Grid connected inverter suitable for economic residential fuel cell operation

Due to environmental concerns and limited hydrocarbon fuel reserves, R&D effort is being put into alternative energy sources like geothermal, photovoltaic, wave and wind, as well as fuel cells which use hydrogen to generate electricity without increasing pollution. Fuel cells for a residential application, with combined heat and power (CHP), may offer a viable energy source when both thermal and electrical outputs are associated with energy storage. The addition of grid connection improves reliability and offers the option to sell surplus energy when economically justified. A fuel cell has a variable, low voltage dc output requiring a power electronic interface to any energy storage and to ac loads. A simple inverter topology can be adopted based on minimum component count. This paper presents the design, simulation and experimental verification of an economic arrangement utilising an intermediate voltage storage battery and a bidirectional dc/ac interface suitable for domestic ac loads and grid synchronisation. The design was modelled in Matlab/Simulink. An economic model of the fuel cell/battery/grid system, operating in micro-CHP mode, was developed to assess the prospects for commercial exploitation and to characterise the relationship between domestic load profile, fuel cell rating and battery capacity to optimize life time cost. This model assumes natural gas for the fuel cell, as hydrogen infrastructure is not yet available. The economic model results and their interpretation will be the subject of a future publication