In this paper a small-scale combined heat, hydrogen and power (CHHP) system, in which ammonia is used as a fuel for a solid oxide fuel cell (SOFC) to produce 100 kg/day of hydrogen (for refueling up to 20-30 fuel cell vehicles) as well as electricity for electric vehicles fast charging and heat for local use, is proposed. The study is carried out by means of experimental and numerical analysis; in particular, the behaviour of a single solid oxide cell fed by ammonia is investigated through experimental tests, while the design and the performance assessment of the proposed CHHP plant configurations are predicted by means of a thermo-electrochemical model, properly developed. The employed methodology and procedure are based on the SOFC power unit "sizing approach" that is performed through two different design concepts: (a) the minimum SOFC power unit size that allows to produce hydrogen and electricity for self-sustaining the electric power demand of the system; (b) the minimum SOFC power unit size that allows to produce hydrogen, to satisfy the system electric power demand and to supply electricity for EVs fast charging. Results in terms of performance (referred to the high heating values of input and output fuels) highlight that low values of electrical efficiency (14% for Concept_2) and thermal efficiency (<= 15% for Concept_l and Concept_2) are achieved, due to the high conversion of ammonia in hydrogen (the hydrogen production efficiencies are 70% and 42%, respectively), while the trigeneration efficiencies are high (81% and 71%).