By George Roddan
Commercial vessels operating in and around the world's ports have been identified as being responsible for a significant element of the total daily air pollution for a given surrounding area.
This pollution has been associated with an increased incidence of respiratory-related disease, in addition to increased greenhouse gas emissions. Governments and regulatory bodies are now focused worldwide on reducing the marine component of pollution in these heavily used ports.
Harbor craft are typically powered by diesel engines regulated by the US Environmental Protection Agency (EPA), whose emission regulations for the new marine engines require the use of low sulphur fuel and other strategies to improve emission profiles. Future EPA regulations are becoming even more stringent and are aggressively geared toward simultaneous reduction of toxic air contaminants, particulate matter (PM) and nitrogen oxides (NOx), as well as greenhouse gas emissions (CO2).
One available solution to achieve these emissions standards is the use of a number of propulsion sources in one vessel (also known as the hybrid propulsion). This technology is not new to the marine world; diesel electric ships and submarines have been common for more than sixty years. These vessels are driven by an electric motor which derives energy from diesel generators, or batteries in the case of the submarine.
Advances in hybrid propulsion technology are accelerating the solution to both emissions and energy efficiency in the marine industry. For certain types of craft, such as the harbor tug, which spends most of its time loitering or in transit at low loads, followed by short bursts of high bollard pull, a hybrid solution can achieve real emissions reductions of particulate matter, carbon monoxide and nitrogen oxides by 50 percent or more, and fuel savings of about 25percent. This is accomplished through the use of a combination of smaller more efficient diesel engines coupled to electric drive systems and a battery bank to assist in the intermittent high load situations.
Other vessels and equipment can benefit from the use of hybrid technologies, depending on the application, including ferries, fishing vessels and port machinery. The return on investment for a successful marine application can be as little as 2 years, which is a compelling reason to seriously consider this option, which also provides significant environmental benefits.
Battery Storage for Marine Hybrids
Hybrid marine applications provide a unique challenge for electrical storage systems, and these challenges are the basis for a new Pacific Northwest industry. The PNW has a long history of marine industrial activity and experience. More recently there has been intense activity in the high tech sectors of electrical power management and advanced battery development. New technology and battery systems development have provided a basis for the marine industry to now look seriously at integrating these advances into projects that require high energy density and power.
The Technology - Lithium Ion Battery Systems
Currently, a state-of-the- art lithium-based battery cell technology is being integrated by Corvus Energy Ltd. to provide a high-density electrical energy storage solution that is safe, reliable and readily adapted to the marine environment.
The team of engineers at Corvus Energy has extensive experience in marine design and powertrain development, as well as the production of battery storage systems for both automotive and undersea applications. Corvus engineers have worked in the fields of naval architecture and ship design, as well as undersea technology with manned and autonomous underwater vehicles.
Previous solutions to battery storage utilized lead-acid based technology. For most large scale applications, (over 200 kWh), the size and weight of the lead acid batteries makes them too un-wieldy and dangerous for marine installations. With recent advances, lithium ion battery technology becomes the choice for certain applications. Although the first cost of the lithium-based systems is high, the advantages of increased number of life cycles, low volume and extremely low weight provide incentive to develop high performance large-scale systems.
Based on life cycle costing, lithium battery systems are more economical than any other chemistry, and over the life of the battery pack become comparable in cost to grid power. This will be a key factor driving the adoption of lithium ion battery packs for years to come.
Li-ion System Benefits
Independently tested to achieve exceptionally high abuse tolerance, Li-ion batteries offer safety by way of inherent cell chemistry and design as well as patented battery management system.
With a wide operating temperature range between -20 degrees Celsius to 60 degrees Celsius, a 3,000 + cycle life and a 10 to 20 year calendar life, advanced lithium-ion battery systems ensure the reliable availability of power under all operating conditions.
Lithium-ion battery systems offer rapid charge and discharge rates, and can respond within milliseconds to required power and energy outputs. The Li-ion systems are scalable to meet different power and energy storage specifications ranging from 5 kWh all the way up to multiple megawatt sized banks.
Finally, lithium ion chemistry provides a clean and recyclable solution to high density storage as compared to the toxic alternatives of lead acid and nickel-metal hydrides. Lithium is non-toxic and 100% recyclable.
Local, state and federal governments worldwide continue to clamp down on maritime emissions. With many tug companies like Foss, Seaspan and Crowley either already using hybrid technology or developing hybrid vessels, lithium ion battery technology could power the next generation of harbor craft.
George Roddan has been involved in consulting and hydrodynamic design of marine craft for the last 28 years. He has extensive experience in physical model testing, computational fluid dynamics (CFD), and performance evaluation, as well as in detailed structural design and driveline engineering for all types of vessels.
