Iron redox flow batteries

Iron redox flow batteries (IRFBs) are gigantic batteries made of molten iron. Each one is about the size of a shipping container, and could store energy for hundreds of homes. This is a possible solution to part of the energy storage problem - to smooth out the intermittency of wind and solar power.

Chemistry and physics

This section is incomplete. For now, read the Wikipedia page on IRFBs for a very long-winded description of how they work.

Viability

#Need for iron	Reasonable
#Ready for deployment?	Maybe
#Usable in vehicles?	No

Need for iron

Iron is a far more abundant metal than, say, the lithium & cobalt used in lithium-ion batteries. In fact, this is the main reason why IRFBs are being developed.

Just to confirm that iron is actually abundant enough:

other_energy.tfc

3290.73 Mtoe/year

Global energy usage, total final consumption minus transport and industrial

Source: Key World Energy Statistics 2020 (IEA report)

Note: This is roughly the amount of on-grid energy consumption that we might need energy storage for. It consists of - for example - lighting, heating, appliances, and other energy used in homes and other buildings. We don't count industrial here, because we can assume (in principle) that most factories could operate during peak sunlight/wind, needing negligable energy storage.

storage_timescale

24 hours

How big the "buffer" of energy storage would have to be to be resiliant against weather fluctuations

The exact number could be up for debate. Join the discussion.

iron.reserves

85 billion tonnes

Global iron reserves - iron metal recoverable

Source: Global iron ore reserves 2010-2021 - Statista

iron.production

1.95 billion tonnes/year

Source: World crude steel production 2021 - Statista

The source doesn't specify whether this is steel from newly-mined iron or steel from recycling scrap. Probably it's both combined.

irfb.energy_by_mass

85 watt hours per kg

Specific energy of an iron redox flow battery

Using half the "theoretical specific energy" of 170 watt hours per kg. This battery hasn't really been commercialized yet, so it's safe to assume that we won't be close to the theoretical maximum in the near future.

Source: https://dornsife.usc.edu/labs/narayan/all-iron-redox-flow-battery/

other_energy.tfc * storage_timescale / irfb.energy_by_mass % iron.reserves (calculation loading) other_energy.tfc * storage_timescale / irfb.energy_by_mass years iron.production (calculation loading)

Ready for deployment?

Several companies have started designing IRFBs, but there isn't a lot of info on whether they're actually being used yet.^{[RESEARCH needed]}

For IRFBs to be useful, we still have to solve the other challenges of large-scale solar and wind. Especially solar/challenge 1: How to make enough solar panels without needing too many rare metals.

Usable in vehicles?

No. IRFBs contain molten metal, and are only safe for stationary energy storage. They can't be made small enough to fit in a car anyway(...)( it would be impossible to contain the heat at that scale, due to physics (surface area to volume ratio) ).