At a Glance
New hybrid off-road equipment includes:
While light-duty hybrid vehicles have proven themselves on the streets, hybrid off-road equipment is still relatively new, with few offerings available.
Komatsu claims to have launched the first hybrid excavator in June 2008. Its HB215LC01 electric-hybrid excavator works through regeneration, using the swing momentum to generate energy, which is stored before it is discharged to power the swing motor and engine.
There are a handful of hybrid off-road options available, but two off-road units released in 2013 may be of particular interest to public fleets — an electric hybrid loader from John Deere and a hydraulic-hybrid excavator from Caterpillar; both these units claim a 25% reduction in fuel consumption in comparison to their conventional counterparts. By estimating the incremental cost along with projected fuel savings, fleet managers can estimate if and when they’ll get a return on their investment in a hybrid machine.
John Deere Offers Hybrid Loader
John Deere released its 644K electric-hybrid wheel loader in 2013, advertising a fuel use reduction estimate of 25% over its 644K conventional wheel loader.
The hybrid loader has a smaller engine and maintains a constant 1,800 RPM when it’s in use for improved fuel economy and consistent boom and bucket response. John Chesterman, marketing manager for John Deere’s large wheel loaders, said while the loader does idle down when not in use, this constant in-use RPM means an operator isn’t constantly revving the machine up and slowing it down. The electric motor recaptures kinetic energy to slow the loader when the operator lets off the accelerator, which then drives the generator and hydraulic pumps to save fuel. Additionally, the unit doesn’t have a torque converter, but instead uses a brushless alternating current generator that generates energy. This energy goes into the power electronics, which controls the electric motor.
The benefit here is a much more efficient drivetrain system, Chesterman said. Even for loaders driven down roads for long periods of time, such as driving on roadways to get places or clearing snow, the drivetrain on the hybrid is more efficient than on the conventional drive system.
In performance, Chesterman said the hybrid engine has only 2 hp less than the conventional engine, less than 1% of difference. The bucket capacity is the same for both units.
Caterpillar Offers Hydraulic Hybrid
Hybrid doesn’t just mean electric hybrid. Caterpillar defines a hybrid machine as one that is equipped with a device to collect, store, and release energy during machine operation. While the company already offers a hybrid diesel-electric powertrain D7E dozer, Caterpillar now offers a hydraulic-hybrid machine — the 336E H hybrid excavator.
Caterpillar explored both hydraulic and electric systems for excavators and found the hydraulic option was the better choice at this time to ensure lower operating costs and improved return on investment (ROI).
The hydraulic-hybrid unit maintains the same 300-hp C9.3 interim Tier 4-certified engine as today’s standard, non-hybrid 336E, but the new machine runs at a reduced 1,500 RPM instead of 1,800. When the machine stops in a swing cycle, it stores or regenerates the hydraulic oil flow energy with the help of two accumulators located at the rear of the machine and then reuses this energy during swing acceleration.
One of the technologies used to achieve fuel savings is a larger displacement electronic standardized programmable pump that maximizes efficiency and productivity by matching engine and pump load. Another key component of the technology is the adaptive control system valve (the system’s “brain”) that optimizes performance by managing restrictions and flows to control machine motion. This provides energy when and where it’s needed. Lastly, the onboard accumulators store the energy captured from the excavator’s upper structure swing brake energy, which is then released during swing acceleration.
Calculating ROI Based on Fuel Savings
Use of equipment and how long the fleet keeps it in service will determine whether or when a fleet will make back the added cost of the hybrid system. There are various factors to take into account when calculating an ROI on a hybrid engine, but fuel savings may be the easiest to calculate.
For John Deere, the hybrid 644K loader costs about 15% more than the conventional drive loader, but with an estimated 25% in fuel savings, fleets can make back that cost in 7,000 hours of use, assuming a $4 per gallon price for diesel, Chesterman said. He added that some customers are seeing a 30-40% reduction in fuel use, and these fleets will see a quicker return.
Tasks that benefit the most from the hybrid system, such as pushing and V-pattern truck loading, will lead to better fuel efficiency, Chesterman said.
Ultimately, what’s going to drive the return on investment will truly be how often a machine is used, he said. The more often the machine is used, the more likely a fleet will recoup the added cost of the hybrid system.
“If they only use the loader on a very as-needed basis, that’s going to play into economics of if the additional purchase price of the machine makes sense versus the fuel savings,” Chesterman said.
How long a fleet keeps its equipment is another factor. While some public fleets keep their equipment for long cycles, others may switch them out much faster.
Caterpillar estimates a 9% cost difference of its hydraulic-hybrid 336E H over the conventional diesel unit. Nick Pinaire, excavator product marketing consultant, indicated the hybrid provides a fuel consumption reduction nearing 25% in many applications. Some customers are seeing upwards of 40% reduced fuel consumption. Consequently, this type of savings can equate to approximately 2-4 gallon savings in fuel per hour in many applications, which means users could save nearly $15,000 or so per year in fuel expenses depending on factors such as application, hours of use per year, working versus idle time, the operator, machine configuration, etc. The savings projections are based on an estimated $3.50 per gallon in diesel costs, so if fuel prices rise, or if fuel is more expensive in a geographic area, the savings would be even higher. In fact, depending on use, Caterpillar
estimates many fleets may find the payback return for the incremental cost of the machine in as little as one year.
“This hydraulic-hybrid excavator technology is focused with our customer’s return on investment in mind and intended for quick payback,” Pinaire indicated.
Savings in Addition to Fuel Costs
Other factors that may affect equipment cost are operation and maintenance. John Deere’s hybrid wheel loader’s constant RPM makes it easier to operate, for example, since it takes more experience, coordination, and skill to maintain proper engine power and speed to coordinate the push of the machine and the loading of the bucket in a conventional loader, Chesterman said.
“We’ve had basic operators hop on these machines and perform much better, getting fuller buckets,” he explained.
Fuller buckets means reduced work time and less fatigue for operators as well as reduced operating time for the machine.
In addition, Chesterman added that running an engine at a constant speed leads to longer equipment life. He added that the hybrid loader’s coast control feature and brake resistor reduce the need to use the unit’s brakes, leading to slower brake wear.
Planning for Future Models
What’s the future for hybrid off-road equipment? The 644K is the first hybrid model John Deere has produced, and Chesterman said the company is currently working on a much larger hybrid wheel loader that will be targeted to the quarrying industry.
“The key thing we see is this is a very efficient form of driving a wheel loader,” he said. In addition, he said as electrical energy storage (i.e., batteries) become more economical and space efficient, these advances can be applied to future designs.
As for Caterpillar’s hydraulic-hybrid technology, Pinaire said while it’s only currently being offered for the 336E excavator, “there is potential to leverage similar technology components across the product line to improve system efficiencies.”
As with vehicles, as manufacturers continue developing hybrid technologies, they’ll only get better.
Emissions vs. Fuel Efficiency
Like any emerging technology, hybrid off-road equipment requires further development before attaining a good combination of fuel consumption, emissions reduction, and price. In a study conducted by the University of California, Riverside, researchers testing first-generation hybrid off-road equipment from two manufacturers found that the equipment did reduce fuel consumption, but not as much as previously estimated, and depending on the application, nitrogen oxide (NOx) emissions could be higher for the hybrids than the conventional models.
Researchers tested two hybrid units available at the time — Caterpillar hybrid D7E dozers and Komatsu hybrid HB215-LC-1 excavators. Since neither had non-hybrid versions, they compared emissions to the most similar non-hybrid machines available.
Manufacturers estimated somewhere around a 20% reduction in fuel use with the hybrids, but researchers found an actual use-weighted average of 14% in fuel reduction for the Caterpillar dozers and 16% for the Komatsu excavators.
Fuel efficiency varies widely depending on application. Since the units were tested under different conditions, researchers were able to draw conclusions about which applications resulted in more savings. For the dozer, they found that using the hybrids for lighter, shorter pushes, such as in slope repairs, maintenance, and road repair work, resulted in greater fuel economy benefit than heavier, longer pushes such as in large excavation and landfills. For the excavators, demolition work, which uses longer swings of the arm that capture and release more energy, averages a much higher fuel savings.
Since benefits are tied to type of use, consumers can evaluate their expected use of the asset to determine what kinds of benefits they can see within their own operations, Kent Johnson, principal investigator on the project, said.
While CO2 emissions are directly tied with fuel savings, NOx emissions aren’t. Researchers found that NOx emissions from the hybrid dozers were higher than the conventional dozer by a use-weight average of 13% and higher in the Komatsu hybrid excavator by 1%.
Both manufacturers disagreed with the emissions findings, and Caterpillar suggested the hybrid dozer should have been compared to another unit, but Johnson maintains that there still would have been higher NOx emissions. The point, however, isn’t how much the emissions disbenefit is, but that there was a disbenefit at all in comparison to currently available technology, he said. In California, the state may not want to offer financial incentives unless emissions are lower.
To solve this problem, manufacturers can calibrate equipment for lower emissions, but this would most likely increase fuel consumption, Johnson said. However, he added that with final Tier 4 engines that use selective catalytic reduction (SCR), equipment manufacturers have more tools to control fuel economy and emissions.
UC Riverside’s Center for Environmental Research and Technology administered the deployment and testing elements of the Hybrid Off-Road Equipment Pilot Project. The California Air Resources Board (CARB) provided vouchers to help fleets purchase the hybrid equipment for testing. Researchers published the report in June 2013.
- John Chesterman, marketing manager, large wheel loaders, John Deere
- Kent Johnson, assistant research engineer, Center for Environmental Research & Technology, University of California, Riverside
- Nick Pinaire, excavator product marketing consultant, Caterpillar