Warehouse trucks are dependent upon electric power – the close confines of the warehouse environment dictate it – and since their introduction to the industrial scene in the middle of the last century, lead-acid batteries have been almost exclusively the sole form of power cell available. However, in recent years the rise of corporate interest in environmental issues has pushed fork lift truck manufacturers and battery makers to look for alternative forms of power cells – solutions that are more in tune with a carbon conscious society.
New technologies relating to the use of nickel cadmium, lithium and hydrogen fuel cells have been developed, tested and applied to a broad range of vehicles, in particular, cars. These technologies have also been put to use in warehouse trucks but, for the buyers of electric powered material handling equipment, the jury is out.
Do the new technologies stack up in terms of capital cost, power efficiency, performance, reliability, durability, total life-time cost and environmental impact? Can the latest power cell formats out-compete the traditional lead-acid battery? Or are we simply looking at technologies that are not best suited to the warehouse?
According to David Culshaw, products and application manager at GNB Industrial Power and a member of the technical policy committee of BITA: “There are some initiatives, including at GNB, where lithium is being introduced into materials handling applications, but one of the things that has to be taken into consideration is the weight of the product.”
One of the key aspects of lithium-ion is its power performance to its size and weight, a particular advantage in its application to electric cars and vans. However, the weight of the battery on a fork lift truck serves a useful purpose in providing a counterbalance for the pallet load being moved. “For your typical application where the weight of the battery acts as a counterweight, the lead acid battery is predominantly the product that is still being used, or is even being considered,” says Culshaw.
Culshaw identifies where lithium-ion technology is currently being tested out. “You get certain applications, the small powered pallet trucks where the weight isn’t as critical, and the loads are quite light, and that’s where they are tending to use it,” he says. “There are a couple of companies doing things along these lines. Our own division, Restore, is contributing to one of the truck manufacturers currently looking at introducing lithium into a similar type of product.”
David Callis, operations manager at Powercell Industrial Battery Engineers, says: “There are truck companies like Jungheinrich and Linde that do have lithium and fuel cell trucks on trial in a number of countries and applications, but they are trial trucks.”
He adds, “The manufacturers have to work together with the fuel cell technology people to generate the full package, so it’s a combination, and nobody wants to invest the money to make it a full scale alternative.”
Until fairly recently all the warehouse trucks that were on trial with Lithium-ion technology were just adapted existing models. However, in Spring 2011 Jungheinrich came to the market with the first truck specifically designed to capitalise on the qualities of lithium-ion. The battery used to power the EJE 112i lithium-ion powered pallet truck weighs just 14kg, which is considerably less than the lead acid batteries used on trucks of a similar capacity. Bill Goodwin, sales director of Jungheinrich UK, says: “The battery looks like a brief case, and its compact dimensions have enabled us to dramatically slash the size of the truck’s battery compartment and, therefore, the overall size of the truck.” According to Goodwin the new truck measures 425cm, which is 70cm less than a comparable model with a similar capacity powered by lead acid technology.
A further advantage of the lithium-ion powered pallet truck is a 30 per cent reduction in the overall weight of the unit when compared with a lead acid powered model of the same capacity. There appears to be obvious wins here with the loading and unloading of lorries with tail lifts or double-decks, and a lighter truck, would of course, require less energy to operate.
There also seem to be clear advantages with regards the charging times for Lithium-ion batteries. Jungheinrich say it takes just 30 minutes to deliver a 50 per cent charge and the battery is fully charged within 80 minutes – which opens up the possibilities of “opportunity charging” for multi-shift operations. Considering also the fact that lithium-ion batteries require no maintenance, they appear to have a lot going for them – particularly, in this application relating to powered pallet trucks.
There are issues with Lithium-ion, however. Not least of all being its cost. Jana Vitkova, warehouse product manager at Linde Material Handling says: “Lithium-ion batteries are much in the news at present due to their small size and fast charging characteristics, however, sales volumes are still very low due to their substantially higher cost.”
David Culshaw of GNB alludes to a cost differential of between six and eight times that of lead-acid.
Linde demonstrated its own prototype lithium-ion power pallet truck at CEMAT last year and Vitkova says: “We believe in the potential of lithium-ion.” But while cost appears to be a barrier to uptake for Lithium-ion, the financial case for another much talked about power option, hydrogen fuel cells, “is even more difficult to make – not just for the fuel cell but also for the filling station,” she says.
David Callis of Powercell explains hydrogen fuel cell technology: “You replace what would be the full lead acid battery on a fork truck with a much smaller battery and a hydrogen recharge unit. Once you’ve got the hydrogen generation station set up, which produces hydrogen from a filtered source of water supply, then the topping up procedure to maintain the power levels in the battery, is quite cheap.” However, the high capital outlay on the equipment is a major consideration. He says, “You would have to run it for five or six years before you break even.”
The advantage of hydrogen fuel cells, says Callis, is that you have a very short top-up time and unlike lead acid batteries, you do not have battery changes. “With lead acid batteries, if you want to run a double shift, you would have to have at least two batteries per truck,” he says. Doubts surrounding the energy efficiency of the hydrogen production process allied to site supply problems and health and safety concerns over the refuelling process have tended to overshadow the positive aspects of the technology.
Lead acid technology on the move
The lead acid battery is predominantly the most economic option for the materials handling industry, compared to the other types of battery available – and lead acid technology itself, is not standing still.
“There are bodies in the industry that have been looking at advancing the lead acid product and our own company is currently undertaking trials of a new generation of lead acid batteries, which will be called Tensor, that’s getting close to being put out there,” says GNB’s David Culshaw.
“This will give a distinct improvement in available capacity and energy and the way the battery reacts in the application,” he says.
“For the same footprint and for a similar weight you will get more energy, so therefore, if you have the same truck you will be able to achieve more working hours with it.”
Over the past five years, people have been looking at the greener aspects of power usage in the warehouse. “There has been quite a significant move to using high frequency chargers. A number of big supermarket distribution centres are moving to this method of AC to DC conversion for charging batteries as it saves a significant amount of energy – compared to conventional systems,” says Culshaw.
The conventional technology for charging, he says, uses a source to convert AC via a transformer to a lower voltage (it goes through a rectifier) and then it becomes DC to the battery. In that arrangement you are using quite high currents at various points – also if it is a regulated charger, you are chopping the energy, resulting in various losses.
“With high frequency charging, as you bring it into the charger, the first thing you do is rectify it, then you change the frequency to a high frequency – by doing this you reduce the size of the transformer at that point significantly – and you reduce a lot of the losses [which goes in heat]. Then you rectify it again and this becomes the controlled DC output to the battery charger. “ says Culshaw.
“The major benefit to a user who has a large battery charging system is that they are probably going to save in the order of 15 per cent from their energy consumption. That can be an awful lot of money year-on-year.”
Matching power requirements to a shift is a critical aspect of the selection process. Linde’s Vitkova says most trucks can be fitted with a range of different capacity batteries. However, the majority of multi-shift applications are also quite intensive, so generally, the largest battery available for the truck is most appropriate. “As the battery represents around 15 per cent of the overall truck price, it is a false economy to fit too small a battery and risk compromising truck shift life.”
Vitkova believes the best-practice way of getting the most from the battery is to ensure you have “a dedicated battery changing/charging area, trained staff, correct utilisation of the batteries (timely changing for fresh batteries), correct selection of the fresh battery, correct maintenance of truck and battery and modern high frequency chargers.”
For Culshaw the key factor in extending the expected life of the battery is good maintenance. “Lots of companies offer battery maintenance contracts. But it isn’t just topping up with water, whether it’s two weekly, monthly or even quarterly, there is a lot more to it than that,” he says. “The critical factor is topping up at the right time and after it’s fully charged. Batteries are tidal, the electrolyte level will rise and fall, depending upon its state of charge. If you top it up before it’s on charge the tidal level will go too high, the electrolyte is then purged from the cell, and the acid goes into the tray.
“Every ounce of acid that is lost is performance lost,” Culshaw says. “The surface of the battery should also be kept clean. The cell should be shiny as it improves the tracking resistance of the product [stops leaking energy] – and this makes a big difference.” In addition, he says, “By having someone maintain the battery they can observe the condition of connections and the equipment.”
Nick Allen is Logistics Manager’s Contributing Editor, Supply Chain
Logistics Manager, January 2012