Lowering the cost of operations is top of mind for most fleets, and the cost of diesel and gasoline fuel has always been one of the biggest components of operational cost. Switching to electric vehicles (EVs) can help reduce fuel costs, but comes with a variety of new challenges around calculating and understanding those costs in the face of complex utility rates.
Previously, we've covered how to save money when charging your EV fleet more broadly. In this article, we'll go over a specific example of a utility rate and a single truck, and see the costs for different charging scenarios. What we'll find is that, depending on your situation, your peak power charges might be as much or higher than your per-kWh energy charges.
We'll also cover how using Flipturn for EV operations and charger management can help fleets handle this more easily, simplifying adoption of medium- and heavy-duty EVs.
The two main aspects of most utility bills: energy costs and power costs
Let's say you drive a class 8 electric truck 100 miles, and use 200 kWh of energy from the battery. How much will it cost you to recharge that truck back to 100%? It turns out the answer is a bit more complicated than just a certain number of dollars per kWh. There are two very important questions that can dramatically affect the result:
- When was it charging? Many utility plans have different rates for different times of day. For example, in one Southern California utility rate, power is most expensive between 4pm and 9pm.
- What was the maximum power level at which it was charged? Many utility plans charge you an additional rate depending on the peak power level used throughout the month, even if that peak power demand was only for a short period of time. As we'll see below, these costs can often be similar or even higher than the time of use rates.
Depending on how the calculations work out, your best bet for reducing costs could be to charge at a cheaper time, lower the peak power of charging, or both. Let's look at an example.
The utility rate details for our example
For this example, we'll use the SCE general service time of use rate, TOU-GS-2. Below is a summary of the 2023 winter rates under TOU-GS-2 (illustrative; current rates differ but the rate structure is the same). You can pull current rates from SCE's tariff books. As mentioned above, the rate has two main components:
Time of use energy charges, dollars per kWh:
Maximum power rates and demand charges, dollars per kW:
As you can already see, there are a lot of different aspects to factor in when trying to optimize costs. Let's see how a few different scenarios can play out:
Different cost scenarios for charging a class 8 truck
Let's look at the example of the specific truck above, which drove 100 miles and used 200 kWh of energy. How much will it cost to charge it back up to 100% under the assumed utility rates?
Because demand charges are determined across a whole month, we'll calculate the results for a whole month's charging, assuming we will charge once per day. For simplicity, we'll also assume that the truck charges at a constant power output rate. Usually, the power output will be decreased significantly as the vehicle nears 100% charge, but that doesn't dramatically affect the calculations below.
Scenario 1: Fast charging during peak time
Truck charges at 100 kW from 5pm to 7pm
- Time of use energy costs: 200 kWh * 31 days * $0.1391 = $862.43
- Maximum power costs: 100 kW * ($20.79 + $9.16) = $2,995
- Total cost: $3,857.43
Scenario 2: Slower charging during peak time
Truck charges at 40 kW from 4pm to 9pm
- Time of use energy costs: 200 kWh * 31 days * $0.1391 = $862.43
- Maximum power costs: 40 kW * ($20.79 + $9.16) = $1,198
- Total cost: $2,060.43
Scenario 3: Fast charging during off-peak time
Truck charges at 100 kW from 9pm to 11pm
- Time of use energy costs: 200 kWh * 31 days * $0.1385 = $858.70
- Maximum power costs: 100 kW * $20.79 = $2,079
- Total cost: $2,937.70
Scenario 4: Slower charging during off-peak time
Truck charges at 40 kW from 9pm to 2am
- Time of use energy costs: 200 kWh * 31 days * $0.1385 = $858.70
- Maximum power costs: 40 kW * $20.79 = $831.6
- Total cost: $1,690.30
Overview
As you can see, in this example, charging the vehicle more slowly results in more immediate cost savings (about $1,800) than charging quickly at the off-peak time (about $900). So it's important to consider several different charging management approaches to find the one that saves your fleet the most money.
Charging multiple trucks and other scenarios
The examples above are for one truck and one charger. How would they generalize to, say, 20 trucks?
The time of use energy rates would just be added up, but the demand charges depend on whether the trucks are all charging at the same time, and at what power levels. So, for example, if all the trucks are charging at the same time, then the demand charges stack up. But if the trucks are charging in multiple shifts, that can help keep the demand charges low.
There are also other ways to reduce costs, like subscribing to SCE's EV-specific commercial rates and adding on-site battery storage and solar. Those add another dimension to the cost calculation; check our EV charging incentives database for utility programs in your area.
Putting peak-power thinking into practice
When trying to charge your electric fleet in the cheapest way, it's important to consider all of the different dimensions of your utility bill, including time of use rates, demand charges, and other fees.
Depending on your specific situation, the highest impact savings might come various places, like charging at a different time, lowering your charging power, making sure your vehicles aren't all charging at the same time, or something else.
Save on energy costs with Flipturn
Doing this math by hand gets unwieldy quickly, especially for fleets with mixed vehicle types or growing EV counts.
Flipturn is hardware-agnostic, OCPP-compliant software that gives you cross-system visibility into your fleet EVs and chargers. Energy management automates charge scheduling against utility rate structures, applies peak shaving so total site draw stays under your demand threshold, and tracks energy and power consumption so you can see the bill before it lands. Per-session cost tracking confirms the savings are real.
Book a demo, or browse how fleets use Flipturn in production.
