One frequent question I hear all the time relates to whether the power grid can handle the expected increase in public and private electric vehicle (EV) charging stations. A simple internet search on this topic will result in several articles stating why the grid can handle the increased demand while also resulting in a few that are not quite so confident. The reason for the discrepancy is due to the context in which the question is being answered. There are several variables that must be considered when evaluating this issue, but the two main differences come down to whether you’re looking at it from a national generation and transmission perspective or a local distribution perspective.
Why is there concern over the power grid?
Before getting into the answer, it’s important to first make sure we understand the potential problem that is the driving force behind the question. EV sales have been increasing in recent years and are projected to continue to grow even more moving forward.
According to the International Energy Agency (IEA), electric vehicle sales increased from 0.2% of total car sales in 2011 to 4.6% in 2021. Due to some government policies and auto manufacturers’ claims, S&P Global Mobility expects EV sales in the United States could reach 40% of total passenger car sales by 2030, while the IEA projects EV sales could exceed 50% in 2030. Obviously, regardless of what the actual percentage increase turns out to be, this increase in EVs carries with it a need for increased public and private EV charging capabilities. It’s forecasts like these that are driving the uncertainty over whether the U.S. power grid is capable of handling the increased demand that will come with the increased EV charging needs.
How do EVs impact the grid?
It is no secret that EVs require electric energy via an electric storage system, or battery, to operate. This battery must be charged before the owner can drive away in their EV. The two primary charging options in use today are home charging or a public EV charging station.
There are two main types of home EV chargers: 120V “Level 1” chargers and 240V “Level 2” quick chargers. Electric vehicles typically come with a Level 1 charger, but having a Level 2 charger at home is often preferred because it allows the EV to reach full charge in less time. The actual power consumed by an individual EV owner will vary depending on the make and model of EV, how many miles per day the EV is driven, and the type of charger that is being used. However, some average statistics can be used to gain some understanding of the potential impact an increasing number of EVs might have on the power grid.
On average, some Level 2 EV chargers use 7,200W, or
7.2kW, of electricity. The amount of power needed to charge the vehicle at home depends on how much the EV was driven, which determines the amount of energy it will take to charge the battery back to full capacity. Kilowatt-hours (kWh) is electrical energy consumption over time, which is how the electric utility measures your energy usage for billing purposes. All electric vehicles have a kWh/100-mile rating — this is the amount of electricity they use per 100 miles driven.
Based on data from fueleconomy.gov, an average value to use is 0.3kWh per mile driven to get an idea of how much energy is needed to charge per week. On average, Americans dry 38.4 miles per day, which equates to an average of 80kWhs of EV charging a week. On its own, this does not seem like a very significant increase in electrical energy demand. However, the Edison Electric Institute predicts 26.4 million EVs will be on the road by 2030, so the 80kWh estimate could be multiplied by 26.4 million across the United States.
Can the U.S. power generation and transmission system meet this potential increased demand?
When evaluating the potential impact of the forecasted increase in EVs coming to the homes of citizens across the country, most industry experts agree that the nation’s power grid is up to the task. However, if you evaluate their answers closely, you will start to notice there are some caveats involved in reaching this confidence level.
Some experts have likened this looming demand increase to that of the challenge found as more homes began to add air conditioning, which also resulted in a rapid increase in overall demand on the power grid. According to numbers compiled by the U.S. Energy Information Administration, the United States generated and consumed about 4.12 trillion kilowatt-hours of electricity in 2021 compared to less than one trillion in the early 1960s. Utility providers stepped up to that challenge, and they believe they can do it again.
Based on the forecast number of EVs to hit the market, experts expect that it will drive a 30% increase in electrical energy demand, which is significantly less than the increase required from 1960 to today. Simply looking at those statistics, it’s easy to say that the generation and transmission systems could be equipped to handle the 30% increase between now and 2030. But the issue may be more complicated than that.
Can the local distribution system handle the increased EV charging demand?
The more complicated answer to this question comes when the context shifts to the power grid that is providing power to residential customers. The average residential home will use less than 2kW of power. This amount will fluctuate as appliances like an HVAC unit or refrigerator turn on, but the average use during peak hours is less than 2kW.
As mentioned earlier, a Level 2 EV charger can require 7.2kW of power. Keeping in mind that consumer demand will likely result in the market providing chargers that will charge EVs faster, which, in turn, will increase the kW power demand. To complicate the potential issue, the typical EV driver will want to get home and plug in/charge their car immediately, which will put this increased load on at peak times across the grid as multiple EVs are charging at the same time.
Obviously, the power distribution systems vary from neighborhood to neighborhood, but let’s take two common examples to put this into perspective. These examples will be simplified for the purpose of making a clear point on how these charging stations can impact the local distribution system.
In a rural area, for example, a single house may have a dedicated pole-mounted single-phase transformer that provides low-voltage power to the house. A 5kW transformer would be a common size that might have been chosen by the utility to provide more than sufficient capacity for a large house for several years. The house may have an average peak demand of 2.5kW, which is easily provided through this pole-mounted transformer. But when customers want a Level 2 charging station added to efficiently charge their new EV, this is now adding 7.2kW of demand based on our earlier example. The charger alone exceeds the rating of the transformer and would require the utility to upgrade it to a larger capacity transformer.
Let’s look at a city subdivision as another example. Today’s subdivisions will often have a green pad-mounted transformer that will provide power to anywhere from four to 10 houses, depending on proximity to the transformer. Assume a 25kW transformer is providing service to five different houses. This would allow for an average of 5kW per house of power demand during peak hours. If one or two of those houses installed a Level 2 charger for their EV, then there probably would not be an issue. But if four or five followed suit, the transformer would not be sufficiently rated for the potential maximum demand.
While these are grossly oversimplified, generic examples, they do highlight the very real potential problems that could arise if the percentage of citizens who own EVs and EV charging stations increases. If these situations can be problematic for homeowners, one can only imagine the impact on apartment buildings or other high-density residential areas — and this is only looking at the issue of power demand. Another consideration is the impact these charging stations might have on power quality issues, such as voltage imbalance, voltage sag or swell, transients, and total harmonic distortion. In addition, due to the nonlinear nature of the EV chargers, the temperature of the transformer and its associated loss rise during EV battery charging, which can result in reducing the transformer’s life expectancy.
What’s the solution?
Just as the problem has some complexity, so does the potential solution. The generation and transmission grid is predominantly an aging infrastructure in need of modernization and upgrading. The U.S. government and major electric utility providers are poised to spend significant amounts of money in modernizing and upgrading the electric infrastructure in the coming years. This is convenient timing to allow for increasing generation and transmission capacity in time to meet the potential EV charging demand. In addition, the current grid was designed with large power stations, such as coal plants, distributing power like the spokes of a bicycle. As a result, there is potential for the grid of the future to become much more of a distributed system — with power generation coming from many smaller smart microgrids at the local point-of-use level. As these changes take place, utility providers will certainly have future demand capacity in mind.
At the current local distribution level, the solution becomes a little more complicated. As a side note, there were no previous examples related to public charging stations because these are typically designed and installed directly off commercial-sized power systems that are more readily capable of handling the additional demand. In the residential zones, it is not practical for the utility to just replace/upgrade the majority of those systems similar to how the generation and transmission systems will execute their improvements. Certainly, there will be cases of replacing individual transformers with larger capacity transformers to meet discrete demand needs, but there must be other options deployed on a larger scale.
Smart charging systems
One way to help avoid overloading the local transformer is to avoid charging EVs during peak times. The distribution system is sized to have sufficient capacity to handle the time of day or night when the demand for power is at its highest level, or peak demand. The peak demand occurs at different times depending mostly on the time of year. Typical variables that impact peak times are when most people are home and when the HVAC or heaters are running the hardest. One method that utilities have already incorporated to incentivize consumers to limit their power use during peak times is to apply time-of-use rates to their billing structure. This means that the energy a home uses during the established peak hours costs more per watt-hour than energy consumed during non-peak hours.
Basic smart charging systems can take advantage of the lower cost energy by scheduling the charger to start charging the vehicle during non-peak times. However, there still could be some complications if multiple houses on the same transformer chose the same time frame to rapidly charge their EVs. There is also the potential for some smart chargers to allow permission for the utility provider to directly control when the EV gets charged. EV owners could tell the utility when they will need their EV to be fully charged, and then the utility would direct the EV owner’s home charging station to deliver electricity at the time and speed with the lowest impact on the power grid. There are even some experts who are discussing vehicle-to-grid technology that would allow the connected EVs to be used by the utility as a power source during high-demand times. As demand for EVs and charging stations increases, more technological advancements will come to market to help minimize cost to the customer and risk to the reliability of their power source.
The forecast of increased EVs and associated EV charging stations is a reality whose magnitude will only truly be known as it manifests. At some level, the power grid will see an increase in demand as technology moves forward. There were predictions that computers would become as big as a house, but as technology advanced, those “supercomputers” turned into smart devices that fit into our pockets. The automotive industry will continue to make advancements — whether it is in the EV market or some other emerging technology. But if the EV forecasts become a reality, there are solutions that can be applied at various levels in our electrical distribution system that can help us successfully adapt to the new demands. The EV revolution will undoubtedly have an impact on the power grid, but it is not a problem we will be unable to solve.
Tommy Northcott is a professional engineer licensed in the state of Tennessee and a senior power engineer with Jacobs Technology, Inc., in Tullahoma, Tenn. He is also an NFPA 70E compliance subject matter expert, a principal member of the NFPA 70B Committee, electrical safety trainer, certified maintenance and reliability professional, and certified reliability leader. He can be reached at [email protected].