traps the solar energy inside the still (the "greenhouse" effect). ..... cheapest way to clean water for a household and is quite economical as compared to.
Water Problems? We Have Solar Solutions
SOLAR POWERED WATER PURIFICATION EQUIPMENT
SOLAR STILL BASICS SOLAQUA, INC. P.O. Box 4976 El Paso, Texas 79914 USA Tel (915) 383-1485 WWW.SOLAQUA.COM
SolAqua, Inc.
INTRODUCTION The basic principles of solar water distillation are simple yet effective, as distillation replicates the way nature purifies water. The sun's energy heats water to the point of evaporation. As the water evaporates, purified water vapor rises, condensing on the glass surface for collection. This process removes impurities such as salts and heavy metals, as well as destroying microbiological organisms. The end result is water cleaner than the purest rainwater. The SolAqua still is a passive solar distiller that only needs sunshine to operate. There are no moving parts to wear out. The distilled water from a SolAqua still does not acquire the "flat” taste of commercially distilled water since the water is not boiled (which lowers pH). Solar stills use natural evaporation, which is the rainwater process. This allows for natural pH buffering that produces excellent taste as compared to steam distillation. Solar stills can easily provide enough water for family drinking and cooking needs. Solar distillers can be used to effectively remove many impurities ranging from salts to microorganisms and are even used to make drinking water from seawater. SolAqua stills have been well received by many users, both rural and urban, from around the globe. SolAqua solar distillers can be successfully used anywhere the sun shines.
SolAqua solar still for a residence in southern New Mexico
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SolAqua, Inc.
SOLAQUA SOLAR STILL Overflow Port
Fill Port Tempered Glass Glazing
Distilled Water Output Collection Port
The SolAqua solar stills are simple and have no moving parts. They are made of quality materials designed to stand-up to the harsh conditions produced by water and sunlight. Operation is simple: water should be added (either manually or automatically) once a day through the stills supply fill port. Excess water will drain out of the overflow port and this will keep salts from building up in the basin. Purified drinking water is collected from the output collection port. Supply Fill Port: Water should be added to the still via this port. Water can be added either manually or automatically. Normally water is added once a day (in the summer it's normally best to fill in the late evening and in the winter in the early morning). Care should be taken to add the water at a slow enough flowrate to prevent splashing onto the interior of the still glazing or overflowing into the collection trough. Overflow Port: Once the still basin has filled, excess water will flow out of this port. SolAqua recommends three times daily distilled water production to be allowed to overflow from the still on a daily basis to prevent salt build-up in the basin (e.g., if your still produced 2 gallons of product water that you should add 6 gallons of fresh feedwater through the fill port). If flushed on a daily basis, the overflow water can be used for other uses as appropriate for your feedwater (e.g., landscape watering). Distilled Output Collection Port: Purified drinking water is collected from this port, typically with a glass collection container. Stills that are mounted on the roof can have the distillate output piped directly to an interior collection container. For a newly installed still, allow the collection trough to be self-cleaned by producing water for a couple of days before using the distillate output.
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SolAqua, Inc.
SOLAR DISTILLATION BACKGROUND Solar Still Background Solar distillation is a tried and true technology. The first known use of stills dates back to 1551 when it was used by Arab alchemists. Other scientists and naturalists used stills over the coming centuries including Della Porta (1589), Lavoisier (1862), and Mauchot (1869). The first "conventional" solar still plant was built in 1872 by the Swedish engineer Charles Wilson in the mining community of Las Salinas in what is now northern Chile (Region II). This still was a large basin-type still used for supplying fresh water using brackish feedwater to a nitrate mining community. The plant used wooden bays which had blackened bottoms using logwood dye and alum. The total area of the distillation plant was 4,700 square meters. On a typical summer day this plant produced 4.9 kg of distilled water per square meter of still surface, or more than 23,000 liters per day. This first stills plant was in operation for 40 years! Over the past century, literally hundreds of solar still plants and thousands of individual stills have been built around the world. SolAqua stills have built upon years of still research and development and use only food grade materials and are the state of the art for commercial solar still distillation. Still Operation A solar still operates on the same principle as rainwater: evaporation. The water from the oceans evaporates, only to cool, condense and return to earth as rain. When the water evaporates, it removes only pure water and leaves all contaminants behind. Solar stills mimick this natural evaporation effect. A SolAqua single basin solar still has a top cover made of glass, with an interior surface made of a waterproof silicone membrane. This interior surface uses blackened silicone to improve absorption of the sun's rays. Water to be cleaned is poured into the still to partially fill the basin. The glass cover allows the solar radiation (short-wave) to pass into the still, which is mostly absorbed by the blackened base. The water begins to heat up and the moisture content of the air trapped between the water surface and the glass cover increases. The base also radiates energy in the infra-red region (long wavelength) which is reflected back into the still by the glass cover, thus the glass cover traps the solar energy inside the still (the "greenhouse" effect). The heated water vapor evaporates from the basin and condenses on the inside of the glass cover. In this process the salts and microbes that were in the original water are left behind. The condensed water trickles down the inclined glass cover to an interior collection trough and is delivered to a storage bottle. The still is filled each morning or evening, and the total water production for the day is collected at that time. The still will continue to produce distillate after sundown until the water temperature cools down. Feedwater should be added each day that roughly exceeds the distillate production to provide proper flushing of the basin water and to clean out excess salts left behind during the evaporation process.
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SolAqua, Inc.
Solar Energy
ing Condens
Distillate Collection
Water
glass
Rising Vapor Brine
still insulation
Inclined glass solar still basic operation The intensity of solar energy falling on the still is the single most important parameter affecting production. The daily distilled water output (Me in kg/m2 day) is the amount of energy utilized in vaporizing water in the still (Qe in J/ m2 day) over the latent heat of vaporization of water (L in J/kg). Solar still efficiency (n) is amount of energy utilized in vaporizing water in the still over the amount of incident solar energy on the still (Qt in J/m2 day). These can be expressed as: Solar still production:
Me = Qe / L
Solar Still Efficiency:
n = Qe / Qt
Typical efficiencies for single basin solar stills approach 60 percent. The silicone lining is used to form a membrane in the pan that should last well over ten years. General operation is very simple and requires facing the still towards solar noon, putting water in the still every morning to fill and flush the basin, and recovering distillate from the collection reservoir (e.g., glass bottles) Stills are modular and for greater water production requirements, several stills can be connected together in series and parallel as desired. As water evaporates from the solar still basin, salts and other contaminants are left behind. Over time, these salts can build to the point of saturation if the still is not properly maintained and basin flushed on a regular basis. Properly operating a still requires adding about three times as much make-up water as the distillate water produced each day (e.g., if the still produced 3 gallons of water, 9 gallons of make-up water should be added, of which 6 gallons leaves the still as excess). The excess water flushes the still basin through the overflow to prevent salt buildup. If this is done on a daily basis, the flushed water is of approximately the same quality as the original feedwater that was added to the still. The excess water is of suitable quality that it can be used to water landscaping, wash pots and pans, etc. No sediments or sludge will buildup
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SolAqua, Inc. if the still is properly operated and flushed daily at about three times daily distillate production. 80
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Still water Still andAir,air temperatures versus ambient temperature over a two day period Still Water, and Ambient Temperature Day 147-148
Source: New Mexico State University, 2000
STILL WATER PRODUCTION Solar still production is a function of solar energy (insolation) and ambient temperature. Production rates in the Southwest U.S. can average about 6 liters per day in the winter to over 15 liters per day during the summer. Measured daily solar still performance for a year in liters per square meter of still per day are shown in the figure below:
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SolAqua, Inc. 9 Observed Fitted Curve
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Measured basin solar still annual performance in Las Cruces, New Mexico on a square Fig. 4.1 Daily Still Water Production For Still #2 Source: New Mexico State University, 2000 meter basis If you know the amount of solar energy in your region (1 sun-hours is defined as 1 kWh/m2/day), you can use the following graph to calculate expected performance in your area based on the number of average sun-hours per day (1 sun-hour = 1 kWh/m2). Note that in a temperate climate, typically there are from 3 to 4 sun hours in the winter, and 5 to 8 in the summer. Tropical climates have less variation in sun-hours across the year and more consistently and often have 5 to 6 sun-hours over the year.
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SolAqua, Inc.
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Recorded Fitted Line
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Production, Liters/m2
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Insolation kWh/m2
Average measured solar still water production per square meter based on daily solar Source: New Mexico State University, 2000 insolation
Fig. 4.4 Expected Daily Production With Given Insolation
Note that a Sol-2 still has a surface area of 1.77 square meters. Typical production for a Sol-2 unit can be expected as follows: Solar Energy Daily Sun-Hours (kWh/m2/day) 3 4 5 6 7 8
SOL-2 Still Approx. Output (liters/day) 4.0 5.6 7.1 8.9 10.4 12.0
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SolAqua, Inc. DISTILLATION PURIFICATION CAPABILITIES Solar stills have proven to be highly effective in cleaning up water supplies to provide safe drinking water. The effectiveness of distillation for producing safe drinking water is well established and recognized. Most commercial stills and water purification systems require electrical or other fossil-fueled power sources. Solar distillation technology produces the same safe quality drinking water as other distillation technologies; only the energy source is different (solar) for producing clean drinking water. Solar stills remove: • • • • •
Salts and minerals (e.g., Iron, Manganese) Heavy metals (e.g., Lead, Arsenic, Cadmium, Nickel) Chlorine Giardia and Cryptosporidium E. Coli and other bacteria
Distillation is the only stand alone point-of-use (POU) technology with NSF (National Sanitation Foundation) international certification for arsenic removal, under Standard 62. Solar distillation removes all salts, as well as biological contaminants (e.g., cryptosporidium, e. coli, etc.). There are many studies in the literature, such as tests conducted on solar stills at New Mexico State University and Sandia National Laboratories, which clearly verify that solar stills are highly effective in eliminating microbial contamination and salts. If you have any questions about what a solar still can effectively clean, please contact SolAqua for additional information. Following are test results conducted on single basin solar stills by New Mexico State University and Sandia National Laboratories. New Mexico State University Still Tests The table below provides the results of the NMSU tests which show the effectiveness of solar stills in eliminating microbial contamination. After the introduction of more than 10,000 viable bacteria per liter in the feed water, 4 and 25 viable cells per liter were found in the distillate (reductions of 99.96 and 99.65% were achieved). Introduction of a billion or more Escherichia coli viable cells, each day over a period of five days, did not change the number of viable cell numbers recovered in the distillate, nor was E. coli recovered in the distillate. These tests conclusively show the effectiveness of solar stills in removing microbes.
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SolAqua, Inc. NMSU Still Microbial Test Results Sample Volume Tested Total Organisms per liter Supply 50 16,000 Distillate 1,000 4 E. coli Seed -2,900,000,000 Distillate 750 11 (No E. coli) E. coli Seed -7,500,000,000 Distillate 1,000 18 (No E. coli) Supply 10 24,000 Distillate 1,000 13 Supply 1 12,000 Distillate 1,000 6 Source: New Mexico State University, 1992
Water Quality Tests on Selected Solar Stills in Columbus, New Mexico Field Still Ref. No. #20 input #20 output #22 input #22 output #29 input #29 output #30 input #30 output
Conductivity, µS/cm 1190 4.8 1180 1.8 1200 5.8 2390 4
Hardness, mg/L CaCO3 260 4 250 0 250 8 480 4
Fluoride, mg/L 6.2 0.1 8.2 0.10 6.0 0 n/a n/a
pH 7.9 9.2 7.4 9.1 8.1 8.8 6.8 9.4
Source: New Mexico State University, 2000
Sandia National Laboratories Still Tests Sandia National Laboratories (SNL) has conducted tests on single basin solar stills to test water quality. The SNL tests were conducted with supply water concentrations of 13 and 16% (standard saltwater). The stills effectively removed salts and the Total Dissolved Salts (TDS) concentration of the water fell from 36,000 and 48,000 TDS to less than 1 TDS. The SNL report also concluded that solar stills are effective in producing microbial free water. The table below shows results from the SNL tests.
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SolAqua, Inc. Sandia National Laboratories Still Water Quality Test Results 13% salinity Distilled 16% salinity Distilled feedwater water (13% case) feedwater water (16% case) Calcium (total) 340 1.5 371
