Boost DC-DC converters are used in many renewable energy sources including photovoltaic and fuel cell. They are also used in Uninterrupted Power Supply, inverters, electric vehicles and robots. In this paper a boost converter was built and its controller was developed using proportional integral (PI) action for current loop and low pass filter (LPF) for voltage loop. The controller was derived analytically based on small signal model. Experiment results show that the boost controller functions well in regulating the output voltage under a variation of load. During the start up without any load it can elevate input voltage from 119.6V to output voltage of 241.6V. The developed controller can regulate the output voltage smoothly under load variation from no load to sudden load of 352W. When a large sudden load change happens from 0W to 1042W the output voltage experiences small drop before it is recovered to 241.6V. It can be concluded that the developed control system satisfies the design specification.

The water is very important to human lives. The best and most appropriate way to have an adequate supply of water is to use solar energy to drive pumps instead of using fossil energy. This research was conducted as a comparative study of a conventional submersible AC motor-pump driven by a photovoltaic system using two types of AC motor which are single-phase and three-phase submersible water pumps. The performance of the system was measured according to the standard test procedure in IEC 62253: 2011 while the depth of the well was simulated by an adjustable pump discharge pressure and a pump installed in a predetermined location of 40 meters. The results showed that the three-phase pump supplied more water and has a good response as indicated by a low irradiance of approximately 75 Watt/m 2 in the morning, around 06.15 AM which runs the pump motor effectively while the one-phase pump required a higher irradiance of 750 Watt/m 2 at around 10.30 A.M. Moreover, the PVWPS system with the three-phase pump also had higher efficiency and PR values with 0.64 and 0.40598 respectively than the system with the single-phase with 0.48 and 0.21388.

The unpredictable weather in Indonesia results in a less effective conventional coffee beans drying process, which usually uses solar energy as a heat source. This experiment aimed to examine the performance of the coffee beans drying using low-temperature geothermal energy (LTGE) with solar energy as the energy source. Heat pipe heat exchanger, which consists of 42 straight heat pipes with staggered configuration, was used to extract the LTGE. The heat pipes have 700 mm length, 10 mm outside diameter with a filling ratio of 50%, and added by 181 pieces of aluminum with a dimension size of 76  mm × 345  mm × 0.105 mm as fins. LTGE was simulated by using water that is heated by three heaters and flowed by a pump. Meanwhile, to simulate the drying process with conventional methods, a system of solar air collectors made of polyurethane sheets with a thickness of 20 mm and dimensions of length × width × height = 160 cm × 76 cm × 10 cm, respectively, was used in this study. Zinc galvalume sheet with 0.3 mm thickness was installed and coated by the black doff color throughout the inner of the container wall. The result showed that the drying process with LTGE and solar energy is faster than with solar energy or geothermal energy only. The drying coffee beans using the hybrid system can speed up the drying coffee beans time by about 23% faster than the solar energy only.

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