[adrian_b]

Even most internal-combustion engines require energy stored in a battery to kickstart them, so this is not different.

Obviously the energy efficiency of this process based on iron is modest. It is likely that the energy efficiency is even lower than for the process of storing energy by making synthetic hydrocarbons (e.g. synthetic gasoline), which are much easier to use once energy is stored in them.

The only advantage is the very low cost even for very large storage capacities.

[moffkalast]

My immediate thought is, why not store it as peroxide? It takes more energy to make too, but at least it's liquid rocket fuel instead of gaseous rocket fuel.

[DrNosferatu]

I hear peroxide conversion efficiency can be as low as 30%, and concentrated peroxide is quite dangerous.

[moffkalast]

> Efficiency Admittedly, the current, non-optimized, technical trial-level efficiency of the here-built system was very low, with an overall storage efficiency of 11.4%,

So far their is even lower, though they claim a theoretical max of 79%. Storing large amounts of energy that's ready to be used is rarely not dangerous in any case. Except maybe potential energy of a tank of water on a mountain.

[mark-r]

There's an advantage to pure hydrogen vs. synthetic hydrocarbons, the lack of carbon means no greenhouse gas production when you use it.