Seawater greenhouse

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A seawater greenhouse is a greenhouse structure that enables the growth of crops and the production of fresh water in arid regions which constitute about one third of the Earth's land area. This in response to global water scarcity, peak water and soil becoming salted. [1] The system uses seawater and solar energy, and has a similar structure to the pad-and-fan greenhouse, but with additional evaporators and condensers. [1] The seawater is pumped into the greenhouse to create a cool and humid environment, the optimal conditions for the cultivation of temperate crops. [1] The freshwater is produced in a condensed state created by the solar desalination principle, which removes salt and impurities. [2] Finally, the remaining humidified air is expelled from the greenhouse and used to improve growing conditions for outdoor plants.

Contents

Projects

The Seawater Greenhouse Ltd

The seawater greenhouse concept was first researched and developed in 1991 by Charlie Paton's company Light Works Ltd, which is now known as the Seawater Greenhouse Ltd. Charlie Paton and Philip Davies worked on the first pilot project commenced in 1992, on the Canary Island of Tenerife. A prototype seawater greenhouse was assembled in the UK and constructed on the site in Tenerife covering an area of 360 m2. [1] The temperate crops successfully cultivated included tomatoes, spinach, dwarf peas, peppers, artichokes, French beans, and lettuce.

The second pilot design was installed in 2000 on the coast of Al-Aryam Island, Abu Dhabi, United Arab Emirates. The design is a light steel structure, similar to a multi-span polytunnel, which relies purely on solar energy. A pipe array is installed to improve the design of the greenhouse by decreasing the temperature and increasing the freshwater production. [3] The greenhouse has an area of 864 m2 and has a daily water production of 1 m3, which nearly meets the crop's irrigation demand. [1]

The third pilot seawater greenhouse, which is 864 m2, is near Muscat in Oman which produces 0.3 to 0.6 m3 of freshwater per day. This project was created as a collaboration between Sultan Qaboos University. It provides an opportunity to develop a sustainable horticultural sector on the Batinah coast. These projects have enabled the validation of a thermodynamic simulation model which, given appropriate meteorological data, accurately predicts and quantifies how the seawater greenhouse will perform in other parts of the world. [4]

The fourth project is the commercial installation in Port Augusta, Australia, installed in 2010. It is currently a 20 hectare seawater greenhouse owned and run by Sundrop Farms which has developed it further. [3] [5]

The fifth design was constructed in 2017 in Berbera, Somaliland. [6] The design was researched to be simplified and inexpensive with advanced greenhouse modeling techniques. This design includes a shading system which retains core evaporative cooling elements. [6]

Sahara Forest Project

The Sahara Forest Project (SFP) combines the seawater greenhouse technology and concentrated solar power and constructed pilot projects in Jordan and Qatar. The seawater greenhouse evaporates 50 m3 of seawater and harvests 5 m3 of fresh water per hectare per day. [7] The solar power production capacity through PV panels produces 39 KW on the 3 hectares area with 1350 m2 growing area. [8] The greenhouses are 15 degrees cooler than the outside temperatures which enables the production up to 130,000 kg vegetables produced per year and up to 20,000 liters of fresh water production per day. [8] Additionally, the project includes revegetation by soil reclamation of nitrogen-fixing and salt-removing desert plants by repurposed waste products from agriculture and saltwater evaporation. [8]

Process

A seawater greenhouse uses the surrounding environment to grow temperate crops and produce freshwater. A conventional greenhouse uses solar heat to create a warmer environment to allow adequate growing temperature, whereas the seawater greenhouse does the opposite by creating a cooler environment. The roof traps infrared heat, while allowing visible light through to promote photosynthesis.

The design for cooling the microclimate primarily consists of humidification and dehumidification (HD) desalination process or multiple-effect humidification. [9] A simple seawater greenhouse consists of two evaporative coolers (evaporators), a condenser, fans, seawater and distilled water pipes and crops in between the two evaporators. [10] This is shown in schematic figures 1 and 2.

Figure 1. Front of Seawater Greenhouse on coast, Tenerife, 22 August 2011 Seawater Greenhouse newly installed in Tenerife.jpg
Figure 1. Front of Seawater Greenhouse on coast, Tenerife, 22 August 2011
Figure 2. Back of Seawater Greenhouse on coast, Tenerife, 22 August 2011 Seawater Greenhouse in Tenerife two years after being installed.jpg
Figure 2. Back of Seawater Greenhouse on coast, Tenerife, 22 August 2011

The process recreates the natural hydrological cycle within a controlled environment of the greenhouse by evaporating water from saline water source and regains it as freshwater by condensation. [1] The first part of the system uses seawater, an evaporator, and a condenser. The front wall of the greenhouse consists of a seawater-wetted evaporator which faces the prevailing wind. These are mostly constituted of corrugated cardboard shown in Figure 3. If the wind is not prevalent enough, fans blow the outside air through the evaporator into the greenhouse. The ambient warm air exchanges the heat with the seawater which cools it down and gets it humidified. [10] [1] The cool and humid air creates an adequate growing environment for the crops. The remaining evaporatively-cooled seawater is collected and pumped to the condenser as a coolant. [1]

Figure 3: Seawater Greenhouse Cardboard 1-s2.0-S0011916417302400-gr2.jpg
Figure 3: Seawater Greenhouse Cardboard

The second part of the system has another evaporator. The seawater flows from the first evaporator which preheats it and thereafter flows through the solar thermal collector on the roof to heat it up sufficiently before it flows to the second evaporator. [10] The seawater, or coolant, flows through a circuit consisting of the evaporators, solar heating pipe, and condenser with an intake of seawater and an output of fresh water. The fresh water is produced by hot and relatively high humidity air which can produce sufficient distilled water for irrigation. [10] The volume of fresh water is determined by air temperature, relative humidity, solar radiation and the airflow rate. These conditions can be modeled with appropriate meteorological data, enabling the design and process to be optimized for any suitable location.

Applicability

The technique is applicable to sites in arid regions near the sea. The distance and elevation from the sea must be evaluated considering the energy required to pump water to the site. There are numerous suitable locations on the coasts; others are below sea level, such as the Dead Sea and the Qattara Depression, where hydro schemes have been proposed to exploit the hydraulic pressure to generate power, e.g., Red Sea–Dead Sea Canal. [16] [17]

Studies

In 1996, Paton and Davies used the Simulink toolkit under MATLAB to model forced ventilation of the greenhouse in Tenerife, Cape Verde, Namibia, and Oman. [18] The greenhouse is assisted by the prevailing wind, evaporative cooling, transpiration, solar heating, heat transfer through the walls and roof, and condensation which is analyzed in the study. [18] They found that the amount of water required by the plants is reduced by 80% and 2.6-6.4 kWh electrical energy is needed for m3 of fresh water produced. [18]

In 2005, Paton and Davis Evaluated design options with thermal modeling using the United Arab Emirates model as a baseline. [19] They studied three options:perforated screen, C-shaped air path, and pipe array, to find a better seawater circuit to cool the environment and produce the most freshwater. The study found that a pipe array gave the best results: an air temperature decrease of 1 °C, a mean radiant temperature decrease of 7.5 °C, and a freshwater production increase of 63%. This can be implemented to improve seawater greenhouses in hot arid regions such as the second pilot design in the United Arab Emirates. [19]

In 2018, Paton and Davis researched brine utilization for cooling and salt production in wind-driven seawater greenhouses to design and model it. The brine disposed by the seawater desalination may disturb the ecosystem as the same amount of brine is produced as freshwater. [5] By using the brine valoristation method of wind-driven air flow by cooling the greenhouse with seawater evaporation, salt can be produced as shown in Figure 4. [5] This brine is the by-product of the freshwater production, but can also be the ingredient to make salt, making it into a product that can be merchandised.

Figure 4: basic concept of seawater greenhouse for brine utilisation. 1-s2.0-S0011916417302400-gr1.jpg
Figure 4: basic concept of seawater greenhouse for brine utilisation.

An additional finding of this research was the importance of the shade-net which is modelled by a thin film in the study shown in Figure 5. [5] It not only provides cooling, but also elongates the cooling plume by containing the cold air plume from the evaporative cooling pad. [5]

Figure 5: Geometric model of shade net for pressure drop determination showing (a) local co-ordinate system and (b) symmetry planes (dotted lines) used to simplify modelling. 1-s2.0-S0011916417302400-gr6.jpg
Figure 5: Geometric model of shade net for pressure drop determination showing (a) local co-ordinate system and (b) symmetry planes (dotted lines) used to simplify modelling.

See also

Related Research Articles

<span class="mw-page-title-main">Brine</span> Concentrated solution of salt in water

Brine is water with a high-concentration solution of salt. In diverse contexts, brine may refer to the salt solutions ranging from about 3.5% up to about 26%. Brine forms naturally due to evaporation of ground saline water but it is also generated in the mining of sodium chloride. Brine is used for food processing and cooking, for de-icing of roads and other structures, and in a number of technological processes. It is also a by-product of many industrial processes, such as desalination, so it requires wastewater treatment for proper disposal or further utilization.

<span class="mw-page-title-main">Desalination</span> Removal of salts from water

Desalination is a process that takes away mineral components from saline water. More generally, desalination is the removal of salts and minerals from a target substance, as in soil desalination, which is an issue for agriculture. Saltwater is desalinated to produce water suitable for human consumption or irrigation. The by-product of the desalination process is brine. Desalination is used on many seagoing ships and submarines. Most of the modern interest in desalination is focused on cost-effective provision of fresh water for human use. Along with recycled wastewater, it is one of the few rainfall-independent water resources.

Geothermal desalination refers to the process of using geothermal energy to power the process of converting salt water to fresh water. The process is considered economically efficient, and while overall environmental impact is uncertain, it has potential to be more environmentally friendly compared to conventional desalination options. Geothermal desalination plants have already been successful in various regions, and there is potential for further development to allow the process to be used in an increased number of water scarce regions.

<span class="mw-page-title-main">Forward osmosis</span> Water purification process

Forward osmosis (FO) is an osmotic process that, like reverse osmosis (RO), uses a semi-permeable membrane to effect separation of water from dissolved solutes. The driving force for this separation is an osmotic pressure gradient, such that a "draw" solution of high concentration, is used to induce a net flow of water through the membrane into the draw solution, thus effectively separating the feed water from its solutes. In contrast, the reverse osmosis process uses hydraulic pressure as the driving force for separation, which serves to counteract the osmotic pressure gradient that would otherwise favor water flux from the permeate to the feed. Hence significantly more energy is required for reverse osmosis compared to forward osmosis.

<span class="mw-page-title-main">Solar still</span> Water distillation and purification system using solar energy

A solar still distills water with substances dissolved in it by using the heat of the Sun to evaporate water so that it may be cooled and collected, thereby purifying it. They are used in areas where drinking water is unavailable, so that clean water is obtained from dirty water or from plants by exposing them to sunlight.

Solar desalination is a desalination technique powered by solar energy. The two common methods are direct (thermal) and indirect (photovoltaic).

An atmospheric water generator (AWG), is a device that extracts water from humid ambient air, producing potable water. Water vapor in the air can be extracted either by condensation - cooling the air below its dew point, exposing the air to desiccants, using membranes that only pass water vapor, collecting fog, or pressurizing the air. AWGs are useful where potable water is difficult to obtain, because water is always present in ambient air.

The solar humidification–dehumidification method (HDH) is a thermal water desalination method. It is based on evaporation of sea water or brackish water and subsequent condensation of the generated humid air, mostly at ambient pressure. This process mimics the natural water cycle, but over a much shorter time frame.

<span class="mw-page-title-main">Dewvaporation</span> Desalination technology

Dewvaporation is a novel desalination technology developed at Arizona State University (Tempe) as an energy efficient tool for freshwater procurement and saline waste stream management. The system has relatively low installation costs and low operation and maintenance requirements.

<span class="mw-page-title-main">Evaporator</span> Machine transforming a liquid into a gas

An evaporator is a type of heat exchanger device that facilitates evaporation by utilizing conductive and convective heat transfer to provide the necessary thermal energy for phase transition from liquid to vapor. Within evaporators, a circulating liquid is exposed to an atmospheric or reduced pressure environment, causing it to boil at a lower temperature compared to normal atmospheric boiling.

<span class="mw-page-title-main">Evaporation pond</span>

Evaporation ponds are artificial ponds with very large surface areas that are designed to efficiently evaporate water by sunlight and expose water to the ambient temperatures. Evaporation ponds are inexpensive to design making it ideal for multiple purposes such as wastewater treatment processes, storage, and extraction of minerals. Evaporation ponds differ in usage and result in a wide range of environmental and health effects.

A solar-powered desalination unit produces potable water from saline water through direct or indirect methods of desalination powered by sunlight. Solar energy is the most promising renewable energy source due to its ability to drive the more popular thermal desalination systems directly through solar collectors and to drive physical and chemical desalination systems indirectly through photovoltaic cells.

Reverse osmosis (RO) is a water purification process that uses a semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distributions. RO can remove dissolved or suspended chemical species as well as biological substances, and is used in industrial processes and the production of potable water. RO retains the solute on the pressurized side of the membrane and the purified solvent passes to the other side. It relies on the relative sizes of the various molecules to decide what passes through. "Selective" membranes reject large molecules, while accepting smaller molecules.

<span class="mw-page-title-main">Desert greening</span> Process of man-made reclamation of deserts

Desert greening is the process of afforestation or revegetation of deserts for ecological restoration (biodiversity), sustainable farming and forestry, but also for reclamation of natural water systems and other ecological systems that support life. The term "desert greening" is intended to apply to both cold and hot arid and semi-arid deserts. It does not apply to ice capped or permafrost regions. It pertains to roughly 32 million square kilometres of land. Deserts span all seven continents of the Earth and make up nearly a fifth of the Earth's landmass, areas that recently have been increasing in size. As some of the deserts expand and global temperatures increase, the different methods of desert greening may provide a potential solution. Planting suitable flora in deserts has a range of environmental benefits from carbon sequestration to providing habitat for native desert fauna to generating employment opportunities to creation of habitable areas for local communities. The prevention of land desertification is one of 17 sustainable development objectives outlined by the United Nations, desert greening is a process that aims to not only combat desertification but to foster an environment where plants can create a sustainable environment for all forms of life while preserving its integrity.

<span class="mw-page-title-main">Evaporator (marine)</span> Fresh water production device

An evaporator, distiller or distilling apparatus is a piece of ship's equipment used to produce fresh drinking water from sea water by distillation. As fresh water is bulky, may spoil in storage, and is an essential supply for any long voyage, the ability to produce more fresh water in mid-ocean is important for any ship.

Membrane distillation (MD) is a thermally driven separation process in which separation is driven by phase change. A hydrophobic membrane presents a barrier for the liquid phase, allowing the vapour phase to pass through the membrane's pores. The driving force of the process is a partial vapour pressure difference commonly triggered by a temperature difference.

<span class="mw-page-title-main">Concentrated solar still</span> High-output water distillation and purification system using solar energy

A concentrated solar still is a system that uses the same quantity of solar heat input as a simple solar still but can produce a volume of freshwater that is many times greater. While a simple solar still is a way of distilling water by using the heat of the sun to drive evaporation from a water source and ambient air to cool a condenser film, a concentrated solar still uses a concentrated solar thermal collector to concentrate solar heat and deliver it to a multi-effect evaporation process for distillation, thus increasing the natural rate of evaporation. The concentrated solar still is capable of large-scale water production in areas with plentiful solar energy.

Sundrop Farms is a developer, owner and operator of high tech greenhouse facilities which grow crops using methods which reduce reliance on finite natural resources when compared to conventional greenhouse production. Sundrop Farms opened its first pilot facility in Port Augusta, South Australia, in 2010. This facility was originally designed as a Seawater Greenhouse. However, significant technology changes led to the Sundrop System, and the dissolution of the joint venture with Seawater Greenhouse Ltd. Sundrop Farms commissioned an expanded 20 ha facility south of Port Augusta in 2016. Sundrop Farms has offices in London, UK and Adelaide, Australia. In October 2016, Sundrop Farms was operating greenhouses in Portugal, the United States and had another facility planned in Australia.

The low-temperature distillation (LTD) technology is the first implementation of the direct spray distillation (DSD) process. The first large-scale units are now in operation for desalination. The process was first developed by scientists at the University of Applied Sciences in Switzerland, focusing on low-temperature distillation in vacuum conditions, from 2000 to 2005.

The IBTS greenhouse is a biotectural, urban development project suited for hot arid deserts. It was part of the Egyptian strategy for the afforestation of desert lands from 2011 until spring of 2015, when geopolitical changes like the Islamic State of Iraq and the Levant – Sinai Province in Egypt forced the project to a halt. The project begun in spring 2007 as an academic study in urban development and desert greening. It was further developed by N. Berdellé and D. Voelker as a private project until 2011. Afterwards LivingDesert Group including Prof. Abdel Ghany El Gindy and Dr. Mosaad Kotb from the Central Laboratory for Agricultural Climate in Egypt, Forestry Scientist Hany El-Kateb, Agroecologist Wil van Eijsden and permaculturist Sepp Holzer was created to introduce the finished project in Egypt.

References

  1. 1 2 3 4 5 6 7 8 Abdulrahim M.Al-Ismaili & Hemanatha Jayasuriya (2016). "Seawater greenhouse in Oman: A sustainable technique for freshwater conservation and production". Desalination. Elsevier. 54: 653–664. doi:10.1016/j.desal.2004.06.211 . Retrieved 2020-12-17.
  2. ↑ M.H.El-Awady; H.H.El-Ghetany & M. AbdelLatif (2014). "Experimental Investigation of an Integrated Solar Green House for Water Desalination, Plantation and Wastewater Treatment in Remote Arid Egyptian Communities". Desalination. Elsevier. 50: 520–527. doi:10.1016/j.desal.2004.06.211 . Retrieved 2020-12-17.
  3. 1 2 P. A. Davies & C. Paton (2005). "The Seawater Greenhouse in the United Arab Emirates: thermal modelling and evaluation of design options". Desalination. Elsevier. 173 (2): 103–111. doi:10.1016/j.desal.2004.06.211 . Retrieved 2015-11-03.
  4. ↑ C. Paton & P. Davies (1996). "The Seawater Greenhouse for Arid Lands". doi:10.1016/j.desal.2004.06.211 . Retrieved 2020-12-17.{{cite journal}}: Cite journal requires |journal= (help)
  5. 1 2 3 4 5 6 T. Akinaga; S.C.Generalis; C.Paton; O.N.Igobo & P.A.Davies (2018). "Brine utilisation for cooling and salt production in wind-driven seawater greenhouses: Design and modelling". Desalination. Elsevier. 426: 135–154. doi:10.1016/j.desal.2004.06.211 . Retrieved 2020-12-17.
  6. 1 2 "Low-cost, rugged and modular". Seawater Greenhouse Ltd. 2017. Retrieved 2020-12-16.
  7. ↑ Yeang, Ken & Pawlyn, Michael (2009). "The Seawater Greenhouse for Arid Lands". Architectural Design. 79: 122–123. doi:10.1016/j.desal.2004.06.211 . Retrieved 2020-12-17.
  8. 1 2 3 "Enabling Restorative Growth" (PDF). Sahara Forest Project. Retrieved 16 December 2020.
  9. ↑ Al-Ismaili & Abdulrahim M (2014). "Empirical Model for the Condenser of the Seawater Greenhouse". Chemical Engineering Communications. Taylor and Francis. 205: 1252–1260. doi:10.1016/j.desal.2004.06.211 . Retrieved 2020-12-17.
  10. 1 2 3 4 Taleb Zarei; Reza Behyad & Ehsan Abedini (2018). "Study on parameters effective on the performance of a humidification-dehumidification seawater greenhouse using support vector regression". Desalination. Elsevier. 435: 235–245. doi:10.1016/j.desal.2004.06.211 . Retrieved 2020-12-17.
  11. ↑ Mahmoudi, H.; Abdul-wahab, S. A.; Goosen, M. F. A.; Ouaged, A.; Sablani, S. S.; Spahis, N. (2007). "Wind energy systems adapted to the seawater greenhouse desalination". Revue des Energies Renouvelables. 10 (1): 19–30. CiteSeerX   10.1.1.533.6677 .
  12. ↑ Ford, Jason (1 March 2012). "Greenhouse uses seawater to grow crops in arid places". The Engineer. Retrieved 7 December 2021.
  13. ↑ Klein, Alice (14 October 2016). "First farm to grow veg in a desert using only sun and seawater". New Scientist . Retrieved 7 December 2021.
  14. ↑ Watts, Geoff (September 2019). "Farming in the desert". Ingenia . ingenia.org.uk. Retrieved 7 December 2021. Charlie Paton is Founder and Director of Seawater Greenhouse. He studied at the Central School of Art and Design in London and began his career as a lighting designer and maker of special effects. His fascination with light and plant growth led to the Seawater Greenhouse concept. Charlie was recognised as a Royal Designer for Industry by the Royal Society of Arts, Manufactures and Commerce.
  15. ↑ "Sahara Forest". Buckminster Fuller Institute . Retrieved 7 December 2021.
  16. ↑ "Managing water for peace in the Middle East". archive.unu.edu.
  17. ↑ "Pipe Headloss & Power calculator - calculate how much energy to pump seawater to the middle of the Sahara or Gobi Desert for desalination in the SeaWater Greenhouse - answer not a lot. - Claverton Group". claverton-energy.com.
  18. 1 2 3 C. Paton & P. Davies (1996). "The Seawater Greenhouse for Arid Lands". doi:10.1016/j.desal.2004.06.211 . Retrieved 2020-12-17.{{cite journal}}: Cite journal requires |journal= (help)
  19. 1 2 P. A. Davies & C. Paton (2005). "The Seawater Greenhouse in the United Arab Emirates: thermal modelling and evaluation of design options". Desalination. Elsevier. 173 (2): 103–111. doi:10.1016/j.desal.2004.06.211 . Retrieved 2015-11-03.
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