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Electricity Storage and Plug-In Vehicles

 

Executive Summary

Plug-in electric 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. 

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However, at least some EV charging will be needed during the day and even during peak demandperiods when the grid is already providing the maximum amount of power. If EV charging occurs in parts of the grid that do not have sufficient capacity “head-room” to accommodate the extra power needs, then there are two basic alternatives. First, the utility could increase the amount ofgenerationtransmission and distribution (GT&D) infrastructure to add needed capacity. The second alternative is to install distributed energy resources (DERs) including distributed generation and storage. To achieve the desired effect, the DER capacity must be installed electrically downstream from congestion points to serve the added on-peak 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.

Discussion

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 demand 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-peak energy when generation fuel use and air emissions are lowest (on a per kilowatt-hour basis). 

Whatever the response to the EV challenges, Smart Grid 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 electrical 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-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 supply 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 chargeEVs 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 battery systems, including system management and grid integration (i.e., monitoring, control, communications, interconnection, 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.

 

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