Using CPV to deliver fresh water

Dr Keith Bowen, Circadian Solar

Could a combination of concentrated photovoltaics (CPV) and micro-generation provide clean, fresh water to places where it is needed most?

In Andhra Pradesh in south central India, more than 80% of hospital admissions are the result of water-borne illnesses. There’s nothing particularly special about Andhra Pradesh. 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. The Stockholm Environment Institute says that, using only a moderate projection for climate change, 63% of the global population will live in countries of significant water stress by 2025.

The Power conundrum

Many places will therefore need to factor in the availability of less fresh water. But treating dirty water to make sure it is safe to use is a power-intensive and expensive business. So can renewable energy be used, to clean, desalinate and distribute water to citizens?

On a more practical level, the lack of clean water is often correlated with an absence of or degradation of existing electricity infrastructure. If new power generation plant is to be built, or a serious refit programme is to be undertaken, then yes, there is an opportunity to incorporate significant levels of renewable generation into the mix.

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 a 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.

CPV - could it be the best option?

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, that 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 very 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 levels of efficiency of CPV also make 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 over-crowded, unplanned urban sprawl, micro-generation has immediate and obvious benefits. Like micro-finance before it, thinking small can help solve big problems.

For example, a basic micro-desalination unit – the size of an average washing machine – requires 800 Watts of electricity to produce 1,000 litres a day. That’s enough for a family’s daily needs. A single CPV unit could power four of five of these machines – thus providing a cost-efficient, space-efficient and energy-efficient power source.

In another example, an individual hospital might need 100 kW - 200 kW to power its own water treatment facility. In the right climate that could prove to be a more robust and more reliable source of essential clean water than an inadequate water (or even electricity) grid.

But there are other considerations when it comes to choosing energy sources, not least of which is support and maintenance. Systems designed for a long lifecycle and minimal maintenance are best. The more moving parts, the more complex its underlying engineering and the more maintenance it is likely to require. That may make it inappropriate for certain countries that could otherwise benefit. But, if you can fix a car you can fix a CPV system. So for places like India – where most small towns and many villages have a mechanic enjoying a lively trade in the repair and refurbishment of Ambassador cars and auto-rickshaws - it could be the argument that seals the deal.

The deployment of renewable energy in general and CPV in particular can also support nascent tourist industries by powering the water treatment required by hotels, swimming pools and even golf courses. The water consumed by these enterprises has long been an area of concern in many areas, particularly where resources are already limited. There is a greater awareness that providing luxuries should not have an unacceptable social and environmental cost, and balancing the need to attract tourist dollars to boost the local economy and ensuring the population has its basic needs met has not always been successful. But using renewable micro-generation to power water treatment can assist in this area.

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. For example CPV technology development is a delicate balance. The sector does have the theoretical advantage of low costs and high efficiency, but flat plate PV continues to improve in these areas and the cost of silicon is currently low, removing one of the earlier selling points of CPV. CPV technologies also require highly efficient tracking and a perfect balance of optics and technology; it is a high wire act with significant potential but requires perfect timing.

But CPV 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. And it also opens the door to a whole host of other renewable energy alternatives.

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