Low-cost Solar Desalinator
Design Team
Lauren Fennelly, Steven Roy, John Shea
Design Advisor
Mohammad Taslim
Abstract
The goal of this project is to improve upon the solar desalination device built as a
previous Capstone project. The original design consists of a pyramid shaped aluminum
frame encompassed by a plastic tent. A tray of saltwater sits within the frame, which
evaporates when heated by solar radiation. Water vapor condenses on the plastic tent and
drips down into a collection basin as drinkable water. The second phase is working to
make improvements to this design, mainly by implementing an automatic water feeding
system. This system will control the flow of saltwater in the trays by setting and keeping
the water level at a shallow height. In addition to the introduction of a water feeding
system, four smaller trays subsitute the single large tray, and a PVC frame replaces the
aluminum frame. Automatic feeding of saltwater into the evaporation tray eliminates the
need to disassemble the device to pour more water into the tray throughout the day. Cost,
size, portability, and ease of use also factor into the redesign of the device. By switching
to a PVC frame, the cost decreases and the portability increases. Replacing the single tray
with four trays minimizes the space used during packing and shipping.
The Need for Project
An inexpensive, easy to use
This low-cost solar desalinator is an invaluable resource to
device is needed to generate approximately 780 million people worldwide that do not have access to
clean drinking water in clean drinking water. The device is high-output, low-cost, easy to use,
impoverished regions. and portable to ensure a life-changing impact on all of its users.
Solar desalination is the process of removing salt from water by
using the sun’s energy. Once saltwater is heated by solar radiation, the
water separates from the salt and becomes pure water vapor. This water
then condenses on a clean surface and collects in large amounts and can
be gathered as drinking water.
The Design Project Objectives and Requirements
The desalinator must be low- Design Objectives
cost, high-output, portable, and
The objective of this project is to develop a solar desalination
easy to use. device that is low-cost, high-output, portable and easy to use by people
of all skillsets. Since the device will mainly be used in impoverished
regions, minimizing the price is of utmost importance. The device must
also produce enough drinking water for a small family, and must be
portable so it can be shipped across countries and easily assembled
upon arrival. Finally, the device must be easy to use so all people can
operate it and benefit from it.
Design Requirements
The desalinator prototype should be priced under $100 and must
yield at least 5 liters of drinking water per day in optimal conditions. A
water-feeding device must maintain a constant height of one-quarter
inch in the evaporation trays at all times. Minimizing cost and
maximizing output ensures the user will get the most value from the
product. When broken down, it must fit inside a duffel bag so it can be
transported by airplane. The device must be user-friendly so an
inexperienced user can easily figure out how to operate it.
Design Concepts Considered
Main design concepts included
In order to increase output of the desalinator, a water-feeding
a hanging feeder, a soft bag system needed to be developed to control the level of water present in
feeder, and a frame feeder. the system at a given time. Limiting this water level allows the water to
heat faster from the sun’s radiation, therefore increasing the overall
yield of clean drinking water.
Hanging Feeder
One concept for this water feeder involves creating a single solid
container that hangs from inside the frame of the device. This container
holds seawater. Branching off from this container are four legs that
each lead to an evaporation tray. Mimicking the simple technology
used in automatic pet feeders, the legs fill each tray until the water level
covers the mouth of the feeder leg, upon which the water stops flowing.
The height of the water is dictated by the height from the bottom of the
tray to the mouth of the feeder leg. If this height is fixed to a quarterinch, then the water will fill only that high.
Soft Bag Feeder
Another concept involves using a large, soft plastic bag in lieu of a
single solid container. Instead of rigid PVC legs, it features four
flexible vinyl tubes of a small diameter. These tubes each lead to an
evaporation tray. Saltwater is stored in the large plastic bag and is
delivered to the tray by the vinyl tubes.
This feeder design would operate based on the same principles as
the hanging feeder; the tubes fill the tray with water until the water
level reaches the mouth of the tube and prevents it from filling any
further. Switching from a large rigid container to soft, flexible plastic
means this component can be rolled or folded during shipping,
therefore making packaging lighter and more compact.
Frame Feeder
The final concept makes use of the hollow PVC frame of the
device as a storage area for the saltwater. Instead of attaching a separate
container for saltwater, this concept stores the water directly in the
frame itself, thus minimizing the amount of parts.
A thicker diameter PVC pipe is used on the four slanted sides of
the pyramid. From each larger pipe extends a thin, flexible vinyl tube.
The thicker pipe will have a removable cap from which it can be filled
with saltwater. When this cap is replaced, water flows out from the
smaller tube and fills the tray based on the same principles as the
previous concepts. The water will fill the tray only until the water level
reaches the mouth of the vinyl tube.
Recommended Design Concept
The frame feeder concept most effectively
The final design of the solar desalinator was developed to most
minimizes the water level while also minimizing effectively minimize cost, maximize the output, and ensure the design
cost and improving portability and ease of use. is portable and easy to use.
Design Description
The final design of the solar desalinator utilizes the frame feeder
concept. The frame of the device is constructed mostly from half-inch
Schedule 40 PVC to keep costs as low as possible and to allow the
device to be broken down, shipped, and reassembled. The slanted side
of the pyramid is constructed from larger 2-inch diameter Schedule 40
PVC. Located within the device are four black, plastic, square trays.
Saltwater is poured into the large 2-inch diameter pipes from a
removable cap and the small vinyl tubes fill the trays to one-quarter
inch. The sun’s radiation will heat and evaporate this water. As the
water evaporates from the trays and the water level slowly drops, the
small vinyl tubes refill the tray to one-quarter inch automatically. As an
added benefit, the water in the 2-inch pipe preheats before it even
enters the tray, thus improving the rate of evaporation.
The upper half of the device is a pyramid shape with a onequarter inch thick piece of plastic holding the four feeder legs together
at the top. A polyethylene film covers the pyramid to allow solar
radiation to enter the device, while providing a surface for the
condensation of water vapor.
Beneath the trays is a large collection basin made from the same
polyethylene film as the upper tent. As the evaporated water condenses
on the upper tent film, it will drip down past the evaporation trays and
into this basin. This basin features a spigot so it can be emptied at the
end of the day or as desired.
Experimental Investigations
The one aspect of the desalinator that needed to be tested
.
extensively was the performance of the automatic water feeder. Testing
showed that we could only rely on the “pet feeder” principle if the
container was airtight. The two initial concepts proposing the large
rigid container and the soft bag each featured the four feeding legs
branching off from the same water source, meaning the system was not
airtight unless all four mouths of the feeder were covered by the water
level. It was found in many tests that one tray would overflow before
the other trays were at the desired level.
This is why switching to the built-in frame feeder greatly
improved the effectiveness of the design. Each water storage
compartment is filled and sealed separately and has only one feeding
tube to each tray. Tests show that this maintains the water level at onequarter inch consistently, since it operates independently from the other
three tray and feeder systems.
Key Advantages of Recommended Concept
Using the frame feeder concept is the most advantageous design
option as it limits the water level in the tray without requiring any extra
effort from the user. A smaller height of water heats and evaporates
faster than a greater height, so minimizing the water height in the
evaporation trays increases the output of drinkable water.
Additionally, this concept does not require more parts to be added
to the design. Since the saltwater storage compartments are already part
of the frame, no extra storage area needs to be added. This means an
improvement in cost by using less material, and an improvement in
portability and ease of use by minimizing the number of different parts.
The portability is also greatly improved since the PVC frame can
be taken apart, unlike the welded aluminum frame of the original Phase
I design. Replacing the single large tray from the Phase I design with
four small trays also greatly improves portability since the small trays
are stacked during shipping.
Financial Issues
The solar desalinator prototype
The device was design for use in impoverished countries, so
cost $90.12 developing an inexpensive solution will maximize the positive effect of
the desalinator. The goal pricing for this project was to develop a
product priced under $100. The prototype desalinator costs $90.12, but
quantity pricing will further reduce this cost.
Recommended Improvements
Molded parts will make the
Molded parts, when buying/selling at large quantities, would
device even more affordable. reduce cost and decrease amount of parts. Different size options could
be available to accommodate the various requirements of the customer.