THE RAIN MACHINE
Mar 10 2014
Using wind energy to extract moisture from the air will go a long way in resolving water scarcity
There is a lot of talk about the water-energy nexus these days. Energy is consumed to treat and pump water (and wastewater), while water is needed in the energy sector (cooling water in nuclear and thermal power plants, irrigation water to cultivate bioenergy-crops, running water for hydropower plants, etc.). Imagine something using its ‘energy content’ to get water out of itself. Far fetched?
May seem so at first read. But not when you get to know about the technology which the Nethe rlands-based Rainmaker is trying to promote globally. One cannot help wondering why no one ever thought about it before.
The Dutch have always been proud of their windmills which used to dot their landscapes in bygone years and provide the mechanical energy needed to pump water and grind corn, though now they usually generate electricity which is fed to the main grid. You see them on souvenirs at Amsterdam’s airport — chocolate wrappers, key chains, fridge magnets, T-shirts and caps etc.
No surprise then that a Dutch entrepreneurial venture now plans to use windmills to produce clean water. Of course, some of you may say that this is happening in other parts of the world, where water treatment plants may have their captive wind-farms supplying part of the electricity needs for the treatment processes. But in those cases, the raw water is extracted from a lake, river, groundwater etc. In Rainmaker’s case, the water is extracted from the same agent which provides the mechanical input to the windmills — wind, or more appropriately air (as ‘wind’ strictly means ‘air in motion’).
In some ways, it is like rainwater harvesting; with a big difference though. Rainmaker’s contraption ‘makes rain’ from air, as the name suggests, while rainwater harvesting would depend on the whims and fancies of the now-errant hydrological cycle. Of course, Rainmaker’s AW75 turbines also depend on the hydrological cycle, as all that can be squeezed out is the moisture content of the air, which is courtesy the action of the ‘natural pump’ which circulates H2O from the terrestrial surface to the atmosphere, and then back again.
So, how does it work? Refrigerant (low pressure, low temperature) is compressed to higher pressure and temperature, in a compressor which is driven by the turbine, which gets its energy input from the wind. The refrigerant then moves through a heat exchanger, first warming up (intermediate) cooled air, and then cooling (input) warmer air. Warmed up air exists the heat pump. After having cooled the input warmer air, the refrigerant circulates back to the compressor to commence the next cycle. The intermediate cooled air (below dew point) gets dehumidified, loses its water vapour which condenses and is collected as water in tanks below.
Of course, in theory, air anywhere in the atmosphere has some entrapped moisture in it, and winds do blow all around the world, albeit at varying speeds. However, the AW75 contraption can perform at its most optimum, as the air gets warmer (and thereby holds more water vapour), and the winds are speedier (thereby providing more mechanical energy for the operation of the compressor).
Thus, the performance depends to a great extent on two forms of energy in the air – kinetic (air in motion, or wind in other words) and thermal. Electricity is out of the picture. That would mean no carbon emissions!
In tests carried out a couple of years ago, 1038 litres of water were produced when the temperature was 8.2 degrees C, relative humidity was 79 per cent and wind was blowing at 6 metres per second, in Leeuwarden in the Netherlands. This increased to 1571 litres in summer (June 2012), when the temperature rose to 10.1 degrees C, though the wind speed dropped a bit.
Water scarcity plagues several parts of the world. Climate change will make situations worse in some parts, in the years to come. Rainmaker has pilot installations of its AW75 system in scorching-hot Kuwait and windy Netherlands. The Caribbean, Indonesia, Papua New Guinea and islands off the north-western coast of Africa (Cape Verde et al) are considered as potential markets for this technology. Perhaps this is just a conservative estimate — a small subset of the huge market that awaits Rainmaker’s water-from-wind systems — as standalones in deserts and remote habitations, as useful additions to the existing water supply system in towns and cities to make up for any shortfall (drinking water, industrial applications, fire-fighting, etc), for military purposes in areas where access to water is difficult, and to serve refugees in camps (as a substitute for bottled water which would need to trucked or airlifted).
In India, 67 per cent of the population is set to receive subsidised food in the run-up to the general elections in 2014. Food, however, is something without which humans can survive longer, but they cannot survive without water. Clean and reliable water supply has been grossly neglected in most parts of India. If provision of subsidised food is a well-timed, politically-motivated exercise being undertaken by the incumbent government, perhaps doing something about water supply also, may prove that the government genuinely has the interests of the populace at heart. A case, surely, for applying the Rainmaker model in our villages. zz
(The writer is a post doctoral researcher at the department of hydraulic and
environmental engineering of the Norwegian University of Science and Technology in Trondheim, Norway)