Power flow control of grid connected hybrid renewable energy system using hybrid controller with pumped storage

This paper presents a grid-connected HRES using a hybrid controller with PHS for optimal power flow control and minimizing the production cost. The novelty of the proposed approach is the joined execution of the SSA and CSA named as SSA-CS are apparently a very new metaheuristic algorithm. Moreover, the proposed method is the cost-effective power production of the microgrids and effective utilization of renewable energy sources without wasting the available energy. Here, the energy sources in particular PV system, WT, MT and battery with PHS are utilized to generate the power of the MG system. In the proposed approach, the required power demand of the energy system is predicted by the ANN technique. After that, the production cost minimization is done in view of the anticipated load demand by utilizing the optimization approaches to be a specific SSA-CS algorithm. The result of the proposed approach is actualized in the MATLAB/Simulink working platform. The performance of the proposed approach is examined by comparing the current methodologies such as SSA and PSO with the proposed SSA-CS approach. The simulation results show that the proposed method generates maximum power and furthermore the proposed framework has less production cost in light of the power demand.     

Biogas from lignocellulosic feedstock: A review on the main pretreatments,inocula and operational variables involved in anaerobic reactor efficiency

Research focused on reusing lignocellulosic waste has been gaining ground, both for the purpose of obtaining energy from renewable sources, as well as for reducing feedstock costs and preventing environmental pollution. Despite being currently evaluated as a promising feedstock, large-scale application of lignocellulosic waste to obtain bioenergy is still scarce. One of the obstacles in terms of reusing it is its recalcitrant composition, often requiring pretreatment applications to break its fibers, increasing its bioavailability. In addition to the type of substrate, there are many operational parameters that may affect the process efficiency, including the type of reactor, temperature, pH, inoculum source, among others. Considering this, it is interesting to consider using statistical tools instead of “one-factor-at-a-time” methods for simultaneous optimization of these variables to increase the production of value-added compounds, such as Plackett-Burman screening design and Central Composite Rotational Design. In this context, this review aimed at compiling data regarding obtaining value-added compounds, focusing on bio-H₂ and bio-CH₄, from different lignocellulosic waste, such as sugarcane bagasse, citrus peel waste, coffee and cereal husks, brewer's spent grain, cocoa processing waste, sawdust, among others, considering the main operational parameters involved (temperature, pH, inoculum) and the type of pretreatment applied (physical, chemical and/or biological). The results described here may support future research on reusing residual lignocellulosic waste, in addition to elucidating the importance of different operational parameters to convert this waste into H₂ and/or CH₄.     

Hydrogen production from phototrophic microorganisms: Reality and perspectives

Hydrogen is a promising alternative to fossil fuel for a source of clean energy due to its high energy content. Some strains of phototrophic microorganisms are known as important object of scientific research and they are being explored to raise biohydrogen (BioH₂) yield. BioH₂ is still not commonly used in industrial area because of the low biomass yield and valuable down streaming process. This article deals with the methods of the hydrogen production with the help of two large groups of phototrophic microorganisms – microalgae and cyanobacteria. Microalgal hydrogen is environmentally friendly alternative to conventional fossil fuels. Algal biomass has been considered as an attractive raw source for hydrogen production. Genetic modified strains of cyanobacteria are used as a perspective object for obtaining hydrogen. The modern photobioreactors and outdoor air systems have been used to obtain the biomass used for hydrogen production. At present time a variety of immobilization matrices and methods are being examined for their suitability to make immobilized H₂ producers.     

Design and performance of asymmetric supported membranes for oxygen and hydrogen separation

Producing syngas and hydrogen from biofuels is a promising technology in the modern energy. In this work results of authors’ research aimed at design of supported membranes for oxygen and hydrogen separation are reviewed. Nanocomposites were deposited as thin layers on Ni–Al foam substrates. Oxygen separation membranes were tested in CH₄ selective oxidation/oxi-dry reforming. The hydrogen separation membranes were tested in C₂H₅OH steam reforming. High oxygen/hydrogen fluxes were demonstrated. For oxygen separation membranes syngas yield and methane conversion increase with temperature and contact time. For reactor with hydrogen separation membrane a good performance in ethanol steam reforming was obtained. Hydrogen permeation increases with ethanol inlet concentration, then a slight decrease is observed. The results of tests demonstrated the oxygen/hydrogen permeability promising for the practical application, high catalytic performance and a good thermochemical stability.     

Recent insights into microalgae-assisted microbial fuel cells for generating sustainable bioelectricity

Power generation from the renewable biomass sources using microbial fuel cell (MFC) has attracted significant attention in recent years, while chemical energy stored in microalgae biomass has efficiently been used for the sustainable production of biofuels and other valuable bioproducts since the decades. The usage of these photosynthetic organisms in MFC can enhance the efficiency of MFC and provide a cost-effective and renewable approach for the bio-generation of electricity. Microalgae are commonly incorporated either with anode or cathode compartment of MFC to generate electron or oxygen, respectively. Despite microalgae-assisted MFC (MA-MFC) would be more sustainable than using MFC alone, further developments in such systems are still required for improving its efficiency and achieving a real-world application on a large scale. In this context, understanding in bio-electrochemical mechanism of MA-MFC, including electrons shuttle and oxygen generation, is very important. Moreover, many factors can limit the efficiency and performances of MA-MFCs that are needed to optimize in further research efforts. This review presents a comprehensive insight into MA-MFC, including the recent developments and potential challenges in this promising bio-electricity generating system. Specifically, it focuses a critical discussion on the configurations of MA-MFC, key operating parameters affecting performances of MA-MFC, challenges and prospective research works for improving the overall energy output of MA-MFC.     

A review on pretreatment methods,photobioreactor design and metabolic engineering approaches of algal biomass for enhanced biohydrogen production

The development of alternative fuels has been promoted by the extreme fossil fuel consumption brought on by urbanisation and deteriorating pollution. Due to its high energy and combustible qualities, biohydrogen has been perceived as a potential fuel substitute in dealing with issues related to the rising emission of greenhouse gases and global warming. As a source of carbon sequestration and sustainable renewable energy, biohydrogen synthesis by algae species has been prevalent in research scale. This review focuses on the novel and recent metabolic approaches for enhanced algal based biohydrogen production. Pretreatment methods available and scaling techniques used for enhancing the biohydrogen productivity using algal species have been elaborated in the review. Algal characteristics that make them suitable alternative for biohydrogen production are discussed briefly. Various pretreatment methods such as physical, chemical, biological and thermal are elaborated. In addition, the factors involved in influencing the biohydrogen productivity and the metabolic engineering approaches for modifying the pathway in algae are highlighted. Scaling up of process using different types of photobioreactors such as tubular, flat panel, airlift and stirred tank are reported that briefs about merits and demerits of each photobioreactor.     

A comprehensive review on lignocellulosic biomass biorefinery for sustainable biofuel production

The increasingly severe environmental pollution and energy shortage issues have demanded the production of renewable and sustainable biofuels to replace conventional fossil fuels. Lignocellulosic (LC) biomass as an abundant feedstock for second-generation biofuel production can help overcome the shortcomings of first-generation biofuels related to the “food versus fuel” debate and feedstock availability. Embracing the “circular bioeconomy” concept, an integrated biorefinery platform of LC biomass can be performed by employing different conversion technologies to obtain multiple valuable products. This review provides an overview of the principles and applications of thermochemical processes (pyrolysis, torrefaction, hydrothermal liquefaction, and gasification) and biochemical processes (pretreatment technologies, enzyme hydrolysis, biochemical conversion processes) involved in LC biomass biorefinery for potential biofuel applications. The engineering perspective of LC biofuel production on separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SSCF), and consolidated bioprocessing (CBP) were also discussed.     

Reinforcement learning based energy management systems and hydrogen refuelling stations for fuel cell electric vehicles: An overview

This paper examines the current state of the art of hydrogen refuelling stations-based production and storage systems for fuel cell hybrid electric vehicles (FCHEV). Nowadays, the emissions are increasing rapidly due to the usage of fossil fuels and the demand for hydrogen refuelling stations (HRS) is emerging to replace the conventional vehicles with FCHEVs. Hence, the availability of HRS and its economic aspects are discussed. In addition, a comprehensive study is presented on the energy storage systems such as batteries, supercapacitors and fuel cells which play a major role in the FCHEVs. An energy management system (EMS) is essential to meet the load requirement with effective utilisation of power sources with various optimizing techniques. A detailed comparative analysis is presented on the merits of Reinforcement learning (RL) for the FCHEVs. The significant challenges are discussed in depth with potential solutions for future work.     

Assessment of ammonia as energy carrier in the use with reversible solid oxide cells

Ammonia represents one of the most promising potential solutions as energy vector and hydrogen carrier, having a higher potential to transport energy than hydrogen itself in a pressurized form. Furthermore, solid oxide fuel cells (SOFCs) can directly be fed with ammonia, thus allowing for immediate electrical power and heat generation. This paper deals with the analysis of the dynamic behavior of commercial SOFCs when fueled with ammonia. Several measurements at different temperatures have been performed and performances are compared with hydrogen and a stoichiometrically equivalent mixture of H₂ and N₂ (3:1 M ratio). Higher temperature led to smaller drops in voltage for both fuels, thus providing higher efficiencies. Ammonia resulted slightly more performant (48% at 760 °C) than hydrogen (45% at 760 °C), in short stack tests. Moreover, different ammonia-to-air ratios have been investigated and the stack area-specific resistance has been studied in detail by comparing numerical modeling predictions and experimental values.     

Harvest of electrical energy from fermented microalgal residue using a microbial fuel cell

The application of microalgal biomass for fermentation has been highlighted as a means of producing a range of value-added biofuels and chemicals. On the other hand, the microalgal residue from the fermentation process still contains as much as 50% organic contaminants, which can be a valuable substrate for further bioenergy recovery. In this study, a microbial fuel cell and automatic external load control by maximum power point tracking (MPPT) were implemented to harvest the electrical energy from waste fermented microalgal residue (FMR). The MFC with MPPT produced the highest amount of energy (1.82 kJ/L) compared to the other MFCs with fixed resistances: 0.98 (1000 Ω), 1.16 (500 Ω), and 1.17 kJ/L (300 Ω). The MFC with MPPT also showed the highest maximum power density (88.6 mW/m²) and COD removal efficiency (620.0 mg COD/L removal with 85% removal efficiency). The implementation of MPPT gained an approximate 12.9% energy yield compared to the previous fermentation stage. These results suggest that FMR can be an appropriate feedstock for electrical energy recovery using MFCs, and the combined fermentation and MFC system improves significantly the energy recovery and treatment efficiency from FMR.     

Simultaneous biohydrogen (H2) and bioplastic (poly-β-hydroxybutyrate-PHB) productions under dark,photo, and subsequent dark and photo fermentation utilizing various wastes

The present study is focused on bio hydrogen (H₂) and bioplastic (i.e., poly-β-hydroxybutyrate; PHB) productions utilizing various wastes under dark fermentation, photo fermentation and subsequent dark-photo fermentation. Potential bio H₂ and PHB producing microbes were enriched and isolated. The effects of substrate (rice husk hydrolysate, rice straw hydrolysate, dairy industry wastewater, and rice mill wastewater) concentration (10–100%) and pH (5.5–8.0) were examined in the batch mode under the dark and photo fermentation conditions. Using 100% rice straw hydrolysate at pH 7, the maximum bio H₂ (1.53 ± 0.04 mol H₂/mol glucose) and PHB (9.8 ± 0.14 g/L) were produced under dark fermentation condition by Bacillus cereus. In the subsequent dark-photo fermentation, the highest amounts of bio H₂ and PHB were recorded utilizing 100% rice straw hydrolysate (1.82 ± 0.01 mol H₂/mol glucose and 19.15 ± 0.25 g/L PHB) at a pH of 7.0 using Bacillus cereus (KR809374) and Rhodopseudomonas rutila. The subsequent dark-photo fermentative bio H₂ and PHB productions obtained using renewable biomass (i.e., rice husk hydrolysate and rice straw hydrolysate) can be considered with respect to the sustainable management of global energy sources and environmental issues.     

Investigation of Zr,Gd/Zr,and Pr/Zr – doped ceria for the redox splitting of water

There is a renewed interest in CeO₂ for use in solar-driven, two-step thermochemical cycles for water splitting. However, despite fast reduction/oxidation kinetics and high thermal stability of ceria, the cycle capacity of CeO₂ is low due to thermodynamic limitations. In an effort to increase cycle capacity and reduce thermal reduction temperature, we have studied binary zirconium-substituted ceria (Zr_xCe_1-xO₂, x = 0.1, 0.15, 0.25) and ternary praseodymium/gadolinium-doped Zr-ceria (M_0.1Zr_0.25Ce_0.65O₂, M = Pr, Gd). We evaluate the oxygen cycle capacity and water splitting performance of crystallographically and morphologically stable powders that are thermally reduced by laser irradiation in a stagnation flow reactor. The addition of zirconium dopant into the ceria lattice improves O₂ cycle capacity and H₂ production by approximately 30% and 11%, respectively. This improvement is independent of the Zr dopant level, up to 25%, suggesting that above 10% Zr dopant level, Zr might be displaced during the high temperature annealing process. The addition of Pr and Gd to the binary Zr-ceria mixed oxide, on the other hand, is detrimental to H₂ production. A kinetic analysis is performed using a model-based analytical approach to account for effects of mixing and dispersion, and to identify the rate controlling mechanism of the water splitting process. We find that the water splitting reaction at 1000 °C and with 30 vol% H₂O, for all doped ceria samples, is surface limited and best described by a deceleratory power law model (F-model), similar to undoped CeO₂. Additionally, we used density functional theory (DFT) calculations to examine the role of Zr, Pr, and Gd. We find that the addition of Pr and Gd induce non-redox active sites and, therefore, are detrimental to H₂ production, in agreement with experimental work. The calculated surface H₂ formation step was found to be rate limiting, having activation barriers greater than bulk O diffusion, for all materials. This agrees with and further explains experimental findings.     

Valorisation of lignocellulosic biomass investigating different pyrolysis temperatures

Presently, sugarcane bagasse (SB) and oat hulls (OH) have a distinctive potential as a renewable source of biomass, due to its global availability, which is advantageous for producing liquid and gaseous fuels by thermochemical processes. Thermo-Catalytic Reforming (TCR) is a pyrolysis based technology for generating energy vectors (char, bio-oil and syngas) from biomass wastes. This work aims to study the conversion of SB and OH into fuels, using TCR in a 2 kg/h continuous pilot-scale reactor at different pyrolysis temperatures. The pyrolysis temperatures were studied at 400, 450 and 500 °C, while the subsequent reforming temperature remained constant at 500 °C. The bio-oil contained the highest calorific value of 33.4 and 33.5 MJ/kg for SB and OH, respectively at 500 °C pyrolysis temperature, which represented a notable increase compared to the raw material calorific value of SB and OH (16.4 and 16.0 MJ/kg, respectively), this was the result of deoxygenation reactions occurring. Furthermore, the increment of the pyrolysis temperature improved the water content, total acid number (TAN), viscosity and density of the bio-oil. The syngas and the biochar properties did not change significantly with the increase of the pyrolysis temperature. In order to use TCR bio-oil as an engine fuel, it is necessary to carry out some upgrading treatments; or blend it with fossil fuels if it is to be used as a transportation fuel. Overall, TCR is a promising future route for the valorisation of lignocellulosic residues to produce energy vectors.     

Dark fermentative biohydrogen production using pretreated Scenedesmus obliquus biomass under an integrated paradigm of biorefinery

In recent times, biohydrogen production from microalgal feedstock has garnered considerable research interests to sustainably replace the fossil fuels. The present work adapted an integrated approach of utilizing deoiled Scenedesmus obliquus biomass as feedstock for biohydrogen production and valorization of dark fermentation (DF) effluent via biomethanation. The microalgae was cultivated under different CO₂ concentration. CO₂-air sparging of 5% v/v supported maximum microalgal growth and carbohydrate production with CO₂ fixation ability of 727.7 mg L^?1 d^?1. Thereafter, lipid present in microalgae was extracted for biodiesel production and the deoiled microalgal biomass (DMB) was subjected to different pretreatment techniques to maximize the carbohydrate recovery and biohydrogen yield. Steam heating (121 °C) in coherence with H₂SO₄ (0.5 N) documented highest carbohydrate recovery of 87.5%. DF of acid-thermal pretreated DMB resulted in maximum H₂ yield of 97.6 mL g^?1 VS which was almost 10 times higher as compared to untreated DMB (9.8 mL g^?1 VS). Subsequent utilization of DF effluent in biomethanation process resulted in cumulative methane production of 1060 mL L^?1. The total substrate energy recovered from integrated biofuel production system was 30%. The present study envisages a microalgal biorefinery to produce biohydrogen via DF coupled with concomitant CO₂ sequestration.     

A review on alloyed quantum dots and their applications as photocatalysts

Semiconductor driven artificial photocatalysis is the most sustainable technology towards addressing the growing energy and environmental pollution issues. In this context, alloyed quantum dots (QDs) are an emerging class of promising nanomaterials gathering tremendous attention in this area due to several beneficial features. Compared to other bulk semiconductors, alloyed QDs are cost-effective, stable, less-toxic with superior optoelectronic features, which significantly enhances their solar energy conversion efficiency. Herein, the present review summarizes the fundamentals of alloyed QDs, various synthesis techniques, and discusses optical as well as structural properties from data interpretation point of view taking suitably reported literature. Moreover, we have provided a comprehensive summary of recent state of art metal chalcogenides based alloyed QD systems towards H₂ evolution, CO₂ reduction, and pollutant degradation. Finally, the review discusses the associated challenges and future prospects of alloyed QDs with a special focus on preparation, property engineering, theoretical aspect, stability and other field application. Additionally, the overarching aim is to provide researchers an in-depth understanding in the field of alloyed QDs relating to synthesis, characterisation, and promotes their photocatalytic applications, and can foster as a manual to future researchers.     

Metaheuristic-based energy management strategies for fuel cell emergency power unit in electrical aircraft

This paper aims at presenting a comparative analysis of different metaheuristic algorithms in the application of energy management for fuel cell-based hybrid emergency power unit within electrical aircraft. Two energy management conventional strategies are employed while optimizing the operating temperature. Both the external energy maximization and the equivalent consumption minimization strategies are dealt with. The most efficient up-to-date metaheuristic techniques such as the artificial bee colony, the grey wolf optimization, the cuckoo search, the mine blast algorithm, the whale optimization algorithm, the moth swarm algorithm, the harmony search, the modified flower pollination algorithm and the electromagnetic field optimization are considered. The overall index of optimization performance is considered as a function of hydrogen consumption, overall system efficiency, variations of states of charge and stresses in different energy sources. The numerical simulations, through Matlab™/Simulink, highlights the capability of the different metaheuristic optimization techniques towards reducing the amount of consumed hydrogen in fuel cell-based emergency power unit in electrical aircrafts. The electromagnetic field optimization method results in significant hydrogen consumption reduction in comparison with the other proposed techniques.     

Leachate valorization in anaerobic biosystems: Towards the realization of waste-to-energy concept via biohydrogen,biogas and bioelectrochemical processes

Leachate generated in landfills is considered as a hazardous waste stream due to its composition and needs adequate treatment for environmental protection purposes. Nonetheless, a contemporary technology should not only be able to deal with its degradation, but at the same time, recover energy in various forms. Such valorization approaches with priority on these dual-aims are potentially those that rely on anaerobic biosystems. In the literature, processes considered on that matter include fermentative, digestive and bioelectrochemical set-ups to deliver energy-carriers such as biohydrogen (DF), biogas (AD) and electricity (BES), respectively. Moreover, to enhance the global efficiency of leachate utilization, it has been recently trending to develop integrated options by combining these systems (DF, AD, BES) into a cascade scheme. In this review, it is intended to give an insight to the research activities realized in these fields and show possible directions towards the better exploitation of leachate feedstock under anaerobic conditions.     

Improving inter-plant integration of syngas production technologies by the recycling of CO2 and by-product of the Fischer-Tropsch process

This paper deals with the emission reduction in synthesis-gas production by better integration and increasing the energy efficiency of a high-temperature co-electrolysis unit combined with the Fischer-Tropsch process. The investigated process utilises the by-product of Fischer-Tropsch, as an energy source and carbon dioxide as a feedstock for synthesis gas production. The proposed approach is based on adjusting process streams temperatures with the further synthesis of a new heat exchangers network and optimisation of the utility system. The potential of secondary energy resources was determined using plus/minus principles and simulation of a high-temperature co-electrolysis unit. The proposed technique maximises the economic and environmental benefits of inter-unit integration. Two scenarios were considered for sharing the high-temperature co-electrolysis and the Fischer-Tropsch process. In the first scenario, by-products from the Fischer-Tropsch process were used as fuel for a high-temperature co-electrolysis. Optimisation of secondary energy sources and the synthesis of a new heat exchanger network reduce fuel consumption by 47% and electricity by 11%. An additional environmental benefit is reflected in emission reduction by 25,145 tCO₂/y. The second scenario uses fossil fuel as a primary energy source. The new exchanger network for the high-temperature co-electrolysis was built for different energy sources. The use of natural gas resulted in total annual costs of the heat exchanger network to 1,388,034 USD/y, which is 1%, 14%, 116% less than for coal, fuel oil and LPG, respectively. The use of natural gas as a fuel has the lowest carbon footprint of 7288 tCO₂/y. On the other hand, coal as an energy source has commensurable economic indicators that produce 2 times more CO₂, which can be used as a feedstock for a high-temperature co-electrolysis. This work shows how in-depth preliminary analysis can optimise the use of primary and secondary energy resources during inter-plant integration.     

Techno-economic feasibility of power to gas–oxy-fuel boiler hybrid system under uncertainty

One of the main challenges associated with utilisation of the renewable energy is the need for energy storage to handle its intermittent nature. Power-to-Gas (PtG) represents a promising option to foster the conversion of renewable electricity into energy carriers that may attend electrical, thermal, or mechanical needs on-demand. This work aimed to incorporate a stochastic approach (Artificial Neural Network combined with Monte Carlo simulations) into the thermodynamic and economic analysis of the PtG process hybridized with an oxy-fuel boiler (modelled in Aspen Plus^®). Such approach generated probability density curves for the key techno-economic performance indicators of the PtG process. Results showed that the mean utilisation of electricity from RES, accounting for the chemical energy in SNG and heat from methanators, reached 62.6%. Besides, the probability that the discounted cash flow is positive was estimated to be only 13.4%, under the set of conditions considered in the work. This work also showed that in order to make the mean net present value positive, subsidies of 68 €/MW_elh are required (with respect to the electricity consumed by PtG process from RES). This figure is similar to the financial aids received by other technologies in the current economic environment.     

MOFs in photoelectrochemical water splitting: New horizons and challenges

Growing energy consumption with the augmentation in universal population to more than nine billion by 2050 and exhausting fossil fuel reserves necessitates a harsh revolution from non-renewable energy reservoirs to renewable energy reservoirs with zero carbon emission. In the present scenario, solar energy prompted photoelectrochemical (PEC) water splitting or “Artificial Photosynthesis” via light gripping semiconductor material, originates out as the most promising methodology in accomplishing the global energy crisis. Recent studies have amply demonstrated the potential of metal-organic frameworks (MOF) towards PEC applications. They are porous crystalline coordination polymers assembled through an appropriate choice of metal ions and multidentate organic ligands. Owing to their structural regularity and synthetic tunability, MOFs integration with PEC is considered in terms of enhancing and broadening light absorption, providing active sites and directing charge transfer dynamics. Here, we have explored MOFs role in PEC and classified them into different categories such as photosensitizers, co-catalysts, counter electrode, template and also for imparting additional stability to the electrode system. MOFs mediated PEC water splitting is promising but is still rare and in its infancy. Therefore, it is pertinent and timely to take stock of the advancements made and develop insight on the use of MOFs, as an emerging solution for the problems encountered in PEC. This review covers the basics of MOF & mainly describes various case studies done during last 10 years and providing adequate impetus to researchers for critically assessing the recent advances and challenges that are faced by scientists and researchers at large.