Bidirectional Charging

Bidirectional charging refers to an electric vehicle charging system that allows energy to flow in both directions. Meaning that in addition to charging the vehicle battery, the energy from the battery can be discharged to power a building or external appliances. Or, if certain conditions are met, even feed energy back into the grid. Essentially, with two-way charging, the EVs can serve as batteries on wheels.

The Basics

When an EV is being charged using alternating current (AC), electricity from the grid is converted to direct current (DC). Typically, this conversion happens inside the car with a converter known as an onboard charger. The DC power can then be stored in the car’s battery. Charging the vehicle battery from the grid is referred to as unidirectional charging because the flow of electricity is in one direction.

EVs have to be equipped with a bidirectional charger or inverter to make use of bidirectional charging. That means the stored DC power is converted back into AC and can be discharged. In other words, this enables the EV to feed power back into the grid or provide AC power for other purposes.

There are three main types of bidirectional charging.

Vehicle-to-load (V2L)

With a vehicle-to-load-enabled EV, the vehicle’s battery can be used to directly power appliances or charge devices on the go. The power from the battery can be accessed through dedicated outlets or ports in the vehicle. This can be especially useful for outdoor activities with no access to electricity or in blackout situations.

Vehicle-to-home (V2H)

Vehicle-to-home charging refers to the capability of an EV to supply power from its battery to a family home. The house must have a bidirectional charge point, and the vehicle with V2H capability needs to be connected to it. By plugging the EV into the home’s electrical system, the energy can be transferred bidirectionally between the EV and the home. 
This functionality is better when combined with solar panels. It enables the parked EV owner to store cheaper energy during off-peak hours. During peak hours, the stored energy can be used to offset electricity consumption. The EV battery can also be used as a backup power source during power outages.

In essence, V2H turns an EV into a large home battery system. For households with limited energy needs or where the vehicle is not used most of the day, the EV battery can serve as a sufficient storage solution, eliminating the need for an additional home battery system.

Vehicle-to-grid (V2G)

Electric vehicles equipped with bidirectional charging capability allow vehicles to send energy directly back to the grid. This is known as vehicle-to-grid technology. 
The energy demand is high during peak periods, and fluctuations can occur in the power supply. To alleviate this issue, EV owners can participate in Virtual Power Plants (VPPs) or other demand-response programs to help stabilise the electrical grid during peak energy demand periods.

Parked EVs can draw power from renewable sources when rates are lower. If there’s a need for extra energy supply, the vehicles are called to discharge the excess energy into the grid. The EV owner can set a predetermined percentage of reserve battery charge to ensure enough energy is available for the rest of their daily needs. The surplus energy can be sent back to the grid. The owner can earn money or receive credits for the electricity supplied by selling the energy during high demand. This can provide an economic incentive for EV adoption and usage.

However, the V2G infrastructure is still not widely available, and there are very few vehicle models with V2G capability currently on the market.

This being said, EVs capable of V2G charging can act as flexible distributed energy resources that make the grid more reliable and reduce the need for traditional fossil fuel-based backup power plants.