Potential Benefits, Limitations, and Reality of V2X (Text Version)
This is a text version of the podcast episode Potential Benefits, Limitations, and Reality of V2X from June 28, 2023.
MOLLIE PUTZIG: Welcome to On the Go, an on-road transportation podcast with Clean Cities. In this episode, we're talking about systems that connect electric vehicles to buildings, the electric grids, and other power infrastructure. To kick us off, let's introduce our hosts. I'm Mollie Putzig.
JOANNA ALLERHAND: And I'm Joanna Allerhand. Today, we will be joined by two guests with expertise in EV integration with power infrastructure. They'll be discussing current research in this area, potential applications, challenges, and opportunities
MOLLIE PUTZIG: Here to tell you more are Andrew Meintz and Jesse Bennett from the National Renewable Energy Laboratory.
ANDREW MEINTZ: Hi, this is Andrew Meintz. I am NREL's chief engineer for EV charging and grid integration activities. I've worked on strategic oversight for NREL's EV grid integration research in this role. Been at the lab for over seven years. And since then, I have focused on multiple efforts in smart charge management, vehicle-to-grid, integration and evaluation of systems, and charging from the megawatt scale all the way down to Level 1, Level 2 charging.
JESSE BENNETT: Hi, my name is Jesse Bennett. I'm a research engineer at the National Renewable Energy Laboratory, with background in electrical engineering. And I'm currently working on the intersection of transportation in the grid, considering the charging requirements for electric vehicles, and the potential impacts they will have on the grid.
I do most of my work supporting the federal intervention program and looking at electrification opportunities for the federal fleet, as well as research on potential grid impacts of EV charging with the Vehicle Technologies Office. Prior to my time at NREL, I was a utility standards and specifications engineer out of Pittsburgh, Pennsylvania looking at the potential design and implementation requirements for distribution equipment.
MOLLIE PUTZIG: Thank you, Andrew and Jesse, for joining us today. So I normally work in the vehicle and infrastructure space. So before we get into discussion of EV integration with power infrastructure, let's talk more about the grid. What do we need to know about the grid that we might not already know?
JESSE BENNETT: That's a great question. And in regards to transportation, I think we're probably all aware that electric vehicle adoption is continuing to expand every year. And that's with a higher number of electric vehicle sales, but also an increasing number of different vehicle models that's also beginning to expand into larger vehicles.
And all of this means that we're going to see much more of the energy needs for transportation being supplied from the grid. And primarily, that electricity is going to be supplied through electric vehicle supply equipment or EVSE.
ANDREW MEINTZ: Yeah. So if we think about the charging basics, essentially vehicles consume electricity from the grid like any other device– a toaster or a laptop computer. But they store it on what we call a traction battery for the vehicle. And so this battery holds on to the energy while the vehicle is disconnected from the grid and driving around.
And so what's interesting about this is that if you think about it, a light duty vehicle uses something on the order of 400 watt hours to drive a mile. And a heavy duty, like classic tractor, dig truck on the road, could use somewhere around 2 kilowatt hours of electricity. So this is– if you think about a laptop– somewhere around the order of running a 50-watt laptop for eight hours a day in a light duty case, or running it for an entire week, five days of work, just for a mile for each of those vehicles.
And so the total amount of energy that these vehicles have is something that we can use to support the grid or support other activities through bidirectional power flow in order to push the power to a load as it's needed. And we refer to this as vehicle-to-everything or V2X.
JESSE BENNETT: And when you're considering all of the energy needs for these vehicles, I think– like you said, Andrew, thinking about energy flowing back to the grid from a vehicle, or even just simply charging it and getting energy from the grid. It's really important to think about the grid interconnection piece. And that's really the point at the grid in which all of the loads that, say your house or your building, connect with the utilities infrastructure or the main distribution lines.
Most often, this is referred to as a point of interconnection. And at your house, you might think of it as just where your electric meter is. But something to consider here is really the power limitations of that interconnection piece. And really, how much power can flow in either direction is really important. And there are sometimes limitations in how much power you could consume at one given site. And one great way to mitigate challenges with those power limitations–
Because maybe you want to install more chargers than a site could potentially support. A great way to limit that is through managed charging– to coordinate loads in a way that do not exceed those power limitations. However, managed charging can also take advantage of some basic grid programs, such as time-of-use rates, that reduce the cost of electricity at periods when electricity and energy are cheapest to produce.
And therefore, you can coordinate charging loads and how you get energy into your vehicle in a way that actually reduces the overall cost for transportation.
ANDREW MEINTZ: And so if we think about more complex services for the grid or grid services, two that really come to mind are frequency support and voltage support. Frequency support is a service that balances the difference between how much electricity is generated at any one given moment and the amount of load that is using it. So on the grid, we have to keep that in balance. There isn't a lot of energy storage in the system.
And so frequency support is a way to keep the system in balance in that way from a wide area perspective. The other grid service, voltage support– it allows more of a distribution line away to push up the voltage of the system in given areas if they're under heavy load. And so as the grid is heavily used in an area, the voltage will drop. And this will keep it in the range that our devices expect for them to function properly.
And how vehicles might do this is through bidirectional flow or something we call reverse power flow, where the charger, instead of taking that energy in as a load, will push it back onto the grid or onto a load utilizing the same converter or charger that it uses to fill the battery with energy.
This can lead to some concerns about what we refer to as backfeeding or where we're pushing power through the meter in the opposite direction, and can be a concern in times in which the grid might be out. There might be an outage of some sort. When you think about the complexity of pushing power back and forth, frequency support or voltage support, there's a lot of ways that vehicles can interact with the grid.
And so an aggregator is an entity that takes into account the needs of the utility, the needs of the grid, and the needs of the EV operator and puts those in balance across many different vehicles in a distribution territory or a utility's region of service.
MOLLIE PUTZIG: OK. That was all really helpful background. Now let's dive in. We hear a lot about different options in this space. So there's vehicle-to-building, V2B, vehicle-to-grid, V2G, even vehicle-to-load or V2L. Let's start with a brief overview. What is vehicle-to-x?
ANDREW MEINTZ: So we'll start with the simplest case, V1G, also known as smart charging. So this is a simple control approach in which the EV responds to some control, either from an aggregator or from some other location. And basically, it just reduces its charging load, pauses, restarts its load at a different time.
And so it accomplishes what the grid is looking for or the building is looking for or other devices are looking for simply by throttling the speed at which it charges or by pausing its charge.
JESSE BENNETT: In addition to smart charging, I think there's another common feature that a lot of newer EVs are providing now. And that's more vehicle-to-load or V2L. And that's where the vehicle is able to take advantage of the energy within its traction battery to power some small equipment or power tools that are directly connected to the vehicle.
And this is just some small equipment that typically takes advantage of some of the energy within the vehicle's battery and are most common in worksite applications, where you might not be near the grid in order to provide some electricity to some of those equipment.
ANDREW MEINTZ: And then I guess maybe moving up in complexity. Vehicle-to-building is probably the next one that falls in this category. It's usually bidirectional charging– allows for the vehicles to provide power back to a building. And say, an outage situation, it would require that the building has been– breaker panel if you will, or other connection to the building, has a switch to allow it to disconnect from the grid so that you're not pushing power back on to the grid during an outage.
And so then the vehicle could provide power to the building. Could be also sometimes called vehicle-to-home as well, if it's a smaller building case. And so essentially, this is a simple microgrid, but the vehicle has to provide the voltage source to the building.
JESSE BENNETT: And I think maybe the largest, or maybe most complex, system here is when you take all these concepts and you apply them in a vehicle-to-grid scenario, where the power is intended to flow back into the grid. And this is typically applied for a number of reasons, but most often for ancillary services and providing support to the grid such as frequency support.
Or really even taking advantage of TOU rates and purchasing energy when it's lower and then selling it back whenever it's higher to take advantage of that difference in price.
MOLLIE PUTZIG: OK. So a lot of different options for what your vehicle could be talking to. Taking that down to the vehicle level, what vehicles could be used in these applications, and how would you determine if your fleet could Participate
ANDREW MEINTZ: Well I think one of the first things that you'd want to figure out for your vehicle is understanding how often it's parked and available for a V2X service. So typically, we would refer to it as the dwell period. And so we'd be looking at vehicle operations in which maybe you have 12 hours of parking time, but you only need about eight hours or six hours of time to fully recharge the vehicle.
And so this way, you could take advantage of that extra time the vehicle is sitting unused and discharge or stop the charge within that period. And then complete the charge before it needs to get on to its next opportunity to provide a transportation service.
JESSE BENNETT: And I think that really maybe leads into some of the operational updates that might be needed for fleets to provide these services. If you're going to be taking advantage of the vehicle's dwell period to provide these grid services or bidirectional power flow, you need to really have a system and a combination of fleet management software and charging management software to ensure that the charging session is designed to provide the vehicle all of the energy it needs by the time its dwell period is over.
And look at the overall flexibility in that charge session to determine when that reverse power flow is capable of occurring, while also ensuring that the vehicle is fully charged at the end of its dwell period.
MOLLIE PUTZIG: So we know what kind of connections we're making with vehicles and what vehicles or fleets might be involved, or what we want to consider with that. But what does that look like in the real world? What are the outlooks for the near-term applications?
JESSE BENNETT: I think currently, there are quite a few V1G applications that are operating in fleets today. Most notably, all smart charging can provide some benefits to both the grid and the fleets, as well as the local building operations, by ensuring that the scheduling of charge sessions is done so in a way that can mitigate peak demand or mitigate equipment upgrades to support EV charging.
And also, even take advantage of time-of-use rates by charging vehicles when their energy is the lowest.
ANDREW MEINTZ: And I think– building on that, we do see that vehicle-to-load use of, say 120 volt outlets in vehicles is pretty common. We've actually seen that in conventional vehicles. But we'll probably see more applications of small vehicle-to-load EVSE or ports within the vehicle that will allow for energy to be extracted from the traction battery.
I think this is really going to be a common application if you think about power tools at a jobsite or maybe just the power devices that you would use while on a camping trip.
JESSE BENNETT: And I think taking that concept even further as vehicle-to-load becomes more popular, I think vehicle-to-building seems like a great transition to expand those capabilities to support building operations, in addition to just the nearby power tool requirements. And vehicle-to-building can really help to mitigate demand charges, even more so than smart charging may be able to, by actually having that reverse power flow reduce the net consumption at the point of interconnection with the grid.
But you can also look at the opportunities for supporting building loads during a grid outage by islanding the building from the grid and taking advantage of the energy within the vehicles traction battery to support lighting loads and other emergency loading requirements. Additionally, in a vehicle-to-loading application, you'll need to make sure that your system is islanded from the grid in the event of an outage.
And that'll be done so with a disconnect switch that must be installed per most utility interconnection agreements. And this will ensure that while you're powering your building during an outage, you're not backfeeding any of that electricity into the grid. Otherwise, that would create an unsafe environment across the utility.
ANDREW MEINTZ: Now one thing to consider in this situation is that now that the vehicle is the only source, it has to maintain voltage for the other devices, the others loads connected to the building. And so other needs around ensuring that you don't exceed the capacity of the vehicle– that you can provide enough power from a control standpoint. And then this ability to act as a voltage setting device may require additional capabilities from the vehicle.
So some that can provide V2G in a grid type situation may not be able to provide it in a grid isolated or an islanded case. Yeah. And then I guess that gets us to the end stage, the holy grail, V2G, where now we're pushing power back on to the grid. And we're using this as a way to provide energy for utility needs as an alternative to perhaps intermittent generation sources.
But we're also seeing that in this case, we would see that there might need to be some changes in how utility programs allow for incentives for these grid services that the EV could provide, similar to what we've seen with PV and net metering and TOU rates for some– perhaps arbitrage of energy across those rates. Really, I think, the end state here is when we're able to not only affect the local use of electricity, but then kind of push that further out into the grid.
JOANNA ALLERHAND: That's great background on the technology and its potential applications. What are some of the technical challenges with implementation?
JESSE BENNETT: Well, I think one of the first considerations is when you're talking about the bidirectional flow of power and you may be having reverse power flow back into the grid, you need to really consider the interconnection between the building and the utility grid. And there's a couple of different pieces of equipment that are really important at this location to ensure safer operations for both the building and the grid.
And number one would be the transfer switch. And that's something that would be needed in a vehicle-to-building environment. If you're going to be supporting building loads during a grid outage, you're going to need to island yourself from the grid. And that's best done through a transfer switch to ensure that while you're powering the building, you're not going to be providing power to the grid in the event of an outage.
Though in the event that you're going to be intending to have that power flow back into the grid in a V2G situation, you'll need to have a net meter to ensure that you're going to be measuring the reverse power flow in conjunction with all of the loads that are going to be going to the building.
ANDREW MEINTZ: And I think there are some additional hardware requirements that are going to be needed in particular in this discussion for a bidirectional charger. You're going to need a EVSE rather, which stands for Electric Vehicle Supply Equipment. You're going to need to have those devices installed in locations and be able to communicate back to the vehicle.
And so whether it's an AC bidirectional charger or a DC bidirectional charger, it's really going to change the operation of these systems. So in the example of a DC system, you could use current vehicles through the– typically known as the fast charging port, and take that DC energy off of the vehicle. And so you really only need to upgrade or have a bidirectional EVSE.
But if you consider an AC EVSE, that power flow actually has to come from the vehicle into its onboard charger, and then be pushed onto the vehicle. And so where we stand today, very few, if any, vehicles on the market have onboard bidirectional chargers that would support transfer from an AC standpoint. And then on the DC side, there are vehicles that will allow for export via some of the ports.
But there's still some work that needs to be done for the communications to allow for that. And so there's certainly some work that needs to be done in developing these chargers and some of the communications between the two.
JESSE BENNETT: And I think considering both the interconnection and the equipment hardware, it really brings us to some of the safety standards that will be in play here. And most often, the interconnection is governed by the National Electric Code. And specifically, Section 625 talks about the installation of electric vehicle supply equipment or EVSE.
And when you're talking about the bidirectional flow of power, you're going to be looking at a couple of different safety standards and UL certifications that ensure that equipment and hardware are built to perform as they were intended. For example, UL 1741 and 9741 are both some safety standards that would deal with the bidirectional flow of power or the single directional flow of power to EVSE.
ANDREW MEINTZ: And so then we get to one of the– maybe common questions that we always get in this discussion about V2G or V2X is the thought about battery life. What's this going to do to the vehicle? And so certainly, as batteries are cycled more, there will be some aspect of their battery life that is degraded. Now of course, the real question here is how does that relate to the typical service life of the vehicle, and how long the battery would have lasted otherwise.
And so there is a difference in how batteries age versus what is known as cycle-life aging and calendar-life aging. Batteries will age if they're just sitting unused. So there is a balance that needs to be understood in how the vehicle is intended to be used and how the addition of some of these functionalities for V2G or V2L or V2B– how that additionally degrades the vehicle.
And so in some cases, there may be fine to discharge the vehicle and the battery life. The battery would degrade to the point where it's acceptable at the end of the life of the vehicle, when you would trade it in and get a new car or what have you. And so there really is some work that needs to be done to understand these implications. And not all uses of these vehicles for V2G or V2L are really equal.
I guess one of the other important notes to make here is that there really is some need to be done on how this would impact the warranty of the vehicle. What equipment is approved for this sort of operation? And whether V2G is actually considered. And so I think as we see this technology progress, there's going to be more thought put into how vehicle manufacturers consider this in their warranty.
JOANNA ALLERHAND: And you've touched on this. But can you expand on what are some of the market challenges?
ANDREW MEINTZ: Yeah. I think one of the things that we're going to see– there's really going to be more investment in infrastructure. We start to see, specifically, a lot of V2G because it's not just flexibility within the period that the vehicle is charging. And you could imagine for larger range vehicles that it might be fine then to discharge in one location and never charge. And then go to the next location and then charge there.
But that would require more EVSE to be installed throughout the built environment to allow for this additional flexibility from a location to location standpoint. So certainly, I think investment in infrastructure and how that value is brought back from these use cases is certainly an area that we're going to see some challenges from a market standpoint.
JESSE BENNETT: And I think in addition to that, not only does the infrastructure deployment needed, but also just market options there. While there are some manufacturers developing and offering bidirectional EVSE, it is not yet common in the marketplace. And one of the reasons for that might be that there are not a lot of incentive programs that utilities put together to push forward this bidirectional capabilities.
Fleets are going to need to invest in this additional infrastructure, as we mentioned before, to ensure safe operating environments. And in order to justify that investment, the fleets are going to have to benefit in some way from the additional services they're providing to the grid. And that will have to come through the offering of different bidirectional programs, such as demand mitigation or new utility rates that will support these types of operations.
JOANNA ALLERHAND: And looking forward, what would be needed to overcome these challenges?
JESSE BENNETT: So I think maybe one of the reasons there are not a lot of incentive programs from the utilities is there's not a lot of knowledge about the operational use cases within fleets and how often these vehicles will be available as an asset to the utility. As we are going through the process of electrifying fleets, we need to really understand not only their driving patterns, but also their charging patterns.
And that will really help us to understand when these vehicles could be an asset to the grid and/or their buildings. And that will just come through deeper penetrations of electric vehicles throughout the fleet and throughout the country so we understand not only their transportation needs, but also their dwell periods and charging requirements.
ANDREW MEINTZ: Yeah. And I mean, really– as you're saying, Jesse, the understanding of that– I think we get a lot of that knowledge from a focus on the pilots or demonstration activities in these early days. We really need to understand how certain use cases may be employed. What are we learning from the technologies as they stand? I'm sure there will be challenges associated with communications and operational constraints.
And so really– I think a focus on pilots and demonstration activities is probably going to be one of the early things that we could do to try to figure out some of these unknown unknowns.
JESSE BENNETT: So I think in addition to understanding all the pilots and demonstration projects, I think as fleets are electrifying, the transition from internal combustion engines to electric vehicles is not trivial for fleets. It's a challenging process. So I think that adding this additional consideration and the potential reverse flow of power from the vehicle to the grid further complicates this process.
And I think that as fleets are electrifying and as they're farther along in the transition to electric vehicles, the idea of considering bidirectional charging for your fleet end to support grid operations, I think, will become a much more important topic of discussion.
ANDREW MEINTZ: Interesting. Yeah. I also wonder about like– there's probably some thought that needs to be put into computing technology, such as stationary storage. I think that the primary mission of a vehicle is to transport goods or people. And so looking at some of these other technologies that might be competing with this approach, it is certainly something that we'll need to take a look at just to understand as those markets develop–
As secondary life, perhaps, for battery use occurs, how those might compete with some of these V2X technologies? But of course, there's always a good camping case for me to tell.
JOANNA ALLERHAND: Great. Thanks so much, Jesse and Andrew, for joining us and sharing your expertise. Any final thoughts you want to share before we close?
ANDREW MEINTZ: Yeah. I don't know. I mean, I guess I would say that V2X is certainly a growing discussion around how we can get additional utility out of these vehicles. And so certainly very interesting to see the ingenuity of some of these approaches. And so it'll be interesting to see how the market evolves, how companies respond. The availability of some of this equipment maybe provides an additional use case for electric vehicles.
JESSE BENNETT: Yeah. I would say I'm also really excited about the opportunities and value that bidirectional charging can provide both fleets and the electric grid. But I also am really excited just about fleet electrification in general. And I understand how the bidirectional flow of power can complicate the transition to electric vehicles. So I wouldn't want fleets to dive in too quickly while there are some of these challenges. But I'm really excited about all of the opportunities that electrification will provide.
JOANNA ALLERHAND: Wonderful. Thanks so much to you both.
ANDREW MEINTZ: Thank you.
JESSE BENNETT: Thanks.
MOLLIE PUTZIG: Thanks, Andrew and Jesse, for joining us and sharing the current research about integrating EVs into power infrastructure. Stay tuned for future episodes on ethanol, electric school bus resources, and best practices for including community engagement in transportation projects.
JOANNA ALLERHAND: That's it for this episode of On the Go. As we wrap up, I want to thank the US Department of Energy's Vehicle Technologies Office and our team here at the National Renewable Energy Lab for their support. Also, a big thanks to Brittany Conrad and Vern Slocum, our podcast editors. We couldn't do it without you.
MOLLIE PUTZIG: If you want to learn more about Clean Cities and its partnerships to develop affordable, efficient, and clean transportation options to accelerate the development and widespread use of a variety of innovative transportation technologies, visit cleancities.energy.gov.