How to store energy -1

2022/11/25 2023/01/03

lenemas

The previous post discussed hydrogen as an energy carrier (see Hydrogen as an energy carrier?).
A short summary of the post is;

The timinigs and locations at which renewable energy is produced are different from those at which energy is needed
To fill this gap, renewable energy needs to be converted into another form of energy for its storage and transport
Hydrogen stands out as such energy carrier in terms of gravimetric energy density
However, due to its quite low boiling point, hydrogen exists in gasous form in standard condition (=difficult to store and transport as it is)

The last drawback, however, does not lead to a conclusion of giving up the use of hydrogen, because hydrogen also has another strong benefits in its production and usage. For innstance, hydrogen can be

produced in a variety of ways
used as a reactant of various chemical reactions
used as a fuel of fuel cells
used as a potential fuel of thermal power generation

Therefore, other energy carriers can be considered in the contexts of "hydrogen".

Hydrogen and its derivative are to be discussed from this point onwards. We consider "how small the volmetric energy density can become".

Make hydrogen as small as possible = compression or liquefaction

When compressing the hydrogen to make its volume small, often quie high pressure is applied such as 350 or 700 bar.^[1] The key technology to its realization is tough and rigid container that can maintain such high pressure. But the production of such material in a cost-efficient manner is quite challenging in the case of hydrogen, because hydrogen is so small that it can penetrate into a variety of substances. This phenomena is called hydrogen embrittlement, making hydrogen leak from the container. The hydrogen fuel cell vehicle, MIRAI by Toyota Moter, is equipped with high-pressure hydrogen cylinder.[2]

When liquified, the energy density of hydrogen is as small as 2.8 [kWh L^-1] or 39.4 [kWh kg^-1].^[3] But this process requires to keep the temperature of the system at the boiling point of hydrogen (approximately -253 degree celsius), which also is technically challenging.

Companies consider to transport liquid hydrogen by ships from Australia to Japan. They are called "CO₂-free Hydrogen Energy Supply-chain Technology Research Association (HySTR)" , and plan to demonstrate the hydrogen supply chain between Australia and Japan on a pilot level.^[4,5]

Posts in coming will see other ways to approaches to achieve high volmetric density of hydrogen-based energy carrier.

References

U.S. Department of Energy, “Physical Hydrogen Storage”, https://www.energy.gov/eere/fuelcells/physical-hydrogen-storage (accessed on 2020/03/27)
トヨタ自動車, “スペック・装備” https://toyota.jp/mirai/spec/ (accessed on 2020/03/27)
E. Akiba, 本燃焼学会誌 2011, 53, 16.
川崎重工業株式会社, “世界初、液化水素運搬船「すいそ　ふろんてぃあ」が進水(Online)”, https://www.khi.co.jp/pressrelease/detail/20191211_1.html (accessed on 2020/03/27).
技術研究組合 CO₂フリー水素サプライチェーン推進機構, https://www.hystra.or.jp/about/ (accessed on 2022/02/03)