Switching to fuel cells

Electric lift trucks have used lead-acid batteries for more than 80 years. Now that hydrogen fuel cells are commercially available as an alternative energy source, it is important to understand that retrofitting the lift trucks to use fuel cells can have an impact on the operation of a lift truck originally designed to use lead-acid batteries. The challenge today is designing fuel cell systems that emulate batteries to ensure lift truck performance is maintained, refueling time is reduced and thus, productivity increases. Lift truck and fuel cell manufacturers should collaborate to ensure optimal lift truck operation is achieved.

Lead-acid batteries have always played a critical role in electric lift truck design beyond just providing power. The placement of the forks, wheels, mast and operator platform must be considered in relation to the placement, size and weight of the battery. Traditionally, lift truck manufacturers have assumed that an electric lift truck design must include a battery that has a specific weight and provides a certain amount of energy to the truck.

“Now that hydrogen fuel cells are commercially available as an alternative energy source, it is important to understand that retrofitting the lift trucks to use fuel cells can have an impact on the operation of a lift truck originally designed to use lead-acid batteries.”

However, hydrogen fuel cells are inherently lighter and not necessarily the same shape as lead-acid batteries, so they do not naturally fill the same space in lift trucks. To evaluate the operation of hydrogen fuel cells in electric lift trucks, The Raymond Corporation (Greene, N.Y., U.S.A.) began a multi-year study on the performance of hydrogen fuel cells in lift trucks in January 2007. Raymond’s research indicates that converting to hydrogen fuel cell-powered lift trucks will eventually impact lift truck design. Future lift trucks may have the fuel cells wholly incorporated into the design of the truck from the original concept, but today, fuel cells are being used as drop-in replacements for batteries. If these fuel cell units sufficiently emulate the lead-acid batteries they replace, then no lift truck modifications are necessary to accommodate the fuel cell.

The Industrial Truck Association (ITA) established the Energy Storage System (ESS) committee in 2008 to facilitate discussions between lift truck manufacturers and energy storage system manufacturers to ensure fuel cells or other energy storage systems — such as lithium-ion batteries or supercapacitors — meet lift truck requirements, especially in trucks that are being retrofitted to accommodate the energy storage system. One current initiative of this committee is considering recommendations that describe the minimum requirements and key characteristics of energy storage systems as they relate to a lift truck originally designed for use with a lead-acid battery. Future lift trucks may fully encompass the fuel cell in the design, but according to the preliminary work of the ESS committee, today’s lift trucks require the fuel cell to emulate batteries in five key areas for a successful retrofit:

• Size
• Weight
• Center of gravity
• Power delivered
• Power absorbed

Size

In today’s lift trucks, the hydrogen fuel cell needs to fit in the same space occupied by the battery. Defining the available space for the hydrogen fuel cell, which varies in different types of lift trucks, ensures the fuel cell will fit in a lift truck designed for a lead-acid battery. In some pallet trucks, for example, the fuel cell height can exceed the battery height because the battery compartment is not enclosed (see Figure 1). However, in a reach truck or counterbalanced truck, the fuel cell must fit within an enclosed battery compartment. For example, a 48-volt counterbalanced lift truck might have a battery compartment that is 38.7 inches long, 27.9 inches wide and 22.8 inches tall.

Weight

Every lift truck displays a specification tag or plate that defines the minimum and maximum battery weights. For example, minimum weight may be 2,600 lbs. and maximum weight may be 3,000 lbs. When hydrogen fuel cells are used as battery replacements, they must meet the same weight requirements listed on this spec tag. Meeting the weight requirement is important because it is a critical factor in ensuring the stability of the lift truck. Hydrogen fuel cells can be significantly lighter than lead-acid batteries, so fuel cell manufacturers typically add steel plates to their fuel cell units to make up for the weight required.

Center of gravity

In a lift truck powered by a lead-acid battery, the center of gravity of the battery is the geometric center of the battery box. In a fuel cell that’s being used as a battery replacement, the fuel cell unit incorporates many separate components, including a hydrogen tank, a fuel cell stack and steel counterweight added to meet the minimum weight requirements. Balancing the placement of these components is necessary to ensure the proper center of gravity. Lift truck manufacturers need to perform tests or analysis on each lift truck they intend to use or approve for use with a fuel cell to determine the exact tolerance for where the center of gravity can be located. The tolerance can be described as the radius of a cylindrical shape, with the top of the cylinder located at the volumetric center of the battery being replaced (see Figure 2). If the center of gravity does not fall within the tolerance indicated, the overall stability of the lift truck will be affected. Sample values for the center of gravity tolerance are included.