June 15, 2023

How Would EV Charging Demands Affect the Electric Grid in California?

 

In 2021, battery electric vehicles (BEVs) accounted for 3% of the light duty vehicle sales in the U.S., with California accounting for 39% of those sales. However, as the U.S. moves towards more widespread BEV adoption, concerns arise about the electric grid’s capacity to manage the surge in demand. By analyzing the power demands that electric vehicle (EV) charging would impose on California’s grid in the case of complete adoption, we can gain insights into the challenges the power sector will face as California moves closer to its target of 100% new zero-emission vehicle sales by 2035. To get a general sense of the added demand, we first evaluate the change in electrical energy needed on an average day.

California had 35,000,500 light-duty vehicles registered in 2021, and of those, 563,100 were electric vehicles (BEV) and 315,300 were plug-in hybrid electric vehicles (PHEVs). Assuming all vehicles, including PHEVs, will need to be converted to BEVs to achieve full adoption, there are roughly 34 million vehicles in California which need to be converted to BEVs.

35,000,500 total light duty vehicles – 563,100 light duty BEVs = 34,437,400 vehicles to convert to BEVs

The average annual distance traveled by light-duty vehicles in the U.S. in 2021 was 10,774 miles. Generalizing this to California and assuming even distribution across every day of the year, we estimate that 30 miles are traveled per vehicle per day.

(10,744 miles/year) / (365 days/year) ≈ 30 miles/day

If most drivers charge their vehicles every day to replenish the amount driven, we estimate users add 30 miles of charge per day. Based on EPA automotive trends, the typical fuel economy for cars and light-duty trucks is 0.3 kWh/mile and 0.5 kWh/mile, respectively. Since this exercise would replace the entire light-duty vehicle mix, we assume a 50-50 split of light trucks and cars and assume the average fuel economy of the BEVs adopted is 0.4 kWh/mile. Then, we can calculate the additional electrical energy needed to add 30 miles of charge, ignoring charging and transmission losses.

30 miles/day × 0.4 kWh/mile = 12 kWh/day per EV

The average American household uses about 30 kWh/day, so one EV requires 30% of the current daily household electricity usage. Now, if California travel patterns remain consistent after people switch to a BEV, we can calculate the additional daily energy needs from all residents converting to a BEV:

34,437,400 vehicles × 30 (miles/vehicle)/day × 0.4 kWh/mile = 413,248,800  kWh/day ≈ 413 GWh/day  needed

Further, the state of California consumed a total of 303,300 GWh annually (based on 2018 and 2019 data), or an average of 831 GWh/day.

(303,300,000,000 kWh/year) / (365 days/year) = 830,958,904 kWh/day ≈ 831 GWh/day

We can now compare the daily energy consumed to the additional energy needed.

(413 GWh/day) / (831 GWh/day) ≈ 50%  increase in energy

On an average day, a 50% increase in electricity consumption is needed to support the conversion of all light duty vehicles to BEVs. Now that we’ve examined the significant increase in energy consumption required to support the conversion, let’s explore the impact this could have on the electricity grid, especially given the increasing focus on renewable energies and the shift away from fossil fuels.

AC Level 2 charging uses 240-volt service, which is the same as what is used for many household appliances, and has a typical power output of around 7 kW which can charge a battery electric vehicle (BEV) to 80% in approximately 4-10 hours. Although the power draw of a Level 2 charger is significantly lower than that of a DCFC, which has a power output of up to 300 kW and can charge a BEV to 80% in as little as 20 minutes, unmanaged home charging has the potential to cause significant problems.

The “duck curve” shown below illustrates the challenges of supplying electricity when using renewable sources, such as solar and wind power.

Currently, utility companies provide power based on demand, resulting in minimum power being supplied overnight, and demand peaking in the mornings and evenings. However, renewable energy sources, such as solar power, are challenging to store. Solar power generates energy when the sun is shining, regardless of demand. The curve illustrates the difference between California’s energy demand and its wind and solar energy production. As peak demand heightens in the mornings and evenings, renewable energy sources are minimal, resulting in a high net load. Then, during the day, when the renewable energy supply is high, the demand is low. The widespread adoption of EVs could exacerbate this issue if charging occurs during periods of high demand. To get a better idea of the scale of this challenge, we evaluate the worst-case scenario in which 100% of California residents adopt EVs and charge their vehicles at the same time in the evening peak.

As noted above, there would be 35,000,500 additional BEVs affecting the power requirements shown in the CAISO duck curve. If we assume that each car owner has access to a Level 2 EVSE which draws power at 7 kW, we can calculate that charging an EV 30 miles would take just over an hour and a half.

30 miles/day * 0.4 kWh/miles = 12 kWh → (12 kWh)/(7 kW) = 1.7 hours ≈ 100 minutes

In the worst-case scenario, each vehicle would charge at the same time during the evening peak, between 6:30pm and 8:00pm.

34,427,000 vehicles * 7 kW/vehicle = 240,989,000 kW*(1 GW)/(1,000,000 kW) ≈ 241 GW

For 2023, the duck curve shows evening peak is approximately 20 GW. An additional 241 GW represents a 12x increase in the evening peak power demands. The current evening ramp goes from about 4 GW to 20 GW in the peak and this change in demand would translate to a huge increase, from 4 GW to 261 GW.

It is important to note that this is an extreme case. One of our major assumptions was that each California resident has access to a Level 2 EVSE. Considering nearly 45% of California residents rent their homes, many Californians will not be able to charge at home and will need to rely on public chargers for their charging needs. Workplace charging represents a significant opportunity to balance energy demands since if people have access to Level 2 chargers while they are at work, they can take advantage of the abundant solar power available during the day in California through “managed charging”.

Managed charging makes it possible to avoid the extreme, concentrated demand on the electric grid calculated previously. For instance, if car owners staggered their 100 minutes of charging into the “belly of the duck”, between 6:00am and 8:00pm, we could lift the level of the “belly” and reduce ramping. This means over a 14-hour time period, there are approximately eight 100-minute time windows for EV owners to charge. Thus, between 6:00am to 7:40am, about 13% of owners charge, and between 7:40am and 9:20am, another 13% charge, and so on. This approach could be supported through energy pricing incentives as well as cell phone alerts (which have proved to be effective in managing California’s energy grid). With this approach, it is possible to reduce the evening ramp and take advantage of the midday solar saturation.

(241 GW) / (8 time windows) = 30 GW

These calculations suggest that managed charging can fill in the low point of net load curve, reduce ramping, and provide more consistent energy demands which would enable utility operators to avoid surpluses of solar energy.

One limitation of our analysis is that we assume that Californian’s travel patterns will stay consistent after they switch to BEVs. People may increase how much they drive after switching from a gasoline-powered vehicle to a BEV which would mean a greater demand for energy. Another limitation is we do not account for a range of charging behaviors when we analyze the unmanaged charging scenario. Instead, we assume that drivers will charge every day which may not represent realistic charging behavior. People who work from home or who have hybrid work schedules may not drive enough to warrant daily charging. Further, EV owners may choose to charge only when their batteries are significantly depleted.

The exercise described above is based on the idea that the conversion of light-duty vehicles to BEVs will happen instantaneously. Although California’s zero-emission vehicle sales regulation is set for 2035, there will still be a sizable number of gasoline-powered vehicles in use beyond 2035 given that the average age of a vehicle is around 12 years. If we estimate that it will take a minimum of 15 years for California to convert to all-electric vehicles, there may be time to upgrade the electric grid and handle the surge in demand. However, as shown here, the challenge is significant. The U.S. Department of Energy (DOE) also offers several options for balancing hourly energy loads:

• Increase the flexibility of generation by adding diverse energy sources.
• Develop better power demand prediction technologies.
• Incentivize evening energy use reduction.
• Store power generated by solar to be used at night.

By employing these strategies, we could potentially produce an economically efficient outcome and support the transition to 100% BEVs without straining the energy grid.