12 volt switch

Nissan Leaf can power your house for a day or two

Nissan says its new electric vehicle, the Nissan Leaf, can provide emergency power to your home during a power failure or brownout (shortage). The charging system that takes power from the wall outlet can, with modifications, run in the opposite direction and provide power back to your house. In Japan, Nissan says there’s enough power to run the average Japanese home for up to two days. In the United States with our higher demands for power, like the beer fridge in the garage, we calculate that you’d fully drain the battery within 20 hours.

Nissan last week said it has a prototype running in Japan and will bring it to market by spring 2012. Systems for other markets would follow later, once Nissan can adapt them for those markets. The system was unveiled at the Kankankyo environmentally friendly model house at Nissan headquarters in Yokohama. The power connection runs from a 200 volt, single phase three-wire connection at the house’s electrical distribution panel to a power control system in the garage to the car’s standard quick charge connector. Normally the switching panel sends current to the car. By flipping a switch, the house can draw power from the car.

The power control system is rated at 6kW (6,000 watts) maximum at any one time and the Nissan Leaf’s lithium-ion batteries store 24 kWh of electricity, theoretically equal to 24,000 watts for one hour or 1,000 watts for 24 hours. Since the average Japanese home draws 10-12 kWh, the Leaf could provide two days of power. That’s in the typical Japanese home. In the United States, the US Household Electricity Report from the government’s Energy Information Association indicates the average home consumed 29 kWh per day in the past decade, almost three times as much as the average Japanese home, and thus the 20-hours-of-power figure for the typical US home.

The beauty of an electric car, once you get past the sticker shock, is that it takes less energy to power a car using electricity than gasoline or diesel consumed directly, and it can be charged at night when the most costly or highest-pollution sources are offline. You’d turn from high-sulfur coal plants to nuclear (clean power most of the time, with a couple big-oops exceptions), natural gas, hydro, or solar (typically not at night). In an area with brownouts where the voltage is reduced, or electrical shortages, such as Japan (getting by this year with 20% less power), the supplemental power from EV batteries could even provide a boost to the system at peak times such as hot summer afternoons.

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