The negative impact of greenhouse gases and emissions of pollutants into the atmosphere force international organizations to take measures to reduce them. The International Maritime Organization (IMO) has worked out the strategy, whose provisions are aimed at reducing harmful emissions from ships into the atmosphere to zero. Achieving this goal is directly related to improving the energy efficiency of marine electric power systems, as the main elements generating, distributing and converting different types of energy. The concept of vessels with electric propulsion is becoming the most promising option for the implementation of “green energy” on ships. There has been considered the current state in solving technical problems to achieve zero emissions through the use of marine unified electric power systems with a DC distribution bus, the use of energy storage devices, supercapacitors. There have been illustrated the single-line diagrams of the electric power system of ships: with an autonomous propeller electric unit, with general DC distribution buses. The dependences of the efficiency of a synchronous generator MSK103-4 type on the frequency of the output voltage for load capacity of 20, 80, 140, 200 kW are given. The frequency fluctuations of the output voltage of a gas-diesel generator at 100% load have been analyzed. The main directions for improving power efficiency are outlined. It has been inferred that using modern technologies and materials is necessary to improve the energy efficiency of the electric power systems of ships and reduce emissions of harmful substances into the atmosphere.