Water From Air

The Prime Minister of India, Mr. Narendra Modi, mentioned the possibility of extracting water and oxygen from air using wind turbines in a recent discussion with the CEO of global wind turbine giant Vestas. There have been some strong responses both for and against these statements. Let us take a look at both these processes.

The point on water extraction has probably led to many people (including myself) finding out about the French company Eole’s wind turbine model named WMS1000 dating back to 2012. (Note: Eole is no longer in business as of 2020)

This model used a refrigeration based system for dehumidification, involving a compressor and fans and some components to achieve the desired air flow into the dehumidification unit. The water extraction system was installed in the nacelle (same enclosure where other equipment such as gears, generator etc. of the turbine are installed) and the wind turbine itself provided power for that arrangement.

Eole WMS1000 Youtube video

The fact is that wind turbines are not at all a critical component in extracting water from the atmosphere. There are several systems already in use for extracting water from atmospheric air all over the world, without involving wind turbines. Meghdoot is an example of such a device made in India, which has been in operation at Secunderabad railway station for almost a year now. In fact, as far as the compressor based system in the Eole turbine is considered, we see water extraction from the atmosphere resulting from this process as an everyday phenomenon whenever we see the ice built up inside our freezer or the water coming out from our air conditioner.

The wind movement due to the wind turbine blades has no role to play in the actual compressor-based water extraction process. The Eole turbine had the system installed in the nacelle as mentioned earlier, but also had additional fans installed for properly directing the air flow through the dehumidification system. The Eole machine could be lowered to the ground as shown in the video due to its small size (only 24 m in height). MW scale turbines are much, much taller and heavier, with just their blade lengths being much more than the total height of the Eole machine (examples: 2 MW turbines from Vestas- blade length of 49m and GE- rotor diameter starting at 116m), plus additional ground clearance required, so a mechanism like the Eole turbine will be extremely challenging, probably impractical, to implement. So it may make more sense to install the water extraction equipment at more easily accessible locations as compared to having to climb a few hundred feet to reach the wind turbine nacelle every time something needs to be checked physically. 

Given below are some more considerations:

1) The Eole turbine had a limited capacity of 30 kW of electricity generation, with some part of it going into operation of the water extraction equipment which meant that its full capacity was not utilized for exporting electricity. In comparison, wind turbines used in large wind farms have rated capacities from several hundred kW to a few MW (thousand kW).

2) Its water generation capacity was also limited. For even a village the water requirements are estimated to be around 80 litres per person per day on including all activities such as bathing, washing etc. So, a single wind turbine producing 1000 litres per day would provide for only 13–14 people as per this metric, and a large number of such turbines will have to be installed to play a significant role in mitigating water issues for even a small settlement. If only drinking water is concerned, a single turbine can provide for the daily requirement of around 800-1000 people.

The water production will be higher in more humid areas. The 1000 litres/day claimed by Eole was achieved in Abu Dhabi in the UAE. It is to be noted that though the UAE has significant proportion of desert area, Abu Dhabi is located on the sea coast. Comparing the average year-round climate data from  https://www.timeanddate.com/weather/ indicates that Mumbai, Mangaluru and Chennai are all more humid than Abu Dhabi, while Hyderabad (where Meghdoot is installed) has comparable levels of mean annual humidity as well as temperature.

3) Maintenance issues: Issues with accessibility have already been pointed out earlier. In addition, as reported in The Hindu, people have expressed concerns over a piece of equipment in which build up of moisture occurs in close proximity to several metallic components which can increase the chances of corrosion and shorten equipment lifetimes if proper sealing/enclosure practices are not adopted.

4) Cost issues: The Eole machine was priced at around 6 lakh (600000) dollars, around INR 2.1 crore (21 million) as per 2012 rates, which Eole themselves had expressed concerns about. A 2 MW turbine designed by Gamesa around the same time was reported to cost around INR 14.5 crore - so around 7x cost for over 60x power generation capacity. For a better dollar-to-dollar comparison, a 2 MW commercial scale wind turbine costs around 3 million (30 lakh) dollars today while a 30 kW turbine could be expected to cost somewhere around 2-2.5 lakh dollars today as per the Windustry website. Pricing trends for MW scale wind turbines on the Statista website show that the price per MW in 2012 was 1.7 times the per MW price in 2020, though it is to be noted that the absolute values on the Statistica and Windustry websites are quite different.

Assuming a similar scaling trend for kW range turbines, a 30 kW turbine can be estimated to have costed somewhere in the range of 3.5-4.3 lakh dollars in 2012. Or going the other way round, the Eole turbine can be estimated to have scaled down to around 3.5 lakh dollars in 2020, assuming the same scaling for the water extraction equipment cost.

The Meghdoot device mentioned earlier, is reported to cost somewhere around Rs. 10 lakh (in 2019) for the same 1000 litres per day capacity reported for the Eole turbine, at comparable humidity levels.

To be feasible, in addition to the technical aspects, the cost of a water generating wind turbine should be comparable to the combined cost of electricity generating equipment and water generating equipment while providing comparable levels of output for both. In the case of the Eole machine, the estimated difference of around 1 lakh dollars should be justifiable using the additional cost of the water extraction equipment and the actual water extracted as well as the electricity fed into the grid. Justifying or reducing this price difference may make it feasible to implement it at a small scale of power generation. Costs and benefits of other competing technologies will also come into the picture. For higher power generation capacities, there is always the argument of using MW scale turbines for power generation which are less costly compared to smaller, sub-100 kW turbines when the cost per MW capacity is considered.

There are other ways of separating moisture from air, for example centrifugal moisture separator and  cyclonic moisture separator. Some may associate these, very loosely, with the statement made about 'sucking water out of the air'. These rely on physical processes, by directing moist air at high speed and high pressure into a confined space with obstructions, causing sudden sharp variations in flow, causing the moisture to strike the surfaces and get separated by gravity while the rest of the air moves along the intended path. But these are mainly used in compressed air systems, where the air is moving through a confined space at a high pressure, and act on the water which is already in liquid state - conditions very different from those encountered around a wind turbine.

There is another report, from the US in 2017, on extracting water from the atmosphere using a wind turbine. However, its principle of operation is completely different from the compressor based method - it uses a specially shaped wind turbine to direct air to an underground location, which being cooler, causes some of the moisture to condense. However, the wind turbine serves to direct the flow of the wind and consumes electricity to achieve this, rather than being a wind driven energy generator. So this method is limited in its ability to generate electricity in addition to extracting water.

Regarding extraction from oxygen from air, this can be done using fractional distillation. This is a process in which air is cooled to a temperature below the boiling point of one of its constituent gases, due to which that particular gas becomes a liquid and is separated from the air, and repeated for the other constituents. A wind turbine plays no direct role in this process. For both moisture separation and oxygen separation, the electricity required for the process can be taken from wind turbines, but any other source of electricity will also yield the same results.