Daniel Ahern, ABB Marine & Ports, VP Navy and Coast Guard Segment
Across the shipping industry, electric power systems incorporating batteries and energy storage systems, fuel cells and other sources of shipboard energy and ship-shore energy integration, are set to transform ship design and operation in the years ahead. At the same time, sensors on board ships are transmitting fast increasing amounts of data between systems, accumulating knowledge on board and on shore to optimize operations and enhance remote support.
Electric power and propulsion systems have established a strong foothold across shipping, with successful deployments onboard high-performance icebreakers, shuttle tankers, offshore construction vessels, icebreaking liquefied natural gas (LNG) carriers, and wind farm support ships.
For navy and coast guard vessels, the power of electricity has great potential to raise operational flexibility, increase efficiency, cut response times and enhance maneuverability, reduce lifecycle maintenance costs, and improve sustainability. Also, due to changing mission load requirements, the flexibility of the electrical system can support varying mission needs.
Sectors of commercial shipping have already embarked on the energy transition. In many cases, this involves the smooth integration of energy generated from different sources, a catalyst in the development of ultra-flexible direct current (DC) grids that are increasingly being chosen over alternating current (AC) arrangements. Suitable for ships operating in the low-to-mid power range, DC-based power systems are based on pre-engineered modules that can be combined to deliver the required balance of power and resilience, and can be scaled up or down to serve a variety of vessel types and operating profiles
Demanding operating profiles
Many Navy and Coast Guard vessels share similar operating profiles with these specialized commercial ships, where variable power demands need to be available in seconds, not minutes. Where efficiency allows for greater range or reduced fuel storage, operating demands range across standby transit, high-speed missions, docking operations with maximum maneuverability and the capability to operate unassisted if necessary.
In contrast to traditional AC systems, today’s DC grids provide the flexibility required to meet these wide-ranging operating profiles. DC power systems lie at the heart of shipping’s energy transformation today and will be essential for the multi-source shipboard energy arrangements that are in development and will be required tomorrow. Ship operators are already hailing their benefits as replacements for conventional AC systems on a growing number of ship types. They cite advantages including simplicity, operational flexibility and lifecycle economics.
In addition to their usefulness in the integration of physical technologies, DC-based power systems provide a unique platform for digital solutions. With sensors on board transmitting data between systems instantly, this opens the way for optimization in bridge- and shore-based performance – as well as to remote support through on-shore support centers. Because digital systems are fully available to the ship and at control centers ashore, both efficiency and safety is optimized at all times.
Why DC power?
The shift to DC power has been a response to the changing energy and operating requirements of many ship types. These include the development of variable speed engines, the integration of batteries and energy storage, scope to integrate other energy sources such as shaft generators and, in the future, fuel cells and power from the wind.
In fact, DC systems have many practical, operational and safety advantages over those based on AC. Many of these benefits are directly relevant to the Navy and Coast Guard sectors and can be summarized as follows:
- Variable speed generators to match power supply and demand at all times, saving fuel, cutting emissions, and reducing maintenance requirements
- Efficient integration of additional power sources, including shaft generators, batteries, energy storage systems, and fuel cells
- Increased flexibility through weight and space savings of up to 30 percent
- Superior fault tolerance supported by remote and real-time diagnostics service
- Effective distribution capability
- Remote and real-time diagnostics service functionality
In terms of safety, the relative simplicity of DC grids provides greater scope to protect against faults, to predict them, to detect them, and for system recovery. Confidence in the overall system has also been shown to encourage more sustainable ship operation because additional power sources are not brought online unnecessarily.
Meanwhile, the simplicity of the setup enables common faults such as governor and automatic voltage regulator failures to be handled more quickly and effectively. The risk of engine overload is dramatically reduced because each generator has a built-in overload protector that limits output power and ensures that engines do not stall.
If the benefits of greater efficiency, real-time vessel management and remote diagnostics are self-evident, the switch from AC to DC offers still more in the way of flexibility for Navy and Coast Guard ships. It can, for example, facilitate zero-noise and/or zero-emission operation for sensitive deployments. Operating range can also be significantly extended, particularly with the adoption of azimuth or podded electric propulsion.
A decentralized DC system can also provide increased redundancy and survivability to the vessel. By segmenting and distributing the power generation and the consumers along a DC bus network, a high degree of survivability can be achieved.
But there are also lifetime benefits that are less apparent at the outset, but which should appeal to Navy and Coast Guard Commanders. These include improved reliability, longer maintenance intervals with digital predictive systems, and fewer spare parts.
Meanwhile, remote support capabilities in real time from expert Navy or Coast Guard personnel can maximize uptime and minimize mission delays. Overall, reduced lifecycle costs, improved sustainability, and significantly smaller carbon footprints should appeal, while the adaptability of DC arrangements provide a strong degree of ‘future-proofing’ as new technologies gain ground in the years ahead.