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1. (WO1980000077) SOLAR DISTILLATION APPARATUS
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SOLAR DISTILLATION APPARATUS
The present invention relates to solar distillation apparatus and more particularly to apparatus for the solar distillation of water.
In pending Application Serial No. 716,065 filed
November 30, 1976 of which I am a co-inventor and the sole assignee, and in pending Application Serial Nos. 807,513 filed June 20, 1977 and 405,136 filed October 30, 1977, of which I a sole inventor, solar energy distillation apparatus are disclosed in which a part of the heat of condensation of the condensing liquid is recovered. In the disclosed embodiments in those applications, the heat of condensation is transferred to a fluid in a fluid lens. The fluid lens is disposed over the liquid to be distilled and is inclined to provide an inclined bottom surface on which the evaporated liquid is condensed and along which the condensate may flow to be discharged from the lower end thereof. However, in order to provide a suitable flow and discharge of condensate along the bottom surface of the fluid lens the inclination of the fluid lens should preferably be between about 10* to about 20*.
The lens is also inclined to increase collection of solar energy and in some locations, however, an inclination of up to about 45* is desirable. At locations where a lens inclination of greater than 20* is desirable to increase collection, the system operates at reduced efficiency since the fluid lens is limited to angles of inclination of les than about 20*. For example, at a latitude of 35*S, the optimum angle of inclination" fpr^. the lens will be about 4 and a system with a lens inclined at about 20* will colle less solar energy than a system with a lens inclined at t optimm angle of 45".
Additionally, the focal distance and concentrat of fluid lenses suitable for use in solar distillation apparatus are competing factors. A large fluid lens is desirable to provide a high concentration factor but the focal distance of the fluid lens increases with its apert Therefore, a comprise must be reached between the concentr tion factor and focal distance of the fluid lens in which concentration factor of the lens may not be as high as desired in order to reduce the focal distance of the lens, and the focal distance may be longer than desired to incre the concentration factor of the lens. Moreover, since the fluid lens must be placed at a greater distance from t liquid than otherwise desired in order to increase its concentration, there is a large volume, which is undesirab between the lens and the liquid to be distilled.
The spacing between the lens plates of the fluid
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lens is determined by the lens characteristics desired and the lens fluid used. The greater the spacing of the lens plates, the lower the transmission efficiency of the lens. For example, with a lens plate spacing of only about two inches at the center of a lens having a convex upper plate

^ S and a flat lower plate, there are important transmission losses through the lens. Transmission efficiency through the fluid lens is also dependent upon the particular lens fluid chosen. For example, when distilling salt water, salt water may be chosen as the lens fluid and circulated through the lens to preheat the water. However, there are also important transmission losses through the salt water. Additionally, when salt water is used as the lens fluid, deposits of salt and minerals will accumulate within the lens requiring cleaning thereof.
In accordance with the present invention, these drawbacks are substantially overcome and improved solar energy distillation apparatus are provided.
It is an object of the present invention to provide solar energy distillation apparatus of improved efficiency in which a substantial part of the heat of condensation of the condensed, distilled liquid is recovered.
It is another object of the present invention to provide solar energy distillation apparatus of improved efficiency in which a substantial part of the heat of condensation of the condensed, distilled liquid is recovered and an increased amount of solar energy collected.
These and other objects of the present invention are accomplished by providing solar distillation apparatus in which the solar energy is concentrated in the liquid to be distilled and conduit means including a heat exchange fluid therein are provided to condense the evaporated liquid vapor

OMPI on a surface thereof, the conduit means being disposed intermediate the liquid to be distilled and means for con trating the solar energy in the^Jiquid.
In accordance with the invention, the apparatus comprises lens means disposed above the liquid to be dist for concentrating the solar energy therein; conduit means passing a fluid therethrough disposed intermediate the le means and the liquid to be distilled and comprising an inclined, lower wall having a smooth outer surface and ha a lower end; a fluid in said conduit means in a heat exch ing relationship with said lower wall; and container mean disposed below said lower end for receiving condensed liq The concentrated solar energy causes the liquid to evapor with the vapor impinging and being condensed upon the out surface of the lower wall* the condensed liquid flowing a the outer surface of the lower wall to the lower end ther and falling therefrom into the container means, a substan part of the heat of condensation of the condensing vapor being absorbed by the fluid in the conduit means.
The conduit means is transparent at least in pa and the solar energy is passed through the transparent portions into the liquid to be distilled, the conduit mea and the lens means being superposed at least in part.
In the disclosed embodiments, the conduit means a flat conduit comprised of transparent upper and lower w sealingly joined, for example welded, to form the conduit.
According to one embodiment of the invention, a plurality of sets or series of Fresnel-type lenses are
arranged over a container holding liquid to be distilled.
Each set of Fresnel lenses incl des a plurality of individual Fresnel lenses arranged end to end to provide an elongated narrow focus. The series of Fresnel lenses are inclined with respect to the horizontal. The container includes a plurality of baffles dividing the container interior into a plurality of distillation compartments for the liquid to be distilled. The container bottom is inclined in the same direction of the Fresnel lenses so that the compartments are offset in height. The elongated focus of each series of Fresnel lenses may therefore be located in and along a different compartment.
Interposed between the Fresnel lenses and the distillation compartments is a flat plate conduit containing a heat exchange fluid. The flat plate conduit is inclined at approximately 5 to 20 degrees with the horizontal and located above the compartments so that evaporated vapor is condensed on the lower surface of the conduit. The container also includes a collection compartment for the condensate disposed adjacent the lower side thereof which is disposed below the lower end of the flat plate conduit. The condensate flows along the lower plate of the conduit to the lower end and is discharged therefrom into the compartment.
An expansion tank for the heat exchange fluid in the conduit is located so as to provide minimal pressure within the conduit.
A heat exchanger is also provided to transfer the

OMPI heat recovered in the heat exchange fluid circulated in t conduit to the liquid being introduced into the container preheat the liquid. The heat exchanger is also located to minimize pressure in the conduit. Another solar energy system may be utilized to further preheat the liquid to be distilled, for instance to 75" in the case of water, befo the liquid is introduced into the container.
In accordance with the invention, more fluid is circulated in the conduit means than the quantity of liqui introduced into the distillation compartments, evaporated therefrom and condensed on the conduit means in order to carry away the released heat of condensation while maintai the temperature of the fluid below that of the condensing liquid vapor.
In the case of the distillation of salt water, t quantity of fluid circulated through the conduit to absorb and carry the heat of condensation released by the condens water vapor, will greatly exceed, for example, by 10 times the quantity of water evaporated, condensed and distilled the apparatus. Much more fluid is circulated in the condu to maintain the fluid temperature below that of the conden ing water vapor.
The liquid concentrated with impurities (in the -case of salt water, concentrated brine at for instance, 80 may be recycled one or several times in separate' distillat units or in the distillation channels or compartments of t same unit, the liquid concentrated with impurities (or the brine) being introduced into the distillation compartments to take the place of at least some of the liquid to be distilled which would otherwise be introduced into the compartments. Thus, the heat of the liquid concentrated with impurities (brine) may be recovered and the concentration of thereof may be increased in successive compartments and units, allowing a more economical extraction of, for example, salts from the brine.
A separate heat exchanger using a fluid heated, for instance, to*150"C by solar energy in a separate solar energy unit can be used to preheat the liquid to be distilled, increasing its temperature, in the case of water to, for instance, 75" C, before introducing the liquid into the distillation compartment.
In accordance with another embodiment of the invention, the sets of Fresnel lenses are arranged so that the elongated focus of at least one set is substantially parallel to the axes of the compartments in the container and the elongated focus of at least one other set is arranged so that the elongated focus is transverse to the axes of the compartments. According to this embodiment, the focus which is transverse to the axis of the compartments extends into varying depths of liquid in the container. The two sets of Fresnel lenses are arranged at an angle to each other so that they meet along an apex with each set having a lower end.
The conduit system on which vapor condenses is made up of two flat plate conduits disposed at an angle along an apex with

O PI each conduit having a lower end disposed above compartmen for the distilled liquid.
In still another embodiment of the invention, a composite system is provided made of of individual, adjac arranged units.
The Fresnel lenses -may be replaced by fluid len if desired. However, the Fresnel lenses are preferred fo the reasons discussed above.
According to the present invention, production distilled water from salt water is substantially higher t by conventional solar ponds. The cost of producing disti water may be reduced to zero in certain locations when, sa (NaCl) and/or magnesium chloride sulfate are extracted f the concentrated brine.
According to another aspect of the invention, t bottom of the compartment containing the liquid -to be distilled is blackened preferably by flexible blackened mater which is impermeable to the liquid. In the case of water, Esso Butyl or a similar material may be used. This allows absorption of solar energy and enhances the heating of the liquid, and also seals the bottom of the compartment.
Alternatively, the compartment bottom can be the ground surface covered by the material instead of concrete, for example.
In accordance with another embodiment of the present invention the relatively large and deep distillation compartments are replaced by an undulated plate or


plurality of adjacent plates on top of an insulating base.
In accordance with a further feature of this embodiment of the present invention, '^single panel or plurality of adjacent panels made of blackened flexible plastic or the like, such as isobutyl, are disposed over all or bottom part of the plates. They are to be attached to the plates in a removable manner which will permit taking them out to remove deposits which may form on them.
Furthermore, it is preferred that the undulated plates be placed above the focal area of maximum concentration obtained from the Fresnel lenses. This permits a wider spread of the heat converging from the lens on the undulated plates so that a wider area of the plates is heated. Another feature of this embodiment is to allow the fluid circulating between the double plates located between the Fresnel lenses and the distilling basin with undulated plated to spread all along the surface between the double plates and to selectively regulate the quantity of fluid circulating, thus controlling the temperature of the fluid by restricting the bottom
passage of the section at an extreme end of the plates
leaving a small opening for releasing the fluid.
In the same type of system, in accordance with another feature of the present invention photovoltaic cells are installed in one or more bottoms or valleys of the
undulated plates at the locations where the' focus area- of the Fresnel lens are most concentrated. As in my previously disclosed systems, the lenses are supported for movement to track the location of the sun using either the systems described in my previous applications or systems to be described in more detail herein// Again, as with my other system, although Fresnel lenses are preferred for a numbe reasons, liquid lenses may also be used.
With such an arrangement the photovoltaic cells will produce electricity at the minimal additional cost avoiding the cost which would be associated with a separa solar installation for producing electricity. Furthermor where concentration of solar energy is used as is the cas with the present invention, the production of electricity be up to for instance 40 times that which it would be wit concentration. For example, the average yearly productio electricity with concentration will be, for example 3 Wat per cell for example, 5cm x 5cm compared with about 0.06 Watts per cell for cells exposed to the sun without conce tion. Cost estimates have shown that installing an array photovoltaic cells in a distillation unit of the present invention permits saving all of the cost of the solar syst otherwise required by the photovoltaic cells. Put another way, it reduces by about half the total cost of the photovoltaic cell system when the solar need to concentrate the solar energy is considered. Thus, the present solar energ system uses a single concentrating means, -i.e., lens syste which supplies energy both for distillation and for genera electricity.
Furthermore, the absorption of infrared rays by fluid in the conduit means and by the water being distilled which circulates above and around the photovoltaic cells permits the production of electricity at higher efficiencies. As temperature goes up the efficiency of silicon photovoltaic cells goes down. At a temperature of 200*C the efficiency is zero, and the cells melt. However, because of the absorption of the infrared radiation by the circulating fluid and by the water being distilled, temperatures are maintained lower.
The photovoltaic cells can preferably be encapsulated in a transparent plastic or glass cover of similar shape either rectangular or round so as to protect the cells from saline water which will flow above such covers. The cells can also be enclosed in a transparent tube in which distilled water such as cooled condensate produced by a distillation unit can circulate and further absorb heat generated by the infrared rays. Such a heat exchange can reduce the temperature of the condensate from about 75* C to, for example, about 30* C. With this arrangement, heated salt water will not flow around the photovoltaic cells and form deposits thereon. And, furthermore, the cells instead of being surrounded by fluid at a temperature of up to 75*C, will be surrounded by fluid at a temperature of only, for example 4θ*C. The efficiency of the electricity production is generally reduced by about 0.4? for every degree C increase in temperature above, for example, 30* C. By encapsulating or enclosing the cells and circulating cooling water around them, the cells will be maintained at their optimum temperature for efficiently producing electricity and at the same time th cells will be protected from any corrosion effects of the salt water or salt deposits.
According to another aspect of the invention involving distillation of salt water, a chemical such as barilium chloride may be added to the salt water to preve the formation of otherwise insoluble deposits such as calc sulfate or unstable sodium bicarbonates which may form in salt water., Barilium sulfate may deposit during the night for example, and can be extracted and sold for use in the petroleum industry for drilling oil wells.
These and other aspects of the present invention will be more apparent from the following description of th preferred embodiments thereof when considered with the accompanying drawings.
The present invention is illustrated by way of example and not limitation in figures of the accompanying drawings in which like references indicate similar parts a in which: *

Fig. 1 is a vertical cross-section schematic vie of solar distillation apparatus according to the invention showing two adjacent sets of Fresnel lenses arranged above container holding water to be distilled, a transparent plate-like conduit on which vapor is condensed being inter posed between the container and the lenses, the plate-like conduit and the lenses being inclined at about the same an to be substantially parallel;
Ǥ*> UR
O Fig. 2 is a top plan schematic view, partly broken-away, of the solar distillation apparatus of Fig. 1;
Fig. 3 is a vertical" '<^foss-section schematic view of solar distillation apparatus according to the invention similar to that shown in Fig. 1 with the Fresnel lenses being inclined at a greater angle than the plate-like conduit;
Fig. 4 is a top plan view, partly broken-away, of the solar distillation apparatus of Fig. 3;
Fig. 5 is an end elevation schematic view, partly broken-away, of the solar distillation apparatus of Fig. 3;
Fig. 6 is a vertical cross-section schematic view of solar distillation apparatus according to still another embodiment of the invention showing two sets of Fresnel lenses arranged above the container for the water to be distilled with an inclined transparent plate-like conduit on which vapor is condensed interposed between the lenses and the container, one set of lenses extending. generally parallel to the axis of container and one set of lenses extending transverse to the container axis, the two sets of lenses being adjacent and inclined with respect to each other
and with respect to the container and plate-like conduit;
Fig. 7 is a top plan schematic view of the solar distillation apparatus of Fig. 5;
Fig. 8 is a vertical cross-section schematic view of a composite solar distillation apparatus utilizing a plurality of systems of the type shown in Figs. 6-7; and
Fig. 9 is a top plan schematic view of the composite system of Fig . 8.
Figure 10 is a cross-sectional elevation view through the first embodiment of distillation apparatus according to the present invention.
Figure 10a is a perspective view of the double plate system of Fig. 1.
Figure 11 is a perspective view of the unit acc ing to Fig. 10, showing the installation of photovoltaic cells.
Referring more particularly to the drawings, ap tus for the solar distillation of water are illustrated. Fig. 1, the distillation apparatus 10 includes a Fresnel system 12 to concentrate the solar energy, a transparent plate conduit 14 on the bottom of which water vapor is condensed, and a container 16 having compartments 1δa,b,c the water to be distilled and a compartment 22 for distil water which is discharged from the bottom of the conduit The sides 26, 28 of the container are offset in height an the lens system 12 extends inclined along the sides of th container between the ends 30, 32 thereof, the lens syste closing the top of the container and being supported by t sides and ends of the container. Compartment 18a in the ontainer is formed by the side 26 of the container, a baf 34 and the ends of the container; compartment 18b by baff 34 and 36 and the ends of the container, and compartment by a partition 38 and the ends of the container. The par tion 38 separates the compartments 1δa,b,c holding water
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OM IP be distilled from compartment 22 holding the distilled water.

Compartments 1δa,b,c extend parallel to the elongated axis of the container.
The bottom 40 of the container is inclined downwardly from side 26 to side 28 at an angle A with respect to the horizontal. The heights "of baffles 34 and 36 are substantially equal to provide the inclined container bottom 40 with stepped compartments l8a,b,c so that during normal distillation operation, the maximum depths of the water to be distilled in compartments 1δa,b,c are substantially equal. The water to be distilled is introduced into compartment 18a and overflows therefrom into the other compartments. The height of partition 38 is higher than the heights of baffles 34, 36 so that the water to be distilled does not flow into compartment 22. Since compartment 18a is separated from the other compartments, the introduction therein of the water to be distilled does not directly cool the heated water in the other compartments.
The lens system 12 is inclined downwardly, extending from the higher side 26 to the lower side 28 of the container substantially parallel to the container bottom 40 at approximately the angle A with the horizontal. The lens system 12 includes two series 42, 44 of adjacently disposed Fresnel lenses 46, each series extending substantially
parallel to the elongated axes of the container and compartments I8a,b,c. The inclined, parallel lenses are spaced by, for example, one inch to preventing shadowing of adjacent lenses. Two series of lenses are shown and each series o

- lenses is shown to include six lenses; however, one or th or more series of lenses and more, or less than six lenses be utilized per series depending upon the size of the installation and the quantity of distilled water desired. Each Fresnel lens comprises longitudinally extending pris 47 which provide an elongated narrow focus. The series o

' lenses are arranged to provide spaced parallel elongated composite foci 48, 50. The composite focus 48 of lens se 42 is located in the water in compartment 18a while the composite focus 50 of lens series 44 is located in the wa in compartment 18b, each focus extending substantially parallel to the elongated axis of the respective compartme Offsetting the height of the compartments, i.e. providing inclined lower surface of the container and spaced baffles permits the foci of the inclined lens system to be located the different compartments.
Interposed between the lens system 12 and the to of the container is the transparent flat plate conduit 14. Conduit 14 is inclined downwardly from side 26 substantial parallel to the inclination of the lens system, i.e. at approximately angle A, and includes spaced opposed transpa plates 52, 54 which extend downwardly from side 26 to abov the compartment 22 for the distilled water. The flat plat conduit 14 is substantially co-extensive with the lens sys and extends between ends 30 and 32 and from side 26 downwa terminating short of side 28 of the container. The flat

^
O plate conduit and the Fresnel lenses are disposed to have a minimal air space therebetween to reduce transmission losses through the lenses and conduits and to reduce heat losses.
In the embodiment shown in Figs. 1 and 2, angle A has a maximum value of about 20*.
The transparent plates 52, 54 are made for example of glass or plastic and are sealed along the peripheries thereof to be fluid-tight and thusly form the conduit 14.
The plates may be sealed at their peripheries by, for example, welding or with a sealant such as silicone. A frame may be provided in which the edges of the plates are mounted fluid-tight using, for example, a silicone sealant. The plates 52, 54 are planar or flat, as mentioned, and are parallel, being spaced by a distance of from about 6mm to about 12mm.
Openings are provided to the interior of conduit 14 to permit the evacuation of air therefrom and for the circulation of a fluid through the conduit 14. The lower. plate 54 forms a vapor barrier over the container.
The plates forming the conduit 14 may alternatively be co-extensive in length and width with each Fresnel lens series or each lens, with the plates being adjacently disposed and sealed and the lower surfaces of adjacently sealed plates forming a vapor barrier over compartments 1δa,b,c to prevent escape of vapor therepast. A frame and/or a sealant may be used to sealingly join adjacent plates.
The lower end 56 of the conduit is supported by frame means and is spaced from the top of partition 38 to

-BUREAU
OMPI - 18 -provide the only opening through which vapor may pass fro the compartments. However, the spacing is small and the escape of vapor therethrough is ^negligible. Water vapor evaporated from compartments 1δa,b,c rises and impinges u the bottom of the conduit 1 and condenses thereon. The condensate flows downwardly past the opening between the partition 38 and the conduit towards end 56 of the condui and is discharged therefrom into compartment 22 for the distilled water. Thus, the opening between the partition and the bottom surface of the conduit need only be large enough to permit the condensate to flow therepast.
As mentioned, the plates are mounted fluid-tigh to form conduit 14 with the lower surface of the conduit forming a vapor barrier. The plates are thus mounted to a fluid-tight, elongated, generally rectangular enclosure through which a heat exchange fluid may be circulated. A mentioned, water vapor impinges upon the bottom of the co and is condensed thereupon. Upon condensation of the wat vapor, the heat of condensation thereof is released and h the bottom plate or plates of the conduit. The bottom pl or plates are also heated by the sensible heat of the vapo and condensate. A heat exchange fluid is circulated throu the conduit to recover a substantial part of the heat of condensation and the sensible heat and to cool the bottom plate(s) of the conduit to enhance condensation thereon.
The interior of the conduit 14 is connected to t coil 59 of a heat exchanger 60 by conduits so that the hea exchange fluid may be circulated through the conduit 14 and the heat exchanger 60. An expansion tank 62 for the heat exchange fluid is provided bettø^n the conduit 14 and the coil of the heat exchanger, conduit 61 connecting conduit 14 to the reservoir. The expansion tank is located at approximately the same height as the conduit 14 to minimize pressure in the conduit. Preferably, the heat exchanger is located within about 50cm vertically from the expansion tank to provide a small height difference in the levels of the heat exchange fluid, thereby requring a low pressure to circulate the fluid. Angle A may be changed to further reduce the pressure required to circulate the fluid. Thus, the conduit need not withstand high pressures. The heat exchange fluid may be circulated by .pump 64 about a closed circuit which passes through the conduit 14, conduit 61, the expansion tank, conduit 63, the coil 59 of the heat exchanger and conduit 67. Water to be. distilled is introduced through inlet 68 into a chamber 69 in the interior of the heat exchanger so that the water in the chamber and the fluid in the coil are in a heat exchanging relationship. The chamber is connected to compartment 18a by conduit 70. Thus, the water to be distilled may be pumped by pump 72 through the heat exchanger and discharged into compartment 18a of the container. Conduits 61 and 67 have been shown to include only one conduit each. However, it is understood that each may comprise more than one conduit depending upon the size of conduit 14 and the quantity of fluid circulated there-

OMPI through .
In operation, solar energy is concentrated by l series 42, 44 in elongated foqi 48, 50 located in the wat in compartments 18a, 18b respectively. Water is introduc into the container in compartment 18a and upon overflowin baffle 34, enters compartment 18b; upon overflowing baffl 36, the water enters compartment 18c. As the water moves from compartment 18a to compartment 18c, it is progressiv heated in compartments 18a and 18b by the concentrated so energy' and a substantial portion thereof is evaporated. the water overflowing into compartment 18b has been heate in compartment 18a by the solar energy concentrated along focus 50, the water in compartment 18b will reach a highe temperature than the water in compartment 18a so that eva ation from compartment 18b in the central part of the con tainer is accelerated. Heated water overflows into compa ment 18c from compartment 18b with evaporation continuing. The water vapor rises and impinges upon the bottom plates the conduit and is condensed thereon. The condensate flow downwardly along the bottom plates and is discharged into compartment 22. Distilled water is removed from compartme 22 through conduit 74. The water in compartment 18c is a concentrated brine also containing other minerals such as magnesium chloride and magnesium sulfate and is removed through conduit 76.
A clear heat exchange fluid is circulated throug the flat plate conduit, as mentioned, to recover a substan tial part of the heat of condensation of the condensing liquid and to cool the bottom plates of the flat plate conduit to enhance condensation. Tne heat exchange fluid is circulated through the heat exchanger and the heat removed from the heat exchange fluid is transferred to the incoming water to be distilled to preheat it. Thus, a substantial portion of the heat of condensation is recovered and used to increase the efficiency of the system.
The heat exchange fluid circulated in the conduit may be Ther inol 66, a clear liquid available from Monsanto, or a similar liquid, or distilled water which may have a product such as glycol added thereto to raise the boiling point of the distilled water and lower its freezing point.
According to the invention, the flat plate conduit is used to condense the water vapor and accordingly the plates thereof are spaced and the heat exchange fluid therein is chosen to permit maximum transmission of solar energy therethrough while accomplishing condensation of the water vapor and recovery of a substantial part of the heat of condensation. The fluid circulating in conduit 14 is also heated by the absorption of solar energy transmitted through the Fresnel lenses and from solar energy reflected to the fluid in the conduit from the water in the container.
In the embodiment shown in Figs-. 1 and 2, the
Fresnel lenses 46 can, for example, be about 84cm wide by about 250cm long and have a concentration factor of about 40 and a focal width of about 2cm; the container can, for

^J E
OMPI example, be about 168cm wide by about 125cm long and the height of baffles 34 and 36 can, for example, be about 50 The width of the compartments ό h , for example, be about The water depth in the compartments can correspondingly b about 5cm to about 50cm, which is relatively shallow. Th apparatus 10 is arranged with its longitudinal axis in th east-west direction and the lens system facing South. Pr ably, the bottoms of the compartments are blackened by a flexible dark sheet 131 such as Esso Butyl or a similar material which' is also water tight and is capable of with standing temperatures of up to 100*C and will absorb heat transfer it to the water to be distilled to increase the temperature thereof. This will allow use of levelled eart instead of concrete for the bottom of the channel, thereb reducing the cost of the installation. The temperature of the water introduced, into compartment 18a is about 55*C an can gradually reach about 85* C therein.
The quantity of fluid circulated in the flat pan conduit 14 is much larger, for instance, by 10 times, than the quantity of distilled water obtained through evaporati and condensation of vapor on the conduit. This large quan of fluid is required to carry off the recuperated heat of condensation while maintaining the temperature of the flui below that of the condensing vapor. Thus condensation of the water vapor continues on the bottom plate of conduit 1

Referring now to Figs. 3-5, the solar distillati apparatus 80 includes a container 82, a Fresnel lens syste 84 and a transparent flat plate conduit 86 similar to that shown in Figs. 1 and 2 and described above. The container bottom 88 and the Fresnel lens-' System 84 are each approximately inclined at an angle B with the horizontal while the transparent flat panel conduit is inclined at the. angle A, as in Figs. 1 and 2. Angle B is in the range of from about 25* to about 60* . The higher side 90 of the container includes a shoulder 92 to support the Fresnel lens system and space it from side 90 so that the focus of lens 46a is located in compartment 18a, as in Figs. 1-2. The transparent flat plate conduit is spaced from the lens system since the lens system and flat plate conduit are inclined at different angles with the horizontal, the lens system and flat plate conduit being inclined with respect to each other at an angle of B-A. The lens system and conduit are therefore separated. The baffles 34 and 36 are of unequal height, baffle 36 being higher than baffle 34 to provide a greater depth of water in compartment 18b.
Apparatus 80 also includes a separate solar heater 92 which is illustrated to be of the type disclosed in West"

'German published patent specification' o.2730839 which is hereby incorporated by reference. The collector 94 of heater 92 includes two conduits carrying fluids therein heated by solar energy concentrated by lens system 96. The coil 59a of heat exchanger 60a is connected to one of the conduits, preferably the outer conduit 97 and a heat exchange fluid is circulated through the outer conduit and coil 59a. Conduits

f OMPI
IPO -2 - 98-100 complete the circuit with the fluid being pumped pump 101. Conduit 102 connects the chambers of the two exchangers, and conduit 70 connects the chamber of excha 6θa to compartment 18a. Heater 92 is used to assist in heating the water to be distilled which is introduced in compartment 18a of apparatus 80. „ The water to be distill passes first through heat exchanger 60 as described for 1 , and then through heat exchanger 60a before being intro duced into compartment 18a through conduit 70.
Apparatus 80 operates similar to apparatus 10 a provides additional heat from heater 92 to preheat the wa introduced into container 82. Additionally, the lens sys is inclined at an optimum angle towards the south to coll additional solar energy. A fluid as described ,for condui 14 of Fig. 1 is circulated through heater 92 and can be heated to about 280*C. The heat exchanger 60 transfers h recovered by the fluid in conduit 14 to the water to be d tilled. In apparatus 80, the water is preheated and intr duced into compartment 18a at a temperature which can rea about 75*C.
Other details of apparatus 80 are similar to apparatus 10. Only two Fresnel lenses have been shown fo apparatus 80 for clarity, but it is understood that the l system may comprise series of lenses as for apparatus 10.
. In Figs. 6-7, solar distillation apparatus 104 includes a lens system 105, container 106 and a flat-plat transparent conduit system 107. Container 106 includes s

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^ 108, 109 and ends 110, 111 which with support 112 support the lens system 105. The container 106 comprises partitions 113, 114 disposed in the container adjacent walls 108, 109 to form compartments 115, 116 for the distilled water. Each compartment is formed by the bottom 118, sides and portions of the ends of the containers and the partitions. Baffles 120-122 are also provided in container 106 extending substantially parallel to the partitions to form with partitions 113 and 114 and portions of the container end, compartments 124a,b, c,d for the water to be distilled. The heights of the baffles 120-122 are less than the heights of the partitions 113, 114 so that the water to be distilled will not overflow into compartments 115, 116 during normal distillation
operation.
The lens system 105 includes lens series 126 and 128 of Fresnel lenses 46. The lenses of series 126 are arranged with their longitudinal axes and the axes of the refracting prisms 47 extending parallel to the longitudinal axes of the compartments. The lenses of series 128 are arranged with their longitudinal axes and with the axes of the refracting prisms 47 of the lenses extending substantially transversely to the longitudinal axes of the compartments. Lens series 126 and 128 are inclined with respect to each other with the two lens series meeting over the~con-' ~ tainer and forming an apex 130 thereabove. Lens series 126 extends from apex 130 downwardly at an angle C with the horizontal and is suppoted by side 108 of the container. Lens - - series 128 extends from apex 130 downwardly at an angle D with the horizontal and is supported on side 109 of the ' container. Support 112 extending at the apex supports the lens system thereat.. Side; #08 is higher than side 109 and the apex 130 is located closer to side 108 than side 109. Therefore, angle D is greater than angle C.
The bottom 118 of the container, coated with a dark, flexible, water-impermeable material 131, is inclined at an angle E with the horizontal, the water to be distilled being introduced into compartment 124a and overflowing into compartments, 124b-d. Concentrated brine is
removed from compartment 124d.
Each of lenses 46a,b,c of lens series 128 has an elongated focus 132a,b,c extending transverse to the axes of the compartments (Fig. 6) and extending through varying depths of water. Each of lenses 46d,e has an elongated focus 132d,e extending within compartment 124a with the axes of foci 132d,e extending substantially parallel to the axis of compartment 124a, each focus exten ing through a substantially constant water depth with the two foci being at different water depths.
The transparent conduit system 107 includes transparent conduits 14a,14b inclined with respect to each other along apex 136, each extending downwardly at the angle A, as described for Figs. 1-5, towards sides 108 and 109, respectively. Supports suspend the transparent conduits above the container with the lowermost ends of the conduits being above compartments 115,116. Each- conduit lower surface forms a vapor barrier as described for conduit 14 in - r

1-5 and the lower surface of the apex is sealed fluid-tight so that the conduit system 107 forms a vapor barrier above the container. The circuit fόr the fluid in the conduits 14a and 14b passes serially through the conduits and the heat exchanger.60. The water to be distilled passes serially through heat exchanger 60 and heat exchanger 60a. The angles of inclinatipn of the lens series exceeds angle A and there is a space between the conduit system and the lens system, as described for Figs. 3-5.
Apparatus 104 also includes the heat exchanger 6θa and the solar heater 92, as described for Figs. 3-5. Moreover, two conduits 14a, 14b are provided and two compartments for the distilled water are provided to increase the production of distilled water.
Apparatus 104 is arranged so that the compartments extend generally east-west and operates similar to apparatus 10 and 80. Apparatus 104 includes the intersecting lens foci which serve to heat the water at different depths transverse to the axis of the compartments as well as substantially parallel to the axes of the compartments. Additionally, the lens system 105 includes lens series which can be tilted to the north and to the south at, for example, 10* and 30*, respectively to collect more solar energy than the apparatus of Figs. 1-5. The temperature of the water in. compartments 124a-d can gradually reach about 85*C.
While the lens series 126, 128 have been shown to include three and two Fresnel lenses, respectively, it is

OMPI _ understood that each series may comprise more or less lens having the same or different sizes so that the lens system extends over substantially the .βfttire top of the container

Although not shown, means may be provided to mov the lens systems to track the sun to further increase prod tion of distilled water.
Mirrors may be disposed along selected portions of the prisms of the Fresnel lenses to further concentrate the solar energy in the liquid to be distilled.
Excess water vapor not condensed in the distilla tion apparatus may be removed and superheated in a heat exchanger using a heater such as solar heater 92. The sup heated steam at 250*C for example, can be expanded in a turbine to obtain power and condensed to obtain additional distilled water.
Referring now to Figs. 8 and 9, a composite distillation system 140 is shown which comprises a plurality of individual, adjacently arranged systems 104a-104d. Each system 104a-104d is similar to system 104 with adjacent systems having common compartments 115a for receiving distilled water. Each system 104a-104d is individually suppli with water to be distilled and heat exchange fluid for circulating in the conduit system of each system 104a-104d. Common conduits, however, may be used to supply and withdra the water and fluid.
The brine which is a high temperature and at a higher concentration than the water (salt water) to be dis-

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«* O tilled, can be serially fed to one or more successive distillation units. Moreover, a countercurrent arrangement may be set up within a single unit'- r among several units in which the concentrated brine of downstream compartments is supplied to the upstream compartments. Thus, the heat in the brine at about 80"C, for. instance, can be recuperated and used to enhance evaporation of water in other compartments or units. Additionally, the brine will be concentrated and allow a more economic extraction of salt and/or other chemicals such, as magnesium chloride, magnesium sulfate, etc., therefrom.
Fig. 10 is a cross-sectional view of another embodiment of solar distillation apparatus according to the present invention. The distillation apparatus 210 of Fig. 10 includes a Fresnel lens system 212 supported base structure 218, having a front wall 220, a bottom wall 222 and a rear w.all 224. On the base structure is a container 219 including an insulating base plate 226 which rests on walls 220 and 224, a bottom end wall 221 and a top end wall 223. The Fresnel lens are supported by supports 214 and 216 which are attached to end walls 221 and 223 respectively. The container will, of course, have appropriate side walls, not shown on the figure. On top of this insulating base plate 226 is an undulated plate system 228 which can be made up as a single system or made up as a plurality of plates. The height of each of the undulations 230 should be, for example, 90 mm (about 3*5 inches). The distance between undulations should be, for

OMPI
. IPO * -~- 3θ - example, 120 mm (about 5 inches). The Fresnel lens syste 212 is tilted to an angle of, for example 30* and base pl 226 with the plate system 228 t'ldreon tilted, in the illu trated embodiment, to an angle of 20*. Interposed betwee the Fresnel lens 212 and the plate system 228 and paralle to base plate 226 is a double plate conduit 232. In this double plate conduit, having a lower plate 231 and upper plate 233, a fluid 35 circulates in the manner described above. Salt water 237 which is to be evaporated is supplied to upper end of the plate system 228 through end wa 223 and flows downward over the undulations 230. In the process, heat from the sun which is concentrated by the Fresnel lens system, in the illustrated embodiment includ a Fresnel lens 212a and a Fresnel lens 212b, evaporates s of the water in salt water flowing over the invention in order to spread the solar energy over a larger area, the focal points of the Fresnel lenses 212a and 212b designate as points 234 and 236, respectively, are located below the insulating base 226. Typically, for example, if the focal distance of the lens is 105 mm [42 inches], i.e., where th is a distance of 42 inches from the lens to the maximum ar of concentration, the plates will preferably be located at for example, 90 cm [35.5 inches] from the lens. The evapo ated water vapor 239 which will typically -be about 75*C ri and is condensed on the bottom plate 231 of conduit 232 wh contains a fluid 235 typically at 30"C. The condensate 24 runs down the inside of the plate and is collected in a co

O partment 238 from which it flows through an opening 239 to a compartment 252. The fluid 235 flowing between the plates 231 and 233 of the conduit 23 *^ collected in a compartment 240. Brine 243 which results from the evaporation of the water from the salt water flows through an outlet 242 of the plate system 228 through plate 226 to a compartment 248.
The plates of the plate system 228 are preferably made out of metal such as steel, stainless steel or coper, having a thickness of, for example, 1 mm. It is preferred that they be covered by a black paint or chrome black. The paint or other agent used should be of an anti-corrosive material and provision should be made, if necessary, to provide cathodic protection for the metal structure to prevent the damage which could result from electrical currents caused by the reaction between the metal surfaces and existing chemicals in an electrolytic solution in the water.
As an alternative to metal, undulated asbestos fiber, glass or plastic plates can be used. Metallic
undulated plates are preferred since they will conduct heat to all sides of the plates, from the location of the striking solar rays in the focal area.
As the water being distilled flows over the undulations, it will be in cavities which are only about 90 mm deep. The thinness of the water in the cavities between the undulations 230, coupled with the thin layer of water which flows over the undulations 230 will result in fast heating and evaporation of the water.

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OMPI Since deposits can form on the plate system 228, a single panel of plurality of adjacent panels made of blackened flexible plastic or the* like such as isobutyl ca be used to cover the wall or the bottom plate system and b attached thereto in a removable manner so that the plastic covering can be taken out and the deposits thereon removed The double plates 231 and 233 are partially obstructed at the extreme ends (see Fig. 10a) by silicone or other means leaving a small outlet 233a for the release of the fluid t compartment 240. This is done so to allow the fluid 235 t spread all over the surface between the plates 231 and 233 A valve 233b at the upper end of the double plate system 2 permits selectively controlling the flow of the fluid 235. The fluid 235 will flow to a collector 43 at the inlet to the double plates 232 from a tank 233c at a height of, for instance 40 cm (about 17") above the collector 243 so- as t allow a maximum pressure between the plates 231 and 233.
In accordance with another feature of the embodi ment of FIG. 1, storage areas are located beneath the insul ing plate 226. Shown is a storage area 248 for brine 242, a storage area 250 for the fluid 235 circulated in the doub plate conduit 232, a storage area 252 for the condensate 24 and a storage area 254 for concentrated brine. By storing the various fluids beneath the insulating base, further insulation and retention of heat within the system is obtained. Circulation of the various fluids can be carried out in the manner described above. Basically the fluid

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- 33 -collected in the compartment 40 which normally starts out at 30" C and is then heated up to approximately 65*C by the vapor at 75*C is circulated to a heat ^exchanger 251 where it transfers heat to the incoming salt water and in the process is cooled back down to 30"C. It is then recirculaed to a container 233c and flows through valve 233b entering the double plate system through end wall 223- Condensate from compartment 252 can also be circulated th rough heat exchanger 251. In addition, recirculation of the brine for concentration thereof and removal of additional heat therefrom in the manner described above may be carried out as shown. Salt water from heat exchanger 251 along with additional preheated saltwater from another solar system 253, such as that of my previous application or as described below, enters plate system 228 through opening in end wall 223.
Fig. 3 is a perspective view of a system such as that shown in the Fig. 1. Once again, the insulating base 226 is shown as is the plate system 228 with its undulations 230. The two Fresnel lenses 212a and 212b are shown as is the double plate conduit 232. However, in this embodiment, at the bottom of the plate system above the points 234 and 236 where the solar energy is concentrated (See Fig. 1), there are installed arrays of photovoltaic cells 259. Photovoltaic cells 259 produce electricity from the visible solar rays only, i.e., those form 0.4 to 0.8 microns. The infrared rays will be mostly absorbed by the fluid flowing in the double plate system 232 and by the water being distilled

OMPI
. WIIPPOO which circulates above and around the photovoltaic cells.

- By using such an arrangement a separate photovoltaic cell installation in order to produce .electricity is not neces- sary. Furthermore, because of the concentration of the so energy by the lenses, a production of electricity up to, f instance, twenty times that can only be produced with conc tration. For example, the average yearly production of el tricity may be increased to about three watss per cell wit the concentration as compared with about 0.061 Watt per ce without concentration.
This arrangement offers many advantages since it allows concentrating the energy on the cell and, at the sa time, removing infrared energy, which should otherwise hea up the cell and reduce its efficiency. The infrared energ is absorbed by the water 237 being distilled and by the fl 235 in the dual plate conduit 232 and the distilled water around the cells circulating in the tube enclosing the cel are shown herein, whereas the visible light is utilized to generate electricity. Thus, simply for the additional cos of the cells themselves, a system which is both a distilli and an electrical generating unit is provided. Without su cooling, the temperature would be higher reducing the efficiency of the silicon voltaic cells and if the tempera ture exceeded 200* C, the efficiency would drop to 0 and th cells could melt.
The array of photovoltaic cells can be installed
* in a transparent square encapsulate protecting the cells from the saline water and over and above which saline water is circulated.
The advantages of the present invention, as well as certain changes and modifications of the disclosed embodiments thereof, will be readily apparent to those skilled in the art. It is the applicant's intention to cover by his claims all those changes and modifications which could be made to the embodiments of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention. Protection by Letters Patent of this invention in all its aspects as the same are set forth in the appended claims is sought to the broadest extent that the prior art allows.