Applied Mechanics and Materials Vol. 839

Abstract: A novel technique has been developed for PV array internal resistance measurement while keeping the plant in operation in contrary to flash test or basic equation (E_b) for which the modules need to be disconnected from the system. We present an equation developed for the array’s internal resistance measurement for PV technologies namely Amorphous Silicon (a-Si), Poly Crystalline Silicon (p-Si) and Hybrid Crystalline Silicon (HIT). Monthly Measured I-V characteristic curves of PV Array were converted to Standard Test Conditions following the IEC 60891 standard. Multiple regression analysis and linear regression technique were used to develop the equation for estimating the PV array internal resistance. The developed equations (E_d) will find the relationships of the 4 variables that are Series resistance (R_s), Shunt resistance (R_sh), maximum voltage (V_m) and maximum current (I_m). The results revealed that the E_d can be applied to measure the PV array internal resistance value with low error margin than E_b. The series resistance calculated using E_d is higher than E_b about 1.11 %, 1.88 % and 0.87 % for a-Si, p-Si and HIT respectively. The shunt resistance calculated using E_d is higher than E_b about 0.07 %, 0.09 % and 0.09% for a-Si, p-Si and HIT respectively.

Abstract: This paper presents the analysis and design of a dual active bridge DC-DC converter for fuel cell applications. The zero voltage switching operating condition of such converter is analyzed to select an appropriate turn ratio of the high frequency transformer for a high efficiency operation. The ratio between the output voltage to the fuel cell voltage should be close to the transformer turn ratio to guarantee the zero voltage switching regimes at a light load. The prototype converter was designed to be suitable for the input voltage of 40 to 65 V and output voltage of 360 to 400 V with the transformer turn ratio of 7.33. The converter was tested with a 48 V DC power supply and with a polymer electrolyte membrane fuel cell stack. The maximum power of 700 W was delivered and the efficiency was better than 94% for the whole load range.

Abstract: In order to control humidity in air conditioning system, various desiccants are used to dehumidify air in air conditioners. One of simple methods, which can be used to coat desiccant materials on surface of heat exchanger in air conditioners, is dip coating. Typical, desiccants used in dehumidifying system is silica gel in a form of solid-state powder. This powder has low adhesion with the heat exchanger surface. To improve adhesion of the silica gel powder, some glue is generally applied on the surface of heat exchanger. The dehumidification properties of silica gel, however, will be remarkably reduced because of less surface area of silica gel powder. Instead of silica powder, this work aims to synthesize silica gel using sol-gel method, which the sol-state material can be suitably used in dip coating. In experimental study, silica gel was synthesized by sol-gel method of precursors with 1 M sulfuric acid (H₂SO₄). The pH was adjusted using sodium silicate solution (Na₂O(SiO₂)_x.xH₂O) and rinsing with DI water. Surface area, pore volume and size, phase composition, morphology, and percentage of moisture adsorption of the synthesized silica gel were characterized. Silica gel fabricated with pH 5 showed the highest percentage of moisture adsorption compared with other samples. In addition to the highest percentage, silica gel with pH 5 could adsorb water up to 28 times of its own weight. X-ray diffraction (XRD) results showed that Na₂SO₄ impurity were successfully eliminated after rinsing with DI water more than 4 times. Finally, adhesive property of silica gel on aluminium-fin samples was tested with scalloped tape-test method. It was observed that, to improve the adhesion property of silica gel on the aluminium fins, prior to dipping of silica gel, the fins should be etched with sulfuric acid. The acid can adjust the surface of fines to be much rougher.

Abstract: Biomass plays an important role in reducing fossil energy. It can be utilized in different ways and one of its usages is to produce electricity. However, to benefit from the gains of using biomass power generation, there are several obstacles to overcome for its competent utilization. The performance of community based biomass power plants (CBP) was studied to access the feasibility and sustainability aspects that caused energy security. The objective of this study was to identify the key factors affecting to CBP establishment. The authors designed the tests to make a comprehensive study considering all the factors published in the Science Direct Database during January 2004 to September 2014. The data was obtained using multi-stage sampling from 1,151 people dwelling in the local community. A questionnaire was used as a tool for collecting the data. The output factors were confirmed by undertaking the Structural Equation Modeling (SEM) analysis. The results show a significant influence on 1) technology of biomass gasification power plant; 2) biomass residues; 3) community; and 4) government, policy and investment at p < 0.05. These findings therefore identified the key factors affecting establishment for biomass electricity generation in Thailand. This in turn has helped bring about the causal model for establishing biomass power plant based on sustainability.

Abstract: Biodiesel is a diesel equivalent fuel produced from biological feed stocks, acting as a substitute for petroleum or fossil diesel. Biodiesel production in Thailand began in 2005, with prices stabilizing after 2008. Biodiesel, along with other biofuels, plays a role in Thailand’s Alternative Energy Development Plan (AEDP). The purpose of this study is to examine factors in the Thai biodiesel prices (2009-2014). The study assessed factors in downstream biodiesel prices at consumer locations like gas stations. The price factors assessed in the study included ex-refinery prices, excise taxes, municipal taxes, oil fund contributions, energy conservation fund conributions, marketing margin and exchange rate (USD). Regression results showed that all of these factors were significant (r² = 0.867). The implication of the study is that while most of the retail price of biodiesel in Thailand is attributable to cost factors, there is some unexplained variance in price. This offers an opportunity for future research.

Abstract: The subject of this article takes benefit from advanced shading technology thought the integration of anidolic collector at clerestory window of building for achieving increment of daylight flux entering into the rear area of the room. This technology is likely to investigate the influence of clerestory aperture on the performance of daylighting collector in term of the interior daylight illuminance distribution by using the lighting tool AGi32. The empirical correlations from the use of anidolic configurations for tropical sky are proposed with high confidence interval (>85%).

Abstract: This present study reports results of performance evaluation of a solar-driven dual parallel-connected ejector (DPE) cooling system using the concept of solar fraction (SF). The experiments were conducted in July and August, 2015 from 09:00 to 16:00 hours at School of Renewable Energy Technology (SERT), Naresuan University, Thailand, with a solar collector area of 2.4 m², auxiliary heater of 3 kW, operating at boiler pressure of 2 bar and using water as working fluid. Temperature was measured for inlet and outlet of solar collector. The results showed that the solar collector supplied about 24% of energy required to operate the system. The solar collector performance was 11% and the monthly average SF was 23.9% for July and 23.5% for August.

Abstract: Nowadays, developing solar cooling technologies, especially ejector refrigeration system, has become preferable to scientific researchers. Exergy analysis is a technique in which the basis of evaluation of thermodynamic losses follows the second law rather than the first law of thermodynamics. An experimental exergy analysis of a solar-driven dual parallel-connected ejector (DPE) refrigeration system was conducted using water as working fluid. Saturated steam with 2 bar and 120oC was provided by heat–pipe evacuated tube solar collector with an assistant of an electric heater. The saturated stream was used as a motive flow for the ejectors. The exergy destruction and exergetic efficiency of the main components of the DPE refrigeration system were determined and compared with those when using a single ejector (SE) under same operating conditions. It was found that the most irreversibilities of both systems occurred at the solar collector, electric boiler and ejectors, respectively. Also, the total irreversibility (Exergy destruction) of the system when using DPE was lower than using a SE. In additions, the exergetic efficiency of the ejector, evaporator, and overall system when using DPE were increased by 21%, 10%, and 27%, respectively. The system thermal ratio (STR) and coefficient of performance (COP) of the system using DPE compared with SE were increased by 20% and 23%, respectively.

Abstract: An innovative software has been developed to measure and identify energy flow for multiple loads and sources like Grid and or other renewables. Algorithms have been developed to indicate status of energy used within a building unit and the Smart Gird as a whole. The software is developed on the AngularJS bases in the model-view-controller (MVC) platform using PHP language and MySQL is used as database for recording the data. The results of this research can support Electricity Generating Authority of Thailand (EGAT) for future grid planning and can be helpful for adaptive forcasting in connection with the consumption and generation. In the future, this software could be applied to improve the functions of energy management system (EMS) in the homes, buildings, and offices.

Abstract: Thailand is located in the tropical zone dominated by monsoons for more than six months in a year. These climatic conditions illustrate elevated relative humidity and temperature that contributes to Potential Induced Degradation (PID). Humidity has been reported to be potential cause of degradation in the systems with high voltages. Moisture helps leakage currents in passing through laminate permeation and back sheet from cell to ground frame. The PID occure in PV systems when connected in series using DC voltages of high orders. This research shows comparisons of both PV systems, with negative grounding and floating grounding with a system voltage about 800 Vdc. Investigations of insulation resistance (MΩ) in PV strings and modules after two years operation has been done. It was found that the decrement in average insulation resistance (MΩ) of PV string using negative grounding, floating grounding was 14.5 MΩ, 11.0 MΩ and average leakage current per string was 68.9 µA, 90.9 µA respectively. Moreover, the wet leakage current per module showed the decrement in average insulation resistance (MΩ.m²) was 174 MΩ.m², 133 MΩ.m² and average leakage current per module was 5.75 µA, 7.51 µA respectively.