Blackouts in the mid-twentieth century in the USA and some European countries implied a necessity of the hierarchical natural monopoly power system (PS) deregulation. The most important target of PS operation is to deliver reliable electric energy (with proper parameters), which implies the necessity to include all existing sources of electrical energy (mostly renewable energy sources – RES) in the power grid. The existing networks could not provide those types of duties hence it was necessary to start with the Smart Grid (SG) idea with new characteristics of the power grid. The rapidly growing number of RES, the ones installed in smart homes in particular, has led to reduced consumption of electricity. This has required a new organization of distribution networks, i.e. development of microgrids and prosumers, changing the static hierarchical information system into a dynamic dispersed electric power system. This consequently implied the need to replace the existing electricity market with a new one. As a result of the electricity and gas system integration, efficiency of the electricity system has increased, however due to different market targets it is necessary to develop a new integrated market. It would also cover smaller energy systems, using such sources as liquid fuel, hot water that potentially could become integral parts of the new integrated market. In the process of building the new integrated energy market it will be necessary to take into account the need for long-term expenses on transmission and distribution networks modernisation applying direct current and using experience of advanced utilities/companies in the U.S.A., Europe, China and some other countries.