The goal of this work is to present and explain a simple techno-economic analysis of a hybrid plant consisting of a floating photovoltaic power plant, a desalination system and a pumped hydro storage plant. It is rare that an island today has sufficient sources of drinking water to meet the needs of the population, especially the additional imapct of increased consumption of the resources due to the tourist season. With the aim of solving this problem, a desalination system was considered, which would replace the current imports of drinking water with its produciton, and on the islands that have their own sources of drinking water, as a guarantee that there would be no excessive pumping of said sources. The necessary energy for desalination would be provided from the solar energy, by means of a photovoltaic power plant, which as a technology is rapidly developing and gaining more importance. Pumped hydro storage plant was considered as a separate system in this task due to the simplification of the techno-economic analysis, although in reality it must be considered as a joint system that can provide additional flexibility. The island of Cres was chosen as the most suitable island for the application of the three observed systems. Due to its natural source of water in the form of lake Vrana, which supplies the entire Cres-Lošinj archipelago, a case of refilling the lake with desalinated water was observed in order to prevent excessive pumping in the future and the risk of salinization of the only source of drinking water on the observed archipelago. Vrana lake, due to its geographical location and large surface area, is ideal for setting up a floating photovoltaic power plant and will also, in this work, serve as the lower storage lake of a pumped hydro storage plant. The results of the analysis show the profitability of this project in terms of economic and energy development of the island.