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Toyota develops mutual power supply system for electric vehicles and homes

Toyota Motor Corporation (TMC) has announced that it has developed a vehicle to home¹(V2H) system for the mutual sharing of power between electric-powered vehicles, such as plug-in hybrid vehicles (PHVs) and electric vehicles (EVs), and homes.

Toyota develops mutual power supply system for electric vehicles and homes

The V2H system is to start testing, using Prius PHVs, at the end of 2012 in approximately ten households as part of the Toyota City Low-Carbon Verification Project² (Toyota City Project) that began in April 2010.

The newly developed V2H two-way electric power supply system can supply power from home to vehicle as well as from vehicle to home. An AC 100V inverter onboard the Prius PHV converts stored power into AC suitable for home use, while power flow is controlled according to communication between the vehicle, charging stand and the home. With this new method, low-carbon electricity (‘green’ electricity) generated from regional or home solar generators, or low-cost late night electricity, can be stored in a vehicle's drive battery and then used to supply power to the household during peak consumption times. This kind of optimal energy flow can be automatically controlled by a home energy management system (HEMS).

Vehicle batteries can also be used as a power source in times of emergency by manually setting the electricity flow to supply power from the vehicle's drive battery through the charging stand to a home's lights and power outlets. With a fully charged battery and full tank of petrol, a Prius PHV can supply power for average Japanese household electricity use (approximately 10kWh) for four days.

Interest in smart grid technology and expectations for the effective use of electric vehicle batteries has increased due to recent anticipated electricity shortages in Japan, the beginning of full-scale renewable energy introduction and an increased need for emergency power supplies.

Households participating in the verification tests in Toyota City will use Prius PHVs which can use the V2H system to supply electric power to homes, as well as function as conventional petrol-electric hybrid vehicles once onboard electricity supply depletes to a certain level.

TMC developed its V2H system while closely complying with existing charging and communications specifications defined by the International Organisation for Standardisation (ISO) and International Electrotechnical Commission (IEC), as well as with electrical safety standards and regulations. In the future, TMC hopes to promote the widespread use of V2H systems while closely studying system, hardware, power generation and other relevant specification standards and at the same time, being conscious of standardisation trends.

In addition to the V2H system, TMC has also developed devices capable of supplying electricity from PHVs directly to home devices for use at emergency shelters in the event of a disaster. The devices will be installed on the PHVs used in this round of the Toyota City Project tests.

The Toyota City Project awards eco-points to consumers who change their lifestyle habits to conserve electricity. In 2011 there was an increasing trend toward households to use low-cost power to charge their vehicles. In light of the recent power supply shortages in Japan, the Toyota City Project is working to promote regional energy management that can respond to shifts in peak usage. In response to the increasing need to control peak electricity use, the Toyota City Project will test synchronised automatic control between HEMS and regional energy data management systems (EDMS) this year. Existing energy usage optimisation technology using household storage batteries will be expanded to V2H systems, making green electricity use even more effective while promoting a shift away from electric power consumption during peak-demand times.

Through the development of the V2H system, TMC aims to contribute to low-carbon and energy-efficient electricity use and to support the Toyota City Project's goal of regional energy independence.

(1) Charging of PHV and EV batteries from household electricity and supplying electric power from onboard automobile storage batteries to the home

(2) Part of the Next-Generation Energy and Social System Demonstration project (a five-year project running from 2010 to 2014) of the Japanese Ministry of Economy, Trade and Industry (METI) with the aim of optimising energy on a regional and community level through citizen-led initiatives. Construction of test model homes was completed in June 2011, with the first group of residents taking residence in September. As of May 31, 2012, approximately 40 households are on the premises.

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