Navigant Research Blog

How to Save a Half Billion Gallons of Diesel

Dave Hurst — April 16, 2014

Hosesteps_webTrying to reduce fuel use by Class 8 over-the-road sleeper cab tractors is a key challenge facing the trucking industry and regulators.  The trucks use a tremendous amount of fuel (averaging about 6.6 mpg and traveling 80,000 to 100,000 miles per year) and have to provide the driver comfort as the trucks stop overnight.  In order to provide the overnight creature comforts (sometimes referred to as hotel power), the trucks need to have a source of energy, whether an offboard source, the large truck diesel engine, or a small energy source called an auxiliary power unit (APU).  The APU industry has been espousing the fundamental truth that utilizing APUs reduces fuel use, emissions, and associated costs by reducing idle times of the large truck engines.

Yet, one of the challenges is trying to understand just how much fuel and emissions are being offset by APUs.  Having spent a large amount of my time at the Mid-American Trucking Show (MATS) this past March, I was able to speak with almost every APU manufacturer displaying at the MATS and have been able to pull together an estimate for these savings.

First, a little more background.  It is not entirely clear when APUs first became widely available, but by the early to mid-2000s, Bergstrom, Thermo King, Carrier, and RigMaster, along with a number of other competitors, were all offering APU systems.  Today there are a lot of commonalities between the machines.  The vast majority of APUs are of two designs, either all-electric or diesel-powered.  Diesel-powered APUs use diesel from the truck’s fuel tank to fuel 2-cylinder small diesel engines from Yanmar, Caterpillar, Perkins, and others.  All-electric systems store energy in absorbed glass mat lead-acid batteries that can then be used to provide power to air conditioning compressors or inverters.  Other technologies that are being tested include fuel cells, lithium ion batteries, and compressed natural gas systems, but the cost-effectiveness of these systems remains essentially unmarketable.

Methodology and Findings

For the purpose of this macro analysis, I had to make several assumptions when it comes to the number of APUs on the road.  First, since there isn’t consensus on when the Class 8 sleeper cab APU market even started, I considered the start date to be roughly 2005, with about 35,000 units on the road by the end of that year.  While recognizing that this is a rough estimate, this at least gave me a starting point for calculating the scrappage rate of APUs.  Based on conversations during MATS and some combing of forums, I assumed the average lifespan of an APU to be about 6 years, and from there the number of APUs on the road today, which is estimated to be about 309,000 units, with about 25% being all-electric.

These 309,000 units translate into 486.5 million gallons of diesel saved by APUs on Class 8 sleeper cabs in 2013 (or about 1,576.5 gallons per APU).  Put into economic terms, at the average retail price of $3.89 per gallon for diesel in January 2014, the fuel costs offset by APUs are a staggering $1.89 billion.  Even taking into consideration the cost of new APU units ($8,000 estimated) and maintenance ($145 annually), the offset is $1.49 billion.  Put into environmental terms, the Argonne GREET model calculated the greenhouse gas emissions per gallon of diesel fuel consumed to be 20.2 lbs carbon dioxide equivalent (CO2-eq) per gallon of diesel fuel, so the emissions offset are 9.827 billion lbs of CO2-eq.  Of course, this analysis does not take into account the 116 truck stops that have electrification to allow drivers to shut off the engines overnight, which would further improve these fuel savings figures.

Estimated Gallons of Diesel Used by Class 8 Sleeper Cabs for Hoteling: 2013Dave H. APU chart for blog

(Source: Navigant Research)

Certainly, from a macro standpoint, it’s hard to argue the benefit of APUs.  Fleets with a large number of trucks are likely to see cost benefits that are compounded over a number of trucks.  The picture is more complicated for truck owner-operators that have to justify the extra upfront cost and calculate the payback on a single unit.  This payback typically ranges between 2 and 4 years depending on the APU selected and the cost of fuel, which makes the owner-operator market seem like a good place for some targeted tax incentives.

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