Fuel Cells: Compact Home Power Plant

Residential Fuel Cells Nearly a Commercial Reality

To meet greenhouse gas emission-reduction targets under the Kyoto Protocol, a less centralized power generation model based on micro power is desired. Generating power at the local level eliminates electricity losses in transmission and has the added benefit of making thermal recycling easier. The core device in making micro power a reality is the residential fuel cell(FC). Toshiba took steps in December 2004 to strengthen its residential FC operations.
FCs work on the principle of the reverse electrolysis of water. This involves a chemical reaction between hydrogen and oxygen that can be harnessed to produce electricity. Since the only by-product is water, the process is completely non-polluting. The efficiency of power generation is also high because the process converts the chemical energy in the fuel (hydrogen) directly into electricity. The heat generated by the reaction can also be used to heat water. This combination raises total thermal efficiency above 80%. In addition to cutting fuel bills, the CO₂ emissions of an FC are 30-40% lower compared with the combination of gas and electric power.
Japan's Ministry of Economy, Trade and Industry (METI) began a large-scale three-year monitoring test involving 3,000 residential FCs in 2005, aiming for commercialization in 2010. Toshiba is actively involved in this project. Soichiro Shimotori, of Toshiba Fuel Cell Power Systems Corporation, who has been engaged in development of home-use FCs since he joined the company, says, "The next three years will be a critical period in the development of residential FCs."

Toshiba Fuel Cell is Highly Efficient

The residential FC being developed by Toshiba has a relatively small generating capacity of 700W compared with potential rival products. Toshiba selected this level of output because survey data indicated that it was ample for residential power consumption during most times of the day.
Although efficiency tends to be lower in equipment if the scale is smaller, Toshiba improved FC efficiency to 38% in 2004, from 28% in 2000. A major element in this improvement in efficiency is the application of technology to keep the enough water in the cell by using an internal humidification process. The polymer membrane used as the electrolyte in the FC must be kept moist, but using energy to import moisture into the cell reduces the overall efficiency. Toshiba's technology, which is unique in Japan, recycles water and heat generated by the reaction within the cell to keep the membrane moist. "Designing the cell so that moisture levels could be kept uniform via an automatic process was extremely difficult," recalls Mr. Shimotori, and it proved to be a major engineering accomplishment.
Toshiba has been able to develop advanced residential FC technology in a relatively short period. Mr. Shimotori explains the reasons: "First of all, Toshiba has been able to apply expertise from other areas, most notably many years of experience with phosphoric acid fuel cell (PAFC) technology. Second, the FC development program benefited from Toshiba's consumer appliance operations in realizing improvements to key components such as inverters. Third, the internal moisture mechanisms were developed jointly with U.S.-based UTC Fuel Cells, LLC." The residential FC represents a collective triumph for Toshiba Group.

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Fuel Cell Mechanism

Quest to Reduce Costs and Boost Durability

Several hurdles remain to be overcome before the FC can become a widely used home appliance. The key challenges are to lower costs and raise durability. Mr. Shimotori projects, "We expect to cut costs by 90% through a combination of optimized design and materials, improved fabrication methods and the economies of scale from mass production." Mr. Mitsuaki Echigo, who is a trial user of Toshiba's latest residential FC, stresses, "Ultimately, the need for repairs should be eliminated completely." In terms of durability, the current goal is to build a cell with an operating life of 20,000 hours. Toshiba is on course to achieve this by 2006, with the next goal to double durability to 40,000 hours, the typical service life of a PAFC, by 2008. Progress has already been made by eliminating the causes of failure in the main cell unit, and work is now focusing on improving the reliability of peripheral devices such as blowers using optimized designs.

Potential Role of the Fuel Cell in a Hydrogen-based Society

Toshiba is testing a wide variety of fuels as the source of hydrogen for FCs, including city gas, LPG methanol, dimethyl ether and various bioderived gaseous fuels. Residential FCs could make a major contribution to resource recycling. Preparing for a hydrogen-based society, Toshiba is also conducting field tests of cell designs that use pure hydrogen gas as a fuel. "In the future, energy generated through weather-dependent renewable sources such as wind or solar power, together with surplus electric power generated at night, could all be stored in the form of hydrogen. Once stored, residential FCs could convert this hydrogen into usable energy on demand." says Mr. Shimotori. In a hydrogen-based society, FCs could contribute significantly to more efficient energy usage.

Residential Fuel Cell Power/Water Schematic