Molten salts have been used to good effect.

The net mass of the fused atomic nuclei is smaller than the sum of the constituents.

Another possibility is to use a phase change material as thermal storage where latent heat is used to store energy.

Because of the lack of impurities in the leftover regions which solidify, the boule can grow as a perfect single crystal if a seed crystal is placed at the base to initiate a chosen direction of crystal growth.