Interest in electrically powered ferry vessels has grown dramatically in recent years. In the U.S., electric ferries – either fully electric powered by shore charging or hybrid powered by on-board generation – are in operation or development in California, Washington and elsewhere.
An established mode of transportation in the Scandinavian region, electric ferries first operated in Norway in 2015, and about 80 electric ferries operate in Norway currently. Other projects are planned, in development, or in operation across Europe, Asia and Australia.
Reduction or elimination of emissions is the most commonly cited benefit of electric ferries and is often the driving force behind the decision to go electric. Rider experience is also improved due to reductions in noise and vibration.
While these benefits are real and important in the decision to go electric, the economics of owning and operating a long-life electrified asset is an equally important consideration.
Electric ferries share some cost categories with diesel-mechanical vessels, but for electric ferries the way the costs are realized is very different and there are additional cost categories that must be considered.
The capital cost of the vessel, energy cost and engine maintenance cost of hybrid vessels are very different for electric ferries. Electric ferries have a capital cost 15-20% greater than a convention diesel vessel, with some reporting a premium cost of up to 40%. This increase in capital cost is offset by significant reductions in electric energy and maintenance costs.
The cost of energy is significantly different for electric ferries, as electricity is generally less expensive and the costs are incurred very differently.
Energy cost for conventional and hybrid vessels is the cost of diesel paid for at an ever-increasing rate by the gallon. For plug-in electric vessels, there is a cost for energy both paid by the kilowatt-hour (think volume) and for demand paid by the kilowatt (think charging rate).
Data shows that electricity costs also increase over time, although historically those costs increase at a significantly lower rate than the cost of diesel. There is also a fixed monthly rate for electric service, but it is typically a small part of the cost.
Electric energy costs are often dominated by demand charges, as charge rates in the megawatt range are typical. Both energy and demand rates vary by location and communication with the electric utility is critical to accurately estimating these costs.
Maintenance and Other Costs
Maintenance cost differences also must be part of the calculation. Maintenance for propulsion and generator engines on conventional ferries ranges from routine preventive maintenance to full-engine rebuilds. These costs are typically an order of magnitude less than capital or diesel costs. For plug-in electric vessels, engine maintenance costs are either eliminated for fully electric vessels or minimized for hybrid vessels with on-board generation for backup power only.
Additional costs unique to electric vessels include electric infrastructure improvements, batteries for energy storage and electrical system maintenance. Infrastructure improvements are capital costs for upgrading electrical systems at ferry terminals.
This typically includes the electric service transformer, transmission conductors, switch gear and filters and a rapid charging system to support vessel charging.
Depending on the charging demand, improvements to the electrical grid may be required, and could include replacing conductors and substation transformers. Grid improvements may be considered an electrification project cost or may be borne by the utility and incorporated into the electrical service rate structure.
Either way, the infrastructure costs to get the necessary energy from the grid and onto the vessel are significant and must be considered.
Batteries, commonly referred to as energy storage systems, are another significant cost associated with electric vessels. Batteries are certainly required on-board the vessel and may be used onshore to manage the demand costs by reducing the charge demand on the grid.
Battery size or capacity requirements depend on a number of factors including design service life, daily charges/discharges, charge/discharge rate and battery chemistry.
Battery service life is significantly less than the vessel service life and replacement costs must be considered in addition to initial battery costs.
Maintenance costs for electrical systems are not substantial, but should be included for maintaining charging systems, motors, drives and generator sets. Maintenance schedules and requirements can be provided by the OEMs to help plan and estimate these costs.
Shoreside electrical systems built to power electric ferries also can, in certain cases, serve to power onshore vehicles (cars, buses) and terminal equipment. These multi-purpose shore charging stations are best suited to passenger-only ferries with relatively small power requirements.
Further, recent developments in floating charging stations serve to add capacity at marinas hosting an electric ferry. WETA (Water Emergency Transportation Authority) in San Francisco Bay is exploring this option with its new Universal Charging stations.
Because the costs are incurred at varying intervals and magnitudes throughout the long vessel life, vessel electrification costs and options are best evaluated using life-cycle cost analysis (LCCA) techniques.
LCCA is a method of assessing the total cost, including acquisition, operating, maintenance and disposal. The results are typically presented as a single net present value for each option, which allows the options to be easily compared and assessed.
While the approach and LCCA methods can be broadly applied, every ferry operation is unique and must be analyzed independently.
Schedule, route configurations and passenger volumes are unique to each ferry system, as are the current status of the electrical grid and power-generating capacity, the local energy costs and the political climate of each location.
There is no “one size fits all” in electric ferries. However, technological advancements are making electric ferries more attractive to more ferry managers every day, and the comfort, quiet and ecologically friendly nature of the ferries make them increasingly attractive for ferry user stakeholder groups, too.
John Hildreth is the Kimmel Distinguished Professor of Construction Management and the Associate Dean for Research at Western Carolina University. He is a civil engineer by training with a developed expertise in the economics of transportation asset management. He recently completed a study of the technical and economic feasibility of electrification options for the North Carolina Ferry System fleet. He serves as a consultant to companies and agencies across the U.S. Professor Hildreth will be a panelist at the 2024 Ferries Conference on Oct. 8 at the Renaissance Seattle Hotel. www.FerriesConference.com