First commercial heat batteries have already been built. Hopefully, the technology will become more widespread, as heat is such a nice form of energy. My guess is, it’s mostly a political and financial problem at this point.

Storing energy in other forms is a lot trickier, but at least there’s no shortage of potential technologies to try. It’s just that most of them tend to be in lab or pilot scale at the moment. That Chinese RFB facility was a notable exception though.