System Specifications

Selected specifications for the 20 kW system are summarized as follows:

Fuel: Pipeline natural gas at 2 in w.c. minimum

AC Power Output: 0-20 kW continuous; 208Y/120 VAC, 60 Hz, 3 phase

Maximum Current: 65 A rms per phase (23.4 kVA to balanced load)

Grid Connection: Normally interconnected. Capable of stand-alone operation during grid outages. Will load-follow or export power as desired.

Ambient Conditions: Outdoor or indoor

Optional Heat Recovery: Water heating to 160°F. Maximum of 18000 BTU/hr.

Emissions: Less than 3 Ib/GWh NOx. Undetectable particulates, CO, organics

Noise Level: Less than 65 dbA at 3 feet

Size: 26 inches square by 78 inches tall


Current Harmonics:


Parallel Operation: Dynamic Response:


Approximately 1000 pounds

Less than 4% total at rated load, grid interconnected Easily meets IEEE-519

Air filter cleaning while operating Once per year preventative maintenance (6-hour outage) Any number of system modules.

1% to 100% output: less than 4 sec. 100% to 1% output: less than 2 ms.

At 100% output: 44% net AC output/natural gas HHV At 70% output: 49% At 40% output 50% At 20% output: 45% At 10% output: 31%


The basic TMI SOFC was designed to overcome problems associated with high-temperature operation and for low cost manufacture using available fabrication techniques. A key characteristic of the patented design (Fig. 1) is the use of porous, non-sintered, particulate electrodes. Non-sintered particulate electrodes eliminate problems caused by coefficient of thermal expansion mismatches at the interfacial boundaries. This allows the use of metal separators and substitution of materials optimized for electrical and other catalytic properties -(such as sulfur tolerant electrodes) rather than for thermal expansion properties. Porous electrodes support the metal separators, which allows use at higher temperatures since creep concerns are eliminated. Radial gas flows do not require external manifolds and allows for improved thermal management.


Air Air

Figure 1. TMI SOFC Stack (exploded view with flows)


Lanthanum Strontium Manganite

Cathode Seal




Anode Seals



Mcfef-Zircon/a Cermet


Metal Alloy

Air Air

Figure 1. TMI SOFC Stack (exploded view with flows)

• Individual cells are currently at near-commercial size and performance (approximately 55 mm diameter by 1.5 mm thick at over 100 mW/cm2) and operates between 900°C and 1000°C.

• Commercial stacks will be about 320 cells (for 120 and 208 VAC models) and operate at close to 90% electrochemical fuel utilization on reformed natural gas. Target stack life is 3 to 5 years.

• Over 500 stack tests (plus thousands of single-cell tests) have been performed to date with some stacks exceeding first-generation commercial performance assumptions.

• Stacks have been operated on military logistic fuels containing up to 0.3 wt%S.

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