In order to build a V2G system, the EV thus requires three things: a specialized charger, power bidirectionality, and communication capacity. Of course, in order to have a connection to the grid, the EV needs to have a charger to which connect with. In this respect, there are several important attributes of a charger, including its power capacity, whether the charger is on-board the vehicle or off-board within the charging station, and its communication and bidirectional capacities [6]. Though V2G is possible with any power level, the power capacity of the charger is important to the economics and aggregation of EVs. Electric vehicle supply equipment (EVSE) , which supply electricity to a charger on-board the EV, are commonly distinguished between three levels: Level 1, typically using the lowest available power outlets, resulting in low power capacities, e.g., ~1–2 kilowatts (kWs), Level 2, which uses higher power capacities ranging from 4 kW to around 20 kW, and Level 3, also known as fast or quick chargers, which, unlike the previous two levels, commonly uses direct current (DC) off-board chargers to provide substantially higher power capacities, such as 50 kW and above [6]. Since batteries require DC power in order to be charged, Level 1 and 2 chargers that use alternating current (AC) use an on-board power inverter to convert delivered AC power into DC power to the battery.

While technically any of these charger levels would suit V2G, it is widely expected that most of the V2G projects will likely occur with Level 2 chargers, at least in the short term, given the balance between sufficient power capacity and the more affordable cost of such chargers for an average consumer at home or work [7]. On the other hand, certain other V2G use cases, such as fleets [8] may be more likely to use chargers closer to the Level 3 standard, especially as the cost of high capacity chargers (both AC and DC versions) decrease in price.

Once the EV has established a power connection to the electricity grid via some type of EVSE , the next step is for the EV to provide bidirectional power and the capacity for communication. Neither of these provide overwhelming technical or economic challenges, however, it is important to note that, from the perspective of the EV, these are integral changes that need to be made at the design stage of the vehicle. Bidirectionality of power simply requires that an EV can provide power back through the EVSE onto the grid, which is essentially the same process as charging the EV’s battery to drive, but now discharged onto the grid. As an aside, unidirectional flow—also called managed charging, V1G, or smart charging—requires only adding communication to the EVSE and only controls the charging level. But since this has less value as compared to V2G, we focus the rest of the book on bidirectional power flows and V2G (while recognizing that smart charging may be a “stepping stone” to V2G). Of course, the process of V2G requires that not only the EV but also the EVSE are bidirectionally enabled. More importantly, apart from the physical flow of power, it also requires a communication pathway in order to direct the power flows.

From a vehicle perspective, the communication ability is most commonly manifested as a simple addition of another communication chip on-board the vehicle. For example, some of the early projects use a communication software component called a vehicle smart link (VSL), first developed by University of Delaware for projects that include a variety of different vehicle types such as converted Scion XB’s and Mini-E’s [9]. It is worth noting that communication technologies such as VSL are quite expensive to design and develop, but once developed, actual construction and inclusion of the chip is substantially cheaper, estimated to be only a few hundred dollars. Despite the development and commercial availability of VSL-type technologies, most EVs purchased today do not currently include such V2G capability, with a few notable exceptions such as Nissan [8]. Nonetheless, a VSL is essential to the V2G system by directing power flows in and out of the EV.

Once this capacity to control bidirectional power is in place, the next step is a means to provide messages to the EV instructing it what power flows the grid currently requires. As such, there needs to be a communication channel between the EVSE (which is connected to the internet and receives the power flow instructions from a third party such as an aggregator or utility) and the vehicle. Currently, there are a variety of ways to enable this communication ability though, with competing national and international standards of communication that vary slightly in their implementation. For example, previous projects have used control pilot line communication specified in IEC 61851 Annex D, or power line communication through Open Charge Point Protocol (OCPP) and Smart Energy Profile 2.0 (SEP 2.0), while future standards are contested between ISO 15118 , SAE J2847, among others [9–11]. Some of these systems of communications are potentially better suited for different types of V2G systems and services, and the adoption of these standards may be essential to the diffusion of V2G services. However, for the time being, the important aspect is that...