At MGL we help fleet operators determine their transition to zero emissions by addressing battery electric feasibility of current and future operations. By addressing EV feasibility initially in the planning phase, fleet operators can comfortably enter the onramp to an electrified fleet with the tried and true options on the market today and buy time to address the portion of the fleet that is more difficult to electrify. This approach is a great strategy to avoid getting wrapped around the axle about near future technology promises and the common pothole of focusing on edge cases, both of which become protracted deliberations. In a previous post Going Beyond Average Range with Electric Fleets the central topic was clarifying electricity consumption for local operating environment, specifically determining daily energy needs to inform fleet transition plans. This article extends the discussion to take the guesswork out of battery sizes and charger power ratings.
The Challenge
Fleet electrification assessments determine which vehicles are feasible to electrify with today’s battery electric capabilities, which becomes the design frame for the vehicle/charging system. What we uncover in the analysis of daily energy requirements is a wide range of energy efficiencies per vehicle (kWh/mile, similar to miles/gallon), and therefore a wide range of battery capacity needs. For example, a school bus traveling a short distance could have worse efficiency than one driving a longer distance if they are both in operation for the same amount time. This is due to the hours of heating or cooling more so than miles driven. Suffice it to say, planning around average miles alone will not specify the necessary battery size; all electricity loads must be included.
Vehicle purchases for fleets planned around the single largest battery needed to fulfill daily operations is the natural inclination, which allows for flexibility to deploy any vehicle for any service. However, that approach runs up the cost of an electric fleet by paying for battery capacities greater than what is needed to successfully complete most daily services. We suggest stratifying batteries in a couple of size groups for each vehicle type if feasible. Operators can absolutely start with the largest battery / greatest range to verify operations, but this could be more capital intensive than necessary, and the overall transition plan does not need to rely on the largest battery, and highest power rating chargers.
A prudent approach is to plan around vehicles that are easily electrifiable with today’s technology (no regrets) and allow technology advances to address more challenging vehicles in due time (threshold advances).
Charger power rating is the other consideration (alongside vehicle battery size). The power rating of chargers should be sized to meet the maximum daily energy delivery, meaning the highest energy consuming days, which is most likely the coldest or hottest days of the year depending on location. Extreme weather days have a significant impact on range given several factors – cabin heating or cooling energy consumption, below optimal battery operating temperature (aka battery thermal management), and preconditioning of the vehicle before the day’s operations. The common approach is to oversize the charger, a safety-factor approach, which causes the costs of chargers and electric infrastructure to skyrocket, a capital budget which fleet operators do not have today. It may be advantageous for operators to install one or two of the highest-powered chargers on site for top-up charging, however, with proper planning, the fleet’s charging strategy can be built around lowest capital costs and managed charging that meets the fleet’s daily energy needs.
A Better Approach
Accurate energy consumption for the local operating environment for every vehicle across all seasons illustrates the range differential between extreme weather months of July and January. This determines the necessary kWh battery size for the lifetime of the vehicle operations, taking into consideration that batteries degrade with use and have less usable capacity in later years. Accurate daily energy consumption matched with the daily operating schedule clarifies how much energy to deliver during non-driving hours, which dictates the proper charger power rating.
Daily energy consumed dictates battery size needed to deliver service, and informs charger power to deliver enough electricity on the coldest/hottest days.
Clarity about the battery size necessary for every vehicle allows the operator to group sizes and make prudent decisions about whether a standard battery size is best for their operations, or if multiple battery sizes are best to reduce costs and cover all service needs. Most important is taking the guesswork out of range and battery size, supporting the fleet operator in considering recommendations of vendors and avoid buying larger than necessary and overly expensive vehicles.
Confidence in charger power ratings that match the operating schedule accomplishes two important elements in charging system design – reducing costs of infrastructure by not oversizing the total electrical capacity demand and minimizing the reliance on managed charging to mitigate peak power demand. The greater the capacity requested from the utility service provider the longer the timeframe for bringing said capacity, delaying the implementation of an electric fleet. Taking the guesswork out of charger power ratings also helps the fleet operator in evaluating vendor recommendations, which often rely on compatibility and fast charging as the sole answer.
There is a better way than overdesigning for fleet electrification. Right-sizing vehicle batteries and charging system design is possible with accurate energy modeling.
The Benefit of Fleet Analysis
Approaching fleet electrification through accurately calculated requirements that take into consideration of the local operating environment and unique fleet operations provides for well-informed procurement decisions about battery sizes and charger power ratings. Designing for operational reliability in the initial phase is prudent, and optimizing the design for follow-on phases to reduce capital costs and time to deploy is wise.
A well-informed fleet operator backed by proper planning is confident about what to buy and where to deploy.
In addition to clarifying procurement decisions about battery size and charger power, the charging strategy becomes crystal clear, formed around the operating schedule, and electricity tariff optimization is easily addressed with an accurate load profile.
The counter approach of course is buy-then-optimize, leaving the fleet operator with oversized vehicles and over-capacity chargers, wondering where to come up with additional capital budget, and chasing down peak electric loads.
Chuck Ray is an energy and mobility expert with fifteen years in energy management and advanced mobility, serving as MGL’s business director.
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