This paper analyses the chemical conversion process of biomass based on a diluted acid hydrolysis step, the Biomass Energy Process (BEM). The discussion starts from the technical point of view on the base of information reported literature, experimental laboratory analyses and pilot plant tests and then the authors tentatively explore the energy related costs of the process giving a comparison of the biomass derived solid fuel and fossil fuels. An evaluation of the product (cellulignin powder compacted into briquettes) and considered as a fuel and other energy sources from fossil resources like oil, natural gas and coal, is reported considering the energy density and energy cost. The main technical feature of the process is the conversion of almost every type of bug wood biomass with a large range of chemical and physical characteristics. The hydrolysis step determines the energy price and the threshold cost of the cellulignin is calculated at 60-70 euro/t about over which the NG energy is preferable. Environmental concerns can be however considered.