Vehicle-to-Grid Definition

V2G technology can be defined as a system in which there is capability of controllable, bi-directional electrical energy flow between a vehicle and the electrical grid. The electrical energy flows from the grid to the vehicle in order to charge the battery. It flows in the other direction when the grid requires the energy, for example, to provide peaking power or “spinning reserves.” It should be noted that this is the way V2G would work if a vehicle had such capability, but there are currently no original equipment manufacturer (OEM) vehicles available to the general public with V2G in the United States.Studies indicate that vehicles are not in use for active transportation up to 95% of the time (Letendre and Denholm 2006) and the underlying premise for V2G is that during these times, the battery can be utilized to service electricity markets without compromising its primary transportation function. Subsets of V2G technology include vehicle-to-home (V2H; when the electric vehicle is at a residence) or vehicleto-building (V2B; when the electric vehicle is at a commercial building). In these cases, the battery power is used to supplement the local building electrical load without transfer to the electrical grid. Note that this still effectively displaces building load from the grid, which effectually provides a load-shed function. Alternatively, if there is a power outage from the grid, this permits emergency backup power to continue building processes

V2G Technology

The concept of V2G technology was introduced by Kempton and Letendre in 1997. In a typical power grid, the power flows between energy producers through the power network to aggregators and homes. In the homes, power outlets provide energy to products such as electric vehicles. By default, the EVs should be able to connect to the grids to recharge their batteries. An electric vehicle that incorporates V2G technology can also provide energy back to the power outlet when the vehicle is parked. The EVs require additional setup to successfully return the power to the grid to perform this type of bidirectional charging.

Implementing a V2G architecture could potentially decrease the stability of the power grid. However, aggregators employ dispatch and control algorithms to optimize that stability and balance the energy distribution to the EVs. In that way, a vehicle can ultimately charge during the times when energy demand is low and discharge when it is high. However, the potential effect that this may have on the stability of the power grid has not  been studied sufficiently. Furthermore, the data that is collected can be susceptible to security issues, and privacy concerns among consumers might arise . Ideally, these challenges will be addressed before the technology becomes adopted on a large scale.

The benefits of V2G technology are technical, economic, and environmental in nature. First, the grid’s power storage capacity will increase gradually with the increase in the number of EVs sharing the power with the grid, allowing more power storage in the grid. Second, the transition to V2G technology can replace 6.5 million barrels of oil usage per day, and it directly amounts to economic savings in a country . Third, the transition can reduce greenhouse gases emitted by gasoline-based vehicles and promote EVs’ usage in society.

The V2G systems need communication protocols to enable the transmission of instructions between the EVs and the electric vehicle supply equipment (EVSE). When the communication chips and protocols are in place to receive the signals, the aggregator can coordinate between the EVs and the electricity grid operator to regulate power supply and demand. The communication protocols related to EVs are divided into front-end and backend protocols. 

The front-end protocols define the link between the EVs and EVSEs, and also specify the requirements related to charging topologies (such as type of charging equipment (on-board/off-board) and type of charging (conductive/inductive), safety, charging plugs, communication, and cybersecurity. A few examples of front-end protocols include IEC 61851, ISO 15118, SAE J2847, and CHAdeMO. 

The back-end protocols define links between the EVs and third-party operators such as charge point operators (CPOs) (companies responsible for operating a pool of charging points ), and specify requirements related to communication and cybersecurity . A few examples of back-end protocols include the open charge point protocol (OCPP), IEC 63110, the open automated demand response (ADR), and EEBUS. More information on these standards can be found in .To technically realize the V2G system, a simple communication chip is added to the onboard charger of the EVs to regulate the power flow between the EVs and the grid.

However, designing this communication technology is expensive. Therefore, most EVs are not equipped with these chips today, except for a few EVs manufactured by companies such as Nissan and Mitsubishi. Besides, energy meters capable of measuring the power flow between the grid and EVs accurately are required. For monitoring the real-time power flow, advanced metering infrastructure (AMI) is used to provide reliable information to aggregators and grid operators for managing the power flow in and out of the grid . Currently, one technology, CHAdeMO, already offers V2G technology, while another technology, CCS Combo, is expected to offer V2G technology in the future.