Electricity Storage and Plug-In Vehicles

Executive Summary

Plug-in electricAn adjective meaning “needing electricity to operate” such as electric motor or wire. IEEE: Containing, producing , arising from, actuated by or carrying electricity. vehicles – including electric-only plug-in electric vehicles and plug-in hybrid electric vehicles (PHEVs) are expected to become much more common in upcoming decades. Presumably a significant portion of charging of electric-only and PHEV vehicles (collectively referred to as plug-in EVs or just EVs) will occur at night and during weekends, when electricity value and price are low or relatively low and while passenger vehicles are not needed/used. 

However, at least some EV charging will be needed during the day and even during peak demand1. The rate at which electric energy1. Energy is the potential of a physical system to perform work. (A common unit of work is foot-pound—the amount of energy needed to lift one pound up a distance of one foot.) Energy exists in several forms such as electromagnetic radiation ... is delivered to or by a system or part of a system, generally expressed in kilowatts or megawatts, at a given instant or averaged over any designated interval of time. 2. The rate at which energy is being used by... periods when the grid is already providing the maximum amount of powerThe rate at which energy is generated, converted, transmitted, distributed or delivered.. If EV charging occurs in parts of the grid that do not have sufficient capacityThe rate at which equipment can either generate, convert or transfer energy. “head-room” to accommodate the extra power needs, then there are two basic alternatives. First, the utility could increase the amount of generationThe manner in which electricity is generated. The electricity that flows through California, transmissionAn interconnected group of lines and associated equipment for the movement or transfer of electric energy between points of supply and points at which it is transformed for delivery to customers or is delivered to other electric systems. and distributionThe practice of and infrastructure for distribution of electricity to end-users by utilities. Typical voltages range from 12 to 138 kiloVolts (kV) (GT&D) infrastructure to add needed capacity. The second alternative is to install distributed energy resources (DERs) including distributed generationSmall, modular electric generation that is interconnected with the electricity grid at the subtransmissionPart of an electricity transmission and distribution system whose voltage is lower than that of the transmission system and higher than that of the distribution system. Subtransmission circuits are usually arranged in loops so that a single line... or distribution level. and storage. To achieve the desired effect, the DER capacity must be installed electrically downstream from congestion points to serve the added on-peakTimes when demand for electricity is highest (a.k.a peak demand). Typically on-peak times occur during weekdays during the hottest summer months, when normal demand is high and when air conditioning is operating. Similarly, in some areas on-peak times... demand locally. 

Coincidentally, depending on the circumstances and after addressing a range of issues and details, idle EVs that are mostly or fully charged and that are connected to the grid (e.g., at charging stations at work) could be used to provide some of the necessary power, locally.


Growing use of EVs has important implications for the electricity grid. EVs will use a growing amount of electric energy – resulting in more generation operation with a commensurate increase of generation fuel use and air emissions. They will require additional capacity to make, transmit and deliver additional energy, especially during the electric grid’s peak demandThe maximum power draw from end-user loads during specified times. For example, most utilities experience peak demand during hot summer afternoons. times (times when end-users’ maximum power draw on the grid occurs). 

So, not only would additional generation be needed – to produce the power –  the transmission and distribution (T&D) systems will also have to be upgraded and enhanced, mostly by adding more capacity to transmit and deliver the additional electricity during the grid’s peak demand times. 

Given the expected proliferation of EVs, there is growing focus by utilities, regulators, policymakers and legislators on development of plans to accommodate the added electric demand that charging during on-peak times will add to the non-EV demand. 

An alternative to the conventional GT&D response is to add distributed electricity storage at or near EV charging stations. Doing so reduces the amount of GT&D capacity needed on-peak to serve the EV charging-portion of the total peak demand. And, the storage is charged using low priced, off-peakThose hours or other periods defined by NAESB business practices, contract, agreements, or guides as periods of lower electrical demand. energy when generation fuel use and air emissions are lowest (on a per kilowatt-hourA measure involving one thousand watts being generated, transmitted, distributed or used continuously for one hour. The kiloWatt-hour is perhaps the most common unit of electric energy; it is used by utilities for billing. (Note the difference between... basis). 

Whatever the response to the EV challenges, Smart GridCollectively; devices, practices and protocols that enable rich monitoring and situational awareness and flexible and robust control of various parts of or entire power systems under varying conditions. Among other objectives, Smart Grid is expected to... will play a role. It will provide the monitoring, communications, control, and computational capabilities to accommodate fast EV charging during peak demand periods in the most efficacious way attainable. 

Using electricity storage for EV charging has some notable synergies with other benefits. For example, distributed storage for EV charging could be part of a localized strategy to integrate distributed photovoltaics and to provide very reliable electrical1. An adjective meaning “pertaining to electricity”. Electrical Engineer. 2. Related to, pertaining to or associated with electricity but not having its properties or characteristics. service in specific parts of the grid. Also, charging at night when demand for electricity is low would increase GT&D utilization, thus reducing the utilities’ overall cost-of-serviceThe total cost incurred by the utility to generate, transmit and deliver electricity and to provide customer service..

EV and Electricity Storage Market Interactions

Notably, EVs which are connected to the grid could be used in lieu of or in conjunction with electricity storage in emergencies or extreme supply shortages, to supply power to the grid. This application is known as vehicle-to-grid or V to G. So, though challenges remain, it is possible that EVs could be a non-trivial electric supplyA source of electric energy and/or capacity, possibly including generation facilities and purchases. resource during rare times when the grid is undergoing an emergency. Further, EVs may complement or compete with electricity storage. 

When EVs proliferate significantly, purchase of energy at night, during off-peak times, to chargeThe process of injecting energy to be stored into the storage system. EVs may increase off-peak energy prices enough to reduce the benefit for some grid-related storage uses, especially energy time-shift and TOU energy cost management. The proliferation of PEVs and PHEVs could also lead to economies of scale and lower prices for advanced batteries and battery1. Two or more electric cells connected together electrically. In common usage, the term “battery” is also applied to a single cell, such as a household battery. 2. A system comprised of identical electrochemical cells. systems, including system management and grid integration (i.e., monitoring, control, communications, interconnectionThe physical and electrical connection between an electricity source and an external power system (i.e. the electric power grid)., and computer algorithms).

Conclusions and Observations

The nexus of EVs and electricity storage nexus is an interesting one. EVs and storage may complement each other and they may be competitive. But electricity storage seems to be a key element of the response to challenges that will arise when EV charging during on-peak hours becomes more common.