Hybrid battery-supercapacitor storage for an electric forklift: a life-cycle cost assessment
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Supercapacitors, more properly named electrochemical capacitors (EC), have a great potential in constituting the premium power reserve in a variety of energy- and power-intensive applications in transport and in electricity grids. EC may be used in conjunction with electrochemical storage systems, such as the batteries of various chemistries (lead-acid, sodium-nickel chloride or sodium-sulphur, nickel-metal hydride and even lithium-based systems), in a hybrid configuration where the functions of energy and power can be conveniently separated between the two storage devices and then optimized. Recently, an electric forklift has been commercialized with such a hybrid storage system, without any demonstrated specification of the advantages achievable with this configuration. In this article, the effective technical and economical benefits of this EC integration are theoretically and experimentally evaluated, by means of a conventional electric forklift. The reference vehicle drivetrain is modified by combining a conventional traction lead-acid battery, already used in the vehicle, and a commercial EC. The performances of the modified electric forklift are simulated with already developed vehicle and components models and validated with experimental data. Simulations and electrical tests confirm the functional relationship, expressed in exponential form, between battery lifetime and peak current and demonstrate the technical and economical potentialities of the use of these hybrid configurations, such as the increased efficiency and the prolonged battery life (more than doubling the life of the battery without EC), due to the reduced battery operating stress, and an economical saving (about 30 %), able to compensate initial extra-costs for vehicle modification and battery replacement.
KeywordsElectric forklift Hybrid energy storage systems Lead-acid battery Supercapacitors Modelling Life-cycle cost assessment
This work is a part of activities supported by the Italian Ministry of Economic Development in the framework of the Program Agreement for the Research on Electric System.
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