SALTWATER-COOLED GREENHOUSE

SALTWATER-COOLED-GREENHOUSE

Water water everywhere but not a drop to drink!

See also: Part I – water is politics – pdf

Shortages of drinking water and increasingly polluted irrigation water is increasingly common in many parts of the world. The Seawater Greenhouse heralded the beginning of a new way of utilizing seawater and sunshine, abundant in various parts of the world, to produce fresh water, energy and food. CEO and inventor Charlie Paton (below Picture)

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Greenhouses that will use seawater to grow crops in one of the hottest and driest places on earth will be designed by researchers at Aston University working with industry partners as part of an international project. Extract from a Press Release from Ashton University 14th July 2015.

The £722k greenhouse project in the Horn of Africa is funded by Innovate UK with support from the DFID: Department for International Development under the Agri-tech Catalyst Industrial Research strategy. The installations are to be erected in specially selected sites across the Horn of Africa, a region where temperatures regularly breach 40°C, water is scarce and food insecurity is very high.

 getresource

The project aims to overcome the region’s inhospitable conditions to help farmers drastically increase their crop yields, providing them with a consistent, sustainable income. Currently in Somalia average annual crop yields per hectare are just 0.5 tons – compared to 700 tons per hectare in commercial greenhouses.

The productivity and quality of crops cultivated in greenhouses is typically much improved upon traditional open field cultivation and the use of water and nutrients is much more economical. Once installed, the innovative greenhouses will pump seawater from the sea using solar energy and convert it into freshwater for irrigation via the desalination process. The remaining seawater will be brought into contact with the air inside the low-cost net structures of the greenhouses, creating a cool and humid breeze to reduce plant transpiration. Salt extracted from the seawater will be utilised in cooking and preserving food.

A team from Aston, led by Dr Philip Davies and Dr Sotos Generalis, will provide their expertise in areas relating to seawater cooling, desalination of saline water and airflow dynamics, helping to design the structure and the layout of the greenhouses. They will collaborate on the project with fellow academics at Gollis University, in Somaliland, and the firm, Seawater Greenhouses Ltd that is leading the whole project.

For further media information, please contact Jonathan Garbett, Aston University Communications on 0121 204 4552 or j.garbett@aston.ac.uk.

Q.3 What are the costs and economics of employing the seawater greenhouse technology?

The Seawater Greenhouse is today a proven technology although it has not yet realized its potential in those areas of the world most indicated.  Design specifications vary according to climatic conditions, grower requirements, irrigation system, local materials and labour. Greenhouse cladding can be polythene, rigid plastic or glass. This means that the cost of installation is variable from USD50 – 150/m2.  Average comparisons between the operation of a 2ha unit of Seawater Greenhouse indicates a potential reduction of fixed costs of 10-15%, lower operating costs of 10-25% and improved returns of 15-35% against a traditional greenhouse of the same size (clad in plastic or glass).  A thermodynamic model is used to predict the most effective solution.

Q.4 What are the technical principles behind the Seawater Greenhouse?

Essentially, a fan draws hot dry air from the outside across an evaporator set into one of the outside walls of the greenhouse. Surface seawater is pumped to the top of the evaporator and trickles down its mesh surface. In the process the air is cooled and humidified.  It is also filtered from salt spray, dust, insects and pollen before entering the greenhouse. The seawater is then channelled through a pipe at ground level to a second evaporator.

Hot dry air from between two layers of the roof (the lower layer being a partial screen) is pulled in by a fan and pushed in by the prevailing wind towards a second evaporator.  The meeting of cooler, humid air with the hot, dry upper air increases its ability to absorb moisture before reaching the second evaporator, where it picks up more water vapor to the saturation point. Pure water then condenses onto the cold surface of the condenser. This is collected and passed to a storage tank for use as irrigation water for the plants or for drinking purposes. Other crops such as fruit trees (or Jatropha for biodiesel) can be grown in the outside now more humid air at the other end of the Seawater Greenhouse.

Under these warm humid greenhouse conditions, plants grow very quickly and their demand for water therefore drops. In the prototype this fell to 1 litre/day/m2, compared to 8 litres/day/m2 in conventional protected cultivation. Solar panels power pumps and fans. Other Seawater Greenhouses are planned for North Africa and Caribbean region after successful trials in Tenerife, Abu Dhabi and Oman. www.seawatergreenhouse.com

Q.5 What do you do with the super-saturated salt solution (brine) at the end of the process and is there no legislation to reduce this environmental pollution?

Importantly, instead of discharging super-saturated salt solution (brine) back into the sea, the Seawater Greenhouse can recover sea-salt and make it a sought-after, saleable product. The discharge of brine from the large desalination plants located around the world continue to  seriously damage large areas of coastal ecosystems. In 2008 about 18.4 million m3/day of brine were discharged into the Arabian Gulf,  9.8 million m3/day into the Mediterranean and 6.8 m3/day into the Red Sea. The reduced inflow on fresh water from rivers such as the Euphrates, Tigris and Jordan worsens the situation.

Some countries now have strict legislation forcing desalination plants to construct long pipelines for discharging the brine far out to sea and not along the ecologically more sensitive coastal ecosystems. However, this is not enough to stop the increasing saline pollution of many of our seas. See: Global Water Forum 2012 http://www.globalwaterforum.org/2012/05/28/seawater-greenhouse-a-new-approach-to-restorative-agriculture/

Since the incoming air is filtered and sterilised, biological production can be more easily achieved with the SG and by using soilless cultivation systems cheap degraded land is sufficient.  It also opens up the possibility of producing all-year-round food crops and drinking water in some of the world’s hottest and driest regions, especially along coastal regions.

Q.6  How can evaporative cooling and concentrated solar power by harnessed together?

The latest 2000m2 pilot plant at Port Augusta in Southern Australia, operated by Sundrop Farms Pty Ltd has become the world’s first fully commercial Seawater-cooled Greenhouse. In reality, the Sundrop pilot plant has significantly modified the original Seawater Greenhouse technology, adding CSP technology (concentrated solar power) to create electricity. A 70m stretch of concave mirrors follow the sun and concentrate solar energy on thermal oil running along a tube heating it to 160°C. This oil is conducted to a heat exchanger. The resulting steam drives turbines that produce electricty.

The remaining brine from the desalination is conducted to ponds where ‘gourmet’ sea-salt and other minerals (such as Calcium, Potassium and Magnesium) are extracted for use in production or sold to other interests. Sea algae can also provide  additional nutrients.  Soilless cultivation (rockwool/hydroculture) is used and the greenhouse air is cooled and humidified by passing cool seawater over evaporative panels. This reduces the air temperature by up to 15°C  compared to the outside. At the other end of the greenhouse water vapour is condensed. Some is used to irrigate the growing crop, part is harvested as drinking water, some is used for the steam turbine and to clean the array mirrors. Solar energy is used to power all other operations (heating and cooling) in the greenhouse. A diesel powered generator is required only for very short period in the winter to make up any shortfall.

The Seawater Greenhouse/Sundrop pilot plant received a grant from the (RDIF) Regional Development Infrastructure Fund from Southern Australia.  It has proved so successful that a further 8ha is planned for 2013 at the same locality. It is estimated that some 5000kg of tomatoes and sweet peppers will be produced each week for 12 months of the year (about 4000 tons/year) and the productivity is high. Further developments could move in the direction of adding algae and fish to the productive output.

The capital costs of incorporating CSP technology into the system is very expensive and financial support is necessary. Thereafter, operating costs are reduced by 10-15%. In general terms, the higher the investment the greater the productivity and profitability. It is most suitable for hot, dry climates on low land near the sea and interest has been expressed from many countries, especially in the Middle East. Sundrop Farms See Video

Political decisions should try to utilize all available environmentally friendly technologies, matching these technologies with diverse local needs and possibilities of extraction and distrubution of fresh water. Now that some desalination plants in the Canaries need replacing or that greater quantities of fresh water are needed, cannot the Seawater Greenhouse feature in future plans, perhaps alongside stand-alone technology being developed by the ITC (Canary Islands Institute of Technology)?

Q.7  How can the saltwater-cooled greenhouse technology lead to a greening of desert coastlines extending further inland?

The Sahara Forest Project AS is a Norwegian private limited liability company for providing a new environmental solution to produce food, water and energy in desert areas.  The Project combines proven technologies, including saltwater-cooled greenhouses, concentrated solar power (CSP) and technologies for desert revegetation around a saltwater infrastructure. The synergy from integrating the separate technologies into a system improves their individual performance and economics. The government of Jordan has also agreed to a direct future involvement in the project and Sundrop Farms Pty Ltd has signed a collaborative agreement with the consortium.  Sahara Forest Project

Sahara Forest Project

In December 2012, the new 1ha Sahara Forest Project pilot facility (above picture*) near Doha, Qatar, realized by The Sahara Forest Project and partners Yara International Asa www.yara.com, Quafco (Quatar fertilizer Company) www.qafco.com, was venue for guests attending the COP18 (UN Climate Negotiations in Doha). On this occasion visitors were served the first cucumbers grown by the pilot facility. This facility also includes an extensive algae research centre. *Courtesy of Sahara Forest Project.

Edward Bent ©2012 | HORTCOM

One Response to SALTWATER-COOLED GREENHOUSE

  1. Pingback: Sahara Forest Project | hortcom

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