This paper deals with the influence of the final drying degree of biomass with a high water content on the operation of energy systems with integrated indirect dryers. For a description of the drying process, experiments with wet bark containing about 50 wt% of water were carried out in a laboratory indirect dryer. Based on the calculations of the dryer and boiler energy balance, the optimal degree of biomass predrying before combustion between 30 and 20 wt% was evaluated in terms of the technical optimisation of the boiler efficiency and the effectivity of the drying process.