THE SIMULATION OF WAVE ENERGY CONVERSION BY FLOATING POINT ABSORBER BUOY IN INDONESIAN SEA WAVES

• Main Author: Aji, Nurvita
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/61833
• Institution: Institut Teknologi Bandung

The sea wave has the potential to be used as a source of alternative energy. The energy density of sea wave farms is 2-3 kW/m2, higher than solar parks (0.1-0.2 kW/m2) and wind farms (0.4-0.6 kW/m2). Besides, sea wave energy is available 90% of the time, whereas solar and wind power availability is hardly 20-30% times. Therefore, sea wave energy is considered a renewable and sustainable energy source, especially in Indonesia, based on the fact that its sea area (about 7.9x106 km2, including an Exclusive Economic Zone) constitutes about 81% of the country's total area. This study presents the simulation of ocean wave energy conversion of Indonesian sea waves, specifically along the west coast of Sumatra, the southern coasts of Java, and Bali waters using Wave Energy Converter Simulator (WEC-Sim). WEC-Sim is an open-source code for modelling wave energy converters. The code is written in MATLAB/Simulink and uses the multi-body dynamics solver. This simulator uses the Cummins equation in the 6 degrees of freedom (DOF) modelling process. The floating-point absorber buoy RM3 model simulated five hot spots with the high potential wave energy. These five hotspots are South Pagai Island II (101.25oE- 4.25oS), Enggano (102.25oE-5.5oS), Cilacap (109.06oE-7.94oS), Jember (113.68oE- 8.56oS), and Bali (115oE-8.75oS). RM3 consists of a float and a spar/plate coupled to a central column, and it converts energy from the axial motion between these components induced by ocean waves. Modification of mass and moment of inertia on float and spare/plate was carried out to determine its effect on the output electrical power. In this simulation, the Pierson-Moskowitz (PM) spectrum was used to model irregular waves. The WEC's power take-off (PTO) mechanism was simulated as a hydraulic system. It consists of a hydraulic cylinder, a check valve, a hydraulic motor, hydraulic accumulators, and hoses to connect the various components. Besides, hydraulic PTO forces were affected by the total force of WEC bodies (float and spar/plate). Based on the simulation, Hydraulic PTO yields the PTO force interval between -0.2 and 0.2 MN in the five selected locations. The simulation ran for 400 seconds of time simulation and 0.01 seconds of time step with the predefined parameters, such as significant wave height and wave period. The average absorbed power by the WEC device is in the range of 21.13 to 26.18 kW. Meanwhile, the range of average mechanical power is from 17.02 to 21.53 kW, and the range of average electrical power is from 14.10 to 18.13 kW. The average value of electrical powers generated during the simulation were 15,84; 15,53; 18.13; 14,10; 15,69 kilowatts (kW) or 129.34; 126.71; 147.96; 115.09; 128.02 megawatts hours (MWh) per year for South Pagai Island II, Enggano Island, Cilacap, Jember, and Bali. Based on Indonesia National Energy Council (DEN) report, electricity demand per capita in 2018 was 964 kW. It means a unit of RM3 buoy is sufficient to provide electricity from between 116 to 148 individuals. The addition of mass and moment of inertia by 25% on the float and a reduction of 0.75% on the spar/plate can increase the electric power by an average of 11.65% - 12.48%. This modification is proven to be able to increase output electrical energy per year to 129.46 MWh - 165.19 MWh or equivalent to electricity needs for 134 to 171 individuals. The WEC device location that generated the highest average electrical power is Cilacap, with the highest significant wave height value. On the contrary, Jember, which has the lowest significant wave height value, generated the lowest average electrical power. It means that the significant wave height is a crucial parameter to determine the output power of the wave energy. In conclusion, Indonesian sea waves are great potential and promising locations to implement WEC devices in the future.