Which each passing year, the world gets thirstier. As the human population continues to grow, and becomes more urbanized, our sources of drinkable water get pushed to their limits. The solution? Desalination — the process of removing salt from ocean water. But given the tremendous costs and energy requirements of doing so, large-scale desalination remains out of reach for the foreseeable future.
But that doesn't mean it's not coming. The solution could come from our sun — a prospect that will finally make desalination a viable global option in the coming decades. Here's how it's going to work.
Top image: Walt Stoneburner/Flickr.
What's the problem?
Humanity's need for water is steadily increasing. Escalating population rates are placing an incredible demand on available water sources — but there's more to it than that. It's estimated that upwards of 70% of all potable water goes into agriculture, which in turn is causing bodies of fresh water to be rapidly drained.
And it's not so much that water is being depleted, as it's being redistributed. Water that falls from the sky doesn't get distributed equally around the globe, which is why the demand for water isn't the same everywhere.
Moreover, we can't move water. Well, actually we can — but it's incredibly expensive. China, for example, is working on a $62 billion project to build a pipe-and-canal system to transport water over hundreds of kilometers from the Yangtze River to parched cities and farms in the north. In California, nearly 20% of all electricity is used to move water around. The impact on the environment, including associated carbon emissions, is not trivial.
As for today's desalination plants, they can only really be used on a small scale, on account of their intense energy requirements. The practice of manually heating saltwater to remove salt with traditional power sources simply doesn't make economic and environmental sense in an era that's striving for sustainability. Additionally, some of the more water-poor areas of the world are located in developing countries, where these technologies are largely out of reach. And even if access isn't a problem, cost certainly is.
Why solar power?
This is why experts believe it's critical that we develop accessible, affordable, and industrial-scale solutions for desalination — and this is where solar power comes in. And indeed, the advent of concentrated solar power (CSP) may finally offer a viable and sustainable alternative to fossil fuels for what will eventually become large scale seawater desalination.
What's both interesting and exciting about CSP is that the technology already exists. This issue right now is primarily one of cost. Solar panels, or more specifically photovoltaic cells, still cost as much (if not more) than the equivalent in fossil fuels like natural gas and coal.
But despite the current cost, the future of CSP as a means to power desalination plants looks particularly bright. When considering the potential power of a CSP plant, it quickly becomes obvious as to why this is the case.
It's suspected, for example, that a CSP plant the size of Lake Nasser in Egypt would be capable of harvesting an amount of energy equal to present Middle East oil production. The total solar energy received on each square kilometre of desert land could desalinate an amount of 165,000 cubic meters per day, or 60 million cubic meters per year.
That's a lot of water.
How does it work?
Interestingly, desalination is actually an afterthought to the development of a more efficient kind of solar power, what has been dubbed hot solar cells. A recent innovation allows for more efficient solar panels by pumping water through micro-channels on the surface of the panels. Concentrated photovoltaic (CPV) cells use lenses to focus large areas of solar energy onto a small patch of photovoltaic material.
The trouble is, temperatures can reach 120°C, making them quite inefficient — and reducing the amount of electricity they can produce. But it's the process of cooling them down where it gets interesting. By using the same technology developed to cool computer chips, water-filled microchannels can be used to cool the cell — and the residual hot water is in turn used for desalination. This solves two problems at once: electricity and desalination.
Looking a bit deeper into the process, IBM has developed a microchannel that is etched onto the cell itself. This makes for better cooling because the water is closer to the heat source. Tests have shown that a one centimeter ultra-high CPV cell can still function between 70 to 90°C — even with 5,000 times the normal amount of solar radiation focused on it (which is five times as much as existing CPVs can handle).
This makes the CPV method far more economic and efficient when compared to the traditional method of desalination which uses hot water to distill seawater.
There is another idea called the Flat Mirror Solar Collector. By using flat mirrors instead of parabolic ones, panels can be made to follow the movement of the sun from east to west, allowing for the concentration of the sunrays from a large area to a fixed horizontal tube on top containing water under pressure. As a result, the concentrated sunrays raise the temperature to produce steam in the tube, which is then used to drive a conventional steam turbine. The waste heat at the end of the turbine can then be used to desalinate seawater.
Who's doing it?
While these technologies are still prohibitively expensive, this hasn't stopped some countries from getting an early start.
Cyprus recently completed a 16-month pilot project to test the feasibility of the concept. They combined a thermodynamical cycle for the production of water while simultaneously producing economically competitive green energy. The next phase will see the installation of a full-scale plant, with the third phase seeing the deployment of refined technology plants for heavy-load commercial operation. The Cypriot government is currently hoping to secure 18 million euros (USD$22.5 million) to keep the project going.
Egyptians are currently working on a four-year test project called Multi-Purpose Applications by Thermodynamic Solar, or MATS. It has received 22 million euros (USD$28 million) from the European Union under a special program. They're planning to build a test site in Burj Al Arab, a desert area near Alexandria. Their units will be powered by both solar energy and renewable energy sources such as biomass and biogass. It's expected that the test facility will generate one megawatt of electrical power and 250 cubic metres of desalinated water per day.
Australia's Acquasol Infrastructure, a company that designs and develops affordable, environmentally-friendly power and water projects, is working on a project called "Acquasol 1" — a concentrating solar power plant that will also double as a desalination station. It will be built just outside Port Augusta, South Australia, and serve as a 200 Mw Solar thermal/gas hybrid facility. They're also planning on using the excess brine derived from desalination to create commercial grade salt.
Other countries are also looking to get in on the action, including Saudia Arabia.
When will everyone have access?
This is ultimately the big question.
Experts predict that the growing freshwater deficits could be increasingly covered starting in the 2020s, and possibly as late as the 2030s. The spread of CSP desalination plants will likely reduce non-sustainable water supply and inspire the development of most of potable water production by the year 2030 and afterwards.
All this is contingent, of course, on the price of photovoltaic cells dropping — which they probably will in time. Current state of the art CSP costs the equivalent of about $50/barrel of fuel oil, but it's thought that there will be a 50% cost decrease in the current decade due to economies of scale, mass production, and technological progress. As a result, we could achieve a cost level of $25/barrel within 10 years, and $15 per barrel by the middle of the century — a rate of decline that simply cannot be matched by fossil fuels.
The result: Large scale CSP desalination plants in parts of the world who need it the most by the 2030s.
Sources: Here, here, here, and here.
Inset images via greencarddesign, Nokraschy Engineering, Cyprus CSP, Masdar.