Exergy & economic analysis of biogas fueled solid oxide fuel cell systems

• Exergy analysis of a pressurized SOFC integrated with an anaerobic digester.
• Capital cost estimation of all major equipment in AD-SOFC power plant.
• IRR economic analyses of AD-SOFC system with sensitivity analysis.
• Compared values of IRR with other available technologies for biogas utilization.
• Of options studied, AD-SOFC achieved both highest efficiency and highest IRR.

We present an exergy and an economic analysis of a power plant that uses biogas produced from a thermophilic anaerobic digester (AD) to fuel a solid oxide fuel cell (SOFC). We performed a 4-variable parametric analysis of the AD-SOFC system in order to determine the optimal design operation conditions, depending on the objective function of interest. We present results on the exergy efficiency (%), power normalized capital cost ($ kW−1), and the internal rate of return on investment, IRR, (% yr−1) as a function of the current density, the stack pressure, the fuel utilization, and the total air stoichiometric ratio. To the authors' knowledge, this is the first AD-SOFC paper to include the cost of the AD when conducting economic optimization of the AD-SOFC plant. Our calculations show that adding a new AD-SOFC system to an existing waste water treatment (WWT) plant could yield positives values of IRR at today's average electricity prices and could significantly out-compete other options for using biogas to generate electricity. AD-SOFC systems could likely convert WWT plants into net generators of electricity rather than net consumers of electricity while generating economically viable rates of return on investment if the costs of SOFC systems are within a factor of two of the DOE/SECA cost targets.