An energy storage life cycle cost study for maritime vessels
Diesel-electric propulsion is a concept that uses an electrical power generation plant to deliver power to the propulsion unit. Previous case studies that The Shearer Group Inc. (TGSI) have produced show potential reductions in fuel and maintenance costs with such systems. Those improvements can be further enhanced by the addition of an energy storage system to the vessel.
There are many configurations and options available to fit a wide variety of requirements. Naval architects can work with the systems engineers for these manufacturers to determine the best system for a particular application, no matter the needs or requirements.
Diesel-Electric with Energy Storage (DE/ES) systems and Hybrid with Energy Storage (H/ES) systems
For typical marine applications, the use of Lithium Ion batteries will add spinning reserve, peak shaving, and efficient engine loading to increase the overall efficiency of the vessels. With those system improvements, operators will experience an overall reduction in engine hours, fuel consumption, and maintenance costs while improving the responsiveness and reliability of the vessel’s propulsion system. These benefits can be realized with a variety of propulsion systems, including both Z-drives and conventional shafted propellers.
A Diesel-Electric with Energy Storage (DE/ES) system operates by having the batteries provide power to the grid at all times. With the batteries controlling the power grid, the power management system (PMS) monitors the state of charge on the batteries, discharge rate, and demand loads. The PMS then manages the generators to provide appropriate power to the grid to keep the batteries properly charged. The “always online” approach to energy storage provides the best overall system performance. The batteries provide the spinning reserve and dynamic response so the DE/ES system can deliver power even faster than mechanical propulsion systems instantaneously.
Hybrid with Energy Storage (H/ES) systems make use of a mechanically driven shaft line with a power take off and power take in connected to a motor/generator (M/G) set. The M/G set can take power from the ships electrical system and/or energy storage to provide additional power to the propeller shaft. A hybrid system such as this can be especially attractive as a retrofit option for existing vessels.
Storage systems should not be considered a one-size-fits-all solution. As with diesel-electric propulsion systems, a careful study of a towboat’s operational profile should be conducted to determine the operational benefits.
Which system is right for your vessel?
A DE/ES system may increase the initial capital costs of the towboat due to the cost of the batteries and associated battery equipment. The fuel savings for the DE/ES system is achieved mostly through the functions of peak shaving and efficient engine loading. By using peak shaving and dynamic response, the overall number of engine hours can be reduced thereby reducing maintenance costs. The initial capital cost of the DE/ES system are nearly offset in the first year of operations through a combination of fuel and maintenance cost reductions. TSGI has analyzed a number of profiles from operators, some returning fuel savings greater than 20% and more than 30% reduction in lifecycle maintenance costs.
While the fuel and maintenance costs are brought down with the use of peak shaving, reliable operation is enhanced with the spinning reserve and dynamic response characteristics of an energy storage solution. In the event of an engine failure, the batteries provide continuous operations while more power is brought online, effectively acting as an uninterrupted power supply for the entire vessel. Such systems can significantly reduce overhaul times. For both the diesel-electric and DE/ES systems, replacing a generator performed quicker than replacing a main diesel engine.
A DE/ES system may not be a viable solution for all vessel owners. Savings over the life of the vessel can be significant with a properly designed system. TSGI recognizes that fuel savings may not return any benefit to the vessel owners depending on contract structure. TSGI expects that the inland market will follow the same pattern that other parts of the marine industry have started to experience, with charterers and commodity owners requesting more fuel-efficient vessels instead of just accepting higher fuel surcharges.
To learn more about cost savings in fuel and maintenance costs by using diesel electric propulsion, click here.
