Researchers from the University of South Australia are working on a unique project that is centred around utilising the sun and the sea to create vertical sea farms that will float on the ocean and produce freshwater for drinking and agriculture.

This self-sustaining, solar-driven system that evaporates seawater and recycles it into freshwater is believed to be the first of its kind as it results in the growing of crops without any human involvement.

This could help address looming global shortages of freshwater and food in the decades ahead, with the world’s population expected to reach 10 billion by 2050.

UniSA’s Future Industries Institute Professor Haolan Xu and Dr Gary Owens have developed the vertical floating sea farm which is made up of two chambers — an upper layer similar to a glasshouse and a lower water harvest chamber.

Dr Owens said the system works similar to a wicking bed that household gardeners might be familiar with.

“However, in this case, clean water is supplied by an array of solar evaporators that soak up the seawater, trap the salts in the evaporator body and, under the sun’s rays, release clean water vapour into the air which is then condensed on water belts and transferred to the upper plant growth chamber.”

In a field test, the researchers grew three common vegetable crops — broccoli, lettuce, and bok choy — on seawater surfaces without maintenance or additional clean water irrigation.

The system, which is powered only by solar light, has several advantages over other solar sea farm designs currently being trialled, according to Professor Xu.

“Other designs have installed evaporators inside the growth chamber which takes up valuable space that could otherwise be used for plant growth. Also, these systems are prone to overheating and crop death,” Professor Xu says.

Floating farms, where traditional photovoltaic panels harvest electricity to power conventional desalination units, have also been proposed but these are energy intensive and costly to maintain.

“In our design, the vertical distribution of evaporator and growth chambers decreases the device’s overall footprint, maximising the area for food production. It is fully automated, low cost, and extremely easy to operate, using only solar energy and seawater to produce clean water and grow crops,” said Professor Xu.

Dr Owens stated that their design is only proof-of-concept at this stage, but the next step is to scale it up, using a small array of individual devices to increase plant production. Meeting larger food supply needs will mean increasing both the size and number of devices.

“It is not inconceivable that sometime in the future, you might see huge farm biodomes floating on the ocean, or multiple smaller devices deployed over a large sea area,” said Dr Owens.

Their existing prototype is likely to be modified to produce a greater biomass output, including using low-cost substrate materials such as waste rice straw fibre, to make the device even cheaper to run.

The researchers have shown that the recycled water produced in this way is pure enough to drink and has less salinity than the World Health Guidelines for drinking water.

The United Nations estimates that by 2050, approximately 2.4 billion people are likely to experience water shortages. In the same period, global supply of water for agricultural irrigation is expected to decline by around 19 per cent.

“Freshwater accounts for just 2.5 per cent of the world’s water and most of this is not accessible because it’s trapped in glaciers, ice caps or is deep underground.

“It’s not that freshwater is dwindling either, but the small amount that exists is in ever increasing demand due to population growth and climate change.

“The fact that 97.5 per cent of the world’s water is in our oceans – and freely available – it is an obvious solution to harness the sea and sun to address growing global shortages of water, food, and agricultural land. Adopting this technology could improve the health and welfare of billions of people globally,” said Dr Owens.

The design experiment is published in the Chemical Engineering Journal.