Simple thermal-electrical model of photovoltaic panels with cooler-integrated sun tracker

This paper presents a simple thermal-electrical model of a photovoltaic panel with a cooler-integrated sun tracker. Based on the model and obtained weather data, we analyzed the improved overall efficiency in a year as well as the performance in each typical weather case for photovoltaic panels with fixed-tilt systems with a tilt angle equal to latitude, fixed-tilt systems with cooler, a single-axis sun tracker, and a cooler-integrated single-axis sun tracker. The results show that on a sunny summer day with few clouds, the performance of the photovoltaic panels with the proposed system improved and reached 32.76% compared with the fixed-tilt systems. On a sunny day with clouds in the wet, rainy season, because of the low air temperature and the high wind speed, the photovoltaic panel temperature was lower than the cooler’s initial set temperature; the performance of the photovoltaic panel with the proposed system improved by 12.55% compared with the fixed-tilt system. Simulation results show that, over one year, the overall efficiency of the proposed system markedly improved by 16.35, 13.03, and 3.68% compared with the photovoltaic panel with the fixed-tilt system, the cooler, and the single-axis sun tracker, respectively. The simulation results can serve as a premise for future experimental models

SÀNG LỌC HOẠT TÍNH KHÁNG OXY HÓA CỦA MỘT SỐ LOÀI RONG NÂU SARGASSUM Ở KHÁNH HÒA, VIỆT NAM

Bài báo này thể hiện kết quả sàng lọc hoạt tính chống oxy hóa của 5 loài rong nâu S. angustifolium, S. aemulum, S. assimile, S. feldmanii và S. ilicifolium ở tỉnh Khánh Hòa. Hoạt tính chống oxy hóa được đánh giá dựa trên các hoạt tính chống oxy hóa tổng, khử Fe và DPPH. Đồng thời cũng chỉ ra hàm lượng phlorotannin/ polyphenol tương ứng ở trong các loài rong này. Những loài này được thu mẫu vào thời gian thành thục sinh sản của chúng. Kết quả cho thấy hàm lượng phlorotannin/ polyphenol ở rong S. angustifolium là cao nhất. ở 5 loài nghiên cứu, hoạt tính khử Fe thể hiện mạnh hơn các hoạt tính khác, hoạt tính khử Fe của S. angustifolium là cao nhất. Hoạt tính bắt gốc tự do DPPH dao động trong khoảng 50% - 96%

Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial

Background Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population. Methods AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921. Findings Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months. Interpretation Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke

A simplified calculation method of electric linear actuators for single-axis sun tracker

At present, the use of small roof-mounted photovoltaic systems is increasingly popular, so the development of a sun tracker to increase the efficiency of the photovoltaic system is essential. In this paper, we give the size analysis of a linear actuator and also its selection method for a single-axis tracker. In addition, we also provide the analysis of the power and energy of the linear actuator and its controller on a typical sunny day

The Impact of Electrical Energy Consumption on the Payback Period of a Rooftop Grid-Connected Photovoltaic System: A case Study from Vietnam

Recently, the use of small-scale grid-connected photovoltaic (GCPV) systems for households has been growing in Vietnam. The installation of a rooftop GCPV system provides many benefits to households, such as lowering monthly electricity bills, reducing absorbed heat of the building, and creating additional income by penetrating electric power to the grid. However, the technical issues of the payback period is complicated and requires a lot of considerations. The main goal of this study is to develop a computational model and investigate the effect of electrical energy consumption on the payback period of rooftop GCPV systems. A case study is used in this study to create a model of a rooftop GCPV system for households in north-central Vietnam under feed-in tariff (FiT) schemes. The results show that the investment rate and electrical energy consumption of the installed household have a strong influence on the payback period of the GCPV system. In the case of the lowest investment rate of 666.4 USD/kWp, the fastest payback period is 43 months for households consuming all of the generating energy of the GCPV system, and the longest payback period is 131 months for households that do not use electricity, implying that all of the generating energy of the GCPV system is connected and sold to the distribution grid. The research findings will actively assist in calculating the installed capacity suitable for households in order to have the most suitable payback period while also assisting policymakers in the future in setting a reasonable rate of feed-in tariff for rooftop GCPV system

Influence of Single-Phase Voltage Loss and Load Carrying Mode on Mine Drainage Pump Motor in Vietnam

Mine drainage pump is the most important load in mining which requires high reliability when operating. Currently, the power supply of a mine drainage pump is connected to the same power line with many nonlinear loads, and is equipped with power electronic converters, which makes the power supply nonsinusoidal. During the working process of a mine drainage pump, the load-carrying factor often changes, and many types of failures occur, among which single-phase voltage loss is the most common problem. In the case of a nonsinusoidal power supply, if a single-phase voltage loss occurs in different load modes, it will greatly affect the working mode of the mine drainage pump leading to influences on the working efficiency, the life of the pump, and sometimes it is necessary to recalculate the protection parameters. This paper studies the influence of single-phase voltage loss and load carrying mode on the working mode of mine drainage pump motor in case the of nonsinusoidal power supply. Research results show that, in the case of nonsinusoidal power supplied with single-phase voltage loss, copper losses in the rotor and stator circuits increase with increases in voltage total harmonic distortion (THD) and load-carrying factor, 5th order reverse harmonic increases copper loss in asynchronous motor the most, and higher harmonic components have less effect on copper loss in the motor. At the same time, the speed ripple decreases with the increase of the motor load factor and decreases in the presence of the 5th order negative sequence harmonic, and increases significantly in the presence of the 7th order positive sequence harmonic. 5th order negative sequence harmonic increases, the torque ripple increases, while the 7th order positive sequence harmonic reduces the torque ripple in the case of single-phase voltage loss. The results of the paper will help improve the operational efficiency of the mine drainage pump in Vietnam's mines

Influence of Harmonics on the Working Efficiency of a 6/1.2 kV Transformer in a Pit Mine

Explosion-proof transformers 6/1.2 kV is important electrical equipment responsible for supplying electricity in underground mine electrical networks. A failure of this transformer will cause an interruption in the power supply and loss of safety in underground mining. Usually, explosion-proof transformers in underground mine electrical networks are designed and manufactured to work with ideal parameters such as sinusoidal currents, and the network structure is symmetrical. However, today in underground mine electric networks, many power electronics are connected to the network, such as inverters and soft starters. As a result, a current flowing through the transformer is non-sinusoidal, overloading the transformer even by working with the design specifications. This paper studies the influence of harmonics on the working efficiency of a 6/1.2 kV transformer in a pit mine. Research results suggest reasonable solutions for transformer operation to ensure longevity and not cause damage to the transformer

Influence of Harmonics on the Working Efficiency of a 6/1.2 kV Transformer in a Pit Mine

Explosion-proof transformers 6/1.2 kV is important electrical equipment responsible for supplying electricity in underground mine electrical networks. A failure of this transformer will cause an interruption in the power supply and loss of safety in underground mining. Usually, explosion-proof transformers in underground mine electrical networks are designed and manufactured to work with ideal parameters such as sinusoidal currents, and the network structure is symmetrical. However, today in underground mine electric networks, many power electronics are connected to the network, such as inverters and soft starters. As a result, a current flowing through the transformer is non-sinusoidal, overloading the transformer even by working with the design specifications. This paper studies the influence of harmonics on the working efficiency of a 6/1.2 kV transformer in a pit mine. Research results suggest reasonable solutions for transformer operation to ensure longevity and not cause damage to the transformer

Effect of Power Quality on the Performance of Explosion-Proof Transformers in Mining in Vietnam

When meeting customer demand, utility companies must consider power quality. Currently, the industrial power network in general and the underground mine power network in particular have long feeder lines, supplying power to many nonlinear loads and power electronic converters, which reduces power quality. Poor power quality can damage sensitive equipment and lead to costly repairs, leading to lost time, data corruption, and lower productivity. In this paper, a fuzzy system is developed to determine the power quality of the power network for different operating conditions and study its influence on the performance of the explosion-proof transformer in the underground mine power network in Vietnam. The simulations and calculations were performed on Matlab-Simulink software for a three-phase, 630-kVA, 6/1.2 kV explosion-proof transformer in power networks with variable power quality. A fuzzy system is developed with four measurable inputs, including frequency deviation, voltage unbalance factor, total harmonic distortion of supply voltage, total harmonic distortion of current, and an output variable, power quality. The simulation results show that the explosion-proof transformer's performance decreases when the power quality degrades, and the proposed fuzzy system can accurately diagnose this

Modeling and Experimental Studies on Water Spray Cooler for Commercial Photovoltaic Modules

This paper presents modeling and experimental studies on water spray coolers for commercial photovoltaic modules. This paper has compared the energy yield of four photovoltaic commercial modules that were installed with a fixed tilt angle being equal to the local latitude in central Vietnam, including one photovoltaic module using a water spray cooler and three photovoltaic modules without cooling. Experimental results on sunny days have been shown that the energy yield difference between four PV modules under the same working condition is lower than 1%. In addition, on sunny days when the set working temperature of the water spray cooler is 45 °C, the average improvement efficiency of a photovoltaic module using a water spray cooler compared to three reference photovoltaic modules is 2.64%, 3.83%, and 6.18%, for an average of 4.22%. A simple thermal–electrical model of a photovoltaic module with a water spray cooler has been developed and tested. The normalized root mean square error between simulated and measured results of photovoltaic module power output on a sunny day without cooling and with water spray cooler reached 6.5% and 8.5%, respectively. The obtained results are also demonstrated that the reasonableness of the simple thermal–electrical model of the photovoltaic module with water spray cooler and the feasibility of a cooling system is improved to increase the efficiency of the photovoltaic module. In addition, they can be considered as a basis for new experimental models in the future