The Seawater Greenhouse creates a new source of fresh water derived from seawater, and a climate that is suited for growing plants, both within and beyond the greenhouse structure. It enables the cultivation of crops in hot and arid regions of the world.
The process uses sunlight and seawater to enable the supply of food, energy and fresh water. The ventilation air, driven by the prevailing wind is cooled, cleaned, sterilized and humidified by seawater evaporators. This creates a climate that enables crops to grow in areas which normally do not provide the right conditions due to high temperatures, a lack of fresh water or both.
Only pure water evaporates, and the seawater is reduced to concentrated brine, which is further evaporated outside the greenhouse to yield salt and other minerals.
Evaporating seawater and cooling the air in the process is much simpler and cheaper than desalination. At the same time the outcome is the same if not greater, as the volume of water lost through plant transpiration is reduced by 10-fold or more. Plants that are not stressed by excessive transpiration grow faster and produce higher yields.
The project is applicable in some of the most water-stressed parts of the world and can play an important role in preventing water and food based conflicts.
Virtuous feedback on microclimate conditions enables increased rain and humidity. An area covered with greenhouses has a similar effect on the climate as an area covered by forest in terms of heat absorption and water evaporation.
Research suggests that re-vegetation of deserts would have a number of beneficial impacts. This has been ascertained by considering the many varied processes and resources of ecosystems that provide a multitude of benefits to humankind. Ecosystem services can range from regulating the climate to producing fuel and food.
The Seawater Greenhouse, like any conventional greenhouse, can provide many types of crop in response to market demand. But for the purpose of a simplified illustrative model, a unit of 1 hectare is chosen as a nominal size with favorable economies of scale and a capital cost of 1 million USD. A tomato crop is chosen as the most widely cultivated greenhouse crop.
A 1 hectare greenhouse will conservatively produce 500 tons of tomatoes per annum giving revenue of 0.5 million USD (at 1 USD/kg). Assuming an annual expenditure on labor and other inputs of 180,000 USD together with an overall allowance of 10% for depreciation, the pre-tax return is 15%.
Greenhouses by their nature have high up front capital costs. We envisage that once established, they will provide sufficient returns for investors.
Stage of development: ready for serial production
The cooler and more humid air that is released by the evaporators creates a climate where plants can grow well, needing only a fraction of the fresh water that they would need otherwise. The high rate of ventilation necessary for cooling results in large volumes of water laden air having a beneficial effect on the area downwind of the greenhouse. We have found that plants will grow spontaneously in these conditions, simply as a consequence of the enhanced water vapor, enhanced dewfall, lower temperature and protection from the wind provided by the greenhouse structure. It thus has a restorative effect, especially in areas where previously vegetation and forests had existed.