Research on natural-fiber-reinforced polymer composite is continuously developing. Natural fibers from flora have received considerable attention from researchers because their use in biobased composites is safe and sustainable for the environment. Natural fibers that mixed with Carbon Fiber and or Glass Fiber are low-cost, lightweight, and biodegradable and have lower environmental influences than metal-based materials. This study highlights and comprehensively reviews the natural fibers utilized as reinforcements in polyester composites, including jute, bamboo, sisal, kenaf, flax, and banana. The properties of composite materials consisting of natural and synthetic fibers, such as tensile strength, flexural strength, fatigue, and hardness, are investigated in this study. This paper aims to summarize, classify, and collect studies related to the latest composite hybrid science consisting of natural and synthetic fibers and their applications. Furthermore, this paper includes but is not limited to preparation, mechanism, characterization, and evaluation of hybrid composite laminates in different methods and modes. In general, natural fiber composites produce a larger volume of composite, but their strength is weaker than GFRP/CFRP even with the same number of layers. The use of synthetic fibers combined with natural fibers can provide better strength of hybrid composite.

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Nowadays, the hybridization of natural and glass fiber has promised several advantages as a green composite. Nevertheless, their different characteristics lead to poor mechanical bonding. In this work, agel fiber and glass fiber was used as reinforcements, and activated carbon filler was added to the polymer matrix of a hybrid composite to modify its characteristics and mechanical properties. A tensile and bending test was conducted to evaluate the effect of three different weight percentages of activated carbon filler (1, 2, and 4 wt%). Vacuum-assisted resin infusion was used to manufacture the hybrid composite to obtain the high-quality composite. The results have revealed that adding 1 wt% filler yielded the most optimum result with the highest tensile strength, flexural strength, and elastic modulus, respectively: 112.90 MPa, 85.26 MPa, and 1.80 GPa. A higher weight percentage of activated carbon filler on the composite reduced its mechanical properties. The lowest test value was shown by the composite with 4 wt%. The micrograph observations have proven that the 4 wt% composite formed agglomeration filler that can induce stress concentration and reduce its mechanical performance. Adding 1 wt% filler offered the best dispersion in the matrix, which can enhance better load transfer capability.

The transition from conventional fossil fuels to renewable energy is necessary, along with the increase in energy consumption and the decline in national energy production. In its application, increasing the renewable energy mix has many challenges, especially cost-efficiency. Thus, to make renewable energy competitive and achieve a significant acceleration of the mix, massive energy incentive policies are being studied and developed. This study provided a specific overview of policies and strategies for tariff incentives related to renewable energy, particularly in developing and developed countries. An essential section of this study discusses the comparison between Indonesia and other countries, as well as the current status and an ideal policy related to renewable energy for this country. The implementation of energy incentive policies in each country is quite different, depending on the potential, technological readiness, and political and economic conditions. Compared with other policy mechanisms such as RPS, FIT policies are more efficient at increasing capacity and stimulating R&D inputs to reduce costs. In terms of the stage of economic development and characteristics of the electricity system, the price adjustment model, such as that used in East Asia, is more suitable for application in Indonesia than other models.

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The failure of water wall tubes in a boiler steam power plant has been analysed. When the first inspection was conducted on the 25-Megawatt steam power plant, leakage was found on several water wall circulating fluidized boiler (CFB) tube. Visual examination, chemical composition analysis, hardness measurement, and metallographic examination on the tube samples cut from the water wall were used to analyse the cause of the failure. Visual examination showed that there is a thick weld joint on the tube inner side that could induce overheat and cause the tube to fracture and, in some locations, there were thick deposits on the tube inner side. A Hardness measurement of the tube near the fracture location showed an increase in the hardness value ranged from 191 – 206 HV. Metallographic examinations showed that there has been some micro-crack along the grain boundary. Composition analysis on the deposit at the inner side of the tube showed a trace of magnesium and calcium indicate that the water quality of the boiler doesn’t meet the standard. To resolve the problem, it is recommended to fix the weld procedure and kept the water quality to meet the standards.

Boiler is one of the critical parts and plays an important role in Steam Generation Power Plant. It transforms the chemical energy of fuel into heat or thermal energy. During plant operations, some problems occurred in the boiler and Superheater leakage is the heaviest problem that interfered the whole operations, and the units needed to stopped for maintenaces outages. Failure analysis is necessary to determine the cause of failure. Root Caused Failure Analysis methods was through mechanical tests in the laboratory, which is Visual Observation included Macrofractography Structure examination, Metallographic or Microstructure Examination, Hardness Test. The metallographic examination result shows that the microstructure of the base metal is ferrite pearlite, and there is no indication of microstructure changes in tube as effect from high operation temperature. Likewise, microstructure in the weld region is in normal conditions, no weld failure phenomenon. Hardness value for base metal, weld and HAZ area are still in a good condition. Macrofractrography structure examination shows that the fracture is in mechanical fatigue condition. Based on those results the source of the tube leak is not caused by operating errors, inside or outside deposit nor weld failure. Superheater tube failures caused by mechanical factors, namely due to cyclic tensile stress as result in vibration by gas flow coupled with an increase in the local area due to the welding heat, therefore, increases the rate of crack propagation. To verified the data from mechanical test, CFD simulation will be used. CFD can detect the direction of the gas flow around the Superheater tube. The simulation result shows the possibility of turbulence flow around the tube, which creates the vibrations on the tube due to gas flow velocity. Thus, the superheater tube leakage mostly because vibration that create cyclic tensile stress.