How A Solar Still Works
A Solar Still is an effective “green product” that uses the sun’s natural light energy in the purification of water. The process of a solar still makes use of the sun’s energy instead of other sources like wood or fossil fuels in gaining the heat energy necessary for the purification processes to take place. Solar stills can supply clean and pure water for cooking and drinking on a daily basis to those places where no other energy sources are to be found.
The solar water distillation method that is gaining worldwide popularity using the unlimited power of the sun is sometimes called solar water disinfection, or the SODIS Method. This procedure can decrease the number of bacteria by 99.999% when done correctly – that’s arguably more effective than boiling or the use of chemicals! This is due in part to the sun’s UVA rays, which have been proven to kill pathogens such as E. coli, Cholera, Salmonella, Rotavirus, Giardia and Cryptosporidium.
If you have the sunlight, the right tools and materials, a DIY solar power disinfection unit is a project that can be built by almost anyone. A solar still/disinfector has a number of benefits. For one, it doesn’t require using precious fuel for boiling or chemical treatments that alter the taste of the water. And because the sun’s rays are not a finite resource, this is a purification and cooking resource(see my blog on The Solar Cooker) that can be counted on for the long-term situation if needed. Another benefit is the sun’s UVA & IR (Ultra-Violet A & Infra-Red) rays, which as afore mentioned work to kill pathogens, there is the sun’s heat. Perhaps the biggest limitation in using solar power is that it can only work when the sun is out. You can’t effectively use solar power for water purification on a rainy (get the rainwater catchers out!), cloudy day or at night. Fortunately, this method works any time of the year. The outside temperature doesn’t matter, as long as there’s sufficient sunlight. Thus, solar disinfection stills are an environmentally-friendly product that can be used the year round.
How Are Solar Stills Used
Solar stills as afore mentioned, are being used all over the world to deliver clean drinkable water to people that have had so little of it. There are some solar stills which are used primarily in “green thinking homes” that help in reducing the cost of energy as well as pollution. There are also some other solar stills which are portable and of such a size to provide clean pure drinking and cooking water for those in disaster-stricken places across the world where there are no clean and pure drinking water sources to be found.
Materials And Tools Needed To Build A Solar Still/Disinfector
The Solar Still we are going to build is a box similar to the one pictured below but with a few minor changes in the parts needed in the construction of it. I will start first with a materials list and then a list of tools needed for this project, followed by as detailed building instructions as I can make them for even the most inexperienced builder. A project like this can also be a lot of fun for your “Family Group” to build as a SHTF backup water source.
For the sake of simplicity, I’ll be using two 1″ thick x 12″ wide x 8′ long boards of white pine. You can use any building material you want to use, just make the necessary adjustments to thicknesses.
- You will need to acquire a sheet of tempered glass (K) or a regular single pane of glass(be careful with this as the edges are sharp and the glass is brittle/fragile) that is approximately 18″ wide by 24″ long. — (I’m using a tempered glass pane that is 21 3/4″ wide by 27 3/4″ long that I got out of an old storm door with the metal framing boarder still attached).
- A 48″ length of 1″ inside diameter, schedule 40 PVC pipe (L), a 1″ PVC cap and a 1″ PVC 45* elbow.
- A small 8 – 10 oz. tube of exterior caulking.
- A large pan (not shown in drawing) should be 4″ shorter than the inside length of the box and have at least 2″ of clearance on either side. — (I’m using a large aluminum turkey roasting pan 13″ wide x 21″ long with sides 3 1/2″ high).
- A small box of deck screws or finishing nails. The length determined by the thickness of the material you are using.
- A tube of wood glue.
- A roll of duck tape or aluminum furnace tape. The furnace tape is better as it is made to stick to hot surfaces.
- A large roll of aluminum foil.
- A large roll of waxed paper.
- A quart of dark blue (navy blue) enamel paint and several 2″ brushes. — (dark blue attracts heat better than black).
- Two 3″ x 4″ light metal hinges and a drawer pull knob or handle.
- An option for part (A) if you can find it would be a piece of sheet metal; mild steel/iron, aluminum, brass or best of all, copper. If that is not possible, cut out a piece of cardboard or panel board equal to the inside edge dimensions of panels (G, J,D & J) less 1/4″ all around and put several layers of foil on one side of it. Secure it with the duck tape or if you have it, the furnace tape. It does a better job of holding the foil down as it is made to withstand higher temperatures. The metal will conduct heat better to the pan.
- A carpenter’s square and a framing angle.
- A measuring tape.
- A claw hammer.
- A #2 Philips Head screw driver.
- A wood rasp and a half round & flat wood file.
- A couple of sheets of #4 grit sandpaper.
- A couple of sheets of #2 grit finishing sandpaper.
- An electric drill with one 3/32″ drill bit for the pilot holes and one 1″ wood auger bit or a 1″ hole bit.
- An electric circular hand saw and/or a table saw. (A hand saw will work just fine only it will take longer to complete the project).
- An electric hair drier or a hot air blower gun as used in stripping paint off wood surfaces.
- Five to eight 5″ C clamps.
- Two or three 36″ bar clamps are a good optional tool to have but not absolutely necessary for this project.
Building The Solar Still/Disinfector
As can be seen in the drawing, you will need to cut four right and left side panels (I & J) of varying heights and lengths. The same is true for the front and back panels (D, H, G & F) Their lengths are governed by the length and width of your glass pane. That is to say that the inside dimensions of the finished assembly of the outer panels (H, I, D & I) is equal to the dimensions of the glass pane you are using +1/4″. — (A good practice to follow in a project like this with so many pieces is to mark the piece identification (A, B, C, D, etc.) on the inside surface of the piece.)
- I’ll first cut my two R & L outside boards (I) 30 3/4″ long.
- I’ll cut the next two boards (J) 25 3/4″ long.
- Cut three more boards (H, G & D) 22″ long.
- Board (F) will be cut from board (G). Board (C) would be cut from (D) but it won’t be used in this construction.
- Take the two boards (I) and measure from the bottom of the front corner up 6″ and mark it. Using the long edge of the carpenters angle, draw the cut line from that mark to the back upper end corner on both boards, then make the cuts.
- On the two boards (J) measure up from the front bottom front corner 4 3/4″ and mark that point. Measure down 1/2″ from the back upper corner and mark that point. Draw your cut line between the marked points on both boards then make the cuts.
- Take the boards (H & G) and measure up from the bottom edge 8″ and mark that point on both boards. Using the carpenters angle line up with the edge of the board and the marked point and draw your cut line and make the cuts.
- For the board/panel (F) measure 1/2″ in from the long edge and mark that point on both ends, draw the cut line and cut off that 1/2″ x 1″ piece. Save it as it will be needed later.
- Take board (D), measure up from the bottom edge 6″ and mark it. Line up the carpenters angle on that mark, draw your cut line and cut it.
- Cut a two boards (B) 30 3/4″ long.
- Take one board of (B), measure in from the long edge 3/8″, mark that point. Do another 3/8″ at the opposite end of the board. Line up the angle on the two marks and draw the cut line and make the cut.
- Take the roll of waxed paper and draw out a 32″ length and place down on your work surface. This is to prevent the overflow of wood glue onto your work surface.
- Put glue on one edge of the two boards to be joined together to make up (B). Place the two boards on the bar clamps if you have them and clamp them together spacing the clamps in 7″ on both sides. Make certain the corners are properly lined up using the carpenter’s angle.
- No bar clamps? Place the glued edges of (B) boards on the center of the length of waxed paper and put bricks , books or anything heavy along the edges to hold the two boards together.
- Cut one board (E) 23 5/8″ long.
- Measure in 4″ from the long edge along the perpendicular edge of both ends of (E) and mark that point. Use the carpenters angle to line up on the marked points and draw a cut line. Do the same measurement of 4″ in on the opposite long edge, mark the points and draw that cut line. Make both cuts. You’ll end up with two 4″ x 23 5/8″ and one slightly less than 4″ wide x 23 5/8″.
- Take one of the 4″ (E) boards, putting glue on the “bottom side” and place on the bottom of boards (B) lining up the edges to the corners and clamp with at least two “C” Clamps placing them in the center of the (E) board 5″ in from the long edge. No “C” clamps? Take something heavy and place it on the center of the (E) board.
- Take your drill with the 3/32″ drill bit and put in pilot holes at each corner of (E) board 1″ in from each edge and put in your four screws/nails to secure the (E) board to the (B) boards at either end.
- Go to the joining point of the two (B) boards and mark that point on the (E) board. Measure in 1″ and out 1″ on both sides of the joining point on both sides of (E) board. Drill your pilot holes at those points and put in your four nails/screws.
- Repeat steps 15 – 17 with the other end of boards (B) with the other 4″ board (E).
- Measure along the long edge of both sides of boards (B) 15 3/8″ and mark those points. Take the third (E) board and find the center of the narrow edge at both ends and mark them. Put glue on the “bottom side” of the (E) board, line up the points on (E) board with the center points of (B) boards and place on the bottom side of boards (B). Put something heavy on it, (E), to hold it in place as you attach it as previously done with the other (E) boards.
- MORE TO BE ADDED TO THE INSTRUCTIONS LATER. I’VE JUST HAD A FAMILY EMERGENCY AND WILL BE BACK MONDAY, THE 16th, TO FINISH. —GERALD—
- — (An alternative is to pull off a 32″ length of aluminum foil and place down on a flat work surface. Glue the edges of the two boards, centering it on the foil sheet, and push the edges together. Place several large books or bricks along the outer edges of the (B) boards to hold them tightly in place. Pull off another 30″ length of foil and center it on the top of the three (B) boards. Place heavy books, bricks, rocks, magazines, etc. on top to assist in the glue bonding process) — Glue the three boards together along the long edge, then clamp them together. Take the two pieces of (H) and line up along the long edge and attach the hinges 3″ in from each outer edge. Glue the panel/board (G) to the in nner side of the lower hinged panel of (H). Be sure to line up all the edges and the hinges are on the other side of the pieces you are gluing together.
Dirty water would be placed in the pan and the pan loaded into the distillery through the hinged back panel. The box will heat up and even though it is unlikely to come to a full boil it will cause the water to begin the process of evaporation. The evaporated water collects on the under surface of the glass and droplets form. These droplets will roll down the glass surface to the trough (L) that is angled to cause the collected water to flow out and into the waiting container (not shown in the drawing)
The glass will be placed on top of panels (J, J, F & C) and given the angle specifically designed into the box, the glass pane will put down directly into the trough. The pan that will contain the dirty water is completely painted inside and out with the dark blue color. This is for the purpose of letting it absorb the energy that came from the sun. There is some arguments regarding the surface of panel (A). Should it be left clean and reflective or should it be painted with the dark blue paint. I am of the opinion, backed up with the Laws of Thermodynamics, that the colored surface (A) will pick up on all the reflected sunlight from the side panels and conduct the gathered heat energy to the evaporation pan.
Solar still effectively works in two scientific idea or principles and that include the evaporation as well as condensation. First and foremost, water needs to be completely purified in the blue bottom of the pan. This will be allowed to sit under the heat of the sun that allows them to absorb the UAV and IR energy that comes from the sun.
As energy is completely absorbed, it begins to heat the water. As water temperature rises, the water would be converted into steam and then it will evaporate towards the ceiling of the glass. This may leave you pure and clean water.
Apart from condensation, another principle that solar still offer is the condensation process. Right after the evaporation of the water, it would immediately hit the ceiling of the glass. After that, the water would condense in a slow manner on the glass that causes the formation of pure droplets of water.
Since the glass is completely angled towards the collection trough, water droplets would roll down into it. Since no minerals, substances and bacteria can evaporate into the pure water, water droplets that would end in the trough would be completely purified and safe for cooking and drinking.
In most purification sources like commercial plants of water bottles, water would be boiled as part of their purification processes. As water is completely boiled, its PH level dramatically drops which may cause a flat tasting type of water. With the solar still, water is naturally purified to make sure that its PH level would always stay at its balanced level.