Offshore vessels offer an attractive business case for hybrid power solutions incorporating batteries. In many operational situations the on-board power demand fluctuates greatly, placing extreme loads on the generating equipment. While the common diesel-electric power and propulsion systems are quite flexible, they tend to operate inefficiently when running at very low loads for extended periods of time while occasional peak loads are expected. Furthermore, battery systems can provide backup power to meet the strict redundancy requirements for dynamic positioning (DP).
During the conference of the Maritime Battery Forum in Flåm, Norway, a number of key challenges for battery systems on board ships were discussed in depth. Manufacturers must meet a variety of regulations and requirements, and standardization is an urgent concern to overcome cost hurdles. Questions regarding economic feasibility, battery capacity, reliability and safety, and specific applications must be answered for the industry to embrace the technology.
These are precisely the topics two industry initiatives have been addressing: FellowSHIP IV, a two-year joint project of DNV GL, Wärtsilä Norway and Eidesvik Offshore, is studying the applicability of maritime hybrid battery power systems under a life cycle perspective; and the recently completed joint industry project (JIP) “Hybrid Power” formed by DNV GL, Taratec Corporation, BG Group, Seacor Marine, ABB, Samsung Heavy Industries, Cummins, C-Rate Solutions and the University of Sao Paulo, has assessed barriers to the adoption of hybrid power, associated technical challenges and potential benefits.
The FellowSHIP IV project, which is scheduled to end in 2017, uses continuous condition and performance measurements conducted on a 442 kWh Li-ion battery system on board the platform supply vessel (PSV) Viking Lady to gain insight into the actual operation of a maritime battery system. In addition a variety of simulations are being performed to draw conclusions regarding fuel savings, emission reductions, power management strategies, design improvements, operational benefits, cost-saving potential and competitive advantages.
The Hybrid Power JIP, tasked with challenging established industry practices and determining the best role for alternative power, has identified specific challenges and quantified all benefits of hybrid power systems. The team found that hybrid power architectures are technically feasible for tugs, OSVs, shuttle tankers, and drill ships, with viable return on investment (ROI) and payback periods. In view of the current economic climate in the oil and gas sector, retrofits are the primary market opportunity while newbuilds will move into focus once oil prices recover. There are currently about 52 DNV GL-classed vessels in operation or under construction with Li-ion batteries as a power source.
Fuel savings and emission reductions
The JIP team analysed four ship types with selected operational profiles to quantify the fuel, emissions, and reliability benefits of hybrid power, including dynamic positioning, industrial services such as drilling, propulsion and backup power. The result is a multifaceted value proposition: operational efficiency is improved by balancing diesel engine loads and avoiding wasteful idling periods; reducing engine running time also cuts CO2 and other noxious emissions. Redundant engines may be dispensable if the battery system functions as a spinning reserve. Avoiding cycles of extreme engine loads reduces engine wear and maintenance costs and may allow maintenance cycles to be extended. What is more, the ability to close the tie switch between buses can greatly improve the hybrid value proposition.
Reliability and operational safety
Batteries can be optimized either for fuel efficiency or for backup power, depending on the given application. In hybrid DP operations, batteries can supply load for approximately one third of the operating time, reducing generator cycles and responding faster than a generator set. As for backup power applications, economic feasibility depends on the ratio of investment cost vs desired duration of backup power availability.
Fire safety is a key concern for battery rooms, which must be designed to be functionally independent of the conventional architecture of the vessel, with fully independent ventilation, cooling and fire suppression systems and a sophisticated, integrated control system.
Payback times for battery systems range between zero and 7,700 engine operating hours. Efficiency improvements of up to 34 per cent were achieved in model studies. Hybrid power technology thus offers tangible benefits; whether they can be reaped will depend on the regulatory environment and a high-quality supply chain.