Electrically-powered forklift trucks are becoming increasingly popular around the world, advancing into application areas that to date have been limited to vehicles with combustion engines. The lead battery is by far the most common energy supply for forklift trucks; it remains efficient and competitive thanks to its numerous advantages and state-of-the-art charging technology. However, alternative technologies are now starting to compete. New developments such as the lithium-ion battery, the fuel cell and the hybrid drive have the potential for use in the intralogistics sector as drive solutions of the future. The forklift truck trend is moving towards electric drives. According to the World Industrial Truck Statistics (WITS), in 2014 the global market volume of motorized vehicles grew by eight percent to 1,088,366, with the volume of forklift trucks with electric motors increasing by 14 percent. In contrast, the demand for devices with combustion engines requiring diesel, petrol or gas grew by just four percent compared to the previous year.
Electrically-powered forklift trucks
There are three main reasons for this development. Firstly, electrically-powered forklift trucks are becoming ever more powerful and, with load capacities of up to nine tons, are now advancing into application areas that had previously been the exclusive domain of the combustion engine. Secondly, electrically-powered forklift trucks operate quietly whilst protecting human health and the environment. This also applies when working in closed halls, as they do not produce any toxic emissions. New, stricter legislation regarding CO2 emissions is also being drafted for forklift trucks, supporting the trend towards electrical solutions. Experts predict that the new laws will come into force in 2020. Thirdly, fossil fuels are becoming increasingly scarce and thus more expensive. Just one impact of this trend has been that, in Western Europe, more electrically-powered forklift trucks have been purchased than those with combustion engines over the past five years. These forklifts are powered by traction batteries, whereby the tried-and-tested lead acid battery that has been in use for over a century is the most common energy storage system. There are many reasons for this. Lead batteries are reliable, comparatively cheap and available in various sizes, voltages and capacities. Their heavy weight also serves as a counterweight in counterbalanced lift trucks.
“New, stricter legislation regarding CO2 emissions is also being drafted for forklift trucks, supporting the trend towards electrical solutions”
Maximum energy-efficiency & increased battery
Traction batteries for forklift trucks come at a price. They can account for up to a third of the purchase price of a forklift truck, so it makes sense to maintain their efficiency for as long as possible. With this in mind, it is worth considering all three components of a forklift truck system in detail – the vehicle, the traction battery and the battery charging system. Over the course of time processes for charging lead batteries have changed drastically; from the first 50 Hz transformer battery charging systems with an unregulated charging process and high frequency battery charging systems with a regulated charging process through to microprocessor-controlled devices with complex charging algorithms. A revolutionary development in this area is the Ri charging process, introduced for the first time in 2013 by Austrian battery charging systems specialist Fronius. This minimizes energy loss during charging, thereby reducing energy costs and CO2 emissions as well as increasing the service life of the battery. Unlike with conventional processes, the charging process does not follow a fixed characteristic with a given current. Instead this is determined by the battery’s effective inner resistance (Ri), which in turn is dependent on the age, temperature and state of charge of the battery. Every single charging cycle is therefore unique and has its own characteristic. Overcharging, which causes high energy loss and harmful battery warming, can thus be minimized. Thanks to this intelligent charging technology, Fronius has achieved a charging efficiency level of 90 percent. Combining this with the device efficiency of 93 percent results in a total efficiency figure of 84 percent from the socket to the forklift truck. Compared with other charging processes, users can reduce their energy costs for battery charging by up to 30 percent. Overall, the Ri charging process is the most modern and most efficient charging technology for lead batteries. Fronius estimates that lead acid batteries or lead gel batteries will also have the highest prevalence in the coming years. “Technical developments, such as improved energy storage systems and rechargeable batteries with greater capacities – which also enable opportunity charging and rapid charging to avoid changing the battery – will make the lead battery competitive even in the future,” emphasizes the head of division, Harald Scherleitner. However, in the meantime there are practical alternatives: with lithium-ion technology, the fuel cell and the hybrid drive, several variants will soon be available for powering forklift trucks.
Currently trending: lithium technology
Lithium-ion technology (Li-ion) in particular – which is also built into every laptop – has developed more rapidly than expected over the past few years. All major forklift truck manufacturers now offer models with a lithium-ion battery. The advantages include the compact design, quick and easy opportunity charging, absence of the Memory Effect, increased performance and a more flexible application range for future forklift trucks. In addition, lithium-ion batteries consume up to 30 percent less energy than lead acid batteries. Li-ion energy systems are completely maintenance and emission-free. Water no longer needs to be topped up, the acid density does not need to be measured and the battery does not need to be cleaned. The Li-ion battery also has many benefits in terms of safety. Hydrogen escapes during the charging of lead batteries, which in combination with oxygen, is highly explosive. Li-ion batteries on the other hand do not produce any dangerous gases. Battery charging rooms and stations that must comply with numerous legal standards and specifications are therefore not required by the user. This technology is indeed expensive by comparison, but prices will drop owing to increasing demand on the global market. Fronius has already developed battery charging systems for charging Li-ion batteries, and a simple software update can convert a battery charging system for lead batteries into one for Li-ion batteries. Lithium-ion batteries do have their disadvantages, though, explains Fronius specialist Scherleitner. “They have extremely flammable electrolytes and require special battery charging systems as well as complex battery management systems tailored to the battery.” And because Fronius doesn’t leave anything to chance regarding safety and quality, the company is even developing its own management systems for Li-ion batteries. Special lithium battery technologies that use a combination of nickel-manganese-cobalt oxide, sulphur, air and in particular iron phosphate (LiFePO4) as electrode materials are not yet in great demand on the market, but are already being offered by a few forklift truck manufacturers. LiFePO4 could in fact be a preferred technology for traction applications in the future, owing to its high performance and low weight. LiFePO4 cells cannot catch fire and do not explode under extreme conditions. They have a higher discharge current, self-discharge only very slightly, are non-toxic and have a long service life.
“Lead batteries are reliable, comparatively cheap and available in various sizes, voltages and capacities”
The fuel cell – powering the future?
The use of fuel cells in drive systems looks extremely promising. These convert the chemical energy of a fuel (hydrogen or hydrocarbons) directly into electrical energy using atmospheric oxygen, with no intermediate mechanical step. The additional heat produced can be used to achieve very high efficiency levels. Fuel cells are lighter than batteries as well as being reliable and quiet. Other benefits include quick refueling with hydrogen in just a few minutes, productivity gains due to reduced maintenance and no emissions – the waste product produced by the fuel cell is just pure water. Due to the future importance of the fuel cell as an alternative drive technology, Fronius has already begun several incentive projects with large companies. However, this technology also has its problems. On the one hand, the significantly higher investment costs put many potential customers off. On the other, there are numerous EU regulations regarding the use of hydrogen that are difficult to comply with. Finally, hydrogen is extremely flammable and difficult to store for long periods, even in metal tanks. Using hydrogen as a fuel supply is also seen as a hindrance in intralogistics, as although hydrogen refueling stations do exist for industrial sites, purchasing and operating costs usually prevent them from being used economically. This is why there are currently only around 100 forklift trucks equipped with fuel cells in Europe. In America, the use of H2 technology is better supported in every respect. This is reflected in a fleet size of approx. 8,000 units. The hybrid drive is also suitable for special forklift truck applications, whereby it is a combination of a diesel engine, generator and electric drive motor. Aside from the unavoidable exhaust emissions from the diesel engine, two systems always mean double the costs for the user. The customer must purchase two components initially, and then bear the additional cost of maintenance and servicing for two systems, since hybrid technology is more complex than conventional technology.
Fronius Perfect Charging