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Fog collection is the harvesting of water from fog using large pieces of vertical
mesh
A mesh is a barrier made of connected strands of metal, fiber, or other flexible or ductile materials. A mesh is similar to a web or a net in that it has many attached or woven strands.
Types
* A plastic mesh may be extruded, oriented, exp ...
netting to induce the fog-droplets to flow down towards a trough below. The setup is known as a fog fence, fog collector or fog net. Through condensation, atmosphere, atmospheric
water vapour
(99.9839 °C)
, -
, Boiling point
,
, -
, specific gas constant
, 461.5 J/( kg·K)
, -
, Heat of vaporization
, 2.27 MJ/kg
, -
, Heat capacity
, 1.864 kJ/(kg·K)
Water vapor, water vapour or aqueous vapor is the gaseous pha ...
from the air condenses on cold surfaces into droplets of liquid water known as
dew
Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation.
As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at wh ...
. The phenomenon is most observable on thin, flat, exposed objects including plant leaves and blades of grass. As the exposed surface cools by radiating its heat to the sky, atmospheric moisture condenses at a rate greater than that of which it can evaporate, resulting in the formation of water droplets.
Water condenses onto the array of parallel wires and collects at the bottom of the net. This requires no external energy and is facilitated naturally through temperature fluctuation, making it attractive for deployment in less developed areas. The term 'fog fence' comes from its long rectangular shape resembling a
fence
A fence is a structure that encloses an area, typically outdoors, and is usually constructed from posts that are connected by boards, wire, rails or netting. A fence differs from a wall in not having a solid foundation along its whole length.
...
, but fog collectors are not confined just to this structural style.
The efficiency of the fog collector is based on the net material, the size of the holes and filament, and chemical coating. Fog collectors can harvest from 2% up to 10% of the moisture in the air, depending on their efficiency.
An ideal location is a high altitude arid area near cold offshore currents, where fog is common, and therefore, the fog collector can produce the highest yield.
Historical origin
The organized collection of dew or condensation through natural or assisted processes is an ancient practice, from the small-scale drinking of pools of condensation collected in plant stems (still practised today by
survivalists), to large-scale natural irrigation without rain falling, such as in the
Atacama
The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in the w ...
and
Namib
The Namib ( ; pt, Namibe) is a coastal desert in Southern Africa. The name is of Khoekhoegowab origin and means "vast place". According to the broadest definition, the Namib stretches for more than along the Atlantic coasts of Angola, Nami ...
deserts. The first man-made fog collectors stretch back as far as the
Inca Empire
The Inca Empire (also known as the Incan Empire and the Inka Empire), called ''Tawantinsuyu'' by its subjects, ( Quechua for the "Realm of the Four Parts", "four parts together" ) was the largest empire in pre-Columbian America. The adm ...
, where buckets were placed under trees to take advantage of condensation.
Several man-made devices such as antique stone piles in
Ukraine
Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inv ...
, medieval
dew pond
A dew pond is an artificial pond usually sited on the top of a hill, intended for watering livestock. Dew ponds are used in areas where a natural supply of surface water may not be readily available. The name dew pond (sometimes cloud pond or mist ...
s in southern England and volcanic stone covers on the fields of
Lanzarote have all been thought to be possible dew-catching devices.
One of the first recorded projects of fog collection was in 1969 in South Africa as a water source for an air force base. The structure consisted of two fences each 100m
2. Between the two, 11 litres of water was produced on average per day over the 14 month study, which is 0.05 litres of water for every square meter. The next large study was performed by the National Catholic University of
Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
and the
International Development Research Centre
The International Development Research Centre (IDRC; french: Centre de recherches pour le développement international, ''CRDI'') is a Canadian federal Crown corporation that funds research and innovation within and alongside developing regions ...
in Canada in 1987. One hundred 48m
2 fog fences were assembled in northern Italy. The project was able to yield on average 0.5 litre of water for every square meter, or 33L for each of the 300 villagers, each day.
In nature
Fog collectors were first seen in nature as a technique for collecting water by some insects and foliage.
Namib Desert beetles live off water that condenses on their wings due to a pattern of alternating hydrophilic (water attracting) and hydrophobic (water repelling) regions.
Redwood forests are able to survive on limited rainfall due to the addition of condensation on needles which drip into the trees' root systems.
Parts of a fog collector
The fog collector is made up of three major parts: the frame, the mesh netting, and the trough or basin.
The frame supports the mesh netting and can be made from a wide array of materials from stainless steel poles to bamboo. The frame can vary in shape. Proposed geometries include linear, similar to a fence and cylindrical. Linear frames are rectangles with the vertical endpoints embedded into the ground. They have rope supports connected at the top and staked into the ground to provide stability.
[“1.3 Fog Harvesting.” ''Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean'', Unit of Sustainable Development and Environment General Secretariat, Organization of American States, 1997.]
The mesh netting is where the condensation of water droplets appear. It consists of filaments knitted together with small openings, coated with a chemical to increase condensation. Shade Cloth is used for mesh structure because it can be locally sourced in underdeveloped countries. The filaments are coated to be hydrophilic and hydrophobic, which attracts and repels water to increase the condensation.
This can retrieve 2% of moisture in the air. Efficiency increases as the size of the filaments and the holes decrease. The most optimal mesh netting is made from stainless steel filaments the size of three to four human hairs and with holes that are twice as big as the filament. The netting is coated in a chemical that decreases water droplet's contact angle hysteresis, which allows for more small droplets to form. This type of netting can capture 10% of the moisture in the air.
Below the mesh netting of a fog fence, there is a small trough for the water to be collected in. The water runs from the trough to some type of storage container or irrigation system for use. If the fog collector is circular the water will be deposited into a basin placed at the bottom of the netting.
Principle
Fog contains typically from 0.05 to 1
gram
The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram.
Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...
s of water per cubic meter, with droplets from 1 to 40
micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
s in diameter. It settles slowly and is carried by wind. Therefore, an efficient fog fence must be placed facing the
prevailing winds
In meteorology, prevailing wind in a region of the Earth's surface is a surface wind that blows predominantly from a particular direction. The dominant winds are the trends in direction of wind with the highest speed over a particular point on ...
, and must be a fine
mesh
A mesh is a barrier made of connected strands of metal, fiber, or other flexible or ductile materials. A mesh is similar to a web or a net in that it has many attached or woven strands.
Types
* A plastic mesh may be extruded, oriented, exp ...
, as wind would flow around a solid wall and take the fog with it.
The water droplets in the fog deposit on the mesh. A second mesh rubbing against the first causes the droplets to coalesce and run to the bottom of the meshes, where the water may be collected and led away.
Advantages and disadvantages
Advantages
Water can be collected in any environment, including extremely arid environments such as the Atacama Desert, one of the driest places on earth.
The harvested water can be safer to drink than ground water. Fog collection is considered low maintenance because it requires no exterior energy and only an occasional brushing of the nets to keep them clean. Parts can sometimes be sourced locally in underdeveloped countries, which allows for the collector to be fixed if broken and to not sit in disrepair. No in-depth training is necessary for repairing the collector. Fog collectors are low cost to implement compared to other water alternatives.
Disadvantages
Fog fences are limited in quantity by the regional climate and topography and cannot produce more water on demand. Their yields are not consistent year round and are affected by local weather and global weather fluctuations (such as
El Niño
El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date ...
). Their water supply can still be contaminated by windborne dust, birds, and insects. The moisture collected can promote growth of mold and other possibly toxic microorganisms on the mesh.
Modern methods
In the mid-1980s, the
Meteorological Service of Canada
The Meteorological Service of Canada (MSC; french: Service météorologique du Canada – SMC) is a division of Environment and Climate Change Canada, which primarily provides public meteorological information and weather forecasts and warnings o ...
(MSC) began constructing and deploying large fog collecting devices on Mount Sutton in
Quebec
Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee ...
. These simple tools consisted of a large piece of
canvas (generally 12 m long and 4 m high) stretched between two 6 m wooden poles held up by guy wires, with a long trough underneath. Water would condense out of the fog onto the canvas, coalesce into droplets, and then slide down to drip off of the bottom of the canvas and into the collecting trough below.
Chilean project
The intent of the Canadian project was simply to use fog collection devices to study the constituents of the fog that they collected. However, their success sparked the interest of scientists in
Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
's National Forest Corporation (
CONAF
The National Forest Corporation or CONAF (Corporación Nacional Forestal) is a Chilean private, non-profit organization, through which the Chilean state contributes to the development and sustainable management of the country's forest resources. C ...
) and
Catholic University of Chile
The Catholic Church, also known as the Roman Catholic Church, is the List of Christian denominations by number of members, largest Christian church, with 1.3 billion baptized Catholics Catholic Church by country, worldwide . It is am ...
to exploit the or clouds which blanket the northern Chile coast in the southern hemisphere winter. With funding from the
International Development Research Centre
The International Development Research Centre (IDRC; french: Centre de recherches pour le développement international, ''CRDI'') is a Canadian federal Crown corporation that funds research and innovation within and alongside developing regions ...
(IDRC), the MSC collaborated with the Chileans to begin testing different designs of collection facilities on El Tofo Mountain in
northern Chile. Once perfected, approximately 50 of the systems were erected and used to irrigate seedlings on the hillside in an attempt at reforestation. Once vegetation became established, it should have begun collecting fog for itself, like the many
cloud forests
A cloud forest, also called a water forest, primas forest, or tropical montane cloud forest (TMCF), is a generally tropical or subtropical, evergreen, montane, moist forest characterized by a persistent, frequent or seasonal low-level cloud ...
in South America, in order to flourish as a self-sustaining system.
The success of the
reforestation
Reforestation (occasionally, reafforestation) is the natural or intentional restocking of existing forests and woodlands (forestation) that have been depleted, usually through deforestation, but also after clearcutting.
Management
A debat ...
project is unclear, but approximately five years after the beginning of the project, the nearby village of
Chungungo began to push for a pipeline to be sent down the mountain into the town. Though this was not in the scope of CONAF, which pulled out at this point, it was agreed to expand the collection facility to 94 nylon mesh collectors with a reserve tank and piping in order to supply the 300 inhabitants of Chungungo with water.
The IDRC reports that ten years later in 2002, only nine of the devices remained and the system overall was in very poor shape. Conversely, the MSC states in its article that the facility was still fully functional in 2003, but provides no details behind this statement. In June 2003 the IDRC reported that plans existed to revive the site on El Tofo.
Dar Si Hmad
![Mahdi Lafram Oxford](https://upload.wikimedia.org/wikipedia/commons/d/d4/Mahdi_Lafram_Oxford.jpg)
In March 2015
Dar Si Hmad (DSH), a Moroccan NGO, built a large fog-collection and distribution system in the
Anti-Atlas Mountains
The Anti-Atlas ( ar, الأطلس الصغير, shi, Aṭlas Mẓẓiyn), also known as Lesser Atlas or Little Atlas is a mountain range in Morocco, a part of the Atlas Mountains in the northwest of Africa. The Anti-Atlas extends from the Atlant ...
. The region DSH worked in is water-poor, but abundant fog drapes the area 6 months out of the year. DSH's system included technology that monitored the water system via
SMS
Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text ...
message. These capabilities were crucial in dealing with the effects of fog collection on the social fabric of these rural areas. According to
MIT
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...
researchers, the fog collection methods implemented by DSH have "improved the fog-collecting efficiency by about five hundred per cent."
International use
Despite the apparent failure of the fog collection project in Chungungo, the method has caught on in some localities around the world.
[Toutohghi]
Could Harvesting Fog Help Solve the World's Water Crisis?
''New Yorker''. March 25, 2015[Nield, Davi]
Yemen is fighting its severe water shortage by harvesting its fog
''Science Alert''. March 25, 2016 The International Organization for Dew Utilization organization is working on foil-based effective condensers for regions where rain or fog cannot cover water needs throughout the year. Shortly after the initial success of the project, researchers from the participating organizations formed the nonprofit organization FogQuest, which has set up operational facilities in
Yemen
Yemen (; ar, ٱلْيَمَن, al-Yaman), officially the Republic of Yemen,, ) is a country in Western Asia. It is situated on the southern end of the Arabian Peninsula, and borders Saudi Arabia to the Saudi Arabia–Yemen border, north and ...
and central
Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
, while still others are under evaluation in
Guatemala,
Haiti, and
Nepal
Nepal (; ne, :ne:नेपाल, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne,
सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in S ...
, this time with much more emphasis on the continuing involvement of the communities in the hopes that the projects will last well into the future. Villages in a total of 25 countries worldwide now operate fog collection facilities. There is potential for the systems to be used to establish dense vegetation on previously arid grounds. It appears that the inexpensive collectors will continue to flourish.
See also
*
Air well (condenser)
An air well or aerial well is a structure or device that collects water by promoting the condensation of moisture from air. Designs for air wells are many and varied, but the simplest designs are completely passive, require no external energy s ...
*
Atmospheric water generator
*
Cloud seeding
*
Water resources
References
Sources
International Development Research Centre article on the fog collection project
Further reading
*
*
*
External links
Fog Harvesting chapter from ''Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean'',
UNEP
The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the United Nations Conference on ...
International Environmental Technology Centre
*
FogQuest: Sustainable Water Solutions Canadian organization, historical information on fog collection projects in developing countries
*
at USGS installation in Hawaii
Fog Harvesting chapter from ''Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean'',
UNEP
The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the United Nations Conference on ...
International Environmental Technology Centre
The Fog Collectors: Harvesting Water From Thin AirFogQuest: Sustainable Water Solutions Canadian organization, historical information on fog collection projects in developing countries
Water supply
Hydrology
Appropriate technology
{{Wikiversity, Rainwater harvesting/Fog harvesting