GB1590841A

GB1590841A - Apparatus for converting concentrated solar energy into heat energy

Info

Publication number: GB1590841A
Application number: GB28560/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-07-09
Filing date: 1977-07-07
Publication date: 1981-06-10
Also published as: ES473530A1; GB1590842A; ES460584A1; CA1084790A; CH626159A5; JPS577332B2; GB1590843A; IL52482A; ES473531A1; JPS5334148A

Abstract

Situated in the region of the focal line of an elongate liquid lens (22) are two concentrically arranged pipes (36, 38). The outer pipe (36) is transparent and the inner pipe (38) absorbs the concentrated solar radiation incident upon it. Both pipes are arranged in a cutout (44) of a collector (24). The collector is connected to the liquid lens by a frame linkage (30, 50, 66). The frame linkage is pivotable about two axes (52, 60) in order that the liquid lens can track the position of the sun. The liquid lens comprises a lower plane transparent plate (28) and a curved transparent plate (26). Situated between the plates is a liquid (31) which lets the solar rays through. A liquid, which has a lower boiling point than the liquid which is guided through the inner pipe, is guided through the outer pipe. The liquid in the outer pipe serves for hot-water preparation while the liquid in the inner pipe serves for preparing steam. <IMAGE>

Description

(54) APPARATUS FOR CONVERTING CONCENTRATED SOLAR ENERGY INTO HEAT ENERGY (71) I, VIRGIL STARK, of 936 Fifth Avenue, New Work, N.Y.. 10021, United States of America, a citizen of the United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following state ment The present invention relates to methods and apparatus for concentrating and collecting solar energy for conversion thereof to heat energy to be used for many purposes.

It is well known that surfaces exposed to the sun collect at least to some degree the solar radiation and that the absorption of this radiation results in a heating of the material constituting the surface. It is also known that electricity can be produced by photoelectric devices exposed to the sun's rays.

A conventional system for obtaining lower temperatures up to about 80"C consists -of dark-colored panels absorbing the solar radiation and means for removing the heat from the panels such as a fluid system circulating a heat-carrying fluid in a heatexchanging manner with the panels. It is also known to improve the efficiency of these systems by placing one or more glass plates above the panels to produce a greenhouse effect for reducing heat losses. However, the efficiency of these panel systems is low, from about 30% to about 40%, and they require large spaces resulting in large heat losses, and they also require a high capital investment. The use of Fresneltype lenses and fluid lenses is known in the art for focusing solar energy. - See, for example, U.S.Patents 3,915,148; 3,125,091; 937,013; 3,965,683; 3,901,036; 60,109; 1,081,098; Japanese Patent No. 28-2130, and Australian Patent No. 131,069. However, none of the known systems is capable of converting and storing solar energy efficiently and none can produce heat at an economical capital investment such that the use of solar energy is competitive with other forms of energy. The prior art also does not disclose obtaining temperatures in the order of a few hundred degrees C while also obtaining at the same time lower temperatures usable for home heating and water heating or other purposes.Nor is there in the prior art a system which is capable of storing heat energy from solar energy during periods of interrupted sunshine for any length of time and which also is capable of providing different temperatures simultaneously and also utilizing the luminous and utilizing or dispersing the heat produced by the infrared rays of the sun.

With respect to electrical generation, it is known that concentrating the solar energy at a photovoltaic cell will increase the electricel output of the cell; however, there is the disadvantage that the increased heat in the photovoltaic cell resulting from the concentration will also limit the cell output.

Known photovoltaic devices produce a maximum of about one watt per cell from non-concentrated solar energy and the number required to generate about 1 kilowatt does not make them competitive for normal uses.

With respect to solar stills, known stills used for distillation of seawater have low efficiencies and the cost of heating the water is high as the least amount of heat required to vaporize the water is not recovered from condensation but rather is lost.

The present invention provides in one aspect apparatus for converting concentrated solar energy into heat energy -comprising an elongate container including at least two elongate conduits for passing fluids therethrough and at least two fluids, said conduits and container having -substantially parallel axes, said container having an elongate opening with an -axis substantially parallel to that of the container, said conduits being disposed so that an inner first conduit containing a first fluid is enclosed by an outer conduit which is transparent at least in part and contains a second fluid therein, the fluids in said inner and outermost conduits being in a heat exchanger relationship, said container including said elongate opening and transparent portion off said outermost conduit being aligned to per mit passage of solar energy through said opening and transparent portion, whereby an elongate focus or line of foci of con centrated solar energy may be located sub stantially on and substantially along the length of said inner conduit.

In another aspect, the invention provides a method for collecting solar energy com prising concentrating solar energy in a narrow elongate focus and locating the focus on and substantially along the length of a first elongate conduit containing a first fluid therein enclosed by a second elongate con duit which is transparent at least in part and contains a second fluid therein, the axes of the conduits and the focus being substantially parallel, the method including the steps of placing the fluids in a heat exchanging relationship, selectively circulating the fluids through the conduits and concen trating the solar enrgy through a transparent portion of the second conduit to said focus.

In preferred embodiments, refringent lens means concentrate the solar energy along said elongate focus or foci. The lens means may comprises economical fluid and/or Fresnel-type lenses (sometimes referred to as Fresnel lenses) and lens systems which focus the solar energy substantially along continuous lines or in lines of substantially discrete points. Means are preferably provided to maintain the focus lines or discrete foci within said conduits regardless of the seasonal and preferably also the hourly (daily) location of the sun and/or means are provided for seasonally and preferably also hourly (daily) tracking the sun. Thus, the at least one fluid in the elongate conduits may be efficiently heated to high temperatures in order of a few hundred degrees C.

The fluid lenses preferably comprise upper and lower solar energy transmitting plates which are advantageously separate plates installed in frame means in a fluid-tight manner, or the fluid lenses including the plates may be formed by gluing, welding, extruding, or being blown in a manner similar to that for glass or plastic bottles. The enclosure in the lens containing the fluid may advantageously be communicated with the collector or heat exchange means to enhance performance. The fluid within the lenses preferably has a high index of refraction.

The lens fluid and the distance between the lens plates may be chosen to absorb varying amounts of infrared solar energy passing through the fluid. For example, more infrared solar energy will be absorbed using water as the lens fluid and less will be absorbed using a suitable transparent and colorless chemical product having a high index of refraction. The heat absorbed by the lens fluid may be recovered and used to preheat or heat fluid in the collector means or for other purposes. An antifreeze product may be added to the lens fluid to pre vent freezing of the lens fluid when it is used in certain locations. It may be advan tageous to absorb infrared radiation in the lens fluid where it is not desired to produce heat from the solar energy at the lens focus such as in certain instances when focusing the solar rays on photovoltaic cells to produce electricity.

The elongate conduits contain a plurality of fluids, adjacent ones of which are contiguous. The fluids are preferably isolated and disposed in adjacent conduits and the fluids preferably differ and have varying boiling points. The theoretical focus or foci of the lens means are preferably on the surface of or within the higher or highest boiling point liquid. In a disclosed embodiment, the first fluid has a different boiling point from that of the second fluid. Preferably, the solar energy is concentrated at the inner liquid which has a boiling point which exceeds that of the outer liquid. The conduits and fluids are solar energy transmitting or opaque or darkened depending on the location of the lens means focus. By solar energy transmitting it is meant that the solar rays are substantially transmitted through the material.In this way, the fluids may be heated to different temperatures and accordingly can be utilized for different purposes, if desired. Regulation of the fluid flow rates and selection of conduit sizes and shapes assist in providing different temperatures which may be utilized for different purposes. Arrangement of multiple conduits carrying multiple fluids can provide energy for many different uses including vapor and super-heated vapor for mechanical devices and expansion means including turbines, motors and engines; advantageously, the lower boiling point fluid has a low latent heat of vaporization and is useful for this purpose. Additionally, heat is stored in the higher boiling point fluid permitting its temperature to rise during periods of sunshine to a temperature substantially higher than that of the lower boiling point fluid which may be used as a working fluid.

Heat is removed from the higher boiling temperature fluid by, for example, circulating the lower boiling point fluid past the higher boiling point fluid.

The invention also provides in some embodiments for the union of individual systems and subsystems to form larger and composite systems. Thus, a high degree of concentration of solar energy and high efficiency are possible. Means may be provided to completely enclose the apparatus while permitting movement of the lens means and collector means to track the sun seasonally or also hourly.

In another preferred embodiment of the invention, both the infrared and luminous rays of the sun may be simultaneously or individually utilized. Photoelectric cells, specifically, photovoltaic cells, are disposed in the inner conduit so that the luminous rays are concentrated thereat for maximum electrical energy production while the heat generated by the concentration of the infrared rays is removed by one or more fluids in the collector means whose flow rates and volumes may be regulated. Heating at the photovoltaic cells can be reduced by utilizing a fluid lens in which the lens fluid and lens plates absorb heat-producing infrared rays which otherwise-would be converted to heat at the- lens focus at the cells while permitting electricity-producing luminous rays to pass to the cells with little absorption by the lensfluid and plates.The use of photovoltaic cells in connection with apparatus in accordance with the present invention is described in more detail and claimed in my co-pending application No. 7942600 (Serial No. 1 590 842), divided from the present application.

Concentration of solar energy may be increased by using several concentrators arranged to have a common focus. In one embodiment described for producing electricity, this is achieved by employing a central fluid (or Fresnel) lens concentrating the solar energy in a focus located at the photovoltaic cells and a plurality of Fresnel-type lenses located adjacent the central lens each provided with engravings thereon angled to direct solar energy to the focus of the central lens. Heating of the photovoltaic cells is reduced by utilizing a central fluid lens to absorb infrared energy and by placing the photovoltaic cells in collector means to remove heat therefrom produced by the infrared energy thereat. This arrangement permits high concentration of solar energy with high conversion efficiency to electricity since heating of the cells is -reduced.Thus, the solar energy can be concentrated by a factor in the order of up to 100 so that one of the known photovoltaic cells is able to produce up to 100 watts per hour instead of, for example, 1 watt per hour during periods of sunshine.

The seasonal elevation position of the sun varies over a total angle of about 47" during the year, the deviation between the equinoxes and each solstice being- about 23.50. This deviation is important and in order to increase solar energy collection throughout the year, sun tracking equipment may be used. For example, in late October at a Latitude of about 43 N, the daily solar radiation received on a stationary horizontal surface is about 300 Langleys while that received by a surface maintained normal to the sun is about 680 Langleys, or more than twice as much. Therefore, it is preferred, as mentioned, that sun tracking means be used or that other means be provided to maximize solar energy reception throughout the year. Both such means according to the invention are disclosed.

In a disclosed embodiment, in which several concentrators are arranged to have a common focus, a system of lenses concentrates the solar energy- along a substantially common focal line located in or on the elongated collector means during the different seasons and preferably during the different times of day without using sun tracking means. This system includes an elongated central Fresnel-type or fluid lens concentrating the solar energy along a focal line, and elongated Fresnel-type lenses located adjacent to and at an angle with respect to the central lens, the adjacent Fresnel-type lenses being provided with engravings angled to direct the solar energy to the focus of the central lens. The lenses are oriented so that they are elongated generally in the east-west direction.A given lens or lenses primarily concentrates the solar energy along the focal line for given times of the year. For example, the central lens primarily concentrates the solar energy during the time closely before and closely after the equinoxes while one adjacent lens primarily concentrates the solar energy up to one solstice and the other adjacent lens during the time up to the other solstice. In the embodiment in which the central lens is a Fresnel-type lens, the lens system preferably includes sets of Fresnel-type lenses in the elongated or east-west direction. The Fresnel-type lenses located towards the extreme east and west - ends of the lens system are positioned at an angle with respect to the inner lenses so that a given lens or lenses primarily concentrates the solar energy along the focus at given times of the day.

However, such lenses may also be located intermediate the east and west ends in a lens system comprised of many lenses oriented along the east-west direction. Thus, at different times of the day and year, one or more lenses will primarily concentrate the solar energy along the focal line without using sun tracking equipment. It is preferred in these embodiments that the elongated collector means comprise two or more adjacent elongated fluid-carrying conduits each of which enclose another fluid-carrying conduit.

Certain embodiments of apparatus in accordance with the invention disclosed herein for producing electricity may be combined with hydroelectric means and apparatus disclosed herein may be combined with -heat pumps and/or refrigration apparatus and/or expansion means such as turbines, motors and engines.

By means of the invention, apparatus and methods having high efficiency and low cost for concentrating, collecting and converting solar energy are disclosed.

These and other aspects of the present invention will be more apparent from the following description of the preferred embodiments thereof when considered with the accompanying drawings.

The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like numerals refer to like parts and in which: FIG. 1 is a schematic perspective diagram showing a system including an elongate fluid lens and an elongate collector, the lens being movable about a transverse axis to track the sun's daytime location and the lens and collector being interconnected and movable about a longitudinal axis to track the sun's seasonal location; FIG. 2 is a perspective view showing one of a series of longitudinally juxtaposed fluid lenses and its lens frame in cross section and an opening for intercommunicating the enclosure of the lens with other lenses, this arrangement being utilizable to arrange a plurality of longitudinally juxtaposed lenses where a single lens is shown;; FIG. 3 is a perspective view of a lens system comprising two separate plates for enclosing a lens fluid and a frame for sealing the plates into a fluid-tight lens: FIG. 4 is a cross-section view of the lens and frame of FIG. 3 taken along line 4-4; FIG. 5 is a schematic perspective diagram showing another system in which panels of four fluid lenses each are arranged longitudinally and are focused on elongate collectors, the panels and collectors being interconnected and movable on a shaft rotated to track the sun's seasonal location and the lenses being movable about a common transverse axis to track the sun's daytime location as described in FIG. 1;; FIG. 6 is a schematic perspective diagram showing another system comprising, elongate planar Fresnel lenses having a linear focus and collectors comprising fluidcarying conduits, the lenses and collectors being interconnected and movable as described for FIG. 1; FIG. 7 is a cross-section view of part of another collector comprising three fluidcarrying conduits in which the innermost conduit is enclosed by the intermediate conduit which is enclosed by the outermost conduit; FIG. 8 is a cross-section view of a photovoltaic cell positioned in the inner fluidcarrying conduit to product electricity from solar energy with fluid circulating inside the conduit and in the outer conduit to remove heat;; FIG. 9 is a schematic cross-section view of a lens system including a central fluid lens and adjacent Fresnel-type lenses each having engravings thereon angled to provide the Fresnel-type lenses with the same focus as that of the fluid lens, the common focus being located at an elongate collector which is interconnected with the lenses, both the lenses and collector being movable to track the sun's position; FIG. 10 is a schematic perspective diagram showing two lenses through which the solar rays pass serially wherein the focus of the lenses may be shortened and a sharper focus may be provided at a collector in which the top of the collector is exposed to disperse heat produced thereat by infrared rays, the lenses and collector being movable to track the sun;; FIG. 11 is a schematic cross-section view showing a lens system including a central lens and adjacent Fresnel-type lenses each having engravings thereon angled to provide the adjacent Fresnel-type lenses with the same focus as that of the central lens, the lenses being positioned to place the lens system focus in or on a collector having two adjacent elongate conduits each enclosing another conduit during different times of the year without using sun tracking means; FIG. 12 is an enlarged schematic crosssection view showing one of the Fresneltype lenses of FIG. 11; FIG. 13 is a schematic perspective diagram showing a set of Fresnel-type lenses oriented in the east-west direction with the lenses at the east end and west end angled with respect to the inner lens, a given lens primarily concentrating the solar energy in or on the collector at given times of the day; and FIG. 14 is a schematic perspective diagram of a composite lens system with the lenses positioned and angled as shown in both FIGS. 11 and 13 to concentrate the solar energy in or on the collector both during the different times of year and different times of day. In FIG. 1 is shown a solar energy collecting system comprising a refringent fluid lens concentrator and a fluid-containing solar energy collector. System 20 comprises an elongate fluid lens concentrator 22 and collector 24 in the form of elongate fluid )containing conduits. Elongate fluid lens 22 comprise solar energy transmitting plates 26, 28, which are preferably separate pieces mounted in frame 30 and spaced to enclose solar energy transmitting fluid 31. In the embodiment shown in FIG. 1, upper lens plate 26 is convex and lower plate 28 is planar. The respective sides 32, 34 of lens plates 26, 28 and the ends of the lens plates (not shown in FIG. 1)-are sealed to be fluidtight in manners which will be described hereinafter. Alternatively, means not shown in FIG. 1 for adding and removing or cir culating fluid 31 and air are provided in the sides and/or ends of the lens plates. Additionally, lenses may be longitudinally and transversely (radially) juxtaposed and will also be described hereinafter. In the embodiment shown in FIG. 1, collector 24 comprises an outer elongate conduit 36 enclosing an inner elongate conduit 38, both shown to be tubular in shape. Conduit 36 is placed in insulating container 40 and is surrounded by insulating material 42 except for a longitudinally extending opening 44 located above conduit 36.Opening 44 is closed off by solar energy transmitting and heat insulating plate 46. Plate 46 is suitably made of glass or plastics and the insulating material 42 is suitably a foam such as polyethylene foam. A sealing material such as, for example, silicone is provided between plate 46 and container 40 to seal the container fluid-tight. Collector 24 is located below lens 22 and the theoretical linear focus 48 is located at or along the collector. The axis of the lens (and of the system) is oriented along the east-west direction.

Frame 30 and lens 22 are supported by and pivotally mounted in frame 50 to rotate about transverse axis 52 by members 53 and pivot joints (not shown). Cables 55 are connected to opposed sides of frame 30 adjacent sides 32, 34 of the lens, at opposed ends of the lens (only one of which is shown) and wound about rollers or pulleys 58 to run the cables in a common direction towards drive means (not shown).

Movement of cables 55 in the direction of the arrows pivots lens 22 about axis 52 moving plate 26 towards the west. Movement of cables connected to the other end of frame 30 (not shown) pivots lens 22 about axis 52 moving plate 26 towards the east.

Thus, lens 22 is rotatable in the east-west direction to track the sun's hourly movement. Lens 22 and collector 24 are also rotatable in the north-south direction about longitudinal axis 60 to track the sun's seasonal movement. Frame 50, in which is mounted lens 22- is pivotally mounted adjacent the ends of the lens to supporting frame 62 by members 64 (only one of which is shown) and pivot joints (not shown).

Rigidly interconnected to frame 50 is collector 24 by members 66. Frame 50 and collector 24 are rotatable as a unit about axis 60 thereby maintaining the relative orientation between the collector and lens unchanged. Cables 68 (only one of which is shown) are connected to one side of the collector to pivot the lens and collector towards the ndrtherly direction and cables 70 (only one of which is shown) are connected to the other side of the collector to pivot the lens and - collector towards the southerly direction to a position such as the one shown in broken lines. Cables 68 and 70 are also wound around pulleys 58 to run the cables in a common direction towards drive means (not shown). The lens and collector are rotatable over a total angle of about 47 degrees during the year in the north-south direction.The drive means may comprise, for example, electric motors activated and controlled by sensors such as phototransistors or by electric timers. Automatic, semi-automatic or manual means may be used to track the sun's location in addition to the one illustrated in FIG. 1 and described above. One system uses an electric motor whose shaft is turned by a small angle whenever the direct or focused sun light hits a photocell or thermo-couple.

Hydraulic systems may also be used to move the lenses and collectors. Other systems use a timer or a weight and pulley device.

Movement of the sun affects the electric output of the photocell to control the motor or the motor is controlled by the timer to turn the shaft in small angular increments, or the weight and pulley device turns the shaft. As mentioned, such complete systems for moving the lenses and sensing the sun's position are known and are not shown.

Parts of systems used for tracking the sun's position are shown in the drawings. While daily or hourly tracking is preferred to en hance solar energy collection, it is not re quired since the collector and lens are gener ally oriented in the east-west direction. By interconnecting and moving the lens and collector, the lens focus is always main tained at the collector regardless of season.

The above-described tracking arrangement substantially increases solar energy collec tion since the system is always oriented in directions directly facing the sun, season ally and preferably hourly.

As mentioned hereinbefore, the collector is located at the theoretical focus 48 of the lens 22 and in the embodiment of HG. 1, conduits 36 and 38 are solar energy transmitting, the theoretical focus 48 being located within the inner conduit 38. Conduits 36 and 38 contain heat-carrying fluids 54 and 56, respectively.Since the concentration of the solar energy will be greatest in the fluid within The conduit at which the lens theoretical focus is located, i.e., in fluid 56 within conduit 38, fluid 56 may be heated to a relatively high temperature and is therefore chosen to have a relatively high boiling point, for example, from about 1500C to about 350 C:. Such fluids may comprise by way of example and ndt limitation lubricating oils, glycerine, mineral oils, paraffin oils, etc.Thus, during periods of sunshine, fluid 56 is heated to a temperature which may be in excess of 100-0 C, for example, 2000 C, the precise temperature attained depending on many factors such as the flow- rate of fluids 54, 56, the diameters of conduits 36, 38 sun intensity and position, insulation, heat exchange rates, etc. Fluid 54 is selected to have a boiling point which is less than the boiling point of fluid 56, preferably at least 50"C less than the boiling point of fluid 56, and preferably in the temperature range of from about -600C to about 100"C. Such a fluid is suitably water.It is al-so preferred that fluid 54 have a low latent heat of vaporization, for example, from about 20 calories per kilogram to about 270 calories per kilogram, and such fluids may comprise by way of example and not limitation refrigerants, solvents, hydrocarbons, alcohol, etc.

In operation, solar energy is concentrated in fluid 56 (chosen to be lubricating oil) within conduit 38 and raises the temperature of the oil to about 200"C. Since the focus to lens 22 is theoretically linear, fluid 56 will be continually heated as it traverses the linear focus. Fluid 54 (chosen to be water) surrounds the oil and conduit 38, and is heated primarily by the oil primarily through conduction. Both fluids, oil and water, are circulated at predetermined rates to obtain desired temperatures and may be used for different heat applications. For example, the water may be heated to about 70"C to 80"C or more and used for space and hot water heating.

The water may be heated to lower temperatures and used, for example, in swimming pools. The higher temperature oil may be used for applications requiring higher temperatures including industrial applications or may be used merely to heat the water.

Since the temperature of fluid 56 increases as it traverses the lens focus, fluids at many different temperatures are realizable by providing taps for fluid outlet and/or inlet at different points along the focus. Fluid 54 may be evaporated and the vapor or superheated vapor used to produce mechanical power in expansion means such as motors, turbines and engines which, in turn, may generate electricity. Preferably, a closed system (not shown) is employed in which the condensed fluid is returned to collector 24. In such applications, fluids such as refrigerants, solvents, hydrocarbons, alcohol, etc., and the like may constitute fluid 54.

As mentioned hereinbefore, a serious drawback of solar energy systems in general and known systems in particular relates to the storage of energy during periods in which there is no sunshine or the intensity thereof is low, as for example during the night or during periods of cloudy weather.

Heat is stored for use in those periods in fluid 56 which is heated during normal system operation to a temperature which is at least about 500C higher than the temperature of fluid 54. Therefore, even when fluid 56 is not being heated by solar energy or being heated at a reduced rate, it stores heat and will continue to supply heat to fluid 54 due to the temperature difference between the two fluids. Preferably, the circulation of fluid 56 is stopped for those periods. Fluid 56 continues - to transfer heat to fluid 54 until the difference in the temperature of the two fluids is relatively small.The time that fluid 56 will transfer and/or store heat depends upon the initial temperature of fluid 56, the difference in temperatures between the fluids, the volumes of the fluid, the characteristics (specific heat, boiling point, latent heat, etc.) of the fluids, the use to which fluid 54 is put, etc.

The fluid 31 in lens 22 may be communicated with one of the conduits is the collector 24 to remove heat from the lens fluid, thereby maintaining it at a suitable temperature while utilizing heat from the solar energy absorbed by the lens fluid to, for example, preheat the fluids circulating in conduits 36 and/or 38.

In FIG. 1, collector 24 was shown to comprise tubular conduits 36, 38. However, the conduits need not be tubular and in some instances other configurations are preferred such as for example, rectangular.

A rectangular configuration may be desirable when the theoretical focus has deviations. Providing a rectangular shape will allow movement of focus 48 while still maintaining it at conduit 36. Focus 48 can be on the surface of conduit 36, and in such a case, the surface of conduit 36 need not be solar energy transmitting and is preferably darkened.

It is to be understood that the systems shown in the remaining figures and described hereinafter are longitudinally oriented in an east-west direction and faced towards the sun. It is to be further understood that the elongate lenses or lens system and the elongate collectors and conduits thereof are arranged substantially along parallel longitudinal axes. It is to be still further understood that it is preferred that the concentrators and collectors are movable and that means may be provided for moving them to track the seasonal and preferably the hourly location of the sun. Movement of the lenses, however, may not be required where the lens focal length is short such that displacement of the focal line will be small from season to season and remain within the periphery of the inside conduit 38 of the collector.

Manual, automatic or -semi-automaic drive means for effecting tracking movement of systems and/or lenses on a seasonal or hourly basis are known. While only part of a single lens is shown in FIG. 1, it is to be understood that many lenses may be longitudinally and transversely located.

Conduits 36 and 38 in FIG. 1 may both include opaque heat conducting surfaces and the lower part of the surface of either conduit 36 and/or conduit 38 is preferably darked by black paint or the respective conduit or conduits are preferably provided at the lower half of the surfaces thereof with black metallic sheets to prevent transmission of solar energy and to enhance heat absorption from the solar energy.

Additionally, plate 46 provides a greenhouse effect in the collectors, and container 40 is preferably made of insulating material toSfurther reduce heat losses. The reduction in heat loss is especially important during periods of no or reduced sunshine. It is preferred that the theoretical focus of the lenses be located at the inner fluid to further reduce heat losses since the outer fluid will act as an insulator. The solar energy transmitting tubes in FIG. 1 are preferably made of colorless and transparent glass or plastics and the tubes which need not transmit solar energy' therethrough are preferably metal, preferably steel, copper or aluminum, and all are preferably darkened at their lower surfaces.

The area of the collector surfaces may be much smaller than the area of the concentrators and may be only from about 1 % to about 10% of the area of the conventional flatpiate collector, thus reducing the heat losses accordingly. As less material is required in the collector, the cost will be reduced.

The collector systems may comprise a number of conduits more than two and configurations other than tubular, and lens configurations and the lenses and lens systems may be other than that shown in FIG.

1.

The lens shown in FIG. 1 is supported by suitable frames and structural members.

For example, lens 80 is supported by frame 88 shown in FIG. 2. As there shown, one of a plurality of lenses 80 are longitudinally juxtaposed - at its ends and supported by longitudinal support stringers 92 and transverse support stringers 94. The lenses may be secured to the frame by, for example, adhesives. The theoretical focus 96 of the lenses is at and along collector 98. Means in the form of openings 100 are provided to add and remove fluid 31 and/or air and the openings may be communicated by, for example, tubes to provide for circulation of the fluid. The openings may be provided in other locations. As mentioned hereinbefore, the plates forming the lenses may be integrally extruded or blown or niay comprise separate plates joined as by welding.Referring now to FIGS. 3 and 4, upper curvilinear plate 26 and lower planar plate 28 are separate pieces and are joined in a fluid-tight manner by means of frame 104. Frame 104 comprises two longitudinal grooves 106, 108. The upper groove 106 is curvilinear and sized to accommodate upper curvilinear plate 26 while the lower groove is linear and sized to accommodate planat plate 28. The edges of the respective separate plates are inserted into the respective grooves along with sealing material 110. The ends of the plates are similarly joined. The material 110 may comprise a gasket or similar flexible piece and / or deformable material such as silicone to form fluid-tight joints. Thus, in which two independent plates are joined or which are extruded or blown, are relatively easy to manufacture and are relatively inexpensive.

The required radius of curvature of the curvilinear convex plate and the focal distance to the collector from the lens will depend on the width of the plates, the maximum distance between the plates and refractory index of the fluid between the plates, and fluids with higher refractory indices shorten the required radius and focal distance.

Depending on the lens fluid used and the distance between the lens plates, a per centage - of the infra-red rays in the wave length range of about 0.7 to about 4 microns impinging on the lens will not pass through the lens. Some of the infrared rays will be absorbed directly by the fluid and heat it. Some of the infrared rays will be absorbed by the lens plates which will be heated and in ;turn partly heat the fluid. Part of the solar energy will be reflected by each plate, part of the reflected solar energy being reflected towards the inside of each plate into the lens to also be partly absorbed Iby the lens fluid. Little of the luminous rays in the wave length range of about 0.25 to about 0.7 microns will be absorbed in a transparent and colorless lens fluid and transparent and colorless lens plates.For certain applications, it is desirable that the absorption of infrared rays be minimized, for example, where it is desired to produce as much heat as possible at the lens focus. In other applications, it may be desirable to heat the lens fluid and/or provide as little heat as possible at the lens focus while transmitting as much as possible of the luminous rays'such as, for example, when photovoltaic cells are located in the inner fluid conduit at the lens focus. In the former case, the distance between the lens plates is minimized, for example, to about 1 inch at the point of maximum separation of the lens plates, and the lens fluid is chosen to absorb at ambient temperature a minimal amount of infrared rays and preferably has an index of refraction of at least 1.35.Fluids such as hydrocarbons, mineral oils, solvents, solutions such as salt water, etc. are transparent, colorless and absorb substantially less infrared radiation than water. The fluids are preferably chosen to be noncorrosive to glass and plastics and to have a suitable boiling temperature. Some fluids having a high index of refraction and low absorption of infrared rays such as tri chioroethylene and toluene are corrosive to plastics such as acrylic plastics. When using such corrosive fluids, the lens plates exposed to the fluid are covered by sheets such as polytetrafluoroethylene or coatings of epoxy such as Lucite RD which are not corroded by the lens fluid.In the latter case, the distance between the lens plates is maximized, for example to about 4 inches at the point of maximum separation of the lens plates, and the fluid is chosen to absorb at ambient temperature a maximum amount of the infrared rays while still being transparent and colorless. The degree of absorption of infrared rays is also dependent upon the material used for the lenses. For example, for low absorption, waterwhite glass with about 1.5% absorp tion or plastic with a similarly low absorption may be used with a lens fluid such as a salt water solution.Where a high degree of absorption of infrared rays is desired, for example, in electricitykproducing applications wherein the solar energy is focused on photovoltaic cells in the inner conduit, glass and plastics lenses with lens fluids having an infrared absorption of, for example, 20% may be used. It is pre ferred that water be used in the latter case where it is desired to absorb infrared radiation. In certain locations, an antifreeze product is added to the water to prevent freezing. If water is used in the collector, an antifreeze product is also added to the collector water. With water used as the lens fluid and the larger distance (for example about 4 inches) separating the lens ~ plates, there will be an increased absorption of the infrared rays by the lens fluid and a corresponding increase in heating of the lens fluid.The heat in the lens fluid can be recuperated in heat exchangers and used for heating and/or preheating the collector fluids as described hereinbefore.

The heat may also be used to heat water for domestic use or for other uses, or to heat buildings, or to produce electricity by superheating low boiling temperature fluids and expanding the vapor in expansion means such as turbines or engines. Since the lens fluid permits most of the luminous rays to be transmitted therethrough, electrical generation by the photovoltaic cells will be essentially undiminished while the lens fluid is being heated and the heat being used as mentioned for heating and/ or production of additional electricity.

Thus, such an embodiment of the invention provides a highly economic combination of simultaneously generating heat and electricity.

Referring now to FIiG. 5, system 70 is made up of panels 71 of fluid lenses 22.

Each panel comprises four fluid lenses 22 arranged transversely and longitudinally adjacent one another. The panels are supported and rotatable to track the sun seasonally and hourly. Frame 50 is supported on shafts 64 which are rotatably connected to frame 62 at opposite ends of the frame by means such as bearings. One end of one of the shafts 64 is connected to drive means (not shown) such as an electric motor. Lenses 22 and frame 50 are rotatable about longitudinal axis 60 by rotating shaft 64 to track the sun seasonally. Frame 30 is pivotally connected to frame 50 by members 52 and is movable with lenses 22 about the common transverse axis 53 to track the sun's position as described for FIG. 1. The collector 24 includes a fluid conduit system similar to that of Fig. 1.

System 130 of FIG 6 is shown employing elongated refringent elements 132 having longitudinal microprisms 134 acting as longitudinal Fresnel lenses. The lenses 132 and collectors 24 are arranged so that the linear focus of a column of lenses is located at a respective collector as described for FIG 5. The lenses and collectors are interconnected and movable as the systems shown in Figs. 1 and 5. The collectors 24 are as described in connection with Fig. 1.

FIG. 7 shows an arrangement for three conduits in which the inner conduit 139 is enclosed by intermediate conduit 141 which in'turn is enclosed by outer conduit 36.

Providing three conduits permits use of three different fluids, allows for use of the fluids at varying temperatures for many different applications and allows for a larger displacement of the focal line. The outer conduit 36 may be transparent and the fluid in the outer conduit may be a gas, the outer conduit and gas providing a greenhouse heating effect about inner conduits 141, 139.

According to another aspect of the invention, the concentrated solar energy is used to generate electricity by means of photovoltaic cells. Referring to F1G. 8, photovoltaic cells 398 made of silicon or cadmium sulfide or other materials are disposed in the interior of inner fluid-carrying conduit 400 shown advantageously to be of rectangular cross-section. The theoretical focus 402 of the lens is gt the cells and preferably on the outer surface thereof.

The cells may be juxtaposed in series and also in parallel if the theoretical focus 402 is linear or spaced if the theoretical focus 402 is a point focus. The concentrated luminous rays are converted to electricity by the cells while the heat absorbed by the cells from the infrared rays is removed by the circulating fluid 404 and also ;by the fluid 406 circulating within the outer conduit 408. The removal of heat can be controlled by the size of the conduits 400, 408 and by the volume and rate at which the fluid is circulated. Preferably fluid 404 is substantially electrically non-conductive such as air or other gases and liquids.

Means (not shown) are provided for connecting the cells in parallel or series and for removing the generated electricity. If fluid 404 is electrically conducting, means (not shown) are provided for electrically insulating the cells and the means for interconnecting the cells and for removing the generated electricity. Conduit 400 has at least its upper surface made of transparent material if the theoretical focus 400 is linear or transparent apertures may be provided above the cells if the theoretical focus 402 is at a point. The upper part of outer conduit 408 is also transparent. The details of inner and outer conduits have been described hereinbefore.

As mentioned hereinbefore, concentrating the luminous energy of the sun with a concentration of up to about 100 permits electricity to be generated at up to about 100 times more power while the increased heat energy is dissipated and removed by the fluids in the conduits. ~ As described hereinbefore, the amount of heat produced at the photovoltaic cells may be reduced by absorption of infrared radiation in a fluid lens. This will increase the efficiency of the cells while reducing the heat dissipating requirements of the collector. The heat absorbed in the lens fluid may be recovered as described hereinbefore. Electricity may be generated in conjunction with other uses of solar energy.For example, using a dual fluid carrying collector, photovoltaic cells may be inserted therein as just described and electricity generated while the heat energy is being used to heat a structure.

Additionally, the electricity generated may be used to electrolyze water and/or salt to produce hydrogen, sodium and chlorine.

The hydrogen may be used with carbon monoxide to manufacture methanol or with nitrogen of the air to produce amonia fertilizer and other nitrogen products such as nitric acid and urea. Still further in accordance with the invention, apparatus generating electricity using solar energy may be combined with hydroelectric means having water storage means. Such a combination provides for the production of electricity at night, during periods of reduced sunshine, or during peak demand periods by the hydroelectric means while the solar energy system produces electricity during periods of sunshine. The solar energy system may be provided as a floating installation on the reservoir and thereby not require additional land.

As mentioned hereinbefore, it may be advantageous in some instances to eliminate the plate 46 of HG. 1 used to produce a greenhouse effect in the collector. Referring to FIG. 9, collector 205 does not include a plate such as plate 46 of FIG. 1 so that heat from the infrared rays is not retained in the collector. Elimination of plate 46 and its associated sealant and the reduction in insulation used reduce the cost of the collector while dispersing heat produced by the infra-red rays. Additionally, conduits in collector 205 are exposed to the sun over a wide angle.

Fluid lenses having upper and lower plates are generally of large size and consequently have long focal lengths which are generally longer than the width of the plates. Longitudinal Fresnel lenses having longitudinal microprisms are generally of smaller size and have shorter focal lengths.

Since the longitudinal microprisms decrease in height toward the center of the lens, the lens width is limited. Also, the width of the glass or plastic sheets used for the Fresnel lenses is limited. This can be used to great advantage.

FIG. 9 shows a combination of a central fluid lens 200 with four adjacent Fresneltype lenses 201 to 204, each having engravings angled to direct the solar rays to a common elongated focus 208 which is also the focus of the central fluid lens. The lens system may be interconnected with collector 205 and be made movable to track the position of the sun as described hereinabove. The lens system may comprise two Fresnel-type lenses instead of four. Also, the lenses may be arranged longitudinally and transversely as shown in FIG. 5 to increase substantially the concentration of solar energy, particularly for use in the production of electricity with photovoltaic cells.

Fluid lenses are larger than Fresnel lenses and are less efficient absorbing and reflecting more solar energy than Fresnel lenses. Thus, a system comprised entirely of fluid lenses is generally less efficient than a system having only Fresnel lenses or at least one Fresnel lens combines with at least one fluid lens.

Solar energy systems according to the invention may be combined with heat pumps (either with a compressor or an absorption system). The combination could be used in air conditioning systems, refrigeration systems and/or as a heat storage system wherein the heat pump provides heat when there is no or reduced sunshine. A heat pump uses either air or preferably water as a source of heat or heat obtained from solar energy collected by the fluid or fluids in the collectors described hereinabove to vaporize the circulating refrigerant: If water is used, a large reservoir is generally required as the outfiowing water is cooled to a low temperature and may freeze if the reservoir is a small one.

The heat obtainable from a heat pump depends on the difference in absolute temperature between the heat source used to vaporize the refrigerant and the condensed refrigerant. The heat obtained by the heat pump can be from two to five times higher than the power required in the compressor for - the refrigerant. The heat pump may be used to provide additional heat during hours without sunshine. The combination of the solar energy system with a hydroelectric plant having a water reservoir can be used to great advantage with a heat pump, wherein the heat is obtained by the heat pump from the water of the reservoir of the hydroelectric plant.

Lenses may also be combined so that the solar rays pass serially through them.

Such an arrangement can shorten the focus of the lens arrangement and may provide a sharper focus at the collector and is par ticularly useful where the lens is focused on photovditaic cells. FIG. 10 shows fluid lens 22 as described hereinabove superposed over Fresnel lens 132 as described hereinabove. The Fresnel-type shortens the otherwise longer focus of the fluid lens.

Collector 414A has photovoltaic cells 398 disposed therein. However, conduits 36, 38 are not enclosed to provide the greenhouse heating effect. In FIG 10, the conduits are disposed entirely in insulating container 412. However, the wide throughlike opening 413 in the container which is not closed off reduced greenhouse effect heating. Other collectors as described hereinbefore may be used where a greenhouse effect is desired. Both lenses are preferably movable to track the normal location of the sun. Lens 22 is supported as described for FIG. 1 while lens 132 is supported below lens 22 in a manner similar to that in which collector 414A is supported. Additionally, either lens may be superposed over the other and two Fresnel or two fluid lenses may be used.

In FIGS. 11-14 are shown a combination of a central Fresnel-type lens or lenses and adjacent Fresnel-type lenses which concentrate the solar energy along a substantially common focal line substantially regardless of season and time of day (FIGS.

13 and 14) without using sun tracking equipment. Referring to FIG. 11, lens system 500 is shown comprising central elongated Fresnel-type lenses 502 and adjacent elongated Fresnel-type lenses 503, 504. The central lens may also be a fluid lens. The lenses extend generally along the east-west direction. The microprisms, references generally by 506, are angled and the lenses positioned to bring the lens system focus in or on collector 508 regardless of season.

By way of illustration only, FIG. 12 schematically shows how the microprisms 506 may be angled to accomplish this.

The central lens 502 is shown parallel to the earth's surface 510, but the entire system may be rotated so that lens 502 is at an angle with the earth's surface, depending upon location of the system. For the system shown in FIG. 11 lens 503 will primarily concentrate the solar energy dur- ing the time closely before and closely after the winter solstice, lens 502 during the time closely before the closely after the spring equinox, lens 504 during the time closely before and closely after the summer solstice, lens 502 during the time closely before and closely after the fall equinox, etc.

The focus F is located in or on collector 508 which comprises two adjacent transparent conduits 36 each enclosing an inner conduit 38. In this way, even with lateral deviation of the focal line, it will still be located in one of the conduits. Additionally, where the focal line may not be sharp, 'providing adjacent conduits permits the focal line to be partially located in a plurality of conduits. A curved reflecting plate 512 is preferably positioned below the conduits to direct any energy falling on it towards the conduits.

Referring now to FIG. 13 it is preferred that the Fresnel-type lenses located at the east and west ends of the system be angled with respect to the inner lens to better orient those lenses for morning and evening concentration. For example, lens 520 at the east end is inclined to face the sun in the morning and lens 522 at the west end is inclined to face the sun in the evening.

The inner lens 524 is oriented to face the sun during the middle of the day. This lens arrangement provides for increased solar energy collection without using sun tracking equipment.

In FIG. 14 is shown a composite lens system including adjacent lenses such as lenses 5Q3 and 504 positioned to primarily concentrate the solar energy during given seasons and lenses such as lenses 522, and 520 (not shown) positioned to primarily concentrate the solar energy during the morning and evening hours. - Thus, with those lenses and lenses such as 502 and 524, the - solar energy is concentrated throughout the - day and year without using tracking equipment. As shown in HG. 14, lenses such as 522 and 520 (not shown) may also be located intermediate the east and west ends.

In some preferred embodiments of the invention, a lens concentration system is combined with a conduit collector system in which the surface area of the concen trating system exposed to the sun is larger than the surface area of the collecting system through which the energy is concentrated. As a result, heat losses are reduced substantially since the collector has an area of, for example, only from about 1 % to 10% of conventional flat plate collector systems. Thus, the efficiency over conventional flat plate systems is in the order of about 50% higher. This reduction in surface area reduces correspondingly the material requirements per unit of surface area exposed to the sun and the investment cost is also reduced correspondingly by about one-half.Additionally, higher efficiency results in a lower cost for energy produced.

In certain -types of apparatus according to the invention, fluid lenses could be used to absorb infrared radiation and the heat obtained used for different purposes.

Absorption of infrared radiation by the lens fluid reduces the heat produced at the lens focus. This is extremely useful where photoelectric cells are located at the lens focus. Efficiency in solar energy systems can be increased and cost lowered by combining in a single system the use of Fresnel and fluid lenses, each of which provide individual advantages to the overall system.

Further in accordance with certain embodiments of the invention, frame means are disclosed for seasonally, hourly and seasonally and hourly tracking the sun, and composite lens systems are disclosed in which individual lenses are positioned so the system concentrates the sun in or on a collector regardless of season and time of day without using tracking equipment.

In this respect, water can be separated into hydrogen and oxygen also by electrolysis, from electricity preferably generated by solar energy, the hydrogen of which in turn may be used with carbon monoxide in the manufacture of liquid methanol which is easily transported and may be used as fuel for automobiles, airplanes, etc. The system. described herein before could be combined with hydroelectric means and / or with known heat pumps (compression and ab sorption) to further utilize the collected solar energy in combination with the heat provided by the heatt pumps, particularly for refrigeration systems. In addition to providing energy for heating, the systems according to the invention could be used for air conditioning and, as just mentioned, in refrigeration systems.Also the multi conduit collectors and fluids are capable of providing temperatures of about 70"C to about 80"C for heating rooms and for heating water, and at higher temperatures, for example, about 180 to about 200"C, for heat storage applications and to produce electricity, and may be combined with expansion motors.

The apparatus according to the invention has been described primarily using schematic diagrams. Accordingly, certain details not essential to an understanding of the invention have been omitted. For example, the materials and support structure comprising the apparatus according to the invention not described in detail will be known to those skilled in the respective arts. The sizes of the parts of the apparatus described hereinbefore will vary depending on the use to which the apparatus is put.

It is pointed out that the heat obtained from the sun using the energy systems according to the invention may be lower in cost than heat energy obtained from fuels which may thus be replaced. Heat storage provided by certain systems in accordance with the invention is a feature which also makes these systems competitive with fuels.

WHAT WE CLAIM IS: 1. Apparatus for converting concentrated solar energy into heat energy comprising an elongate container including at least two elongate conduits for passing fluids therethrough and at least two fluids, said conduits and container having substantially parallel axes, said container having an elongate opening with an axis substantially parallel to that of the container, said conduits being disposed so that an inner first conduit containing a first fluid is enclosed by an outer conduit which is transparent at least in part and contains a second fluid therein, the fluids in said inner and outermost conduits being in a heat exchanging relationship, said container including said elongate opening and transparent portion of said outermost conduit being aligned to permit passage of solar energy through said opening and transparent portion, whereby an elongate focus of concentrated solar energy may be located substantially on and substantially along the length of said inner conduit.

2. Apparatus according to claim 1 comprising at least one elongate Fresnel and/or at - least one elongate fluid lens having an axis extending substantially parallel to the axes of said conduits and being disposed to concentrate solar energy through a transparent portion of said outermost conduit to the elongated focus located substantially on and substantially along the length of said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. throughout the - day and year without using tracking equipment. As shown in HG. 14, lenses such as 522 and 520 (not shown) may also be located intermediate the east and west ends. In some preferred embodiments of the invention, a lens concentration system is combined with a conduit collector system in which the surface area of the concen trating system exposed to the sun is larger than the surface area of the collecting system through which the energy is concentrated. As a result, heat losses are reduced substantially since the collector has an area of, for example, only from about 1 % to 10% of conventional flat plate collector systems. Thus, the efficiency over conventional flat plate systems is in the order of about 50% higher. This reduction in surface area reduces correspondingly the material requirements per unit of surface area exposed to the sun and the investment cost is also reduced correspondingly by about one-half.Additionally, higher efficiency results in a lower cost for energy produced. In certain -types of apparatus according to the invention, fluid lenses could be used to absorb infrared radiation and the heat obtained used for different purposes. Absorption of infrared radiation by the lens fluid reduces the heat produced at the lens focus. This is extremely useful where photoelectric cells are located at the lens focus. Efficiency in solar energy systems can be increased and cost lowered by combining in a single system the use of Fresnel and fluid lenses, each of which provide individual advantages to the overall system. Further in accordance with certain embodiments of the invention, frame means are disclosed for seasonally, hourly and seasonally and hourly tracking the sun, and composite lens systems are disclosed in which individual lenses are positioned so the system concentrates the sun in or on a collector regardless of season and time of day without using tracking equipment. In this respect, water can be separated into hydrogen and oxygen also by electrolysis, from electricity preferably generated by solar energy, the hydrogen of which in turn may be used with carbon monoxide in the manufacture of liquid methanol which is easily transported and may be used as fuel for automobiles, airplanes, etc. The system. described herein before could be combined with hydroelectric means and / or with known heat pumps (compression and ab sorption) to further utilize the collected solar energy in combination with the heat provided by the heatt pumps, particularly for refrigeration systems. In addition to providing energy for heating, the systems according to the invention could be used for air conditioning and, as just mentioned, in refrigeration systems.Also the multi conduit collectors and fluids are capable of providing temperatures of about 70"C to about 80"C for heating rooms and for heating water, and at higher temperatures, for example, about 180 to about 200"C, for heat storage applications and to produce electricity, and may be combined with expansion motors. The apparatus according to the invention has been described primarily using schematic diagrams. Accordingly, certain details not essential to an understanding of the invention have been omitted. For example, the materials and support structure comprising the apparatus according to the invention not described in detail will be known to those skilled in the respective arts. The sizes of the parts of the apparatus described hereinbefore will vary depending on the use to which the apparatus is put. It is pointed out that the heat obtained from the sun using the energy systems according to the invention may be lower in cost than heat energy obtained from fuels which may thus be replaced. Heat storage provided by certain systems in accordance with the invention is a feature which also makes these systems competitive with fuels. WHAT WE CLAIM IS:

1. Apparatus for converting concentrated solar energy into heat energy comprising an elongate container including at least two elongate conduits for passing fluids therethrough and at least two fluids, said conduits and container having substantially parallel axes, said container having an elongate opening with an axis substantially parallel to that of the container, said conduits being disposed so that an inner first conduit containing a first fluid is enclosed by an outer conduit which is transparent at least in part and contains a second fluid therein, the fluids in said inner and outermost conduits being in a heat exchanging relationship, said container including said elongate opening and transparent portion of said outermost conduit being aligned to permit passage of solar energy through said opening and transparent portion, whereby an elongate focus of concentrated solar energy may be located substantially on and substantially along the length of said inner conduit.

inner conduit.

3. Apparatus according to claim 2 wherein said inner conduit is transparent at least in part, the elongate focus passing through a transparent portion of said inner conduit and being located substantially within and substantially along the length of said inner conduit.

4. Apparatus according to claim 2 or claim 3 wherein said Fresnel lens comprises a plurality of longitudinally disposed point focus lenses for concentrating the solar energy at substantially discrete points.

5. Apparatus according to claim 2 or claim 3 wherein said fluid lens comprises a solar energy transmitting lens fluid and spaced, solar energy-transmitting lens plates enclosing said lens fluid, said lens fluid and said lens plates being selected to transmit therethrough substantially undiminished the infrared portion of the collected solar energy.

6. Appartus according to claim 5 further comprising means for connecting said fluid lens with one of said inner and outermost conduits for transmitting said solar energy transmitting fluid between said lens and one of said inner and outermost conduits.

7. Apparatus according to any one of claims 2 to 6 comprising a plurality of Fresnel and/or fluid lenses positioned along the axis of said lenses.

8. Apparatus according to any one of claims 2 to 6 comprising a plurality of Fresnel and/or fluid lenses poistioned along an arcuate axis transverse to the axes of said lenses.

9. Apparatus according to any one of claims 2 to 8 comprising means for moving said lenses for maintaining said focus substantially on or within and substantially along said length to track the sun's position.

10. Apparatus according to any preceding claim wherein said inner and outermost conduits are substantially tubular.

11. Apparatus according to any preceding claim wherein at least one of said inner and outermost conduits is rectangular at least in part.

12. Apparatus according to any preceding claim wherein the said fluids are liquids.

13. Apparatus according to any preceding claim wherein the fluids in the two conduits are different from one another.

14. Apparatus according to claim 13 wherein the fluid within the said inner conduit has a higher boiling point than the fluid in said outermost conduit.

15. Apparatus according to claim 14 wherein the boiling points of said two fluids are separated by more than 50"C.

16. Apparatus according to any one of claims 13 to 15 wherein the fluid having the higher boiling point has a boiling point in excess of 1500C.

17. Apparatus according to any one of claims 13 to 16 wherein the fluid having the higher boiling point has a boiling point less than 350"C.

18. Apparatus according to any of one claims 12 to 17 wherein the fluid having the higher boiling point comprises at least one fluid selected from lubricating oils, glycerine, olive oils, and paraffin oils.

19. Apparatus according to any one of claims 12 to 18 wherein the fluid having the lower boiling point has a boiling point not greater than 100"C.

20. Apparatus according to any one of claims 13 to 19 wherein the fluid having the lower boiling point has a boiling point in excess of about --62"C.

21. Apparatus according to any one of claims 13 to 20 wherein the fluid having the lower boiling point has a low latent heat of vaporization.

22. Apparatus according to claim 21 wherein said low heat of vaporization is from 20 calories per kilogram to 270 calories per kilogram.

23. Apparatus according to any one of claims 13 to 22 wherein the fluid having the lower boiling point comprises at least one fluid selected from water, fluorocarbons, butane, propane, ethyl ether, ammonia and methyl alcohol.

24. Apparatus according to any preceding claim comprising means for circulating said fluids through said inner and outermost conduits, for controlling the circulation of said fluids and for selectively stopping the circulation of at least one of said fluids in its respective conduit.

25. Apparatus according to any preceding claim further comprising insulating means for insulating said apparatus against heat loss to its environment.

26. Apparatus for converting concentrated solar energy into heat energy, substantially as herein described with reference to the accompanying drawings.

27. A method for collecting solar energy comprising concentrating solar energy in a narrow elongate focus and locating the focus on and substantially along the length of a first elongate conduit containing a first fluid therein enclosed by a second elongate conduit which is transparent at least in part and contains a second fluid therein, the axes of the conduits and the focus being substantially parallel, the method including the steps of placing the fluids in a heat exchanging relationship, selectively circulating the fluids through the conduits and concentrating the solar energy through a transparent portion of the second conduit to said focus.

28. A method according to claim 27 wherein the inner conduit is transparent at least in part and the elongate focus is passed through a transparent portion of the inner conduit and located substantially within and substantially along the length thereof.

29. A method according to claim 27 or claim 28 wherein the fluids are liquids.

30. A method according to claim 29 wherein the liquids in the two conduits are different from one another.

31. A method according to any one of claims 27 to 30 wherein the boiling point of said first fluid is at least 50"C greater than that of said second fluid.

32. A method according to claim 31 wherein said first fluid is permitted to rise in temperature to at least 50 C above the temperature of said second fluid and heat is selectively transferred from said first fluid to said second fluid.

33. A method according to claim 32 wherein the rate of circulation of said first fluid is selectively controlled to transfer heat to said second fluid.

34. A method according to any one of claims 31 to 33 wherein said focus is located within said first fluid and said first fluid has a boiling point of from 150"C to 350"C.

35. A method according to claim 34 wherein the boiling point of said second fluid is from 62 C to 100"C.

36. A method according to claim 35 wherein said second fluid has a latent heat of vaporization of from 20 to 270 cal/kg.

37. A method according to any one of claims 27 to 36 wherein there is used apparatus according to any one of claims 1 to 26.

38. A method according to claim 27 substantially as herein described with reference to the accompanying drawings.