In recent years, there has been an increased emphasis worldwide on the quality of the environment, especially with an orientation towards the application of renewable energy sources. In addition, we are increasingly encountering experimentation aimed at obtaining new green energy sources. One of such sources is biomass. Biomass has been used since the middle ages as a source of heat and light energy. Today, however, we have technologies that allow us to obtain not only heat but also electricity from biomass, or to convert biomass into materials with high energy density and purity. The energy thus transformed can then be used, for example, as a propellant. At the same time, this valuable source of clean energy can be easily transported to the place of consumption. By applying biomass as a source of green energy, we can make a significant contribution to relieving the environment from harmful effects. In recent years, an increased interest in energy obtained from biomass can be observed in Slovakia. Its technical potential is the greatest among other renewable energy sources, and its non-use would essentially be wastage. Therefore, the aim of the paper was to describe two possibilities of transformation of biomass in the form of its energy recovery into the type of energy used for the production of mechanical, thermal and electrical energy. At the same time, in addition to obtaining a suitable form of energy from biomass, another environmental benefit was sought in the form of soil decontamination. In this regard, there is an energetically important crop, which is known under the Latin name Amaranthus caudatus. It is an energy crop that can be grown on slightly contaminated soil with some restrictions. Two methods of energy recovery of this crop were compared. In the first case it was its compaction into briquettes, in the second case it was a process of anaerobic fermentation with subsequent production of biogas. Based on the performed analysis, it was found that these are almost equivalent energy sources. Although both methods of transformation and energy recovery of the green part of Amaranthus caudatus crops have a number of advantages and disadvantages, it can be clearly stated that the positives significantly outweigh the negatives. Therefore, it is recommended to apply this crop as a valuable source of energy for use in real conditions.