Grid Coordination Opens Road For Electric Vehicle Flexibility

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Published on August 14th, 2020 |
by Guest Contributor





August 14th, 2020 by Guest Contributor 


Originally published by NREL.

Unlocking the Value of Electric Mobility Technologies to Drive Efficiency and Reliability Across the Power System

As electric vehicle (EV) sales continue to rev up in the United States, the power grid is in parallel contending with the greatest transformation in its 100-year history: the large-scale integration of renewable energy and power electronic devices. The expected expansion of EVs will shift those challenges into high gear, causing cities to face gigawatt-growth in electricity demand and higher amounts of variable energy.

Coordinating large numbers of EVs with the power system presents a highly complex challenge. EVs introduce variable electrical loads that are highly dependent on customer behavior. Electrified transportation involves co-optimization with other energy systems, like natural gas and bulk battery storage. It could involve fleets of automated ride-hailing EVs and lead to hybrid-energy truck stops that provide hydrogen and fast-charging to heavy-duty vehicles.

Those changes will all test the limits of grid integration, but the National Renewable Energy Laboratory (NREL) sees opportunity at the intersection of energy systems and transportation. With powerful resources for simulating and evaluating complex systems, several NREL projects are determining the coordination required for fast charging, balancing electrical supply and demand, and efficient use of all energy assets.

Smart & Not-So-Smart Control

To appreciate the value of coordinated EV charging, it is helpful to imagine the opposite scenario.

“Our first question is how much benefit or burden the super simple, uncoordinated approach to electric vehicle charging offers the grid,” said Andrew Meintz, the researcher leading NREL’s Electric Vehicle Grid Integration team, as well as the RECHARGE project for smart EV charging. “Then we compare that to the ‘whiz-bang,’ everything-is-connected approach. We want to know the difference in value.”

Chevy Bolt and BMW i3 charging at a ChargePoint station in Florida, by Zach Shahan, CleanTechnica.

In the “super simple” approach, Meintz explained that battery-powered electric vehicles grow in market share without any evolution in vehicle charging coordination. Picture every employee at your workplace driving home at 5 p.m. and charging their vehicle. That is the grid’s equivalent of going 0 to 100 mph, and if it does not wreck the system, it is at least very expensive. According to NREL’s Electrification Futures Study, a comprehensive analysis of the impacts of widespread electrification across all U.S. economic sectors, in 2050 EVs could contribute to a 33% increase in energy use during peak electrical demand—the costly intervals of the day when energy reserves are procured. In duck curve parlance, EVs will further strain the duck’s neck.

Meintz’s “whiz-bang” approach instead imagines EV control strategies that are deliberate and serve to smooth, rather than intensify, the upcoming demand for electricity. It means managing both when and where vehicles charge to create flexible load on the grid.

At NREL, smart strategies to dispatch vehicles for optimal charging are being developed for both the grid edge, where consumers and energy users connect to the grid, as in RECHARGE, and the entire distribution system, as in the GEMINI-XFC project. Both projects, funded by the U.S. Department of Energy’s (DOE’s) Vehicle Technologies Office, lean on advanced capabilities at NREL’s Energy Systems Integration Facility to simulate future energy systems.

At the grid edge, EVs can be co-optimized with distributed energy resources — small-scale generation or storage technologies — the subject of a partnership with Eaton that brought industry perspectives to bear on coordinated management of EV fleets.

At the larger-system level, the GEMINI-XFC project has extended EV optimization scenarios to the city scale—the San Francisco Bay Area, to be specific.

“GEMINI-XFC involves the highest-ever-fidelity modeling of transportation and the grid,” said NREL Research Manager of Grid-Connected Energy Systems Bryan Palmintier.

“We’re combining future transportation scenarios with a large metro area co-simulation — millions of simulated customers and a realistic distribution system model—to find the best approaches to vehicles helping the grid.”

GEMINI-XFC and RECHARGE can foresee future electrification scenarios and then insert controls that reduce grid congestion or offset peak demand, for example. Charging EVs involves a sort of shell game, where loads are continually moved among charging stations to accommodate grid demand.

But for heavy-duty vehicles, the load is harder to hide. Electrified truck fleets will hit the road soon, creating megawatts of localized demand. No amount of rerouting can avoid the requirements of charging heavy-duty vehicles or other instances of extreme fast-charging (XFC). To address this challenge, NREL is working with industry and other national laboratories to study and demonstrate the technological buildout necessary to achieve 1+ MW charging stations that are capable of fast charging at very high energy levels for medium- and heavy-duty vehicles.

To reach such a scale, NREL is also considering new power conversion hardware based on advanced materials like wide-bandgap semiconductors, as well as new controllers and algorithms that are uniquely suited for fleets of charge-hungry vehicles. The challenge to integrate 1+ MW charging is also pushing NREL research to higher power: Upcoming capabilities will look at many-megawatt systems that tie in the support of other energy sectors.

Renewable Inroads for Hydrogen

At NREL, the drive toward larger charging demands is being met with larger research capabilities. The announcement of ARIES opens the door to energy systems integration research at a scale 10-times greater than current capabilities: 20 MW, up from 2 MW. Critically, it presents an opportunity to understand how mobility with high energy demands can be co-optimized with other utility-scale assets to benefit grid stability.

“If you’ve got a grid humming along with a steady load, then a truck requires 500 kW or more of power, it could create a large disruption for the grid,” said Keith Wipke, the laboratory program manager for fuel cells and hydrogen technologies at NREL.

Such a high power demand could be partially served by battery storage systems. Or it could be hidden entirely with hydrogen production. Wipke’s program, with support from the DOE’s Hydrogen and Fuel Cell Technologies Office, has been performing studies into how electrolyzers — devices that use electricity to break water into hydrogen and oxygen — could offset the grid impacts of XFC. These efforts are also closely aligned with DOE’s H2@Scale vision for affordable and effective hydrogen use across multiple sectors, including heavy-duty transportation, power generation, and metals manufacturing, among others.

“We’re simulating electrolyzers that can match the charging load of heavy-duty battery electric vehicles. When fast charging begins, the electrolyzers are ramped down. When fast charging ends, the electrolyzers are ramped back up,” Wipke said. “If done smoothly, the utility doesn’t even know it’s happening.”

As electrolyzers harness the cheap electrons from off-demand periods, a significant amount of hydrogen can be produced on site. That creates a natural energy pathway from discount electricity into a fuel. It is no wonder, then, that several well-known transportation and fuel companies have recently initiated a multimillion-dollar partnership with NREL to advance heavy-duty hydrogen vehicle technologies.

“The logistics of expanding electric charging infrastructure from 50 kW for a single demonstration battery electric truck to 5,000 kW for a fleet of 100 could present challenges,” Wipke said. “Hydrogen scales very nicely; you’re basically bringing hydrogen to a fueling station or producing it on site, but either way the hydrogen fueling events are decoupled in time from hydrogen production, providing benefits to the grid.”

The long driving range and fast refuel times — including a DOE target of achieving 10-minutes refuel for a truck