This paper presents the results of an experimental analysis performed on a miniaturized, 6We Proton Exchange Membrane Fuel Cell (PEMFC) system, integrated with on-site hydrogen production by electrolysis; in particular, the effects of environmental parameters such as the external temperature and the humidity on the performance of fuel cells are investigated. PEMFC systems are zero-emissions power technologies when they are fed with pure hydrogen (at concentration higher than 97%); also, being the only results of system operation the produced electricity and some pure water, when produced by renewable sources hydrogen can be considered an attractive alternative to fossil fuels and may concur to the reduction of pollutant and greenhouse gas emissions deriving by combustion processes. A miniaturized, few watts capacity system may represent a safe and unexpensive solution to perform analysis and predict the on-site performance of larger FC applications. The micro-model used for the experimental characterization is a module of a flexible, larger scale system, which is briefly described in the paper; the entire system is equipped with Nafion 112 membranes, two electrolysers, hydrogen storage devices and a Photovoltaic (PV) panel. The results presented in this paper are only a first set of results; others are expected to be obtained in the future by an outdoor monitoring campaign of the entire system, needed to allow an effective prediction of the on-site performance for stand-alone PEMFC systems fed by solar energy. After having simplified the analysis by excluding the parameters that the experimental data revealed to be less influent, at the end of this paper the characterization of the PEMFC system is completed by introducing a semi-empirical model, derived by graphic analyses and data regressions.