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Research Papers

# Techno-Economic Optimal Design of Solid Oxide Fuel Cell Systems for Micro-Combined Heat and Power Applications in the U.S.

[+] Author and Article Information
Robert J. Braun

Division of Engineering, Colorado School of Mines, Golden, CO 80401

Ejector efficiency is defined as $ηejector=(V̇2/V̇1)⋅(P2⋅ln(P3/P2)/(P1−P3))$ where $V̇$ is the volumetric flow rate and $P$ is the static pressure at the denoted location in the ejector. Subscripts 1, 2, and 3 refer to the primary driving flow (fresh air), the secondary flow (recycle), and the mixed flow at the ejector outlet, respectively.

The value of heat is estimated as the difference between $COEeo−COECHP$.

J. Fuel Cell Sci. Technol 7(3), 031018 (Mar 16, 2010) (15 pages) doi:10.1115/1.3211099 History: Received February 15, 2009; Revised June 01, 2009; Published March 16, 2010; Online March 16, 2010

## Abstract

A techno-economic optimization study investigating optimal design and operating strategies of solid oxide fuel cell (SOFC) micro-combined heat and power (CHP) systems for application in U.S. residential dwellings is carried out through modeling and simulation of various anode-supported planar SOFC-based system configurations. Five different SOFC system designs operating from either methane or hydrogen fuels are evaluated in terms of their energetic and economic performances and their overall suitability for meeting residential thermal-to-electric ratios. Life-cycle cost models are developed and employed to generate optimization objective functions, which are utilized to explore the sensitivity of the life-cycle costs to various system designs and economic parameters and to select optimal system configurations and operating parameters for eventual application in single-family, detached residential homes in the U.S. The study compares the results against a baseline SOFC-CHP system that employs primarily external steam reforming of methane. The results of the study indicate that system configurations and operating parameter selections that enable minimum life-cycle cost while achieving maximum CHP-system efficiency are possible. Life-cycle cost reductions of over 30% and CHP efficiency improvements of nearly 20% from the baseline system are detailed.

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## Figures

Figure 1

Process flowsheet of methane-fueled SOFC-CHP system with external reforming (Case 2a)

Figure 2

Process flowsheet of hydrogen-fueled SOFC-CHP system (Case 1a) and with CGR (Case 1b)

Figure 3

Process flowsheet of CH4-fueled SOFC-CHP system with IR and tail gas recycle (Cases 4b and 5)

Figure 4

Normalized capital cost for each system configuration

Figure 5

Normalized cost-of-electricity and life-cycle cost for each system configuration: (a) normalized COE and (b) normalized LCC

Figure 6

Breakdown of life-cycle cost contributions: (a) Case 2a cost breakdown and (b) Case 5 cost breakdown

Figure 7

Normalized life-cycle savings versus system configuration

Figure 8

The effect of cell voltage on normalized LCC, system efficiency, and stack size: (a) system efficiency and number of cells in SOFC stack, and (b) normalized LCC

Figure 9

The effect of cell temperature and air temperature rise on normalized SOFC-CHP LCC: (a) LCC versus cell temperature and (b) LCC versus cathode air temperature rise

Figure 10

Comparison of SOFC-CHP and conventional system life-cycle costs

Figure 11

Sensitivity of normalized life-cycle and capital costs to production volume and system size: (a) LCC sensitivity to production volume and (b) LCC sensitivity to power rating

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