The European offshore wind farm industry is booming. In 2015, 3,10MW of grid-connected capacity was added, 108% more than in the last 10 years! With this growth comes a need for evolution in service vessels that support the industry. Energy storage technology is a major part of the current evolution of the maritime industry; hybrid and fully electric systems have successfully been installed on a variety of commercial vessels including ferries, offshore support vessels, fish boats, and tugboats. While environmental regulations have helped to create demand for this sustainable technology, the primary market driver is increased safety and reliability of the vessels and a significant decrease in operational and fuel costs.
Rough weather and high waves often characterize the working environment for people and equipment during the installation, and maintenance of offshore wind farms. This means that wind farm services vessels have extraordinary requirements for immediate power, endurance, robustness and safety in order to maintain their operational duties in all weather. A service vessel requires powerful bollard pull capabilities, and in general excellent sea keeping abilities to withstand wind, waves and currents. In these demanding environments, human safety as well as operational expenditures are of key concern, thus service vessels must be built to the highest standards.
Here is Where Energy Storage Will Improve Wind Farm vessel operations:
Wind farm vessels spend the majority of their time stationary at the wind farm, and generally do not exceed 6-8 knots while amongst the turbines. This means energy storage can often be used as the sole power supply, thereby reducing fuel and maintenance costs as well as improving working conditions. As the crews are working at the turbines, there will be no noise, air pollution or vibration from the vessel.
Hybrid vs. Electric?
Electric: Full electric vessels usually require fixed power and cycle demand, and regular access to charging facilities (similar to ferry operations). Wind farm vessels often have unpredictable operational profiles, run on high speeds, and have no access to charging offshore, therefore full electrification is unlikely today.
Hybrid: Hybrid systems offer more flexibility for dynamic operational profiles. When used on a wind farm support vessel, the energy storage solutions is charged using shore power overnight. The vessel will transit through the harbour on battery power, operating in zero emissions mode. When high-speed transit is needed to reach the wind farms, the diesel engine/generator takes over. Many vessels have hours of waiting and loitering in the wind farms on standby. This low speed loitering, in a typical system, is done using inefficient load cycle for diesel engines. Inefficient loading leads to increased maintenance and reduced engine life. In a hybrid, this part of the operational profile is powered by the energy storage solutions. An added benefit is a quiet, vibration and emission free environment for vessel workers.
Hybrid Wind Farm Support Vessel Example:
Below is a typical duty cycle and standard vessel characteristics for an example wind farm support vessel that might be found working offshore.
Vessel: 20 m catamaran
Engine: 2×600 kW
Battery size: 390 kWh
Travel speed: 25 knots
Idling at wind farm: 6-8 knots
In this example, the vessel would typically spend 2 hours sailing to the field, 10 hours working, and 2 hours back again. The vessel goes out to the wind farm at 25 knots. When in operation at the wind farm, it would run solely on battery power at 6-8 knots or at idle, saving roughly 10 hours of idling run time per engine per day of operation, see figure 1.
Benefits of Hybridization:
The cost of energy storage in wind farm vessels must be determined on a project basis, but in the example above, the reduced fuel consumption and maintenance costs will achieve return on investment very quickly. Further, by using energy storage as redundancy, WFSVs will become much safer vessels, reducing risk by ensuring backup and work continuance. Modern lithium-ion energy storage is also capable of providing high power for extreme conditions and demanding situations.
The crew will benefit also; the electric motors run with less noise, vibration and have no fumes. Anecdotal reports show far less crew fatigue at end of shift, which may result in fewer lost man hours, fewer injuries and less risk to the machinery.