Journal of Renewable Energy and Technology

Control strategy of a standalone variable speed wind energy conversion system based on direct drive permanent magnet synchronous generator

2022-05-09T08:41:03+00:00

In this paper, we propose a control strategy for a stand-alone wind energy conversion system (WECS) based on a direct drive permanent magnet synchronous generator (PMSG), loaded on a DC-type charge. In the considered wind-power generating system, the generator provides a DC voltage to the load through a three-phase rectifier, controlled by the Pulse Width Modulation (PWM) technique. The main control strategy target is to maintain the DC voltage insensitive to fast changes in wind speed and load, by offsetting the generator output current with the charge current. The approach adopted in this paper is based on the estimate of the PMSG electromagnetic torque assuming that wind velocity remains quasi-stationary in a steady state. The instant power reference is assessed by the charge controller according to the rated DC bus voltage, using actual electrical measurements as the voltage and current. To achieve adequately the power decoupling, the field-oriented control is used with conventional PI-type regulators to provide direct and quadrature control reference voltages and ensure DC bus voltage regulation. To assess the proposed control strategy efficiency, the simulation model was subjected to different load and wind speed variations. Simulation results performed using the MATLAB Simulink model show high accuracy and strength during steady-state and transient operations.

Numerical and experimental investigations of heat transfer inside a rectangular channel with a new tilt angle of baffles for solar air heater

2022-03-05T13:57:20+00:00

This work represents an experimental and numerical study of heat transfer by forced convection inside a channel containing the baffles of a solar collector. The study chose the shape of the baffles as an important factor to improve heat exchange, which has a rectangular shape and is transversal with air flowing at an angle of inclination ? = 90 degrees. The study was conducted at different mass flow rates and different times of the day, to find out the effect of these conditions on the convective heat transfer from the absorber plate to the air through the channel of the collector. The operating conditions taken from the experiment were entered as boundary conditions in CFD, for a comparative study between the heat transfer coefficient by convection of the measurement data, and the simulation data. It was found that the results of it in the numerical and experimental methods gave a good approach, also it can be concluded that this coefficient was affected by different parameters such as the mass flow rate, absorber temperature, and shape of the baffles. Through the results, it was confirmed that when the Reynolds number increases, it means an increase in velocity, which means that the air passing through the duct becomes cooler, therefore there is a difference in temperature between the passing air and the absorber plate, and this leads to an increase in heat transfer between the air and the absorber plate.

A highly efficient InGaP thin film solar cell structure, optimization and characteristics

2022-05-09T08:23:58+00:00

Inorganic solar cells based on III-V semiconductor materials are widely used owing to their high efficiencies. In this work, we aim to improve the performance of the single heterojunction solar cell InGaP. The InGaP cell is constituted of a back surface field (BSF), a base, an emitter and a window layer with InAlAsP material. The simulation is done after optimization, modeling, and choice of the used materials and the thickness of different layers constituting the solar cell. The choice of materials whose gap energy is decreasing allows the absorption of the solar spectrum in its almost totality. Then, we varied the temperature to know its effects on the gap energy and the efficiency of the InGaP cell. The InGaP and solar cell with optimal parameters are illuminated by an AM1.5 solar spectrum through InAlAsP window layer. The simulation and optimization at 300K of short circuit current parameters (J_sc), open circuit voltage (V_oc), fill factor (FF) and efficiency (?) are done using Tcad Silvaco software. The characteristics obtained are: the minimized thickness of 665 nm, electrical efficiency is about ? = 21.87% for InGaP cell, Jsc = 14.43 mA/cm2, Voc = 1.63 V, and FF = 91.21 %.

Assessment of the performance of Photovoltaic system in high altitude region of Jos, Nigeria

2024-07-14T03:03:32+00:00

This study examined two years of temperature, humidity, and irradiance data collected at intervals of fiv minutes for the city of Jos, Nigeria to determine the relationship between temperatures Photovoltaic system voltage, and power output. Descriptive statistical tools were used to investigate the relationship between temperature, power output, and voltage. There is a wider range of responses to temperature change in the output power. The findings showed that the power output values range from 227.82 kWh to 950.10 kWh, and Voltage values range from 14.41 V to 16.12 V. Additionally, the average monthly temperature ranged from 20.42 ? to 25.76 ?. The result shows a positive correlation between temperature below standard test condition (STC = 25 ^oC), and high output power, while a high temperature above STC negatively affects the output power. Notably, Jos has a higher power output and voltage while maintaining the lowest average temperature compared to other locations within the region. The study concludes that power output and voltage are strongly and inversely related to temperature, refuting the notion that operating solar panels above STC would improve performance.

Effects of Temperature and Pressure Conditions on the Quantity and Quality of Bio-Oil Produced from Pyrolysis of Biomass Material: A Review

2026-01-13T07:17:35+00:00

The pyrolysis process of biomass results in bio-oil which functions as a sustainable renewable fuel that can substitute for traditional fossil fuel resources. The research presents current findings about temperature and pressure effects on bio-oil manufacturing and its physical and chemical characteristics through new quantitative results from recent investigations. The amount of moisture in the system reduces the production of liquid products because the condensable organic compounds decrease from 19.6 wt.% to 15.2 wt.% when the moisture content rises from 2.7 wt.% to 10 wt.%. The process requires feedstock drying to reach moisture levels that stay under 10 wt.%. The optimal pyrolysis temperatures between 450–550°C produce the highest liquid yields between 45–75 wt.% from lignocellulosic and mixed biomasses which results in better bio-oil quality because of lower oxygen levels (from 42 to 28 wt.%) and lower water content (from 20-25 to 7–10 wt.%) and higher HHV values which increase from 18 to 25–30 MJ.kg?¹ because of better dehydration and decarboxylation reactions. The characteristics of bio-oil become more stable and energy dense when pressure conditions reach 0.5-2 MPa because this leads to decreased oxygenate and moisture content, which results in higher HHV values from 27.8 to 31.4 MJ.kg?¹ and prevents viscosity increase through polymerization. The vacuum conditions help to enhance aromatic compounds while protecting them from additional cracking that results in decreased overall production levels. The process has shown progress, but it still faces major challenges because bio-oils show unstable properties, and their high oxygen content and acidic nature make them difficult to apply in various industries. Research in the future needs to concentrate on developing complete process enhancement systems which combine catalytic upgrading with hydrogen-assisted or pressured pyrolysis and machine learning prediction systems and renewable thermal energy sources and waste heat recovery systems.