Water consumption from electrolytic hydrogen in a carbon-neutral US energy system

Abstract

Hydrogen is an energy carrier with potential applications in decarbonizing difficult-to-electrify energy and industrial systems. The environmental profile of hydrogen varies substantially with its inputs. Water consumption is a particular issue of interest as decisions are made about capital and other investments that will affect the scale and scope of hydrogen use. This study focuses on electrolytic hydrogen due to its path to greenhouse gas neutrality and irreducible water demand (though other pathways might be more water intensive). Specifically, it evaluates life cycle consumptive freshwater intensity of electrolytic hydrogen in the United States at volumes associated with 12 scenarios for a deeply decarbonized 2050 US energy system from two modeling efforts for which both electricity fuel mix and electrolytic hydrogen production were projected (America's Zero Carbon Action Plan and Net Zero America), in addition to volumes for a stylized energy storage project (500 MW hydrogen-fired turbine). Freshwater requirements for hydrogen could be large. Under a central estimate for 2050 US electrolytic hydrogen production, electrolytic freshwater demand for process and feedstock inputs alone (i.e., excluding water for electricity) would be about 7.5% of total 2014 US freshwater consumption for energy (1 billion cubic meters/year, 10⁹ m³/y; [0.2%, 15%] across scenarios, for 2050 electrolytic hydrogen production of [0.3, 18] exajoules, EJ). Including water associated with production of input electricity doubles this central estimate to 15% (2 × 10⁹ m³/y; [1%, 23%] across scenarios). Turbines using electrolytic hydrogen are estimated to be about as freshwater intensive as a coal or nuclear plant, assuming decarbonized, low-water electricity inputs. Although a decarbonized energy system is projected to require less water for resource capture and electricity conversion than the current, fossil-dominated energy system, additional conversion processes supporting decarbonization, like electrolysis, could offset water savings.