Seawater Greenhouse

Q: What do you do with the salt?
A: We make salt. Salt is used for hundreds of processes from making glass and plastic to preserving food and de-icing roads. The world market for salt is roughly 300 million metric tons per year. Table salt has the highest value, but it does require careful handling and packaging.

After the salt (Sodium Chloride) has been crystalised out of sea water, the remaining brine contains numerous minerals that can be further separated into useful products and even used as bath salts! These minerals can also provide all of the micro nutrients needed by plants providing they are balanced with other fertilizers in the correct ratios.

Q: Where will it work?
A: The Seawater Greenhouse works best in hot, arid and sunny conditions. Access to seawater and high solar intensity are essential. Such locations can be found in North Africa, India, the Middle East, southern United States, Mexico and Australia. Every metre of elevation above sea level adds seawater pumping costs, thus low lying coastal plains are ideal.

Q: Doesn’t agriculture in desert soils result in soil salinisation?
A: Soil salinity problems often occur when ground water is extracted from aquifers at a rate that exceeds natural recharge from rainfall. The Seawater Greenhouse makes its own supply of fresh water and thus has the potential to restore soils that have been damaged through salinisation.

Q: Will it work inland with brackish water?
A: Yes and no. Inland brackish water is often the result of over abstraction, and by using that water in the Seawater Greenhouse would accelerate its depletion and increase its salinity even more. However there are situations where it could work provided the rate of abstraction does not exceed the rate of recharge from rainfall.

Q: How much does it cost?
A: As a rule of thumb, $140/m2. However, it can be half or more than that, depending on scale, location and what the objectives are. As with any conventional greenhouse, there are many choices to be made regarding type of structure and cladding materials and how durable they need to be.

Q: What size does it have to be?
A: There is no fixed rule, but commercial greenhouses tend to be larger than 2,000m2 to be viable. In some countries, commercial viability is only reached at a scale of several hectares.

Q: How much water does it make?
A: Water production depends on the design and the climate conditions. It will always be able to make sufficient water for its own irrigation needs and producing a surplus is generally desirable. Water production can be increased by providing extra heat, say from solar panels or the waste heat from some other process, or by providing extra cooling. In some locations, very cold seawater can be found at a depth within a reasonable distance to the location. The best solution will always be location specific.

Q: How much power is needed?
A: The Seawater Greenhouse uses very little electrical power as most of the work of evaporative cooling and distillation is performed by the sun and the wind. However it does need electrical power for pumps and fans. Typically this is in the region of 2-3W / m2 or 20-30kW / hectare. Electrical power is only needed in the daytime which makes solar photovoltaic power an attractive option.