Energy willow as a species with broad adaptation possibilities, large production capacity and a wide range of applications, takes a special place among the plants grown for energy production. In this work an analysis was conducted in respect of the usefulness of this type of wood from experimental plantations as a clean source of energy generated in the combustion process. The heat of combustion and net calorific value of dry matter of energy willow wood, including selected sorts and classes of thickness were determined. Energy willow has a natural ability to accumulate heavy metals which are oxidized during the combustion process or remain in the ash, and consequently repollute the environment. In order to determine the environmental impact the content of heavy metals was examined in energy willow wood and in the soil of the experimental plantation. Metal concentrations were determined by the Atomic Absorption Spectrometry method (AAS). Results of the tests confirmed a close relationship between the heat of combustion, calorific value and wood thickness as well as its location in the tree structure. Furthermore, very large differences were found in the content of heavy metals in the samples of both willow wood and soil. The levels of heavy metal content in the wood of energy willow determine the agricultural use of ashes produced during combustion.