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House Energy Innovation in Japan

Homes Generate, Store & Sell Electricity


Photo: A residence in the Akaishidai housing community where a project is underway to turn the entire community into “an energy supply base for a broader area.” © Sekisui House, Ltd.

Japan is coming up with innovative housing "with a zero energy bill" -- in fact, an entire community of houses that actually produce more energy than they consume. Now Japanese companies, leaders in developing eco-friendly technologies, are working hard to find ways of using a lot less power to light, heat and cool homes. In so doing, they count on natural power, like solar energy, to produce all the electricity a household needs, aiming at significantly reducing conventional energy consumption and turning instead to these natural energy sources. The goal is to establish a self-sufficient lifestyle based on the capability of storing and selling electricity generated at home.

Community Generates Power


Artist’s image: The newest HEMS housing system combining a fuel cell and a solar cell, to generate more power than the household consumes. Surplus electricity will be sold to power companies.

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Akaishidai is a new housing community located in Tomiya town, Miyagi Prefecture, in the northeastern Tohoku region of Japan, hit by the massive March 2011 earthquake. The houses here are all being built using technology that makes it possible to generate electricity at home by combining fuel cells and solar power generation. The result will be a community that actually produces more electricity than it consumes, with the surplus fed into the regional power grid for use elsewhere.

It’s estimated this housing community will soon be able to generate 2,508 MWh of electricity a year, 70% more power than Akaishidai and its 2,650 people need. The surplus 1,039 MWh will be supplied to nearby communities, making the Akaishidai community a virtual power generation plant.

Akaishidai is one of many communities across Japan, including the Tohoku region, where home builders have begun to make it possible for homeowners to slash their household energy bills to zero -- and even sell surplus electricity to power companies serving their region.

Ene-Farm: Japan’s Unique Fuel Cells for Home Use


Photo: The Ene-Farm system generates power by having hydrogen react with oxygen. Heat generated as a byproduct is used for hot-water supply and floor heating. © Tokyo Gas Co., Ltd.

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In Akaishidai and many other parts of Japan, the home power generation system being used is a gas co-generation system known as "Ene-Farm." In 2008, Japan became the first country in the world to begin selling such a system. Ene-Farm consists of a fuel cell unit and a hot water storage unit, developed by gas companies in Tokyo and Osaka and home appliance manufacturers.

The fuel cell unit generates power by allowing hydrogen -- extracted in a steam-reforming process from natural gas, liquefied petroleum gas or kerosene -- to react chemically with oxygen from the atmosphere. The fuel cell can produce 750 W to 1,000 W of electricity, which can be used throughout the house after being converted to home AC current by a power conversion unit. Additionally, a heat-recovery device, known as a recuperator, efficiently recovers heat generated as a byproduct, and uses it to heat water to about 60 C for supply to the bathroom and kitchen – and even to heat the house through piping beneath room floors.


Photo: A roof with built-in solar panels. The roof design matches the environment well. © Daiwa House Industry Co., Ltd.

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Gas utilities say Ene-Farm has proven to increase energy utilization efficiency -- the percentage of energy put to actual use -- to as much as 81%. That’s a huge improvement from 37% for conventional power, or electricity provided through the grid, as so much energy is lost in transmission and as unused exhaust. A single Ene-Farm system can supply 40% to 60% of the electricity consumed by a household.

Generate, Store & Manage Energy by HEMS at Home


Photo: Home Energy Management System (HEMS) shows household electricity consumption on a home TV screen, helping control energy use. © Sekisui House, Ltd.

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In the 1970s, Japanese electric appliance makers became the first to make devices powered by solar energy, a vital natural energy source. Now 40 years later, Japanese housing companies are introducing new products one after another, such as roofs with built-in solar panels, to harness this free and vast energy source. Japanese housing companies use solar panels with conversion rates of 18.6% at the highest and around 16% on average, the best among commercially available panels in the world.

Japanese companies have also worked hard over the years to improve power storage batteries. One housing products maker offers an 8.96 kWh mass storage battery that can keep an entire home lit all night in a blackout. And Japanese companies have developed equipment to enable electricity to be transferred from an electric car's batteries to the owner's house.

Japanese companies have also developed the Home Energy Management System (HEMS) to monitor and control all these home systems. The computer-controlled HEMS displays household power consumption and storage data on PC or mobile-phone screens. It also controls power usage to maximize efficiency and power savings. The display of power consumption data is also expected to encourage homeowners to conserve energy, adding to the synergy effect of efficient use and saving.

Zero Energy Bill by Heat Insulation

Efforts to minimize energy bills for hot water supply and air conditioning not only help reduce the cost of living, but also reduce greenhouse gas emissions, thus helping to conserve the environment.

Some housing makers achieve energy conservation at the construction stage by employing a prefabricated construction method. While the two-by-four construction method is widely used in Western countries, in 1958 Japan began developing a prefabricated system of construction in the form of a “pipe house.” Today over 60% of roofs, walls, windows and other home construction components are made at factories and brought to construction sites. Japanese prefabricated houses are easily assembled on site and maintain factory-level quality, key to ensuring highly effective insulation for keeping the house warm in winter and air-conditioned cool in summer thanks to air-tight construction.

Some houses are even made to maintain the same room temperature in summer or winter through other building structure improvements. Like using two-, or even triple-pane windows. Or coating the exterior walls with a patented photocatalyst that decomposes nitrogen oxide and curbs ultraviolet rays, thereby helping stabilize room temperature. A house with photocatalyst-coated walls can reportedly reduce carbon dioxide emissions by an amount equal to what 14 poplar trees collectively absorb.

Geothermal Heating


Artist’s image: Underfloor geothermal air can be effectively utilized to keep the home cool in summer and warm in winter without air conditioners.
© PanaHome.

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There is a unique temperature control method now under development. Japanese houses are said to maintain a stable temperature of about 15 C under the floor, when measured 10 cm from the ground. A method is being devised to exploit that feature to maintain a constant room temperature inside Japanese houses as well through a sort of reverse ventilation system. Conventional ventilation systems take in outside air. But a unique ventilation system developed by a Japanese home appliance company increases indoor air pressure to force room air outside, and then uses the resulting pressure difference to draw in air from beneath the floor, air that is cool in summer and warm in winter.

Japanese housing makers are constantly working on innovations to make homes more energy efficient and eco-friendly, and just as comfortable – or even more so.

(August 2012)

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