|Fig. 1: Illustrative schematic of proposed power line and wireless control connections between vehicles and the electric power grid. (Source: N. Corti, after Kempton and Tomia. )|
The basic concept of vehicle-to-grid process is that electric vehicles provide power to the grid while parked. The vehicle in question can be a fully electric vehicle, a fuel cell vehicle, or a plug-in hybrid. The batteries from these vehicles can charge during low demand times and discharge when power is needed in the rest of the grid.
The connections between vehicles and the electric power grid are illustrated in Fig. 1. Electricity flows one-way from generators through the grid to electricity users. The flow is two ways from electric vehicles. A control signal is needed in order to communicate with the electric vehicles when the grid needs energy. In Fig.1, the grid operator is labeled ISO, for Independent System Operator.  The control signal from the ISO could be a broadcast radio signal, or through a cell phone network, direct Internet connection, or power line carrier. In any case, the grid operator sends requests for power to a large number of vehicles. It may do so directly to individual cars, or it may communicate with parking lot operators for example, who in turn would communicate with the fleet of parked cars at their disposal. 
The power grid only has about a 2.2% storage capacity, so generation and transmission must be continuously managed to match fluctuating customer demands.  Currently, this fluctuating demand is met by using large generators. These generators are turned on and off or ramped up and down, some on a minute by minute basis.  By contrast, the electric vehicle fleet inherently must have storage since the vehicle must be mobile and must be able to keep running uninterrupted and independently for the entirety of the drive. These electric vehicles (as shown in Fig. 2) are cheap per unit of power and are utilized only 4% of the time for transportation, making them potentially available the remaining 96% of time for a secondary function of providing energy to the power grid. 
|Fig. 2: Electric vehicles like the one shown here could help power the grid more effectively. (Source: Wikimedia Commons)|
The electric vehicle fleet has 20 times the power capacity, less than one-tenth the utilization, and one-tenth the capital cost per prime mover kW. On the other hand, utility generators have 10 - 50 times longer operating life and lower operating costs per kWh.  This means that the effectiveness of the vehicle-to-grid process is largely determined by the type of power the vehicles would be linked to. For example, vehicle-to-grid does not seem to work well for baseload power. This type of power is a constant, around-the-clock electricity supply. Vehicle-to-grid is not as effective in this scenario because baseload power can be generated cheaply by generators.  However, vehicle-to-grid would be effective in quick response, high value electric services. These services account for up to 10% of electric costs in the US (about $12 billion per year). One major drawback of the vehicle-to-grid process is the possible degradation of the electric vehicles' batteries. Studies have shown that the batteries used in the vehicle-to-grid process deteriorate at a significantly faster rate than those used for simply driving. 
The vehicle-to grid system only makes sense if the vehicle and power market are matched. While current research shows that current batteries are degraded by the process, technological advancements are certain to address these technical issues. The reality is that this system offers a path to both reliable renewable electricity and a path to a low pollution vehicle fleet independent from fossil fuels. 
© Nico Corti. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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