This research focuses on novel designs of powder-to-water hydrogen generators for "on-demand" use, with hydrogen-based fuel cells. Hydrogen is produced in a chemical reaction between water and hydride sodium with the assistance of a catalyst. This configuration allows high energy density, together with portability, and easy to use, refill or clean. We describe our experience in implementing powder-to-water generators for a portable integrated power system. Five different prototype designs were developed, built, examined and characterized. Tests have been carried out in order to monitor hydrogen production, operation, and reaction conditions (i.e., hydrogen flow, motor power, reactor temperature, and pressure) and to evaluate the prototypes feasibility, efficiency and performance. We show relatively constant on-demand hydrogen flow (of about 400 mL/min) for extended durations (5-7 h), with short (<15 min) operation breaks, with a hydrogen density of 4.5 wt % (out of reactants) and estimated energy density of 1400 Wh/kg. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.