The ultimate goals of sustainable development of the modern societies are planning and development of energy systems, thus the most of developed countries focused their energy policies on the development of sustainable energy systems. These systems should provide security of energy supply, they should be competitive and cause minimal impact to the environment. In a long term, only renewable energy sources supported by energy storage could fulfil these requirements. There are many RES and storage technologies so it is important to optimize their selection and integration in the energy systems. Today, there are many methods, methodologies and computer tools for solving problems of energy planning with high share of distributed and renewable energy sources but only few of them successfully integrate energy storage and provide adequate results. To enhance the security of energy supply, efficiency and safety of the grid connected energy systems, in the conditions of increased penetration of distributed and renewable sources, it is necessary to increase the flexibility of the system. This also includes increasing the capacities of energy storage, on the side of the power plants as well as on the end-use side. RenewIslands/ADEG methodology for the integration of energy storage is based on mapping of local needs for electricity, heating and cooling energy, transport fuels and similar, mapping of local potentials of RES, cogeneration and polygeneration and feasibility of energy storage and demand management measures, such as reversible hydro, batteries, compressed air storage, hydrogen, production of different fuels, water desalination, etc. Combined, with IEA FAST methodology for integration of variable renewable energy sources they qualitatively determine more detailed way towards 100% RES systems. As support of the methodology two energy planning models H2RES and EnergyPLAN were used for analysis of scenarios for development of 100% RES systems with integrated energy storage. Presented results include 100% RES islands, 100% RES electricity production for Portugal and 100% RES energy system of Croatia. Today the most widespread storage in the power systems is the pumped or reversible hydro storage which has many advantages but as any other storage technology it can be economical under certain conditions, and it has an impact to the environment. To ensure of necessary construction and minimize the risk to investors, feed-in tariff for storage system have been proposed. Thesis answers the question what is the role of energy storage in a planning of an independent energy system based on RES energy supply. It also shows how under a given circumstances energy storage maximises utilization of RES, provides security of energy supply and minimizes environmental impact of energy systems.