With the growth of the renewable-natural energy use, inclusion of “Power-to-Gas” concepts into the energy system has been proposed, where the conversion of electric energy to hydrogen chemical enthalpy is key process. In the "Power-to-Gas", stored electric energy, hydrogen, is not only returned to electricity, but also used to, without change, such as fuel for fuel cell vehicle or further converted to methane as the fuel for CNG-car. From the points of higher conversion efficiency from electricity to hydrogen, and flexibility of further conversion to other energy carrier, hydrogen has the major position at the electric energy conversion in “Power-to-Gas”. It is different from the case in conventional electric energy storage, where electric energy is extracted from and later restored to electric energy supplying system.

As whole “Power-to-Gas” system does not fit into the electric energy supplying system, the business with power-to-gas as core technology might be deployed beyond the range of electric supplying business.

In Japan, the renewable energy generation has been increasingly deployed under the feed-in-tariff program and, in order to secure stable operation of a power system, it is decided to implement infrastructure to control the output the renewable energy generation to curtail a part of the generation. Under the situation, it is expected that the curtailed renewable energy generation could be a major low-cost and carbon-free resource for the production of hydrogen. This article compare the features of hydrogen and electricity as a secondary energy, and discuss the possibility the hydrogen production from renewable energy generation.

Plenty of surplus electricity derived from various kinds of renewable energy is utilized to generate hydrogen through water electrolysis systems, in what is known as Power-to-Gas (PtoG). This PtoG is believed to be indispensable technology to utilize the surplus electricity of renewables and reduce CO₂ emissions. In Germany in recent years, a number of PtoG pilot plants have been constructed rapidly, so that the total electric input of the plants in operation and in construction reaches approximately 45 MW. However PtoG is still far away from the self-sustaining business. This article describes the various paths and potentials of the PtoG projects and ends with implying the perspective of PtoG in Japan.

Though the electricity in Canada is still mainly produced by hydropower and nuclear, wind power is emerging recently. However, wind power variability could make grid unstable and waste excess energy over the electricity demand. In Ontario, where more than 4,000MW wind power is installed, Independent Electricity System Operator (IESO) developed the energy storage project as a part of the Long-Term Energy Plan which targets 50MW energy storage by 2025. In the project, hydrogen, as well as other technologies, is tested for regulation service and reactive support and voltage control to grid.

Besides, the Power-to-Gas in Canada has the potential for isolated grids in remote communities. Raglan Mine, Northern Quebec, had relied on diesel which accounts a significant portion of operating cost. Likewise, Ramea Island, Newfoundland and Labrador, has no connection to hydroelectricity grid and operated isolated diesel power plants. To reduce diesel consumption and the reliance on diesel generators, wind power was introduced. To increase wind penetration, Raglan mine installs a variety of energy storages including hydrogen. The Ramea project, on the other hand, incorporates a hydrogen storage and generator system. The projects are expected to start in 2016.

Some variety of hydrogen energy storage and supply system has been developed. The basic concept of those systems is to utilize hydrogen that is derived from renewable energy, such as photovoltaic power, aiming to provide carbon-free energy systems. A stand-alone energy supply system “H2One^TM” has developed for a “Business Continuity Plan Model”, and has been under demonstration in Kawasaki-city. The other “H2One^TM” equipped with solid metal hydrate storage has constructed in a hotel as a “Resort Model”. A large scale and high efficient hydrogen power storage system “H2Omega^TM>” using solid oxide electrolysis cell and solid oxide fuel cell is also under developing. Some elemental experiments and conceptual design study suggest that 80% system efficiency of charge and discharge can be achievable.

Study of economical model on hydrogen storage and utilization to electric power generation in a remote island was done, where the hydrogen was obtained from the surplus renewable energy (RE). In order to evaluate the relationship between the total cost of electric power supply and the ratio of RE introduction quantitatively, case studies (1)RE output restriction, 2)battery electric storage and 3)hydrogen storage and utilization to electric power generation) were carried out under a real remote island where the cost of RE electricity is cheaper than one of diesel generation. The simulation results showed that (1)the total supplying cost was declined according to the introduction of RE, (2)hydrogen storage and utilization to electric power generation became competitive when an RE introduction ratio reached more than 20% in the view of the energy supplyer.

For prevention of global warming, a significant reduction of CO₂ emissions is immediately required, and a great effort for the use of renewable energy has been made in the world. One of key technologies is a large-scale storage of electricity generated from unstable renewable energy. Although conversion of surplus electricity to hydrogen is considered, mass transportation technologies and combustion systems of hydrogen have not been established. Since natural gas is widely used in the world, we have been proposing so far carbon dioxide recycling for the use of renewable energy in the form of methane via electrolytic hydrogen generation using carbon dioxide as the feedstock.

HyGrid Study Group, founded in August 2012, is aiming to establish and introduce hybrid grid system which can connect and utilize hydrogen grid and electricity grid in order to contribute to the expansion of renewable energy. The Group believe that initially HyGrid System can be introduced from local and remote areas, where daily energy cost for residents is relatively higher than city areas, so that the system can contribute to the reduction of energy cost and revitalization of local economy.

In response to international climate policy agenda, low carbon technology assessment is a crucial issue of energy research community. International Energy Agency released technology roadmap on hydrogen and fuel cells in 2015. It aims at review of hydrogen related technological options, vision to 2050, research and development milestones as well as policy actions. Roadmap contents are summarized and long-term view on research and development is discussed.