I think you know how! Plantation is the only way. For more information you have to elaborate your question.

First, you need to define or adopt a charcoal - wood conversion factor.

This means you need to know the amount of wood (weight or volume) to reach one ton of charcoal. Thus, you'll be able to estimate the amount of wood needed to meet your annual charcoal demand.

Finally, assuming that your forest has any annual productivity (average annual productivity per hectare), you can estimate the amount of area needed to equalize your annual consumption of charcoal and wood production.

concerting biomass to charcoal really depends on biomass quality and fire conditions, like temperature, oxgen, etc.