The expected spread of electric vehicles (EVs) has led stakeholders to look at them not only as a burden for the grid but also as a resource, according to the concept of vehicle-to-grid (V2G). Electric vehicles can act as a mobile storage device and provide support to a grid based on intermittent and distributed energy resources (DER) but what is the basic requirement to enable an EV as a resource for the grid rather than a burden?
EVs must be equipped with bidirectional chargers to allow the flow of energy in both directions. In a V2G paradigm, charging of the EV batteries from the grid is enabled when there is a plenty of electric energy production, while power delivery from the EV batteries to the grid is exploited when there is a plenty of electric energy demand. Before going into the details of V2G capabilities of EVs, it is crucial to discuss the following topics. What is the current state of charging infrastructure installed around the globe? Has the technology evolved to the state where it can provide bidirectional flow of energy?
Snapshot of Global EV Chargers Market
With the increasing number of EVs around the globe, EV charging has become an essential aspect of car ownership. The availability of EV charging infrastructure in a region directly impacts EV adoption. A higher density of charging outlets means a reduction in the point-to-point distance between stations, minimizing range anxiety. In addition to the number of chargers, the power capacity of chargers has also increased, paving the way for fast charging station networks based on direct current (DC) technology.
Globally, several utilities have announced large scale installation of publicly accessible charging stations and State Grid Corporation of China (SGCC) is one of them. In the recent years, China has emerged as a market leader in installed charging infrastructure as it has increased its publicly accessible charging stations by almost 51 percent in 2017. This has brought China’s public charging outlets market share close to 48 percent globally. The graph below from Power Technology Research, 2018 shows the global distribution of public EV charging outlets in 2017.
Chart: Global distribution of EV charging outlets in 2017
Grid Ancillary Services
The modern grid is extremely complex when it comes to the keeping the grid within Goldilocks operating range i.e. balancing generation and consumption in real time. Generation reserves are maintained to overcome sudden imbalances over short period of times ranging from one to several seconds. According to the United States Federal Energy Regulatory Commission, ancillary services are defined as: “services necessary to support the transmission of electric power from seller to purchaser, given the obligations of control areas and transmitting utilities within those control areas, to maintain reliable operations of the interconnected transmission system.”
An overview of grid ancillary services needed for smooth grid operation are summarized in the table below.
Frequency Regulation (Active Power Support)
Regulation services are a likely first step for V2G because of high market value and minimal stress on the vehicle power storage system. In a power system, frequency is an indicator of its health and it needs to be maintained at nominal value all the time. Frequency can be impacted by an imbalance between supply and demand of active power. Such an imbalance can either be positive, which causes the frequency to go higher than the nominal value (i.e. generation is higher than demand) or negative, which results in system frequency lower than the nominal (i.e. demand is higher than the generation). Balance between demand and generation (frequency regulation) is managed by system operators real-time by utilizing the spinning and non-spinning reserves.
Given that the generation mix is tipping towards renewables, which are inherently intermittent in terms of power supply, the need for faster frequency regulation is becoming more critical than ever.
Currently, frequency regulation is achieved mainly by cycling large generators, which is costly and can be slow in terms of response time. Storage devices like batteries, pumped hydro and flywheels have shown promise with a faster response times. Batteries are the most promising candidate for robust regulation of supply and demand which brings EVs into consideration. Fast C-rates of EV batteries makes V2G a promising alternative for frequency regulation. EVs can respond quickly to regulation signals, which could be controlled independently by each vehicle.
Fast response is just one aspect because the actual benefit of providing ancillary services through EVs lies in the cost structure. In case of large hydro plants, which are operated at reduced output so that ancillary support can be provided, the cost structure can be divided into three parts: capital costs, infrastructure costs and operating costs. Capital cost is a plus, frequent changes in output result in damage and reduced efficiency of the generator and it must compensated as well. However, in the case of batteries, which store energy, these factors could be avoided, potentially reducing the market price for ancillary support services.
Voltage Regulation (Reactive Power Support)
Voltage regulation is achieved by maintaining a balance between supply and demand of reactive power in a grid. Mostly, the consumption of reactive power is through inductive load, which requires the addition of capacitive reactive power to balance the demand.
Up until recently, reactive power support (normal and contingency scenarios) was injected at the transmission or distribution grid stage i.e. no involvements from the end-users. However, EVs and the associated power electronics in charging equipment can provide necessary reactive power support to the system. Today, the market for reactive power support is quite consolidated as only large generation plants financially benefit by providing reactive power support to the network. However, with the increased penetration of EVs and charging equipment, diversification of this market in the future is possible.
Distribution system operators (DSOs) are responsible for operating and maintenaning the distribution grid without any interruptions. Sudden demand of electricity in certain distribution grids due to electric vehicles can lead to congestion in the netwok due to limited transfer capacity.
At the moment, EV chargers have entered into the ultra-fast 350kW capacity range and multiple charging positions at a single location can certainly put burden on the distribution network installed in that area unless the system is upgraded. However, through V2G capability, the EVs located in a specific area can help in congestion mitigation in those networks.
The Situation Today
V2G applications are slowly picking up. We are seeing some pilot projects being launched that test the feasibility of V2G solutions for large-scale use. Here is a list of V2G pilot projects in some European countries:
EVs are going to play a significant role in the future smart grid and energy transportation systems. Different hardware and software solutions enabling grid services are still premature and non-standardized however, a consensus among most automobile manufacturers could help to bring change.
Although markets exist for these solutions, with clients who are willing to pay for V2G services, at this point there are so many complicating factors around the integration of EV batteries into the power grid that the scalability of the business model at this time is limited