The Economic and Environmental Aspects of <i>Miscanthus</i> × <i>giganteus</i> Phytomanagement Applied to Non-Agricultural Land

<i>Miscanthus</i> × <i>giganteus</i> (<i>M</i> × <i>g</i>) is a promising energy crop in phytotechnology with biomass production. Despite considerable vegetation and harvest under varying climate conditions and across different soils, field-scale studies on utilising <i>M</i> × <i>g</i> remain scarce. Analysing the literature and our own findings, this study intends to highlight the potential of <i>M</i> × <i>g</i> phytotechnology for revitalising non-agricultural lands (NAL), including brownfields, and illustrate the expediency of applying biochar to enhance biomass yield, energy efficiency, and economic feasibility. To validate the feasibility of <i>M</i> × <i>g</i> production on brownfields, two scenarios within the value chain “biomass–biogas–electricity” for green harvest were examined. The assumptions were as follows: (1) a methane yield of 5134 m³ ha⁻¹ y⁻¹, and (2) substrate-specific methane yields of 247 and 283 mL (g oDM)⁻¹ for the first and subsequent years, respectively. The findings suggest that Scenario 2 is better suited for cultivating <i>M</i> × <i>g</i> on brownfields/NAL, being more sensitive and eliminating inaccuracies and the generalisations of results. From the third year onward, the revenue of <i>M</i> × <i>g</i> production on biochar-amended brownfields showed greater potential for future profitability. Future research should confirm the positive trend in the energy efficiency ratio of <i>M</i> × <i>g</i> phytotechnology on a larger scale, particularly in real brownfield applications.