Energy Alternative II: Solar and Geothermal Desalination

What about using solar or geothermal energy?

Though we don’t currently have the technology necessary to efficiently or economically collect solar and geothermal energy, the renewable energy resources are both environmentally friendly and extremely safe. Let’s take a closer look at both of these sources of energy!

Solar energy is actually the oldest energy source. Over two thousand years ago, Aristotle wrote, “Salt water when it turns into vapor becomes sweet, and the vapor does not form salt water when it condenses again. This is known by experiment.” In medieval times, alchemists experimented with solar power to turn saltwater to freshwater. They also applied these distillation techniques to make advancements in medicine and chemistry. In 1558, Giovani Batista Della Porta wrote about solar desalination technology in his book, Magiae Naturalis. Following his explanations, no true advancements were made until the 19th century. For developments since then, see the timeline below.1

Using solar energy to drive the desalination process is a very straightforward process to understand because it mimics the natural water cycle. See the diagram below to understand the process.

Photo courtesy of solarcps.com

The solar collector collects energy from the sun’s radiation that is then evaporated, condensed and separated into seawater and distilled fresh water. The seawater is then recycled to be used as cooling fluid for the condenser, and the cycle continues!

Geothermal energy is a similarly underused source of energy. The process is described by the diagram below:

Photo courtesy of washtec.wordpress.com

See http://washtech.wordpress.com/2009/12/09/geothermal-desalination-hot-rocks-key-to-producing-low-cost-fresh-water/ for a detailed description of the technology. For all intents and purposes, the process is similar to the basic humidification-dehumidification process of solar desalination, but the heat energy is coming from the ground in this case.

Geothermal energy is not as old as solar energy, nor is it as easy to harness, but it is still certainly worth considering as an alternative source of energy. It is minimally invasive to the environment, it’s sustainable (unlike fossil fuels), and it’s not dangerous (like nuclear power). Unfortunately, it’s fairly cost-prohibitive because of the price for installation, and it can only work under very specific geographical and climatic conditions. Let’s go through some of the history and debate and decide if its worthwhile!


What’s happened with solar energy?

1870: first American patent on solar desalination, made by Wheeler and Evans1

1872:  first solar desalination plant constructed in Sweden1

1930-1940: California experiences a particularly harsh drought that encourages further research into desalination techniques, including solar desalination, but the economy is bad for funding research1

WWII: Research is even further motivated by soldiers experiencing droughts, stimulates patents from the MIT lab and the US National Research Defense Committee, which invents a solar desalination apparatus to be used on rafts and lifeboats in the war1

late 1940s:  Research booms with urban development and increasing public demands to Congress1

1952: US Secretary of the Interior establishes the Office of Saline Water to finance desalination research and the construction of 5 plants, one of which is solar in Daytona Beach, Florida1

1950s: Research continues in the Caribbean, the National Physics Lab in India, Australia, and the (then) USSR1


What about geothermal energy?

24 countries are currently using geothermal resources for energy, and Iceland leads this pack, boasting 27% of its electricity coming from geothermal resources and 87% of its heating. It’s not as invasive as solar or wind as a renewable energy resource, but its installation cost is prohibitive.1

Photo courtesy of ecology.com

Energy Efficiency & Renewable Energy News

So what’s the debate over?

Currently, there is a great deal of research going into solar and geothermal desalination plants, but no large plants have been constructed recently, due largely to economic reasons. Desalination plants run by these renewable energy resources amount to less than 1% than that of conventional fossil fuel desalination plants. They are expensive and require sophisticated technology, even though they don’t rely on fuel. See http://m.wpi.edu/Images/CMS/UGP/Solar_Desalination_Poster.pdf for an informative comparison between solar-powered desalination plants and plants run from other energy resources, and read http://cdn.intechopen.com/pdfs/13755/InTech-Application_of_renewable_energies_for_water_desalination.pdf for a comprehensive technical report on the application of renewable energy technologies for desalination.


For solar desalination,

Photo courtesy of awards.earthjournalism.org

-It’s difficult to engineer a design of a plant that maximizes heat transfer efficiency, economy, and reliability.1

-These goals conflict with each other; to get the optimal temperature difference between solar-generated vapor and the seawater-cooled condenser requires a great deal of energy and engineering ingenuity. Maximizing efficiency requires money and therefore is not advantageous economically. Economy promotes cutting corners in research, testing, and construction.1 

-In general, solar energy is hard to rely on because it isn’t entirely predictable. It also requires a great deal of physical space to set up the plant, and a great deal of solar energy is needed to drive the desalination process.1


-Yet, the sun a virtually unlimited resource. It’s extremely environmentally friendly to harness solar energy, and it doesn’t emit any harmful greenhouse gases or dangerous radiation.1

-It’s possible that we could find ways of recycling the energy harnessed by the expensive panels, by reusing the waste energy to cool the seawater in the condenser.1

-Again, the process features simplicity and environmental friendliness.1


-But, it requires very large upfront capital. The solar panels are expensive and must be perfectly maintained, and we can’t predict the behavior of the sun, which makes relying on solar energy a risky business.1


For geothermal energy,

Photo courtesy of diwtech.com

-It features low running costs and no reliance on fossil fuels.3

-It doesn’t create any pollution or emit greenhouse gases.3

-It would stimulate new job growth in research, development, and implementation.3

Read about Algeria's case study on geothermal desalination technology at http://www.sciencedirect.com/science/article/pii/S1364032109001877.


-But, no current technological solutions are of a large enough scale to provide substantial potable water sources.3

-Further, the installation cost is extremely high and very few have the required training and expertise.3

-We also don’t know everything about the chemical composition below the surface of the Earth, so it’s possible that we could risk releasing poisonous compounds by accessing geothermal energy deep below the surface.3

-Finally, it’s only feasible under ideal geographical conditions.3


Are there any political or social problems associated with either technology?

Honestly, not really. The largest hurdles preventing either technology from becoming popular are economic and problems of technological scale, availability, and expertise. Economic issues are certainly influenced by politics, but neither energy source is particularly more politically advantageous. Socially, both technologies represent a chance to provide potable water, which we’ve established is of the utmost importance; however, the economic issues are integrally related to social ones. It wouldn’t pose any serious health or safety risks to use either technology, but we need expertise and capital to take advantage of these environmentally friendly resources.


What do we think?

Which renewable energy resource should we put more effort into research for practical application?

This choice depends greatly on the geographical location. Both sources of energy are extremely environmentally friendly, but both also require a great deal of economic stability and expertise to install and run. Of the two, solar energy is currently a more economical energy resource than geothermal, and it's easier to implement and operate, but neither solution is practical for right now. Solar desalination also offers the opportunity for stand-alone desalination plants that don't require MSF or RO technology at all. Besides just offering a power source for a facility, research in solar energy has brought recent advancements in a simpler, environmentally friendly desalination method.

So what should we do now?

Considering the fact that we should put most of our energy (no pun intended) into supplying potable water to regions in most desperate need, we have to assess the feasibility of technological solutions. According to The Encyclopedia of Earth,  “more than 2.8 billion people in 48 countries will face water stress or scarcity conditions by 2025. Of these countries, 40 are in West Asia, Northa Africa or Sub-Saharan Africa...Over the next two decades, about 40% of the global population could face water stress or scarcity.” 4

Find more statistics from this report here: http://www.eoearth.org/article/Freshwater

These countries desperate for efficient and effective desalination technologies are often not the most economically stable; so, using either solar or geothermal energy is not particularly practical given that substantial funding is required for research, development, testing, installation, and maintenance. 

Photo courtesy of eoearth.org

We need solutions now.  We need practical solutions, and we can’t neglect our environmental impact, either. If solar and geothermal energy resources are researched and made more practical by countries in better economic conditions, then they would present a wonderful solution for countries around the world; but until that happens, we can’t expect the most desperate countries to seriously consider either renewable resource.


While it may affect countries differently, we each have a global responsibility to improve desalination technology.


External Links on this Page (5):

http://washtech.wordpress.com/2009/12/09/geothermal-desalination-hot-rocks-key-to-producing-low-cost-fresh-water/

http://m.wpi.edu/Images/CMS/UGP/Solar_Desalination_Poster.pdf

http://cdn.intechopen.com/pdfs/13755/InTech-Application_of_renewable_energies_for_water_desalination.pdf

http://www.sciencedirect.com/science/article/pii/S1364032109001877

http://www.eoearth.org/article/Freshwater


Works Cited on this Page:

1E. Delyannis, Historic background of desalination and renewable energies, Solar Energy, Volume 75, Issue 5, November 2003, Pages 357-366, ISSN 0038-092X, 10.1016/j.solener.2003.08.002.http://www.sciencedirect.com/science/article/pii/S0038092X03002779)

2K. Bourouni, R. Martin, L. Tadrist, M.T. Chaibi, Heat transfer and evaporation in geothermal desalination units, Applied Energy, Volume 64, Issues 1–4, 1 September 1999, Pages 129-147, ISSN 0306-2619, 10.1016/S0306-2619(99)00071-9. http://www.sciencedirect.com/science/article/pii/S0306261999000719

3Conserve Energy Future, "Advantages & Disadvantages of Geothermal Energy." Last modified 2012. Accessed May 12, 2012. http://www.conserve-energy-future.com/GeothermalEnergy.php.

4McMichael, Christine. The Encyclopedia of Earth, "Freshwater." Last modified May 31, 2011. Accessed May 12, 2012. http://www.eoearth.org/article/Freshwater.

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