Fuel-Cycle Analysis of Fuel Cells for Combined Heat, Hydrogen, and Power Generation

Abstract

The fuel-cycle energy use and greenhouse gas (GHG) emissions associated with the application of fuel cells to combined heat and power (CHP) generation and combined heat, hydrogen, and power (CHHP) generation are evaluated and compared with the combustion technologies of internal combustion engines and microturbines, as well as with the various technologies associated with hydrogen production and grid-electricity generation in the United States. Two types of fuel cells are considered in this analysis: a phosphoric acid fuel cell (PAFC) capable of following either heat or electric load and a molten carbonate fuel cell (MCFC) that typically follows the electric load. Three types of facilities (hospital, large office building, and warehouse) are examined in two different climatic regions (Chicago and Los Angeles) to span a wide range of electric-to-heat load ratios. Two different approaches for fuel cycle analysis of CHP and CHHP applications are considered in this analysis: a total demand approach and a displacement approach. The total demand approach provides an accurate assessment of the impact of actual demand on total energy use and GHG emissions, while the displacement approach projects the potential for more energy savings and GHG emissions benefits relative to the supply of electricity from the grid generation mix. The fuel cycle results are primarily impacted by the efficiencies of hydrogen production and electric power generation, as well as by the utility factor of the co-produced heat. The energy use and GHG emissions associated with the electric power generation represent the majority of the fuel-cycle’s total energy use and emissions for all pathways. More energy and GHG emissions benefits are realized from fuel cell technologies with increased use of available coproduced heat. In general, CHHP systems exhibit more energy and GHG emission benefits than CHP systems for any of the investigated fuel cell technologies.