Calorimetric efficiency measurements of supercapacitors and lithium-ion batteries

This paper presents efficiency measurements for a 125 V/63 F supercapacitor module (SC) and a 96 V/90 Ah lithium-ion (li-ion) battery system as a function of charge-discharge current frequency. The result would be useful in the design of efficient power flow control in systems using SCs and li-ion batteries as parallel energy storages, and offers a possibility to predict energy storage power losses from the frequency spectrum of the energy storage current. In order to obtain accurate measurement results a calorimetric test setup has been built. In addition the li-ion battery efficiency is analyzed according to draft standard ISO 12405-1 and with a small scale straddle carrier laboratory drive. The calorimetric measurements indicate that frequency has only a minor impact on the energy storage efficiencies, but the efficiency of the SC is approximately 3 % better than that of the li-ion battery system. The standard measurements and straddle carrier measurements indicate an even greater difference in li-ion battery efficiency in comparison to the SC. Hence, in parallel SC and li-ion battery energy storage systems the control of power flow should be arranged so that the SC is utilized as much as possible.