GB2345002A

GB2345002A - Collapsible solar still.

Info

Publication number: GB2345002A
Application number: GB9828123A
Authority: GB
Inventors: John Dominic Michaelis
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-12-21
Filing date: 1998-12-21
Publication date: 2000-06-28
Anticipated expiration: 2018-12-21
Also published as: GB2345002B; GB9828123D0

Abstract

A solar still comprises a transparent roof 1, a gutter (3, Fig. 3) running around the internal periphery of the base of the roof, an evaporative tray 2 and legs 14 for supporting the still above a container 13 for collecting distilled water and a passive solar panel 7 for preheating the water to be purified. The gutter collects water which condenses on and runs down the roof. Water circulates between the solar panel and the evaporative tray by means of the thermosiphon effect. An insulated reservoir (26, Fig. 6) may be provided below the evaporative tray so that distillation continues after sunset, the cooler air temperature improving condensation. Hinged reflectors 8 may be fitted to the solar panel. The whole arrangement is collapsible to fit in a case (Figs 8-10) for portability.

Description

DEMOUNTABLE SOLAR STILL This invention relates to a demountable solar distillation apparatus, or solar still.

Solar stills have existed since many years, and generally consisted of inclined large areas of glass planes held over shallow dark basins of sea water; the sun heats the water, the greenhouse effect being provided by the glass, so that the water evaporates, its saltless vapour condensing on the cooler glass into drops that run down the lower surface of the glass to collector channels, so providing saltless drinking water to coastal populations with no other sources of drinking water. During World War 2, an American physicist, Dr Maria Telkes, designed a near spherical inflatable solar still some 35 cm in diameter which provided sufficient drinking water for the survival of pilots who crashed into the sea.

This principle is very little used today, and it is the object of this invention to provide a compact transportable lightweight solar still that can provide sufficient drinking water, at family scale, from saline or polluted water sources.

According to the present invention in its simplest form, there is provided a flat bottomed square basin the bottom of which is of a dark colour, and the edge of which is formed by a perimeter U shaped channel at the outer edge of which rest four transparent triangular sections which, when brought edge to edge, form a pyramid. Polluted or saline water is poured into the basin through a hole in the pyramid with a funnel to form a thin layer of water which heats up rapidly because of the dark colour of the base and the greenhouse effect of the transparent pyramid and evaporates, so that its vapour, condensing on the underside of the pyramid, runs down the sloping triangular section and is collecte along the perimeter by the continuous U section channel, the condensate being generally pure distilled water In a more complex version of the invention, a flat plate solar water heater fitted with two folding reflectors, the panel being the same size as the still base, and so able to form its cover when packed, is placed below the still which can either benefit directly from the added energy to increase output, or to be fitted with a lower insulated hot water storage container linked to the panel and located below the evaporating tray, so that, accumulating energy as heat during the daytime, it permits the still to operate at night, when temperature differentials can make the overall system more efficient and more productive of clean water.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a plan view of the simpler still, with an optional solar panel attached.

Figure 2 shows an elevation of the basic still with the distillate running into a collector vessel.

Figure 3 shows the evaporative tray edge detail, illustrating in section the pyramid component, the distilled water collector channel and the evaporative tray.

Figure 4 shows an elevation of the more complex still, with a lower water storage insulated container and a solar panel.

Figure 5 shows a plan view of the more complex still with sections at different levels to illustrate its functions.

Figure 6 shows a section through the more complex still, to illustrate the thermosyphon systems in operation, including that of the solar panel.

Figure 7 shows a perspective view of the whole assembly of the still, the solar panel and the distillate receiving vessel.

Figure 8 shows a plan view of the packed still.

Figure 9 shows a section through the packed still and the solar panel.

Figure 10 shows a perspective of the still and panel packed down to form a case with a handle for ease of transport and storage.

Referring to the drawings, the basic still comprises a transparent pyramid 1 made up of four collapsible triangular elements held together by angles at their contiguous edges, or possibly made from a collapsible light metal or plastic frame supporting a flexible transparent film membrane, this pyramid providing the greenhouse effect and constituting also the condenser. The transparent cover can also be of a small roof shaped geometry 38 as shown in Figure 2. It also comprises a shallow tray 2 with a perimeter edge channel 3 into which falls the condensate 36 which has run down the transparent sheet 1 cooled by the outside air. The perimeter channel is white and the transparent sheet 1 located by the base angle 11 is protected from the sun by a strip of aluminised tape 10, to avoid evaporation of the distillate. A thin layer of water 4 in the tray which is insulated at its base 9 evaporates as it is rapidly heated by direct or diffuse solar radiation, and its vapour condenses on the pyramid 1 running into the edge channel 3 which can be made to slope down to the distillate tubular exit point 5 to which is attached a flexible tube 6 taking the distillate to a clean water containing vessel.

With this basic still operating in sunlight, the vapour condenses on the pyramid 1 in small droplets which eventually create a white reflective layer which significantly reduces solar input and the consequent evaporation of water. To overcome this inherent problem, a flat plate solar water heating panel 7, made up of a top and bottom manifold linked by tubes or channels, insulated at the rear and glazed with glass or plastic at the front, is placed against one of the legs of the still such that the panel can be fixed at the top at various heights by a clip 5 held by a releasable plastic tie, to allow the panel to take up different inclinations to best face the sun, and to be rotated periodi! cally around the circular leg to follow the rotation of the sun, without having to move the still.

Flow and return tubes 20 from the still are linked to the panel 7, wound spirally round the leg to avoid airlocks and insulated by a flexible foam sleeve 21 fixed also by releasable plastic ties. A thermosyphon water circulation system is thus induced in the panel with the colder water being ducted to the base manifold of the panel 18 and the water rising in the panel to the top manifold 19, so heating the water in the still. The panel can be fitted with aluminised reflector flat sheets 8 held in position by struts 34 which increase radiation on the panel, but hinge back flat for packing.

In the more fully developed version as shown in Figures 5 and 6, below the pyramid 1 and the evaporative tray 27, which is designed to be removable for periodic cleaning of the whole basin, there is an insulated reservoir 35 of the same plan shape as the tray but of a deeper section that contains a significant amount of water, introduced with the help of a funnel into a hole in the pyramid 34, which has a round pivoting keyhole plate to close it when not in use.

Gravity forces the water first to fill the solar water heating panel 7 and its connecting tubes 20, then filling the reservoir 35, and then providing a thin sheet of water 4 over the evaporative tray itself, since they all intercommunicate.

In this version, the evaporating layer, as it cools, tends to flow through the pipe outlet 24, whilst hotter water from the panel 7 fed to the top layer of the reservoir 35 feeds the tray 4 through the inlet 23, establishing a thermosyphon flow constantly feeding the tray with hot water. In parallel, colder water from the base of the reservoir 35 falls through the tube 25 through the spirally wound connecting tubes 20, allowing height adjustment without airlocks, to the base manifold 18 whence it is heated in the panel and rises to the upper manifold 19 to be delivered to an inlet pipe 22 which is provided with a lightweight plastic non return flap to prevent nighttime reverse thermosyphon. In this way, a significant amount of heat is stored in the reservoir 35, constantly feeding heat to the evaporative tray, and allowing the distillation cycle to continue to operate after sunset, and also, with the help of the solar panel, to operate in higher latitudes.

As shown in Figures 8 and 9, the still is designed to pack down so that the tray can contain the elements forming the pyramid 32, whether plastic or glass, the removable legs 14 which can be provided at their base with screw height adjustor plates 37 to level the apparats, the level being given by graduations marked in the four corners of the evaporative tray, the insulation sleeve, pipe work, plastic clips, funnel and other components, the tray so containing all necessary elements, is closed by the flat solar panel and its folded reflector sheets, the whole so packing down to a flat rectangular case, provided with a handle, as shown in Figure 10 When sources of clean water are becoming scarce, or when they are polluted by industry or natural disaster, a still using solar energy producing a few litres of distilled water per day can become vital, producing sufficient clean water for safe use in some specific cases, medical for instance, and, as drinking water, for sheer survival in others.

Claims

CLAIMS 1 A demountable solar still comprising a pyramidal, prismatic or mini-roof shaped transparent cover, acting as greenhouse and condenser, placed over a shallow dark tray, containing the polluted or saline water to be evaporated, with an edge U channel, shaded and of a light colour, collecting the condensate and delivering distilled water to a vessel placed below the still, that is placed high on four legs fitted with adjustable screw base plates for levelling. Below the tray is a reservoir feeding the tray, whilst the tray and reservoir are linked to a flat plate solar panel, the whole operating in thermosyphon.
2 A demountable solar still as claimed in claim 1 in which the channel slopes from an upper point, in opposite directions, to the distillate outlet point located opposite.
3 A demountable solar still as in the previous claims whose evaporative tray is fitted with flow and return connectors that can be linked to a solar flat plate water heater.
4 A demountable solar still as claimed in claim 1 and 3 whose solar heating panel is the same size as the tray, is fitted with hinged flat reflector flaps that increase its efficiency, and an upper central hook receiver that allows it to clip onto a cylindrical leg at various heights, such that it can take different angles and be rotated to face different directions, without needing to disturb the stationary still ; the said panel being fitted with flow and return pipes helically wound round the cylindrical leg, in its higher position, to avoid airlocks, linked to the flow and return connectors from the tray, and insulated with a flexible foam sleeve allowing the tubes'passage at different heights, the sleeve being held in position by plastic releasable ties.

CLAIMS (cont)
5 A demountable solar still of more complex design as claimed in previous claims in which a removable evaporative tray is located over a water storage container of considerable comparative volume, linked both to the tray and to the solar panel, such that thermosyphon forces allow the tray to be constantly fed with the hottest water, whilst the insulated container retains energy in the form of heat which allows the distillation process to continue after sunset, when efficiency is increased by lower night temperatures.
6 A demountable solar still as in claim 5 in which the return flow arrival point in the storage container is fitted with a non-return valve to prevent reverse thermosyphon which would cool the stored water.
7 A demountable solar still as in previous claims that can be filled with unclean water, with a funnel, through a closable circular hole located in the transparent condenser top.
8 A demountable solar still as in previous claims that can be levelled with adjustor plates on the four legs, the level being read by the water to be distilled against graduated markers in the four corners of the evaporative tray.
9 A demountable solar still, as in the previous claims, all components of which can be packed into the shallow tray of the basic still, or into the deeper tray of the more complex still, in both instances the solar panel and reflectors forming the lid, so that the stills can be demounted and packed into a rectangular shallow closed case, with a carrying handle for ease of transport and storage.
10 A demountable solar still substantially as described herein with reference to figures 1-10 of the accompanying drawings.