Credit: Hapag-Lloyd AG
TWO-STROKE ENGINES
PEAK SHAVING The white paper assessed the viability of peak shaving which keeps the engine load constant while peaks in the required power are supplied by a battery - for a main engine equipped with a PTO/PTI and a battery. A modelling simulation was carried out using a 6G70ME-C9.5 engine with an SMCR of 15,570 kW at 72 rpm. The mean SFOC was calculated by integrating the total injected fuel mass and the energy delivered by the crankshaft. The integration was performed in an SFOC evaluation window of 100 seconds. The study assessed that transmission and conversion losses in the electric generator and motor, which were estimated at 10% or around 1% of the overall load, exceeded the 0.4% SOFC savings achieved by peak shaving. BARRED SPEED RANGE A separate discussion concerned the potential applicability of energy storage systems to permit passage through the barred speed range. The topic is topical as tankers and bulk carriers are reducing the installed power on board to meet EEDI requirements, reducing the amount of power available to accelerate the shafting and the vessel. The white paper provides a detailed explanation of the potential applicability of an ESS or auxiliary engine to boost the acceleration of the shafting through the barred speed range. MAN ES notes that the in the case of adverse weather conditions, a battery solution would not be able to keep the operational point of the main engine above the barred speed range for an extended period. An alternative option during adverse weather conditions would be to utilise energy from the auxiliary engines to provide additional torque to the shaft via a PTI. BENEFITS OF BATTERY HYBRID SYSTEMS IN THE ELECTRIC GRID The white paper concludes with an overview of the potential application of energy storage systems into the electric grid aboard a deep-sea vessel. The potential for achieving savings by using a battery as a spinning reserve every time two or more auxiliary engines
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run at constant low load for safety purposes is identified. This can optimise the fuel consumption of the auxiliary engines by increasing the load on the engine by running only one of them. By operating auxiliary engines closer to their optimal load, it increases their efficiency, reduces their operating costs and lowers maintenance. Meanwhile, the potential of peak shaving of auxiliary engines (or more) is examined. A battery installed for peak shaving leads to an operating cost reduction from acting as spinning reserve as well, as it will be possible to limit the time during which two auxiliary engines operate simultaneously. MAN noted that introducing a high-power 217kWh energy storage system capable of operating for 15 minutes (sufficient to avoid blackouts and to restart a tripped auxiliary engine) in addition to three auxiliary engines would cost USD108,500 at current ESS prices, with a payback period of around 6 years. If ESS prices fall to close to USD250/kWh, the cost of the installation would halve, as would the payback period. By comparison, the commonly assessed solution of replacing an auxiliary engine with a larger capacity ESS would have a higher cost, and a payback period of over 14 years. 8 The costs of peak shaving outweighed the benefits in modelling of the applicability of ESS systems based on MAN's 70-bore ultra long-stroke G-type engine
Credit: MAN Energy Solutions
solutions to reduce the energy consumption more attractive on large vessels
8 Supplying a 20,000 teu container vessel such as the Barzan (pictured) via a shore power connection would require 256MWh of energy per port call
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