At present, when fuel resources are becoming increasingly limited, in the face of ever-increasing demand for energy, and constantly risingjuel prices, energy efficiency evaluation issues are of particular importance. The above factors alsoforce activities almedat obtaining energy from renewable sources (RES). Furthermore, the current global climate changes, caused by emissions of greenhouse gases (GHGs), that accompany the production of energy, force an action to be taken in order toprotect the environment. Conseąuently, the directions ofthe current research studies, and financing there of, are oriented towards the search for new technologies and the development of new eguipment which provide energy efficiency even higher than before as well as the possibility of obtaining energy from renewable sources. The problem of drawing up the energy balance, presented in this paper, has been narrowed to issues related to maritime transport, and especially to the assessment of the energy efficiency in the process of marine power plant operation. The article presents the concept ofdrawing up the energy balance, together with the results of studies in this regard, concerning a selected marinę power plant. On the basis of research results obtained, one can assess the energy efficiency of the selected marine power plant and analyse the potential of its increase. The article also presents directions of efforts undertaken in marine power plant design, and dlscusses their examples, with the aim of increasing their energy efficiency and protection of the marine environment.