2nd IEEE ENERGYCON Conference & Exhibition, 2012 / Sustainable Transportation Systems Symp
The Plug-in Electric Vehicles for Power System Applications: The Vehicle to Grid (V2G) Concept Sayed Saeed Hosseini 1, Ali Badri 1, Masood Parvania 1
Department of Electrical Engineering, Shahid Rajaee Teacher Training University
[email protected],
[email protected],
[email protected]
Abstract—The emergence and implementation of advanced smart grid technologies will enable enhanced utilization of electric vehicles (EVs) as mobile energy storage devices which can provide system-wide services. With significant penetration of EVs in the near future, the concept, introduced in literature as vehicle to grid (V2G), will be practically possible. The V2G concept eases the integration of renewable energy into power system and gives new force to inevitable move toward power generation by clean energy resources. Therefore utilizing energy storage in EVs is undeniable due to economic and environment benefits. The V2G concept has been the field of many researches in different aspects so far. This paper presents a study conducted to reveal the different aspects of V2G in power systems. In this study, we analyzed V2G from the perspectives of power system services and electricity market applications. Specifically, we have focused on smart parking lots importance in V2G concept, their opportunities and challenges, as well as the application of V2G to provide ancillary services. The paper also discusses points which will make the V2G concept feasible as fast and simple as possible.
the power systems if they are not supported by smart grid technologies.
Keywords—vehicle to grid (V2G); electric vehicle; distributed energy storage system; smart grid
V2G concept as an energy storage system could help to overcome the difficulties associated with the intermittent nature of renewable energy like wind and solar energy [3], [5]. V2G gives a new path toward power supplying by clean energy in different scales and levels of power system, especially in distribution and micro grids. This benefit of V2G is so remarkable and many research works have highlighted the application of V2G for renewable energy integration [3-6].
1. INTRODUCTION The prospect of vehicles plugging into the electric grids as known plug-in electric vehicles (PEVs) bolsters by the undeniable economic and national-security benefits that result in independence from petroleum and displacing gasoline with electricity [1]. The importance of this trend with the evolution towards revolution in future power systems will be strengthened much more than before. For instance, US department of energy (DOE) report in 2009 identifies and highlights the electric vehicles (EVs) as one of the 20 metrics for measuring the status of smart-grid deployment and impacts [2]. The EVs have potential to lower fuel cost, reduce petroleum consumption and decrease harmful emission that are described elsewhere. The evolution of EVs causes to allow charging them from the electric grid that is presumed by many to be desirable [1]. The EVs which can plug into the grid include plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs). These vehicles offer performance, safety, versatility and can be charged from the electric grid with providing convenient and low-cost at-home charging. Obviously, according to the needs of this group of vehicles through charging from the grid, they have the potential to strain
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The most important issues that are represented in different articles are assessment of the increased load that EVs would present and EVs serving as distributed energy resources. In the second issue using of the EVs' power back to the grid as an energy storage system is the main object. This service provided by EVs is known as vehicle to grid (V2G) concept and have been considered in many researches from different point of view [1], [3-6]. In next 10 to 20 years, with significant penetration of EVs enhanced with smart grids capabilities, it would be beneficial to take advantage of opportunities such as V2G [7]. These opportunities include economic and environment benefits. In this way, these new loads could be also used as an electric source under smart grid facilities in terms of a controllable instrument.
This paper presents the results of a comprehensive study conducted with the aim of revealing the different aspects of V2G in power systems. In this study, we have focused on V2G from the perspectives of power system services and electricity market applications. This classification is based on concern and interest in order to make this purpose practical. The classification is collected due to representing an accurate and detailed outlook to V2G system, in different levels of power system with various purposes. The paper has a realistic view regarding V2G and also discusses points which will make the V2G concept feasible as fast and simple as possible. The rest of this work is organized as follows: Section 2 introduces the V2G concept from various aspects. This section also considers the relationship between V2G development and key factors in society, power and transportation systems. Section 3 presents the classification of V2G applications in power system. Section 4 discusses about smart parking lot which is the underlying facility which makes V2G more
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feasible. Possible markets for V2G services are introduced in section 5. Finally, section 6 presents the concluding remarks.
depends on various issues that some of them are not directly related to the vehicle technologies and development.
2. V2G APPROACH: SOLUTION OR DELAY Conventional thinking is based on the idea that EVs would be connected to the grid for charging during the evening until next day morning hours. This point of view lacks a significant proposition that is made possible by the fact that vehicles are parked over 90 percent of the time. If these distributed energy resources are connected to the grid, it could be used to provide possible grid services as V2G system [1]. Using energy stored in EVs delivered back to the grid can be addressed from two perspectives: [1], [4], [7] •
•
Believing that EVs represent an historic business opportunity for the electric utility industry and disrupt the supply and demand correlation by making a distributed energy resource at demand side. Critical views present that presence of EVs in power grids is a factor to postpone the updating, modernization and enhancement of power systems that is inevitable.
The second perspective is not regarded by the industry. The reason is that it leaves EVs as an unwanted load for system operator (SO) and takes any chances from them for providing services that are capable to serve specifically in smart grid structure. Also critical views decrease customer desires to purchase an EV. But on the other side, V2G concept causes vehicle owners to be satisfied due to income from selling the stored energy in EV batteries. In addition, it offsets an electric vehicle high purchase and maintenance costs and also reduces money payback period. On the supply side, it delivers benefits for SO by providing possible grid services through V2G. Making this mutual satisfaction feasible, needs to provide awareness in customer side and create appropriate incentives and infrastructure in supply side. EV owners are not completely convinced to allow their vehicles to be used by SO for providing system services. Battery degradation and power system impacts on EV batteries are the major reasons for this doubt. On the other hand, V2G concept can be met in a dynamic economic market for EVs management and scheduling that would be feasible in smart grid structures [8], [9]. Because EVs need a communication and control infrastructure to be capable for fast and accurate responses to signals received from a central grid operator, the significance of smart grid is undeniable in the presence of EVs in different electric markets. Apart from above, in the first step, making this concept practical depends on commercializing EVs because providing the grid services with V2G system seeks a large number of vehicles due to their small energy storage. Also development in battery storage and power electronic devices which are suitable for V2G system applications have to be considered by manufactures [10]. The need for grid infrastructure should be concerned at the same time when these technologies are in progress. Therefore, challenges exist in the path toward this approach. Overcoming these challenges is complicated and
Figure 1. Hybrid share of U.S. light vehicle retail registrations in 2010 [11]
Figure 2. U.S. hybrid vehicle market share and gasoline prices in 2010 [11]
The fuel price and the fickle nature of consumers are the most important parts of these issues. When fuel prices raise customers buy EVs and when fuel prices are lower EVs are less popular [11]. Figure 1 shows that, hybrid market share dipped in 2010. This decline can be explained by lower gasoline prices shown in Fig. 2 [11]. Also, the growing availability of fuelefficient nameplates is effective for EV acceptance [11] and makes uncertainty in market share of EVs. In addition, a significant gap exists between customer expectations of EV capabilities and what an EV can deliver today. Customers generally feel that EVs should be able to go farther, on less charge time and for a cheaper price than automakers are already able to offer. The fact is that no more than 2 to 4 percent of population in any country would have their expectation met today [12]. The U.S. DOE forecasts, presented in the Annual Energy Outlook in 2009, is conservative about EVs market penetration [2]. Figure 3 shows the respondents’ purchase likelihood scores after reviewing vehicle information conducted by US southern company [13]. On the other hand, at this moment also due to the differences between power markets among countries, it is possible that V2G would not be beneficial for some power markets. For example, employing this technology is not considered as a useful option in German market in comparison with U.S market [14]. Therefore, in the initial stages, EVs can be used in terms of unidirectional storages for grid services
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instead of bidirectional ones [15]. This needs few additional communication infrastructures and is simple for contribution to the market and more acceptable from consumer side [15]. It can also increase the experience at the beginning of EVs emergence in power markets before using them as a distributed energy resources. However, the purpose of EVs using for grid services is generally considered as a bidirectional source in terms of V2G system.
•
By 2014, reduces the production cost of market-ready, high-energy, high-power batteries by 70% from 2009 costs.
•
Provides a $7,000 tax credit for the purchase of advanced technology vehicles as well as conversion tax credits. And to help create a market and show government leadership in purchasing highly efficient cars. 3. CLASSIFICATION OF THE V2G APPLICATIONS
Attention to the available capacity of EV batteries, grid scale and characteristic V2G improvements could be considered from various aspects. These aspects could be categorized in two sections as below: 3.1. Power System Applications 3.1.1. As a virtual power plant (VPP)
Figure 3. Engine type of next new vehicle [13]
Accordingly achieving to V2G capabilities seek corporation between various industry players and education of consumers. For instance the amount of power that an EV could deliver back to the grid is limited by: • • • • •
Size of the battery pack, The state of charge (SOC) when the vehicle is plugged-in, The capacity of the plug circuit, Battery cycle life and degradation, Maximum battery charge and discharge.
Besides, the available capacity of EVs' power is also an important issue, because it is possible that there is a large amount of EVs' storage in grid but out of availability [8]. Improving these barriers depends on both development of grid infrastructure and vehicle technology and also consumer behaviors. Therefore, it should be noted that transition to the V2G concept includes different barriers that are not just technical. Consumer behavior, economic incentives, cultural and social value, business exercises and challenges related to the resistance against infrastructural changes are other obstacles toward V2G system [3], [4], [6]. As the most important issue, government supports are needed to overcome these challenges. For example the American policies prepare programs such as [16]: •
By 2015, puts 1 million plug in hybrid electric vehicles (PHEVs) on the road, based on DOE report 2011 [17], that can get up to 150 miles per gallon.
•
By 2014, makes PHEVs cost competitive and by 2016, ready for commercialization for volume production.
This approach considers the capacity of EVs fleet for power system as a virtual power plant (VPP) [14], [18-19]. This outlook can be generally used for evaluating the V2G capacity alongside the generation and transmission sectors and in the large scale view of power grids. VPP can be evaluated in order to balance power supply and demand, decrease the generation of power plants and also with the aim of replacing the costly generation units especially in peak periods [14], [20]. Minimizing the energy cost and pollution with focusing on the integration of large scale renewable energy resources in power grids are an important approach that can be considered in researches from this point of view [3], [5-6], [9], [19-20]. In this application, EVs energy dispatch is not accounted and the total capacity of batteries is available for the SO to prepare the possible grid services. In fact, VPP concept is considered due to small and straggly capacity of EVs. From this point of view, it can be used in all power system levels along with other existing resources. Accordingly, VPP concept can be considered in micro grids and isolated islands for evaluating power resources, especially as a backup for poor and intermittency nature of renewable energy resources. 3.1.2.
V2G application enhancement
in
power
system
security
The optimal placement of EVs is determined for more secured services of the V2G approach that has been less concerned. Obviously this approach is considered in distribution sector and micro grids for the variety of grids such as radial or ring [18]. Optimal placement and dispatch of EVs is noticeable in distribution sector due to issues such as outage management, system security and emergency conditions. This application raises the importance of parking lots in the system for identifying the optimal placement and location of parking in order to supply EVs power [21]. Most EV owners tend to recharge their vehicles in two hours or less [12]. This tendency requires high voltage levels of charging facility for fast charging. Therefore, the optimal placement can be performed with the aim of charging station developments in possible MV voltage stations of distribution system [22]. This in turn reduces the need for the required infrastructures.
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3.1.3.
Application in micro grids
V2G can be considered for services like voltage and frequency regulation and stability in micro grids and autonomous islands [23]. EVs availability as an energy storage can be very beneficial in micro grids because most considered recourses that supply power in such grids are renewable energy. EVs can reduce the uncertainty of renewable energy resources and bring about an innovation in autonomous and island power systems through charge scheduling [23]. These facilities can create an advanced demand side management (DSM) in autonomous power grids [23-24]. 3.1.4.
Utilizing as V2B/V2H
V2G can also be utilized to meet demand in the peak hours and to supply energy in commercial and residential building as vehicle to building (V2B) and in houses as vehicle to house (V2H) [21], [25]. There is strong interest in public charging locations such as place of work, gas stations and shopping centers/malls that could be used for V2G purposes [26]. Subsequently, equipping parking lots with bidirectional chargers and controllers makes it possible to use EV energy storage in buildings and integrate this energy with building load curve [21]. If V2G concept is outlined in any size and sector of power system the, requirements for a proper power market should be considered. V2G benefits can be met in a dynamic real-time market. 3.2. Electricity Market Applications EVs may be interpreted as pioneers in electricity markets in term of restructuring market rules and providing liberalization in demand-side market. Evaluation and assessment of dynamic real-time market is implemented by EV owners as a key participant in V2G system. Such a competition is more considerable in distribution section and corresponding markets [27-28]. For accelerating the development of an efficient market various related issues should be considered.
fleet and DSO. Overcoming this challenge in order to create an efficient market is intended by placement of EVs in smart parking lots [20-21]. Therefore, parking lots can ease the EVs management and control for aggregators. 4. SMART PARKING LOTS: OPPORTUNITIES AND CHALLENGES Given the V2G applications introduced in section 3, it can be deduced that emergence of smart parking lots for EVs in power system and generally in distribution sector will help V2G concept to be successful [20-21], [27]. This concept is appropriate due to EVs faster development in comparison with smart grids technologies like communication and intelligent sensors and devices. Parking lots reduce the need to establish communication platforms for EVs management and equip the infrastructures like higher levels of power for fast charging and discharging due to fast response to grid services. A parking lot is easier and faster to equip than individual houses. Also parking of EVs within the parking lots helps to make V2G concept being more feasible since the owner behavior is very stochastic and unpredictable. Constructing the parking lots in the low-load areas of grid or the areas with high capacity lines and transformers could help the power system to bear the EVs power requirements. Therefore parking lots could be effective even the V2G concept is not considered. A typical structure of smart parking lot is showing in fig.4 [31]. On the other hand, parking lots can serve fast and safe charging (defined as a less than 20 minute public charge facility) that have a strong influence on customer satisfaction. The various issues associated with parking lots are listed below:
The need for an aggregator is considered for market contribution due to limited and small capacity of EV batteries. This aggregator could be a distribution system operator (DSO), retailer or a private owner like a parking lot owner. The aggregator earns his profit from selling energy to EV owners and providing grid services. Additionally, the aggregator is responsible for meeting the participants' requirements based on their contracts and criteria [15], [29]. In every size of EVs fleet and power grid, an aggregator is essential for monitoring, control and management of EVs, charging as a load or discharging as a V2G resource which is taken into account in our study. Besides, one of the important roles of aggregator is coordinating V2G system and renewable energy resources. The aggregator could manage EVs charge and discharge when renewable generation exceeds and when it decreases, respectively. From this point of view, the aggregator would be very useful in autonomous grids. Since EVs are large number of distributed energy resources in the V2G application, an intelligent and wide communication infrastructure is needed for signaling between distributed EVs
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1.
Parking scheduling for competition in power market to achieve maximum profit or handle system problems such as peak shifting and load curtailment.
2.
Defining criteria and incentives for EV owners’ satisfaction such as equip parking lots with protection systems against network transient and failure that damage EVs battery.
3.
Economic incentives such as battery swapping which gives driver to exchange a deed battery for a freshly charged battery. This could reduce the cost of the battery and remove the concern about the charge time.
Figure 4. Typical structure of a parking lot for V2G system [31]
Table 1. Classification of various charger levels and capabilities [12] Characteristic Voltage Charge power (kW) Estimated charge time Estimated price
Normal Charger
Rapid Charger
Level 1
Level 2
Level 3
110-120
208-240
480
1.8-1.9
