An ongoing project designed and implemented at Universidad Tecnològica de Coahuila in Parras de la Fuente, Coahuila México to provide safe drinking water purified by the process of solar distillation.
Please note this document is currently a work in progress. uncompleted sections are noted as appropriate by TBD.
Numerous different methods exist for purifying water, all with the same intended result: to obtain water that is safe for humans to drink, referred to as potable. Some of the most common methods of water purification are boiling, addition of chemicals (iodine or chlorine), reverse osmosis, and filtration. All of these methods are effective, but may require resources that are unavailable in some locations. For example, while it may be very difficult to obtain chemicals or maintain a fire in remote areas, sunlight is often a readily available resource useable for water distillation. This document is a proposal to implement a passive solar distillation system prototype as a working example of utilizing energy from the sun to provide safe drinking water for human consumption.
Passive solar water distillation is considered an appropriate technology because it operates on the same principles that produce rainfall, purifying water through a process of evaporation, condensation, and collection. Solar distillation could be considered a form of biomimicry because of its relation to the rain cycle and the [greenhouse effect]. The solar distillation process can be performed on brackish, salty water or from sources such as rain, municipal, well, or spring. By utilizing the plentiful energy of the sun to evaporate water, dissolved metals and minerals, such as arsenic, barium, cadmium, chromium, and lead are separated from contaminated water . Distillation also removes salts and biological contaminants such as E.Coli.
A conventional solar distiller is a box with a glass roof, referred to as a glaze, set at and angle from the horizontal to ensure optimal sun exposure. This angle is roughly equal to the latitude of the location. The distiller faces south if in the northern hemisphere, north in the southern hemisphere. Untreated water is routed into a holding basin inside the distiller. Radiation from sunlight penetrates the glass and heats the inside of the distiller, causing the water in the basin to evaporate. The absorption of higher frequency radiation heats the water and solar still internals. The glaze traps infrared re-radiation causing a greenhouse effect resulting in higher temperatures . The evaporation process separates contaminants from the water and results in a thin condensate on the underside of the glass cover. The the condensed, distilled water then runs off the glass into a trough, and is transferred to a water storage container for domestic use. Contaminants and particulates remain in the basin and must be washed away periodically.
Scott Harris and Jeffrey M. Hinton, participants of the Parras 2005 program constructed a solar water distiller and provided a final analysis of their project on 5 August 2005. The unit they constructed is located in the laboratory at the Universidad Technologia de Coahuila, Parras Campus. This project provides a solid basis for further research and development of small scale water distillation in Parras. However, after reviewing their final analysis, construction infrastructure, and materials used, we propose some design changes and plan to research different building materials. Modifications include: substitution of the insulation material, floor coating, basin structure, and design of the collection trough. The intention is to improve upon the existing design, utilize more affordable, durable materials, and research additional methods for increasing efficiency. Portability is not a consideration with this prototype design. The materials and design chosen do not lend themselves to easy transport. The glaze is fragile, the wood veneer internal frame is frail, and the metal basin is not secured. This unit will only operate at the UTC campus, subsequent iterations of this design should consider portabilty issues.
Tentative Table of Material Substitutions
|Function||Current Material||Possible Alternatives||Justification||Possible Issues|
|Insulation||Styrofoam||Lechugilla fiber, Wool, Clay/straw mixture , recycled denim, Perlite [Details], Fiberglass as a last resort.||A natural insulator would be preferable, and the styrofoam tends to melts with heat||Flammability, water absorption, R-Value, cost, availability, lifespan|
|Collection Trough||PVC pipe||metal, ceramic, wood||The PVC melts from heat||Heat resistance, Conductivity removing heat from system|
|Black coating for heat retention||Spraypaint||Ceramic tile, black woven tarp, tinted glass||Spraypaint may be the only solution, but a more natural black coating would be preferable||Chemical leeching, heat resistance, fragility|
|Untreated water basin||Spraypainted galvanized metal||Stainless steel, Ceramic||Spraypaint and silicone caulking may contaminate water distillation process||Difficulty obtaining high temperature black sealant. Finding basin of proper size|
|Internal frame||Thin wood veneer||Thicker wood with sturdier construction, or metal||Veneer is too thin, lacks structural support||Affordability, availability, weight, ease of color adhesion|
This passive solar water distiller experiment is intended for Universidad Tecnològica de Coahuila campus located on Madero Street, Parras, Coahuila. UTC has a student, faculty, and employee population of 205 people, comprising a continuous demand for potable water. The water demand is important because it directly affects the design of the distiller in respect to desired quantity of water output.
The public supply is the most likely source of water. Although municipal water has been given some treatment, it is not always potable. Municipal water is currently the easiest method of water aquisition. In the future a rainwater catchment system could be implemented. At this time, the location of the distiller on the UTC campus is undetermined pending investigation of the best possible placement. A flat and level area with direct access to water and sun is necessary. considerations must be taken to ensure it is not in a place where the glaze can be easily damaged by vandalism or accidental breakage. The system must be located in an area that facilitates easy access and maintenence.
Currently, the UTC purchases their drinking water from SierrAzul in 5-gallon jugs (19-litres) at a cost of approximately $1.40 USD ($14.50 pesos) each. (TBD: Buyback time). Potential benefits of implementing this system are reduced cost of water and self-sufficiency. The presence of this project at UTC may influence students to pursue additional education in solar technology, possibly taking the knowledge with them in their daily lives, and into the future.
If we successfully implement the solar water distiller at UTC, there may be increased potential for expansion and installation to other locations in Parras. Solar water distillation may apply to small systems for homeowner usage, as well as larger installations in businesses or agricultural locations.
Project Update: Week 5
Week 4: Disassembly initiated. Melted components partially removed and inspected. These components include Styrofoam, PVC pipe, and plastic coating.
Fig 3: Sawdust may be a decent insulator but it's very messy when uncontrolled. Also encountered were styrofoam peanuts, and various loose ceramic tiles. *Materials
Fig 4: Silicone glue was used extensively. *Materials
Fig 5: PVC did not survive the heat. *Materials
Currently in progress.
Insulation is by far the most difficult material to choose. Many options are available, and we have not yet made a decision what material will be most appropriate when comparing cost, availability, and effectiveness. Some possible solutions:
Note: Any flammable insulator may require additional measures to prevent fire. * Fire protection means some type of sealing and/or chemical treatment of loose-fill insulation. Insulation should have minimal or no contact with both liquid and vaporized water.
A fairly inexpensive fire retardant and insect deterrant is 2.5 ounces borax mixed with 2 cups boiling water 
Possible Insulation Materials
|Material||Justification||Concerns||Estimated R Value |
|Cotton fiber from denim factory||Locally available||Possible toxic chemicals (dyes, etc), fire hazard.||3 to 3.8 (Cellulose)|
|[Perlite] - loose fill||Common material, naturally occuring glass, hopefully available from [Parras Farm Stores]. High temperature tolerance.||price, availability, possible water contamination||2.7|
|Vermiculite ||Very similar to Perlite, fire resistant||May contain asbestos ||2.13 to 2.4|
The water basin is fairly small, spraypainted black, and sealed with silicone glue. Some ideas for improvement:
- Fabricate or purchasing a larger basin
- Search for possible alternatives to metal basin
- Reuse a dark colored sink basin
- Fabricate a ceramic basin
- Line current basin with tinted glass or dark ceramic tile
- The additional weight is acceptable for this prototype distiller due to the stationary design. Additionally, the water basin can be removed if transportation is necesary.
- Search for possible alternatives to metal basin
- Purchase a second identical basin and place the two side by side
- Remove spraypaint
- Find an alternative non-toxic black paint, with high temperature tolerance.
- If a metal trough is the only choice, research other darkening solutions such as patination, or staining.
- Look into the possibility of using a wick system to draw untreated water into the still.
This could be replaced with fabricated metal, ceramic, or another material with high temperature durability. Considerations should be taken regarding the conductivity of the material chosen.
Fasteners and sealant
Much of the exiting glue needs to be removed and replaced with sturdier fasteners such as brackets and screws. More research TBD.
Week 5: June 19-25
- Research appropriate materials for the following components:
- Collection Trough
- Fasteners and sealant
- Begin searching in community for materials
- Solidify tentative materials list and budget
Week 6: June 26-July 2
- Finish design
- Purchase materials definitely needed
Week 7: July 3-9
- Purchase materials from Home Depot in Torreón
Week 8: July 10-16
- Construction of water intake system
- Test intake system
- System chassis and insulation construction
- Pending arrival of insulation on order
Week 9: July 17-23
- Finish construction.
- test entire system under full sun
- Physical project completion July 20.
Week 10: July 24-28
- Write-up completion
- Project presentation
Project Update: Week 8
- Implemented plumbing for water intake system including external storage bucket and basin float valve system.
- Determined insulation to consist of perlite. Visited several local nurseries in town and found a nursery that can order bulk perlite.
- Visited local construction stores for black high temperature silicone. Not available locally.
- Instead purchased two small tubes of red high temperature caulking from Home Depot in Torreón.
- Finalized materials list
- Went to Home Depot in Torreón to purchase materials
- Proposed budget-to-date for distiller is $100.00 (US)
- Money spent to date is $35.00 (US)
- Ordered Perlite from nursery. Two large buckets are currently on order and should arrive Thursday 10/13. Because of a planned trip, they must be picked up Saturday 10/15.
Summary of Purchased Items:
|Cubeta Multiusos||5 Gal Bucket||1||$69.00||$69.00|
|Silicon Rojo||Red Gasket Silicon||2||$28.50||$57.00|
|Valvula 3/4"||3/4" Valve||2||$38.50||$77.00|
|Union Por Manguera||Hose union||3||$25.00||$75.00|
|Flotador #3 Por Tanque||Toilet float valve||2||$17.91||$35.82|
|Spray Master Paint||Spray Master Paint||1||$19.00||$19.00|
|Tapa Por Cubeta||Bucket Top||1||$25.00||$25.00|
|Manguera Jardin 1/2" 3m||1/2" Garden Hose 3m||1||$16.80||$16.80|
|1 Hoja Triplay 9mm||One Sheet 3-Plyood 9mm||1||$290||$290|
|1 Hoja Triplay 60cm x 1.80 cm||One Sheet of 9mm 3-Plyood||1||$109||$109|
|Barrotitos 1x2x1.46||Misc 1"x2"||2||$10||$20|
|Pijas varios||various screws||50||$.35||$17.30|
|Cinta Medir 3m||3m Measuring Tape||1||$30||$30|
|Collecionador de agua metale - hecho de encargo||Metal water collector - custom built||1||$95||$95|
|Estimated US Dollars||(11.8:1 Pesos:Dollar)||$79.32|
Automatic water intake system
- Implemented Sunday, 9 July 2006
Detailed Time to Completion
Tuesday, 11 July:
- If time permits, purchase material to reconstruct or reinforce internal wood frame.
- Purchase metal for collection trough.
- Research options for basin improvement.
Wednesday, 12 - Friday 14 July:
- Planned trip. No physical work.
Saturday, 15 July:
- Pick up perlite shipment if it has arrived.
- Add perlite to distiller.
- Reinforce/repair internal wood frame.
Sunday, 16 July:
- Add collection trough.
- Internal frame construction.
- Testing if possible.
Monday, 17 July:
Tuesday, 18 July:
Wednesday, 19 July:
Thursday, 20 July:
- Project completion and presentation.
Project Update: Week 10
Cloudy in the morning. Rain storm later in the day.
- The entire distiller got wet and the underside is saturated.
- No water was evaporated.
- Finished setup in the morning.
- Moved the distiller to face south and maximize sun exposure. Because of this, the system is no longer in reach of the nearest spigot and the storage bucket had to be filled manually.
- The glaze was not properly sealed until 5:00 pm. Heat constantly escaped and no evaporation occured.
- After the glaze was sealed, evaporation began immediately.
- About 10ml of water was successfully distilled and recovered.
- A significant amount of water was lost because the plastic tube used to catch water drops and deposit them in the collector was not completely sealed to the glass. Additionally, the circular shape of the tube may be allowing for water droplets to slip past and fall on the wood frame at the bottom of the glaze.
- Due to other commitments such as class and lunch, temperature readings were sporadic. All temperature data had to be thrown out because the system was unsealed and not retaining heat.
- Replacement of the internal frame
- the addition of black plastic reused from defective water storage tanks, as a replacement for spraypaint
- Float valve water intake system
- Perlite insulation as a replacement for styrofoam
- Having access to tools, help and transportation thanks to Angela's host, the Madero family. Without them this project would not have been possible to implement.
- water input systems
- bucket with float valve is unnecessary
- However, it has been very essential for us because we do not have a long enough hose to reach from the nearest spigot to the testing site.
- thread mismatch -- fine thread on float valve, coarse on hose connector
- hose coupling leaks (currently using plastic bags and drip catch)
- Connect hose from water source to bucket
- Turn on water and monitor basin and bucket as they fill
- Wait patiently
- Change clean water receptacle when full
- wash basin periodically
- clean outside of glass
- check for hose leaks
- cover with tarp if it rains
- Replace float valves as necessary
- Check seals
- Check hose connections for leaks, repair if necessary
Possible Points of Failure
- Water collecting in the bottom of the system
- glaze seal
- hose connector leakage
- rotting wood from water leakage and exposure to the elements
Future Changes and Upgrades
- Fix thread mismatch.
- The float valves use a fine thread, but hose connectors use coarse thread. This mismatch causes unreliabilty of connections, and constant leakage. Currenty plastic bags are being used to partially seal the connections. Teflon tape may improve this situation, however the best solution is a thread adapter or purchasing fine thread hose connectors.
- Construct the system out of something other than wood, especially not particle board.
- Metal or cement may hold up better than wood when exposed to rain, wind, and high amounts of sun.
- use a different method of depositing condensed water droplets in the collection trough. The tube is not completely effective.
- One possible solution is a curved piece of plastic running from the bottom edge of the glaze diagonally into the collection trough.
- Install easy hose connect/disconnect the rear of distiller.
- Completely seal perlite insulation.
In progress. For now, use inline references.
How did you use these references (i.e. citing) and please describe the pertinent material from the reference here.