Generation 3 SOFC APU system

Solid oxide fuel cells use a hard, ceramic compound of metal oxides as an electrolyte, rather than the thin, permeable polymer electrolyte sheet in a PEM. Compared to other fuel cells, solid oxide fuel cells deliver more total power with relatively high efficiency. They run at much higher temperatures than PEM cells, however: more than 1,300º F (about 700º C). The APU system consists of the SOFC stack, a fuel reformer, and the balance of plant (power management, heat exchanger, and so on).

The Phase 1 test, completed by Delphi in April and validated by the DOE in May, included four key performance and cost goals. The DOE determined that Delphi’s SOFC unit met them all:

• Peak Power Performance. The demonstration system produced peak power of 4.24 kW using methane, achieving the goal of 3-10 kW.

• Peak Efficiency. The system demonstrated a peak efficiency of 37%, exceeding the Phase 1 goal of 35%.

• Power Degradation. The system matched the durability goal with power degradation of just 7% over 1,500 hours of operation.

• Factory Cost. The system met the Phase 1 goal of $800 per kW for the total power unit, assuming volume production, by achieving an estimated $770 per kW.

The Delphi team has passed an important test. In meeting SECA’s Phase 1 goals, Delphi has delivered to DOE’s National Energy Technologies Laboratory a fully operational, highly compact demonstration system, capable of meeting the space constraints of many potential mobile and stationary power applications. Their leadership at the systems level has greatly advanced this team’s progress toward a modular, broadly applicable SOFC power system by 2011.

—Wayne Surdoval

The DOE identified the SOFC as one of the ways to generate electrical power more cleanly and efficiently for a wide variety of stationary and mobile power applications. Coordinated by the DOE, SECA is currently undergoing a 3-phase, 10-year program that began in 2001 to develop the SOFC technology to help reduce US dependence on oil, while mitigating environmental concerns. SECA’s Phase 1 goals called for industry-led development teams to make meaningful progress in achieving cost, performance and durability improvements.

In addition to the Delphi team, there are five other industry teams working on different SOFC projects.

Delphi now moves on to Phase 2—a three-year, $45-million cost-shared contract between Delphi and the DOE. Phase 2 goals include reducing cost to $600 per kW; increasing efficiency to 40% or more; and increasing tthe powerdensity.

SECA’s final goal in Phase 3 is to deliver an SOFC power system capable of 40% or greater at a factory cost of $400 per kW. This performance will open up a wide range of mobile and stationary applications, from small-scale multi-kilowatt auxiliary power systems for vehicles and homes to larger-scale multi-megawatt industrial and utility fuel cell power plants.

Delphi has been developing SOFC systems since 1999. After demonstrating its first generation SOFC power system in 2001, Delphi teamed with Battelle under the SECA program to improve the basic cell and stack technology, while Delphi developed the system integration, system packaging and assembly, heat exchanger, fuel reformer, and power conditioning and control electronics, along with other component technologies.

Compared to its first-generation system in 2001, the Delphi-led team has reduced system volume and mass by 75%. By January 2005, the Delphi team was able to demonstrate test cells to DOE with power density more than required to meet the SECA 2011 goals.

In addition to its compactness, another benefit of the SOFC is the system fuel-efficiency, particularly if its high temperature co-product heat can be used in combination with its high electrical output. Heavy-duty trucks, for example, could utilize SOFC auxiliary power systems for both heat and electrical power when parked, to save 85% of the fuel that today they consume when idling their main engine, and likewise reduce idling emissions.

For the United States in total, extended idling of truck engines today consumes around a billion gallons of fuel annually.

SOFC systems can potentially operate on a full range of conventional and alternative fuels. This includes natural gas and conventional petroleum-based fuels like low-sulfur gasoline, diesel and propane; high-sulfur military fuels like JP-8 and jet fuel; low-CO₂ renewable fuels from biomass like ethanol, methanol and biodiesel; synthetic liquid fuels from coal and natural gas; and non-hydrocarbon fuels such as hydrogen and ammonia.

Resources:

• SECA Core Technology Peer Review Workshop (2005)

• Solid State Energy Conversion Alliance Delphi SOFC Annual Report

• SOFC APU: The Revolution Through Evolution (Delphi)