Fundamental Technology of Energy Carriers for Transportation, Storage and Utilization of Renewable Energy/CRDS-FY2012-SP-08
Executive Summary

This strategic proposal recommends that the government should strategically promote the research and development of fundamental technology of energy carriers, i.e., energetic chemicals, for massive introduction of renewable energy.

Implementation of renewable energy is required to resolve the problems of fossil fuel depletion and climate change. On the earth, there are considerable amounts of available renewable energies such as wind power, solar irradiation and hydraulic power, and they are expected to serve as primary energy feedstock for future human society. However, Japan does not have a large land area, so the available amount of solar and wind power is smaller compared to other regions. If we want to introduce a large quantity of renewable energy, we should import such resources from countries having abundant renewable energy. The renewable energy has two inherent problems as follows.

1) The renewable energy resources are unevenly distributed globally and locally. A huge amount of solar irradiation is available in the desert areas close to the terrestrial equator, while wind power is often abundant at the high latitudes such as Hokkaido and Tohoku areas in Japan. On the other hand, they are not abundant in energy-consuming cities.
2) Most of the renewable energy is associated with large daily and seasonal fluctuations, so they should be leveled off as base energy supplies. Solar and wind power are affected by weather and fluctuates over a period of several days or weeks, which is much longer than the day and night leveling off of electricity.

To materialize a society utilizing massive renewable energy, these problems on transportation and storage of energy should be resolved. Renewable energy has already been widely used as an electric power supply, although electricity is not suitable for long-distance transportation and large-scale storage. Hence, it is most appropriate to produce energy carriers such as hydrogen, ammonia, organic hydrides and metals/metal oxides from renewable electricity or directly from renewable energy, and to transport and storage them before finally supplying them as electricity, mechanical power and/or heat.
There are only a limited number of known technologies for producing energy carriers from renewable energy, and, in particular, direct conversion of renewable energy to energy carriers is extremely difficult. Moreover, there are only a few technologies to obtain electricity, mechanical power and heat from such energy carriers. For instance, hydrogen can easily be produced by water electrolysis and used for producing secondary carriers; it is being used for commercially available fuel cells. However, we have only primitive technologies for synthesizing ammonia and organic hydrides from water with nitrogen or hydride-precursors. The direct-carrier fuel cells and direct-carrier engines also require fundamental research and development. Since our country has set forth a goal of stable utilization of renewable energy, we should strategically promote basic and applied research in order to lead the world by developing these technologies.

The energy carriers mentioned above have individual characteristics in their energy density, utilization method, safety, stability, cost and so forth, so they should be selected and used depending upon the purpose. At present, there is no single carrier that is generally most promising. For example, it is assumed that gaseous hydrogen will be used for fuel cell vehicles, but hydrogen cannot be stored in large scale and for long periods of time. For such storage, liquids and liquefied gases such as organic hydrides and ammonia are clearly preferable. Hydrogen and ammonia can also be directly supplied as fuels into internal combustion engines, but organic hydrides should not be burned because of their recycling as precursors. Therefore, extensive research work on various conversions of carriers for production and utilization is mandatory, and it is most important to obtain sufficient scientific knowledge to judge which carriers would support future energy systems based on renewable energy.

So far in our energy technology development, electricity has been?identified as the most useful final energy source, so that the production of energy carriers from electricity have not attracted much attention resulting in that the related technologies are left primitive. In a future society based on renewable energy, however, electricity will be a source of energy, and the production of carriers from electricity will play an important role in the utilization of renewable energy. Moreover, direct production of carriers from renewable energy such as solar irradiation will be the ultimate technology. Our country has much advanced technologies in electrochemistry, catalysis and IC engines, so we should prepare for large-scale dissemination of renewable energy by exploiting these advantage technologies for the development of carrier technologies. The energy industry is the basis of the national economy. It is presently supported by petroleum and natural-gas plants and should be replaced by the renewable energy carrier and/or derived electricity plants in the future. The social receptivity, compatibility to present infrastructures, environmental friendliness, and margin of safety should be investigated from a wider perspective, as well as the research and development of elemental technologies. Our country should develop technology in renewable energy carriers ahead of other countries and supply them to the world for the promotion of renewable energy as a world leader in science and technology.

A variety of disciplines such as chemistry and chemical, mechanical and systems engineering should be integrated to address the science and technology for energy carriers. Furthermore, a wide range of cooperation and collaboration is necessary from atomic-scale reaction mechanisms in electrochemistry and catalysis to real-scale reactors design, system structuring and environmental impact assessment. This synergistic attempt with a common view of energy conversion should certainly cultivate human resources of chemistry and chemical, mechanical and systems engineering, which can put R&D themes on energy in perspective.