The Global View

Power with a purpose: Solar energy for water treatment

More than a billion people in the world today lack access to clean drinking water and there are more people in the world’s hospitals today suffering from water-borne diseases than any other ailment.

As glaciers shrink, droughts increase and salt-water intrusion spreads, the world’s current fresh water shortage is set to worsen. But treating water is a power-intensive and hence expensive business. It’s also one that can only become more costly as the price of fossil-fueled electricity in social, political, environmental and economic terms becomes apparent. The world needs to find ways of cleaning, desalinating and distributing water to its citizens. And it is an area for which the use of renewable energy seems particularly apt.

However, to talk of renewable generation as a single entity is misleading. Wind and solar power — the most likely candidates for water treatment in non-coastal areas — are very different beasts. Even within the category of solar power there are myriad technologies. And each one has distinct properties that affect where and how it can best be deployed.

Naturally, the prevailing weather conditions will be the major factor. There is no point in erecting wind turbines in an area where the wind is but an occasional occurrence. The reality is that the areas where availability of clean water is currently the most pressing issue, and the countries where it is most likely to become one, are best suited to solar power.

In particular, concentrated photovoltaics (CPV) may prove to be the likeliest candidate for water treatment. Like other solar technologies, CPV converts the power of the sunlight into usable energy. But the advanced design of its solar cells delivers far higher energy yields than standard photovoltaics. CPV units also have an optics system, which magnifies the power of the sun even further, and a sun-tracker unit so that the cells follow the path of the sun and are able to “harvest” a larger fraction of the sun’s rays.

The result is a system that is incredibly efficient and capable of delivering far greater levels of power from a single unit than other forms of solar electricity generation. The net result is a system that has the potential to be much more cost-effective.

The high efficiency of CPV also makes it suitable for micro-generation. In the developed world, micro-generation is often seen as a well-intentioned whimsy on the part of wealthy but committed environmentalists. But in the developing world, where significant proportions of the population live in off-grid rural areas or in overcrowded, unplanned urban sprawl, micro-generation has immediate and obvious benefits. Like micro-finance before it, thinking small can help solve big problems.

But perhaps the biggest advantage of linking technologies like CPV to very specific functions such as water treatment and desalination plant is that they make perfect demonstration projects in which the benefits of renewables can be immediately seen. In an industry that needs to boost its profile, demonstrate effectiveness and encourage greater investment, this is exactly the kind of venture that developers like. It creates something of a virtuous circle where greater investment leads to greater penetration, which in turn leads to lower costs which encourages further deployment.

There is no one easy answer to the world’s water problems. And certainly CPV does not provide the complete solution. But it does tick a lot of immediate boxes, and could play a significant role in ensuring that clean, healthy water doesn’t become the preserve of the wealthy few. But more than that, it opens the door to a whole host of other renewable energy alternatives.

Editor’s note: This was a guest commentary by Professor Keith Bowen, a non-executive director and acting director of engineering at Circadian Solar, a UK-based technology company that’s working to develop large-scale solar power generation on a global basis.

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