Solar Desalination in Arid Lands

Abstract

Freshwater consumption has already exceeded natural replenishment in many parts of the world. With a constant population growth, this unbalance does nothing but to accelerate. Being agriculture the largest water consumer, food production will be extremely challenging in the future; particularly in the most arid regions of the world. Migration to the cities will continue, and by the year 2050 about half of world’s population will live within 200 kilometers of the coast. This situation will undoubtedly make of seawater desalination an attractive alternative. However practically all desalination techniques are energy-intensive and produce large volumes of saline waste; both with potential environmental implications. To date, less than 1% of the roughly 20,000 desalination plants worldwide are powered by renewable energy directly, the reminder relies on fossil-fuels or the power grid (which also heavily relies on non-renewable energy sources in most countries). In this context, a growth in global desalination capacity, will also mean an increase in global CO2 emissions. In addition, current waste management by most desalination plants essentially consists of returning brine back to the environment. Therefore, an increase in desalination capacity in coastal areas, will also add to the stressors of marine ecosystems; which already include over-exploitation, pollution and climate change. With the objective of exploring sustainable desalination alternatives for the future, this work performed a literature review of large-scale solar thermal desalination, their integration to concentrating solar power plants and its potential implementation in the Sonoran Desert. In addition, this work proposed and mathematically evaluated a hybrid desalination unit (HDU) powered by high concentration photovoltaics with thermal collection capability for remote non-serviced homes at the Navajo Nation. As discussed in this work, the combination of solar power tower plants with thermal desalination can provide electricity and water at the same time cost-competitively and with a possibility of zero-liquid discharge (ZLD). It is also shown that this technological integration has the potential to secure water and electricity for Arizona, through binational desalination plants in the Sea of Cortez, with minimal environmental impact. In addition, experimental results from modeling the proposed HDU show that these units can offer potable water at nearly half the cost of hauling it at the Navajo Nation. Furthermore, it is shown that these units can double the amount of water available, offer ZLD, deliver a surplus of electric power and provide the means for growing food all year round.