SOFC System Costs

There is a large potential market for distributed power and CHP that can be fulfilled by SOFC systems. The high SOFC system cost is the main obstacle to penetration of this market. A capital cost of SlOOO-Sl 500 per kW is very often quoted for SOFC systems to be competitive. Current capital costs are considerably higher, although these costs are continually coming down as the development proceeds. 

The main operational costs for a SOFC system are desulphuriser absorbent and catalyst replacement regular gas turbine maintenance (including air filter replacement) for hybrid systems SOFC stack replacement and plant operation and administration. Siemens Westinghouse expects Operation and Maintenance 

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Even at these low sulfur concentrations, desulfurization of the fuel gas is needed. Pretreatment of the fuel can solve this problem, but a sulfur-tolerant anode would eliminate the need for pretreatment, helping to reduce SOFC system costs. It has recently been shown that trace amounts of SOx in air could potentially also be a problem for cathodes during long-term operation. 

The benefits and feasibility of hybrid systems have been established with conceptual studies and small-scale demonstrations fueled with natural gas. If large-scale, greater than 100-MW, fuel cell/turbine hybrid systems are to become a reality a reduction in fuel cell costs and scalability to larger units is required. The SECA program demonstrated 3 to 10 kW SOFC systems with costs of less than 800/kW in 2005. 

Hydrogen can be separated from the flue gas at low cost in high-temperature fuel cells. A SOFC system may be able to cogenerate hydrogen for about 3.00 per kg which can match gasoline. Since these fuel cells could be part of the fueling station, there would be no need for a hydrogen delivery infrastructure. 

Additionally, nickel is a well established steam-reforming catalyst. An ideal SOFC system operated on natural gas applies internal steam reforming, i.e., the reforming of the methane takes place in the anode compartment of the stack. This type of system is favored for system simplicity and costs (no external reformer), and for system efficiency because the heat generated by the cell reaction is directly used by the reform reaction, and hence the cooling requirements of the stack (by air at the cathode side) are significantly reduced. 

Detailed cost and design studies for both PEFC and SOFC systems at sizes ranging from 5kW to 1 MW were made that point to the fundamental differences between PEFC and SOFC technology that impact the system design and by implication the cost structure. These differences will be discussed in the following paragraphs. 

The main difference in SOFC stack cost structure as compared to PEFC cost relates to the simpler system configuration of the SOFC-based system. This is mainly due to the fact that SOFC stacks do not contain the type of high-cost precious metals that PEFCs contain. This is off-set in part by the relatively complex manufacturing process required for the manufacture of the SOFC electrode electrolyte plates and by the somewhat lower power density in SOFC systems. Low temperature operation (enabled with electrode supported planar configuration) enables the use of low cost metallic interconnects which can be manufactured with conventional metal forming operations. 

Figure 1-16. Projected cost structure of a SkWnet APU SOFC system. Gasoline fueled POX reformer, Fuel cell operating at 300mW/cm, 0.7 V, 90 % fuel utilization, 500,000...

Given the large number of potential beneficial effects of lowering the nominal operating temperature of the SOFC stack and their corollary affect on system cost, intermediate temperature SOFC concepts are being pursued by many organizations throughout the U.S. and the World. 

Compressor Intercooling Whether a compressor should be intercooled or not depends on the trade-off between the increased efficiency of the intercooled compressor and its increased capital cost. In general, intercooling is required for large compressors with pressure ratios that exceed approximately 5 1 (44). The designer also should consider whether the heat is advantageous to the process. For example, when near the 5 1 pressure ratio, it may not be appropriate to intercool if the compressed stream will subsequently require preheating as it would with the process air stream of an MCFC or SOFC system. 

The main differences in high-temperature fuel-cell stack cost structure relate to the fact that they do not contain high-cost precious metals, on the one hand, and that they demand more complex manufacturing process, on the other. It must be noticed therefore, that, the fuel-cell stack is, in many cases, responsible for less than one third of the total capital cost of a fuel-cell system, and that a large portion of the total cost is caused by fuel pretreatment (reforming, cleaning etc.), plant control, and power conditioning. For small-scale SOFC systems, the cost of the stack is of the order of 40-45% of the total cost. 

Table 3.8. Estimates of SOFC and MCFC distributed power generation system cost (Blesl el al., 2004)...

The utilisation and the on/off cycles of a CHP system affect its potential benefit. Furthermore, higher overall efficiency leads to lower fuel consumption, while longer lifetimes lead to lower annualised capital costs. Concerning the relative influence of the demand profile, the nominal electric capacity, the efficiency and the lifetime of AFC, PAFC, PEMFC and SOFC systems, target costs were found to lie in a rather wide range. 

In order to reduce the capital costs of SOFC systems, Steele has suggested operating a SOFC at lower temperature, 800-1050 K, such that the expensive bipolar ceramic plate can be replaced by a metallic alloy or stainless steel (Steele et al. 1994, Steele 1996). In order to select a suitable electrolyte, for any given operating temperature, Steele has provided a comparison of the electrolyte area resistance ... 

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