Nissan and other makers are beginning to view electric cars not just as transportation, but as mobile energy-storage units that can provide emergency power and take stress off electrical grids.

This month the carmaker will begin testing its Leaf-To-Home energy station in Japan, testing the ability of electric cars to provide temporary electrical power to buildings in real-world circumstances.

MORE: Nissan Leaf-To-Home Power Station: Will It Make It To U.S.?

The station converts high-voltage direct current from a Leaf's lithium-ion battery pack into the 100-volt alternating current used by homes in Japan.

For the test, Leaf plug-in cars will be stationed at Nissan dealerships, where they will be used to provide power for lighting during regular business hours.

Two or three tests--taking about three hours each--will be conducted each month between now and January 2015.

Nissan Leaf-To-Home power station

Under the demand response scheme, utilities ask consumers to limit energy use during times of peak demand.

Normally, residents comply by turning down air conditioning or shutting off lights. But Nissan believes the Leaf-To-Home system could allow them to power their homes from an electric-car battery instead during those periods, or during emergencies when power grids are completely offline.

ALSO SEE: Nissan, Mitsubishi, Toyota Turn Electric Cars Into Backup Batteries

This idea was put into practice a few times in the wake of the earthquake and tsunami, but most electric cars still lack the battery capacity to provide power for long periods of time.

Bigger packs, better for U.S.?

So just as bigger battery packs are needed to increase range, they'll likely also be needed to make electric cars a viable source of backup power, at least in the U.S.

U.S. homes use roughly three times as much energy per day as do Japanese homes.

The U.S. Energy Information Administration puts average U.S. consumption at 32 kWh a day—though it varies regionally, with Tennessee residents using more than two and a half times as much as Maine residents.

Nissan Leaf-To-Home power station

The figure for a Japanese household is just 10 kilowatt-hours, or half the capacity of a fully-charged Leaf battery pack.

Still, many electric-car owners are aware of and like the concept of using their vehicles for emergency backup power during outages.

The potential to relieve stress on the grid has also attracted some interest from U.S. utilities.

NRG--which operates the eVgo network of charging stations--has discussed using electric cars to balance the grid by temporarily storing excess electricity, and discharging it during periods of high demand.

The company is participating in a test program operated by the University of Delaware, which has a small fleet of electric cars equipped to discharge power back into the grid.

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