In my page Shipping Batteries I made a case for powering shipping using Mg-air primary batteries housed in shipping containers.
Magnesium is abundant in nature and can be reduced to the metal using renewable energy. As blocks of metal it would be non-toxic, almost indestructible, very easy and safe to transport and store with a high energy density.
The idea is that, given a means of manufacturing Mg-air batteries, the metal would provide the ideal means of transporting and stockpiling energy. Energy will always be in demand, so Magnesium metal could be used as a global currency with a globally recognised, meaningful value.
The metal could be produced by installations located on the coast of tropical deserts. Typically these would consist of salt pans to obtain sea salt, which contains about 10% MgCl, as the source of the element, a farm of photovoltaic panels as the source of energy, and an electrolyses plant designed to work just during the day. There would be suitable docking for loading the reduced metal onto carriers and housing for workers.
Alternatively installations could be built based on a concentration of wind power in reliably windy locations such as the North sea. The plant could be built on an artificial island or a floating platform. The electrolysis plant could be designed to work for prolonged periods of windy weather but shut down during still periods. It would probably be more economic to use magnesium oxide recovered from spent cells as a source of the element. (The same could be true for desert based photovoltaic installations but new sources of the metal will be needed as stockpiles are built up around the world.)
National energy demand is quoted in million tonnes oil equivalent, mtoe. Thus the UK energy consumption in 2018 was 143 mtoe.
The calorific value of 1 Tonne of medium fuel oil is about 4000 TJ.
The energy density of magnesium metal is about the same but can be turned into electrical energy with considerably greater efficiency because it can be used in a fuel cell, whereas oil has to be burnt in a thermal power station with, at best, about 60% efficiency.
Magnesium-air batteries have already been commercialised
Many of the current major oil producing counties are very economically dependent on oil and will be strongly affected when demand for oil disappears. Several of these countries happen to have extensive tropical deserts near coasts, so building magnesium production will provide a useful alternative.
Because of the low cost of storage and relative ease of turning it into energy, it could have a useful role for stockpiling energy and for barter in global markets
Hopefully that it also removes the economic justification for nuclear energy.
The idea of a Magnesium economy will unjustifyably be seen as a rival to the Hydogen Economy.