During the IEA’s 2022 conference on energy efficiency in Sønderborg, Denmark, Danfoss showcased its hybrid electric-hydraulic drive solutions in operation on a real construction site. MechChem Africa, visits the site and talks to Eric Alström of Danfoss Power Solutions.
This year’s International Energy Agency’s Energy Efficiency conference was moved from its home in Paris to a small town in Denmark called Sønderborg, which is the global headquarters of Danfoss: the energy efficiency, heating, cooling, power and drives specialist.
The reason for the shift? Sønderborg’s passion and ambition for implementing integrated energy efficiency initiatives across the municipality, which led conference leaders to name Sønderborg the “energy efficiency capital of the world”. Through ProjectZero, which was initiated as a private-public partnership back in 2007 – with Danfoss as a key partner – Sønderborg is currently on track to be carbon neutral by 2029, some 20 years before the critical 2050 deadline for global warming mitigation.
The stated ambition of the town’s ProjectZero initiative is ”to create an integrated, microcosmic, carbon-neutral energy system that can inspire much larger cities and municipalities” – and throughout the conference, the city demonstrated its willingness to “exchange ideas and collaborate with the world.”
One of the visits we attended during the conference was to a building site showcasing the feasibility of switching a range of construction equipment away from using diesel engines. We saw excavators, graders, loaders and dump trucks in various sizes operating on a quiet and very clean building site, all powered by electricity via batteries.
“If using a diesel engine to power an excavator, for example, 70% of the energy is lost before any productive work is done by the machine,” notes Eric Alström, president of Danfoss Power Solutions. “These machines are actually hybrid electro-hydraulic systems, which is a very nice combination of conventional rugged hydraulics combined with the new generation electrical propulsion systems powered by batteries as the energy source,” he says, noting that, even though not fully electric from a component perspective, this is a zero-emissions construction solution.
Highlighting the commercial availability of these machines from several OEMs, he notes the simplicity of making the transition. “Just like traditional diesel-driven construction equipment, the power transmission side of these systems – slew and track drives and the cylinders – all remain hydraulic. The power source for driving the hydraulic pumps is electric and a Li-ion battery stack is the energy source to power the electric motor – with the excavator demonstrated having a 266 kWh battery. The very significant change, however, is that the diesel power unit has been replaced,” says Alström.
“At some point, it may make sense to replace the track motors with electric motors, which we can then also do relatively simply by removing the hoses and installing electrical wiring. For now though, we haven’t developed electrical motors with the same power densities as hydraulic motors. But electric motors are getting smaller and more powerful, and the day may come when full electrification makes sense,” Alström tells MechChem Africa.
Electrification, however, brings further efficiency and control advantages to hydraulic actuators. “We use electronic converter drives connected to a fully digitally control system to simultaneously manage the electric motors driving the hydraulic pump and, hence, all the hydraulic needs of the machine. This gives us much better control over total operating efficiency, precision and performance of these construction machines.
“A diesel engine on these machines typically runs at a relatively constant rpm, no matter what the machine is doing. By using a converter to control the electric motor driving the pump, we can continuously regulate the speed of the hydraulic pump to match instantaneous demand. So the energy used is better matched to the energy actually needed,” he explains.
Alström adds that hydraulic energy losses can further be reduced through solutions such as Individual Metering Control (IMC), direct-driven hydraulics, digital hydraulics or multi-chamber actuators. “In this excavator, the Danfoss Digital Displacement® pump makes it possible to operate multiple actuators simultaneously by setting independent pressures and flows for each of them, allowing for a significant energy reduction,” he adds.
According to Danfoss’ calculations, a diesel-engine powered (ICE) excavator requires an input of 8.3 units of energy to produce 1 unit of productive work, while an electrified excavator with a conventional hydraulics system requires an input of 3.7 units to produce the same amount of work. So from an efficiency perspective, these vehicles are emission free, and they use less than half the energy.
A fully electric and digitalised drive train based in Danfoss’ Digital Displacement technology, would require an input of 1.9 units of energy to produce 1 unit of productive work, which is a further 48% reduction on energy use. For certain machines, like excavators, the calculations show that this total electrification solution can offer better total costs of ownership (TCO) than a standard diesel engine within five years.
For the drive side of hybrid electric-hydraulic construction vehicles, Alström notes that Danfoss’ hydraulic components are used for everything except the cylinders. “We do the joysticks, hoses, fittings, track and slew hydraulic motors, the pump and the valve stack. We also manufacture the electric motor, the converter and the entire control system,” he says.
“Having recently acquired Eaton Hydraulics, we remain stronger than ever in hydraulics, which we see as a part of our emission-free future for years to come, and when electrical actuators with the power densities required become available, we will happily supply these instead so that the larger construction vehicles can also be fully electrified,” he says.
When asked if there is a future role for vehicles powered by hydrogen via fuel cells, he responds that fuel-cells technology may be the way forward for very heavy construction vehicles. “It also depends on the duty cycle of the machines. If the excavator is not used for many minutes during a working day, it makes sense to keep it electrical, because it can be charged when the workers go to lunch and after 30 minutes, it will be ready for the rest of the day.
“In a mining scenario that might not be possible, so fuel cells might be preferred, particularly for really heavy duty operations. There are also some large excavator developers exploring fuel cell technology, though as parallel developments. The diesel engine power unit can just as easily be replaced by a hydrogen fuel cell, which drives the electric motor – and the rest of the drive train can also be hydraulic or fully electric.
“More efficient construction machines are good for people, the planet and profits – and the technologies already exist to improve energy efficiency and electrify construction equipment,” Eric Alström concludes.