The Seawater Greenhouse, however, provides what may be an economical and sustainable way of producing fresh water and crops in hot, dry regions near the ocean, and has the potential to impact on the lives of millions of people living in water-starved areas. As conventional farming and climate change aggravates water and food shortages, a handful of entrepreneurs are growing food in the world’s driest regions. A seawater greenhouse produces crops year-round in hot dry areas using only seawater and sunlight. The award-winning technology, invented by Charlie Paton, was inspired by the natural water cycle where seawater heated by the sun evaporates, cools to form clouds, and returns to earth as precipitation. The humidification and de-humidification that result from differences in temperature between surfaces heated by the sun and cold water from the sea are the keys to the seawater greenhouse system.
How it Works
Seawater greenhouse acts as a cool house for growing crops while producing fresh water for irrigation. Ideally sited on flat, arid land close to the sea, seawater is pumped to the greenhouse and piped over honeycomb cardboard pads that provide a large surface area for evaporative cooling. The air cools, humidity increases and the now concentrated brine is discharged from the system. This can be used outside to cool evaporative hedges – honeycomb cardboard structures that cool passing air – reviving surrounding agriculture.
Seawater is pumped into pipes in the greenhouse and is trickled down over the first evaporator, a large spongy honeycomb-like surface. As air is drawn through the honeycomb and into the greenhouse by fans, it is cooled by the seawater and becomes more humid. The cool humid air creates favorable growing conditions for the greenhouse crops. At the back of the greenhouse, the cool air is drawn through a second evaporator containing seawater that has been heated by the sun in the ceiling pipes. The air then becomes hot and humid to the saturation point. When the hot humid air meets an array of vertical pipes containing cold seawater, fresh water condenses (just like hot steamy air in your shower condenses on the cooler mirror and tile surfaces). The fresh pure water is then piped to a storage container and used to irrigate the crops.
The sustainable system is clean, efficient, and elegant in its design. The greenhouse control system, pumps and fans are powered by electricity produced completely by solar power. The honeycomb evaporator filters out pollen and pests that are killed by the saline water so the greenhouse doesn’t need much pesticide. Nutrients harvested from the brine are pumped back into the irrigation system to fertilize the crops, and the rest of the salt is made into gourmet salt crystals that can be sold. According to Renee Cho, “the greenhouse produces its own fresh water, and uses no fossil fuels or pesticides, its operating costs are up to 25% less than those of a traditional greenhouse because it doesn’t need to purchase cooling, heating, or desalination equipment, and because it is usually built on cheap land where little can grow.”
The Future of Seawater Technology
As the world faces up to the challenges from population explosion which is forecast to increase from 7 billion to rise to over 9 billion by 2050, to water shortage and food security, this technological innovation offers real hope. To combat the challenges of food security, we need to rethink Agriculture in the 21st century, and work towards adopting more sustainable water supply systems. Seawater farming, as an example, addresses the severe lack of freshwater and undesirable soil conditions for agricultural activities in coastal regions. Saltwater, instead of freshwater, can be used to directly support a wide range of sustainable agricultural activities and enrich the soils in the coastal regions. On the other hand climate change extremities increasingly pose a threat to agricultural systems. Thus, new adaptive forms of sustainable water management in agriculture including irrigation, urban agriculture, aquaculture, and agroforestry must be explored and implemented in a comprehensive way.
In summary, to meet water and food challenges will require dynamic institutions and actions that can balance soil-water use efficiency that result to increased crop and animal productivity. Such institutions are required to play vital role in mitigating environmental externalities; device innovative soil and water management techniques. In addition, they should readily provide governance frameworks to enable key decision makers to accurately assess and respond to the growing water and food risks.
Case Study: Sahara Forest Project .