There are many factors to consider before making a decision.Just...

There are many factors to consider before making a decision.

Just considering energy storage (to melting point only).
Aluminium - Specific Heat~= 0.9 kJ/kgK (ie 900 Joules to raise 1KG by 1 degree)
- Latent heat of fusion ~= 390 kJ/kg
Silicon - Specific heat ~= 0.71 kJ/kgK (less than aluminium)
- Latent heat of fusion ~= 1800 kJ/kg
So to take 1kg of each from 20 degrees to a solid at the melting point
Aluminium ~= 576 kJ
Silicon ~= 990 kJ
To then melt each takes an additional
Aluminium ~= 390 kJ
Silicon ~= 1800 kJ

The materials will release the same amount of energy as they freeze & cool.
So silicon stores about 50% more as specific heat (due to much higher temperature) but about 400% more as latent heat.

So why would anyone consider aluminum over silicon? They will both boil water/heat air sufficiently.
The higher temperature of silicon imposes more issues with storage - aluminum wouldn't do as a container for a start.
Also need to consider effects on materials over time due to the higher temperature and what reactions may occur with materials stored in once melted and heating method.
Also safety - what would happen if there is a container failure? How viscous is the material, how toxic and difficult to contain?
How available is the material and ease to purify & prepare?

There are likely to be cases where each material is the best choice.