Published on February 14, 2019: The Denki Shimbun (The Electric Daily News)
Shojiro Matsuura
Advisor

A distinctive feature of Japan’s Fifth Basic Energy Plan, which the Cabinet approved in July 2018, is how renewable energy is positioned as an important energy source, and wind and solar power have significant promise for future expansion.

The development of generators for wind power has entered the mature stage where there appears to be considerable room for efficiency enhancements as well as technological improvements for operation and collaboration with other power sources. It is also very unlikely that exceptional expansion in scale may be hoped for on account of geological, environmental, climactic and other conditions. With solar power as well, the basic stage for research and development of solar batteries has come to a close and the principal issue for the future is improving photoelectric conversion efficiency.

The remaining great hope for both wind and solar power is that, although both have the common shortcoming of severe fluctuation over time with their low energy densities, there is significant potential for quantitative expansion. However, supplementing these energies with some other carbon-based power source will significantly impair their role and value as key energies. The capability to definitively compensate for this defect hangs on the potential for developing batteries with conclusively higher capacity than batteries currently in use, in other words, much higher mass energy density (energy storage capacity per unit weight = Wh/kg unit).

Currently, the battery that has attained the highest mass energy density is the lithium-ion battery, which has been frequently discussed recently. The lithium-ion battery has a density of almost 150 Wh/kg.

This battery is suitable for mobile devices, but entirely inadequate for stabilizing several hundred thousand-kilowatt class wind and solar power generation. What’s more, the batteries are expensive and thus not economically viable. The number of available recharges is roughly 3,500, which is insufficient for use in power stabilization. Also, lithium is a scarce resource. It is hardly possible that large quantities can be used for stabilizing large-scale power generation.

Current research and development making rapid strides on high mass energy density batteries that surpass the lithium-ion batteries currently in use. The potential that solid oxide and air batteries possess is being thoroughly investigated. Should ultra-high mass energy density batteries become feasible someday, then carbon-based power as well as nuclear power will likely be no longer necessary.

However, all current batteries are chemical batteries, which are based upon a chemical reaction and for which the energy level of the basic reaction is always electron volts (eV). The size of the chemical reaction space varies depending on whether it is at the nuclear, molecular or ionic level, thereby determining the limit of the mass energy storage density according to this spatial size. Even if current research and development succeeds, the greatest density, as long as the resulting product is a chemical battery, could not exceed 100 times that of the current lithium-ion batteries.

Incidentally, the energy available to us on this earth which has the greatest density and may be stably stored is the nuclear force that lies dormant inside the atomic nucleus of various substances.

Nuclear power has been able to quite freely and safely utilize this nuclear force through nuclear fission reactions. On a side note, if we compare the mass energy density of nuclear fuel utilized in our current power reactors to the mass energy density of a battery using the specific burn up of ordinary spent nuclear fuel (approx. 45,000 MWd/ton) as a basis, mass energy density of nuclear fuel would be approximately 100 million Wh/kg. Even if enormous progress were to be made in research and development on current batteries, there would still be no comparison with the value stably stored in nuclear fuel.

For the benefit of the future of mankind, I believe that we need to properly reconsider the combination that will offer the best balance of renewable energy and nuclear energy and strive to gain the understanding of society as well as its trust in that mix.

End