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.

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Please note this document is currently a work in progress. uncompleted sections are noted as appropriate by TBD.


Introduction

Project Participants

Summer 2006:


Purpose

Numerous different methods exist for purifying water, all with the same intended result: to obtain water that is safe for humans to drink, or potable. Some of the most common methods of water purification are by 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, it may be very difficult to obtain chemicals or maintain a fire in remote areas. The sun, however, is a very effective resource in many parts of the world. 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.

General Description

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. It is possible to use a readily available source of water, for example municipal, well, spring, brackish, salt, or otherwise. By utilizing the plentiful energy of the sun, it is possible to remove harmful contaminants such as parasites, bacteria, high salt levels, industrial and agricultural pollutants, waste from septic tank runoff, and other heavy metals from water, rendering it potable.


A conventional solar distiller is typically a box with a glass roof angled to ensure optimal sun exposure. This angle should be such that the face of the glaze is directly facing solar noon, or as close as possible. The angle of solar noon depends on the latitude of the location being used for solar distillation. Radiation from sunlight penetrates the glass and warms the water, the evaporation process separates the contaminants from the water forming a thin condensate on the underside of the glass cover. The distilled (potable) water then runs off the glass into a trough, or collection site, and transferred to a water storage container for domestic usage. Meanwhile, leaving the contaminant residue on the floor of the collection box. (See diagrams referenced below, found at thefarm.org, as an example of distillation process.)

(TBD: More diagrams, will accurately reflect our specific design. ETA:...)

Perspective

Side

Construction Plans

Scott Harris and Jeffrey M. Hinton 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 UTC Campus. The initial project implemented and constructed by Scott and Jeffrey provides us with a point from which we may begin. This duo has done quite a bit of legwork and design possibilities for a single-basin solar water distiller. However, after reviewing their final analysis and glancing at the construction infrastructure and materials used, we propose some design changes and intend to research different (possibly more effective) materials. For example, modification or substitution of the insulation material, the floor coating, the basin-still design, and the collection trough process. This will require a significant amount research by the project participants, in addition to many consultations with the project director, Lonny Graffman. Our intention is to improve upon the existing design, utilize more affordable, durable materials, and research additional methods for increasing efficiency.


(TBD: Further analysis of materials ETA: soon --20:43, 11 June 2006 (PDT))


Tentative Table of Material Substitutions

Function Current Material Possible Alternatives Justification
Insulation Styrofoam Lechugilla fiber, Wool? Clay/straw mixture [[1]] (need more research), recycled denim, Perlite [Details], Fiberglass as a last resort. A natural insulator would be preferable, and the styrofoam tends to melts with heat
Collection Trough PVC pipe metal, ceramic, wood The PVC melts from heat
Black coating for heat retention Spraypaint Not yet known Spraypaint may be the only solution, but a more natural black coating would be preferable
Untreated water basin Thin wood veneer Stainless steel or painted plain steel. Ceramic? The wood is flimsy, difficult to seal, and coated with black spraypaint

Proposed Location

This passive solar water distiller experiment will be implement for Universidad Tecnològica de Coahuila (UTC), Parras Campus located on Madero Street, Parras, Coahuila. UTC has a student, faculty, and employee population of 205 people, who have a necessity for fresh water. The number of people who need access to the water is important because it directly affects the design of the distiller in respect to desired quantity of water output.

The most likely source of water will be the public supply. Although this water has been given some treatment, it is not always guaranteed to be 100% safe to drink. It is also currently the easiest method of water aquisition. In the future it may be possible to implement a rainwater catchment system, or utilize runoff from other water used at the university. At this time, the location of the distiller on the UTC campus is undetermined pending investigation of the best possible placement. A flat, level, and direct access to water and sun is absolutely necessary. Also, considerations must be taken to ensure it is not in a place where the glaze can be easily damaged (by a soccer ball, for example).


Justification

Currently the UTC purchases their drinking water/fresh water supply from SierrAzul in 5-gallon jugs (19-litres) at a cost of approximately $1.40 USD ($14.50 pesos). More research will be needed to determine the exact operating cost of a solar still, but after the initial investment, the monetary price of water production should be far less than purchasing bottled water. By implementing this system, UTC would reap many long term benefits in economics, reduced reliance upon an external source of water, and self-sustainability. Additionally, by implementing this project, 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 our desired location it will also make the process easier for expansion and installation at other locations around town. This may apply to small systems for homeowner usage, as well as larger installations in businesses or agricultural locations.




Project Update: Week 5

Physical Progress

Week 4: Disassembly initiated. Melted components partially removed and inspected. These components include Styrofoam, PVC pipe, and plastic coating -- plastic TBD -- 23:10, 18 June 2006 (PDT).


Proposed Materials

Currently in progress.

Insulation

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 [[2]]


Possible Insulation Materials

Material Justification Concerns Estimated R Value [[3]]
Cotton fiber from denim factory Locally available Possible toxic chemicals (dyes, etc), fire hazard. 3 to 3.8 (Cellulose)
[Perlite] - loose fill

[[4]] [[5]]

Common material, naturally occuring glass, hopefully available from Parras Farm Stores. High temperature tolerance. price, availability, possible water contamination 2.7
Vermiculite [[6]] Very similar to Perlite, fire resistant May contain [asbestos] [[7]] 2.13 to 2.4

It may be necessary to combine a solid insulator with some type of loose-fill [[8]] or spray-in-place [[9]]

Water Basin

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
  • 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.

Collection Trough

This could be replaced with fabricated metal, ceramic, or another material with high temperature durability. Important to consider conductive properties of material.

Fasteners and sealant

Much of the glue needs to be removed and replaced with sturdier fasteners such as brackets and screws. More research TBD.




Timeline

Week 5: June 19-25

  • Research appropriate materials for the following components:
    • Basin
    • Insulation
    • Pipe
    • Collection Trough
    • Fasteners and sealant
  • Complete materials list and budget
  • Begin searching in community for materials

Week 6: June 26-July 2

  • Finish reconstruction plan for distiller
  • Begin construction of distiller
  • Possible preliminary testing

Week 7: July 3-9

  • Construction and Testing

Week 8: July 10-16

  • Construction and Testing

Week 9: July 17-23

  • Physical project completion

Week 10: July 24-28

  • Write-up completion
  • Project presentation

References

How did you use these references (i.e. citing) and please describe the pertinent material from the reference here.

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