Difficulties and New Idea

We had some difficulties with sealing the water leakage in a few spots of our final prototype.
Therefore, we came up with a new idea: using a 2.5 gallon recycled plastic water bottle that has a faucet for draining. This 2.5 water container is designed to sit on a flat surface and is sold anywhere in the US. We wrote to GrupoFenix to check whether they have such bottles over there. We have not heard back from them, but we decided to go ahead and try this new idea.

Advantages of this design:
Sustainability- It is made of recycled material, an empty water bottle.This unit will not leak! The base is made of the bottom half of the bottle--all one piece. The unit already has a faucet for draining the water at the bottom The plastic is soft and very easy to work with. It can be cut with a scissors or a utility knife. No need to worry about cutting with electrical machine It will use recycled water (base) and coke bottle plug (to refill water). It eliminates the need of creating a draining plug, and it takes less time to make. It is also inexpensive, saving on material for gluing/sealing the joints of the distiller. 

Disadvantages of the Design:
The sides of the unit are semi clear. The unit will perform best when the sun is shining on the top of the panel. This may reduce the rate of evaporation by a significant amount. However, because it is inexpensive we can create as many units as needed to supply the two gallons of distilled water needed per month. 

To create this new prototype, we cut the top of the bottle to create an angle. We then glued a plastic divider used from the same bottle to create the large and small compartment of the bottle. 

Process:

We first cut the top of the bottle diagonally, leaving one inch above the water plug/tap

We cut a small round opening through which we will insert a plug we cut from a cola bottle.  

Next, we cut a divider and glued it using silicon.

Next, we cut the glass and strips of left over plastic to help seal the gaps between the glass and the container. 

We attached the plastic strips on the back of the glass to help seal the gap on top of the container. 

Next we used silicon to attach the glass on top of the container.

Final Prototype

We wanted to create a final prototype with plastic sides so the community in Nicaragua could potentially create a water distiller kit themselves, as it would be nice to have several different options that the community could choose from.

With this goal in mind, we measured all the pieces and cut them. We first tried cutting the plastic pieces using a plastic cutter knife, however, it was extremely difficult. We ending up using a machine in the machine shop, which wasn't great, as this wouldn't happen in Nicaragua. However, Amy said that the people there were very handy and could probably figure something out. With that in mind, we went ahead with our plan.

We took two of our plastic pieces and used a hand drill to drill a hole in each of them: One for letting in water, one for letting out water. We originally thought of using plastic water bottles for the nozzles of the water distiller, however, we found they were much weaker and could potentially let out water. Therefore, we decided to use soda bottles.

We then cut a plastic Pepsi bottle for the nozzle and the cap, took off the cap and the small plastic ring, and put the nozzle piece inside the drilled hole, and screwed the cap back on. This would be used for letting out water.

For letting in water, we sliced a plastic coke bottle diagonally so that the cap would be at an angle and it would be easier to pour in water.

We then glued everything together minus the glass top. We first used tape to fasten the cut plastic pieces together and then glued the pieces from the inside using a silicone adhesive (as this would be the glue they would have in Nicaragua). We also glued both soda bottle pieces and waited a day to let the glue dry.

After the glued dried, we took the tape off and tested if the container would hold water. It was indeed leaking, and we had to fill in all the holes we saw and wait a bit longer to test again. A second run-through showed that it was still leaking; there were places in the corners of the container and the water was leaking from the "letting out" water bottle cap as well. We had to keep gluing to make sure we stopped all the leaks.

We came to the conclusion that silicone adhesive was not the best material from stopping water flow, as even though we put massive amounts of glue, we couldn't stop all the leaks. Also, the adhesive was extremely messing and not very aesthetically pleasing at all. We ended up scraping much of the silicone off and using hot glue to seal the holes, which eventually worked.

Our final product:

Further testing

After creating our initial prototype, we wanted to test different materials for the top of the water distiller, as well as different angles. We decided to test glass and acrylic for the tops, and made two new prototypes:

Two new prototypes with different materials for tops.
Left is acrylic and right is glass.

These prototypes have a few key differences. We decided to not cut out an angle, and instead, tilt the box to create the slope. This approach has both advantages and drawbacks, the advantage, being that it made the distillers incredibly easy to build. The drawback, however, is that the angle makes it so that the surface area of the water becomes smaller, and therefore, water is slower to evaporate. Our former prototype allowed the water to be flat, so since the water was spread out and thinner, it evaporated quite well. However, since it was such a pain to cut, we decided to try this approach.

We put in 400 mL in each box and then sealed the tops with tape. The boxes were left under the solar lights for 12 hours, and then the distilled water was measured. The undistilled water was measured as well, in order to calculate how much water was lost in this whole process. This process was repeated twice for both boxes, each time with a different angle. The angles were created by propping the boxes with wooden blocks of the same size. The blocks had a height of .75 inches. The first time, we propped the boxes with two blocks, the second time with 4 blocks... and got these results.

Our results from testing

In the first run through with two blocks, we immediately noticed some disadvantages with the plastic. It appeared that the plastic curved with the heat, and even through the top was securely taped down with lots of tape, too much water was escaping through the edges of the curves. It also pointed to the fact that the plastic could potentially degrade very easily in intense heat. In the end, it didn't produce any distilled water, and 50 mL of water was lost, as 400 mL was originally put in. The glass was noticeably heavier, and did not have any apparent curving. 35 mL of distilled water was produced, while 15 mL of water was lost in the process.

In the second run through with the four blocks, we made sure to tape the plastic extremely throughly in order prevent water loss. 22 mL of distilled water was produced, while 13 mL was lost. The glass, on the other hand, produced 37 mL of distilled water and 13 mL of water was lost as well.

Significant amount of water loss coming from the sides of the glass top box

For our testing, we had use tape/remove the tape to easily take out and measure the amount of water produced, as we did not create the mechanisms for filling and taking out the water yet. However, in our final prototype, will will glue the tops down, and this will hopefully prevent more water loss. Looking at the second run-through, it appears that glass is far more effective than plastic, as it had the same amount of water-loss, yet glass produced more distilled water. Adding more height/angle to the boxes did not appear to make a significant difference. Given that we only had two run-throughs, we may need to test more to come to more concrete conclusions. However, judging by previous water distillers that other have made, we concluded that glass does appear to be the best material for the top, and we will proceed with that.

Creating our First Prototype

We first created a cardboard prototype (rectangular base, triangular sides with slope) for our Solar water distiller. We were inspired by the designs of currently used water distiller that we saw on various websites.

  

Our Solar Distiller paper prototype 

Next we tested two different versions:

Round glass bowl: We placed a low cup in a deep glass salad bowl. We then put 400 ml in the bowl. We sealed the bowl with a clear plastic shrink wrap and placed a small item on top at the center of the shrink wrap to make the center of the wrap lower than the edge. To mimic the heat of the sun, we placed the bowl under a heat lamp that emitted UV light. We hypothesized that the heat from the lamp would penetrate through the clear wrap and warm the water. The water would then start to evaporate. When it touched the shrink wrap, condensation would occur; upon touching the shrink wrap, the water droplets would flow from the edges of the bowl toward the lower center of the bowl and drop into the cup. We checked the process every 24 hours.

Results: no water accumulated in the cup after the first two days. By the third day there was less than 10ml in the cup.

A rectangular clear plastic base: Based on our initial paper prototype, we used a clear 11” x 6” plastic box (bought from The Container Store). We cut it with a slope so that one side was lower than the other. We then cut a rectangular piece and used it as a divider to form two compartments. The larger one for was for the undistilled water, while the smaller compartment to collect the distilled water. We filled the large compartment with tap water, covered the whole container with clear plastic shrink wrap, and placed it under the heat lamp.

This design ended up working. After three days we accumulated 97 ml of distilled water.

 

We cut the clear box based on the cardboard prototype 

We secured the divider with a piece of tape prior to permanent adhesion

We then used a hot glue to connect the divider

                      We tested the designs for 3 days

After three days about 93 ml of distilled water accumulated in the small compartment

Because water accumulated at the edge of the shrink wrap, we lost some water in the process.

We decided to use a permanent material top for our next design, and we needed to test which material would be the best. This will be discussed in the upcoming post.

Solar Water Distiller Questions

Solar Water Distiller

Diana and Alice

1. How many liters should a personal solar distiller produce per month? (How much water is needed to charge the battery of a solar installation? How many batteries does a solar installation use? How many solar installations does the average person have?)
2. According to Trojan batteries: The frequency of the watering “depend on how the battery is used and the operating temperature. “With this in mind new installation should be monitored closely, perhaps weekly, to establish the watering frequency required.”   Was monitoring done? If yes, how many liters of water per month does the battery require?
3. How much money can a person afford to build/buy the solar water distiller?
4. What is the cost of locally manufacturing labor?
5. What is the cost of local glass sheets? Please provide sizes available.
6. What is the cost of clear polycarbonate sheets? Please provide sizes available
7. Portability: Does the Solar water distiller stays outside day and night, or does it need to be transferred into the house nightly?

Attribute	Metric (how to assess)	Unit	Value
Distilled water production	volume of water	liter/kg	?
Affordability/Material and Labour	cost	money	?
Locally manufactured and maintained	manufacturing time	hours	1 hour
Safe to touch	temperature of outside of distiller	Celsius	*Max 48°C
Portability? Need to store at night?	how heavy the distiller is	kilograms	7 kgs

Goals:

We aim to build a personal solar distiller for households that use solar panels. We want the distiller to be affordable, safe, easy to assemble, quick to evaporate water, and made with with local materials.

Because water distilling is a slow process, we want to optimize the ratio between the volume of water the distiller is capable of holding and the speed of the evaporation, as both are ideally our priorities.  Also, the higher the temperature, the faster the water evaporation. However, this might compromise safety.

*According to the American Burn Association SCALD INJURY PREVENTION Educator’s Guide A Community Fire and Burn Prevention Program Supported by the United States Fire Administration Federal Emergency Management Agency: “The most common regulatory standard for the maximum temperature of water delivered by residential water heaters to the tap is 120 degrees Fahrenheit/48 degrees Celsius. At this temperature, the skin of adults requires an average of five minutes of exposure for a full thickness burn to occur. When the temperature of a hot liquid is increased to 140o F/60o C it takes only five seconds or less for a serious burn to occur. (Source: http://www.ameriburn.org/Preven/ScaldInjuryEducator'sGuide.pdf)