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EPSEA Solar Water Purification Project

Saving energy and reducing pollution are subjects that are discussed by many, but for those of us who are lucky enough to be active in a field we enjoy and believe in, the completion of a solar installation brings immediate satisfaction.

For me, installing a solar system has always been accompanied with a feeling of accomplishment, whether it was a simple batch water heater, a pool system, or an industrial installation of more than 100 collectors. None of these can compare, however, to the satisfaction felt after installing a solar still.

The major component of EPSEA's Water Purification Project is the construction and installation of more than 40 solar stills. The stills are given to families living in "colonias," ad hoc communities lacking proper infrastructure, which do not have a supply of safe drinking water.

Although most of these families understand that their shallow wells are probably contaminated, too often they cannot afford to purchase bottled water, and when desperate, they drink the well water. These shallow wells draw water from the Rio Grande flood plain, which is badly contaminated by nearby septic tanks, as well as industrial and agricultural waste. Many residents store drinking water in 55 gallon drums, which previously were used to hold chemicals or solvents. Where well water has been tested and found to be free of pathogens, the water is often too salty to drink. Sanitation problems due to both poverty and ignorance add to contamination.

The rates of water-related illness in colonias is many times greater than national averages. For many of the children recovery is slow, affecting their normal childhood development, and in turn their entire life. In many colonias, water-related diseases are the leading causes of sickness and death.

The installation of solar stills will not solve all of the problems in colonias, but they can provide something most of us take for granted: safe drinking water. EPSEA's solar stills not only destroy water-borne pathogens, they also remove salts and deliver water that tastes good. There was never a question about whether the stills would work, but as with any social program, the question was whether colonia residents would both accept and use this technology.

EPSEA enlisted the help of area health workers from clinics located in or near colonias. Our association with the local clinics helped us gain acceptance by area residents, and the health care personnel helped us to identify potential still recipients. With a limited number of stills to be installed, it was important to have the input of someone who knew the residents, to identify the most needy. The acceptance of the still technology was made easier when families learned they were recommended to receive a still by someone they knew and trusted.

In our efforts to ensure the stills would be used, we made every attempt to provide for a complete installation and make the operation as simple as possible.

The next step was to install a few stills, under real world conditions, for evaluation by the target audience. Although the EPSEA design team was a great source of both expertise and experience, few, if any of us, can fully understand life under the conditions in a colonia. Only a resident could tell us if the still was easy to use, and what could be done to improve it.

All of our questions were soon answered and it was apparent that the still project would be a success. One still owner reported that his friends and neighbors all want one, and want to know where to buy a still and how much they cost. He also asked if he could get a job as a salesman. On a follow up visit with another owner, we found that he had built a fence around his still. Not only was the technology accepted, it was valued. Probably the most telling and gratifying comment made by a still owner was that the water tasted very good, and her children now drink more water than ever before. The 55 gallon drums in the back of Mr. and Mrs. Arredondo's truck contain their drinking water. Today, that water is the supply water for their solar still.

The Solar Still

Solar stills operate on the same principles that produce rainfall. The sun is allowed into and trapped in the still. The high temperatures produced destroy all pathogens. The water evaporates, and in this process, only pure water vapor rises in the still to condense on the glass. The glass is sloped to the south, and the condensed water runs down the glass and is collected in a trough. The water is allowed out of the collector through silicone tubing, and is collected in 5 gallon glass jugs. There are no moving parts in the solar still, and only the sun's energy is required for operation.

The design of the EPSEA solar still began with many hours spent researching previous designs, both successes and failures. The next step was to consult with Mr. Horace McCracken, of McCracken Solar. Horace has been designing and building solar stills for more than 30 years, and as the saying goes, he's been there and done that. We learned that McCracken had a basin still design which could be site built. Our goal for the still project was to design and develop plans for a still which could be replicated using "off the shelf" materials, and although the McCracken still could be site built, it could not be easily replicated.

Inspired by McCracken, EPSEA designed a still which is easy to replicate, using standard building materials, of which 95% are available "off the shelf." The exterior materials were chosen for their ability to withstand our desert climate with minimal maintenance. The still produces an average of 3 gallons per day in the summer months. Winter production is expected to be half that amount. The EPSEA construction manual for solar stills utilizes a standard size patio glass replacement, 34"x76". Our material costs per still are approximately $150. Our costs were kept low through bulk, wholesale purchases, and the use of recycled glass.

Too often, in our efforts to solve problems, we are quick to turn to the latest technology, while ignoring the obvious and proven solutions. The solar still offers an inexpensive solution to the problems of safe drinking water. The still is easily installed and can be used in the most remote locations. Using only solar energy, it does not require a pressurized water supply. While most high-tech systems require maintenance, a trained operator, and treat only specific water problems, the solar still has the widest range of applications, and with its low tech design, is maintenance free.

The Solar Basin Still

The still is filled each morning or evening, and the day's production is collected at that time. The still will continue to produce after sundown as the water continues to be very hot. The still is over-filled each day to flush out sediment. The over flow water can be used for irrigation. The only maintenance is to clean the glass occasionally.

A Solar Still
Chuck Reed

I take my health very seriously and modern water systems are not trustworthy. Miles of PVC pipe supply all of the water to my house and PVC is known to put carcinogenic substances into water. Plus, who knows how many other chemicals find their way into the water system.

To be as safe as possible about drinking water, I stopped drinking tap water many years ago and had been purchasing bottled drinking water. I needed to buy several gallons per week and I still never really trusted it because who knew if it wasn't just tap water put in a bottle. And of course it added an extra expense to my life that I really didn't need.

I knew a solar still would alleviate the health problems associated with tap water, but nobody had a still on the market to buy. I had studied solar still designs for many years and knew that there were several problems to an efficient working design. Since water wants to lie flat due to gravity, it would be more efficient to tilt the still to be more perpendicular to the incoming sun's rays. This would require troughs inside the still or materials to wick the water at an angle. A reflector on the north side of a flat still had been tried on some commercial models. The best way seemed to be to simply oversize a normal flat basin type still design and give up a little efficiency. Another serious problem was that the solar-heated brine and even the hot distillate would eat virtually all metals, plastics and other materials it came into contact with.

Enter Horace McCracken, who has devoted much of his life to solar still technology. His design incorporated two heavy pieces of concrete which robbed the still of a large chunk of efficiency, and the design could not be easily replicated, which was essential for the El Paso Solar Energy Association's Water Purification Project. EPSEA consulted with Horace and designed a still based on McCracken's dimensions, using materials that not only solved the replicability problem, but also improved efficiency. Horace loved it and began producing lightweight portable solar still models of his own design, mixing in some of EPSEA's ideas.

I ended up verifying and evaluating still performance with a 6.5 by 3 foot model installed in April, 1995. The most water this still has produced was 3.5 gallons on May 24th. The best entire week of production was June 5-11 when it produced 3.25 gallons every day. The least the still has produced to date was 1.75 gallons in a day. The still has operated well ever since installation, with only two minor incidents that slightly diminished performance.

When I went on a two-week hunting trip in September, I pinched off the still's drain pipe but forgot to pinch off the vent tube. Thus, when I returned home, the still had run dry and some of the silicone had outgassed, which can create a film on the glass preventing the water beads from running back down to the trough. Thus, water beads formed on the underside of the glass which would drop back into the basin instead of into the collection trough. After several days of pounding on the glass for a few minutes with the side of my fist, I finally corrected this problem completely. Pounding seemed to cause the water droplets to work themselves down the glass, which may have helped eliminate the beading problem.

My next trip in October lasted nine days, and this time I put a tarp over the still and pinched off all of the tubes. It still beaded up a little in places but now I knew to pound the glass repeatedly, which I did for a couple of days to help bring the still back up to normal performance.

For a while I filled the still by hand, but that quickly became a hassle. Gregg Todd of EPSEA gave me a new, small taste/odor filter made for an icemaker, which I hooked up to the still with 1/4 inch UV resistant vinyl line. Now I simply turn on a 1/4 inch valve in my kitchen as I eat breakfast and the still is filled and flushed for a while before I turn it off.

The still produces incredibly soft water compared to the locally available hard water. I quickly had more distilled water than I could use and began giving it away to friends, relatives and neighbors. One neighbor who has tasted unfiltered distilled water from another still says that my filtered distilled water tastes better. Gregg Todd used some of this non-mineralized water to keep his solar powered evaporative cooler from clogging up. I drink lots of soft Tang made from this water every day, and make my oatmeal as well as other dishes with this excellent water.

I love this solar still!

These articles were originally published in the December 1995 edition of Season, a monthly publication of the El Paso Solar Energy Association; PO Box 26384, El Paso TX 79926;


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