The short version is that solids have merely ok heat capacity. The molar heat capacity of many solids at high temperatures is approximately 3R or approx. 25 J/molK. Google "Dulong-Petit Law" and "Debye Model" if you'd like to see why.

By comparison, the polar molecule water, which has extraordinarily good heat capacity, due in part to hydrogen bonding, is 75 J/molK at room temperature.

So water has almost 31x the heat capacity of tungsten by weight.

It may be I'm missing some obvious implication of something you've written that I've missed due to negligible background here, but I'm confused by the numbers you've cited here.

You list many solids as having a molar heat capacity of "25 J/molK", water as having a molar heat capacity of "75 J/molK", and conclude that water has almost 31x the heat capacity, but naively comparing the numbers cited only gets you 3x. Where does the other 10x factor come from?

3X molar heat capacity difference, yes. But water is 18 g/mole, and W is about 183 g/mole. So tungsten is about 10x heavier per mole than water.

The parent post happened to pick a solid material for a nice round molar mass ratio.

Ah, thanks!

10x comes from weight. 1 mol of Tungsten weights 10x 1 mol of water.

Mass, not weight.

Solids are notoriously hard to pump.

underrated

Naive question maybe but why not use steam instead of salt? Well insulated pressure tank can hold a lot of steam, heat capacity is good, it's non-toxic, and it is ideal for driving turbines.

Focused sunlight is certainly capable of boiling water.

Requires pressure vessels and has low heat capacity per unit volume.