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Maximize Renewable Energy Use with Daytime EV Charging

Last week, we explored the question of whether renewables can meet current and future energy demands in California. Despite renewable energy sources providing enough energy to meet demand during certain times of day on relatively low load days, renewables will not be able to provide enough energy for peak load days. This is because peak energy demand time does not coincide with peak renewable energy production time.

This issue is further complicated with the expanded adoption of electric vehicles (EVs) in both private and commercial uses. Prescient predicts that by 2035, there will be over 4 million EVs cars on the road in California, plus an additional 1.5 million electric light and medium duty trucks, 30,000 electric buses, 90,000 heavy duty trucks, and 250,000 electric motorcycles. This number of EVs will require more than 200,000 MWH of energy every day.

The standard EV charging practice of today is to charge all EV batteries overnight when they are not in use. As more EVs are charged overnight, electric utilities will find that peak load periods migrate from early evening to late night and early morning, times when renewable energy sources are far less productive.

Electric utilities need to employ different charging techniques to meet the daily energy demand of 2035 with renewable energy sources. Charging EVs during the day will maximize the use of renewable energy resources. Let’s take a closer look at how that can happen.

Last Year’s Peak Load is Next Year’s Dilemma

On August 16, 2023, the highest peak load day for California in 2023, the state consumed over 200,000 MWH of energy. On this day, the temperature in Los Angeles was above 90°F from 11 AM until 6 PM, with a high temperature of 97°F. Peak load on this day was about 44,000 MW at 6 PM.

To accommodate energy demand that day, Cal ISO initiated demand response procedures, including activating natural gas power plants. In fact, most of the energy needed on this day was produced using natural gas.

Electric utilities will struggle to meet future energy demand with renewables, when several million EVs need to be charged every day and daily load consistently resembles peak load from August 16, 2023. This won’t happen next year, but it will in the near future. With California’s ambitious clean energy goals in mind, electric utilities must strive to meet energy demand with renewable energy sources.

EVs Mean Significant Infrastructure Investment

If today’s practice of charging EVs overnight is maintained into 2035, electric utilities in California will need to invest in increasing their transmission and distribution systems to accommodate a 60% increase in peak load. This is likely to increase the cost of electric rates by up to 250%. If 75% of EVs are charged at night, electric utilities can anticipate a 40% increase in peak load. This will also require a large infrastructure build out, increasing electric rates by about 150%.

If 50% of EVs are charged at night, only a 25% increase in peak load should be anticipated. This will require the least amount of investment in new infrastructure, though consumers could still anticipate a 100% rate increase.

Energy Demand from Expanded EVs

Figure 1 shows the predicted hourly peak energy demand in California in 2035. All numbers are based on August 16, 2023, energy demand, which is the yellow line (continued under the red line between 6 AM and 9 PM).

The graph in Figure 1 shows the predicted hourly peak energy demand in California, considering EV charging.

Figure 1 shows the predicted hourly peak energy demand in California, considering EV charging.

The red line shows EV charging by today’s best practice – charging overnight for approximately 8 hours. In 2035, when the number of EVs in California will be in the millions, it is expected that peak load will increase from about 44,000 MW at 6 PM to nearly 70,000 MW at 10 PM. Demand will remain above 55,000 MW throughout the late night hours.

Alternatively, if 75% of EVs are charged at night and 25% charged during the day, as shown by the light blue line, peak load will be reduced to 60,000 MW. However, demand remains above 50,000 MW throughout the late night hours, meaning renewables will still not be providing most of the energy required to charge EVs.

Another alternative is represented by the black line, which shows 50% of EVs charged overnight. This reduces peak load to 55,000 MW, while demand remains above 44,000 MW throughout the late night hours.

The best alternative is to encourage EVs to be charged during the day. When 75% or more of EVs are charged during the day, as represented by the green line, energy demand will increase when renewable energy sources are most productive. In addition, peak load will be reduced to 53,000 MW.

The Best Alternative: EV Charging During the Day

To reduce the need for more infrastructure and use renewable energy when it is available, EVs should be charged during the day. Ideally, EV owners will charge their EVs when at home on the weekends or working from home. Low rates for electricity at this time will create an incentive for daytime charging.

EVs that are used to commute can also be charged during the day when solar energy is available. Level 2, 8-hour chargers can be installed at commuter parking lots, including transit centers, office and industrial buildings, and schools. This would allow commuters to leave their cars connected to the charger throughout the workday. Alternatively, Level 3, 30-minute chargers with valet parking could be installed in commuter parking lots; in this case, valet drivers would move EVs every 30 minutes to maximize EV charging during the day.

Fleet EVs used to deliver materials, transport people, etc., on a continuing basis will need to be charged when the EV is parked for the night, unless EV manufacturers develop EVs with replaceable batteries. This may be the preferred alternative for buses and heavy duty trucks.

Interested in learning more about EVs and electric utilities? Register for Prescient’s free webinar Electric Vehicle Infrastructure: Homework for Electric Utilities, happening April 30 at 11:00 AM PDT.  Or sign up for my upcoming course on Electric Vehicles at the University of Wisconsin – Milwaukee, School of Continuing Education, on May 29 and 30, 2024.


A Note About the Data

The curves in Figure 1 were developed assuming that automobiles and motorcycles will require charging every few days, while buses and trucks will require daily charging. During high travel periods, such as Thanksgiving, the demand on the electric grid will be higher.

The focus is on summer peak load because the demand for electric energy in California is much greater in summer months than in winter months. As heating in residences and businesses transitions from oil and natural gas to electricity, the difference between summer loading conditions and winter loading conditions will be negligible. Summer indoor climate control via air conditioners is already all electric. In northern states, for example, Minnesota, the challenge will be during winter months rather than during summer months.

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