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Annals of Arid Zone-15(3), 177-205, 1976

Systems for Solar DistillationT. A. LAwAND

Brace Research InstituteMacdonald College of McGill University

Ste. Anne de BellevueQuebec, Canada

INTRODUCTIONDefinition:

Solar distillation is not really a new process. Its principle was knownto the ancients. Although there may be others, the first mention of solardistillation known to the author was reported by Mouchot who stated thatthe Arabs "se servaient de vases de verre pour operer certaines distillations ausoleil". He then elaborated on their method as follows: "Au dire des a1chi-mistes, les Arabes pour operer certaines distillations au soleil, se servaient demiroirs concaves, poli, fabriquees a Damas". In 1'Histoire Naturelle, pub-lished in 1551, Adam Loncier depicted by means of an illustration a similarprocedure for distilling, amongst other items, the essential oils of flowers.

The next report on solar distillation comes in the excellent historicalreview of desalination by Nebbia and Menozzi (1966). They quote the workof Della Porta, published in 1589, whose apparatus was described in detail,for the distillation of herbs.

Obviously, the distillation capabilities of solar energy were well under-stood although no specific reference to water desalination was made. It mustbe noted, however, that Della Porta published several other books on desalina-tion experiments.

The first specific reference to the possibilities of solar distillation weremade by an Italian, Nicolo Ghezzi, who wrote a short treatise in 1742 wherehe proposed the following which has been freely translated from the originalItalian script:

"Perhaps placing a cast iron vase containing sea water in such amanner that the sun's rays will strike it (and during mild days andseasons, not an insignificant amount of vapour will be formed)and if the spout of the vase is shaded from the sun, it will resultin a more copious and more extended flow of fresh water".

The next reference to solar distillation was given by Harding (1883) whoreported on a 4800 square metre still erected near Las Salinas, Chile. Thisunit was of the greenhouse or roof type solar still. No mention is made of what

178 : T.A. LAWAND

inspired the builder, a Mr. wilson, regarding this design. It is known thatthe productivity of the still in summer was of the order of five kilograms offresh water produced per square metre of evaporating surface per day. It isan interesting reflection on the simplicity of the process that productivitiesreported from solar stills recently built are of the same order of magnitude.

For a while after this, few reports of solar stills appear to have beenpublished. In the decade following World War I, interest was renewed insolar distillation. Many publications have followed with reports on the pro-cess in general, often accompanied by descriptions of small stills of the rooftype, V-Covered, tilted -wick, inclined tray, suspended envelope, tubular, orair inflated design.

In order to increase the productivity, several workers have tried forcedcirculation systems to condense the water vapour externally from the still.Others tried to recapture the latent heat of evaporation through multiple-effect systems or humidification systems.

Several large solar distillation schemes have been proposed while othershave considered combination plants which generated poweras well as desaltingsaline water.

Alternative uses besides desalination were also found for solar stills,such as regenerating solutions, and obtaining fresh water from the ground.

There are a number of plans and specifications for the building of solarstills which have been published.

Quite a few patents have also been issued in this field. With a fewexcep-tions, they generally deal with small solar stills, etc.

H goes without saying that small stills of under fifty square metres inarea, as have been described, are most useful for individual family units inisolated areas. Stills of this type have been extensively tested, particularly atthe University ofCa1ifornia, Berkeley, as reported in 1961 by McLeod, et a/.

They give results of productivity of a small solar still for seven years, 1952-1959.The Las Salinas still in Chile was reputed to have run for 40 years but recordsdo not appear to have been published.

Work on larger solar stills was initiated through the efforts of the officeof Saline Water, U. S. Department of the Interior, reported mainly by Lof(1954,55) and the Battelle Memorial Institute. This work was carried outchiefly at the Solar Research Station, Daytona Beach, Florida.

These stills were glass covered units, and one was 250 square metres in area.Although primarily designed ai deep basin evaporators with a depth of sea

SYSTEMS FOR SOLAR DISTILLATION; 179

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180: T.A. LAW AND

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\ARIATION OF PRODUCTIVITY WITH TIME OFSOLAR DISTILLATION UNITS, NISSYROS, GREECE ,.~.

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SYSTEMS FOR SOLAR DISTILLATION: 181

Fig. No.9 S·olar Stills PelitSt. Vincent West Indies

Fig. No. 10 Solar Still, Haiti, 1969

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182: T.A. LAWAND

Fig. No. 11 Haiti Solar StilI

Fig. No. 12 Portable Solar Still Under Construction

SYSTEMS FOR SOLAR DISTILLATION: 183

Fig. 13 Windmill, Haiti, 1971

184: T.A. LAWAND

ifig. No. 14 Solar Still, Greece, Nissyros Island

Fig. No. 15 Solar Still, Anguilla, WI, 1958

--- • ~""="~. I"~"·; ,.. ~......•., .. -.~

SYSTEMS FOR SOLAR DISTILLATiON :-185

Fig. 16 Clay Still, 1973

Fig. 17 Solar Still, Greenhouse, Ankara, Turkey.

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186: T.A. LAWAND

Fig. No. 18 Solar Still on Bathroom Roof, 1973

SYSTEMS FOR SOLAR .DlSTILLATION: 187

water up to 30 centimetres,l~re was continuous exper't"'~tation in solar'stilloperation, which was excelIenfly re,ported in the publications of this series.

Concurrently, several other designs of stills were tested, including the airinflated plastic and tilted wick stills. The former were tested for the ChurchWorld Service who were instrumental, in 1964, in the installation of the firstlarge plastic solar still on Symi, a small Greek Island in the Dodecanese.Subsequently, several other stills were built on small Greek Islands.

This work was taken over by the Hellenic Industrial Development Bankwhich financed some of the largest and longest operating solar stills in theworld.

Other significant activities have resulted in solar still installations inSpain and Australia (Morse, 1967,19~7). In b~th ~~uritries, glass covered stillshave been favoured. The Australians havl< built a large still, 3800 squaremetres of evaporator area at Caober Peby, South, Australia. In Pakistan, aneven larger solar stilll1as been buiit jn Givadar. - ~ '

The important work of Howe, Tieimat et ai. (1974) in this field must bementioned. In particular, their colla~orative efforts with the South PacificCommission in the testing and installation of solar stills on small islands inthe Pacific Ocean have been most informative and useful in resolving probiemsaffecting fresh water provision to small communities. These installations arenot quite so large as the others, having been designed mainly for family use.One unit on Fiji was nearly 30 square r.netres in area. The work of this groupin stressing the importance of rainfall ,collection and storage in combinationwith solar stills clearly ,parallels the pt:esent.study.

The Brace Research Institute (Lawand,'1962, 68, 69, 70 A,B) has been asso-ciated with the construction testing and operation of severaI' large solar stills inthe West Indies at Petit St. Vincent (230 square metres) and in a rural applicationin Haiti (300 square metres). Both units are combined with rainfall -collection.

One of the better overall assessments of this field is Solar Distillation ofSaline Water, prepared by the Battelle Memorial Institute, (1965), June 1970 forthe United States Department of the Interior. This manual reviews the wholesubject and lists the different units, both experimental and practical, whichhave been built during the last few decades

The short resume given above is indicative of the very nature of solardistillation technology. It is by no means stagnant. Improvements are con-tinuously being made which hopefully will reduce the costs and increase theproductivity of solar stills. With this in mind, further advances in technologyshould make the future use of solar distillation even more feasible.

188 T.A. LAWAND

EXPERIENCES WITH OPERATING SOLAR STILLS

The Manual of Solar Distillation of Saline Water is the most completedocument to date describing the different solar stills which have been built todate in different parts of the world. The situation is constantly changing dueto the variable conditions under which these units are tested and installed.

Delyannis at the 1973 Fresh water from the Sea Conference in Heider-berg prepared a more up to date list given in Table I, and illustrated in Figures1 to 7.

It is evident from this list that solar distillation technology has been triedon a fairly extensive basis in a number of different areas and climatic regions.Obviously not all these units will represent success stories. This is because bytheir very nature, they will be of a pilot plant nature as various organizations andresearch teams acquire increased operating knowledge. Nonetheless in orderto ensure that this technology is adequately treated, it will be necessary tocompile a comprehensive assessment of different systems and how they haveperformed in practice. It is equally important that the sociocultural aspectsof each of these installations also be monitored so that it will be possible toascertain whether these have been given sufficient attention in"the preparation ofthese projects. It is apparent that solar distillation is often an appropriatetechnology. The question that must be raised however is whether this tech-nology has been effectively and appropriately applied.

Many organizations have published details of operating experiences andproductivity. The Hellenic Industrial Development Bank in Greece has mon-itored the performance of the solar still at Nissyrosin the Aegean and thesefigures are given in Figure No.8. What this does show is a reduction of pro-duction of roughly 12 to 15% during the summer months over a period of 5years. What has caused this reaction? It is essential to determine these fac-tors in order to illustrate the effectiveness of this type of technology. Thisin addition underlines the necessity for global assessment of the various com-ponents of these systems in order to ascertain their short and long termappropriateness.

A series of photographs illustrate the different solar distillation unitslisted in Table 1. In addition, some smaller, individual basis solar stills havealso been shown. It is essential to realize that one of the prime advantages ofsolar distillation is its flexibility. It is exceedingly easy to increase the capac-ity of these solar stills by adding additional units .. On the other hand, solarstills can be used in very small scale operations by providing fresh water forindividual needs in units adjacent to residences or integrated directly into theroof of buildings. A number of commercial finns now exist which provide

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SYSTEMS FOR SOLAR DISTILLATION: 189· -

Table I.

The most Important Solar Distillation Plants.

Country Location Design Year M2 Feed Cover Remarks

Australia Muresk I 5 1963 372 Brackish Glass Rebuilt

Muresk II 5 1966 372 Brackish Glass Operating

Coober Pedy 5 1966 3160 Brackish Glass Operating

Caiguna 5 1966 372 Brackish Glass Operating

Hamelin Pool 5 1966 557 Brackish Glass Operating

Griffith 5 1967 413 Brackish Glass Operating

Cape Verde Is. Santa Maria 3 1965 743 Seawater Plas tic

Santa Maria 3 1968 Abandoned

Chile Las Salinas 5 1872 4460 Brackish Glass Abandoned

Quillagua 5 1968 100 Seawater Glass Operating

Greece Symi I 2 1964 2686 Seawater Plastic Rebuilt

Symi II 4 1968 2600 Seawater Str. plst. Dismantled

Aegina I 3 1965 1490 Seawater Plas tic Rebuilt

Aegina II 4 1968 1486 Seawater Str. Plst. Abandoned

Salamis 3 1965 388 Seawater Plastic Abandoned

Patmos 6 1967 8600 Seawater Glass Operating

Klmolos 6 1968 2508 Seawater Glass Operating

Nlsyros 6 1969 2005 Seawater Glass Operating

Plskardo 6 1971 2200 Seawater Glass Operating

Klonlon 6 1971 2400 Seawater Glass Operating

Meglsti 6 1973 2528 Seawater Glass Operating

India Bhavnagar 5 1965 377 Seawater Glass Operating

Mexico Natividad Isl 4- 1969 95 Seawater Glass Opera ting

Pakistan Gwadar I 6 1969 306 Sea wa ter Glass Operating

Gwadar 11 7 1972 9072 Seawater Glass Operating

Spain Las Marinas .\966 . 868 Seawater Glass Operating

Tunisia Shakmou 4 1967 440 Brackish Glass Operating

Mahdla 4 1968 1300 Brackish Glass Operating

U.S.A. Daytona Beach 1 1959 228 Seawater Glass Rebuilt

Daytona Beach 1 1961 246 Seawater Glass Dismantled

Daytona Beach 2 1961 216 Seawater Plastic Dismantled

Daytona Beach 2 1963 148 Seawater Plastic Dismantled

U.S.S.R. Bakharden 5 1969 600 Brackish Glass Operating

West Indies Petit St. Vincent 2 1967 1710 Seawater Plastic Operating

Haiti 4- 1969 223 Seawater Glass Operating

190 : T•.A. LAWAND

hardware either in the form of installations on a turn-key basis or in the formof pre-fabricated units.

Components of Solar Distillation Systems:

There are many ways in which Solar Distillation Systems can be built. Itis generally agreed that it would be most advantageous for these systems tohave a long life. At the same time full appreciation and use must be made oflocally available materials and technologies. In this manner, truly appropriatesystems can be developed and maintained by the local population.

Specifications for Solar Still Components

Many designs of solar stills exist. One aim of this study is to evaluateand adapt various materials for use in still construction. Hence, it has beendecided to split up the material requirements in relation to their function withinthe unit. These are listed below:

1. General Specifications of Solar Stills

2. Transparent Cover

3. Evaporator Liner

4. Solar Still Frame

5. Sealants

6. Insulation

7. Auxilaries-Piping, Pumping and Reservoirs.

1. General Specifications of Solar Stills

There are certain basic requirements which must be met. In general, the unit

a) must be easily assembled in the field.

b) materials imported to the region should be packageable so that- transpor-tation costs will not prove excessive. (This is particularly true not onlyfor shipment from one country to another, but especially for internalmovement within a given area, i. e. from the port to final destination.)

c) should be lightweight for ease of handling and shipping.

d) must have an effective life, with normal maintenance, of 10 to 20 years.

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SYSTEMS FOR SOLAR DISTILLATION: 191

e) must have access ports for ease of maintenance.

f) should not require or depend upon external power sources.

g) should serve as a rainfall catchment surface.

h) should be able to withstand the effects of severe storms.

i) must be manufactured of materials which will not contaminate the collect-ed rain water or the distillate. (It must be continuously stressed thatsolar stills constitute the water supply system for the communities servedand hence must be non-toxic in every respect to the fresh water produced.)

j) must be fabricated so that the maximum size of solar still componentscan be directly related to economic shipping dimensions as sp,ecified byfreight carriers.

k) In general must make use of as many local resources - whether materialor labour-as possible.

In summary, the solar stills must meet standard civil and structuralengineering standards.

2. Transparent Cover

This serves to cover the distillation segment and permit access of thesolar radiation to the interior.

Properties required are listed below:

a) The material must withstand the effects of weather-wind, sunshine, raindust, etc.

b) The material must have a transmissivity for short wave solar radiation(between the limits of 0.3 to 3.0 microns) of over 85% and preferablyhigher.

c) Essentially, it must be nearly opaque to long wave (over 3.0 microns)radiation.

d) It should not have a high water absorptivity, both from its use as rainfallcatchment surface on the outside and its probable use as a condenser onthe inside.

e) The solar reflectivity at normal incidence should not exceed 10 per centwhere possible.

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192 : T.A. LAW AND

f) The solar absorptivity of the material should be low, especially if thecover is also to be used as a condenser.

g) The heat capacity should be high in order to reduce the cover temperature.

h) The material properties should not alter with age.

i) The material should not possess electrostatic properties which would con-centrate dust particles on the outside surface.

j) If the cover is to be used as a condenser, then the material must withstandtemperatures of up to 80°C. In addition, one side will experience extreme-ly high relative humidities (up to 100%), while the other surface mustconcurrently withstand the low humidities prevalent in arid regions.

k) The cover must be able to withstand the ravages of small animals.

1) The cover must be able to withstand a wind load of up to 45 metres persecond.

3. Evaporator Liner

The evaporator of basin liner serves as the absorbing surface for solarradiation as well as a container for the saline water. Materials used for thispurpose should have the following properties and characteristics:

a) The liner must be impervious to water.

b) The liner must have a solar absorptivity of the order of 0.95. Generally,black materials are used.

c) The surface should be fairly smooth so as to discourage the deposition ofscale from the saline water. It also becomes easier to clean when this isnecessary.

d) As liners are often placed directly on the ground, the material should notdeteriorate or decompose on contact with normal soils.

e) The material must withstand the effects of continuous immersion in hot,saline water. Temperatures should not exceed 80°C to 100°C upon beingheated.

f) The basin liner should not emit any gases or vapours which could taintthe taste of the fresh water distillate.

4. Solar Still FrameThis section refers to materials which are used to form the frames of the

evaporators.

SYSTEMS FOR SOLAR DISTILLATION: 193

Any materials used in this fashion should possess the followingcharacteristics :

a) They should be resistant to attack from the saline water or atmosphere.

b) In case they are exposed to the evaporator, they should be covered with aprotective coating.

c) They should be sufficiently heavy so as to anchor the stills to the groundduring periods of high winds.

d) Solar stills vary in width from I to 3 metres and are generally up to 50metres in length. Frame components should be available in a series of sizes,which could be easily disassembled for shipping and erection on the site. Insitu construction must also consider logical sizing.

e) The frames should be made of such materials as to permit ease of workingor attachment.

f) These materials should not be affected by direct contact with the groundor exposure to normal weather conditions.

g) As the frames separate different evaporator bays, they will more often. than not be used as a walkway and must be able to withstand usage inthis capacity.

h) 'Any sections of the frame exposed to the exterior will invariably serve aspart of the rainfalJ catchment surface. In this regard, the material shouldneither absorb too much of the incident rain water nor contaminate it.

5.. Sealants.

This section includes materials used to seal transparent cover materialsto one another as well as to the other components of the distillers.ln addition,

it includes any members used to support the superstructure of the distilla-tion units as they will invariably come in contact with the transparent cover.

a) The materials should not be adversely affected by exposure to the weatheron one face and by their possible exposure to the interior of theevaporator on the internal face.

b) If the transparent cover is to be used as a condenser, then the sealantsand structural components should intercept a minimum amount of solarradiation in order to keep the efficiency high. In addition, all heat inputsto the cover area increase its temperature and reduce the evaporationpotential of the system.

\194 : T.A. LAWAND

c) A minimum number of sealants should be utilized. Preferably the samesealant should be employed to bond the transparent Cover materials aswell as to seal other materials used in the solar still construction.

d) The sealants must be easily applicable under extreme field conditions, asit is likely that they will be utilized during erection phases on the site.

e) If structural cover supports are not used, the transparent cover materialsealants must withstand the effects of winds of up to 45 metres persecond.

6. Insulation.

The insulation used in solar distillation units· is used beneath the seawater evaporator basins in order to reduce ground heat losses. The materialsused for this purpose require the following properties:

a) they must be lightweight and structurally self supporting.b) They must bf waterproof and basically water impermeable.c) They should insulate the edges as well as the base of the evaporator.d) The insulation must withstand temperatures of up to 80°C and must not

warp or change shape.e) The insulation must withstand the effects of the ground on which it is

placed.f) Insulation materials could also serve as basin dividers in large solar still

bays.

7. Auxiliaries-Piping, Pumping and Reservoirs

This section includes all fluid systems-gutters for rainfall and conden-sate collection, piping for feed and rain lines, and reservoirs for saline andfresh water. In addition, some form of pumping mechanism should be pro-vided for water transfer.

a) All auxiliaries in contact with either fresh or rain water should have aprotective coating of inert material in order to avoid contamination ordamage to the system.

b) All internal gutters or piping systems must be of continuous, single piececonstruction so as to avoid internal joints which are difficult to maintain.

c) All joints which must be made to piping or gutters must be easily under-taken under field conditions.

d) All auxiliaries and reservoirs must be so fabricated as to meet generalshipping dimension regulations.

SYSTEMS FOR SOLAR DISTlLLA'TION : 195

e) Where conventional power sources do not exist, the pumps should bemanually operated or wind powered units.

f) The distillate reservoir should exceed at least the maximum daily produc-. tion capacity by a factor of three.

g) The rain water reservoirs should be rated to existing short term rainfallintensities.

8. Note on the Use of Windmills for Providing Water for Solar Stills

As longer solar stills are considered, it becomes necess.ary to pump largequantities of water. There are several modes of operation that can beenvisaged.

a) the continuous. flow of water through solar stills-this type of operationhas been followed in Australia. The amount of saline water generallyfed into solar stills is of the order of 0.5 kgjhr-sq. metre of evaporatingarea. A reservoir is needed to permit gravity feed of the water into the solarstill. Water must be pumped from a :.veIl,salt lake, the sea etc. into thisreservoir. In this case a smaller reservoir can be envisaged because of thecontinuous nature of the operation. Experience has indicated that thebuildup of scale algae etc. can be considerable with this system.

b) Water can· be flushed through the solar still periodically, i.e. everyone,two or three days, removing all of the concentrated saline solution, andreplacing this with fresh brine. This method requires a longer reservoirthan method (a) but it is more suited to manual operation, and results inless sealing within the solar still basins. If wind speeds are variable, thenthis method has greater advantage, as the larger capacity reservoirs caninsure that some water can be replaced in the solar stills.

Selecting a proper windmill for these applications depends 0)1 the followiQgconditions:

A) the availability of the saline water.

B) the volume of water to be pumped per unit time and the total headthrough which the pump must work.

C) the availability of wind during the periods of operation of the solarstill.

D) the suitabiIilty of this equipment under the somewhat severe climaticconditions prevailing in locations where solar stills are often used.

The careful selection of a windmill-pump system is an integral part of asolar still system for remote locations. Some backup pumping system whether

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196: T.A. LAWAND

manual or conventional should be provided to ensure the continuous operationof the stills.

If electricity or diesel power is available, on the site, its use should beconsidered provided the cost and operations can be absorbed by the local auth-orities. In all cases, all the alternatives must be explored.9. Note on Fresh Water Reservoirs

In all cases, fresh water distillate and rain water collection reservoirsshould be provided. This will permit the measurement, collection and storageof water from these sources. Generally, separate collection systems should beprovided to avoid contamination from:-

a) dirt, dust, animal and bird droppings in case of the rainwater collection.b) salt water overflow in case of the distiIlate production.

The fresh water should be carefully handled and possibly sand filteredif the need arises,

It is obvious that these specifications do not cover all types ofapplications of solar stills. Rather they should be viewed as criteria whichshould be adhered to if we wish to develop appropriate technology in solardistillation.

COSTING PROCEDURE FOR SOLAR STILLSIn 1970, A. Delyannis proposed the establishment of a standardized

procedure for costing, applicable to all designs of solar stills and to all count-ries. This procedure was designed to allow the comparison of the cost of thevarious solar stills at a given locality, as well as the calculation of the cost ofa given design in various localities. Therefore, such detailed information mustbe provided for each case to make this aim possible and any comparison relia-ble. A modified version of this procedure is given below.

A principal item of equipment for this comparison should be the distilla-tion plant proper, as representing a particular design. Auxiliaries, more or lessnot directly dependent on the specific solar still design, e. g., site preparation,fencing, storage facilities, pumping, piping, etc., must be quoted as well in det-ail, but as separate or independent items.

Units of necessary materials and total amounts needed must be reportedseparately for each item. Cost of materials and labour in the currency appli-cable to the proposed site mus t be given.

A description of the proposed mode of operation, including continuousor batch feed, brine evacuation and renewal, necessity of cleaning cover orbasin, etc., should be given.

Special mention should be made ifrainfall is to be collected. Only addi-tional cost for this purpose, on top of the conventional solar distillation plant,should be included in this item.

SYSTEMS FOR SOLAR DISTILLATION: 197

J. PLANT DESCRIPTION

(a) Location:Place Country .Latitude , .. Longitude .Elevation m over sea level

(b) Feed:

Type of water .Salinity mgjl NaCITotal hardness meqjl CaOCarbonate hardness meqjl CaOPermanent hardness meqjl CaO

(c) Plant Area:

Water evaporating surface m2

Cover projected area m2

Area inside boundary of the still m2

(d) Available area for future enlargement . . . . , m2

(e) Number of distilling units:

Water evaporating surface m2 per unitCover projected area m2 per unitDepth of brine in basin mmCover material .

(f) Mean daily output per year Ijm2 day or IjdayMaximum output Ijm2 day or Ijday

2. CONSTRUCTION OF DISTILLATION UNITS

(a) Basin structure per unit :

•

m3 x =Kg x =m3 x .pieces x .

Gravel and sandCementConcrete MixPrecast concrete beams

(No. of dimensions)Precast concrete posts

(No. of dimensions)Steel for reinforcementOther materials

pieces x .

....... kg x ... ' x . . - .....

)

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198 : T.A. LAWAND

•

(b) Lining:Butyl rubber sheetAsphalt matsPolyethylene, sheetOthers - specify

(c) Sealing materials:Silicone rubberAsphalt cemen t

(d) Gutters and weirs:Stainless steel stripAluminium ChannelPlastic channelAsbestos - cement anglesAsbestos - cement stripsOther specify

(e) Insulation:PolystyreneOther materials specify

(f) Labour for::1. Basin: concrete skilled

unskilledother work

2. Lining: skilledunskilled

3. Sealing: skilledunskilled

4. Gutters: skilledunskilled

5. Insulation: skilledunskilled

• •••••• 012 X •.•••

• •••••. 012 X •.•.•

• •••••• 012 X.

• •••••• 012 X ••.•. =

· tu bes x......•.... x

· x .

01 X .

m x .01 X.

01 X ...•

o1x........ mx ... , =.

m2 x ..x ... = .

mhx.mh x .mh x .

mh x.· mh x .

· mh x .· mh x.

mh x.mh x.

mh x.mh x.

(g) Any other (specify)

(h) Total cost of basin:Cost per m2 evaporating surfaceCost per m2 of cover projected area

SYSTEMS FOR SOLAR DISTILLATION: 199

3. COVER CONSTRUCTION

(a) Materials used:

Concrete curbs (dimensions) pieces x, .Aluminium angles (dimensions) .. kg x .Aluminium T-ees (dimensions) ... m x .

Cover: glassTedlarOther plastics

. . m2 x . '.m2 x .

.. m2 x ..

Sealing Materials:

Silicone rubberSilasticOther sealantsPrimer

· tubes x .....· tubes x

x· ... lit. x

(b) Labour for:

Cover structure skilled .. . mh x .unskilled. mh x .

Cover material skilled .. mh x .unskiIled . mh x .

(c) Total cost of cover :

Cost per m2 evaporating surfaceCost per m2 cover projected area

4. COST OF DISTILLATION UNITS (total of 2 and 3)

(a) Basin(b) CoverTotal of distillation units

Cost.Cost.

per m2 of evaporating surfaceper m2 of cover projected area

5. SITE PREPARATION

Minimum area required for projected output .......• m2

Cost m2 x = .

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200 : T.A. LAWAND

Removal and relocation of -

(a) Earthen materials .(b) Rocky materials .

Type of mechanical means used :

m3 x .

m3 x .

Machine hours h x .Labour, skilled mh x .Labour, unskilled mh x .

Any other special

Total cost of site preparation .....Cost per m2 of evaporating surfaceCost per m2 of cover projected area

6. PIPING AND PUMPS

(a) Salt water:

...... m pipe.

...... m pipe... m pipe.

valvesvalvesvalvesfittings

. fittings .fittings .

(b) Distillate:

m pipem pipem pipevalvesvalvesvalvesfittingsfittingsfittings

mm 1> xmm 1> xmm 1> xmm 1> x .mm 1> x .mm 1> x .mm 1> 'x .mm 1> x .mm 1> x .

mm 1> x .....mm 1> x .mm 1> x .mm 1> x .mm f/> x.mm 1> x .mm 1> x .

. mm 1> x .. mm 1> x .

= .== ••••

== •.••

== •••••

=.

SYSTEMS FOR SOLAR DISTILLATION : 201

(c) Pumping (specify HP per pump)

· salt water pumps· distillate pumps· windmill pumps

mm if1 x ." mm if1 x ,

... capacity, cost.

(d) Total cost of piping and pumping:

Cost per m2 evaporating surfaceCost per m2 cover projected area

7. STORAGE

Capacity for salt water .. mllCapacity for distillate ., m'l

(a) Materials used(specify by item)

(b) Labour, skilled mh x. -unskilled roh x .

(c) Total cost of storage

Cost.CostCost

8. FENClNG

. per m3 of storage capacityper m2 of evaporating surface

. per m2 of cover projected area

Total area included inside fencing

(a) Materials used(specify by item)

.... m2

(b) Labour, skilledunskilled

(c) Total cost of fencing

... roh x .. . . mh x .

Cost per m2 of area includedCost per m2 of evaporating surfaceCost per m2 of cover projected area

202: T.A. LAWAND

9· OTHER ITEMS OF INVESTMENT COST

(a) Facilities for pretreatment of salt water(specify by item)

(b) Facilities for post-treatment ofdistillate (specify by item)

(c) Transportation of materials to thesite (specify by item)

(d) Engineering and design

(e) Supervision of construction

(f) Testing

(g) Brine disposal

(h) Power supply

(i) Total cost of other items

Cost per m2 of evaporating surfaceCost per m2 of cover projected area

10. RECAPITULATION

Cost of distiIlation unitsSite preparationPiping and pumpsStorageFencingOther items

Total

Contingencies, 10% of totalInsuranceInterest during construction

Grand total

Cost ..Cost ..

per m2 of evaporating surface. per m2 of cover projected area.

SYSTEMS FOR SOLAR DISTILLATION : 203

Why Consider Solar Distillation:The need for water in arid areas of the world is taking on increasingly

large proportions as the population of the world increases. There are 35,000kilometres of coastal deserts located in some of the most favoured climatolog-ical regions of the world . .The time will come when it will be necessary tomake use of these areas not only for habitation but also for increased agricul-ture production. Given these conditions, technology which by large make useof locally available resources wiJl obviously be favoured and decidedly moreappropriate. The use of solar distillation could therefore be considered not'only for the provision of water, but also for the production of agriculturalproduce when combined with structures like greenhouses which can controlthe often harsh natural climatological conditions experienced in these areas.

One would consider the use of Solar Distillation if the foJlowing condi-tions are met:

A) The availability of saline water.

B) Small populations living in arid areas where inexpensive cor.ventiQnalsources of energy are not available.

C) No natural sources of fresh water, under the control of the localpopulation are easily exploitable.

D) For extended periods of time, there is adequate levels of solar radi-ation intensity and reasonably high ambient air temperatures.

E) Areas where the annual rainfall generally does not exceed 600millimetres.

F) Land is available and has little opportunity cost.It must be pointed out that generally Solar Distillation should only

be provided in quantities less than 20 cubic metres per day. Even this cons-titutes an exceedingly large size of installation. It can be that the cost willbe excessive and the size relatively unmanageable in attempting to build inst-allations close to this upper level. This does not necessarily mean however,that only small populations need be supported given that man can surviveeasily on 10 litres of fresh water per day for his basic needs, approximately2000 persons per community could be supported in a 20 cubic metre per dayplant. In this method of operation however, all other forms of water wouldbe derived from saline water sources.

What criteria should the decision makers in the developing arid areasutilized in considering solar distillation as an option for fresh water provisionfor rural communities. The prime advantages of Solar Distillation are that:

1. The units can be built to a large extent using locally available materialor materials from manufacturers in the country or the general region.

l

204 :'T .A. LAW AND

2. The local labour force can undertake all the principal jobs in the construction,installation, operation and maintenance of the system.

3. Generally, apart from the amortization of the capital investment thecost of the operation is not high if the unit has been appropriatelyconstructed in the first instance.

No desalination process should even be envisaged until full exploitationhas been made of all natural fresh water sources-surface, ground and rainwater. This applies as equally to solar desalination as other conventional pro-cesses. In the solar case, the energy cost is nil but the cost of collecting this"free" energy is not without value.

REFERENCES

Battelle Memorial Institute. 1965. Second Two Years' Progress onStudy and Field Evaluation of Solar Sea Water Stills. UnitedStates Department of the Interior, Office of Saline Water,R & D Report No. 147: 1-86.

Della Porta, G.B. 1589. Magiae Naturalis Libri XX. Napoli. LibroX: 183.

Howe, E.D. and Tleimat. B.W. 1974. Twenty Years of Work on SolarDistillation at the University of California. Solar Energy.16 (2) : 97-107.

Howe, E.D., Tleimat B.W. and Laird. A.D. Solar Distillation. Universityof California. Sea Water Conversion Laboratory, Report No.67-2. Water Resources Center, Desalination Report No. 17:1-52.

Lawand, T.A. 1962. A Description of the Construction of Solar Dem-ineralization Still No.1. Brace Research Institute, McGillUniversity, Montreal, Canada, Technical Report No. T-l:1-11.

Lawand, T.A. 1968. The Engineering and Economic Evaluation of SolarDistillation for Small Communities. Proceedings of the SolarEnergy Society Annual Meeting, Palo Alto, California, BraceResearch Institute Report No. R. 30: 21-23.

/

Lawand, T.A. 1969. Description of a Large Solar Distillation Plant inthe West Indies. Solar Energy. 12 (4):509-512, Brace ResearchInstitute Report No. R. 40.

Lawand, T.A. 1970 A. The Technical Evaluation of a Large Scale SolarDistillation Plant. Paper No. 69-WAI Sol-8, Presented at the

iI

~

~YSTEMS FOR SOLAR DISTILLATION: 205

ASME Winter Annual Meeting, Los Angeles, California, 16-20November, 1969. Transactions of the ASME : Journal of Engineer-

ing for Power, 92. (2) : 95-102. Brace Research Institute. ReportNo. R.49.

Lawand, T.A. 1970 B. Experiences with Solar Stills used by Developedand Primitive Societies in the West Indies. Presented at the1970 lnternational Solar Energy Society Conference, Melbourne,Australia. Paper No. 5/12. Brace Research Institute. ReportNo. R.5S ..

Lor, G.O.G. 1954. Demineralization of Saline Water with Solar Energy.United States Department of the Interior, Office of SalineWater, R & D Report No.4: 1-80.

Lof, G.O.G. 1955: Solar Distillation of Sea Water in the Virgin Islands.United States Department of the Interior, Office of SalineWater, Progress Report No.5: 1-39.

McLeod, L.R. and McCracken, H. 1961. Performance of Grc::enhouseSolarStills. Sea Water Conversion Programme, University of Califor-nia, Series 75, Issue 26, Contribution 46: 1-57.

Morse, R.N. 1967. The Construction' and Installation of 'Solar Stills inAustralia. Second European Symposium on Fresh Water fromthe Sea, Athens, Greece, Preprints of Papers, Vol. 7" PaperNo. 101 : 101-1-101-8.

Morse, R.N. and Read, W.R.W. 1967. The Development of a SolarStilI for Australian Conditions. Mechanical and ChemicalEngineering Transactions of the lnstitution of Engineers, Australia,MC3 (1) : 71-80.

Nebbia, G. and Menozzi, G. 1966. A Short History of Water Desalina-tion. Acgue Dolce Dal Mare, JIa 'Inchiesta Internazionale,,Milano: 129-172.