When you start charging your shiny new EV at home, you’ll notice a difference in electricity consumption on your next electric utility bill. Deciding when to plug in your EV and charge is important, especially if it costs more to do it at certain times. You may even be eligible for a special EV rate offered by your utility, making refueling your EV even cheaper.
Standard vs. Time of Use (TOU) Rates
Electric rates are not all the same, so it’s important to know the details of yours and how to better understand your monthly electric bills. Residential electric rates come in a couple types depending on where you live. You may have a standard rate, where the cost per kWh is the same every day all day. Alternatively, you may have a Time of Use (TOU) electric rate where you are charged a different price for electricity based on the time that the electricity is consumed.
TOU rates are designed to shape consumption of electricity to help the electric grid to run as efficiently as possible. In short, it costs more to produce and deliver electricity when demand is higher, like when people get home from work and all turn their AC on and less to produce it when demand is lower like at night when everyone is asleep or at work during the day.
How to determine your TOU rate structure (when the best time to charge is)
Taking a peek at your utility bill is usually the quickest way to determine if you have a TOU rate. However, utility bills are often far from simple and deciphering it is easier if you know where to focus. Below is an example of utility bills with the TOU portion of the bill outlined in red.
Southern California Energy (SCE) provides a sample bill that does a great job of highlighting the “on”, “mid”, and “off-peak” times during the summer hours. Based on this breakdown, it’s best to avoid charging your EV between 4 pm and 9 pm during the week and weekends. I would recommend programming your EV charger or vehicle to start charging after 9 pm or wait to plug in your vehicle until then.
Source: SCE
Like electric rates, not all utility electric bills are the same. If yours looks like it could be a brochure for calculus summer camp, or you’re just having trouble figuring out the TOU rates or “peak” times generally, I’d recommend checking your utility’s online portal or website for more specific information. Online portals typically have excellent graphics to better explain TOU rates. Generally there are “off-peak” and “peak” times of usage that accompany a TOU rate. In certain service territories, there can be Mid-day rates. These are more typical for island or isolated electric grids where there is an abundance of solar generation during the afternoon hours.
Visual Examples of TOU rates:
The below graphics visually depicts SCE’s TOU summer rates for (first) a normal residential customer and (second) for a customer on a special EV rate.
TOU-D-4-9PM (one of the residential TOU rates SCE offers)
Source: SCE
TOU-D-PRIME (TOU rate for PHEV/EV residential customers)
Source: SCE
As you can see from the difference in the “off-peak” price between the regular and EV rate is 10 cents, which translates into considerable savings. To better visualize the savings achieved of charging at the best time let’s do a little back-of-the-envelope math. We’ll assume you have an EV you charge at home and that you consumed 10 kWh during a typical day of driving 30 miles everyday.
| Electricity consumed daily | Cents per kWh at time of charge | Total for one day | Total for month (30 days) |
| 10 kWh | 17 | $1.70 | $51 |
| 10 kWh | 27 | $2.70 | $81 |
| 10 kWh | 33 | $3.30 | $99 |
| 10 kWh | 45 | $4.50 | $135 |
As you can see, when you charge your EV on a TOU rate, it has a significant impact on the cost to operate your daily electric commute. As an added bonus, on a special EV rate you realize additional savings for off-peak electricity.
Bottom line: Understanding how you are charged for electricity and being mindful of when you consume electricity, will help add to the perks of being an EV owner.
Can’t figure out what your utility rate is?
If you’re still not able to find the information you need on your electric rate, try reaching out to your customer service department directly. Alternatively, the OpenEI database provides rate information for utilities across the country. Put in your zip code, county, or search by utility name and be sure to select “residential” as your criteria to view basic information on the rate.
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