As discussed in our previous articles, the California Air Resources Board (CARB) is near to codifying the Advanced Clean Fleets (ACF) Regulation, which will require public agencies to begin electrifying their vehicle fleets in 2024.

As the preferred provider for the Association of California Water Agencies (ACWA), TerraVerde Energy supported ACWA in surveying member agencies to collect details on their vehicles in an effort to better understand and highlight the unique needs and challenges that will be presented in electrifying these fleets. Among other challenges, one of the common concerns is the limited commercial history and availability of medium and heavy duty electric vehicles that can provide a viable replacement for special purpose vehicles currently in use by water agencies.

In the following article we will summarize the responses to the water agency vehicle fleet survey, explain the relationship between vehicle weight and energy consumption, discuss ambient temperature impacts on EV range, explain how we calculate the onboard battery storage (kWh) capacity needs of these vehicles, and we reveal the significant challenge that many water agencies will face in finding suitable, feasible EV replacements.

Summary of Responses

Our survey yielded responses from 33 water agencies. The counts of various vehicles by GVWR classification and water agency vehicle “Type” are shown below.

Count of Vehicle Type, by Weight Class (where weight information was provided by the respondent)

The Relationship Between Vehicle Weight & Electricity Consumption

Based on validating the following physics-based formulas and assumptions, by comparing results to OEM specifications for vehicles from OEMs like Ford, Kenworth and BYD, we can see that 75% or more of vehicle energy consumption comes from wind/”aero” drag and, that there is – in accordance with the rules of physics – a mathematically strong relationship between vehicle weight and OEM-specified “fuel” consumption.

Cd * p * Cd * A * (V + W)^3 / BtWE

Crr * GVW * G * V / BtWE

(In * A * G * V * proportion of trip up grade) / BtWE

Cd * GVW * V * i * ((1 / BtWE) – BtWE * R) 


p = air density

V = velocity (drive-cycle speed)

Cd = coefficient of drag

Crr = rolling resistance

A = frontal area

G = acceleration due to gravity

BtWE = battery-to-wheels efficiency

R = regen efficiency

In = grade inclination

W = headwind speed

i = inertia

Ambient Temperature Impacts on EV Range

Furthermore, we can appreciate from a study performed by GEOTAB (a vehicle telematics provider with customers in 150 countries) how ambient temperature impacts electric vehicle range; actual range varies substantially from OEM specifications depending on outside temperature.

Data source: GEOTAB, May 25, 2020

Representation of observations of 4,200 connected EVs, 102 different make/model/year combinations and 5.2 million trips

Onboard Battery Storage (kWh) Capacities Needed

When we apply our understanding of the impacts of aero drag and ambient temperature – at a moderate 77-deg. F, for example – to the water-agency fleet, and survey responses regarding daily miles traveled/drive cycle specifications, we observe important required-battery-size groupings represented the Table 1 & 2 below. For example, the Ford Lightning electric pickup (a Class 2a truck with a 98 kWh battery) will be an important and effective replacement for hundreds of water agency vehicles. And, we can see that for many Class 2b to Class 6 vehicles much larger batteries will be required (note the yellow highlight vehicle-counts in Table 2).

Table 1 (minimum kWh requirements based on moderate temperature assumption)

We can see that as temperatures move towards seasonal extremes in California’s colder and hotter climates (e.g., 32-deg. F, as represented below) ZEV replacements will require significantly larger batteries to meet range-requirements dictated by water agency drive cycles (see yellow highlight areas, below). It’s important to note that the summary herein does not consider the use of power take-off (PTO) equipment, which is significant for vehicles like dump trucks, leak trucks and vacuum (“vac”) trucks.

Table 2 (minimum kWh requirements based on colder temperature assumption)

Note: Results are similar at 32F and 104F, varying by only a few vehicles in each battery-size category.

Many Water Agency Vehicles Do Not Appear to Have Suitable EV Replacements Available

 Finally, when we consider the above summary of required battery sizes, we can see that some water agency fleet-vehicle functions may not have suitable EV replacements available. The table below represents 256 light, medium and heavy duty vehicles considered available by California’s HVIP program and by the EPA ( Vehicles requiring batteries in categories showing zero available make/models do not currently have suitable EV replacements available – compare observations in Table 2, above, with Table 3 below

Table 3

TerraVerde Energy Can Help Your Agency Develop A Compliance Plan

As proceedings continue regarding the Advanced Clean Fleets regulation, CARB is expected to post a “15-Day Change Package” this month, which will open up a formal comment period. A Second Board Hearing is planned for April 27-28.

TerraVerde Energy is an independent energy consulting firm proudly supporting California public agencies since 2009 and serves as ACWA’s Preferred Provider for fleet electrification planning services. As your agency looks to identify the path forward, TerraVerde can provide your agency with a clear, actionable assessment of your options, costs, challenges, and opportunities; enabling your team to take an intelligent, risk-mitigated approach to fleet electrification. We would welcome the opportunity to meet with your team and discuss your fleet electrification planning needs. Write to us at to get started today.

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