Generation of high-pressure hydrogen for fuel cell electric vehicles using photovoltaic-powered water electrolysis

Increasing the utilization of electric drive systems including hybrid, battery, and fuel cell electric vehicles (FCEV) will reduce the usage of petroleum and the emission of air pollution by vehicles. The eventual production of electricity and hydrogen in a renewable fashion, such as using solar energy, can achieve the long-term vision of having no tailpipe emissions, as well as eliminating the dependence of the transportation sector on dwindling supplies of petroleum for its energy. Before FCEVs can be introduced in large numbers, a hydrogen-fueling infrastructure is needed. This report describes an early proof-of-concept for a distributed hydrogen fueling option in which renewably generated, high-pressure hydrogen is dispensed at an FCEV owner's home. In an earlier report we described the design and initial characterization of a solar photovoltaic (PV) powered electrolyzer/storage/dispensing (ESD) system that was a proof-of-concept for a single FCEV home fueling system. In the present report we determined the efficiency and other operational characteristics of that PV-ESD system during testing over. a 109-day period at the GM Proving Ground in Milford, MI, at a hydrogen output pressure of approximately 2000 psi (13.8 MPa). The high pressure was achieved without any mechanical compression via electrolysis. Over the study period the photovoltaic solar to electrical efficiency averaged 13.7%, the electrolyzer efficiency averaged 59%, and the system solar to hydrogen efficiency averaged 8.2% based on the hydrogen lower heating value. A well-documented model used to evaluate solar photovoltaic power systems was used to calculate the maximum power point values of the voltage, current, and power of our PV system in order to derive the coupling factor between the PV and ESD systems and to determine its behavior over the range of environmental conditions experienced during the study. The average coupling factor was near unity, indicating that the two systems remained coupled in an optimal fashion. Also, the system operated well over a wide range of meteorological conditions, and in particular it responded quickly to instantaneous changes in the solar irradiance (caused by clouds) with negligible effect on the overall efficiency. During the study up to 0.67 kg of high-pressure hydrogen was generated on a sunny day for fueling FCEV. Future generations of high-pressure electrolyzers, properly combined with solar PV systems, can offer a compact, efficient, and environmentally acceptable system for FCEV home fueling. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.