# Systematic Analysis of the Hydrogen Value Chain from Production to Utilization
## 1 Introduction  
In recent years, with the definition of national and international strategies that encourage and strengthen the energy transition, hydrogen produced from renewable resources has emerged as a potential energy vector to tackle climate change and energy dependency [1, 2]. In Europe, the European Green Deal [3], the European Union Hydrogen Strategy [4], and the RePowerEU plan [5], among other initiatives, have strengthened the commitment to low-carbon hydrogen. The first is a set of policy initiatives designed to guide the EuropeanUnion (EU) towards a green transition, the second defines key actions to develop a hydrogen economy, and the third outlines a plan focused on reducing Europe's dependence on fossil fuels and accelerating the transition to green energy. Hydrogen is particularly interesting as a pathway to decarbonize our economies for several reasons; it is light, storable, and reactive, its energy content per unit mass is high, its utilization does not generate greenhouse gas (GHG) emissions or other air pollutants, with the only byproduct being water, and it can be generated from diverse low-carbon energy sources, like renewable electricity, biomass, and nuclear energy [1]. Hydrogen produced from renewable sources has the potential to tackle various critical energy challenges. It can be used as an energy carrier to allow cost-effective transportation of renewable energy from production to consumption regions, with much lower costs than electrical transmission for long distances [6]. It can facilitate seasonal energy storage. Hydrogen can help decarbonize intensive industries and long-haul transport, among others. It can also be used as a decarbonization solution for the current natural gas system. According to the International Energy Agency (IEA), to achieve net zero emissions by 2050, it is expected that 200 Mt of hydrogen will be produced by 2030, 130 Mt more than in 2018, of which 70% was produced from low-carbon technologies [7]. This value will further increase to 500 Mt by 2050, when almost 100% of the hydrogen will be produced by low-carbon technologies [7]. To simultaneously support the exponential growth of hydrogen production and the shift from fossil fuel-based to low-carbon technologies, the research needs to focus on the development of green hydrogen value chains. Currently, there are some barriers and challenges that need to be addressed to create a fully renewable hydrogen economy. First, renewable hydrogen production costs (USD 3.4 to 12/kgH2 for electrolysis with low-emission electricity) are still higher than other competing energy carriers (USD 0.2 to 1.6/kg for ammonia production) and higher than hydrogen produced from fossil fuels (USD 1.0 to 3.0/kgH2) [8; 9]. It is expected that this tendency will remain until 2030 [10]. Moreover, adding to the high production costs, storage, transportation, and delivery to end users also contribute to the increase in the hydrogen unitary cost. Secondly, current hydrogen value chains are mostly designed based on the use of fossil fuels as feedstock. To create a fully renewable hydrogen economy, new suitable pathways to design cost-effective hydrogen value chains need to be created. Due to hydrogen's versatility of production, storage, and distribution, associated with local characteristics, such as weather and geographical conditions [11], existing infrastructures, demand sectors, and demand profile, it is not possible to define only one pathway as the most cost-effective option to design green hydrogen value chains, meaning that for each possible value chain, specific assessments and investments need to be carried out. The hydrogen value chain is essentially composed of four different phases, namely production, storage, transportation and distribution, and end-use. Figure 1 illustrates a hydrogen energy system. Depending on the hydrogen end-use, five main value chain configurations can be defined based on the hydrogen end-use, namely power-to-gas, power-to-mobility, power-to-industry, power-to-synfuel, and power-to-power [12].