System (SACS) to maintain the an appropriate temperature and prevent overheating. 
     Another object of the invention is to provide a receiver body at the focal point of the concentrating optics that serves as a steam generator to drive a turbine generator for the production of electrical power. 
     In the invention the scalable array structure is constructed with pipes with joints that allow the flow of liquid and vapor phases of the working fluid through out the structure. 
     In the invention the open piping system of the array structure can serve as a heat exchanger to condense hot vapor phase working fluid back to the liquid phase for both the PV system as well as the turbo generator. 
     The invention provides the open piping system of the array structure that serves as a manifold for the collection of the liquid phase of the working fluid and returns it by force of gravity back to a holding tank at the bottom of the array. 
     The open piping system of the array structure also serves as a separate manifold for pumping liquid phase working fluid back to the nodes of the array, where it is used by the receiver body for conversion of liquid to vapor phase for one of two purposes, for cooling in the case of the PV SACS system, or for the generation of high pressure steam in the case of the turbo generator, or both. 
     The invention provides a receiver body that contains a float valve which regulates the flow of liquid into the receiver body, maintaining a proper liquid working fluid level as the working fluid is converted to vapor when heated by the concentrated solar illumination. 
     As a further object of the invention the receiver body contains a pin/fin arrangement at the base of the illuminated area to facilitate the conversion of liquid phase to vapor phase. 
     It is a further object of the invention that the Fresnel lens that concentrates the light on the receiver body has multiple focal lengths at the center and at the external portions of the square lens in order to maximize the collection of light on the surface of the receiver body. 
     An object of the invention is to reduce costs. The new scalable array structure is composed of panels that can be mass produced in a factory environment and are joined in such a fashion that they can be folded up and stowed in a transportable package that can be unfolded at the deployment site with minimum use of personnel and equipment and used for any purpose. The physical dimensions of the new modular cell structure provide transportable modules that may be rapidly assembled in the field. 
     These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a perspective front view, and  FIG. 1   b  is a side view of the array structure. 
         FIG. 1   c  is perspective top and side view of one of the modular cells within the array. 
         FIG. 1   d  and  1   e  are perspective views of the open array structure and the array structure with side panels. 
         FIGS. 2   a  through  2   e  are component panels that make up the array structure. 
         FIG. 3   a  is a side view of the deployment of the folded array structure panels. 
         FIG. 3   b  is a perspective view of the full extension of the folded array with side panels rotated into position. 
         FIG. 4   a  is top view of a receiver.  FIGS. 4   b  and  4   c  are side views of the receiver body in two orientations (low angle and high angle). 
         FIGS. 5   a  and  5   b  are cutaway views of the valve at the bottom of the receiver body with valve closed in  FIG. 5   a  and open in  FIG. 5   b.    
         FIGS. 6   a  and  6   b  are perspective views of the Fresnel lens concentrating the solar illumination on the top of the receiver body photovoltaic (PV) cells, with the focal points of the bifocal lens below the PV plane in  FIG. 6   a  and above the plane in  FIG. 6   b.    
         FIG. 7  is a side view of the Stray Light Recovery (SLR) system optical paths. 
         FIGS. 8   a  through  8   g  show one embodiment of a 2-axis tilt/roll tracking mount to support the 36 kW array illustrated in  FIGS. 1   d  and  1   e.    
         FIG. 9  is a side view of the receiver body acting as a steam generator for the turbine driven generator/alternator. 
         FIG. 10  shows a radar erected on the new array structure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The SOLFIRE 36 kW array illustrated in the following descriptions has 36 lenses and 36 PV cell receivers in a 40 ft×40 ft square array structure  11  8 ft deep as shown in  FIGS. 1   a  (perspective view) and  1   b  (side view).  FIG. 1   c  is a blow up of on of the 36 cells that make up the array. The lenses and receivers are held in place by a tetrahedral substructure, hereafter referred to as the Modular Cell, MC.  FIG. 1   c  shows the MC as a inverted tetrahedral structure with the base formed by four 2 meter (6.6 ft) long pipes  1  (1″ galvanized pipe), connected at each corner  2  with four 2.66 meter (8.25 ft) long pipes  3  forming the sides of the inverted tetrahedron, joined together at the apex  4 , providing a very stabile platform for the PV receiver  5 . The receiver is located at the focal point of the flat Fresnel lens  6  contained in the base of the tetrahedron. The dotted lines  7  indicate sites where the MC is connected into the larger array structure. 
       FIG. 1   d  shows an open frame version of SOLFIRE.  FIG. 1   e  illustrates a slightly more complex closed frame version with sheet metal sides and bottom providing more protection against the weather, and more surface area for dissipating heat from the SACS system. This truss system, which is described in more detail later, is relatively light weight, but rigid, and can be built up with standard pipes and fittings common in the electrical and plumbing industries. It therefore is low in cost, since these parts are manufactured in quantity for other markets. 
     Although the array in  FIGS. 1   a - e  are shown with flat Fresnel lenses, it is possible to also use curved lenses or domes, as has been demonstrated by ENTECH, which are more tolerant to pointing errors, but may be more costly to produce, and possibly to maintain. Although less tolerant to tracking error, a flat lens would be easier to keep clean from the dust and sand, which can lower the optical efficiency. 
     The new array structure is composed of modular cells. The 40 ft×40 ft array structure is built up by fabricating 40 ft long sections, approximately 8 ft wide, containing piping as shown in  FIG. 2   a . The piping  8  is connected in such a manner that the interior of the piping  8  is open and can transport liquid or vapor ranging in pressure from 2 to 40 or more psi as required by the SACS system, depending on the vertical orientation of the receivers. 
     The piping can be welded at the joints  9 , or connected through threaded joints, with connectors and seals similar to those found in the electrical and plumbing industries. At the deployment site, after the structure is fully extended, the threaded joints can be brazed or soldered if necessary to lower the risk of leaks in the sub-ambient and the higher pressures of the sealed SACS system. The soldering of the joints also adds structural rigidity. Prior to the final disposition, the threaded joints allow some of the joints to rotate, which is necessary in one of the deployment embodiments as described. The threaded joints also act as couplers for mating panels to each other at the deployment site. 
       FIG. 2   b  shows a 40 ft wide 8 ft deep panel containing the same layout of piping but with the addition of sheet metal  12  that is can be tack welded and/or brazed to the piping at the factory. This configuration is utilized for the closed truss system shown in  FIG. 1   e . Also shown is optional sheet metal stiffeners  13  affixed to the sheet metal to increase its stiffness without adding substantial weight. All of the attachment points  15  are threaded couplings that allow for on site connection of the panels to each other through these couplings. The sheet metal panels  12  can serve as end panels  12   a  or as side panels  12   b  enclosing the truss structure. 
       FIG. 2   c  shows a 40 ft×6.5 ft panel containing the Fresnel lenses  16  which when coupled together, form the top of the array structure shown in  FIG. 1   c . The 3M company manufactures silicone lenses in a 1 m wide continuous process which could be ordered in 40 ft lengths to be affixed to acrylic sheet to provide structural stability. 
       FIG. 2   d  shows an interior bottom panel  17 , which when joined through the couplers to other interior panels and to the 40 ft×3.3 ft end bottom panels  18  serves as the bottom of the truss structure enclosure. The piping in the bottom panels are colored black to indicate they are normally filled with the liquid phase working fluid, while the rest of the piping is shown as open piping, is normally associated with the vapor phase in the SACS system.  FIG. 2   e  represents a half width bottom panel, which is required if the sides of the array are perpendicular to the bottom plane as shown in  FIG. 1   e.    
     All of the piping is linked together through welded joints or with the threaded connectors, but the interior of the piping system is open so that it can act as a heat exchanger for the whole array, returning the condensed liquid back to a reservoir where it then can be recirculated to PV cell receivers through the liquid phase network shown in the bottom panels,  FIGS. 2   d  and  2   e.    
       FIGS. 3   a  and  3   b  shows how the array truss structure can be fabricated at the factory. The large 40 ft panels shown in  FIG. 2  can be prejoined at the factory in a manner that allows the whole array structure to be folded up like an accordion, with the lens panels  16  and the bottom panels  17  nested within the folded up truss structure. At the deployment site, the accordion truss structure is unfolded as shown in the  FIG. 3   a  overview, with the pleats formed by the pipe structures  10  linked alternately top and bottom by rotatable joints or hinges. The side panels  12   a  and  12   b  are rotated around the corner hinges and connected to the extended truss structures  10  through connectors that can then be soldered or brazed as shown in  FIG. 3   b . The left side of  FIG. 3   a , which is an end-view of the folded truss structure, illustrates how the 40 ft×8 ft sections needed to make up the truss system including lenses and bottom panels are nested into the accordion-like structure. Starting from the left: side panel  12   a  is joined to end panel  12   b  via rotatable joints or hinges along the 8 ft front side. The end panel  12   b  in turn is attached to the first of the pipe structures  10  through rotatable joints or hinges along the top of the 40 ft long structure. 
     Bottom panels  17  and  18  are nested between truss structure panels  10 , which are each joined top and bottom sequentially to form the stowed structure. This sequence of pipe structures  10  hinged top and bottom with rotatable joints or hinges form the pleats of the accordion structure. The lens panels  16  and the end and interior bottom panels  17  and  18  are nested between the pleats, but are attached also to the adjacent pipe structures  10  at the top in the case of the lens panels  16 , or at the bottom in the case of the end and interior bottom panels  17  and  18 . 
     The midsection of  FIG. 3   a  shows how the accordion structure is unfolded with panels  10  forming the backbone of the pleats. In sequence, bottom panel  18  is rotated down and attached to the bottom of the next pleat edge, with panel  16  rotated up and attached to the top edge of the subsequent pleat edge. This sequence of pipe structure pleats ( 36  in the case of our 36 kW system) is terminated at the right hand side with the reverse order of the left hand side, that is, with an end panel  12   b  attached to a side panel  12   a  via hinges along the 8 ft dimension on the back side. 
       FIG. 3   b  illustrates how these side panels  12   a  on the exterior of the folded up package, will be rotated 270 degrees after the accordion structure is extended to form the sides of the truss array.  FIG. 3   b  shows the packaged array after deployment resting on two or more 40 ft beams which provide the back structure of the array, and the primary structure of whatever tracking mechanism is employed which will be described later. 
     In the above paragraphs, reference has been made to pipe structures, end and side panels, lens panels and bottom panels as being hinged, or joined with rotatable joints. The term rotatable joints refers to versions of SOLFIRE where panels can be joined by sharing a common pipe along the seam of the “pleat.” This adds a level of complexity but eliminates redundant pipes at the pleat edges. 
     This accordion-like structure is the preferred way of transporting the panels to the site for deployment, but not the only way. In alternative methods the panels could be transported separately to the site and joined at the site, although this would require additional equipment such as cranes, and additional manpower to handle, align, and attach each panel. This could become a daunting task with 40 ft×8 ft panels only 1½ inches thick, subject to winds, bending, etc. 
     Photovoltaic receivers have thermal management system.  FIGS. 4   a - 4   c  show views of a photovoltaic (PV) receiver  5  located at the apex  4  of the modular cell.  FIG. 4   a  is a top view of the multi-junction PV cell connected in series and parallel depending on the desired line voltage, mounted on the base of the conical-shaped receiver. 
       FIG. 4   b  is a side view of the cone-shaped receiver body, which has of a number of components required for the SACS two-phase thermal management system. The PV cells  20  are mounted on a base plate  21 , to which are attached or cast into the plate numerous fins or pins  22  that facilitate the transfer of heat from the PV cells to the liquid phase of the SACS system. The liquid phase of SACS (glycol water mixture or methanol) is shown filling most of the body of the receiver  23 , touching the lower portion of the base plate. 
     The conversion of liquid to the vapor phase, occurs in the matrix of pins in the base plate. The vapor collects at the top of the receiver  24 , exiting through an orifice  25  at the top of the receiver. This orifice, as shown in later graphics, must always be higher than the level of the liquid phase, regardless of the orientation of the receiver, within certain limits. The orifice  25  is connected into pipe  5 , which allows the vapor to be transported throughout the array structure, which is in contact with the ambient air. The vapor, losing heat, re-condenses into the liquid phase and through gravity trickle down to a holding tank at the base of the array. 
     Because the system is maintained a low, sub-ambient pressure of 2-3 psi, the liquid boils at a low temperature (60-65 C), and thus can remove kilowatts of waste heat in the receiver, maintaining the temperature of the PV cells at an acceptable level. 
     As the liquid boils away, it is replenished through a valve system  26  at the apex of the cone-shaped receiver that meters the liquid working fluid from a manifold  27 , which is maintained a much higher pressure (30-40 psi) than that of the receiver.  FIG. 4   c  shows the receiver tilted up when the sun angle is closer to the zenith. The two orientations shown in these figures correspond to the minimum and maximum angles that the receiver will be tilted for systems deployed between latitudes 30 and 40 degrees, which include the desert Southwest, United States, the most desirable deployment area for large power grid applications. 
     The valve is controlled by a float system having a float  28  connected by a rod  29  to hinge  30  mounted on the side of the receiver body. The rotational motion of the float is transferred to liner motion by a connecting rod  31  that transfers the motion of the float  28  to the valve body  26 . 
     The float system described above is mechanical, with a mechanical feedback loop. Other systems may be used such as an electromechanical system. A sensor located between the liquid/vapor interfaces  32 , triggers a solenoid electromechanical valve when the liquid level is low and replenishes it. 
     The same type of float system can be used for the turbo generator where concentrated sun light impinges on the surface (base of the cone) containing a heat absorber, which transfers heat to the pins or fins, which in contact with the liquid phase (water) generates steam. This system would operate at a much higher internal pressure in order to generate high-pressure steam for the turbo generator. 
     The new mechanical valve systems control flow of the fluid.  FIGS. 5   a  and  5   b  show the operation of a pilot valve driven main valve, which is opened and shut by the translational motion of the connecting rod  31  between the float system and the pilot valve. The connecting rod  31  is linked to an intermediate rod  33  hinged at  34  to the side of the receiver body. The intermediate rod is connected to yoke  35 , which is mechanically linked to the pilot valve  36  and the relief valve  37 . 
     The pilot valve is shut, and the relief valve  34  open, as shown in  FIG. 5   a , caused by the float being in the up position meaning the receiver is full of liquid. The main valve  38  is shut and held shut by spring  39 . The higher pressure liquid shown as heavy shading, in manifold  27 , is not allowed to enter the valve body. The volume  41  above the large valve piston head  40  is in equilibrium with the low-pressure liquid in the interior of the receiver, because relief valve  37  is open. 
       FIG. 5   b  shows the situation when the liquid in the receiver goes down and requires replenishment. In this situation, connecting rod  31  reverses direction, opening pilot valve  36 , closing relief valve  37 , allowing high pressure liquid in  27  to enter the volume  41  above the piston head  40 , compressing spring  39 , depressing the piston and opening valve  38 , which admits high pressure liquid into the receiver body to replenish the level of the reservoir. After the liquid level has risen and again raised the float, the process is reversed, shutting the pilot valve, opening the relief valve, and allowing the compressed spring  39  to push the liquid in volume  41  out into the receiver through relief valve  37 , restoring the equilibrium condition shown in  FIG. 5   a.    
     Bifocal Fresnel lens are preferred.  FIGS. 6   a  and  6   b  show a flat Fresnel lens that has separate focal lengths for the interior and exterior portions of the lens in order to efficiently utilize all portions of the square lens to project onto a round PV cell receiver assembly.  FIG. 6   a  show the circular symmetric portion of the lens  42  bounded by the four corners of the square projecting onto focal point  43  intersecting the full width of the circular PV assembly  20 . The four sectors of the outer portion of the lens  44  the shaded portion outside of the circular portion designated  42 , but bounded by the square, is constructed with a shorter focal length  45  so that its rays also intersect the circular PV assembly. In  FIG. 6   a , the focus points are below the PV assembly  20 . 
     In an alternative embodiment shown in  FIG. 6   b , the focus points are above the PV assembly, between the lens and the PV assembly. In order to project fully on the PV assembly, the order of the focal points are reversed. The rays from the outer portion of the lens  44 , converge on focal point  46 , above the PV assembly  20 , but below the convergence of rays from the interior portion of the lens  42 , which converge at focal point  47 . Both portion of the lens flood the PV assembly  20 . 
     A new reflective optics assembly provides stray light recovery (SLR).  FIG. 7  shows a reflective optics scheme, the Stray Light Recovery system (SLR)  48  that redirects light resulting from pointing errors (1 to 2 degrees) back onto the PV module. Solar irradiance concentrated by the Fresnel lens enters the top of the SLR assembly  49  through the focal point  50  and onto the PV cells  20 . Ray traces  51  and  52  representing light that emerged from the outer portion of the Fresnel lens which were subject to 1 to 2 degrees of pointing error respectively, are shown reflected off of curved reflective optical surfaces  53  at the bottom, on either side of the PV assembly  20 , back up to the opposite side and upper portion of the SLR  48 , where it is again reflected downward from reflective optical surfaces  54  onto the plane of the PV module  20 . Although there are some losses due to the reflection off of the two surfaces  53  and  54 , it is estimated that 80% or better of the light which would have been lost falling outside of the boundary of the PV cells, could be recovered to generate current in the PV assembly. 
     The SLR system in  FIG. 7  is illustrating use in a spot focus application, but could also be used in a line focus application similar to that used by ENTECH and others. The SLR system could also be used for the turbo generator application by increasing the amount of light impinging on the heat absorber. 
     The new SOLFIRE dual axis tracking mount provides solar or target pointing accuracy.  FIGS. 8   a  through  8   g  show one embodiment of a 2-axis tilt/roll tracking mount to support the 36 kW array illustrated in  FIGS. 1   d  and  1   e .  FIG. 8   a  is a frontal view of the array structure  11  rotated 90 degrees in a diamond configuration with one corner at the uppermost point of the array and the opposite corner in the lowest point. This diamond configuration as will be seen in  FIG. 8   b  aids the flow of the re-condensed working fluid of the SACS system, where the liquid phase flows back to the lowest point of the array through the influence of gravity. 
       FIG. 8   b  is the back view of the array showing the various manifold systems for distributing the liquid phase working fluid to each of the receivers  5  through the bottom panel piping system  17  and  18  shown in  FIGS. 2   d  and  2   e . Liquid accumulated in the holding tank  65  is pumped via pump  66  up the array shown as black piping  67  up to the auxiliary tank  68  where it is distributed to all the receivers  5  via the piping network  67 . After the liquid phase has been converted to the vapor phase in receivers  5 , the vapor is distributed throughout the open piping system  69  (shown as white piping in the figure). When the vapor phase is re-condensed into the liquid phase by contact with the piping at ambient air temperature, it is returned to the holding tank through the open piping system  69  shown by the white arrows in the figure. From there the liquid is pumped to the auxiliary tank  67 , for redistribution to receivers  5  through manifold  67 . 
       FIG. 8   c  shows the backside of the array supported by pillar  55 , which is linked to the array through a gimbaled mechanism  56 , which is described in the accompanying figures. The light-weight array  11  is supported by a stout array support structure  57  shown as a cross-hatched rectangular structure in the interior array, attached to the backside of the array, and hinged top and bottom  58  to a T-shaped member shown in side view  FIGS. 8   d  and  8   e . This “T bar” is linked to the pillar  55  via a rotatable joint  60  and acts as the tilt mechanism for adjusting the array in the North-South direction as shown in side views  FIGS. 8   d  and  8   e . The “T bar” is augmented structurally by diagonal support members  61 , is driven by an extendable screw jack  62  which positions the T bar and secures it in place at the angle required for sun tracking, rotating the array in the North-South plane. The insert above  8   e  shows this N-S rotation around axis b. The insert figure above  FIG. 8   e  also shows the array roll mechanism in the East-West plane where support structure  57  linked to the T bar  59  via rotatable joints  58  is allowed to rotate around axis a in the E-W direction, driven and held in place by a large diameter wheel  63  driven by means of a motor at  64 . This motion is illustrated in the top view of the array in  FIGS. 8   f  and  8   g . Alternatively, the large diameter wheel can be driven and held in place by a cabling system as described in U.S. Pat. No. 6,302,009 “Modular Solar Tracking Frame” issued Oct. 15, 2001. 
     Turbo generator alternative uses similar methods and apparatus. The turbo generator would share many of the attributes of the SOLFIRE concept for PV electrical generation such as: (1) the distribution of the liquid working fluid to each of the nodes via the piping system shown in  FIG. 8   b ; (2) the metering of the liquid phase into the cone shaped steam generator shown in  FIG. 4 ; (3) the mechanism for maintaining the pressure differential between the liquid and high pressure gas phase as shown in  FIG. 5 ; (4) the lens concentrator and SLR systems shown in  FIGS. 6 and 7 ; (5) the open piping system used to condense the gaseous phase back to liquid phase. 
       FIG. 9  shows additional turbo generator hardware that processes the steam coming from receiver  24  through orifice  25  into turbine  70 , which is connected to the alternator/generator  71 . Note the steam exiting the turbine  72  is connected into the open piping system  69  for circulation into the SOLFIRE structure, with subsequent condensation by contact with the piping at ambient air temperature, and return of the condensed working fluid back to the holding tank  65 . 
     The turbo generator variant differs from the PV variant in several ways. The turbo generator could use working fluids including, but not limited to water, glycol, or methanol, and could operate in different pressure regimes than were discussed for the PV system. For example, the vapor side of the system would not necessarily operate at 2-3 psi, which was required to keep the base of the photovoltaic at 60-65 C. The turbo generator could run a pressures greater than ambient pressure (14 psi) and thus at higher temperature for the steam exiting the receiver. In fact, for the turbo generator case, it is desirable to have the pressure and temperature as high as possible coming out of the receiver  25  with lower pressure, lower temperature steam exiting the turbine  72 . 
     In place of the photovoltaic cells  20 , the turbo generator alternative would have a heat absorber  73  which could use a phase change salt that would liquefy, store and spread the heat at hundreds of degrees Centigrade, and a layered insulator plate  74  having optically coated gas enclosing a vacuum chamber  75 . 
     Solid state radar and other alternative systems employ the erecting and pointing and tracking methods and apparatus. 
     Although the principle application of SOLFIRE described above relates to generation of electricity via photovoltaic or turbo generators, nonetheless, many of the concepts and designs related to SOLFIRE could be utilized in other applications, such as a large solid-state radar, the front view of which is shown in  FIG. 10 . The new methods and apparatus include the basic transportable and deployable structures shown in FIGS.  1 , 2  and  3 , valve system shown in  FIGS. 4 and 5 , the two axis tracking system shown in  FIG. 8 , and aspects of the two phase SACS cooling system described throughout 
     In the case of the radar, the lenses of the SOLFIRE are replaced by large panels of solid-state, high power electronics  76  and radiating elements that require cooling which can be accomplished with the two phase SACS system. In the case of the radar shown in  FIG. 10 , the liquid phase supply manifold is on the font face of the array instead of the back as shown in  FIG. 8 . The liquid working fluid accumulated in holding tank  65  is pumped up to auxiliary tank  68  and then distributed via the black piping  67  to nodes  77  where the liquid phase can be distributed into four adjacent panel  76  for use in cooling the high power electronics. Each node  77  contains one of the valve systems shown in  FIGS. 4 and 5  without the photovoltaic cells, to regulate the pressure of the liquid phase, which is distributed to the four adjacent panels around the node. Here the liquid phase is converted to vapor phase, removing heat from the high power electronics. The vapor phase is connected to the return manifold  69  shown as open piping and is distributed throughout the open piping structure of SOLFIRE for condensation to liquid phase, which in turn is returned by gravity to the holding tank  65 . 
     For lower power radars not requiring two phase cooling, some of the attributes of SOLFIRE could also be utilized such as the transportable and deployable structure and the two axis tracking. 
     SOLFIRE provides for a large array of individual modules that collect light from a Fresnel lens onto a unique PV assembly that allows excess heat to be removed via the SACS thermal management system, or in the case of the turbo generator, with steam condensed at higher pressures. The structure itself is composed of open piping. Vapor generated in the receiver can circulate throughout the piping, the exterior of which is exposed to the ambient air at a lower temperature than the vapor. This allows the vapor to be re-condensed into a liquid, with gravity pulling the liquid down through the structure into a holding tank at the bottom of the array, where it can be pumped back to the receivers though a high-pressure liquid phase manifold. Or, preferably, as an alternative, the liquid from the holding tank can be pumped up to an auxiliary tank at the top of the array where it can be connected into the manifold so that gravity feeds liquid through the manifold back to the individual receivers. In the case of the PV system, the vapor pressure in the piping structure is 2-3 PSI. In the case of the turbo generator, the vapor side of system could operate at much higher pressures than the SACS system, since it is desired that the boiling temperature of the working fluid be maximized for turbine efficiency, rather than being minimized for photovoltaic cell efficiency. It is an object of the invention to develop a scalable array structure containing Fresnel lenses that concentrates sun illumination on a receiver body containing photovoltaic (PV) cells for the generation of electrical power. 
     While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is defined in the following claims.

Technology Classification (CPC): 7