Is electric drive a reality for mainstream tractors?
Electric drive is already here for some types of farm vehicles, but is it a practical reality for mainstream tractors or will it remain an engineer’s dream? Future Farming looks at the technology and whether they will soon be cultivating fields.
Open the door, step into the cab, turn the key and – silence. But don’t worry; this is not the time to look under the hood to find out why the engine will not start on this chilly morning with 100 cattle to feed. Instead, it is the experience of an operator firing up his electrically driven loader; or his electrically driven mixer-feeder, for that matter.
While battery-powered loaders and feeders can be purchased today, electric-power transmission for mainstream farm tractors looks to be some way off. Main advantages cited by loader makers Avant, Kramer and Weidemann, and feeder manufacturer Meyer are easy to appreciate – virtually silent operation and zero emissions from the vehicle within the confines of farm buildings, glasshouses and storage barns.
There are also low or zero emissions from electricity generation if the power to charge the batteries is created from renewable sources on the farm; and lower running costs from a cheaper source of energy than diesel. Battery power for these vehicles is a practical option, partly because of relatively low power demand and intermittent use in a predictable routine that leaves time for recharging.
However, tractors handling tillage, seeding, transport and harvesting are significantly more demanding – they need lots of power over longer periods (preferably a full day) to compete with diesel.
Electric drive benefits
- Zero emissions from the vehicle
- Cheaper, especially when charged using renewable energy created on farm
- Less noise and vibration
- Fewer wearing components
- Consumes no energy when standing idle on a field headland
- Greater opportunities to control wheels individually
- Greater flexibility to vary pto speed independent of driving speed
Exponents of this power source are hopeful that, as all the major auto manufacturers pile into the growing market for electric cars, battery development in terms of power duration and charging time will improve and component costs will come down. That has spurred renewed interest in electric power research for tractors, such as the project Sustainable Energy Supply for Agricultural Machinery (Sesam).
This is headed by the Kaiserlautern technical research university, located 60km west of John Deere’s European tractor factory in Mannheim, Germany, and a Munich-based energy research consultancy. It has received financial support from the German federal ministry for economic affairs and energy.
While small-scale battery-powered tractors have been tested before, the Sesam researchers say their prototype is the first fully electric battery-powered high-performance tractor to provide comprehensive functionality for agricultural applications. They support that claim by operating the 130kW (174hp) tractor, which is based on a Mannheim-built John Deere 6R-series, with a sprayer, cultivator, slurry tanker and silage trailer.
Using current technology, one battery charge lasts up to four operating hours in typical mixed applications or for about 55km (34 miles) of transport. Charging time for the battery, which is designed to last for 3,100 charge cycles, is about three hours, and braking energy is recovered through the reverse-charging capability, with more than 90% efficiency, say researchers.
They also highlight the potential for reduced operating costs from a tractor optimised to exploit the high efficiency of electric power and the number of maintenance- and wear-free drivetrain components involved. And, of course, an electric tractor can stand idle cost-free, consuming no energy at a field headland or in the yard, unlike a diesel tractor that, as telematics data has revealed, can soon get through an alarming quantity of fuel unless its engine is turned off.
Electric power has even greater potential when used in bespoke fashion rather than simply as a substitute for a diesel engine, as research at the Technical University Dresden has explored. Researchers have worked with a diesel-electric hybrid version of the specialist four-wheel-drive tractor produced by Swiss manufacturer RigiTrac, which normally has a 74kW or 80kW (101hp or 110hp) Deutz engine and two-range hydrostatic drive.
For the research project, it has been given a 91kW (126hp) Deutz engine powering a 650V DC, 85kW generator, and individual electric wheel motors at each corner. This arrangement provides new opportunities for controlling the vehicle’s dynamics, either by torque vectoring or separately regulating the speed of the front and rear axles.
When a single electric motor is used to power a conventional drivetrain, steering angle remains constrained by the limits of shaft-driven beam axles and the relative speed of the front and rear axles must remain constant to avoid transmission “wind-up”. Using individual motors on conventional axles eliminates the wind-up problem and provides an opportunity to separately increase front/rear wheel speed where that would be advantageous.
Dispensing with beam axles by placing electric motors at each wheel introduces further possibilities, including sophisticated electronic traction control and torque vectoring for stability. It also eliminates the mechanical tension inherent in a conventional axle drivetrain, reduces the mechanical components involved and frees up the constraints on vehicle layout.
That last attraction is being exploited by the Dutch team behind the Multi Tool Trac, a bespoke long-wheelbase tractor that can operate powered implements in front-, mid- and rear-mounting positions for the best weight distribution and to carry out multiple-pass operations in one go.
It is also designed with controlled-traffic systems in mind, so power-adjustable axles extend the track width setting from 2.25m (7ft 5in) for road travel to 3.25m (10ft 8in) when running along permanent tramlines. Electric drive was chosen for its installation versatility, fine speed control and instant high-level torque, which delivers great pulling power.
The prototype’s powertrain comprises a 160kW (210hp) six-cylinder diesel engine and generator for use as a range extender for the 30kWhr battery pack, and four electric motors with a nominal output of 22kW, up to 44kW maximum.
The new vehicle architecture allows a moveable cab to sit on chassis rails above the 5.5m (18ft) wheelbase so that the operator can be positioned wherever provides the best visibility and/or ride comfort for different applications. The first prototype, tested since 2015, was followed by a second built last year, with test results leading to a further redesign planned in 2017.
Mixing feed quietly
The 8cu m Siloking Truckline self-propelled feed mixer has 100% electric power, promising lower running and maintenance costs compared with its diesel-fuelled equivalent. This is especially the case on farms generating power from renewable resources.
It has a front axle-mounted 18kW electric motor for ground drive up to 25kph and a 15kW motor to power the mixing auger, which German manufacturer Mayer says is sufficient to break up round bales and produce a homogenous mix of ingredients.
One battery charge is said to be sufficient for three mixes for up to 100 dairy cows, with a larger battery option handling up to five mixing cycles a day. In all other respects, the machine is the same as its engine-powered counterparts.
Members of the Multi Tool Trac team anticipate a commercial product in 2019-20 and, as farmers invest in renewable energy, are convinced of a sound future for electric-drive tractors and other farm vehicles.