Lifting heavy bricks to store renewable energy
cnn.com
cnn.com
Less mature tech is also ramping up. We are building out factories to build out iron-air batteries. A 20,000 ton weight suspended on cables in a deep mine shaft. Pumped hydro from a deep earth cavity. Pumped hydro out of deep ocean tanks. Methane and kerosene synthesis.
The most remarkable quality of energy storage tech is how its cost is plummeting even faster than solar and wind generation.
The chemical synthesis and liquified-air tech is interesting in that the production apparatus remains useful even after the tanks are full, and building out tanks for more storage is very cheap. They call attention to the separate qualities of storage that will be optimized for each use: (1) How fast can it bank energy, (2) how much power can it release when needed, (3) How quickly can power output be adjusted, (4) how much of the energy you put in do you get back, (5) Is the storage medium or equipment useful for more than storage, (6) Is the stored energy transportable?
Places at high latitudes, and in general places where the mix of renewables and transmission-line power are not stable enough, can still ship in and stockpile chemical storage banked in places with reliable power. Equatorial, coastal desert land will be an excellent place to site solar collection for this purpose: Coastal Peru, Boa Vista in the Cape Verde Islands, coastal Mali or Senegal, numerous sites on and near the Arabian peninsula and the Horn of Africa, northwestern Australia. Other coastal sites with reliable wind, likewise. (Political stability is likely to be more important than convenience, though.)
Perhaps the most surprising thing about storage is that, in common cases, its round-trip efficiency doesn't matter very much. Other things have come to matter more, as raw generating cost continues on down. Hydrogen is a good example: it is so useful, industrially and as a feedstock for other chemical synthesis, that use for storage is just an easy bonus. Ammonia, similarly; demand for fertilizer and ship fuel makes production a major source of revenue when the storage tanks are full.
Pumped hydro admits interesting variations. The reservoir may be deep underground. The reservoir may be a rigid tank deep under the sea. The fluid may be air, and the reservoir a bladder tank deep under the sea, or under the water table.
Solid admits one interesting variation: crane at ground level, a single extremely weight suspended in an existing, deep mine shaft.
Without data on how its efficiency, capacity, and cost compare to pumped hydro, batteries, flywheels, and other alternatives, it looks like a student science project done at larger scale.