Electrification 101: Enabling Truck Charging with Flexible Service Connections

How small shifts in charging schedules can enable faster trucking electrification and lower costs for both fleets and utilities.

Trucking is the lifeblood of the United States economy, transporting two-thirds of all goods. However, heavy-duty trucks are responsible for 20 percent of all transportation system pollution in the United States and have even greater localized impacts on air quality in high-freight traffic areas such as near ports. Electrifying trucks can not only improve health impacts and reduce greenhouse gas emissions but can also save fleets money on fueling costs.

Purchase costs of electric trucks are declining, with analysis showing that they are becoming increasingly economically competitive with diesel-powered trucks. While there have been recent federal rollbacks on supportive policies, some states, such as California, are still offering substantial incentives, continuing to increase adoption. A major hurdle that remains is bringing power to the large charging facilities needed to support these trucks. This is where a flexible service connection can help.

A flexible service connection is an approach in which the utility makes power available to fleets sooner than they would usually be able to, as long as they can manage the charging stations’ consumption during certain peak periods. This can:

• Decrease the time it takes for fleets to get power to their chargers;
• Allow utilities to get better asset utilization, delivering more energy with existing infrastructure; and
• Save fleets money on site upgrade costs and allow utilities to defer upgrade costs.

The grid challenges of truck charging

Truck chargers create high power demand and can be built very quickly. As more trucks electrify, adding these chargers will cause grid components to reach their capacity limits faster than utilities are able to build upgrades. If the grid is too constrained to accommodate charging, fleet operators can experience long delays in receiving the power they need to charge their trucks.

While expansion of data centers has become the main driver of load growth and grid constraints, electric truck charging depots — facilities with a number of charging stations for electric vehicle fleets — will also bring large loads to the grid. Charging depots can bring loads of 5–10 MW per site online in the coming years with very different characteristics than data centers (see Exhibit 1).

Truck depots often have shorter development timelines than utilities are used to for energizing a site, as the time between fleets making a purchase decision and accepting delivery of a new vehicle is only a matter of months compared to the years it can take to plan and construct more conventional large load sources like data centers or heavy industry. Additionally, trucking depots are more likely to be built in areas where land is cheap and in proximity to other trucking depots, not necessarily where there is abundant spare electrical capacity.

Fortunately, one of the characteristics that makes electric truck charging a challenging load type for utilities to plan around — variable charging schedules — is precisely what can make it an asset under flexible service connections.

Exhibit 1

The challenge with normal new service connections

A load request for a normal new service connection may push the local grid infrastructure beyond its rated capacity on the highest-demand load hour of the year in that location. If so, it triggers the utility to upgrade the infrastructure. This upgrade often creates multi-year delays, due to long utility interconnection queues, and significant costs that usually fall on the site owner. This creates a major barrier to electric truck adoption, particularly in regions where utilities require proof of vehicle purchase before beginning the upgrade process. Fleets may be forced to rely on costly public charging sites or temporary gas generators while awaiting energization.

These delays stem from traditional load-planning practices, which evaluate new connections based on the single highest-demand load hour of the year. If a new site’s load would exceed available headroom during that peak, typically in the early evening of the hottest summer days in places like California when air conditioning demand is high, the project is delayed until capacity is expanded. This approach leaves much of the grid’s capacity underused for most of the year, and even some spare capacity unutilized on peak days.

For example, the plot below shows a feeder in California at which available capacity for new connections is limited to 2.4 MW, even though 4.6 MW is available for all but a few peak hours in July. To address this, some utilities are now piloting the new energization paradigm of flexible service connections, which will allow managed or time-varying loads such as truck charging to tap into latent grid capacity without waiting for infrastructure upgrades.

Exhibit 2

The benefit of flexible service connections

A flexible service connection allows utilities and customers to tap into this underutilized capacity. The utility provides a certain level of power all the time, and a higher capacity only during times when there is less load elsewhere on the feeder. This could be during specific scheduled times during a day, different days of the week, or seasonally, with the customer agreeing to adjust their energy use according to the utility’s schedule. It can even be dynamic with day-ahead limits provided by the utility based on real-time grid load monitoring although dynamic approaches are more complex to administer.

Enforcement of these limits by the utility is either done with hardware or software solutions to ensure the customer  does not exceed safe load levels. This solution can either be used as a bridge solution, where the flexible limits are enforced only until the utility is able to complete upgrades, or it can be permanent, allowing for the long-term deferral of new capital investments by the utility.

Why are flexible service connections a particularly useful solution for truck charging?

Unlike data centers, fleets can (and in many cases already do) relatively easily shift their load away from peak hours, which tend to be more expensive. RMI analysis of heavy-duty truck telematic data in California and New York found that many fleets would be able to shift to slow, overnight charging or charge during peak solar hours based on existing time at the charger, with no shifts to operational schedules. These changes also enable significant capital cost savings of between 40 and 70 percent by better optimizing charger size.

When charging isn’t as optimized, the load from just one truck can be significant, with charging powers of 350 kW to 500 kW common for fast charging, not to mention megawatt chargers starting to roll out. Just a handful of trucks shifting their charging schedules away from peak-hour fast charging could make a substantial difference to constrained areas of the grid. Precisely what makes electric trucks a challenge under conventional service connections makes them an asset under flexible service connections.

However, while fleets can have some degree of load flexibility, they do need certainty that they will be able to charge their vehicles in a schedule fitting with their operations. This makes them more ideal candidates for longer-term scheduled flexible service agreements, rather than dynamic day-ahead limits.

Where is this happening today?

This approach is currently being piloted by several utilities, including National Grid, Southern California Edison, and Pacific Gas & Electric (PG&E). The pilots currently working on demonstrating software and hardware methods to accurately measure this spare capacity in real time to ensure any new flexible connections never exceed their set limits during restricted time periods. When available at scale, these programs could save fleets years in waiting for necessary utility upgrades to energize a charging location, in addition to providing better asset utilization for utilities, as they can sell more energy with the current grid.

PG&E has now begun to offer its Flex Connect program more widely. One of its early pilot customers for the program, PepsiCo, was able to increase a site from 30 to 50 electric trucks 18 months sooner than conventional load planning would have allowed. PepsiCo estimated that this saved the company $1 million in fuel costs.

What’s next?

When available at scale these programs will have three major benefits:

1. Faster energization timelines for charging depots. This enables fleets to save time, allows them to save money from fueling with electricity instead of diesel, and prevents their new electric trucks from sitting idle.
2. Better asset utilization for utilities. More electricity will be able to be sold using existing grid infrastructure, representing economic savings for utilities.
3. Cheaper energization costs for fleets. Choosing flexibility as a permanent solution could avoid capital costs for customer-incurred utility upgrades.

These programs need to work for fleets’ schedules, creating value for both fleets and utilities.

These topics and more will continue to be analyzed by RMI in the coming months. The next article in this series will showcase an analysis of 2,000 PG&E feeders to demonstrate the value of how many additional trucks can be charged by today’s grid, with just a few hours of flexibility on a handful of high load days.