Regenerative hydrogen fuel cell for remote, off-grid telecommunication towers

Abstract

There is an urgent need to provide cost-effective, clean, distributed electricity to ensure the reliability of remote, off-grid telecommunication towers in Sub-Saharan Africa. Extensive literature research resulted in the design of a novel system architecture for hydrogen-based energy storage, which uses the thermodynamics of solid-state hydrogen storage in a Titanium-based metal-hydride, coupled with a Polymer Electrolyte Membrane (PEM) Electrolyser (PEMEL) and PEM Fuel Cell (PEMFC) to form a Regenerative Hydrogen Fuel Cell (RHFC). Electrochemical Impedance Spectroscopy and Polarisation Curves of a single-cell PEMFC have been obtained through empirical testing to determine the effect of cross-sectional flow-field geometry on the performance of the PEMFC. Results indicate that a Hemispherical cross-sectional flow-field design shows a reduced concentration overpotential of 42 millivolts (mV) at 1.04 Ampere/square centimetre (A/cm2) compared to second-best Trapezoidal with 83 mV. A holistic modelling approach is followed for a hybrid energy system, resulting in a comprehensive semi-empirical MATLAB/Simulink model including dynamic losses of the power conditioning equipment. The model is optimised through semi-empirical parameterisation of the PEMFC and metal-hydride model using Levenberg-Marquardt algorithms. Empirically obtained dynamic telecom tower load data is used. The results show the overall system efficiency of the hybrid energy system drop from 21.05% for a Solar Photovoltaic (PV)/Battery system to 17.43% of the most cost-effective hybridised system; 16.2 kilowatt (kW) Solar PV coupled to a 10kW/40 kilowatt-hour (kWh) Lithium-Ion (Li-Ion) battery and an RHFC (consisting of a 10kW PEMEL, 1,000kWh Titanium-based Solid-Hydrogen Storage Cell, and 5kW PEMFC). This system achieves a Levelised Cost of Electricity (LCOE) of 21.51 ¢/kWh compared to 82.65 ¢/kWh for a Diesel Genset, with a Net Present Value of $98,876.81 and an Internal Rate of Return of 13.08%. Furthermore, an additional case study is performed to assess the feasibility of telecommunication towers doubling as a microgrid. The system uses a Solar PV/Wind/RHFC system, and the financial and environmental benefits are assessed. The proposed system is modelled in MATLAB/Simulink and consists of 45 kW Solar Photovoltaics and 60 kW Wind Turbine primary power generators and an autonomous RHFC consisting of a 35kW PEMEL, 20,000 kWh metal-hydride hydrogen storage and 25kW PEMFC. The system shows a low LCOE of 37.35¢/kWh compared to 100.51¢/kWh for a conventional Genset.