Journal of Renewable Energy and Environment
Volume:8 Issue: 4, Autumn 2021

In the present work, natural biomass and chemical materials were applied as the heteroatom resources for modifying the Porous Graphene (PG) structure by pyrolysis method at 900 ºC. The physical and chemical characterizatons were performed by means of Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), Raman Spectroscopy, N2 Adsorption-Desorption, and X-ray Photo-electron Spectroscopy (XPS). Furthemore, the behavior of the prepared materials was investigated by Cyclic Voltammetry (CV) and Rotating Disk Electrode (RDE). The obtained results indicated that doping of heteroatoms into the graphene framework was possible using a low-cost and environment-friendly biomass material as well as chemical sources. Moreover, one-step quarternary and tersiary co-doped graphene could be acheived using natural biomass. The prepared electrocatalysts using grape leaves and sulfur trioxide pyridine complex exhibit higher electrocatalytic performance as exampled which conducted the electrocatalyst in 4e- pathway and showed high stability in methanol solutions during the process, confirming their considerable potential to Oxygen Reduction Reaction (ORR) as an electro-catalyst. Moreover, the onset potential of Gl300G-900 and GSP 900 (0.93 V vs RHE) is almost equal to the Pt/C 20 wt % (0.99 V vs RHE). These optimal prepared cathodes (Gl300G-900 and GSP 900) in the Microbial Fuel Cell (MFC) test lead to considerable power densities of 31.5 mW m-2 and 30.9.mW m-2, which are close to 38.6 mW m-2 for the Pt/C 20 wt % cathode.

The wastewater treatment of Medium Density Fiberboard (MDF) is a harsh process because of its contents of high suspended solids, chemical oxygen demand, high molecular weight of lignin, and fatty acids. Electrocoagulation (EC) process was used for efficient removal of pollutants and reusing the water. The impact of aluminum and iron as sacrificial anodes on removal of Chemical Oxygen Demand (COD), Total Suspended Solid (TSS), turbidity, and Total Solid (TS) were investigated. A full quadratic model was deployed to optimize the EC process variables for pretreatment of MDF effluent through response surface methodology. The model results confirmed that the COD and TSS removal efficiency was enhanced upon increasing voltage and residence time; hence, other pollutants initially increased and then, decreased at higher levels. The comparison between aluminum and iron electrodes indicated that the polluted removal efficiencies of aluminum were higher than the iron electrode for MDF wastewater. The optimum values of voltage and residence time for electrocoagulation of MDF wastewater with aluminum were 33 V and 25 min, which resulted in 93 %, 89 %, 67 %, and 76 % for COD, TSS, turbidity, and TS removal, respectively. The implementation of electrocoagulation provided a possibility for reusing water and reducing water consumption in the MDF manufacturing process.

Studies on renewable energy are essential topics that help find new energy sources to replace fossil sources and promote environment friendliness. Hydrogen is the most practical alternative energy carrier source that meets the mentioned purposes. The mass of hydrogen element in the Earth's water was calculated and found to be about 2.1×1020 kg, which is greater than the mass of the world oil reserves by about 9×105 times. In addition, essential details of water molecular arrangement were investigated in order to better understand the electrolysis of water. Also, the energy of covalent and hydrogen bonds per molecule of water was theoretically calculated and found to be about 8.17×10-19 J/molecule and 3.87×10-20 J/molecule, respectively. In the electrolysis process, two stages should be undertaken: the first stage was to break hydrogen bonds between water molecules, in which all water eclectic dipoles would align in the direction of the Applied Electric Field across the electrolysis unit. The second stage was to break water covalent bonds to generate H2 and O2 gases. Moreover, the lowest cost to generate one kg of hydrogen (0.4 $/kg) by electrolysis method using solar energy was about 0.4 $, which has already been proven, while this value was about 2.8 $/kg upon considering the average price of electricity of Oman in comparison.

In this study, the effect of covering the aperture area of a conical cavity receiver with an ultra-white glass on operational parameters of a Parabolic Dish Collector (PDC) was numerically and experimentally investigated under climate conditions of Tehran (35.44° N latitude and 51.10° longitude). The main components of the experimental setup include a dish reflector, a conical cavity receiver, Heat Transfer Fluid (HTF), hydraulic and cooling cycle, and a sun tracker. For this purpose, a conical cavity receiver with an ultra-white glass cover on its aperture was numerically modeled in Fortran software. During the evaluation, environmental parameters including ambient temperature, solar radiation, and wind speed were considered as inputs of the model. The results revealed fair agreement between the numerical and experimental data with the maximum error of approximately 4.63 % and 7.89 % for receivers with and without the glass cover on the aperture, respectively. For a steady-state analysis, the mean values of useful energy ( ) absorbed by the receiver were calculated as 1,253.25 W and 987.68 W, while thermal efficiency ( ) of the receiver was calculated as 52.61 % and    40.69 % for receivers with and without glass cover, respectively. The results revealed that both  and  followed a similar trend of the variations in the HTF’s temperature between the inlet and outlet of the receiver. Also, the overall heat loss coefficient ( ) and the collector heat removal factor ( ) were calculated as 420.76 W/m2°C and 0.62 for the conical cavity receiver with the glass cover.

One of the best and most important types of concentrating solar power plants is the linear Fresnel collector. The thermal performance and application of absorber in a solar power plant can be enhanced using direct steam generation technology. A particular discrepancy between the present study and others lies in our attempt at applying a new method for calculating critical heat flux based on Look-up Table. In the current study, effects of nanofluid on the length of the critical heat flux and convection heat transfer coefficient were investigated. The nanoparticles considered in this study were aluminum, silver, nickel, and titanium dioxide at concentrations of 0.01, 0.1, 0.3, 0.5, 1 and 2 %. Modeling results revealed that the heat transfer coefficient increased upon enhancing the volumetric concentration of nanoparticles, thereby improving this coefficient at 2 vol. % nickel nanoparticles, which was 10.6 % above the value of pure water. On the other hand, thermal efficiency was enhanced when nickel nanoparticles were dispersed in pure water such that increase rates of thermal efficiency equaled 11.2, 10.8 and 11.3 % in the months of June, July, and August, respectively, when the volume concentration of nanoparticles was 0.5 %.

Energy plays a vital role in all human life activities. Due to the problems caused by fossil fuels in recent decades such as global warming, greenhouse gas emissions, ozone depletion, etc., the use of renewable and clean energy has been considered. An experimental facility for the acquisition of reliable data from Parabolic Trough Solar Collectors (PTCs) was established to develop a robust analytical model. A wide range of Heat Transfer Fluid (HTF) flow rates (0.0372-0.1072 kg/s) and solar radiation (400-900 W/m2) were used to determine PTC parameters such as the outlet temperature of HTF loss and temperature distribution. Vacuum conditions in the receiver were considered effective in terms of thermal efficiency. Also, three types of HTF including two oil fluids (Syltherm 800 and S2) and water were examined. The temperature distribution showed that when Syltherm 800 or S2 passed through the absorber tube, the outlet temperature was higher than water: 2.84 % for Syltherm 800 and 3.72 % for S2. Since the absorber tube temperature was much higher than water, the heat loss in this condition was considered for oil HTF. Of note, the results demonstrated that use of the vacuum tube could diminish heat loss for the oil HTF. The effect of solar intensity increases from 600 W/m2 to 900 W/m2 on the maximum temperature of the receiver tube indicated that when Syltherm 800 was used as an HTF, this temperature increased by 35.1 % (from 167 °C to 219 °C), while this percentage was 32.7 % and  6.8 % for S2 and water, respectively.

The use of small-scale Combined Heat and Power (CHP) to meet the electrical and thermal needs of buildings has grown exponentially and plans have been made in Iran to expand these systems. In view of the above, in the present work, for the first time, sensitivity analysis has been performed on the parameters of natural gas price, annual interest rate, and the price of pollutant penalties. The CHP system studied included fuel cell, biomass generator, solar cell, wind turbine, and gas boiler. The techno-econo-enviro simulations were performed by HOMER software and the study area was Abadan. The use of a dump load to convert excess electricity into heat and heat recovery in a biomass generator and fuel cell are other advantages presented by the present work. The minimum Cost of Energy (COE) is 1.16 $/kWh. The results also showed that the use of biomass generators was economical when the annual interest rate was 30 %. The significant effect of using dump load on the required heat supply and the lowest price per kg of hydrogen produced equal to $ 35.440 are other results of the present work. In general, the results point to the superiority of solar radiation potential over wind energy potential of the study area and the prominent role of dump load in providing heat on a residential scale is clearly seen. Also, for the current situation, using biomass is not cost-effective.

This study conducts a comparative evaluation of the performance of modules and the arrays under standard test conditions. An equivalent circuit model was developed alongside a computational scheme. The model input data were obtained from the manufacturer’s specification datasheets. They were used to analyse the maximum Fill Factor (FF) and Relative Power Losses (RPL) for Parallel (P), Series (S) and Series-Parallel (SP) configurations. For matching modules, the RPL was insignificant, but for mismatched modules, the parallel configuration (P) and series-parallel (SP) yielded RPL of 1.3 %, while the series configuration (S) produced RPL of 2.6 %. Thus, short circuit defects associated with the P and SP configuration were well below the open circuit defects associated with the series configuration (S). These results clearly show that the large photovoltaic plant needs to be configured with multiple blocks or strings of SP configuration in order to suppress RPL. In addition, the designer and installers of large solar power plants should adopt modules with uniform electrical and thermal properties in the construction of large solar power plants. The trivial RPL associated with the matched modules should be taken into consideration, as well.

As a result of growing energy demand, shortage of fossil fuel resources, climate change, and environmental protection, the need for renewable energy sources has been growing rapidly. However, there is an urgent need to cope with intermittency and fluctuation of renewable energies. Various energy storage systems are considered as appropriate solutions to the above-mentioned problem. In the present manuscript, a novel compressed carbon dioxide energy storage system was proposed. Furthermore, an extra thermal energy storage with Therminol VP-1 as a working fluid, coupled with Parabolic Trough Collector (PTC), was added to the system. This integration is conducive to rising the inlet temperature of turbines and reducing the work load that should be done by the compressors. In the present study, a method based on software product including Engineering Equation Solver (EES) for determining thermodynamic characters per component and System Advisor Model (SAM) was employed to model the solar field for a desired location. Energy and exergy analyses were conducted to evaluate the whole cycle performance during charging and discharging periods. In this study, the city of Kerman located in the south-eastern part of Iran, with Direct Normal Incidence (DNI) of 950 , was selected for the present modeling. The results of a random day (June 22/2019) at time 15:00 represented the exergy efficiency of 66.98 % and the round trip efficiency of 93.14 %. High exergy efficiency and round trip efficiency of this system make this idea applicable to enhancing the total performance of the entire system.

In the context of increasing emission of greenhouse gasses in the environment due to fossil fuel burning, this paper attempts to describe the significance of Maximum Power Point Tracking (MPPT) by investigating the power performance of photovoltaic modules with MATLAB simulation. MPPT algorithm was employed to secure maximum power from PV module. The boost converter whose pulse is linked to MPPT algorithm restricts the flow of load power and controls the current and voltage of PV panels. The whole design of the solar model, boost converter, and MPPT controlled algorithms was done in the SIMULINK to prioritize the system in simulation. The main concept employed in this paper was to develop a power generation process with MPPT algorithm and to provide information for future use. In this paper, all simulations along with the PV power generation process were done in MATLAB. This research could potentially play a vital role in mitigating the world fuel crisis.

This study conducts thermodynamic analysis on three trigeneration cycles including Organic Rankine Cycle (ORC), Liquefied Natural Gas (LNG) cold energy, and absorption refrigeration cycle in order to select appropriate working fluids. Different types of ORC cycles including simple ORC, regenerative, and ORC with Internal Heat Exchange (IHE) were investigated. For those types, the operation of six working fluids with different thermodynamic behaviors (R141b, R124, R236fa, R245fa, R600, and R123) was evaluated. In power plants, a low-grade heat source was provided by condensing boiler hot water energy while the thermal sink was prepared by cold energy of LNG. The effect of boiler temperature variation on energy and exergy efficiencies was investigated. According to the derived results, regenerative ORC-based systems possessed maximum energy and exergy efficiencies, while simple ORC and ORC with internal heat exchanger exhibited approximately the same quantities. Also, among these analyzed working fluids, R141b had the maximum energetic and exergetic efficiencies, while R124 and R236fa had minimum performance.