This thesis tackles the designing of a small-scale alkaline electrolysis cells (AEC) unit for large-scale production. This apparatus is applied for the production of pressurised hydrogen by employing solar energy. The goal is to minimise production costs while ensuring the safety of the unit operation throughout its lifespan. Although the employed technology is mature in the industry, large-scale production of such units still represents a novelty. Zero Emissions Fuel, ZEF, is currently carrying on the development of an electrolyser able to autonomously operate by two standard photovoltaic panels. The study includes the designing of a bipolar electrolysis cell with thermoplastics and its optimisation for injection moulding. Likewise, methods for ensuring the leak-tightness of the unit are investigated and evaluated through distinct experiments. The concept development is focussed on the satisfaction of the main functional requirements for the AEC unit. Hence, operating conditions of stress, temperature and chemical corrosion he been taken into account to identify the material selection of each component.The proposed design is as twice as powerful compared to the previous development, within a much smaller and lighter form factor. Similarly, the unit cost has been reduced by a third.