Nine things you need to know about bi-directional charging

Moving Well | Tim Nicholson | Posted on 04 June 2021

New bi-directional charging technology enables electric vehicle owners to use their car to power their home. Here's how it works.

Electric vehicles are slowly gaining traction in Australia as buyers weigh up the pros of low running costs and environmental benefits against lingering concerns about pricing, charging infrastructure and driving range. But what if we told you could use an EV to power your house? Or that you could make some money by selling power from your vehicle’s battery back to the grid? 

Welcome to the emerging world of bi-directional charging. But what is bi-directional charging and how does it work? Here is RACV motoring expert Tim Nicholson's guide to everything you need to know.

Nissan Leaf car plugged into charging unit

Electric cars with bi-directional charging capability can supply power back to the grid, or power a home, using energy from the EV battery.  


Nine things you need to know about bi-directional charging

What is bi-directional charging 

A vehicle with bi-directional charging capability – also known as vehicle-to-grid (V2G) or vehicle-to-home (V2H) charging – can not only take power from the grid to charge the EV battery, it can also supply power back to the grid, or power a home, using energy from the EV battery. Effectively it enables your electric vehicle to act as a home battery, storing energy that can be used to power your home or sold to the grid. 

How does it work?

To charge a conventional EV, you need a unidirectional charger to convert AC (alternating current) electricity sourced from the grid to DC (direct current) electricity. This is done by a converter, either built into the vehicle, or housed in the charger. If you want to use the energy stored in the EV’s battery to power your home or send it back to the grid, the DC electricity from the car must be converted back to AC electricity. That’s done by a bi-directional charger, which looks similar to a regular home EV charger. 

Bi-directional charging is already being trialled overseas in the United States, United Kingdom and Denmark and has been used to power houses, office buildings and even to power tools in the aftermath of several natural disasters in Japan. Nissan says the 62kWh battery in the Leaf e+ can store enough energy to power an average Japanese home for up to four days.  

Is it available in Australia?

Not yet, but a trial backed by the Australian Renewable Energy Agency (ARENA) is underway in Canberra to test the technology here. The Realising Electric Vehicles-to-grid Services (REVS) trial involves 51 Leaf EVs that are part of the ACT Government fleet and when plugged in will inject power back into the grid when the vehicles are not in use. 

Once the charging units have been tested and certified by the relevant authorities the technology will be ready to roll in Australia. It’s anticipated that will happen mid-year. RACV is also looking at conducting a bi-directional charging trial in the not-too-distant future. 

Are all EVs capable of bi-directional charging? 

No. Well, not yet anyway. Only those vehicles with a CHAdeMO charge port can facilitate bi-directional charging and, in Australia, that is limited to the Nissan Leaf EV and the Mitsubishi Outlander plug-in hybrid. Other EVs are fitted with the more widely used CCS2 charge port which  is gradually becoming the globally accepted standard. However, a draft standard for bi-directional charging using CCS is expected some time this year. 

Manufacturers including BMW, Honda, Volkswagen, Tesla and more are looking at rolling out bi-directional capability in their future EV models. 

How much will a bi-directional charging unit cost?

The price of units that are expected to be sold in Australia has yet to be announced, but they are expected to cost about $5000-$6000. 

Will it save me money? 

A car with bidirectional charging capability effectively acts as a home battery enabling you to store excess energy that can then be used to power your home or sold back to the grid. If that energy used to charge the car comes from a free or cheap source, such as rooftop solar, a free charger at your local shopping centre, or even your workplace, there’s the potential to substantially reduce your home power bills. Alternatively, you may be able to sell electricity back to the grid, charging your car off peak and selling back to the grid during peak afternoon and evening hours to optimise your profits.   

Close up of car plugged into bi-directional charger

Curently, in Australia, only the Nissan Leaf EV and Mitsubishi Outlander plug-in hybrid have bi-directional charging capabilites.  


Will vehicle-to-home charging drain the car’s battery?

According to Nissan Australia national manager of electrification and mobility Ben Warren, you’re likely to still have quite a bit of charge in the car battery by the time you get home at the end of the day. For example the Nissan Leaf e+ has a driving range of 385km and the typical daily commute is just 32km round trip, so if you fully charge your car you might still have about 350km of range (about 57kWh of battery capacity, out of 62kWh) remaining in the battery when you get home. 

Ben says you can also set user parameters using a smartphone app, to ensure for example that the EV battery charge doesn’t fall below 40 per cent when discharging power to the house. When the car battery gets to 40 per cent, the charger shuts down and the house resumes taking power from the grid. 

Is bi-directional charging safe?

There are measures built into the chargers to mitigate any safety issues. Bi-directional chargers work in a similar way to solar inverters, and have a sensor to monitor the load of the house and how much power is being pumped in and out of the house. If the sensor detects that system voltage has been breached, the charger will switch off. 

Will the car battery deteriorate faster if I use bi-directional charging? 

Ben says bi-directional charging does not have a detrimental long-term impact on the battery because charging and discharging is less intensive than driving – you can only charge or discharge at a rate of 7kW. 

He says Nissan’s eight-year/160,000km battery warranty is not impacted by bi-directional charging, as long as the charger you use has been approved for use by Nissan.