Sunday, July 08, 2018

When Will Electric Vehicles Act as a Grid Resource Under the V2G Paradigm?

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. 

Global distribution of EV charging outlets in 2017 Click to Enlarge (Chart Credit: Click to Enlarge.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.

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.

(Credit: Click to Enlarge.

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. 

Read more at When Will Electric Vehicles Act as a Grid Resource Under the V2G Paradigm?

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