Hydrogen production methods are energy consuming, thus during its life cycle there is always production of pollutants. One potential way to reduce pollution is the electrolysis combined with renewable electrical energy sources, such as solar or wind sources. In the present paper a thermo-economic optimization is accomplished for localized small to medium capacities hydrogen electrolyser production plants for cars fuelling. The optimization is achieved by means of the Genetic Algorithms considering energetic, economic and environmental objectives. In addition, an investigation on the properties of CNG-H2 mixtures and their effects on the engine performance and vehicles range is carried out.