A schematic diagram showing how the Toyota V2H system works.

Toyota has developed a vehicle-to-home system that allows plug-in hybrids and battery cars to share power both ways with the mains circuits of the homes they're plugged in to.

The V2H system will start testing with Prius plug-in hybrids at the end of 2012 in about a dozen households as part of the second Toyota City low-carbon project that began in April 2010.

A 100V AC inverter onboard the Prius converts stored power into AC suitable for home use, while 'green' electricity generated from regional or home solar generators, or low-cost late night electricity, can be stored in the cars battery and then used to supply power to the household during peak consumption times.


The car's battery can also be used as a power source in times of emergency by manually setting the electricity flow to supply power through the charging stand to the lights and power outlets in the house - and when the battery goes flat the Prius' engine will start running to keep it going.

Starting with a fully charged battery and full tank of petrol, a Prius plug-in hybrid could supply enough power for an average Japanese household (about 10 kWh) for four days.

Interest in emergency use of electric vehicles' batteries as an alternative power source has grown since the tsunami disaster of March 2011, and due to anticipated electricity shortages in Japan.

Effectively, the car then becomes a petrol-powered household generator - but wouldn't that be very expensive?

Let's see.

With a litre of unleaded petrol costing R11.67 in Gauteng from Wednesday, 6 June, a 45-litre tankful for Prius is worth R525.15. If that will provide 10kWh for four days or 96 hours, a total of 960kWh, then each kWh of electricity will cost 54.7c, about the same as Eskom will be charging us after the 2011/2012 tariff increases and a lot less than it will be charging us in 2013.