Renewable Hydrogen Energy

This chapter provides a broad overview of the current status and prospects of hydrogen energy. Emphasis is placed on compiling up-to-date information in order to discuss the real opportunities of renewable hydrogen for contributing to the future energy system taking into account energy policy trends, energy efficiency issues and technology and infrastructure limitations. The chapter consists of four sections. In the first one, the challenges posed by the climate change and energy security threats are considered. It is shown that there is a disturbing mismatch between the future energy consumption trends and what would be needed to stabilize the greenhouse gas concentrations in values compatible with an increase of the average global temperature below 2 °C. It is also highlighted that the current energy policies assign a minor role to hydrogen. In the second section, the evolution of the hydrogen economy concept is discussed. Production of hydrogen from renewable electricity to reconvert it again into electricity in a fuel cell is an inherently inefficient process that cannot be the basis of a sustainable energy system. It may be considered for temporary storage of energy but only in situations where convenience outweighs inefficiency. Some segments of the transport sector and the management of the electric grid using the excess power during overgeneration periods for producing hydrogen are main examples of such situations where hydrogen can play a relevant role. The third section is devoted to hydrogen production. Hydrogen from nonrenewable resources is treated first because only fossil fuels with carbon capture and storage would be capable in the short and medium terms of providing the huge amounts of hydrogen necessary for its introduction in the transport sector. In the long term, hydrogen should be obtained from renewables. It is shown that biomass gasification and water electrolysis have great potential, whereas solar energy is the most versatile regarding possible production pathways. The chapter ends with a brief presentation of the major figures of the enthusiastic hydrogen community that is working with the goal that hydrogen energy use soon becomes a reality.