In this paper, the significance of CO2-free hydrogen is discussed using a long-term global energy system. The energy demand supply system including CO2-free hydrogen was assumed, though there are still large uncertainties as to whether a global CO2-free hydrogen energy system will be deployed. System analysis was conducted using the global and long-term intertemporal optimization energy model GRAPE under severe CO2 emission constraints. Applied global CO2 constraints for 2050 were a 50% reduction from 1990 levels. CO2 constraints accounting for Intended Nationally Determined Contributions (INDCs) in each region were also considered. A variety of energy resources and technologies were considered in this model. Hydrogen can be produced from low-grade coal or natural gas with CO2 capture and electricity from renewable energy. The hydrogen CIF (cost, insurance, and freight) price for Japan was about 3.2 cents/MJ in 2030. Hydrogen demand technologies considered in this paper are hydrogen -fired power plants, direct combustion, combined heat and power (fuel cells, gas engines, and gas turbines), fuel cell vehicles, and hydrogen internal combustion engine vehicles. The majority of CO2-free hydrogen was deployed in the transportation sector. CO2-free hydrogen was utilized in the power sector, where deployment of other zero emission technology has some constraints. From an economic viewpoint, CO2-free hydrogen can reduce the global energy system cost. From the viewpoint of a localized region, such as Japan, deployment of CO2-free hydrogen can improve energy security and environmental indicators. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.