Are cranes electric?14 February 2019
Diesel engines are polluting, and face ever-stricter controls on their use. But mobile cranes need power, and lots of it. Is electric power for mobile cranes a realistic possibility? Julian Champkin plugs in to the possible technologies.
The most high-profile casualty so far of stricter diesel emission controls has been Volkswagen (VW). The car-maker has paid over $25bn in fines and restitution costs for installing software in its vehicles that falsified diesel emissions test results, and its reputation with customers is in tatters.
VW had resorted to the falsification move because, quite simply, despite its world-renowned expertise in vehicle diesel engines it realised that its cars would not meet US diesel-emissions standards and would probably be barred from the market.
VW admittedly specialises in cars rather than trucks or cranes; but ironically, its engineers got the idea for its test-cheating engine-running software from perfectly legal, and indeed laudable, diesel-management software that had been developed for emergency and off-road equipment like bulldozers and cranes.
This software was permitted by European regulators as a way to override emission controls in short spurts, when high engine performance was required, as, for example, when a heavy-lift load is actually being raised by a crane. Only VW’s engineers changed the concept. Instead of running clean by default and dirty under brief exceptional loading, they changed it to run dirty by default and clean when testers were looking.
The strategy failed them spectacularly. It is reported that VW now plans to turn itself into the world’s largest maker of electric vehicles.
Emission controls worldwide are being severely tightened. “Nobody wants diesel,” says Martin Lottes, engineering manager for Tadano Faun. Low-emission engines, which in practice means electric or hybrid-electric, is what legislators want, and what customers want, for almost any machinery operating in cities. For some lifting applications it is here already: small capacity cranes, as from Maeda and UNIC, have been offered in electric options, either plug-in or battery powered, for several years.
These cranes frequently operate in indoor environments, such as shopping malls, where the incentives for zero-emission construction machinery is clearly even greater.
Tower cranes also have moved to electric power, supplied either by generator or from the city grid. In some cities, like New York, where diesel-powered heavy luffers had been popular, legislators have banned these cranes. However, this poses challenges for operators, particularly in older areas of a city where there is limited grid power. A typical tower crane uses around 800 amps, and increases the electricity demand at a construction site by around 45%. These are not small grid-loadings, and infrastructures in older city centres frequently struggle to supply it.
Tower cranes are static; minicranes operate over small areas where supply by cable from a grid is possible. Mobile cranes, such as all-terrain cranes and rough terrain cranes, do not have that luxury and would have to rely on batteries. But the power demands of such cranes can be very large.
The question arises, therefore, whether replacements for diesel is actually possible for such large, power-hungry vehicles.
Their demands include: sustained medium power, delivered over several hours at a stretch, to move the carrier vehicle on the road over adequate distances; and short bursts of high power for lifting loads on-site. Is current battery technology capable of supplying this? It is a live issue with, as yet, no definite consensus on the answer.
Liebherr believes that at present the answer is 'No'. Liebherr management gave Cranes Today a statement on the subject: “There are no alternative drive concepts for medium to heavy mobile cranes in the foreseeable future. For smaller sizes, one can imagine an electric drive, but operated by electricity on site ("construction site electricity"). We do not consider a hybrid drive to be sensible. There will be many changes in the logistics sector, especially for the so-called "last mile", but not for construction machinery. In the medium term, we see no alternative to diesel for our industry.”
This is not to say that Liebherr is lacking in ambition in the field of large, sometimes very large, electric-powered vehicles. The company’s mining sector, for example, produces a huge dump-truck, the T 282, of some 450t capacity, for opencast mines, that is diesel-electric powered. One version of it has a pantograph, like that on a railway locomotive, that takes electric power from overhead cables, for transport on regular routes such as the road to the unloading bay, or on steep gradients out of the mine. The option gives significant fuel (and therefore emissions) savings. What the vehicle does not have is batteries.
More optimistic would seem to be Volvo Penta, a major supplier of diesel engines to the truck and crane market. It has announced that it intends by 2021 to be supplying electric power solutions for all its business segments—which includes large mobile cranes. “Volvo Penta is embracing the electric transformation and will be at the forefront in delivering compelling business cases to customers using this new technology,” says Björn Ingemanson, president of Volvo Penta. Clearly then Volvo Penta believes the technical problems of powering a fully-mobile crane by electricity are solvable.
Dr Peter Harrop is the author of Electric Vehicles in Mining, Agriculture and Construction 2019–2029, a 163-page report released in January this year from Cambridge-based company IDTechEx. He, too, sees no technical problems in medium-to-large electric-powered mobile cranes, even with current technology; and points to what is already in use. “There are 300kW double-decker electric buses in London. In mining, excavators are going pure electric. There are trials of an excavator with a 700kWh battery and a 550kW motor, so high power is not beyond even the current state of battery technology. And these vehicles are three times as efficient as their diesel equivalents.”
Another energy- (hence also emissions- and cost-) saver in electric power is regenerative braking: when an electric vehicle is braking, or an electric crane is lowering rather than raising a load, the energy generated can be fed back into the battery instead of being wasted as heat, which is what happens in a diesel operation.
“Whatever you can do with diesel you can do with electricity. New types of battery and of motors are a very lively area. We are in a game-changing situation,” says Harrop. “The sector will grow six-fold in the next ten years. It will be worth $130bn a year, and a significant part of that will be cranes.”
Part of the reason that mining has moved more quickly than lifting in this area is the cost distribution. “The overall cost of an electric vehicle is lower over its lifetime, but the upfront cost is higher. Mining is a feast and famine industry, which at the moment is having a feast; so there is investment money available for those up-front costs of electrification which will save money in the long run. Construction is much less volatile, so up-front costs need financing.”
Batteries are of course at the heart of it. Great advances have been made in recent years; nevertheless, batteries are bulky, heavy, expensive and can carry only limited charge. Finding space for a large battery pack on an already crowded all-terrain chassis is not easy, especially since that chassis may already be pushing the size and weight limits for road travel.
Despite his words about new types of battery, there is no replacement for lithium-ion on the horizon, says Dr Harrop.
“There is the issue that lithiumion batteries can be flammable. There is work to be done on that; but lithium has no competitor over the next ten years, except for supplying surges of power.”
Special forms of lithium battery have been developed for fast charge-discharge rates, he says, but for sudden short-lived demands for power—clearly useful for lifting applications—there is another option that is already in use. So-called super capacitors store energy, as a battery does, but much less densely. That is, you get less punch for a given volume or weight of them, therefore they are not good for sustained power delivery. On the other hand, they charge and discharge very quickly, and can complete hundreds of thousands more charge-discharge cycles than a battery can because there are no chemical reactions involved. So they are good for burst-mode power delivery, such as the current surges that electric motors experience on starting.
Shanghai has run buses powered entirely on super capacitors that are charged, in seconds, at every third bus-stop. They apparently experienced overheating problems, but those may be solvable, and Elon Musk of Tesla has said that the future of electric vehicles may be in super capacitors rather than batteries. Super capacitors can also be used on electric cranes powered by the grid, to even out surges in demand. At Yangshan deep-water island port, south of Shanghai, operation of 23 quayside cranes caused sags in the power lines and power losses on the island. Rather than installing 20 miles of new transmission lines the port chose a supercapacitor energy storage system to balance power fluctuations caused by crane operation. The 3mW system provides 20 seconds of reserve power, gives a 38% reduction in peak demand grid energy, and an estimated $2.9m saving over the system’s lifetime. For more on electric-powered portside lifting, see the Q1 2018 issue of our sister magazine, Dockside Lift & Move.
What then of the problem with which we started, electric or low emission power for truly mobile cranes? Martin Lottes of Tadano Faun again: “There is very high interest in this in Germany, and Tadano in Japan has made in-depth investigations. I speak often with customers, especially Scandinavian and Dutch customers, who are asking for exactly that.
“My first question to them is ‘How much would you pay for an electric solution?’ And often I get the feeling that the answer is that customers are not willing to pay very much.
“Nevertheless, it will come. The environment will demand it,” he says. He means the social and legislative environment, as well as the planet’s.
The problems, he says, are not insuperable. “The main issue is the battery pack. At the moment, batteries are very, very expensive.
Everything else is solvable. The power available is OK. The idea that a customer can drive a hybrid or electric machine to a site and when he is there can plug it in to the local grid—that is the aim, but the grid at present is not always prepared or adequate. That will adapt in future.
Up till now some of the technical problems have not been solved, but they are solvable.
“Battery power will remain lithium-ion. I cannot imagine that we could develop an alternative battery ourselves. We must wait for solutions from research labs for that. What we need are solutions that we can buy as standard, off-the- shelf units at affordable, mass produced costs. Those will come, time will work for us.”
On his main issue, the cost of batteries, time would seem to be on his side. A key price determinant is the cost of lithium. As a raw material lithium makes up around 10% of the battery cost. Electric vehicles have now surpassed electronics as consumers of lithium. Bloomberg expects demand for lithium to quadruple by 2025.
Lithium is not scarce in the world in the absolute sense. It is mainly sourced from the curiously-named mineral Spondumene, mined in Australia and China, but it is found also in, and can be extracted from, brine pools created in deserts: Chile’s Atacama desert provides the highest quality. But extraction at present is by evaporation and is expensive and extraordinarily slow: the process takes vast amounts of water (half a million gallons per ton), and the processing time to completion is a whopping two years. But extraction is an area of active research that may well bring results: at least one startup is promising a new method, using ion exchange, that will half the cost of extraction and, more importantly, speed up the process, from two years to just six hours.
And prices are volatile: they have risen from $5,000 per ton to $15,000 per ton, thanks of course to the burgeoning demand. Price and supply forecasts are also volatile: Morgan Stanley expect a supply glut by 2021 along with a 45% fall in price, but others disagree.
Other elements are also used in lithium-ion batteries. One of them is cobalt, most of which comes from the politically unstable Democratic Republic of Congo, and this complicates the predictions; but here technology may provide work-arounds that reduce or eliminate the need for them. Elon Musk has promised cobalt-free vehicle batteries, but the details and timings are unclear.
Battery costs—for the complete battery rather than just the lithium—are certainly falling. In 2011 average prices were $800 per kWh; by 2017 they were $190 per kWh. Batteries need to be sold at around $100 per kWh for electric vehicles to become competitive with internal-combustion ones; Bloomberg has forecast that that will happen by 2026.
“All the other issues are solvable in our mind,” says Lottes. “What the timescale will be I do not know, but even the largest cranes can go electric or hybrid. It will start, of course, with smaller and medium machines; for larger ones, carrying capacity on axle loads becomes an issue because batteries are heavy. But imaginative thinking can help there: for example why not use the batteries as the counterweight, so you don’t need to carry ballast? That would help solve the axle-loading problem.”
Legislation will accelerate the process. “Cities like Copenhagen say ‘Please send only electric machines.’ They are not available now. But they will be in the near future.
“When my customers say ‘I want an electric all-terrain crane to use in the city’ I say to them ‘How many Spierings cranes do you have in your fleet?’ The answer is almost always 'zero.' I ask them because the Spierings is very nearly an allterrain crane, and it is electric powered,” says Lottes.
The Spierings City Boy is a truck-mounted tower crane with a 7t capacity that drives by battery and can plug in to city grids for its lifting power. “The first 100% fully electric- powered mobile crane” say Spierings. It was introduced in 2011. In 2018 Spierings introduced a redesigned and updated version, the SK487-AT3 City Boy.
Spierings could hardly ask for a more satisfactory recommendation than from the engineering supremo of Tadano; nevertheless, Koos Spiering, owner of the company, takes issue with one point. “The City Boy is not nearly an all-terrain crane,” he says. “In our minds it is an all-terrain crane."
Spierings was founded by Leo Spierings; in 2017 he sold all his shares to his nephew Koos. “It was my uncle who came up with the City Boy idea,” says Koos.
“He was considering the problem of making the most efficient crane possible. Everyone was researching a diesel carrier truck with its engine powering a hydraulic crane. But my uncle thought ‘Why not choose instead an electric motor powering the pump for the crane?’” Hence the City Boy.
The crane can be operated in fully electric, hybrid or diesel modes, with all wheels steered and axles one and three driven by electric motors; their power comes from a standard 42.5kWh, or an optional 85kWh, lithium-ion battery pack. Charging by cable is at 400V/25 amps through an on-board 50m spring cable reel.
There is also a Stage IV John Deere diesel on board, connected via a one-way clutch to a generator that charges the batteries.
“The power transfer is very efficient,” says Koos. “You can do 80km an hour on electric power down the highway on your way to the job. Going uphill, when you need more power, you use also the small diesel engine; but because it is only for charging the batteries and for that extra power uphill, it needs to be only a small diesel, just 170kW. That saves space on the vehicle. So you can fit a 40m tower crane onto three axles.
“Back in 2011, emissions were not a topic in the way they are now. The benefit then of the City Boy was reach and height, and those are as valid today. There are many fewer moving parts to an electric motor, so that also gives a saving. We have had 50 orders, almost 60 in fact, for the SK487-AT3 since November 2018.” Another step on the electrification road is from Hiab. Their truck mounted knuckleboom cranes are familiar, and are hydraulically powered from a pump usually driven by the carrier truck’s diesel engine.
In 2014 Hiab introduced its electric power take-off (ePTO) system, to instead run the knuckleboom electrically. It consists of a battery, an electric motor, a hydraulic pump, and an electronic control system, all packaged in a stainless steel box that is mounted on the truck chassis.
The battery and motor run the pump, which operates the crane. The system means that the carrier truck’s engine can be switched off during crane operations. The 40kWh battery capacity is enough to power an average day of crane work.
The battery is recharged, from the grid, at night; it can also be supportcharged at the work place if a grid supply is available. There is also a standard hydraulic pump, driven by the truck engine, for back-up.
“The product is doing well,” says Kent Lindberg, Hiab sales and product business manager, “though it hasn’t yet taken off with high volume sales. But there is a lot of interest because almost everyone is beginning to think about replacing diesel in urban equipment to deal with load handling for inner cities.
“Legislation about diesel emissions is the basis for it, but there is also a desire on the part of our customers for equipment to be eco-friendly— and that desire in turn is partly driven by their own customers’ demands. The users wanting things lifted are beginning to want them lifted in an eco-friendly way.
“There are technical challenges of course. For the crane we have replaced the diesel engine with an electric motor. It is not a complex system in that sense. The challenge is to deliver energy-efficient cranes, and that is what this system does.”
It is not restricted to small capacity lifting: “The load is not the limitation. The ePTO hydraulic pump generates the pressure and therefore the oil flow that any crane uses.
"A bigger crane would need bigger batteries, but we can run any of our crane products on the batteries that we have. There is room on the carrier truck for them.” They are carried under the flat-bed, and therefore take up no useable cargo-space.
“Our truck-mounted cranes are concept-built for the customer,” he says. “Most use conventional diesel truck as carriers.”
One customer, though, builders merchants Lawsons of North London, specified a truck running on compressed natural gas; many of Lawsons deliveries are in London’s Low Emissions Zone, which covers most of greater London—and which from 8 April this year will be joined by an Ultra-Low Emissions Zone covering the central area. The truck is a converted 26t IVECO. “We identified natural gas as the only realistic alternative to diesel for the carrier,” says Paul Sexton, Lawson’s managing director.
The vehicle emits 70% less NOx, less particulate matter, and up to 95% less CO2, and is also quieter than a diesel.
“The advantage of ePTO is not just zero emissions and quietness,” says Lindberg. “Those mean that you can operate them in residential neighbourhoods, and at night. But the operators also benefit.
Operators frequently comment to us how much less stressful it is to use electrically-driven machines. At the end of the day they do not go home having spent all their time with a diesel engine throbbing in their ears.
It is quieter, and so less stressful, and therefore safer as well.
“It is a new technique. We want to develop products to fit the future in ways that are better for the environment.”
Where Spierings and Hiab have pioneered, others may follow.
Future large mobile cranes may or may not look like current offerings, but the engine or motor that drives them will probably be very different indeed.
“Electrification is coming; it becomes more and more important,” says Lindberg, and adds: “The future is hard to predict, but absolutely I believe it will need this kind of product.”