Exploring the carbon emission reduction effect of all-electric tugboats in ports

All-electric tugboats（AETs） produce fewer carbon emissions, but their battery charging requirements can lead to ship delays, which may increase the overall carbon emission costs in ports. Therefore, it is essential to study the carbon emission reduction performance of AETs in ports and compare their effectiveness with that of diesel tugboats（DTs）. This paper establishes scheduling optimization models for AETs and DTs, respectively, using the sum of tugboat carbon emissions and ship delay carbon emissions as the objective function. Taking a day’s data from three port areas in Ningbo-Zhoushan Port as an example, the Gurobi solver is employed to find the optimal solution. A comparative study is conducted on the minimum tugboat carbon emission cost and total carbon emission cost when AETs and DTs with the same horsepower and quantity are used to handle the same ships. The results show that if only the carbon emission cost of tugboats is considered, AETs can reduce carbon emission costs by 9.5% to 22.9% compared to DTs. However, when considering the overall carbon emission cost of the port areas, AETs still demonstrate good carbon emission reduction effects when handling fewer than 8 ships. When the number of ships exceeds 8 and the port is busy, the charging requirements of AETs increase the overall carbon emission cost of the port by 24.68%, which is not conducive to port carbon emission reduction.