This paper presents an attempt to assess the potential use of Calamagrostis epigejos (L.) Roth. as a renewable energy source. Abandonment of human management is often followed by a decrease in species richness in semi-natural grasslands, mainly due to the increased dominance of clonal grasses such as Calamagrostis epigejos which were formerly repressed by management. The biomass resource of this, and its accompanying, species, i.e. species of the Solidago genus and others e.g. Cirsium rivulare, Deschampsia caespitosa, Molinia coerulea and Filipendula ulmaria, was evaluated in the green wastelands of the River Bytomka valley (Upper Silesia, Poland). It was found that approx. 1.2 t·ha⁻¹ of dry matter can be obtained from approx. 30% of the average share of Calamagrostis epigejos in plant communities of unmown meadows. This is 10 times less than in the case of Miscanthus giganteus, a non-native cultivated grass. An increase in the biomass component of Calamagrostis epigejos reduced that of Solidago sp. (−0.522176, p< 0.05) and other species (−0.465806, p< 0.05). The calorific value of Calamagrostis epigejos biomass is approx. 15.91 MJ·kg⁻¹, which is comparable to the calorific value of coal and close to, inter alia, that of Miscanthus sacchariflorus (19 MJ·kg⁻¹) as an energy crop. The presented research is in its preliminary stages and therefore, it is necessary to investigate the reaction of Calamagrostis epigejos to regular mowing and to removal of the biomass from the studied areas.