ALBERT

Description: The paper aims to investigate the holistic environmental benefits of using a battery system on a roll on/roll off (ro-ro) passenger ship which was originally fitted with a diesel engine engaged in Korean coastal service. The process of this research has multiple layers. First, the operating profiles of the case ship were collected, such as speed, output, operation time and the configuration of the diesel propulsion system. Second, the full battery propulsion system, in place of the diesel system, was modelled and simulated on a power simulation software (PSIM) platform to verify the adequacy of the proposed battery propulsion system. Then, the life cycle assessment method was applied to comprehensively compare the environmental footprint of the diesel-mechanical and fully battery-powered vessels. A focus was placed on the life cycle of the energy sources consumed by the case ship in consideration of the South Korea’s current energy importation and production status. Three life cycle stages were considered in the analysis: ‘production’, ‘transport’ and ‘use’. With the aid of Sphera GaBi Software Version 2019 and its extensive data library, the environmental impacts at the energy production and transport stages were evaluated, while the same impacts at the use stage were determined based on actual laboratory measurements. The environmental performance of the two scenarios in four impact categories was discussed: global warming potential (GWP), acidification potential (AP), eutrophication potential (EP) and photochemical ozone creation potential (POCP). Results of the comparative analysis are presented based on estimates of the overall reduction in the environmental impact potential, thereby demonstrating the overall benefits of using a battery driven propulsion, with a decrease of the GWP by 35.7%, the AP by 77.6%, the EP by 87.8% and the POCP by 77.2%. A series of sensitivity analyses, however, has delivered the important message that the integration of batteries with marine transportation means may not always be the best solution. The types of energy sources used for electricity generation will be a key factor in determining whether the battery technology can ultimately contribute to cleaner shipping or not. By casting doubts on the benefits of battery propulsion, this paper is believed to offer a meaningful insight into developing a proper road map for electrifying ship propulsion toward zero emission of shipping.

Description: Since recent marine application of fuel cell systems has been due largely limited to small-sized ships, this paper was aimed to investigate the technical applicability of molten carbonate fuel cell (MCFC) for medium and large-sized ships, using a 180 kW class hybrid test bed with combined power sources: A 100 kW MCFC, a 30 kW battery and a 50 kW diesel generator. This study focused primarily on determining whether the combined system designed in consideration of actual marine power system configuration could function properly. A case study was conducted with a 5500 Twenty-foot Equivalent Unit (TEU) container vessel. The operation profile was collected and analyzed in order to develop electric load scenarios applicable to the power system. Throughout the experiment, we evaluated the power quality of the voltage and frequency in the process of synchronization and de-synchronization across the power sources. Therefore, research results revealed that power quality continued to be excellent. This outcome provides insight into the technical reliability of MCFC application on large marine vessels.

Description: In the case of the electric propulsion system on the vessel, Diode Front End (DFE) rectifiers have been applied for large-sized ships and Active Front End (AFE) rectifiers have been utilized for small and medium-sized ships as a part of the system. In this paper, we design a large electric propulsion ship system using AFE rectifier with the proposed phase angle detector and verify the feasibility of the system by simulation. The phase angle derived from the proposed phase angle detection method is applied to the control of the AFE rectifier instead of the zero-crossing method used to detect the phase angle in the control of the conventional AFE rectifier. We compare and analyze the speed control, Direct Current (DC)-link voltage, harmonic content and measurement data of heat loss by inverter switch obtained from the simulation of the electric propulsion system with the 24-pulse DFE rectifier, the conventional AFE rectifier, and the proposed AFE rectifier. As a result of the simulation, it was confirmed that the proposed AFE rectifier derives a satisfactory result similar to that of a 24-pulse DFE rectifier with a phase shifting transformer installed according to the speed load of the ship, and it can be designed and applied as a rectifier of a large-sized vessel.

Description: The need for technological development to reduce the impact of air pollution caused by ships has been strongly emphasized by many authorities, including the International Maritime Organization (IMO). This has encouraged research to develop an electric propulsion system using hydrogen fuel with the aim of reducing emissions from ships. This paper describes the test bed we constructed to compare our electric propulsion system with existing power sources. Our system uses hybrid power and a diesel engine generator with a combined capacity of 180 kW. To utilize scale-down methodology, the linear interpolation method is applied. The proposed hybrid power source consists of a molten carbonate fuel cell (MCFC), a battery, and a diesel generator, the capacities of which are 100 kW, 30 Kw, and 50 kW, respectively. The experiments we conducted on the test bed were based on the outcome of an analysis of the electrical power consumed in each operating mode considering different types of merchant ships employed in practice. The output, fuel consumption, and CO2 emission reduction rates of the hybrid and conventional power sources were compared based on the load scenarios created for each type of ship. The CO2 emissions of the hybrid system was compared with the case of the diesel generator alone operation for each load scenario, with an average of 70%~74%. This analysis confirmed the effectiveness of using a ship with a fuel-cell-based hybrid power source.

Description: In the case of DC power distribution-based variable speed engine synchronous generators, if the output reference voltage is kept constant regardless of the generator engine operating speed, it may cause damage to the internal device and windings of the generator due to over-flux or over-excitation. The purpose of this study is to adjust the generator reference voltage according to the engine speed change in the DC distribution system with the variable speed engine synchronous generator. A method of controlling the generator reference voltage according to the speed was applied by adjusting the value of the variable resistance input to the external terminal of the automatic voltage regulator using a neural network controller. The learning data of the neural network was measured through an experiment, and the input pattern was set as the rotational speed of the generator engine, and the output pattern was set as the input current of the potentiometer. Using the measured input/output pattern of the neural network, the error backpropagation learning algorithm was applied to derive the optimum connection weight to be applied to the controller. For the test, the variable speed operation range of the generator engine was set to 1100–1800 rpm, and the input current value of the potentiometer according to the speed increase or decrease within the operation range and the output of the voltage output from the actual generator were checked. As a result of neural network control, it was possible to confirm the result that the input current value of the potentiometer accurately reached the target value 4–20 mA at the point where the initial speed change occurred. It was confirmed that the reference voltage was also normally output in the target range of 250–440 V.

Description: Kesterite-structured Cu2ZnSnSe4 (CZTSe) is considered as one of the Earth-abundant and non-toxic photovoltaic materials. CZTSe films have been prepared using a single-step co-evaporation method at a relatively low temperature (i.e., below 500 °C). Due to the volatile nature of tin-selenide, the control over substrate temperature (i.e., growth temperature) is very important in terms of the deposition of high-quality CZTSe films. In this regard, the effects of growth temperatures on the CZTSe film morphology were investigated. The suitable temperature range to deposit CZTSe films with Cu-poor and Zn-rich compositions was 380–480 °C. As the temperature increased, the surface roughness of the CZTSe film decreased, which could improve p/n junction properties and associated device performances. Particularly, according to capacitance-voltage (C-V) and derived-level capacitance profiling (DLCP) measurements, the density of interfacial defects of CZTSe film grown at 480 °C showed the lowest value, of the order of ~3 × 1015 cm−3. Regardless of applied growth temperatures, the formation of a MoSe2 layer was rarely observed, since the growth temperature was not high enough to have a reaction between Mo back contact layers and CZTSe absorber layers. As a result, the photovoltaic (PV) device with CZTSe film grown at 480 °C yielded the best power conversion efficiency of 6.47%. It is evident that the control over film growth temperature is a critical factor for obtaining high-quality CZTSe film prepared by one-step process.