Results quantify the ability to time-shift charging and protect distribution assets

Electric vehicles offer utilities a unique flexible resource for navigating the energy transition. But tapping into EVs’ potential benefits – which include reducing utility customers’ costs, protecting distribution assets, and proactively addressing load growth – requires a clear understanding of what those benefits are in practice.

With that in mind, a recent study of EnergyHub’s managed charging solution offers valuable insights for utilities planning for EV load growth. Our analysis looked at the benefits of active managed charging; specifically, it measured the effectiveness of EnergyHub’s approach, which uses a continuously running optimization algorithm to enable dynamic, automated control of EVs throughout a utility’s service territory. 

How it works: Managed charging simultaneously optimizes for multiple grid benefits 

EnergyHub’s managed charging solution optimizes the shape of EV load to simultaneously achieve multiple utility goals and deliver benefits at the bulk and distribution grid levels.

• Bulk system benefits: Shift EV charging load out of bulk-system peak periods to reduce wholesale energy and capacity costs.
• Distribution system benefits:  Reduce EV charging during distribution-level peaks to extend the lifespan of equipment and prevent failures of specific distribution grid assets.
• Customer benefits: Give customers control over their charging experience while reducing their energy costs.

Rather than setting a static charging schedule for each vehicle with staggered start times, our solution automatically optimizes each EV’s charging schedule according to driver preferences and updates those schedules every 15 minutes based on changing EV load and grid conditions. So, for example, if an unusually large number of vehicles plug in on a given night, drivers with more urgent charging needs will be prioritized within grid limits. The optimization always ensures customers get the charge they need by their departure time, deferring charge only when a vehicle has the flexibility to do so.

Study design and key findings

Over 100 EV drivers from the Northwestern U.S. participated in the study, which lasted for more than six months. Incentives were provided to drivers upon enrollment in the program and for ongoing participation. In this study, the goals of the managed charging program were to minimize EV load during peak hours (10 AM to 9 PM on weekdays) and reduce distribution asset overloads by managing the EV peak demand to below a load limit — all while ensuring customers got the charge they needed by departure time. 

In the study, we compared EnergyHub’s active managed charging performance to a baseline “unmanaged charging” scenario where EVs are assumed to charge immediately upon plugging in. Two key findings from the study are especially relevant for utilities. 

#1. Bulk system benefits: Managed charging can shift ~60% of on-peak charging to off-peak hours

Peak demand periods stress the grid and drive up costs for utilities and consumers. Given steep electricity demand growth projections and rising EV charging needs, utilities are increasingly focused on managing EV impacts during peak periods.

When we compared EnergyHub’s active managed charging solution to an unmanaged charging scenario, we found that managed charging successfully shifted about 60% of on-peak charging energy to the off-peak periods (Figure 1). This allows for substantial savings both by reducing a utility’s wholesale energy costs and by avoiding additional generation and transmission capacity costs as loads increase. 

Figure 1. Average weekday EV load: Managed charging “actual” vs. unmanaged charging “baseline”. (Source: EnergyHub.)

#2. Distribution system benefits: Managed charging reduces distribution-level peak demand by as much as 30%

Perhaps most concerning to utilities are the potential impacts of EV charging on the distribution system and specific assets such as substation transformers, feeders, and distribution transformers. As we explained in a prior blog, while EV charging demand largely evens out at the transmission system level, it can strain distribution networks in pockets of as little as 10 vehicles.

Time-of-use (TOU) rates give customers a price incentive (a lower electricity rate) to charge during off-peak periods. But as EVs continue to proliferate, TOU rates aren’t a good long-term solution for managing EV loads because of the new timer peaks they can cause on distribution assets. According to the U.S. Department of Energy, though, managed charging techniques can decrease the cost of distribution grid investments needed to support EV charging by 30%. 

Our analysis provides hard data supporting that conclusion. We evaluated the effectiveness of EnergyHub’s active managed charging solution at keeping maximum charging demand below a specified threshold, or “distribution load limit”, while simultaneously shifting charging out of the bulk peak period.  We found that by applying a distribution load limit, we can reduce EVs’ peak demand on a distribution asset by as much as 30% relative to an unmanaged charging scenario (Figure 2).¹

In the example below, vehicles were grouped under one distribution asset, but EnergyHub’s managed charging solution can handle multiple groupings that reflect the complexity of real distribution grids. Our solution can be configured to group EVs hierarchically to limit distribution load at multiple levels, from substations down to distribution transformers.

Figure 2. EV load on July 16, 2024: Managed charging actual vs. unmanaged charging baseline. (Source: EnergyHub.)

Since distribution transformers degrade exponentially faster at higher current levels, we also evaluated our solution’s distribution load limiting capability by looking at how much load was reduced during the top 5% of EV load hours. We found that with managed charging, we were able to reduce EV load by 12% on average during the highest EV load hours (Figure 3). This means, for example, that if this technology were used to manage load for a group of EVs behind a 250kVA transformer that also serves 90 kVA of uncontrolled load, the frequency of overloads the transformer experienced would be dramatically reduced from 221 hours per year to 9 hours per year.

Figure 3. EV load duration curve for top 5% of EV load hours: Managed charging actual vs. unmanaged charging baseline. (Source: EnergyHub.)

Delivering reliable flexibility with EV managed charging

EnergyHub’s EV managed charging solution is easily adapted to serve each utility’s unique needs and circumstances. For example, some utilities don’t have grid asset data readily available to enable localized, distribution load limiting. In this case, they could still apply a load limit to the entire group of vehicles in their active managed charging program along with customer cost optimization. This achieves similar goals to a traditional TOU program with the added benefit of reducing timer peaks — thus reducing strain on distribution assets overall without singling them out for individual management.

No matter how it’s done, controlling EV charging can buy utilities valuable time in making distribution system upgrades while reducing wholesale energy costs. Over time, in a carbon-free distributed energy future, EVs will evolve to play a key role in managing a flexible, reliable grid — and the sooner utilities gain valuable experience here, the better.

If you have questions about your EV program strategy and how EnergyHub’s managed charging can help, reach out to us today.

¹ We assume that EV penetration is sufficiently high that the EV load being served by a distribution asset determines the timing of, and coincides with, the distribution asset’s peak load.