The water intensity of the transitional hydrogen economy
The water intensity of the transitional hydrogen economy is analyzed by quantifying the direct and indirect water requirements to annually manufacture 60 billion kg of hydrogen partly by thermoelectrically powered electrolysis. It is determined that up to 143 billion gallons of water would be directly consumed as a feedstock, with a total consumption including evaporation of cooling water at power plants of 0.5–1.7 trillion gallons annually. Total water withdrawals for thermoelectric cooling (most of which is not consumed) are expected to increase by 27–97% from 195 000 million gallons/day today, depending primarily on the aggregate efficiency of electrolyzers that will be in place and the portion of hydrogen that is produced by thermoelectrically powered electrolysis. On a per unit basis, thermoelectric power generation for electrolysis will on average withdraw approximately 1100 gallons of cooling water and will consume 27 gallons of water as a feedstock and coolant for every kilogram of hydrogen that is produced using an electrolyzer that has an efficiency of 75%. Given that water withdrawals have remained steady for decades, this increase in water use represents a significant potential impact of the hydrogen economy on a critical resource, and is consequently relevant to water resource planners. Thus, if minimizing the impact of water resources is a priority and electrolysis becomes a widespread method of hydrogen production, hydrogen production would need to be from hydrogen production pathways that do not use much water (such as wind or solar), or effective water-free cooling methods (e.g. air cooling) will need to be developed and widely deployed.