The purpose of the work is a simulation model (in the Matlab environment) of a hypothetical stand-alone energy system in design conditions. This system is based just on renewable sources (solar and micro-hydroelectric energy) integrated with a hydrogen energy system (electrolyzer, hydrogen storage, PEM (proton exchange membran fuel cell). It could supply the whole electric and part of the heat requests of a small residence situated in a remote mountainous area (e.g. an isolated village in the Italian Alps) during a complete year of operation. The work is made up of two. The subject of this first paper is the simulation of the performances of the micro-hydro power source. To obtain the flow duration curve necessary for a correct design of the micro-turbine, the following hypothesis have been made: the behavior of the mountain basin is modeled like a linear reservoir, the rainfall is described as a marked Poisson process and the snowmelt is modeled using the empirical temperature-index approach. The result of the simulation is the hourly electrical output as a function of the daily flow of available water. A single micro-turbine is enough for this basin. The maximum value of electric power obtained during spring months corresponds to 1400 W and the annual electric energy produced by this plant is in the order of 4 MWh/yr.