One of my favorite high(ish)-concept energy storage proposals takes the "store heat in tanks of something that melts and stays hot for long periods of time" is the "sun in a box"[0] idea: use excess electricity to heat silicon up to an incandescent 4500 deg F. Later, when you want to extract the store energy, just shine some of that incandescent light into some super efficient multi-junction solar panels!

Sounds pretty wild but apparently scales up very well thanks the to square cube law.

[0] - https://news.mit.edu/2018/liquid-silicon-store-renewable-ene...