SOLAR STILLS

The present invention relates to improvements in solar stills for producing fresh water from saline or brackish water.

The capability of providing enough clean fresh water for many purposes including providing drinking water and irrigating crops without the salt build up in land structures commonly associated with use of artesian water, is becoming an increasing problem for the planet. This is particularly the case for relatively dry areas such as Australia, but is also a problem for many other areas of the world, particularly for treating polluted sources of water. Solar stills are known where otherwise unusable water such as artesian water, sea water, or polluted water sources such as water from mines or industry can be heated by exposure to the sun, condensed as clean fresh water and collected for subsequent use. There have been many proposals for solar stills, however, they generally are all characterized by being expensive to produce and use relative to the quantity of fresh clean water produced. Solar stills that are currently in use are used for particular applications where the cost of clean fresh water production is not a major issue, such as for example, survival applications. Examples of some solar still configurations can be seen in US Patent No. 7008515, US Publication No. 2003/0033805, WO 91/14487, UK 2345002, DE 19704046 and DE 10044344. For reasonably larger scale production of clean fresh water, solar stills despite using a relatively free source of energy, have remained a quite expensive option.

US Patent No. 4966655 discloses a solar still configuration having a base container with an open top adapted to receive and contain a pool of liquid to be treated. Above the open top an open rigid mesh support frame is positioned defining an inclined plane covered by a flexible thin film solar energy transmissive sheet disposed generally above the pool of liquid to be treated, the lower edge or edges of the solar energy transmissive sheet is configured to extend inwardly and subsequently upwardly to define a collection trough on one or both sides of the base container, the collection trough or troughs being intended to collect condensate that forms on the inside surface of the solar energy transmissive sheet above the pool of liquid to be treated and which runs down the inside surface into the side located collection trough or troughs.

US patent no. 5628879 also discloses a solar still configuration having a base container having base, side and end walls constructed from insulated panel material, the container having a generally open top that in use is covered by a transparent flexible plastic material film stretched across the open top. In one disclosed embodiment the base wall of the base container is tilted or inclined to the horizontal and a wicking mat of potentially a variety of materials is positioned over the base wall. Liquid to be treated is discharged into the base container onto an upper end region of the wicking mat and it is allowed to flow down the wicking mat while being at least partially evaporated by solar energy passing through the transparent flexible plastic film stretched across the top of the base container. Condensate is collected in a trough structure secured to an inside surface of the transparent plastic film at a lower end and is removed via a discharge tube and waste liquid being treated is also removed via a discharge tube positioned at a lower end of the base wall of the base container. International patent specification no. WO 02/24576 discloses a solar still configuration comprising an insulated housing in a tilted or inclined configuration with a transparent top or front cover sheet allowing solar energy to pass into the housing interior. The interior of the housing is divided by an evaporation panel that allows vapour flows to circulate through an upper evaporation chamber between the evaporation panel and the transparent top cover sheet, around a top edge of the evaporation panel into a lower condensation chamber between a lower face of the evaporation panel and a base wall of the housing. One or more condenser panels are positioned at an upper end of the lower condensation chamber and an internal trough receiving liquid to be treated is positioned at a lower end of the condensation chamber. Liquid to be treated is pumped from the internal trough through the condenser or condensers while it remains relatively cool and from there to the top end of the evaporation panel from where it flows down the top surface of the evaporation panel while being subjected to solar energy. Any such liquid not evaporated falls from a lower end of the evaporation panel back into the lower internal trough. Condensate formed in the condenser or condensers drops into the lower internal surface of the housing and flows downwardly to be collected and discharged from a lower end region of this

surface. The arrangement requires the use of at least one condenser panel and pumping means to pass liquid to be treated therethrough.

International patent application no. PCT/AU2004/001841 discloses in one embodiment a solar still configuration comprised of a space frame wrapped with clear or translucent film of black or darkly opaque film in certain zones that is believed to provide a much cheaper construction cost for a solar still. While such a construction will lessen the cost of solar stills, there still remains a need to improve the efficiency of condensate production for such stills to become cost effective for operations where cost of water production remains an important factor.

Accordingly the objective of the present invention is to provide an arrangement for use in a solar still and a solar still incorporating such an arrangement that will improve the efficiency of condensate production and collection in solar stills, preferably without increasing the capital cost of the stills construction or increasing operating costs to a stage where the solar still becomes uneconomical to produce or run.

In accordance with a first aspect of this invention there is provided, a solar still module having a treatment chamber and a water treatment panel member positioned below an upper extremity of said treatment chamber, said water treatment member defining an upwardly facing surface treatment zone, water supply means arranged to supply water to be treated to be spread over said treatment surface zone in a thin gravitational surface flow, said treatment chamber having at least an upper solar energy transmission wall positioned above said upper extremity of the treatment chamber enabling solar energy to be applied to the upwardly facing surface treatment zone of said water treatment member, water vapour evaporated from said water treatment member being at least partially condensed on an inner surface of said upper solar energy transmission wall above the water treatment member and collected therefrom at a lower location or locations in condensate collection means. Conveniently said water treatment panel member is formed as a panel including an internal frame structure about which a flexible plastic film web or webs has been wound. The internal frame structure might be a simple perimeter frame, a frame structure with internal diagonal or crossed frame members, an internal mesh formation, a semi-

rigid sheet member such as corrugated sheet metal, or corrugated plastics sheet material. Any combination of the aforesaid could also be used.

In one preferred option the panel of the water treatment member is formed with a black or darkly opaque said treatment surface zone. The panel of the water treatment member may have a substantially flat upwardly facing treatment surface zone. Alternatively the upwardly facing treatment surface zone may have a curved ripple or wave surface forming said treatment surface zone, preferably configured so as to be transversely disposed relative to the direction of water flow over the panel of the water treatment member. In yet another possible arrangement, the panel of the water treatment member may have an upwardly facing concertina surface formed by alternating ridges and valleys forming the treatment surface. Again preferably the ridges and valleys are disposed transverse to the direction of water flow over the panel member.

In a particularly preferred embodiment the surface treatment zone has a lower water impervious surface and an overlying layer of web material, fabric material, or netting material adapted to allow water to flow to said water impervious surface to flow there over in said thin gravitational surface flow, said overlying upper layer also allowing water vapour to pass upwardly therethrough. In a possible alternative, the treatment surface zone of said water treatment member may have an upwardly facing surface effect to promote water flow evenly across the treatment surface zone.

Conveniently, the solar still module may include a space frame with an outer flexible skin formed by at least one plastic material film web wound thereon, said outer flexible skin being at least partly transparent or translucent to form said upper solar energy transmission wall to allow passage of solar energy to said water treatment member. Preferably, the outer flexible skin is highly transparent / translucent to maximize the transmission of solar energy therethrough. The outer flexible skin may completely enclose the space frame. Preferably the condenser means is formed by a defined inner surface region or regions of the outer flexible skin, said defined inner surface region of the outer flexible skin being formed by at least an innermost said plastic material film web wound onto said space frame with applied or retained tension. The inner surface of the upper solar energy transmission wall on which the water vapour is condensed may be formed by a

continuous plastic material web absent of any intermediary joins or discontinuities. Preferably the aforesaid inner surface is inclined, in use, at an angle whereby condensate formed on the surface will gravitationally flow to a lower collection point from where it may be drained to a desired locality. The plastic material film web used in the construction of the outer skin of the module or in the construction of the water treatment member may include self adherence and/or self sealing characteristics. The plastic film web or webs may have been pre-stretched to beyond its yield point to increase its length and decrease its thickness, while retaining an ability to constrict onto the space frame. Alternatively or in addition the plastic film may be capable of being heat shrunk onto the space frame. As a result of this, substantially flat surfaces are created for water flow, either as condensate or as water to be treated, to promote performance of the solar still module.

In one preferred embodiment, the condensation collection means may be formed as a channel or duct means at a lower extremity of said defined inner surface region or regions of the outer flexible skin, said channel or duct means being configured to collect condensate flowing downwardly thereon. In another preferred arrangement the condensation collection means may simply be a lower zone within the outer flexible skin from which zone a suitable condensate collection drain is provided.

In a further preferred embodiment, the space frame of the solar still module may include a first pair of elongate frame members crossing one another in an X configuration, outer ends of the first pair of frame members being located at the corners of a polygonal shape. Conveniently the polygonal shape is a square or rectangular. The outer ends of the first pair of elongate frame members may have corner arms extending generally perpendicularly to said first pair of elongate frame members, a second pair of elongate frame members joining said corner arms on opposed sides of the space frame. In a preferred configuration, the first pair of frame members are tubular in form and the corner arms are at least partially formed by bending the outer end regions of the frame members. Preferably the second pair of elongate frame members is also made from tubular material with the ends also bent in a right angle configuration and sized to telescopically engage with the bent ends of the first pair of elongate frame

members. In this manner minimal, if any fixing of the frame members to each other is required. Conveniently at least one peripheral web of plastic material film may be wound about the corner arms, the outer flexible skin being formed by plastic material film web or webs wound about said space frame including said peripheral web or webs of plastic material film. The aforesaid structure for the solar still module provide an effective, simple and inexpensive construction arrangement.

The space frame of the solar still module may define a substantially uniform cross-section along a longitudinal length dimension defining said treatment chamber, an upper or front face of said outer flexible skin forming said upper solar energy transmission wall and said outer flexible skin further defining a rear face, two opposed side faces, and two opposed end faces. Conveniently the aforesaid uniform cross-section is substantially rectangular. In use the solar still module would be positioned with said upper or front face of the outer flexible skin generally inclined to the horizontal and facing in a direction to maximize exposure to solar energy. Conveniently a said panel of the water treatment member will be located in the treatment chamber, water from said water supply means flowing onto an upper end of said panel and downwardly over the surface treatment zone formed on said panel, said surface treatment zone having a lower water impervious surface and an overlying upper layer of web material, fabric material, or netting material adapted to allow water to flow to said water impervious surface to flow there over in said thin gravitational surface flow, said overlying upper layer also allowing water vapour to pass upwardly therethrough. Preferably the panel may be supported in the treatment chamber a short distance below the front or upper face of the outer flexible skin. The panel may be supported on its own in the treatment chamber or it may be positioned within a liquid impervious tray member that is open in an upward direction facing towards the upper or front face of the outer flexible skin. The tray member may be a moulded plastics material tray or it may be a tray manufactured from a space frame wrapped with plastic material film web with an upper face of the film web removed to form the required tray construction. Conveniently the upper or front face forms an acute angle with a first said end face of the space frame, said first end face forming a lower end of the solar still module in use whereby the space frame in use extends upwardly at

an inclined angle from said first end face. Conveniently, the first end face includes or comprises the condensate collection means to collect condensate formed on and flowing downwardly on an internal surface of at least the upper or front face of the outer flexible skin. In a particularly preferred embodiment fan means may be provided within the treatment chamber to move gas and/or water vapour over the panel in the treatment chamber. Preferably the gas flow, with or without water vapour, may circulate about said panel within the treatment chamber. Conveniently the fan means may be provided to direct a flow of gas downwardly along an inner surface of the upper or front face of the outer flexible skin to promote condensate flow downwardly along the inner surface. It is believed that this functionality both enhances the rate of condensate collection while improving solar energy transmission to the panel of the treatment member as a result of slow moving condensate droplets not obstructing the solar energy transmission. The fan means may also be operated at conditions where a vibration is imposed on the flexible outer skin to further enhance condensate flow. The fan means may also be arranged to oscillate gas flow across the inner surface of the upper or front face of the outer flexible skin.

In a further preferred embodiment, the water supply means for the water to be treated may include at least one hose or pipe with outlet means disposed along its length to release water therefrom to the surface treatment zone of the panel of the water treatment member. The outlet means may be one or more sections of porosity along the hose or pipe. Conveniently the hose or pipe will be located at an upper end of the panel so that when the panel is inclined, water released from the hose or pipe will gravitationally flow towards a lower end of the panel. In an alternative, the water to be treated might be sprayed via one or more spray nozzles onto an upper region of the panel. It is preferred that a collection gutter is provided to collect and drain any treatment water reaching the lower end of the panel, from the treatment chamber. Conveniently this drainage collection gutter may be formed by plastic film web secured to the panel at its lower end providing a collection zone between the gutter web and a lower front face of the treatment panel.

According to one preferred aspect, a solar still module may be provided having heating means positioned within the treatment chamber associated with the panel of the water treatment member. When the panel is formed by an internal frame structure about which a flexible plastic film web or webs is wound, the heating means may be positioned within the flexible plastic film web or webs wound on the internal frame structure, the heating means being activated or deactivated to externally heat water to be treated flowing on said panel in response to variations in solar energy supplied to said solar still module. The heating means may be operated by electrically supplied energy. The heating means may alternatively be heated by a heated fluid. Preferably the heated fluid may be heated by any suitable means, but most preferably by waste energy from an external source.

In another preferred arrangement a heat exchanger arrangement may be provided beneath the treatment panel within the treatment chamber. The heat exchanger arrangement may receive heated water from an external industrial user of same that is required to be cooled, and cold or cool water to be treated in the solar still with the heated water giving up heat to the treatment water in the heat exchanger. The heated treatment water may then be directed to the upper surface of the panel to be treated as previously described. If desired insulation may be provided between the heat exchanger arrangement and the treatment panel. If desired, the heat exchanger arrangement might be arranged externally of the solar still.

According to a still further preferred aspect, a solar still arrangement is provided including a plurality of solar still modules as described above where the modules are arranged in a series flow relationship such that water to be treated progressively flows from one said module to a next adjacent said module in said series. Conveniently at least two groups of said modules are provided arranged in a series flow arrangement, each said group of said modules being arranged in a parallel flow relationship with other said groups of said modules. Preferably a final one or ones of said modules in a said series flow arrangement deliver salt concentrated water to be further evaporated in a treatment zone to produce salt.

In a second aspect of this invention a panel member is provided for use in a solar still module in a position adapted to receive solar energy, said panel

member having an upwardly facing surface zone with a surface effect to slow water flow and to promote even water flow there across, and water delivery means being provided to deliver, in use, water to be treated to said panel member whereby said water flows substantially evenly across said surface zone. In this aspect, the panel member may be formed by providing a frame and positioning a layer of a plastic material film web or laminated plastic material film web layers over said frame. Conveniently the plastic material film web or said laminated plastic material film web layers are positioned on said frame with applied or retained tension. The laminated plastic material film web layers may be formed by winding at least one plastic material film web about said frame. The plastic material film web or webs may have been pre-stretched to beyond its yield point to increase its length and decrease its thickness, while retaining an ability to constrict onto said frame. Alternatively the plastic film might be heat shrunk onto the frame. Conveniently the at least one said plastic material film web is black or darkly opaque, and preferably water or liquid impervious. In a particularly preferred embodiment the laminated plastic material film web layer or layers provide a lower water impervious surface treatment zone, the panel member having an overlying upper layer adapted to allow water to pass downwardly to said water impervious surface treatment zone to flow along same in a thin gravitational surface flow, said upper layer permitting water vapour to pass upwardly therethrough. Conveniently the upper layer may also be black or darkly opaque in colour. In preferred arrangements, the upwardly facing surface zone may be either substantially flat or comprise a concertina surface formed by alternating V-shaped ridges and V-shaped valleys. The V-shaped ridges and V- shaped valleys are desirably transverse to the intended water flow direction on the upwardly facing surface zone. Alternatively, U-shaped ridges and U-shaped valleys may be formed transverse to the intended water flow direction.

In a third aspect of this invention there is provided a water treatment panel having a treatment surface formed by laminating plastics material film web or webs with differing tension levels, at least partially relieving the tension level in the laminated plastics material film web or webs to form a series of ridges and valleys in said treatment surface. Conveniently the plastics material film web or webs is carried by a frame structure. The upwardly facing zone may be formed

by laminating plasties material film web or webs with differing tension levels, at least partially relieving the tension level in the laminated plastics material film web or webs to form a series of ridges and valleys in said treatment surface.

The arrangements as described above are believed to significantly increase the efficiency of solar stills or solar still assemblies in producing greater quantities of clean fresh condensate from solar energy applied to any given land area. Moreover, if the stills are produced using primarily plastics material film, then the capital costs of the stills and still arrangements can also be substantially reduced. The use of stretched plastics material film webs, Ie those film webs stretched beyond their yield point but retaining some memory or internal tension recovery characteristics are particularly useful as they are inexpensive but also tend to constrict on the frame structure to provide taut surfaces on which water can condense and flow to a collection point. Stretched linear low density polyethylene may be used in many applications. Other polyolefin film webs might also be used. Heat shrunk plastic material film webs can also be used.

Several preferred embodiments are described in the following with reference to the accompanying drawings, in which:

Fig 1 is a perspective view of a space frame used as a first stage in the construction of a solar still module in accordance with a preferred embodiment of the present invention;

Fig 1a is a detailed view of a corner zone (marked X) of the space frame shown in Fig 1 ;

Fig 2 is a perspective view of a second stage in the manufacture of a solar still module utilizing the space frame shown in Fig 1 ; Fig 3 is a perspective view of a third stage in the manufacture of a solar still module utilizing the space frame of Fig 1 ;

Fig 4 is a perspective view of a fourth stage in the manufacture of a solar still module utilizing the space frame of Fig 1 ;

Fig 5 is a schematic cross-sectional view taken along line B-B of Fig 4; Fig 6 is a schematic sectional view taken along line A-A of Fig 4 disposed at right angles to section line B-B;

Fig 7 is a detailed view of the area marked X in Fig 6;

Fig 8 is a schematic block diagram of a solar still arrangement utilizing a plurality of solar still modules capable of producing both clean fresh water and salt from saline water input;

Fig 9 is a schematic longitudinal section view through a further preferred embodiment of a solar still module according to the present invention;

Fig 10 is a view showing the angles required to gain a continuous thin gravitational water flow on the water treatment member shown in Fig 9;

Figs 11 and 12 are cross-sectional views of structures usable for creating the formed treatment surfaces shown schematically in Fig 9; Fig 13 is a partial schematic longitudinal section view similar to Fig 9 showing the upper regions of a still further preferred embodiment of this invention;

Fig 14 is a schematic flow diagram view illustrating how the solar still modules disclosed herein might utilize waste heat to improve performance characteristics; Fig 15 is a partial perspective view of a further preferred embodiment of a solar still module according to the present invention; and

Fig 16 is a partial schematic section view along line C-C of Fig 15.

Referring now to Figs 1 to 4 of the annexed drawings, there are shown progressive stages in the production of a first preferred form of solar still module 10. Fig 1 shows a first stage comprised of a space frame 12 constructed of a first pair of elongate frame members 13, 14 crossed at an intermediate point 15 with their outer ends 16, 17, 18 and 19 located at the corners of a square or rectangle when viewed in plan view. The frame members 13, 14 might be made from tubular self supporting material including substantially rigid plastics material and metals and might, in a preferred construction be secured one to the other at the cross over point 15. The two frame members 13, 14 provide an X configuration when viewed in plan view. As is shown in Fig 1 , the outer ends of the members 13, 14 are conveniently bent in the same direction to be substantially 90° to the main lengths of the frame members 13, 14. The space frame 12 further includes a second pair of elongate frame members 20, 21 that are parallel to one another and spaced apart by the distance between the outer ends 16, 17 and 18, 19 of the first pair of members 13, 14. The outer ends of the second pair of elongate frame members 20, 21 also include parts 22, 23, 24 and 25 disposed at 90° to the

remainder of the members 20, 21 and are also tubular such that they telescopically engage with one of the outer ends 16 to 19 of the frame members 13, 14. The end zones 16/22, 17/23, 18/24 and 19/25 together form corner arms 26, 27, 28 and 29 of the space frame 12. Fig 2 of the drawings illustrates the next or second stage of manufacturing a solar still module according to this preferred embodiment. In this stage a perimeter web of plastics material film material 30 is dispensed from a roll 31 and wrapped about the space frame corner arms 26 to 29. Several web thicknesses of the film might be wound depending on performance characteristics required. The plastics film web material may be as described elsewhere in this specification having self adhering or self sealing characteristics and preferably be of the type, once applied that will constrict between the corners 26 to 29 to provide a firm perimeter band 32.

Fig 3 illustrates the next stage where a water treatment member 33 formed as a panel is introduced into the zone 34 within the perimeter band 32 applied around the corners 26 to 29 of the space frame 12. One preferred structure of the panel of the water treatment member 33 is described in greater detail hereafter with reference to Figs 5, 6 and 7, however, in this embodiment the panel of the water treatment member 33 is substantially flat having a generally rectangular perimeter 35 just smaller than the zone 34 whereby its perimeter 35 is spaced inwardly from the perimeter band 32. The panel 33 rests on the cross structure formed by the frame members 13, 14 and may be secured thereto to prevent the panel 33 moving within the zone 34. The panel 33 has at least one upwardly facing water impervious surface 36 whereby water to be treated delivered at one end 37 will flow in a thin gravitational flow to the other opposed end 38 when the solar still module is used with the one end 37 disposed above the opposed end 38. Fig 3 shows a hose 39 for delivering water to be treated to the one end 37 with a plurality of spaced outlet openings 40 provided to allow the water to reasonably evenly flow from the hose 39 onto the surface 36. In a possible alternative, the outlet openings 40 may be replaced by one or more sections of porous walled hose. In yet another possible alternative, the hose 39 might lead to one or more spray nozzles to direct a water spray onto the surface 36. At the opposed end 38 (lower in use), a collection gutter 41 is provided to

collect any treatment water reaching the end 38 and remove same from the solar still module via a suitable drain line 42. Each of the hoses or lines 39, 42 passes through the perimeter band 32 of plastics material film web.

The solar still module 10 is largely completed by taking the structure shown in Fig 3 and forming an outer flexible skin 43 about the space frame 12 and the perimeter band 32. The outer flexible skin 43 might be formed by winding at least one plastic material film web 44 as described elsewhere in this specification from at least one roll 45 of such film about the space frame 12 and the perimeter band 32. Multiple layers of such film may be built up by winding the film web multiple times. The film web 44 might be wound longitudinally as represented in Fig 4, at 90° to this direction, or both these directions such that the film webs 44 may cross one another. It is, however, desirable that the first or inner layer of film web forming particularly the upper or front surface 46 of the solar still module 10 and the rear or lower surface 47 of the solar still module 10 be substantially continuous without film web joins formed by overlapping edges or other such discontinuities. This assists with the flow of condensate along these surfaces when the solar still module 10 is in use. The outer flexible skin 43 may be formed solely by the film web 44 or by this film web and the peripheral band 43. Any overlapping regions of the film web, ie the edge zones will be folded down against an underlying layer and adhered or sealed to same. By this construction an internal treatment chamber 34 is formed that is substantially uniform in cross-section along its length.

The construction of the water treatment member 33 is preferably as set out in the following. The member 33 has an internal frame structure 48 which may be a perimeter frame as shown or it may be an X frame with diagonal frame members. A first or base covering is formed by wrapping the frame 48 with an outer skin 49 of plastics material film web to provide a water or liquid impervious surface. The plastics material film web or webs may be as described elsewhere in this specification and preferably has a black or darkly opaque colour. In this manner, a substantially flat panel is formed that may be supported on and secured to the frame members 13, 14 of the space frame 12. Above the skin 79 a further layer 50 is provided loosely resting on the water impervious skin 49, the layer 50 being a fabric or mesh / net material having sufficient porosity to allow

water to be treated to pass to the space between the layer 50 and the skin 49 and to flow downwardly there along in a thin surface gravitational flow. The porosity of the layer 50 also permits water vapour to pass upwardly, in use, to impinge on and condense into water droplets (condensate) on the inside surface of the upper or front wall 46 of the module 10. This condensate may then flow under gravitational forces or assisted by a fan 51 to be collected in a pool 52 in a lower region of the module 10 and be removed therefrom by a clean condensate outlet line 53. Conveniently the layer 50 is also coloured black or darkly opaque. In use, the module 10 is positioned to direct the front or upper face 46 towards a source of solar energy so that solar energy enters the treatment chamber 34 impinging on the treatment panel 33 and the saline or similar water for treatment flowing downwardly thereon in a thin relatively slow gravitational flow. The water progressively evaporates and the water vapour is condensed as described above. Any treatment water reaching the lower end 38 of the panel 33 is collected in the collection channel 41 to be removed via the drain line 42. The collection channel 41 is conveniently a U-shaped plastic film arrangement sealed to the rear face 53 of the panel 33 and sealed at its lateral ends to provide the collection space 54 for any water reaching the lower end.

Fig 8 illustrates schematically in block diagram form, a possible solar still arrangement 60 for producing clean fresh water condensate from a source of contaminated or saline water 61. This water to be treated is fed into parallel lines of solar still modules 10 arranged in groups. There may be two, three or more groups 62, 63, 64 of such solar still modules 10. Suitable valves 65 are provided to control the flow of the water to be treated as desired. The groups 62 to 64, of solar still modules 10 might feed treatment water therefrom where the salt has been further concentrated, into a further group of solar stills 66 with the treatment water being discharged therefrom selectably (via a two way valve 67) into evaporation tanks 68, 69 to evaporate the remainder of the water to produce salt that might then be recovered for sale. Fresh clean water condensate collected from each of the solar still groups 62, 63, 64 and/or 66 may be directed into a storage zone 70 from which it can be discharged via line 71 and valve 72 as desired. It is desired, as far as is possible to have water flows occur by gravity,

however, some pumping may be needed and if so it would be desirable to utilize solar powered pumps.

Referring now to Fig 9, another embodiment is illustrated schematically in longitudinal cross-section. The solar still module 10 shown in Fig 9 includes a space frame 12 with four longitudinally extending frame members 71 joined by end corner members 72 positioned to define a rectangular cross-sectional space 73 therewithin that is relatively uniform along its length. The space frame 12 includes an outer skin 74 of clear or highly translucent plastics material film web. A preferred method of forming the outer skin 74 is to use the arrangements disclosed in International Patent Application No. PCT/AU2004/001841 , ie by winding plastics material film web about the space frame 12. It is preferred, however that the inner most layer of plastics film web on both the front face 75 and rear face 76 of the still 10 extend longitudinally of the still module, and further wherever possible, that this inner most layer is formed by a single web of sufficient width to cover the whole front and rear face of the still module 10. As illustrated, the front face 75 might be substantially flat to define a rectangular uniform cross-section within the space frame 12. The still module 10 further includes a support or brace 77 to maintain the still in an inclined position generally as shown in Fig 9 although other support arrangements could also be used.

The base region 78 of the still module 10 is formed by one end of the space frame 12 and may include a hollow channel structure 79 that clips onto the end frame members 80 as illustrated. The upper regions of the hollow channel structure 79 has divergent flange members 81 that press against the internal surface of the outer skin 74 to strip condensate therefrom as it flows downwardly along this inner surface. The condensate may then pass through or past the end frame members 80 to the hollow section 82 and from there to a clean / fresh water outlet 83 to be collected or used as desired.

The base region 78 may be closed by a portion of the outer skin 74 covering the channel structure 79 whereby water to be treated might be allowed to pass to and be retained in this space as with the previous embodiments. If this is the case, inlets and outlets for such water might be provided leading to this space, however, as will be apparent from the following, this is not essential.

Within the space 73, a tray like structure 84 is provided supported on cross supports 85 positioned along the longitudinal length of the still module such that it is maintained separate from the rear face 76 of the outer skin 74. The tray like structure 84 has an internal shape defining space frame that is completely wrapped in, preferably black or darkly opaque plastics material film web (as disclosed in PCT/AU2004/001841) with the top face being substantially cut off and remaining parts thereof being folded down and adhered to the upstanding side and end walls of the tray like structure 84. As a result this tray like structure is provided with an open top face 94 adjacent the top or front face 75 of the still module 10 and a liquid impervious base layer 95. Within the tray like structure 84, a former member 86 is provided capable of being formed into a desired shape and retaining such shape in use. In Fig 9, the former structure 86 defines a series of V-shaped ridges / valleys extending substantially transversely across the base 67 of the tray like structure 84. As best shown in Fig 10, it is desirable that all surfaces of the former member 86 allow for liquid flow across the surface, rather than falling from, for example a ridge to the next surface. As shown in Figure 10 it is desirable that the angles α and X remain positive. The following table shows possible (but not exclusive) figures for these angles for differing angles of inclination α of the still module as a whole:

Water to be treated is supplied via a hose 88 with a plurality of outlets 89 extending across an upper end of the tray like structure 84. The delivery pipe or

hose 88 may include a serpentine like path through the solar energy collection zones 73 of the still module 10 to preheat the water before it is discharged onto the evaporation surface. The delivery pipe might be coloured black or darkly opaque to increase the heat transference. This water is allowed to flow on to a woven web or fabric material sheet 90 to promote an even thin flow across same. The woven web or fabric sheet 90 is preferably black or darkly opaque and is positioned to receive solar energy through the front face 75. In a possible alternative sheet 90 might be made from a net or mesh material. The sheet 90 is porous to allow water to flow between the sheet and the underlying water impervious sheet with water vapour passing upwardly through the sheet 90. Edges 91 of the former member 86 are preferably relatively flexible and can be folded up against the side walls of the tray like structure 84 to retain the water being treated on the sheet 90 as it flows downwardly. Provision is made at the lower end at 42, 92 to remove any excess such water that reaches the lower end. In the alternative, where a pool of such water is also maintained in the base zone 93, this excess water might be allowed to flow out of the tray and into the zone 93.

The former structure 86 may be secured to the base wall of the tray structure to maintain its shape and configuration if desired. The former structure 86 may comprise an internal frame formed by, for example, a wire mesh material, that is wrapped with a black or darkly opaque plastics material web (as per International Patent Application No. PCT/AU2004/001841 ) to form an outer water impervious skin 95. Conveniently at least the longitudinal edges of the wrapped plastics material film extend beyond the mesh material edge to provide flexible edge zones 91.

Figs 11 and 12 illustrate one convenient method of making a panel construction generally equivalent to the tray 84 and former structure 86 of Fig 9. In this further preferred arrangement, the panel construction 100 includes a rectangular frame 101 with end members 102 and 103 and two side bar members 104, 105. In the illustrated embodiment each of the end members 102, 103 have short hollow side arms 106 telescopically receiving end regions of the side bar members 104, 105 therein. The arrangement allows the end members 102, 103 to move towards one another (Ze to shorten the frame 101 ) or move away from

one another (Ze to lengthen the frame 101) within defined limits. Any other construction arrangement could of course also be used so long as the same degree of relative movement is achieved. For example, instead of two end members 102, 103, a single moveable end member might be used with a greater length of movement. An internal temporary brace member 107 maintains the end members 102, 103 initially at their longer position (as illustrated), and in this position, a first roll of film 108 having a width dimension wider than the frame 101 dispenses the plastics material web 109 longitudinally onto the frame passing around the end members 102, 103 forming a single continuous web or a plurality of such webs overlaid on one another. The width of the film webs is such to be sure that the edge regions along both sides of the frame 101 can be folded and sealed to one another. The colour of this film web is preferably black or darkly opaque except when a highly transparent or translucent panel construction might be desired to allow solar energy to partly transmit therethrough. This film web is also wound onto the frame 101 with no or minimal applied or internally retained tension. Thereafter a second plastic film web 110 is dispensed from a roll 111 over the first web 109. The film web 110 is applied with relatively high applied or retained tension. While the drawing illustrates one such web 110, it will be appreciated that two or more webs with longitudinally overlapping edges could also be used. The colour of the film web or webs 110 might be black or darkly opaque or substantially clear or translucent regardless of the colour adapted for the film web 109. On the other hand, if the panel construction is to be transparent or highly translucent, then the second film web 110 would have to have these characteristics. Once the film webs 109, 110 have been wound onto the frame 101 , the laminated film webs on one side face of the panel construction is cut from that side face leaving an edge zone that may eventually be folded down and secured to the inside of the frame 101. Once this has occurred the temporary brace member 107 (or any equivalent restraining member) is removed and the two end members 102, 103 move towards one another to their shorter position under action of forces applied by the tension in the film web 110. As a result the laminated film webs 109, 110 spanning the internal space within the frame member 101 scrunch together to form concertina or wave shapes 113 illustrated

schematically in Fig 12. If a more formal shape is required individual rigid or semi-rigid former members might be laid across the film 89 on the outer side of same prior to application of the outer film web 110. The former member might be cardboard sheets, plastic semi-rigid sheets, semi-rigid mesh sheets or the like. It will also be appreciated that while the temporary bracing member 107 has been disclosed, other means of achieving a similar result might also be used.

Fig 13 shows yet another preferred embodiment of the present invention similar to that illustrated in Fig 9. In this further embodiment, the solar still module 10 includes a space frame 12 including frame members 71 , 72 defining a generally rectangular cross-sectional space 13 therewithin that is relatively uniform along the length of the space frame. The space frame 12 includes an outer skin 74 produced as described above in relation to Fig 9 as also are those portions of the still not illustrated in Fig 13. Within the space 73 a substantially flat panel 33 is positioned, constructed as described with reference to preceding embodiments, extending substantially across the space 73 and along its length. Saline water (or other water to be treated) is supplied to the upper surface 120 of the panel 33 via one or more spray nozzles 121 directing the water to be deposited on the surface 120 in a thin coating to gravitationally flow down the panel 34 towards its lower end. As with other embodiments the water is evaporated from the panel surface 120 and condenses on the inner surfaces of the outer skin 74, particularly, the upper downwardly facing inner surface 121. Once condensed the condensate flows downwardly to a lower region of the still 10 to be collected by a suitable means and discharged therefrom via a discharge line. At least one fan 122 is provided within the space 73 to circulate air / vapour flows downwardly across the top of the panel 34 and upwardly along the lower surface of the panel 33 as represented by arrows 123, 124. The fan may be operated by any suitable means including a solar generated power system. The air / vapour circulation together with spray delivery of the water to be treated has substantially improved efficiencies of condensate production. While the fan 122 is shown at the upper end of the space 51 , however, it could be located in other positions to create the flow represented by arrows 123, 124. Positioned as illustrated allows the fan created air stream to also assist with moving condensate on the surface 121 downwardly to the collection zone.

Fig 14 shows schematically a possible use of the still module 10 shown in Fig 13 or in fact other described and illustrated solar still modules as referred to in this specification. It has been found that condensate production can further be enhanced by increasing the temperature of the water to be treated on the upper surface 120. This may, in one preferred arrangement be achieved by passing the water to be treated in heat exchange relation with a source of heat 131 via a heat exchanger 130. This may be via any commercial or engineering activity including power generating facilities or engineering facilities represented schematically at 127. The water to be treated might, in some applications be heated "cooling water" utilized in power generating or engineering or commercial facilities. In Fig 14, water to be treated originates from a source 140, passed via line 132 in heat exchange relationship at 130 with the heat source 131 and is delivered via spray nozzles 121 or other delivery means to the upper surface 120 of the panel 33. Condensate is collected via line 128 and delivered to a collection tank or similar 129. Water to be treated that is not evaporated and condensed is collected via line 134 and removed to the source 140 or provides the feed for treatment in a second or further still module 10 in a cascade arrangement as previously described. If a waste source of heat is not available, then the feed water to be treated may have its temperature artificially increased but such arrangements increase power or energy consumption and therefore increase the cost of condensate production.

Fig 14 illustrates a further possible arrangement where heating means 125 is provided associated with the treatment panel 33, the heating means being arranged to circulate a heated fluid therethrough. The heated fluid may be sourced at 133, pumped via pump means 135 and valve 142 through a heat exchanger 128 and via line 129 to the panel 34. It would be preferred to utilize such heating means only when solar energy is insufficient to provide sufficient performance of the solar still. In this regard a temperature sensing means 138 might be provided within the treatment chamber 73 to sense when additional heat may be needed to then activate or deactivate the pump means 135 and valve 142.

Referring now to Figs 15 and 16, a possible further preferred embodiment is illustrated. In this case, the space frame 12 for the solar still module 10 of this

embodiment is made of aluminium (or similar) extrusion in the form of a channel section having two spaced opposed side channel members 130 as illustrated with an outwardly facing base web 131 , upper and lower inwardly directed arms 132, 133 and a pair of spaced internal arms 134, 135 partway along the base web 131 and also facing inwardly. The space frame 12 also includes a pair of channel members (not shown) connecting the two side channel members 130 to form a square or rectangular perimeter space frame 12. Any suitable means are provided to connect the channel members together at the corners of the space frame 12. The internal spaced arms 134, 135 support a treatment panel assembly 136 spanning the treatment chamber 73 within an outer skin 74 of plastic film web wrapped about the space frame 12 as described with other embodiments. The treatment panel assembly 136 is described in greater detail hereafter with reference to Fig 16. The treatment panel assembly 136 has, in a basic form a support frame member 137 formed of semi-rigid corrugated sheet such as corrugated metal (iron) or corrugated plastic material used commonly as a roofing material but capable of many other applications. The corrugations of this sheeting are transversely disposed to the intended water flow thereon. The corrugated frame member 137 may be wrapped in a plastic film web 138 and if desired, the top face of this film web might be removed. The film web 138 preferably extends beyond the lateral edges of the frame member 137 to provide an edge region that can be folded upwardly so as to ensure treatment water flowing over the treatment panel assembly 136 is retained thereon with any excess such water being collected in a collection channel at a lower end and drained from the module 10 as with other embodiments. A layer of porous web material 139 overlays the upper surface of the treatment panel assembly 136 following the contours of the corrugations. This layer is the same as described previously for other embodiments. At the upper end, in use, of the treatment panel assembly 136 is a treatment water supply means, again similar to previously described embodiments and may comprise one or more spray nozzles, or a delivery tube including a porous tube or a tube with spaced water outlets permitting a trickle flow down the assembly 136. These items have not been illustrated as they may be the same as with other embodiments.

In some situations where there is an ability to do so, the treatment panel assembly 136 may include a heat exchanger 140 comprising a cool or cold water section 141 acting as a feeder supply for the treatment water flowing to the panel assembly 136, and a hot water section 142 receiving hot water from an industrial or other similar source. Heat insulation 143 isolates the panel assembly 136 from the heat exchanger 140 but the heat exchanger 140 and the treatment panel assembly 136 may be supported by the arms 134, 135. The hot water delivered to the hot water section may come from heated water in a power generation plant that otherwise needs to be cooled before reuse in the power generation plant. The heat exchanger 140 uses this waste heat to heat the feed treatment water to augment solar energy when desirable to do so. Using hot water in this manner, it has been found, using a 1 metre by 2 metre treatment panel, 50 litres of water at 50 - 55 ⁰ C produced 1 litre of distilled water. The treatment water should go to at least a second set of distillation modules as the water remains hot, of the order of 30°C to 60 ⁰ C depending on solar energy conditions.

It will be recognized by those skilled in this art that many variations can be made to the solar still arrangements and methods of making same disclosed herein within the scope of the annexed claims. For example, it would be useful to provide rainwater collection gutters to collect rainwater that may fall onto the solar still modules outer upwardly facing surfaces and deliver same to the solar still condensate collection system.