○Electricity Generation and Storage [6]

     The crucial point lies in deciding whether the produced biogas is used directly as gas, electricity, or converted into hydrogen, affecting the complexity of the equipment. While simpler setups are preferable, the choice might vary depending on the regional circumstances.

    Additionally, hydrogen-stored magnesium, transportable as magnesium hydride, has already been developed. These come in various forms, from solid to powder, generating hydrogen when mixed with water. Being lightweight and capable of storing a significant amount of hydrogen, it's easily transportable and has been integrated into vehicles. Hence, for vehicles and heavy machinery like excavators, the energy source could be either magnesium batteries, hydrogenated magnesium, or a hybrid of both. This becomes a sustainable method that could be utilized for the next 100 or even 500 years.

    Other methods for hydrogen storage include high-pressure compression, liquid hydrogen cooled to -253°C, hydrogen-absorbing alloys, etc. Subsequently, facilities for transporting these become necessary. However, due to the large-scale and complex nature of these facilities, their priority as a choice is lower.

    Another candidate for storing substantial power obtained from tidal power generation is the sand battery. Already operational in Finland, it accumulates electricity obtained from solar or wind power as heat in sand. An insulated tank, sized 4 meters wide and 7 meters tall, contains 100 tons of sand. This stored heat is utilized to provide heating for surrounding areas, buildings, and warm water pools. The sand, heated to over 500 degrees, can store energy for several months and has a lifespan of several decades. It can use any dry and non-combustible sand without any mixed-in combustible waste, making it feasible even in Japan.

    In Finland, to supply heat to an area equivalent to 35,000 people, calculations indicate the need for a storage tank measuring 25 meters in height and 40 meters in diameter, filled with sand.

    This sand battery boasts a simple structure, consisting only of pipes, valves, fans, and electric heating elements, resulting in low construction costs.