Energy density calculations for ball-lightning-like luminous silicon balls

The energy density of a luminous silicon ball [Phys. Rev. Lett. 98 048501 (2007)] is calculated for a model with a metal core surrounded by an atmosphere of silicon oxides. Experimental data combined with the molecular orbital calculations of the oxidation enthalpy lead to a mean energy density of 3.9 MJ m$^{-3}$, which is within the range of estimates from other ball lightning models. This result provides a good evidence to support the silicon-based model.