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Why SOFC Technology?

Like most fuel cell technologies, SOFCs are modular, scalable, and efficient. They are not subject to Carnot cycle limitations because they are not heat engines. Also, they benefit the public by minimizing emissions, such as oxides of nitrogen (NOx) <0.5 PPM compared to earlier combustion-based electrical power generation technologies due to lower operating temperatures. There are more reasons why SOFCs are the fuel cell technology of choice in USDOE/FE.

First, relative to other fuel cell types, SOFCs are fuel-flexible – they can reform methane internally, use carbon monoxide as a fuel, and tolerate some degree of common fossil fuel impurities, such as ammonia and chlorides. Sulfur-bearing contaminants, such as hydrogen sulfide, are tolerated less but can be dealt with using available commercial desulfurization methods. With internal reforming, this reaction is heat-absorbing and will tend to cool the cell and the module. This advantage can reduce the need for cooling air consequently reducing the parasitic power needed to supply that air.

Second, experimental data and analyses suggest that advanced SOFCs have an economic entitlement relative to prior established commercial technologies and the National Energy Technology Laboratory (NETL) evaluated fuel cell types. Planar SOFCs using a thin ceramic (yttria-stabilized zirconia, or YSZ) electrolyte could operate at lower temperatures (<800°C) than predecessor SOFC topologies, allowing the use of lower-cost stainless steel interconnects, rather than a costly and difficult-to-process ceramic interconnects required of higher-temperature SOFCs. Furthermore, the short conduction path from the anode of one cell to the cathode of the next results in lower ohmic losses and, therefore, higher stack efficiency and lower cost than many of its predecessors.

Third, SOFC is a high-temperature technology, thus its exhaust streams will tend to have high temperatures. High grade exhaust heat can enable high-efficiency combined cycle combinations such as SOFC/gas turbine/steam turbine.

Lastly, SOFCs are ideal for carbon capture in that the fuel and oxidant (air) streams can be kept separate by design, thereby facilitating high levels of carbon capture without substantial additional cost.

The Solid State Energy Conversion Alliance (SECA)

In 1999, USDOE/FE, through the NETL, founded SECA to develop low-cost, environmentally friendly SOFC technology. The SECA fuel cell program supports the emissions goals of FE’s technology portfolio. As previously discussed SOFC technology was an invention necessitated by environmental, climate change, and water questions about fossil fuel.

NETL, the SECA Industry Teams, and other organizations have conducted numerous system analyses for various integrated gasification fuel cell system configurations, with the most recent published in 2011. This work projects that SECA fuel cell technology can achieve 45 percent to 50 percent efficiency based on higher heating value [HHV] of coal, including 99 percent+ CO2 capture with near-conventional (e.g., enhanced ConocoPhillips) gasifiers. With advanced catalytic gasification, efficiency potential is 60 percent HHV, with 97 percent+ CO2 capture. These are near-zero emissions plants with significantly reduced water consumption relative to competing prior technologies due to the ability to capture and reuse the water produced within the fuel cell. In certain carbon dioxide pricing scenarios, NETL studies revealed the cost of electricity could be superior to prior technologies under consideration. Other technologies evaluated were supercritical pulverized coal, integrated gasification combined cycle, with scenarios for carbon capture, utilization or storage (CCUS). Natural gas fuel cell systems utilizing SECA technology may also be an alternative to the natural gas combined cycle with CCUS.

The SECA program is pursuing a fuel cell paradigm that in the longer term could have a dramatic impact on energy use in America. The program's ultimate goal is to scale-up and deploy fuel cells in high-efficiency, near zero-emission coal plants. This technology minimizes fuel use and carbon dioxide production, can potentially capture 99 percent of the CO2 and greatly reduces water requirements while maintaining low energy costs. The realization of this goal will ultimately create energy security, reduce the world’s carbon footprint, and help conserve increasingly precious natural resources, such as water.

The program has made substantial progress in developing fuel cell technology for virtually any stationary application using fossil fuels. SECA research and development (R&D) teams have reached their latest set of technological milestones to put fuel cell power systems on the path to commercialization and more widespread use in the near future. The demonstrations of SECA fuel cell technology in auxiliary power units that produce power and reduce emissions for the trucking industry and as potential power sources for Unmanned Underwater Vehicles for the U.S. Navy speak to the success of SECA fuel cell technology. SECA is also interested in early spinoffs in diverse applications since design and operating experience derived from them, particularly related to cell and stack robustness and reliability, can be reinvested into the SECA program.

From its inception, SECA was configured as a unique alliance among government, industry, and the scientific community. SECA is comprised of three groups: Industry Teams, Core Technology participants, and the Federal Government (NETL) management. The Industry Teams design the fuel cells and the systems to use them and handle most hardware and market penetration issues. The Core Technology program element, made up of universities, national laboratories, small businesses, and other R&D organizations, addresses applied technological issues common to multiple Industry Teams. Findings and inventions under the Core Technology program are made available to all Industry Teams under unique intellectual property provisions (an exception to the Bayh-Dole Act) that serve to accelerate development. The Federal Government management facilitates interaction between Industry Teams and the Core Technology program element as well as establishes technical priorities and approaches. Program funding was established and maintained at approximately 65 percent for the Industry Teams and 35 percent for the Core Technology suite of projects.

Aggressive targets were established for the SECA program products. The inaugural round of Industry Team 3-10 kW system tests was conducted between 2005 and 2007. All teams met the interim system cost ($800/kW in 2000 dollars) and steady-state degradation (4 percent/1,000 hours) targets over the required 1,500 hour test duration. The efficiency of these small simple cycle systems ranged from 35 percent to 41 percent (based on the lower heating value of natural gas).

In 2005, SECA transitioned from the natural gas program to the Strategic Center for Coal, with an emphasis on coal-fueled central generation with carbon capture.

In 2006, the Office of Management and Budget (OMB) cited the SECA program as leading the way in government-industry partnerships: "The SECA program leverages private-sector ingenuity by providing Government funding to Industry Teams developing fuel cells, as long as the Teams continue to exceed a series of stringent technical performance hurdles. This novel incentive structure has generated a high level of competition between the Teams and an impressive array of technical approaches. The SECA program also develops certain core technologies that can be used by all the Industry Teams to avoid duplication of effort. The program exceeded its 2005 performance targets, and it is on track to meet its goal for an economically competitive technology by 2010."

In 2010, a study showed that FuelCell Energy/Versa Power, a SECA Industry Team, met the $400/kW (2000 dollars) target in testing of 120-cell 25 kW stacks comprised of scaled (e.g., 550 cm2) cells when produced in quantity. By way of comparison, the typical planar SOFC stack at SECA’s inception consisted of maximum 40 cells, each with an active area of ~100 cm2, capable of perhaps 2 kW.

The baseline for the SECA cost goals was informally updated in 2008 to $700/kW (power block) and $175/kW (stack), in 2007 dollars. This update was formally reflected in the OMB targets in fiscal year 2011.

As the cost study revealed, FuelCell Energy/Versa Power met the cost goal in 2010. In 2011, two later-awarded Industry Teams – (United Technologies) UTC/Delphi and (Rolls Royce) RRFCS – worked to complete SECA cost goal validation. In FY 2012 and beyond, all three Industry Teams will focus on improving the reliability, robustness, and endurance required for commercial central generation. This work will encompass materials R&D, design, failure analysis, and manufacturing development. It will also consist of considerable stack testing, including progressively larger stacks, to validate performance and gather the required data to make further enhancements to the stack technology.

Driven by Industry Team feedback and extensive systems analyses, SECA is pursuing R&D to address remaining hurdles if cleared could reveal pathways toward a minimum viable manufacturable product. This work will emphasize SOFC stack robustness, systemic reliability and warrantable endurance. This work will encompass materials R&D, design, failure analysis, and manufacturing development. It will also consist of considerable stack testing, including progressively larger stacks, to validate performance and gather the required data to make further enhancements to the stack technology.

The goal is the validation of scaled, low-cost entitlement stacks in a system configuration, up to and including modules suitable for use as the building blocks of multi-MW systems. SECA will ultimately enable fuel cell-based near-zero emission coal plants with greatly reduced water requirements and capable of capturing 99% of carbon at costs not exceeding the typical cost of electricity available today. Achievement of this goal could have significant impact for the Nation in some scenarios, given the size of the market, expected growth in energy demand, emissions requirement trends and the age of the existing power plant fleet. This is important to the Nation’s energy security. Federal funding support of this research is justified by precedents when the benefits help multiple states or the costs or risks may exceed what the private sector and individual states could justify in relation to their individual cost/benefit ratios. Some precedents can be found in pollution control devices, satellite power sources, submersible power sources and unmanned aircraft. The program has an elevated payoff, extended time horizon and elevated risk that has historically been beyond what individual states or private investors could afford on their own. Specifically this technology is considered game-changing as it offers a societal benefit of reducing emissions plus a shared benefit of headroom for improving efficiency. In parallel, SECA Industry Teams will take advantage of the scalability and fuel flexibility of SOFCs in seeking nearer-term, smaller-scale commercial applications for this efficient, environmentally friendly technology which have less risk than a first-of-a-kind full-scale IGFC (or NGFC) system. Success in these spin-off applications (e.g., distributed generation, military, etc.) will further SOFC technology advancement and spread commercial deployment through the resultant manufacturing and operational experience.