Impact of Counting Methods & Objectives on Expected Battery Lifetime & Fuel Consumption

As energy transition gains momentum, batteries emerge as pivotal components facilitating the adoption of cleaner power sources in the maritime industry. Despite uncertainties surrounding battery degradation mechanisms, numerous counting methods offer insights into predicting battery lifetime. This study investigates the impact of counting methods on estimating battery lifetime using an hybrid powered offshore support vessel as a case study. Throughput counting and rainflow counting are examined, revealing discrepancies in potential battery lifetime estimation. The study considers fuel consumption and depth of half cycles as objectives within the mixed integer linear programming framework, highlighting their impact on the trade-off between battery lifetime estimation and fuel consumption. Commercial lithium iron phosphate batteries are used in this study. Results consistently show that degradation-aware operation of batteries can yield at least a 10.3 % and 49.4 % increase in the number of trips before end of life when using energy throughput counting and rainflow counting methods to estimate lifetime. Between the two counting methods, rainflow counting always estimates a higher number of trips compared to energy throughput counting, with a minimum difference of 55. 8% and a maximum difference of 194.1%. By showcasing how relying solely on depth of cycle versus number of cycles curves can lead to varied estimations, this work emphasizes the necessity of employing precise methods for reliable lifetime forecasts in maritime applications.