Marine goes green: energy-efficient hydraulics in hybrid electric applications
10 February 2020
At first glance, it looked like any other car ferry, carrying people and vehicles to-and-fro across a fjord off the coast of Norway. However, appearances can be deceptive. For this 80-metre vessel, tellingly named the Ampere, featured one of the world’s first all-electric battery-powered marine architectures – resulting in virtually zero greenhouse gas emissions and near-silent operation.
The Ampere, launched in 2015 by the Norled shipping company, represented the start of a significant trend towards hybridisation and electrification in the marine sector. Since then, many other forward-thinking operators of car ferries and workboats such as trawlers, fish-farming vessels and tugs have embraced a new wave of greener power and propulsion systems. These types of vessels spend much time in near-shore operation and are therefore subject to a robust legislative drive to reduce harmful emissions.
Moving on from fossil fuels
Historically, marine vessels have been heavily dependent on fossil fuels, with diesel-electric ships mainly using an internal combustion-powered engine connected to an electrical generator, with the power shifted to the propeller shaft via an AC inverter and electric motor. But this conventional power and propulsion arrangement has started to evolve in some quite exciting ways. Advances in hybridisation and electrification have resulted in some novel architectures that boast some specific performance advantages, particularly in the area of energy efficiency.
So, what are options for greener marine vessels? Firstly, there are serial hybrids which in most cases use an onboard engine to provide power to a generator, with the propeller spun by an electric motor. Batteries can also be used to provide energy storage capability. For parallel hybrids, meanwhile, the engine is mechanically coupled to the drive shaft, as well as to an electric motor. The propeller can be powered from the engine, or the electric motor, and power can be delivered from both sources at once. Then, finally, there is pure electric, which usually comprises a lithium-ion battery stack to power the electric motors.
The chosen architecture depends very much on the types of work cycles of the vessels involved. However, there is one constant, regardless of the final selection: ship operators are increasingly looking to maximise the overall performance of the vessel by reaching optimal energy efficiency of all onboard systems. This is achieved through the seamless integration of power and propulsion – be that serial hybrids, parallel hybrids or pure electrics – with other technologies such as hydraulics, which are commonly used to drive steering systems and gearbox lubrication and to power ancillary systems such as bow ramps and drive ramps.
Overcoming integration challenges
Integrating energy-efficient hydraulics systems involves several considerations. The switch to battery-powered systems in marine environments, for instance, means careful thought needs to be given to how to optimise the amount of installed battery power. Heavy battery banks are still expensive and accommodate a lot of space onboard the vessel. Thus, the energy consumption of all onboard systems – right down to coffee machines – needs to be assessed.
Conventional hydraulic power units, primarily found on older stock diesel-powered vessels, have traditionally required oversized pumps and motors to ensure performance during a system’s highest duty-cycle demands. However, as energy costs have become more of an issue, and environmental regulations have become more stringent, the wasted energy and high CO2 emissions are increasingly problematic in marine applications. This has required a transition to more efficient systems where power is precisely modulated to the requirements of specific tasks.
As a result, new technologies such as drive controlled pump systems are providing a more synergistic approach in which hydraulic power units, frequency drives, electric motors and hydraulic pumps are successfully integrated to meet each local load demand within a hydraulic system. Specifically, variable frequency drives manage the electric motor’s operating torque and speed, producing the precise, variable pressure and flow required at any given point in the machine or duty cycle. Drive control is directed through the use of field-tested control algorithms designed to provide reliable, standardised and customisable hydraulic functions.
These technical challenges have encouraged traditional hydraulic component suppliers to modernise and evolve to become motion control specialists – capable of understanding the complex interface between a host of electro-hydraulic technologies and their control systems. At Parker, the response has been to merge the hydraulics, pneumatics and electromechanical divisions to create a dedicated Motion Systems Group which has the depth of technical expertise in marine environments.
Electrification brings connectivity benefits
The drive for energy efficiency onboard hybrid and electric vessels does not stop with the installation of modern motion systems based on the latest technology, such as drive-controlled pump solutions. With the emergence of the Internet of Things, it is now possible to install versatile digital ecosystems onboard marine vessels, enabling the reliable connection of electronic control hardware and software to the cloud. This connectivity gives ship operators real-time access to a host of data parameters, bringing many benefits.
Digital integration through the use of mobile IoT can provide valuable insight into the real-time condition of hydraulic equipment, making it possible to continually track a host of variables including engine speeds, torque and other motion system parameters. The ability to share this data by assigning multi-tiered user types and permissions means that maintenance can be handled in a more predictable manner, which improves uptime and supports more efficient operation. Ultimately, mobile IoT is a game-changer in marine environments, resulting in more cost-effective, energy-efficient and environmentally friendly operations.
Looking further forward, the widespread adoption of 5G wireless systems promises even higher levels of connectivity, making it possible to transmit vastly higher levels of data with much lower latency. This is likely to result in a new wave of IoT-enabled business cases in the marine sector, particularly in the areas of port logistics and more energy-efficient route planning.
Technologies such as 5G will also underpin the increasing use of automation onboard the smarter ships of the future. Automating onboard operations is viewed as a valuable means of saving time and money, while the requirement for fewer crew members at sea lowers the risk of accidents and injuries. These days, most major marine organisations are investing heavily in IoT/automation research, with ship autonomy becoming a recognised mega-trend across the globe.
It is clear, then, that greener operations in marine environments present plenty of opportunities for technical enhancement. Vessels such as ferries and workboats are becoming cleaner and more efficient, making the very most of the installed power onboard. Electrification also brings the potential of advanced connectivity, giving operators real-time insight into the performance of key equipment such as hydraulics. In short, greener ships are better ships – and that brings benefit for all.
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