CA1139255A - Solar distillation apparatus - Google Patents

Abstract

ABSTRACT

Solar distillation apparatus are disclosed in which a substantial part of the heat of condensation of the condensing liquid is recovered. A conduit having an inclined smooth lower surface is disposed above the liquid to be dis-tilled and on which the evaporated liquid condenses and re-leases its heat of condensation. A fluid is circulated through the conduit in a heat exchanging relationship with the lower surface thereof, the fluid absorbing a substantial part of the released heat of condensation. The condensed liquid flows along the bottom of the inclined lower surface and is discharged from the lower end thereof and collected. The conduit in the pre-ferred embodiments is flat and transparent and the spacing between the upper and lower walls of the conduit is selected so that only a small part of the solar energy is absorbed in the conduit while the fluid in the conduit recovers a substantial part of the released heat of condensation. In accordance with the invention, more fluid is circulated in the conduit means than the quantity of liquid evaporated from the distillation compartments and condensed on the conduit means in order to carry away the released heat of condensation while maintaining the temperature of the fluid below that of the condensing liquid vapor. In accordance with the preferred embodiments;
salt water is distilled and the quantity of fluid circulated through the conduit to absorb and carry the heat of condensation released by the condensing water vapor, will greatly exceed, for example, by 10 times, the quantity of condensed water evapor-ated, and distilled by the apparatus. Much more fluid is circulated in the conduit to maintain the fluid temperature below that of the condensing water vapor. The concentrated brine at for instance 80°C may be recycled one or several times in separate distillation units or in distillation channels or compartments of the same unit wherein brine instead of preheated water to be distilled is introduced into the distillation compartments. Thus, the heat of the brine may be recovered and the concentration of the brine may be increased in successive compartments and units, allowing a more economical extraction of 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 water to be distilled, increasing its temperature to for instance 75°C before introducing the water into the distillation compartment. The production of dis-tilled water according to the invention is substantially higher than by conventional solar ponds and the cost of producing distilled water reduced to zero in certain locations when credit is obtained for the salts extracted from the concentrated brine. Preferably, the bottoms of the distilla-tion compartments are blackened by a water-proof flexible material such as Esso Butyl or a similar material.

Description

~3~

SOLAR DISTILLATION APPARATUS
.
The present invention relates to solar distillation apparatus and more particularly to apparatus for the solar distillation of water.
In United States Patent No. 4,134,393 issued January 16, 1979 of which I am a co-inventor and the sole assignee, and in United States Patent No. 4,194,949 issued March 25, 1980,of which I am sole inventor, solar energy distillation apparatus are disclosed in which a par~ of the heat of conden-sation 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 ~13925S

the fluid lens i5 limited to angles of inclination of less than about 20-. For example, at a latitude of 35 S, the optimum angle of inclination for the lens will be about 45-and a system with a lens inclined at about 20' will collect less solar energy than a system with a lens inclined at the optimm angle of 45-.
Additionally, the focal distance and concentration 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 aperture.
Therefore, a comprise must be reached between the concentra-tion factor and focal distance of the fluid lens in which the 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 increase the concentration factor of the lens. Moreover, since the fluid lens must be placed at a greater distance from the liquid than otherwise desired in order to increase its concentration, there is a large volume, which is undesirable, between the lens and the liquid to be distilled.
The spacing between the lens plates of the fluid 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 ~139;~SS

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 impGrtant 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 clean-ing 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 conden-sation 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 ~392S5 --4_ on a surface thereof, the conduit means being disposed intermediate t'ne liquld to be distilled and means for concen-trating the solar energy in the liquid.
In accordance with the invention, the apparatus comprises lens means disposed above the liquid to be distilled for concentrating the solar energy therein; conduit means for passing a fluid therethrough disposed intermediate the lens means and the liquid to be distilled and comprising an inclined, lower wall having a smooth outer surface and having a lower end; a fluid in said conduit means in a heat exchang-ing relationship with said lower wall; and container means disposed below said lower end for receiving condensed liquid.
The concentrated solar energy causes the liquid to evaporate with the vapor impinging and being condensed upon the outer surface of the lower wall, the condensed liquid flowing along the outer surface of the lower wall to the lower end thereof and falling therefrom into the container means, a substantial part of the heat of condensation o~ the condensing vapor being absorbed by the fluid in the conduit means.
The conduit means is transparent at least in part and the solar energy is passed through the transparent portions into the liquid to be distilled, the conduit means and the lens means being superposed at least in part.
In the di,sclosed embodiments, the conduit means is a flat conduit comprised of transparent upper and lower walls sealingly joined, for example welded, to form the conduit.
According to one embodiment of the invention, a ~1392SS

plurality of sets or series of Fresnel-type lenses are arranged over a container holding liquid to be distilled.
Each set of Fresnel lenses includes 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 dis-tillation 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 dispo~ed 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 i9 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 113~ZSS

heat recovered in the heat exchange fluid circulated in the conduit to the liquid being introduced into the container to 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'C in the case of water, before the liquid is introduced into the container.
In accordance with the invention, more fluid is circulated in the conduit means than the quantity of liquid introduced into the distillation compartments, evaporated therefrom and condensed on the conduit means in order to carry away the released heat of condensation while maintaining the temperature of the fluid below that of the condensing liquid vapor.
In the case of the distillation of salt water, the quantity of fluid circulated through the conduit to absorb and carry the heat of condensation released by the condensing water vapor, will greatly exceed, for example, by 10 times, the quantity of water evaporated, condensed and distilled by the apparatus. Much more fluid is circulated in the conduit to maintain the fluid temperature below that of the condens-ing water vapor.
The liquid concentrated with impurities (in the case of salt water, concentrated brine at for instance, 80-C) may be recycled one or several times in separate distillation unitq or in the distillation channels or compartments of the same unit, the liquid concentrated with impurities (or the ~39%~;S

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 dis-tilled, 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 inven-tion, 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 compart-ments. 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 ~392S~

each conduit having a lower end disposed above compartments for the distilled liquid.
In still another embodiment of the invention, a composite system is provided made of of individual, adjacently arranged units.
The Fresnel lenses may be replaced by fluid lenses, if desired. However, the Fresnel lenses are preferred for the reasons discussed above.
According to the present invention, production of distilled water from salt water is substantially higher than by conventional solar ponds. The cost of producing distilled water may be reduced to zero in certain locations when salt (NaCl) and/or magnesium chloride sulfate are extracted from the concentrated brine.
According to another aspect of the invention, the bottom of the compartment containing the liquid to be dis-tilled is blackened preferably by flexible blackened material 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 distilla-tion compartments are replaced by an undulated plate or ~1392SS

plurality of adjacent plates on top of an insulating base.
In accordance with a further feature of this embodi-ment of the present invention, a 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 ~t the locations where the focus area of the Fresnel lens are most concentrated. As in my previous-ly disclosed systems, the lenses are supported for movement ~392S~

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 f`or a number of 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 separate solar installation for producing electricity. Furthermore, where concentration of solar energy is used as is the case with the present invention, the production of electricity can be up to for instance 40 times that which it would be without concentration. For example, the average yearly production of electricity with concentration will be, for example 3 Watts per cell for example, 5cm x 5cm compared with about 0.06 Watts per cell for cells exposed to the sun without concentra-tion. Cost estimates have shown that installing an array of photovoltaic cells in a distillation unit of the present invention permits saving all of the cost of the solar system otherwise required by the photovoltaic cells. Put another way, it reduces by about half the total cost of the photo-voltaic cell system when the solar need to concentrate the solar energy is considered. Thus, the present solar energy system uses a single concentrating means, i.e., lens system, which supplies energy both for distillation and for generating electricity.
Furthermore, the absorption of infrared rays by the 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 encap-sulated 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 40-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 i~3g25~

-12_ efficiently producing electricity and at the same time the 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 prevent the formation of otherwise insoluble deposits such as calcium sulfate or unstable sodium bicarbonates which may form in the salt water. Barilium sulfate may deposit during the nights, 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 the 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 and in which:
Fig. 1 is a vertical cross-section schematic view of solar distillation apparatus according to the invention showing two ad~acent sets of Fresnel lenses arranged above a 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 angle to be substantially parallel;

Fig. 2 is a top plan schematic view, partly broken-away, of the solar distillation apparatus of Fig. 1;
Fig. 3 is a vertical cross-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 len~es 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 ad~acent and inclined with respect to each other and with respect to the container and plate-like conduit;
Fig. 7 is a top plan schemati¢ view of the solar distillation apparatus of Fig. 5;
Fig~ 8 is a vertical cross-section schematic view of a compo~ite solar distillation apparatus utilizing a plurality of ~ystems of the type shown in Figs. 6-7; and Fig. 9 i~ a top plan schematic view of the composite . ,. ~

~13~5S

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 1Oa is a perspective view of the double plate system of Fig. 1.
Figure 11 is a perspective view of the unit accord-ing to Fig. 10, showing the installation of photovoltaic cells.
Referring more particularly to the drawings, appara-tus for the solar distillation of water are illustrated. In Fig. 1, the distillation apparatus 10 includes a Fresnel lens system 12 to concentrate the solar energy, a transparent flat plate conduit 14 on the bottom of which water vapor is condensed, and a container 16 having compartments 18a,b,c for the water to be distilled and a compartment 22 for distilled water which is discharged from the bottom of the conduit 14.
The sides 26, 28 of the container are offset in height and the lens system 12 extends inclined along the sides of the container between the ends 30, 32 thereof, the lens system closing the top of the container and being supported by the sides and ends of the container. Compartment 18a in the ontainer is formed by the slde 26 of the container, a baffle 34 and the ends of the container; compartment 18b by baffles 34 and 36 and the ends of the container, and compartment 18c by a partition 38 and the ends of the container. The parti-tion 38 separates the compartments 18a,b,c holding water to `` ~139ZS5 be distilled from comp2rtment 22 holding the distilled w2ter.
Compartments 18a,b,c extend parallel to the elongated axis of the container.
The bottom 40 of the container is inclined down-wardly from side 26 to side 28 at an angle A with respect to the horizontal. The heights of baffles 34 and 36 are substan-tially equal to provide the inclined container bottom 40 with stepped compartments 18a,b,c so that during normal distilla-tion operation, the maximum depths of the water to be dis-tilled in compartments 1Ba,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 compart-ment 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, extend-ing 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 ~eries extending substantially parallel to the elongated axes of the container and compart-ments 18a,b,c. The inclined, parallel lenses are spaced by, for example, one inch to prevent shadowing of adjacent lenses. Two series of lenses are shown and each series oflenses is shown to include six lenses; however, one or three or more series of lenses and more or less than six lenses may be utilized per series depending upon the size of the installation and the quantity of distilled water desired.
Each Fresnel lens comprises longitudinally extending prisms 47 which provide an elongated narrow focus. The series of lenses are arranged to provide spaced parallel elongated composite foci 48, 50. The composite focus 48 of lens series 42 is located in the water in compartment 18a while the composite focus 50 of lens series 44 is located in the water in compartment 18b, each focus extending substantially parallel to the elongated axis of the respective compartment.
Offsetting the height of the compartments, i.e. providing an inclined lower surface of the container and spaced baffles, permits the foci of the inclined lens system to be located in the different compartments.
Interposed between the lens system 12 and the top of the container is the transparent flat plate conduit 14.
Conduit 14 is inclined downwardly from side 26 substantially parallel to the inclination of the lens system, i.e. at approximately angle A, and includes spaced opposed transparent plates 52, 54 which extend downwardly from side 26 to above the compartment 22 for the distilled water. The flat plate conduit 14 is substantially co-extensive with the lens system and extends between ends 30 and 32 and from side 26 downwardly, terminating short of side 28 of the container. The flat -16~ 25~

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 18a,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 il39~5 provide the only opening through which vapor may pass from the compartments. However, the spacing is small and the escape of vapor therethrough is negligible. Water vapor evaporated from compartments 18a,b,c rises and impinges upon the bottom of the conduit 14 and condenses thereon. The condensate flows downwardly past the opening between the partition 38 and the conduit towards end 56 of the conduit and is discharged therefrom into compartment 22 for the distilled water. Thus, the opening between the partition 38 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-tightly to form conduit 14 with the lower surface of the conduit forming ~ vapor barrier. The plates are thus mounted to form a fluid-tight, elongated, generally rectangular enclosure through which a heat exchange fluid may be circulated. As mentioned, water vapor impinges upon the bottom of the conduit and is condensed thereupon. Upon condensation of the water vapor, the heat of condensation thereof is released and heats the bottom plate or plates of the conduit. The bottom plate or plates are also heated by the sensible heat Or the vapor and condensate. A heat exchange fluid is c~rculated through the conduit to recover a substantial part of the heat of condensation and the sensible heat and to cool the bottom platets) of the conduit to enhance condensation thereon.
The interior of the conduit 14 is connected to the coil 59 of a heat exchanger 60 by conduits so that the heat 1~39:255 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 between the conduit 14 and the coil of the heat exchanger, conduit 61 connecting conduit 14 to the reservoir. The expansion tank is located at approxi-mately 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 pro-vide 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-1~392~S

through.
In operation, solar energy is concentrated by lens series 42, 44 in elongated foci 48, 50 located in the water in compartments 18a, 18b respectively. Water is introduced into the container in compartment 18a and upon overflowing baffle 34, enters compartment 18b; upon overflowing baffle 36, the water enters compartment 18c. As the water moves from compartment 18a to compartment 18c, it is progressively heated in compartments 18a and 18b by the concentrated solar energy and a substantial portion thereof is evaporated. Since the water overflowing into compartment 18b has been heated in compartment 18a by the solar energy concentrated along focus 50, the water in compartment 18b will reach a higher temperature than the water in compartment 18a so that evapor-ation from compartment 18b in the central part of the con-tainer is accelerated. Heated water overflows into compart-ment 18c from compartment 18b with evaporation continuing.
The water vapor rises and impinges upon the bottom plates of the conduit and is condensed thereon. The condensate flows downwardly along the bottom plates and is discharged into compartment 22. Distilled water is removed from compartment 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 through the flat plate conduit, as mentioned, to recover a substan-~139ZSS

tial part of the heat of condensation of the condensing liquid and to cool the bottom plates of the flat plate con-duit to enhance condensation. The 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 Therminol 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 con-densation. 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 ~3925S

exa~ple, be about 168cm wide by about 125cm long and the height of baffles 34 and 36 can, for example, be about 50cm.
The width of the compartments can, for example, be about 40cm.
The water depth in the compartments can correspondingly be about 5cm to about 50cm, which is relatively shallow. The apparatus lO is arranged with its longitudinal axis in the east-west direction and the lens system facing South. Prefer-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 and transfer it to the water to be distilled to increase the temperature thereof. This will allow use of levelled earth instead of concrete for the bottom of the channel, thereby reducing the cost of the installation. The temperature of the water introduced into compartment 18a is about 55 C and can gradually reach about 85 C therein.
The quantity of fluid circulated in the flat panel conduit 14 is much larger, for instance, by 10 times, than the quantity of distilled water obtained through evaporation and condensation of vapor on the conduit. This large quantity of fluid is required to carry off the recuperated heat of condensation while maintaining the temperature of the fluid below that of the condensing vapor. Thus, condensation of the water vapor continues on the bottom plate of conduit 14.
Referring now to Figs. 3-5, the solar distillation apparatus 80 includes a container 82, a Fresnel lens system 1~39;;~

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 approxi-mately 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 blaffles 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 United States Patent 4,134,393 issued on January 16, 1979. 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 1139~55 98-100 complete the circuit with the fluid being pumped by pump 101. Conduit 102 connects the chambers of the two heat exchangers, and conduit 70 cornects the chamber of exchanger 60a to compartment 18a. Heater g2 is used to assist in pre-heating the water to be distilled which is introduced into compartment 18a of apparatus 80. The water to be distilled passes first through heat exchanger 60 as described for Fig.
1, and then through heat exchanger 60a before being intro-duced into compartment 18a through conduit 70.
Apparatus 80 operates similar to apparatus 10 and provides additional heat from heater 92 to preheat the water introduced into container 82. Additionally, the lens system is inclined at an optimum angle towards the south to collect additional solar energy. A fluid as described for conduit 14 of Fig. 1 is circulated through heater 92 and can be heated to about 280 C. The heat exchanger 60 transfers heat recovered by the fluid in conduit 14 to the water to be dis-tilled. In apparatus 80, the water is preheated and intro-duced into compartment 18a at a temperature which can reach about 75 C.
Other details of apparatus 80 are similar to apparatus 10. Only two Fresnel lenses have been shown for apparatus 80 for clarity, but it is understood that the lens 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-plate transparent conduit system 107. Container 106 includes sides il3~32~5 108, 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 compart-ment 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 substan-tially transversely to the longitudinal axes of the compart-ments. 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 hori-zontal 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 108 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 is inclined at an angle E with the~hori-zontal, the water to be distilled being introduced into compartment 124a and overflowing into com?artments 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 extending through a substan-tially con~tant water depth with the two foci being at different water depths.
The transparent conduit system 107 includes trans-parent conduits 14a, 14b inclined with respect to each other along apex 136, each extending downwardly at the angle A, as described for Fig~ 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 Figs.

~13~255 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 for 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 inclination 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 60a and the solar heater 92, as described for Figs. 3-5. More-over, two conduits 14a, 14b are provided and two compartments for the distilled water are provided to increase the produc-tion 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 understood that each series may comprise more or less lenses having the same or different sizes so that the lens sy.stem extends over substantially the entire top of the container.
Although not shown, means may be provided to move the lens systems to track the sun to further increase produc-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 super-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 dis-tillation 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 dis-tilled water. Each system 104a-104d is individually supplied with water to be distil'ed and heat exchange fluid for cir-culating in the conduit system of each system 104a-104d.
Common conduits, however, may be u~ed to supply and withdraw the water and fluid.
The brine which is athigh temperature and at a higher concentration than the water (salt water) to be dis-~139255 tilled, can be serially fed to one or more successive dis-tillation units. Moreover, a countercurrent arrangement may be set up within a single unit or 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 ôO-C, for instance, can be recuperated and used to enhance evaporation of water in other compart-ments 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 embodi-ment 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, hav-ing a front wall 220, a bottom wall 222 and a rear wall 224.
On the base structure is a container 219 including an insulat-ing 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 i9 an undulated plate system 228 which can be made up as a single system or made up a~ 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 ~139ZSS

example, 120 mm (about 5 inches). The Fresnel lens system 212 is tilted to an angle of, for example 30 and base plate 226 with the plate system 228 thereon tilted, in the illus-trated embodiment, to an angle of 20-. Interposed between the Fresnel lens 212 and the plate system 228 and parallel 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 sup-plied to upper end of the plate system 228 through end wall 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 includes a Fresnel lens 212a and a Fresnel lens 212b, evaporates some 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 designated 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 there is a distance of 42 inches from the lens to the maximum area of concentration, the plates will preferably be located at, for example, 90 cm [35.5 inches] from the lens. The evapor-ated water vapor 239 which will typically be about 75-C rises and is condensed on the bottom plate 231 of conduit 232 which contains a fluid 235 typically at 30 C. The condensate 241 runs down the inside of the plate and is collected in a com-~13~; :S~i 3o -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 232 is 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 pro-vide 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 undula-tions, it will be in cavities which are only about 90 mm deep.
The thinness of the water in the cavities between the undula-tions 230, coupled with the thin layer of water which flows over the undulations 230 will result in fast heating and evaporation of the water.

1139;~5 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 can be used to cover the wall or the bottom plate system and be attached thereto in a removable manner so that the plastic oovering can be taken out and the deposits thereon removed.
The double plates 231 and 233 are partially obstructed at the extreme ends (see Fig. 1Oa) by silicone or other means leaving a small outlet 233a for the release of the fluid to compartment 240. This is done so to allow the fluid 235 to spread all over the surface between the plates 231 and 233.
A valve 233b at the upper end of the double plate system 232 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 to 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 insulat-ing plate 226. Shown is a storage area 248 for brine 242, a storage area 250 for the fluid 235 circulated in the double plate conduit 232, a storage area 252 for the condensate 241 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 ~39;;~5S

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 trans~
fers heat to the incoming salt water and in the process is cooled back down to 30-C. It is then recirculaed to a con-tainer 233c and flows through valve 233b entering the double plate system through end wall 223. Condensate from compart-ment 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. Photo-voltaic cells 259 produce electricity from the visible solar rays only, i.e., those form 0.4 to o . 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 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 solar energy by the lenses, a production of electricity up to, for instance, twenty times that can only be produced with concen-tration. For example, the average yearly production of elec-tricity may be increased to about three watss per cell with the concentration as compared with about 0.061 Watt per cell without concentration.
This arrangement offers many advantages since it allows concentrating the energy on the cell and, at the same time, removing infrared energy, which should otherwise heat up the cell and reduce its efficiency. The infrared energy is absorbed by the water 237 being distilled and by the fluid 235 in the dual plate conduit 232 and the distilled water around the cells circulating in the tube enclosing the cells are shown herein, whereas the visible light is utilized to generate electricity. Thus, simply for the additional cost of the cells themselves, a system which is both a distilling and an electrical generating unit is provided. Without such cooling, the temperature wou,d 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 the cells could melt.
The array of photovoltaic cells can be installed in a transparent square encapsulate protecting the cells ~1~9~55 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 embodi-ments 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.

Claims (59)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:-

1. Apparatus for distilling a liquid such as water using solar energy comprising:
means for containing the liquid to be distilled;
lens means disposed above said containing means for concentrating the solar energy in said liquid to be distilled;
elongated conduit means disposed between said lens means and said containing means for condensing evaporated liquid thereon, said conduit means being transparent at least in part so as to allow solar energy concentrated by said lens means to pass therethrough and reach said containing means, said conduit means including means for admitting fluid to and withdrawing fluid from said conduit means such that a fluid can be passed through said conduit means, said conduit means including a substantially smooth surface disposed above the containing means and positioned such that rising liquid vapor im-pinges upon said surface and is condensed thereon, said smooth surface being operative to transmit at least in part the heat of condensation released by evaporated liquid condensing thereon to the interior of said conduit means where such heat may be absorbed by the fluid in said conduit means and thereby may be recovered, said smooth surface having a vertically lower portion such that condensed liquid flows along said surface to said vertically lower portion thereof and is discharged therefrom, and liquid collecting means disposed below said lower por-tion of said smooth surface for collecting condensed liquid discharged from said lower portion.

2. The apparatus as recited in claim 1, wherein said conduit means comprises a planar lower wall which forms said smooth surface.

3. The apparatus as recited in claim 2, wherein said conduit means comprises an upper wall spaced from said lower wall.

4. The apparatus as recited in claim 3, wherein said upper wall is planar.

5. The apparatus as recited in claim 4, wherein said upper and lower walls are parallel.

6. The apparatus as recited in claim 3 wherein said upper and lower walls are transparent at least in part, said lens means and the transparent portions of the conduit means being disposed so that solar energy concentrated by said lens means passes through the transparent portions into the liquid to be distilled.

7. The apparatus as recited in claim 5, wherein said upper and lower walls are transparent at least in part, said lens means and the transparent portions of the conduit means being disposed so that solar energy concentrated by said lens means passes through the transparent portions into the liquid to be distilled.

8. The apparatus as recited in claim 6, wherein said upper and lower walls are parallel upper and lower transparent flat plates sealingly joined to form a flat conduit, said smooth outer surface being the outer surface of said lower plate.

9. The apparatus as recited in claim 8, wherein said lens means comprises at least one Fresnel-type lens which con-centrates the solar energy through said plates in an elongated focus in the liquid to be distilled.

10. The apparatus as recited in claim 9, wherein said conduit means comprises two conduits disposed adjacent each other with the lower surfaces thereof being oppositely inclined, and including an elongated container in which said containing means and said liquid collecting means are disposed, said containing means being disposed centrally in the container and a liquid collecting means being disposed below each said lower end separated by said containing means, said lens means comprising at least two adjacently disposed Fresnel-type lenses, a first of said Fresnel-type lenses being inclined in the direction of one of said conduit, and a second of said Fresnel-type lenses being inclined in the direction of the other of said conduits.

11. The apparatus as recited in claim 10, wherein said container includes side and end walls and two partitions therein disposed adjacent opposed side walls thereof, each partition with walls of said container forming a liquid collecting compartment, each of said liquid collecting compartments being disposed below a respective lower end to receive condensed liquid falling there-from, and wherein said conduits substantially cover said con-tainer, and wherein said container includes at least two baffles extending said containing means to separate said container means into at least three compartments for containing liquid to be distilled, an elongated focus of the first Fresnel-type lenses being substantially located in one of said compartments for con-taining liquid to be distilled and the elongated focus of the second Fresnel-type lens being located at least in part in an-other of said compartments for containing liquid to be distilled.

12. The apparatus as recited in claim 11, wherein the axis of the first and second Fresnel-type lenses are substantially normal to each other, the elongated focus of the first Fresnel-lens extending through varying depths of liquid in at least said one and another compartments.

13. The apparatus as recited in claim 11, and compris-ing a plurality of said apparatus adjacently arranged to form a composite apparatus, adjacent apparatus having common compart-ments for receiving condensed liquid.

14. The apparatus as recited in claim 13, and compris-ing means for recycling the liquid concentrated with substances in at least one successive apparatus, recycled liquid being introduced into said successive apparatus to replace at least in part liquid to be distilled, whereby part of the heat of the re-cycled liquid is recuperated and the liquid is further con-centrated with substances.

15. The apparatus as recited in claim 8, and compris-ing a container in which said containing means and said liquid collecting means are adjacently disposed, said container includ-ing side and end walls and a partition disposed adjacent one wall of the container, the partition and walls of the container forming a compartment disposed below said lower portion of said lower plate to form said liquid collecting means for collecting condensed liquid falling therefrom, said lower plate sub-stantially covering said containing means and forming a vapor barrier thereabove.

16. The apparatus as recited in claim 15, wherein said container is elongated and said lens means comprise a plurality of elongated Fresnel-type lenses each concentrating the solar energy in an elongated focus in the liquid to be distilled, the elongated axes of said Fresnel-type lenses and said elongated container being substantially parallel.

17. The apparatus as recited in claim 16, wherein said elongated container includes at least one baffle extending in said containing means substantially parallel to the elongated axis of the container to form at least two compartments in said containing means, and wherein the bottom surface of said contain-ing means is inclined in the same direction as the Fresnel-type lenses and the conduit means.

18. The apparatus as recited in claim 17, wherein said elongated container includes a plurality of spaced baffles extending said containing means substantially parallel to the elongated axis of said elongated container dividing said contain-ing means into at least three adjacent compartments which are off-set in height, and which define an upper compartment, an inter-mediate compartment and a lower compartment, said plurality of Fresnel-type lenses being disposed to concentrate solar energy in a first elongated focus located in said intermediate com-partment and in a second elongated focus located in said lower compartment, said elongated container including inlet means for introducing the liquid to be distilled into said upper compart-ment.

19. The apparatus as recited in claim 18, wherein said elongated container includes outlet means for removing liquid to be distilled concentrated with substances to be removed therefrom in said lower compartment.

20. The apparatus as recited in claim 18, and compris-ing a plurality of said apparatus adjacently arranged to form a composite apparatus, adjacent apparatus having common compartments for receiving condensed liquid.

21. The apparatus as recited in claim 20, and compris-ing means for recycling the liquid concentrated with substances in at least one successive apparatus, recycled liquid being in-troduced into said successive apparatus to replace at least in part liquid to be distilled, whereby part of the heat of the recycled liquid is recuperated and the liquid is further con-centrated with substances.

22. The apparatus as recited in claim 17, wherein said conduit means and said Fresnel-type lenses are disposed adjacent each other and are substantially parallel to each other.

23. The apparatus as recited in claim 22, wherein said conduit means and said Fresnel-type lenses are inclined at an angle of from about 5° to about 20° with the horizontal.

24. The apparatus as recited in claim 17, wherein said conduit means and said Fresnel-type lenses are spaced and dis-posed at an acute angle with each other, said conduit means being disposed at an angle of from about 5° to about 20° with the horizontal and said Fresnel-type lenses being disposed at an angle of up to 60° with the horizontal.

25. The apparatus as recited in claim 15 and compris-ing a flexible, dark material which is impermeable to the liquid to be distilled disposed on the bottom of said containing means and which is operative to absorb solar energy to produce heat and transfer such heat to the water to be distilled.

26. The apparatus as recited in claim 25, wherein said material is disposed on suitably worked ground and forms the bottom of said containing means.

27. The apparatus as recited in claim 1, and comprising a heat exchange fluid passed through said conduit means and heat exchanging means for transferring heat from the fluid in said conduit means to the liquid to be distilled.

28. The apparatus as recited in claim 27, wherein said heat exchanging means comprises a heat exchanger comprising a first circuit for the liquid to be distilled including a first inlet for the introduction of the liquid to be distilled into said circuit and a first outlet connected to the interior of said con-taining means; and a second circuit for the heat exchange fluid including a second inlet and a second outlet connected to the interior of said conduit means.

29. The apparatus as recited in claim 1, and compris-ing a solar energy heating means for preheating the liquid to be distilled before the liquid is introduced into said containing means.

30. The apparatus as recited in claim 1 wherein the lens means comprises at least one fluid lens.

31. Apparatus as recited in claim 1 and including a heat exchange fluid passed through said conduit means and means for passing a quantity of fluid through said conduit means which exceeds substantially the quantity of liquid evaporated and con-densed on said conduit means as to enable the fluid in the conduit means to carry the heat of condensation released by the condensing liquid while maintaining the temperature of the fluid lower than the temperature of the liquid vapor.

32. The apparatus as recited in claim 1, wherein said containing means comprises a container including side and end walls and a bottom surface inclined with respect to the horizontal, at least one baffle being disposed in said container to provide at least two compartments in said container for holding liquid to be distilled, inlet means being disposed in an upper of said compartments for introducing liquid to be distilled therein and outlet means being disposed in a lower of said compartments for removing a concentrate of the liquid being distilled whereby liquid to be distilled can be introduced into the upper compart-ment, conducted to the lower compartment and removed from the lower compartment.

33. The apparatus as recited in claim 1 wherein said means for containing the liquid to be distilled includes means for conducting the liquid to be distilled below said lens means.

34. The apparatus as recited in claim 33 wherein said lens means is linear and has a focal length f, said lens means being located a distance less than f from said means for conduct-ing and arranged so as to direct concentrated solar energy on said means for conducting with the focus of said lens means on or below said means for conducting.

35. The apparatus as recited in claim 33 and compris-ing means for collecting the condensed liquid, the liquid con-ducted over said means for conducting and fluid passed through said conduit means.

36. The apparatus as recited in claim 33 and compris-ing an array of photovoltaic cells disposed in said means for conducting at a location of the concentration of the solar energy by said lens means.

37. The apparatus as recited in claim 34 and compris-ing an array of photovoltaic cells disposed in said means for conducting at a location of the concentration of the solar energy by said lens means.

38. The apparatus as recited in claim 35 and compris-ing an array of photovoltaic cells disposed in said means for conducting at a location of the concentration of the solar energy by said lens means.

39. The apparatus as recited in claim 36 and compris-ing means encapsulating said array and means supplying a cooling fluid to said encapsulating means to cool said array.

40. The apparatus as recited in claim 33, wherein said means for conducting comprises an undulated plate system.

41. The apparatus as recited in claim 33 wherein said conduit means comprises a double plate conduit having upper and lower plates.

42. The apparatus as recited in claim 40 wherein said conduit means comprises a double plate conduit having upper and lower plates.

43. The apparatus as recited in claim 41 wherein the longitudinal sides of said plates are fully obstructed by a joint, with only a part of the plates being obstructed along their width leaving a small free outlet space so as to allow a wide spread of fluid along the surface between plates.

44. The apparatus as recited in claim 40 wherein said lens means comprises at least one linear lens aligned so as to direct energy onto said plate system.

45. The apparatus as recited in claim 40 and further including an insulating base plate disposed below said plate system.

46. The apparatus as recited in claim 45 and further including at least one storage means disposed below said insulating plate for storing fluid used in said apparatus.

47. The apparatus as recited in claim 40 wherein said plate system comprises plates having an undulation with a depth on the order of up to 90 mm separated by approximately 120 mm.

48. The apparatus as recited in claim 40 wherein said plate system comprises plates made out of a metal selected from the group consisting of stainless steel, steel and copper.

49. The apparatus as recited in claim 40 wherein said plate system comprises plates covered with a material of an anti-corrosive nature.

50. The apparatus as recited in claim 40 wherein said plate system comprises plates made of a material selected from the group consisting of asbestos fiber, tightened precast concrete, glass and plastic.

51. The apparatus as recited in claim 40 wherein said plate system comprises plates, and including a blackened flexible material disposed over at least part of said plates in a manner such that it is removable to permit removing deposits therefrom.

52. The apparatus as recited in claim 40 and including at least one array of photovoltaic cells installed in one of the valleys of the undulations in alignment with the focal track of said lens means.

53. The apparatus as recited in claim 33 wherein said means for conducting conducts water to be distilled.

54. The apparatus as recited in claim 33 wherein the cooling fluid passed through said conduit means comprises dis-tilled water.

55. The apparatus as recited in claim 53 wherein the cooling fluid passed through said conduit means comprises dis-tilled water.

56. The apparatus as recited in claim 54 wherein said distilled water comprises condensate obtained from said water being distilled.

57. The apparatus as recited in claim 41 and further including a tank filled with the fluid to be passed through said double plate conduit disposed thereabove as to maintain a constant pressure of about 40 cm of water column between said double plates.

58, The apparatus as recited in claim 1 and further including means supporting said lens means to track the location of the sun.

59. The apparatus as recited in claim 33 and further including means supporting said lens means to track the location of the sun.