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Hydrogen in every home

How the Japanese are trying to slash energy use and CO₂ emissions—by installing fuel cells in people’s backyards.

The monitor on the Kawamori's kitchen wall lets them know exactly how much electricity each device uses.

Photo: Makoto Ishida

Home heating and power account for one-fourth of global energy consumption, according to a study by the economic research company McKinsey Global Institute. So savings on that scale could make a significant dent in energy use, and thus in CO₂ emissions. Yet fuel cell cogeneration systems depend on natural gas to produce electricity, so emit some carbon dioxide. And with an average generation capacity of 1 kilowatt (kW), they don’t meet all home electricity needs; an electric clothes dryer, for example, can use up to 5 kW, and even toasters consume about 1 kW. That makes the technology more of a first rather than final step towards a hydrogen economy, but proponents say that in the future, hydrogen could come from more sustainable sources like biomass, waste gas from landfills or even water.

While hydrogen is the simplest and most abundant element, it’s rarely found on Earth in its elemental form. Instead, it bonds with other elements to form everything from water to hydrocarbons. Breaking those bonds, or the bonds between two hydrogen atoms in its gaseous form, H₂, releases energy—the energy that becomes electricity in Toshiba’s cogeneration fuel cell system and others like it. The question is, Where do we get the hydrogen?

“The cleanest way is water and sunlight; that’s the ultimate answer,” says Peter Pintauro, chair of the chemical and biomolecular engineering department at Vanderbilt University in Nashville, Tennessee. One way to do that is to use solar or wind energy to split water into oxygen and hydrogen gas, with the help of a simple device called an electrolyzer. The resulting energy can be stored and used in residential, industrial and automotive applications. The potential to integrate transportation and electricity infrastructures is an added appeal of hydrogen; Honda is working with U.S. fuel cell maker Plug Power on a fuel cell that would generate energy for your car and home at the same time. And Osaka Gas is looking into combined solar-hydrogen systems.

For the time being, however, almost all residential fuel cells use natural gas. Here’s how it works. First, the gas (made up mostly of methane, a hydrocarbon) is piped to the house and enters a device called a reformer, where a reaction using steam turns it into hydrogen gas and carbon monoxide (CO). The poisonous CO then reacts with oxygen to become carbon dioxide and is released, while the hydrogen gas enters the fuel cell “stack” and splits into two protons and two electrons. These energy-carrying electrons become a DC electric current, which is used in the home before returning to the fuel cell. The Toshiba system generates 700 watts; others make 1 kW. The electrons then combine with the hydrogen protons and oxygen to form water.

However, only a portion of the energy stored in the molecular bonds is transformed into electricity. The rest—60 percent or more—escapes as heat. But instead of wasting that heat as most conventional electric plants do, home fuel cell systems use it to make hot water. The Toshiba system can store 53 gallons (200 liters) of water at 140 degrees Fahrenheit (60 degrees Celsius), enough to meet the daily needs of the average Japanese family of four. (A back-up on-demand gas water heater is also included in the unit). This is where the major efficiency gains come in, since the same energy source produces both hot water and electricity.

With two teenage children—including a daughter on the lacrosse team—the Kawamori family runs through the 53 gallons of hot water in the tank most days and has to fall back on the gas water heater while they wait for it to fill again. “With the kids around, the stored water is gone before you know it,” says Kumiko. “I don’t know the best way to use the system yet; for example, how to adjust when we’re using electricity and hot water.”

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