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Tokyo Gas, Kyocera, Rinnai and Gastar Co-Developed SOFC System Begins Residential Trial Operations

Realizing large improvement in horizontal-stripe cell stack durability

December 15, 2009
Tokyo Gas Co., Ltd.
Kyocera Corporation
Rinnai Corporation
Gastar Co., Ltd.
Tokyo Gas Co. Ltd. (President: Mitsunori Torihara; herein "Tokyo Gas"), Kyocera Corporation (President: Tetsuo Kuba; herein "Kyocera"), Rinnai Corporation (President: Hiroyasu Naito; herein "Rinnai") and Gastar Co. Ltd. (President: Seiichi Nakanishi; herein "Gastar") are currently engaged in the joint development of a solid oxide fuel cell (SOFC)*1 system with a horizontal-stripe cell stack power generation module (herein "this SOFC system").

From this month, Tokyo Gas has commenced the first trial operations of this SOFC system, as part of the New Energy and Industrial Technology Development Organization (NEDO) "Demonstration Research on Solid Oxide Fuel Cells" project (herein "the SOFC demonstration research project").

Compared with conventional systems*2, this SOFC system reduces primary energy consumption by approximately 45% and CO2 emissions by approximately 55%.

Moreover, the durability of the horizontal-stripe cell stack power generation unit had previously been confirmed up to about one year. By advancing subsequent development, the latest tests showed that the durability of the cell stack bundle*3 has now been improved to the equivalent of five years.

SOFC Demonstration Research Project Trial Operations

The SOFC demonstration research project is being implemented over four years from FY2008 through FY2011 to identify future technological development issues by installing SOFC systems in regular households and other locations, operating them under actual power loads, collecting empirical data, and conducting evaluation analyses.

From this month, Tokyo Gas has commenced trial operations of this SOFC system at two single-family homes, one in Yokohama City (Kanagawa Prefecture) and the other in Kokubunji City (Tokyo). Tokyo Gas plans to conduct trial operations on four additional units from FY2011, and to collect data from a total of six units.

Tokyo Gas is implementing these trials to operate this system under actual power loads, verify durability and reliability, and use the issues identified for future development. The company plans to commercialize this system by the early 2010s by further improving the power generation efficiency, making the system more compact, and realizing a projected durability of 10 years for both the cell stack and the system.

System Installed for the SOFC Demonstration Research Project

This system comprises the horizontal-stripe cell stack power generation unit and a hot water storage unit for efficient use of the recovered exhaust heat. The development of both of these units are primarily being advanced by Tokyo Gas, Rinnai and Gastar.

To gain the maximum performance from the horizontal-stripe cell stack, the power generation unit size is made compact to regulate the heat radiation loss and is designed to optimize the internal temperature distribution and the fuel and air flow distribution.

Considering energy conservation and environmental burden, the "Eco-Jozu"*4 high efficiency water heater, which recovers latent heat, has been adopted for the hot water storage unit as a supplementary heat source. The hot water storage unit is exclusively designed to work with the power generation unit.

The power generation and hot water storage units both incorporate control systems for safe and easy use, assuming trial operations at actual residences. They also feature a compact design for installation in crowded urban areas.

Approach to Improving the Durability of the Horizontal-Stripe Cell Stack

The horizontal-stripe cell stack development is being advanced by Tokyo Gas and Kyocera. Structurally, multiple single cells, which are the smallest units of the power generation module, are sintered on a single ceramic substrate, with the cells connected on the substrate in a series. Lower costs are expected in mass production because inexpensive insulation materials are used for the substrate, which comprises most of the cell stack.

The horizontal-stripe cell stack development has focused on extending durability, which is one important point for commercialization. These efforts have combined the horizontal electrode configuration designed by Tokyo Gas with Kyocera's materials and manufacturing technologies. The durability has been extended by revising the detailed design, developing components, improving manufacturing technologies, and devising all-ceramic cell stack technologies, which avert the use of alloy materials that might affect durability. Development has also incorporated numerous technological improvements, such as developing materials that can control electrode degradation even after long-term power generation.

Electric-furnace durability tests on cell stack bundles, which bundle together multiple cell stacks, have confirmed that the cell stack durability has now been extended to the equivalent of five years.

Horizontal-Stripe SOFC Development History

Tokyo Gas, Kyocera, Rinnai and Gastar initiated development of an industrial power generation unit for early commercialization of SOFC systems from February 2004.

From FY2008, the companies changed the application field to residential use and expanded the range of the development from the power generation unit to the entire cogeneration system.

In the current division of work, Tokyo Gas and Kyocera are responsible for the development of cell stack bundles, while Tokyo Gas, Rinnai and Gastar are responsible for the development of the power generation unit and the hot water storage unit.

Tokyo Gas, Kyocera, Rinnai and Gastar will continue diligently advancing development toward the early commercialization of SOFC systems for the realization of a low-carbon society.

System Specifications

Power Generation Unit
Power output 700W
Power generation efficiency 42% LHV
Exhaust heat recovery efficiency 35% LHV
Dimensions (mm) (W × D × H) 650 × 350 × 1040

Hot Water Storage Unit

Tank capacity


Water heater

Latent heat recovery type model 24

Dimensions (mm) (W × D × H)

890 × 350 × 1620

*1 A solid oxide fuel cell (SOFC) is a type of fuel cell which produces electricity and water from a chemical reaction, typically between hydrogen extracted from city gas or other fuels, and oxygen in the atmosphere. The cell stack which is the power generation module primarily uses ceramics, and produces electricity at a high temperature of 700°C or higher. Among other advantages, this system surpasses the average thermal power generation efficiency (41% LHV), has the highest power generation efficiency of all fuel cells, can use a small hot water tank because of the high exhaust heat temperature, has a small number of parts, and is expected to reduce costs.
*2 The format whereby electricity is supplied from thermal power plants and heat is supplied by conventional water heaters burning city gas supplied by Tokyo Gas.
*3 The output of a single horizontal-stripe cell stack is approximately 10 watts. Practical electric output is achieved by bundling together multiple cell stacks and connecting them electrically. These bundled cell stacks are called cell stack bundles, which are the units that are incorporated into the SOFC system.
*4 “Eco-Jozu” is a high-efficiency water heater which improves the hot water supply efficiency from around 80% to around 95% by recovering exhaust heat which was previously wasted.