Journal of Renewable Energy and Environment
Volume:9 Issue: 2, Spring 2022

Wind turbines can be controlled by controlling the generator speed and adjusting the blade angle and the total rotation of a turbine. Wind energy is one of the main types of renewable energy and is geographically extensive, scattered and decentralized and is almost always available. Pitch angle control in wind turbines with Doubly Fed Induction Generator (DFIG) has a direct impact on the dynamic performance and oscillations of the power system. Due to continuous changes in wind speed, wind turbines have a multivariate nonlinear system. The purpose of this study is to design a pitch angle controller based on fuzzy logic. According to the proposed method, nonlinear system parameters are automatically adjusted and power and speed fluctuations are reduced. The wind density is observed by the fuzzy controller and the blade angle is adjusted to obtain appropriate power for the system. Therefore, the pressure on the shaft and the dynamics of the turbine are reduced and the output is improved, especially in windy areas. Finally, the studied system is simulated using Simulink in MATLAB and the output improvement with the fuzzy controller is shown in the simulation results compared to the PI controller. Fuzzy control with the lowest cost is used to control the blade angle in a wind turbine. Also, in this method, the angle is adjusted automatically and it adapts to the system in such a way that the input power to the turbine is limited. Compared to the PI controller, by calculating different parameters, the power quality for fuzzy controller is enhanced from 2.941 % to 4.762 % for wind with an average speed of 12 meters per second.

Environmental and economic aspects are two remarkable pillars toward a sustainable agro-system. Accordingly, this study aimed to assess the sustainability of autumn rainfed agro-systems in northern Iran by the Eco-Efficiency (EF) indicator. The data of the production processes of wheat, barley, canola, and triticale were collected in the three crop years of 2016-2019. Results indicated that the canola production system with 720 kgCO2eq ha-1 had the highest greenhouse gas (GHG) emissions; however, wheat with 604 kgCO2eq ha-1 was attributed to the lowest GHG emissions. The results of the economic analysis also highlighted that the barley production system had the lowest while the canola production system had the highest production costs. The canola production system had the highest profitability, while the barley production system had the lowest in terms of net income and average benefit to cost ratio indicators. The EF indicator for wheat, barley, canola, and triticale was determined to be 1.4, 0.6, 1.8, and 1.1, respectively, indicating the highest EF value for the canola production system.

The effectiveness of trailing-edge flaps and microtabs in damping 1P-3P loads has been proven through a series of research work during the past decade. This paper presents the results of an investigation into the effectiveness of these devices in power enhancement and power control for responding to the issue of where these devices can be used with dual function of load and power control on a medium size turbine. The 300 kW-AWT27 wind turbine is used as the base wind turbine and the effects of adding trailing-edge flaps and string of microtabs of different lengths positioned at different span locations on the aerodynamic performance of the rotor are studied. In each case, the wind turbine simulator WTSim is used to obtain the aerodynamic performance measures. In the next step, the original blade twist is redesigned to ensure that the blade is optimized upon the addition of these active flow controllers. It is found that blades equipped with flaps can increase the annual average power and reduce the blade loading at the same time for constant speed and variable speed generators. Power enhancement is more visible on constant speed rotors, while load reduction is more significant on variable speed rotors. To achieve constant speed rotors, an average power enhancement of around 12 % is achieved for a flap of size 25 % of the blade span located at about 72 % of the blade span. Microtabs are less effective in power control and can improve the produced power only by a few percentage points.

Recently, novel techniques have been developed in building industries to use solar heating and cooling systems. The current study develops a Solar-powered Heating and Cooling (SHC) system for an office building in Kerman and assesses the transient dynamics of this system and office indoor temperature. To this end, TRNSYS simulation software is utilized to simulate system dynamics. The developed system comprises Evacuated-Tube solar Collectors (ETCs), heat storage tank, heat exchanger, circulating pumps, axillary furnace, cooling tower, single-effect absorption chiller, and air handling unit. The office indoor temperature is assessed in two scenarios, including commonly-insulated and well-insulated envelopes, while window awnings are used to prevent the sun from shining directly through the windows. The results illustrate that the SHC system can meet the thermal loads and provide thermal comfort in line with ASHRAE standards. The indoor temperature reaches 21 °C and 24 °C on cold winter and hot summer days by using the SHC system; however, without the SHC system, the indoor temperature experiences 15 °C and 34 °C on cold and hot days, respectively. The SHC system provides 45 °C and 15 °C supply air on cold and hot days to keep the indoor temperature in the desired range. A thermostat monitors the indoor temperature and saves energy by turning off the system when no heating or cooling is required. Furthermore, the ETCs can run the SHC system for a long time during daytime hours, but the axillary heater is still essential to work at the beginning of the morning.

Smart homes are considered to be the subset of smart grids that have gained widespread popularity and significance in the present energy sector. These homes are usually equipped with different kinds of sensors that communicate between appliances and the metering infrastructure to monitor and trace the energy consumption details. The smart meters trace the energy consumption data continuously or in a period of intervals as required. Sometimes, these traces will be missed due to errors in communication channels, an unexpected breakdown of networks, malfunctioning of smart meters, etc. This missingness greatly impacts smart home operations such as load estimation and management, energy pricing, optimizing assets, planning, decision making, etc. Moreover, to implement a suitable precautionary measure to eliminate missing of data traces, it is required to understand the past behavior of the data anomalies. Hence, it is essential to comprehend the behavior of missing data in the smart home energy consumption dataset. In this regard, this paper proposes an analytical approach to detect and quantify the missing data instants in all days for all appliances. Using this quantification, the behavior of missing data anomalies is analyzed during the day. For the analysis, a practical smart home energy consumption dataset ‘Tracebase’ is considered. Initially, the existence and the count of missing instants are computed. From this, the appliance ‘MicrowaveOven’ is considered for further analysis as it comprises the highest count of missing instants (84740) in a day when compared to all other appliances. Finally, the proposed analysis reveals that the large number of missing instants is occurring during the daylight period of a day.

Response surface methodology is employed to statistically identify the significance of three parameters of separator assembly arrangement, wastewater flow rate, and relative flow patterns of anode and cathode influencing the generation of power and coulombic efficiency of Microbial Fuel Cells (MFCs). Three different assemblies of Nylon-Cloth (NC), artificial rayon cloth as Absorbent Layer (AL), and J-Cloth (JC) were investigated as proton exchange mediums instead of common expensive polymeric membranes. Statistical analyses (ANOVA) revealed that although the addition of the AL after the JC layer had no significant impact on the enhancement of maximum power density, it could improve the coulombic efficiency of the MFCs by  15 %, owing to the crucial impact of oxygen permeability control between the MFC chambers. In the counter-current flow pattern, higher trans-membrane pressure and more oxygen concentration differences diminished the MFC performance and marked the importance of efficient separator layer arrangement, compared to       co-current influents. The maximum power density of 285.89 mW/m2, the coulombic efficiency of 4.97 %, and the internal resistance of 323.9 Ω were achieved for the NC-JC-Al arrangement in the co-current mode along with the flow rate of 6.9 ml/min. The higher the flow rate of influent wastewater, the higher the performance of the MFCs.

Over the past decades, power engineers have begun to connect power grids to other networks such as microgrids associated with renewable units using long transmission lines to provide higher reliability and greater efficiency in production and distribution besides saving resources. However, many dynamic problems such as low frequency oscillations were observed as a result of these connections. Low frequency oscillation is a normal phenomenon in most power systems that causes perturbations and, thus, the grid stability and damping process are of paramount importance. In this paper, to attenuate these oscillations, a novel method for designing Power System Stabilizer (PSS) is presented via Linear Parameter-Varying (LPV) approach for a Single Machine Infinite Bus system (SMIB). Because the system under study is subject to frequent load and production changes, designing the stabilizer based on the nominal model may not yield the desired performance. To guarantee the flexibility of the stabilizer with respect to the aforementioned issues, the power system polytopic representation is used. In order to apply the new method, the nonlinear equations of the system at each operating point, located in a polytope, are parametrically linearized by scheduling variables. Scheduling variables can be measured online in any operating point. By using this model and following the H∞ synthesis, feedback theories, and Linear Matrix Inequalities (LMIs), LPV controllers at all operating points are obtained. Finally, the simulation results verify the effectiveness of the proposed controller over classic and robust controllers with regard to uncertainties and changes in system conditions.

The Gravitational Water Vortex Power Plant (GWVPP) is a power generation system designed for ultralow head and low flow water streams. Energy supply to rural areas using off-grid models is simple in design and structure and sustainable to promote electricity access through renewable energy sources in the villages of Nepal. The objective of this study is to determine the most favorable gap between the booster and main runners of a Gravitational Water Vortex Turbine (GWVT) to ensure maximum power output of the GWVPP. CFD analysis was used to evaluate the 30 mm gap between the main and booster runners, which was the most favorable gap for enhancing the plant’s power. In this study, the optimum power and economic analysis of the entire plant was conducted in the case of mass flow rates of 4 kg/s, 6 kg/s, and 8 kg/s. The system was modeled in SolidWorks V2016 and its Computational Fluid Dynamic (CFD) analysis was performed utilizing ANSYS R2 2020 with varying multiple gaps between the main and booster runners to determine the most favorable gap of the plant’s runner. This research concluded that optimum power could be achieved if the distance of the main runner’s bottom position be fixed at 16.72 %, i.e., the distance between the top position of the conical basin and the top position of the booster runner. At a mass flow rate of 8 kg/s, the plant generated maximum electric energy (3,998,719.6 kWh) comparatively and economically contributed 268,870.10 USD on an annual basis.

Environmental sustainability encompasses various problems including climate change, clean air, renewable energy, non-toxic environments, and capacity to live in a healthy community. Many researchers focus their attention on alternative energy sources, such as ethanol and hydroxy gas, to enhance environmental health and quality of life. The introduction of hydroxy gas as a clean source of energy is gaining significant traction. Also, ethanol has a greater octane number than gasoline. Therefore, the ethanol–gasoline blend has a higher octane number than conventional gasoline. A new combination of hydroxy gas, ethanol, and gasoline is environmentally benign while significantly improving the performance of gasoline engines. This paper tested hydroxy gas in a 197-cc gasoline engine power generator powered with ethanol–gasoline blend. The results demonstrated that thermal efficiency increased up to 23.6 % and fuel consumption decreased up to 36 % on a volume basis, which was a significant improvement over the base engine. Furthermore, the hazardous carbon monoxide reduction reached 11.45 % and the unburned hydrocarbon emissions reached 17.6 %.

The purpose of this study is to present a renewable energy policy model in the agricultural sector of Iran. To achieve this goal, a questionnaire consisting of 57 items was designed. The reliability of the questionnaire was confirmed by Cronbach's alpha (0.916). Also, to analyze the validity and reliability of the research tool, the Average Variance Extracted (AVE) and Composite Reliability (CR) were calculated. The validity of the questionnaire was determined using face validity, Content Validity Ratio (CVR), and Content Validity Index (CVI). The statistical population of the study consists of energy policymaking experts who were estimated at about 80 people. The sampling method was random and 70 samples answered the questionnaire using the Krejcie and Morgan table. Using structural equation modeling and the maximum likelihood method and using LISREL software, the model fit was estimated at a favorable level. Based on the findings, it was found that the priorities of the agricultural sector and the needs of this sector had not been considered in renewable energy policymaking. Policymaking is done top-down and stakeholders are not considered. Renewable equipment market policies are not adequate and the market is not properly managed. Interaction between policymaking institutions is not in good shape. The results of this study can help address the various shortcomings of the renewable energy policy as well as reduce the common inconsistencies in this area. Finally, suggestions were made for the development and promotion of policies in the field of renewable energy in the agricultural sector of Iran.