Cycle life cost assessment of a hybrid lead acid battery-supercapacitor storage for an electric microcar

The adoption of composed (hybrid) lead acid battery-supercapacitor (SC) storage systems is able to improve performances (availability, durability, range) of an electric microcar. As a matter of fact, the supercapacitors extend the operation time not only by improving the energy efficiency (thanks to a higher contribution of regenerative braking), but also by reducing the power down caused by voltage drop at higher discharge rates. The integration of battery with supercapacitors requires careful analysis and calculation of the relationship between battery peak power and size of the SC bank, needed to have a balanced composition of the hybrid storage system. For this purpose, the optimization process, summarized here, is based on the combination of a conventional lead-acid battery and a commercial SC, with the vehicle running the ECE15 driving cycle. A Matlab/Simulink model has been developed in order to characterize the benefits of the adoption of such hybrid storage system and experimental tests have been used to calibrate it. A techno-economic analysis of the proposed electric storage, aimed to assess cycle-life costs and convenience with respect a conventional one has also been done. The paper will assess with experimental results the technical and economical potentialities of the use of hybrid storage configurations, by demonstrating that it is not only beneficial to improve the vehicle performances, but also convenient, because the reduced stress of the battery prolongs its life, being able to compensate extra-costs for replacement. Copyright © 2014 SAE International.