Solar assisted multi-generation system using nanofluids: A comparative analysis

In this comparative study, a parabolic trough solar collector and a parabolic dish solar collector integrated separately with a Rankine cycle and an electrolyzer are analyzed for power as well as hydrogen production. The absorption fluids used in the solar collectors are Al₂O₃ and Fe₂O₃ based nanofluids and molten salts of LiCl–RbCl and NaNO₃–KNO₃. The ambient temperature, inlet temperature, solar irradiance and percentage of nanoparticles are varied to investigate their effects on heat rate and net power produced, the outlet temperature of the solar receiver, overall energy and exergy efficiencies and the rate of hydrogen produced. The results obtained show that the net power produced by the parabolic dish assisted thermal power plant is higher (2.48 kW–8.17 kW) in comparison to parabolic trough (1 kW–6.23 kW). It is observed that both aluminum oxide (Al₂O₃) and ferric oxide (Fe₂O₃) based nanofluids have better overall performance and generate higher net power as compared to the molten salts. An increase in inlet temperature is observed to decrease the hydrogen production rate. The rate of hydrogen production is found to be higher using nanofluids as solar absorbers. The hydrogen production rate for parabolic dish thermal power plant and parabolic trough thermal power plant varies from 0.0098 g/s to 0.0322 g/s and from 0.00395 g/s to 0.02454 g/s, respectively.     

Experimental study on coal multi-generation in dual fluidized beds

An atmospheric test system of dual fluidized beds for coal multi-generation was built.One bubbling fluidized bedis for gasification and a circulating fluidized bed for combustion.The two beds are combined with two valves:one valve to send high temperature ash from combustion bed to the gasification bed and another valve to sendchar and ash from gasification bed to combustion bed.Experiments on Shenhua coal multi-generation were madeat temperatures from 1112 K to 1191 K in the dual fluidized beds.The temperatures of the combustor are stableand the char combustion efficiency is about 98%.Increasing air/coal ratio to the fluidized bed leads to theincrease of temperature and gasification efficiency.The maximum gasification efficiency is 36.7% and thecalorific value of fuel gas is 10.7 MJ/Nm3.The tar yield in this work is 1.5%,much lower than that of pyrolysis.Carbon conversion efficiency to fuel gas and flue gas is about 90%.     

Underground hydrogen storage: A comprehensive review

Increased emissions of greenhouse gasses into the atmosphere has adversely been contributing to global warming as a result of burning fossil fuels. Therefore, the energy sectors have been looking into renewable sources such as wind, solar, and hydro energy to make electricity. However, the strongly fluctuating nature of electricity from such energy sources requires a bulk energy storage system to store the excess energy as a buffer and to fulfill the demand constantly. Underground storage is a proven way to store a huge amount of energy (electricity) after converting it into hydrogen as it has higher energy content per unit mass than other gases such as methane and natural gas. This paper reviews the technical aspects and feasibility of the underground storage of hydrogen into depleted hydrocarbon reservoirs, aquifers, and manmade underground cavity (caverns). Mechanisms of underground hydrogen storage (UHS) followed by numerous phenomena such as hydrodynamics, geochemical, physiochemical, bio-chemical, or microbial reactions have been deliberated. Modeling studies have also been incorporated in the literature to assess the feasibility of the process that are also reviewed in this paper. Worldwide ongoing lab study, field study together with potential storage sites have been reported as well. Technical challenges along with proper remedial techniques and economic viability have been briefly discussed. Finally, this paper delivers some feasible strategies for the underground hydrogen storage process, which would be helpful for future research and development of UHS.     

Gas resources and gas markets: A global view

Although natural gas constitutes 42% of the energy content of world hydrocarbon resources, it accounts for only about 8% of total international oil and gas trade. Gas-trade projects are costly and require large scale “anchors” at each end: a substantial market in the importing region and a significant gas reserve in the exporting country. Due to the small size of many gas deposits, and for other reasons, many of the world's gas reserves are not well-suited as a basis for international trade. They will be used increasingly to support local economic development or will remain in the ground until markets emerge. Gas reserves may be classified according to their degree of accessibility to local and international markets. Countries facing gas-development decisions must consider such questions as how best to encourage gas exploration, what volume of gas to set aside for future domestic consumption and, if reserves are sufficient to justify an export project, how to determine the value of gas in the markets of importing countries.     

Distributed photovoltaic generation and energy storage systems: A review

Currently, in the field of operation and planning of electrical power systems, a new challenge is growing which includes with the increase in the level of distributed generation from new energy sources, especially renewable sources. The question of load redistribution for better energetic usage is of vital importance since these new renewable energy sources are often intermittent. Therefore, new systems must be proposed which ally energy storage with renewable energy generators for reestablishment of grid reliability. This work presents a review of energy storage and redistribution associated with photovoltaic energy, proposing a distributed micro-generation complex connected to the electrical power grid using energy storage systems, with an emphasis placed on the use of NaS batteries. These systems aim to improve the load factor, considering supply side management, and the offer of backup energy, in the case of demand side management.     

Production of first and second generation biofuels: A comprehensive review

Sustainable economic and industrial growth requires safe, sustainable resources of energy. For the future re-arrangement of a sustainable economy to biological raw materials, completely new approaches in research and development, production, and economy are necessary. The ‘first-generation’ biofuels appear unsustainable because of the potential stress that their production places on food commodities. For organic chemicals and materials these needs to follow a biorefinery model under environmentally sustainable conditions. Where these operate at present, their product range is largely limited to simple materials (i.e. cellulose, ethanol, and biofuels). Second generation biorefineries need to build on the need for sustainable chemical products through modern and proven green chemical technologies such as bioprocessing including pyrolysis, Fisher Tropsch, and other catalytic processes in order to make more complex molecules and materials on which a future sustainable society will be based. This review focus on cost effective technologies and the processes to convert biomass into useful liquid biofuels and bioproducts, with particular focus on some biorefinery concepts based on different feedstocks aiming at the integral utilization of these feedstocks for the production of value added chemicals.     

Biodiesel synthesis from Acacia concinna seed oil: A comprehensive study

In the present investigation, biodiesel (BD) production from Acacia concinna nonedible seed oil using physical pretreatment (turbulent agitation method) and transesterification process has been optimized and modeled using neural network Artificial neural network- Adaptive neuro-fuzzy inference system (ANN-ANFIS), Grey relational analysis? and desirability function approach? approach considering both quantity (production yield) and quality (fuel properties) responses. Different process parameters were examined for their relative significance on output responses. At optimized process variables, methanol/oil (8.3:1), catalyst KOH (0.95 wt%), and reaction temperature and time (65°C and 37.5 min), augment the yield and calorific value by 17.2 and 5.77% and reduce the viscosity and free fatty acid? valueby 18.26 and 57.30%, respectively, with global desirability of D= 0.664. The produced BD was characterized by ¹H NMR, fatty esters (GC analysis), and fuel properties. The developed model equations for output responses help in accurate prediction of results. A. concinna feedstock proved to be a viable source for biodiesel production.     

A chromium complex under water oxidation: A conversion mechanism and a comprehensive hypothesis

Water splitting toward hydrogen production is a promising method to store energy, but water oxidation is a bottleneck for water splitting. First-row transition metal complexes have been extensively used for water-oxidation reaction. However, only one chromium complex has been applied for water-oxidation reaction until now. Thus, the reinvestigation of water-oxidation reaction by this chromium complex in detail is interesting. Herein, water-oxidation reaction by the chromium complex with diphenoxy N,N′-ethylenebis(salicylimine) (SALEN) ligand is reinvestigated using scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction studies, X-ray photoelectron spectroscopy, thermal gravimetric analysis, elemental analysis, Fourier-transform infrared spectroscopy, and electrochemical methods. All the experiments showed that the chromium complex is neither a catalyst nor a precatalyst for water-oxidation reaction. During OER, a relationship between first-row transition metal complexes and the related metal oxides has been proposed.     

Development and exergoeconomic evaluation of a SOFC-GT driven multi-generation system to supply residential demands: Electricity,fresh water and hydrogen

In this study, a novel multi-generation system is proposed by integrating a solid oxide fuel cell (SOFC)-gas turbine (GT) with multi-effect desalination (MED), organic flash cycle (OFC) and polymer electrolyte membrane electrolyzer (PEME) for simultaneous production of electricity, fresh water and hydrogen. A comprehensive exergoeconomic analysis and optimization are conducted to find the best design parameters considering exergy efficiency and total unit cost of products as objective functions. The results show that the exergy efficiency and the total unit cost of products in the optimal condition are 59.4% and 23.6 $/GJ, respectively, which offers an increase of 2% compared to exergy efficiency of SOFC-GT system. Moreover, the system is capable of producing 2.5 MW of electricity by the SOFC-GT system, 5.6 m³/h of fresh water by MED unit, and 1.8 kg/h of hydrogen by the PEME. The associated cost for producing electricity, fresh water and hydrogen are 3.4 cent/kWh, 37.8 cent/m³, and 1.7 $/kg, respectively. A comparison between the results of the proposed system and those reported in other related papers are presented. The diagram of the exergy flow is also plotted for the exact determination of the exergy flow rate in each component, and also, location and value of exergy destruction. Finally, the capability of the proposed system for a case study of Iran is examined.     

Solar power engineering in the future world: A view from Russia

The paper suggests an energy model for the future world based on solar power engineering and new Russian energy technologies. Chlorine-free solar silicon technologies, stationary concentrators, solar modules with service lives doubled up to 40 years, matrix solar elements with an efficiency factor of 20% at a concentration of 5–500, and resonance waveguide methods for transmitting energy for solar energy systems are considered.     

Psychological factors influencing sustainable energy technology acceptance: A review-based comprehensive framework

Environmental and societal problems related to energy use have spurred the development of sustainable energy technologies, such as wind mills, carbon capture and storage, and hydrogen vehicles. Public acceptance of these technologies is crucial for their successful introduction into society. Although various studies have investigated technology acceptance, most technology acceptance studies focused on a limited set of factors that can influence public acceptance, and were not based on a comprehensive framework including key factors influencing technology acceptance. This paper puts forward a comprehensive framework of energy technology acceptance, based on a review of psychological theories and on empirical technology acceptance studies. The framework aims to explain the intention to act in favor or against new sustainable energy technologies, which is assumed to be influenced by attitude, social norms, perceived behavioral control, and personal norm. In the framework, attitude is influenced by the perceived costs, risks and benefits, positive and negative feelings in response to the technology, trust, procedural fairness and distributive fairness. Personal norm is influenced by perceived costs, risks and benefits, outcome efficacy and awareness of adverse consequences of not accepting the new technology. The paper concludes with discussing the applicability of the framework.     

A comprehensive modeling study of iso-octane oxidation

A detailed chemical kinetic mechanism has been developed and used to study the oxidation of iso-octane in a jet-stirred reactor, flow reactors, shock tubes and in a motored engine. Over the series of experiments investigated, the initial pressure ranged from 1 to 45 atm, the temperature from 550 K to 1700 K, the equivalence ratio from 0.3 to 1.5, with nitrogen-argon dilution from 70% to 99%. This range of physical conditions, together with the measurements of ignition delay time and concentrations, provide a broad-ranging test of the chemical kinetic mechanism. This mechanism was based on our previous modeling of alkane combustion and, in particular, on our study of the oxidation of n-heptane. Experimental results of ignition behind reflected shock waves were used to develop and validate the predictive capability of the reaction mechanism at both low and high temperatures. Moreover, species’ concentrations from flow reactors and a jet-stirred reactor were used to help complement and refine the low and intermediate temperature portions of the reaction mechanism, leading to good predictions of intermediate products in most cases. In addition, a sensitivity analysis was performed for each of the combustion environments in an attempt to identify the most important reactions under the relevant conditions of study.     

A comprehensive review on PEM water electrolysis

Hydrogen is often considered the best means by which to store energy coming from renewable and intermittent power sources. With the growing capacity of localized renewable energy sources surpassing the gigawatt range, a storage system of equal magnitude is required. PEM electrolysis provides a sustainable solution for the production of hydrogen, and is well suited to couple with energy sources such as wind and solar. However, due to low demand in electrolytic hydrogen in the last century, little research has been done on PEM electrolysis with many challenges still unexplored. The ever increasing desire for green energy has rekindled the interest on PEM electrolysis, thus the compilation and recovery of past research and developments is important and necessary. In this review, PEM water electrolysis is comprehensively highlighted and discussed. The challenges new and old related to electrocatalysts, solid electrolyte, current collectors, separator plates and modeling efforts will also be addressed. The main message is to clearly set the state-of-the-art for the PEM electrolysis technology, be insightful of the research that is already done and the challenges that still exist. This information will provide several future research directions and a road map in order to aid scientists in establishing PEM electrolysis as a commercially viable hydrogen production solution.     

Carbon futures and macroeconomic risk factors: A view from the EU ETS

This article examines the empirical relationship between the returns on carbon futures – a new class of commodity assets traded since 2005 on the European Union Emissions Trading Scheme (EU ETS) – and changes in macroeconomic conditions. By using variables which possess forecast power for equity and commodity returns, we document that carbon futures returns may be weakly forecast on the basis of two variables from the stock and bond markets, i.e. equity dividend yields and the “junk bond” premium. Our results also suggest that the forecast abilities of two variables related to interest rates variation and economic trends on global commodity markets, respectively the U.S. Treasury bill yields and the excess return on the Reuters/CRB Index, are not robust on the carbon market. This latter result reinforces the belief that the EU ETS is currently operating as a very specific commodity market, with distinct fundamentals linked to allowance supply and power demand. The sensitivity of carbon futures to macroeconomic influences is carefully identified following a sub-sample decomposition before and after August 2007, which attempts to take into account the potential impact of the “credit crunch” crisis. Collectively, these results challenge the market observers' viewpoint that carbon futures prices are immediately correlated with changes in the macroeconomic environment, and rather suggest that the carbon market is only remotely connected to macroeconomic variables. The economic logic behind these results may be related to the fuel-switching behavior of power producers in influencing primarily carbon futures price changes.     

The food v. fuel debate: A nuanced view of incentive structures

The rapid rise in crude oil prices and the geo-political uncertainty associated with ensuring uninterrupted supplies have compelled researchers, economists and politicians to look for indigenous substitutes. Liquid biofuels – ethanol and biodiesel – are widely recognized, technically feasible alternatives. Even as the jury is out to determine the environmental footprint of biofuels, the surrounding frenzy has often led to the announcement of unsustainable support prices for feedstock and unviable procurement prices for the finished product. This paper makes a detailed assessment of incentive structures facing the agriculturists, refiners and the consumers. Data from the Indian market are employed to illustrate.     

A comprehensive review on hydrogen production from coal gasification: Challenges and Opportunities

This paper comparatively discusses hydrogen production options through coal gasification, including plasma methods, and evaluate them for practical applications. In this regard, it focuses on numerous aspects of hydrogen production from coal gasification, including (i) state of the art and comparative evaluation, (ii) environmental and economic dimensions, (iii) energetic and exergetic aspects, (iv) challenges, opportunities and future directions. Furthermore, this review paper outlines what differences it brings in and what contributions it makes to the current literature about such a significant domain of potential hydrogen production which can be used as clean fuel, energy carrier and feedstock. Accordingly, this comprehensive review offers some results as follows: (i) plasma gasification system produces higher amount of hydrogen from other gasification processes, (ii) less amounts of solid wastes (slag, ash, tar, etc.) are released during plasma gasification process compared to other gasification processes, and (iii) it is overall more sustainable Thus, plasma gasification is proposed as a potential option for hydrogen fuel production from coals and for practical application in energy sector. As a case study, some plasma gasifiers in the literature are analyzed in terms of the exergetic sustainability. Furthermore, the case study results show that the exergetic sustainability index decreases from 0.642 to 0.186, and the exergetic efficiency drops from 0.342 to 0.156, while the environmental impact factor increases from 1.556 to 5.372 with an increase of waste exergy ratio from 0.839 to 0.532, respectively.     

Public awareness of hydrogen energy: A comprehensive evaluation based on statistical approach

Climate change and environmental problems, increasing global energy demand, and uncertainties in energy supply have brought the production and use of sustainable energy resources to be crucial. Hydrogen, which is an important energy carrier, is being produced and used globally within the perspective of sustainable energy and environmental technologies. Public awareness is an important step toward the spread of hydrogen energy (HE). In the literature, while public awareness studies focus on renewable energy sources, no study that examines public awareness in the field of HE in a way that addresses different perspectives has come across. This pioneering study aims to explore public awareness of HE by analyzing survey data collected from individuals via basic statistical techniques. Findings indicate that individuals' awareness of hydrogen energy mainly varies according to their knowledge level, education level, and age group. The results of the study will provide an important perspective for all stakeholders on hydrogen energy. Especially the policymakers should consider these results to constitute the frameworks of policy without compromising any perspective of public awareness.     

Co-production of electricity and hydrogen from wind: A comprehensive scenario-based techno-economic analysis

The aim of this study is to investigate the economic prospects of producing electricity and hydrogen using wind energy under different scenarios. For this, the most essential criteria to investors including Levelized Cost of Wind-generated Electricity (LCOWE), Levelized Cost of Wind-based Hydrogen (LCOWH), payback period, and rate of return are examined. Technical and environmental impacts are factored into the LCOWE formulation to obtain comprehensive insight. Owing to the uncertain nature of future, five degradation rates concerned with wind turbine performance and five likely rates as to the future value of money are investigated under the scenarios of I) utilizing wind electricity to replace fuel oil electricity, II) to replace natural gas electricity and III) without considering environmental penalties. The results indicate that LCOWE would be in the range of 0.0325–0.0755 $/kWh, while the corresponding LCOWH being in the range of 1.375–1.59 $/kg. Moreover, payback period of the related LCOWE and LCOWH would be in the range of 2.55–9.48 yr during the lifetime of wind power plant and 3.91–8.41 yr during that of hydrogen production system, respectively. The corresponding rate of return pertinent to the above-mentioned ones would be respectively in the range of 14.15–23.54% and of 9.87–21.55%.