Water scarcity is one of the biggest problems facing the world today. An essential but limited resource, fresh water makes up only 3 percent of the Earths water resources and of this 3 percent, two thirds are locked up in ice caps and glaciers and a fifth is located in remote areas where they are not easily accessible.
All in all, of the available freshwater in the world, only 0.08 percent is available for use. And this 0.08 percent is needed by billion for sanitation and drinking purposes, not to mention for economic activities in the manufacturing, industrial and agricultural sectors.
With global demand for water increasing, freshwater sources are becoming more and more scarce. In contrast, salt water found in the world’s oceans makes up 97 percent of the Earth’s water. One possible solution to the lack of naturally available freshwater would be to create fresh water supplies from seawater or brackish water through desalination.
Meeting demand with new sources of freshwater
Desalination is the removal of sale and minerals from seawater and brackish water. This can make salt water suitable for human consumption as well as in human activities such as irrigation. Along with the recycling of wastewater, desalination is considered one of the few reliable rainfall independent water sources available today.
According to a report from the International Renewable Energy Agency released in March 2012, global desalinated water production amounts to around 65.2 million cubic meters a day or 24 billion cubic meters per year. The Middle East and Northern Africa region (MENA) accounts for about 38 percent of the global desalination capacity.
While desalination could pose a way to increase the world’s water supplies, it poses a considerable drain to its energy supply. Desalination requires large amount of energy which makes its expensive.
The problem of high energy demand
Major desalination technology options are based on thermal processes which use both heat and electricity and membrane technologies which use electricity. Reverse osmosis (RO) is the dominant technology, accounting for 60 percent of the global capacity, followed by multi stage flash (MSF) with a 26.8 percent share.
Large scale RO requires about 3.5 to 5.0 kilowatt hours of electricity for every cubic meter of water. MSF meanwhile consumes around 80.6 kWh of heat energy and 2.5 to 3.5 kWh of heat energy. The global production of desalinated water is estimated to involve the use of about 75.2 terrawatt hours per year.
Currently, the International Desalination Association reports that there are about 15,000 desalination plants worldwide with a global capacity of 71.7 million cubic meters a day. Over the past years, the MENA region has led the deployment of desalination plants with approximately 2,800 of the world’s plants producing 27 million cubic meters a day of fresh water.
According to IRENA, global demand for desalination is projected to grow by 9 percent a year from 2010 to 2016, spurred by rising water demand and declining freshwater sources. In the MENA region alone, water demand is expected to increase from 9 billion cubic meters in 2010 up to 13.3 billion cubic meters in 2030.
Because of this rising demand, desalination capacity in the MENA region is expected to grow quickly from 21 cubic meters a day in 2007 to almost 110 million cubic meters a day by 2030. This will also spur an increase in energy consumption for the sector and for the countries involved. Electricity demand for desalination in the MENA region is expected to rise to some 122 TWh by 2030.
High levels of solar to meet power demands
One way to solve the problem of the rising demand for desalination without the subsequent rise in demand for energy would be to utilize renewable in water desalination. Solar power is particularly attractive for areas like the MENA region as their high levels of solar irradiation ensure that this particular energy source is available in abundance.
The idea of solar desalination is not a new one. Simple solar stills have been in use for remote desert and coastal communities since around the 1950’s. The basic principle of these solar still is that the sun heats the water to the point of evaporation. As the water evaporates, the water vapour condenses on a glass surface where it can then be collected. The process removes impurities such as salts and heavy metals and even eliminates microbiological organisms. The collected water is clean and pure as rainwater.
The principle behind solar stills is also basically the ones behind thermal desalination technologies. Thermal desalination heats saline water till it vaporizes and the water vapour is condensed and collected. The MSF process is a thermal desalination technology.
RO is an example of membrane desalination technology which uses membranes to separate fresh water from saline feed-water.
Both thermal desalination technologies and membrane desalination technologies could benefit from incorporating solar into their operations.
For thermal desalination projects, solar heat could be collected and used in the evaporation process. Associating a thermal desalination project with a concentrating solar power plant (CSP) is a particularly attractive option.
CSP plants collect solar radiation and provide high-temperature heat for electricity generation. They could also provide both energy and heat for the desalination process. Desert regions in particular, with high direct solar irradiance, could find CSP a promising multi-purpose technology. CSP could provide a reliable and clean source of electricity, heat and water desalination.
For membrane desalination technologies such as RO, photovoltaic technologies might be the more attractive way to harness solar power. These technologies need electricity as an input energy and attaching a P.V. system to a desalination project could provide it with all the power it needs.
Answering the water needs of dry and arid regions
Because of its dry and arid climate, the MENA region in particular is in dire need of desalination technologies. It’s already home to many of the world’s major desalination projects and will be seeing more in the future.
When it comes to the problem of the energy needs of desalination projects, the MENA region also has a distinct advantage and that is its high level of solar irradiation. The region could well power its desalination needs with solar energy.
The United Arab Emirates in particular is a frontrunner when it comes to solar desalination.
The UAE relies on desalination for more than 90 percent of its potable water, producing more than 2,700 million litres of desalinated water in 2011 alone. Unfortunately, these plants are mostly power by natural gas and are responsible for almost a third of the UAE’s greenhouse gas emission.
Recognizing the need to find new renewable and environmentally friendly energy resources to produce water, the environment Agency – Abu Dhabi has been studying the feasibility of solar desalination.
In 2009, the EAD launched two pilot projects that used solar energy to desalinate brackish and saline groundwater with promising results. This led to the construction of 22 solar desalination plants which were completed in January of 2012.
The systems use photovoltaic panels to provide power for pumps which bring salty groundwater up to the surface where they are put through an RO process to remove the salt and other impurities.
Currently, the 22 solar desalination plants have the capacity to produce around 6,600 gallons a day each.
Meanwhile, clean-energy company Masdar announced at the start of this year that it’s set to build the UAE’s first large-scale water desalination plant power by renewable energy by 2020. While the company is also open to other forms of renewable energy, it’s expected that solar power will be the frontrunner.
This article come
s from Ecoseed
