Solar Still Prototyping & Initial Testing


Still Prototype Version 1 

Day 1 of Testing

At home I built a small solar still prototype (1’ x 1’ footprint) constructed of PVC and vapor barrier that knocked down and fit in my suitcase. Upon arrival in Tanzania I constructed the prototype and gave it a preliminary test. During the first day I did not get it out into the sun until 3 pm and all I saw by the end of the day was some condensation but no droplets and no water output. The other variable that affected the output was the greywater tray I used was an aluminum foil tray which was reflective. That evening I duct taped over the tray with a dark colour so it would absorb more heat and got the still full and ready to go by 7:30 a.m. 

Day 2 of Testing

The second day of testing was a success, just over a litre of dirty water was placed in the still in the morning, and when we checked after sunset the still had produced about half a litre of distilled water. The temperature was 33C and the UV index was 14; almost ideal conditions for a solar still. The issue with this test was although it produced half a litre of water it was lying around in the bottom of the still and hardly any flowed down into our water bottle trough.

The angle on the front was not severe enough so condensed droplets were dropping back into the feedwater tray as well as forming down the sides and back of the still and not being collected in our trough at the front of the still. Several books and resources had suggested that the condensing surface (in this case the plastic covering) must be only a few inches from the feedwater for the still to work properly. This test proved this is not the case as it performed quite well and there is almost a foot of air space in between at the back. For future prototypes it would be ideal but not essential to try minimize the space between the feedwater and the condensing surface.

Still Prototype Version 2

Inter-disciplinary building still version 2
Building still version 2
After this I decided to clean up the appearance of our still with Alanna and see if we could make it work better. The first prototype consisted of a tarp wrapped around the PVC frame which combined with duct tape provided a very good air tight seal. For the second generation prototype we created 3 panels for the still; two separate side panels and a middle panel that spanned from front to back. We then duct taped the seams as best we could and it looked quite a bit cleaner than the clunky first generation prototype. 

In the field with the feedwater ready to be sealed up
Close-up of the feedtray and water-bottle trough
Here you can see condensation and the water-bottle trough
The results from prototype version 2
But,  when we returned later that day we found very little water had been collected in our trough; the vast majority had leaked out of the still all over the ground. With this second prototyped I learned the importance of sealing the still (for efficiency and collection of the water) and the importance of being able to control where the clean water goes through the shape and design of the still.

 Influence on Project Direction

During our two weeks in Tanzania I worked closely with Alanna and Avery on the TEMBO guesthouse solar still. They were invaluable for their input on technical details and the business aspect of the project. 

Before flying over to Tanzania I was focused on creating a larger scale (2m x 2m) still for the guesthouse using PVC piping as a construction material. After a week of observing and talking to Virginia, Caroline, and a visit to the local hardware store I realized PVC was not a great material choice. There would be difficulty in acquiring the appropriate joints as well as sealing the still would be very difficult between the proposed glass pane and the PVC frame. 
Exploration of traditional still form and design

Since both 2x4 lumber and glass panes are available at the local lumber store the design then changed to include these materials. A base out of concrete or possibly 2x4 with a wood frame all enclosed with a glass panel on top for condensing. Working on a permanent still for the guesthouse would require a systems approach; how would Caroline get the water to the still, how would it be cleaned, where would the clean water be stored? We could also utilize the design for storage tanks the other group was working on and build that into our system. There is also the question of how to seal the design which would be tricky without precision wood and glass-working. Another big factor is the cost of the system; not many people get a chance to save in Longido and live day-to-day financially. Paying for a large still would require a period of time to pay back or a loan which is difficult to get.

Current Project Direction

Quick prototype of a personal solar still

While we were in Tanzania I spent one evening drawing up plans for a personal still for the people of Longido. That day we had seen people getting water from the public tap and carrying many buckets to collect the water. I came up with the idea to use the ubiquitous bucket (readily available) as the basis for a solar still. It could be very low cost and will solve many issues if it works: cost (5 gallon pails are all over the place and very affordable), sealing (the bucket is airtight to start with), portability, and maintenance. Testing will need to be done to ensure it can meet the required criteria.

Mocking up a still based on a 5 gallon pail
Prototyping a dome shaped lid for the bucket still

I will continue to explore the 5 gallon pail as the basis for my project and experiment with additions and modifications that could easily transform it into a low cost yet effective portable water still.

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