Is there enough water for hydrogen?
A recent article in Reuters argued the lack of water could threaten the shift to hydrogen. That article specifically started with the example of the recent cancelation of a green hydrogen project in Australia due to a lack of water.
Do the concerns make sense? Can the lack of water kill the shift to hydrogen?
Concerns about water availability make sense. In several regions of the world, climate change lowers average rain patterns. This year’s summer draught in Europe and California of 20 years mega draught show how blatant the water crisis can get.
However, how much water does the shift to hydrogen needs? Does the article make sense?
Future Hydrogen water needs
First, how many Kg of water do you need to get 1 Kg of hydrogen?
Water couples two hydrogen atoms with one oxygen. But hydrogen, as the first element in the periodic table hydrogen, has the lowest mass. Oxygen sits at number eight on the periodic table with a much larger mass.
Doing the stoichiometry calculations, 1 Kg of hydrogen requires 9 Kg of water.
But the water needs do not stop there. Water electrolysis generates heat, which requires more water as a cooling fluid. Estimates give a water consumption of 20 Kg of water for each 1 Kg of hydrogen.
Adding water use related to PV or wind generation adds up to 32 or 22 kg of water for each Kg of H2, respectively.
Water consumption and availability
Hydrogen generation has three sources: sweetwater, seawater, or brackish.
Electrolysis works best with sweet water. Using saltwater would quickly reduce electrolysis efficiency as salt would deposit on the electrodes.
IRENA estimates a demand of 49 EJ of green hydrogen by 2050. That demand would require 25 Billion cubic meters of water per year. This consumption seems small compared with agriculture (2,800 bcm), industry (800 bcm), or municipal use (470 bcm).
Another estimate calculated the future hydrogen market of 2.3 Gt, requiring 20.5 Gt, corresponding to 20.5 billion m3 of sweet water, a demand of 1.5 parts per million.
However, sweet water availability varies significantly depending on the region and season. Furthermore, climate change will make its supply in any given area more unreliable.
Which argues for seawater use in hydrogen generation. Easy to use land sweet water makes less than 1% of seawater. Seawater adds to 1.4 billion km3.
A paper estimated that future H2 needs would consume 41 billion m3 of seawater, equivalent to 30 ppm, a negligible amount. The study assumed 9 Kg of seawater per H2 Kg, which disregards both cooling and PV water use. However, even increasing the water consumption by one order of magnitude to 300 ppm, the seawater consumption would remain negligible.
Using seawater increases the quantity of water to source from and the number of regions where hydrogen production can happen.
However, seawater requires desalinization which adds energy consumption and brines to manage. Desalinization via reverse osmosis (RO) only adds less than 2% energy consumption on top of electrolysis while increasing costs by $0,01.
The increase in water scarcity already propels desalinization’s growth, bringing its cost down. However, it may be possible to produce hydrogen by electrolysis using seawater as the feedstock.
Returning brines directly to the sea brings environmental problems. It increases local salinity and toxic elements concentration, harming marine life. However, for the same reason, the brines also have economic potential.
Brines contain several salts and elements with industrial value, including rare earth metals (cerium, lanthanum), precious metals (palladium, platinum), radioactive metals (uranium, radium), and alkaline metals like potassium and magnesium (labeled a critical material according to the European Union).
As a consequence, electrolysis for hydrogen adds little energy and cost while opening a secondary income source from brine exploration.
Another pathway for desalinization uses brackish water as feedstock. Brackish water has several sources: waste rainwater, wastewater, and water from brackish natural sources.
Research focuses on achieving efficiencies above Reverse Osmosis. The literature shows different methods like capacitive deionization or electrodialysis delivering lower energy consumption.
As for seawater, more direct path lies in producing hydrogen straight from brackish waters.
Synergies between hydrogen, desalinization, and wastewater management
Green hydrogen production and desalinization may reinforce each other. Several proposals push for integrated hydrogen and desalinization plants. Further still, a recent paper proposes integrating photovoltaics, wastewater treatment, and desalinization to provide both hydrogen and freshwater.
Not all green hydrogen will come from electrolysis.
As covered before, white hydrogen extraction and use already happen for years (here and here). White hydrogen (also known as geological, natural, or native) refers to naturally occurring H2 in underground deposits or seeping to the surface.
Despite the unfortunate cancellation of a specific Australian project due to lack of water, extrapolating that water scarcity strangle the development of an H2 economy does not seem to match with numbers.
Furthermore, hydrogen, desalinization, brine mining, and wastewater management may converge. Integrated plants mutually support each other, increasing their joint feasibility.
This article is part of a hydrogen series. Read more here.