Three unconventional herbaceous energy plants – sida (Sida hermaphrodita Rusby), elephant grass (Miscanthus giganteus) and reed canary grass (Phalaris arundinacea) – were grown and investigated in the experimental fields of Aleksandras Stulginskis University, and the technical means of plant preparation and usage for energy purposes were investigated. The physical-mechanical characteristics (moisture content, density, flow angles) of chopped and milled unconventional energy plants were investigated. These characteristics are required to project and choose the supply, transportation and storage equipment. In evaluating the quality of plant chopping and milling, the fractional compositions of reed canary grass, sida and elephant grass chaff as well as the mill were determined. The largest chaff fraction was found in a sieve with 8-mm diameter holes (from 52.0 to 62.7%), and the largest mill fraction was found in a sieve with 0.5- and 0.63-mm diameter holes (from 37.6 to 46.4%). The pellet moisture content was sufficiently low and varied from 6.7% to 9.6%. The highest density was determined in reed canary grass pellets (1035.1±63.9 kg m^-3 DM), and the lowest density was in elephant grass pellets (653.6±67.1 kg m^-3 DM). The emission of harmful gases was determined when various unconventional energy plants were burned. The highest concentration of carbon monoxide (CO) was observed when burning elephant grass (2294.7 ppm), and the smallest concentration of CO was observed when burning reed canary grass (905.2 ppm). The most carbon dioxide was detected when burning sida (7.9%), and the smallest when burning elephant grass (5.2%). The nitrogen oxide emissions differed only insignificantly; the values ranged from 176.2 ppm (Reed canary grass) to 216.1 ppm (Elephant grass). The production of granules, when biomass was not dried artificially in a dryer, was calculated to have a prime cost of 0.12 EUR/kg. When energetic grasses were dried using dispergation, the primary cost increases to 0.13 EUR/kg.