GB1590842A - Apparatus for converting solar energy into electrical energy - Google Patents

Description

PATENT SPECIFICATION

( 21) Application No 42600/79 ( 22) Filed 7 July 1977 e ( 62) Divided out of No 1 590 841 1 ( 31) Convention Application Nos.

7620986 ( 32) Filed 9 Ju.

7630248 8 O O Cm 746065 30 No ( 33) France (FR) France (FR) United States of America (US) ( 44) Complete Specification published 10 June 1981 ( 51) INT CL 3 H Ol L 31/00 ( 52) Index at acceptance H 1 K l EB 5 D 1 5 D 5 5 D 7 SH 2 N PG ( 11) 1 590 842 ly 1976 At 1976 v 1976 in ( 54) APPARATUS FOR CONVERTING SOLAR ENERGY INTO ELECTRICAL ENERGY ( 71) I, VIRGIL STARK, of 936 Fifth Avenue, New York 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 statement: -

The present invention relates to apparatus for collecting solar energy and conversion thereof to electrical energy to be used for many purposes.

In preferred embodiments the invention relates to apparatus using fluid and/or Fresnel concentrating lenses and lens systems and elongated collectors comprising at least one fluid-carrying conduit located at the foci of the lenses.

It is well known that surfaces exposed to the sun collect at least to some degree the solar radition 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 800 C consists of dark-coloured 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 heat-exchanging 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 %, and they require large spaces resulting in large heat losses, and they also require a high capital investment The use of Fresnel-type, 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 50 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 55 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 pur 60 poses 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 65 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 70 is known that concentrating the solar energy at a photovoltaic cell will increase the electrical output of the cell; however, there is the disadvantage that the increased heat in the photovoltaic cell resulting from 75 the concentration will also limit the cell output Known photovoltaic devices produce a maximum of about one watt per hour per cell from non-concentrated solar energy and the number required to generate 80 about 1 kilowatt per hour does not make them competitive for normal uses.

In accordance with the present invention' there is provided an elongate collector for converting solar energy to electrical energy 85 comprising an inner elongate _conduit adapted to pass a fluid therethrough and an outer elongate conduit adapted to pass a fluid therethrough enclosing said inner conduit, said outer and inner conduits 90 having substantially parallel axes, said outer conduit being transparent at least in part, and photoelectric means disposed in or on said inner conduit in a heat extn 1 590 842 changing relationship with the fluid adapted to be passed through said inner conduit, said photoelectric means being in alignment with the 'transparent part of said outer conduit and being positioned and orientated to receive solar energy passing through the transparent part of said outer conduit Refringent lens means may be used to concentrate the solar energy along the length of the collector The lens means may comprise 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 elongate collector means regardless of the seasonal and preferably also the hourly (daily) location of the sun and/or means may be provided for seasonally and preferably also hourly (daily) tracking the sun Thus, the at least one fluid in the elongated collector means may be efficiently heated to high temperatures in order of a few hundred degrees C Various lens systems and mountings for tracking the sun are disclosed in the parent application No.

28560/77 (Serial No 1 590 841).

The fluid lenses preferably comprise upper and lower solar energy transmitting plates which are advantageously separate plates installed in frame means in a fluidtight 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 prevent freezing of the lens fluid when it is used in certain locations It may be advantageous 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 collector preferably cornprises a plurality of different fluids, adjacent ones of which are contiguous but isolated from one another The fluids preferably differ and have varying boiling points The theoretical focus or foci of 70 the lens means are preferably on the surface of or within the higher or highest boiling point liquid In a disclosed embodiment, one of the conduits containing a first fluid having a first boiling point is 75 located within a second conduit containing a second fluid having a second boiling point Preferably, the solar energy is concentrated at the inner liquid which has a boiling point which exceeds that of the 80 outer liquid The conduits and fluids are solar energy transmitting or opaque or darkened depending on the location of the focus By solar energy transmitting it is meant that the solar rays are substantially 85 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 90 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 95 different uses including vapor and superheated vapor for mechanical devices and expansion means including turbines, motors and engines; advantageously, the lower boiling point fluid has a low latent heat of 100 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 105 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 110 boiling point fluid.

Individual systems and subsystems may be joined to form larger and composite systems Thus, a high degree of concentration of solar energy and high efficiency 115 are possible Means may be provided to completely enclose the apparatus while permitting movement of the lens means and collector to track the sun seasonally or also hourly 120 In another preferred embodiment of the invention, both the infrared and luminous rays of the sun may be simultaneously or individually utilized The photoelectric means, preferably photovoltaic cells, are 125 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 130 1 590 '842 or more fluids in the collector 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 heatproducing 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 lens fluid and plates.

Concentration of solar energy may be increased by using several concentrators arranged to have a common focus In one embodiment described 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 470 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 430 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 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 elongate 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 adja 70 cent 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 75 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 80 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 85 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 90 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, 95 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 100 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 elongate collector comprise two or more adja 105 cent elongated fluid-carrying conduits each of 'which enclose another fluid-carrying conduit.

Certain embodiments of apparatus in accordance with the invention disclosed 110 herein may be combined with hydroelectric means and apparatus disclosed herein may be combined with heat pumps and/or refrigeration apparatus and/or expansion means such as turbines, motors and engines 115 The present invention is illustrated by way of example and not limitation in the which like numerals refer to like parts and in which:

FIG 1 is a schematic perspective diagram 120 showing a system including an elongated fluid lens and an elongate collector suitable for use with the present invention the lens being movable about a transverse axis to track the sun's daytime location and the 125 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 130 1 590 842 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 elongated 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 elongated, planar Fresnel lenses having a linear focus and collectors comprising fluid-carrying 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 typical photovoltaic cell to be positioned in or on the inner fluid-carrying conduit of any of the embodiments of Figs 1-7 to produce electricity from solar energy with fluid circulating inside and/or outside the 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 elongated 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 lens may be shortened and a sharper focus may be provided at the collector, in which the position of the photovoltaic cell is shown, the top of the collector being exposed to disperse heat produced thereat by infrared rays and 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, 70 the lenses being positioned to place the lens system focus in or on a collector having two adjacent elongated conduits each enclosing another conduit during different times of the year without using suntracking means; 75 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 80 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 85 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 16 and 18 to concentrate the 90 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 95 fluid lens concentrator and a fluid-containing solar energy collector System 20 comprises an elongated fluid lens concentrator 22 and collector 24 in the form of elongated fluid-containing conduits Elongate 100 fluid lens 22 comprises 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 105 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 fluid-tight in manners which 110 will be described hereinafter Alternatively, means not shown in FIG 1 for adding and removing or circulating fluid 31 and air are provided in the sides and/or ends of the lens plates Additionally, lenses may be 115 longitudinally and transversely (radially) juxtaposed and will also be described hereinafter In the embodiment shown in FIG.

1, collector 24 comprises an outer elongated conduit 36 enclosing an inner elon 120 gated 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 125 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 seal 130 1 590 842 ing material such as, for example, silicone is provided between plate 46 and container 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.

Suitable photoelectric means such as photovoltaic cell is positioned on or in the inner conduit 38, as will be described below in connection with Figs 8 and 10.

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 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 northerly 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 sunlight-hits a photocell or thermo-couple Hydraulic systems may also be used to move the lenses and collecors 70 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 75 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 track 80 ing the sun's position are shown in the drawings While daily or hourly tracking is preferred to enhance solar energy collection, it is not required since the collector and lens are generally oriented in the east 85 west direction By interconnecting and moving the lens and collector, the lens focus is always maintained at the collector regardless of season The above-described tracking arrangement substantially increases 90 solar energy collection since the system is always oriented in directions directly facing the sun, seasonally and preferably hourly.

As mentioned hereinbefore, the collector is located at the theoretical focus 48 of the 95 lens 22 and in the embodiment of FIG 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 100 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 105 to a relatively high temperature and is therefore chosen to have a relatively high boiling point, for example, from about 1500 C to about 350 WC Such fluids may comprise by way of example and not limi 110 tation 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 C, for example, 2000 C, the precise temperature 115 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 120 which is less than the boiling point of fluid 56, preferably at least 50 VC less than the boiling point of fluid 56, and preferably in the temperature range of from about -600 C to about 100 C Such a fluid is suitably 125 water It is also 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 130 1 590 842 and not limitation refrigerants, solvents, hydrocarbons, alcohol, etc.

i 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 'C to 80 CC 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 system 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 50 WC 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 of the two fluids is relatively small The time that fluid 56 will transfer andlor 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 in the collector 24 to remove heat from the lens 70 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 75 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 rect 80 angular 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 85 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 90 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 elongated lenses or lens 95 system and the elongated 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 100 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 105 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-automatic drive means for 110 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 115 transversely located.

Additionally, plate 46 provides a greenhouse effect in the collectors, and container is preferably made of insulating material to further reduce heat losses The reduction 120 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 125 act as an insulator The solar energy transmitting tubes in FIG 1 are preferably made of colorless and transparent glass or plastic and the tubes which need not transmit solor energy therethrough are preferably metal, 130 71.590842 preferably steel, copper or aluminium, 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 flatplate 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 less 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 may 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 planar plate 28 The edges of the respective separate plates are inserted into the respective grooves along with sealing material 10.

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, lenses 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 percentage of the infrared 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 70 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, 75 part of the reflected solar energy being reflected towards the inside of each solar energy being reflected towards the inside of each plate into the lens to also be partly absorbed by the lens fluid Little of the 80 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 It is desirable to heat the lens fluid 85 and/or to provide as little heat as possible at the lens focus while transmitting as much as possible of the luminous rays to the photovoltaic cells located at the lens focus, To achieve this, the distance between the 90 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 95 while still being transparent and colorless.

The degree of absorption of infrared rays is also dependent upon the material used for the lenses Since a high degree of absorption of infrared rays is desired, glass 100 and plastics lenses with lens fluids having an infrared absorption of, for example, 20 % may be used It is preferred that water be used In certain locations, an antifreeze product is added to the water to prevent freez 105 ing If water is used in the collector, an antifreeze product can be added to the collector water With water used as the lens fluid and a distance such as 4 inches separating the lens plates, there will be an increased 110 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 115 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 120 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 125 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 130 1 590 842 economic combination of simultaneously generating heat and electricity.

Referring now to FIG 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 is as described in connection with Fig 1 and contains suitable photoelectric means such as photovoltaic cells.

System 130 of FIG 6 is shown employing elongated refrigerent elements 132 having longitudinal microprisms 134 acting as longitudinal Fresnel lenses The lenses 132 and collectors 24 such as those of Fig 1 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.

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 at least is 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.

The photoelectric means is positioned in or on one of the two inner conduits.

Referring to FIG 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 crosssection The theoretical focus 402 of the lens is at 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 70 which the fluid is circulated Preferably fluid 404 is substantially electrically nonconductive such as air or other gases and liquids Means (not shown) are provided for connecting the cells in parallel or series 75 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 80 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 85 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 90 the luminous energy of the sun with a concentration of up to about 100 permits electricity to be generated at up to about times more power while the increased heat energy is dissipated and removed by the 95 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 100 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 105 solar energy For exam Dle, 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 Addi 110 tionally, 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 115 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 120 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 125 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 130 1 590 842 require additional land.

As mentioned hereinbefore, it may be advantageous in some instances to eliminate the plate 46 of FIG 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 infrared 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 lonigtudinal 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.

For example, plate 46 may be eliminated but the greenhouse effect retained by reducing the distance between the lenses and the collector in an enclosed system.

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 :'40 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.

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 particularly useful where the lens is focused on photovoltaic cells Fig 10 shows fluid lens 22 as described hereinabove superposed over i Fresnel lens 132 as described hereinabove The Fresnel-type shortens the otherwise -longer focus of the fluid lens.

:60 Collector 414 A 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 70 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 414 A is supported Additionally, 75 either lens may be superposed over the other and two Fresnel or two fluid lenses may be used.

In Figs 11 to 14 are shown a combination of a central Fresnel-type lens or lenses and 80 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 Re 85 ferring to FIG 11, lens system 500 is shown comprising central elongated Fresnel-type lenses 502 and adjacent elongated Fresneltype lenses 503, 504 The central lens may also be a fluid lens The lenses extend 90 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 95 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 100 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 ' 16, lens 503 will primarily concentrate the solar energy during the time closely before 105 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 110 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 115 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 120 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 125 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 130 _ 9 1 590 842 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 with using sun tracking equipment.

In FIG 14 is shown a composite lens system including adjacent lenses such as lenses 503 and 504 poistioned 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 FIG 14, lenses such as 522 and 520 (not shown) may also be located intermediate the east and west ends.

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.

Claims (13)

WHAT I CLAIM IS:

1 An elongate collector for converting solar energy to electrical energy comprising an inner elongate conduit adapted to pass a fluid therethrough and an outer elongate conduit adapted to pass a fluid therethrough enclosing said inner conduit, said outer and inner conduits ha Ving substantially parallel axes, said outer conduit being transparent at least in part, and photoelectric means disposed in or on said inner conduit in a heat exchanging relationship with the fluid adapted to be passed through said inner conduit, said photoelectric means being in alignment with the transparent part of said outer conduit and being positioned and orientated to receive solar energy passing through the transparent part of said outer conduit.

2 The apparatus of claim 1, including elongate lens means having an axis extending substantially parallel to said axes of said outer and inner conduits and having 65 an elongate focus in which the solar energy may be concentrated, said lens means and said outer and inner conduits being positioned so that the elongate focus of said lens means is adapted to extend substan 70 tially in or on and substantially along the length of said inner conduit.

3 The apparatus of claims 1-2, wherein said inner conduit is transparent at least in part, said photoelectric means being dis 75 posed in said inner conduit in a heat exchanging relationship with the fluid adapted to be passed through said inner conduit, said photoelectric means being in alignment with the transparent parts of said 80 outer and inner conduits and being adapted to receive concentrated solar energy passing through the transparent parts of said outer and inner conduits.

4 The apparatus of claims 1-3, wherein 85 said photoelectric means comprise photovoltaic cells.

The apparatus of claims 1-4, and comprising the fluid which is adapted to be passed through each of said inner and outer 90 conduits.

6 The apparatus of claims 1-5, where the fluid in each of said inner and outer conduits is different.

7 The apparatus of claims 1-6 which 95 further comprises an elongate fluid lens having an axis parallel to the axes of said inner and outer conduits to concentrate solar energy on the photoelectric means.

8 The apparatus of claim 7 wherein said 100 fluid lens means includes a fluid characterized by substantially undiminished transmission therethrough of luminous rays and high absorption of infrared rays, whereby conversion of solar energy to heat energy 105 proximate the photovoltaic means is reduced and the efficiency of the production of electricity by the photovoltaic means is increased.

9 The apparatus of claim 8, wherein said 110 lens means comprises opposed plates enclosing said fluid, said plates being separated for a high degree of absorption by said fluid of the infrared rays and a high degree of transmission through the plates and fluid 115 of the luminous rays.

The apparatus of claims 8-9 further comprising heat exchanger means and means communicating said lens fluid thereto, whereby heat may be removed from said 120 to 1 590 842 lens fluid.

11 The apparatus of claims 1-10, which further comprises lens means operative to concentrate solar energy in substantially discrete points along said length of said inner conduit and wherein said photoelectric means are spaced apart along said length in said inner conduit, said lens means and and adapted so that respective photoelectric means receive the solar energy concentrated in the discrete points.

12 The apparatus of claims 1-11, wherein which further comprises lens means operative to concentrate solar energy along said length in said inner conduit at a con 15 centration factor of up to 100.

13 An elongate collector according to claim 1 substantially as herein described with reference to the accompanying drawings 20 R G C JENKINS & CO, Chartered Patent Agents, Chancery House, 53/64 Chancery Lane, London WC 2 A IQU.

Agents for the Applicants.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd, Berwick-upon-Tweed, 1981.

Published at the Patent Office, 25 Southamp ton Buildings, London, WC 2 A l AY, from which copies may be obtained.