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Biomass raw materials are widely regarded as a significant source of renewable energy, which significantly reduces the dependence on traditional fossil fuels, especially in the case of countries that are able to obtain biomass from various sources. Recently, pelletization has been widely used for mass and energy densification of biomass to overcome the problems associated with raw material use. As the global pellet market has developed quickly, the use of wood residues became no longer sufficient to fulfill the market needs. The standards of pellets provide limits for both physical and mechanical characteristics of produced pellets. Characteristics of produced pellets depend mainly on the feedstock characteristics as particle size and moisture content and operating conditions as applied pressure and die temperature. Thus, this paper provides rich information on the factors affecting the physical and mechanical properties of granules included in pellets. The main goal of the paper is to review the latest and comprehensive research on the physical and mechanical properties of most types of single and mixed pellets from biomass. The analysis of the effect of properties, adhesives, humidity, pressure and temperature as well as the physical and mechanical properties of the pellets studied was carried out. In addition, the critical and optimal values of various factors for different materials in which the following is of importance: high quality of pellets and biomass from which they are produced were analyzed. The principle and effect of applying post-production conditions as steam explosion and torrefaction on the characteristics of the pellets were reviewed in details. Moreover, this study proposes some recommendations for further development of the pelletization analysis and characteristics.

The expedition for inexpensive, renewable and environmentally friendly source of energy to replace the conventional sources like coal and petroleum is currently the most focused research area. Biomass resource in the form of crop residues is the abundant and readily accessible renewable resource. Wheat, rice and maize are the major cereal crops around the globe and are found to be the major sources of residual lignocellulosic biomass in the form of straw. In India, this is usually burnt in the field and is thus underutilized. These residues may be harnessed for bioenergy production by thermal and biochemical processes. This review is exclusively focused on chemical pretreatment of these residues to generate biomethane by unmasking lignin. The paper also reviews the essential properties of the residual biomass such as proximate, ultimate and compositional for the quality of derived biofuels (bioethanol and biomethane). Biomass to bioenergy conversion process, biomethane and bioethanol fermentation process and comparison of biomethane and bioethanol in terms of yield and energy value is also discussed. These cereal crop residual biomass contribute in the production of renewable and sustainable energy.

The palm oil industry generates significant amounts of solid wastes. The solid wastes, also known as oil palm biomass, includes the trunk (OPT) and fronds (OPT) from the plantation, and empty fruit bunch (EFB), mesocarp fibre (MF) and palm kernel shell (PKS) from the processing mills. Oil palm biomass is not effectively recycled for other applications, and existing disposal practices can cause adverse impacts on the environment. As oil palm biomass is a readily available lignocellulosic biomass, it has the potential to be a low-cost feedstock for conversion into higher value products. The first part of this study provides a comprehensive review of utilisation of oil palm biomass for the production of biofuels, chemicals and biomaterials through direct utilisation and physical conversion, biochemical conversion, thermochemical conversion and synthesis of lignin-based materials. The second part of this study discusses the opportunity for biorefinery development based on existing bioproducts from oil palm biomass, for the production of advanced fuels and platform chemicals that have not been explored in oil palm biomass research. This study proposes integrated biorefinery concepts via the integration of existing oil palm biomass biorefinery products with thermochemical process for upgrading the bioproducts into higher values products. The high-value products integrated biorefinery products include advanced biofuels, fuel additives and platform chemicals. The integrated biorefinery development for oil palm biomass processing is expected to improve the economics of the production of biomass-derived renewable energy and enhance the sustainability of palm oil industry.

Biomass is an interesting option as renewable energy source around the world. In this work, the Eucalyptus urosemente, a hybrid formed from the combination of Eucalyptus grandis x Eucalyptus citriodora, was energetically characterized considering the logs diameter and the number of days after cutting. The main objective of the present work is to define the best condition for its use as fuel in boilers. For the experimental evaluation of this new species, the samples were divided into fine or mixed, both with 1, 30 60, 90, 120, and 150 days after cutting. Following the Brazilian standard norms, were performed tests of moisture content, proximate analysis, and calorific values. Additionally, in some samples was applied the torrefaction thermal treatment. The results showed that the moisture content and the low heating value were influenced by the diameter and number of days after cutting. Furthermore, torrefied samples presented an increase of calorific values and hydrophobicity. Based on the low heating value, it was concluded that firewood should be consumed within a range of 90–120 days after cutting, avoiding the biodegradation process. Finally, the torrefaction method proved to be an attractive treatment to allow the surplus biomass commercialization and distribution.

Bioethanol is an attractive biofuel having potential for energy security and environmental safety over fossil fuels. To date, numerous biomass resources have been investigated for bioethanol production, which can broadly be classified into sugars, starch and lignocellulosic biomass. However, conversion of biomass into ethanol varies considerably depending on the nature of feedstock, primarily due to the variation in biochemical composition, and so, only a few feedstocks have been exploited commercially. In recent years, the conversion process of biomass has been improved significantly, even though most of these achievements are yet to be implemented in commercial facility. All the major steps in a typical conversion process, particularly fermentation of sugars that is the common step for all biomass, are greatly influenced by microorganisms. A traditional yeast, Saccharomyces cerevisiae, and a bacterial species, Zymomonas mobilis, are widely used in the ethanol fermentation technology. Many factors affect ethanol production process, and the final yield is directly associated with the optimum conditions of these attributes. This review paper presents an overview on the first and second generation bioethanol production with a particular attention to the potential of various biomass sources, technological approaches, role of microorganisms and factors affecting ethanol production process.

The growing of food waste generation is gradually becoming a global problem due to the improper management of it. According to the Food and Agriculture Organization (FAO), United Nation, more than 1.3 million tonnes of food is being wasted. Food waste and food processing waste are abundant - which are rich in organic acids and nutrients. These acids and nutrients can be utilized for attractive and efficient generation of renewable and sustainable fuels such as biohydrogen through fermentation process. Many investigations have revealed a significant biohydrogen generation using food wastes from restaurant, dining hall and food processing industries. During the hydrogen generation through fermentation, several parameters influence the yield of hydrogen. Some of them are method of pre-treatment, feed composition, fermentation temperature, culture and substrate, solution pH, etc. Also, the presence of inert intermediates produced during the reaction in fermentation process reduces the process efficiency. Few studies have shown that the use of nanoparticles in fermentation process along with the application of short & cyclic ultrasound is beneficial to increase the process efficiency. The augmentation in ultrasound-assisted process is due to the physical and chemical effects of ultrasound in the medium through the phenomenon of cavitation. During the transient collapse of cavitation bubbles, several reactive species are produced which further participate in the thermochemical and biochemical reactions. Thus, enhances the rate of reaction by annihilation the complex sugars in food wastes. Additionally, the cavitational effect helps to reduce the growth of hydrogen inhibiting microorganism in the feed. This review demonstrates the potentiality of food waste for production of biohydrogen through fermentation process including a brief overview of process parameters that affect the fermentation process. Additionally, an overview of integrated fermentative process coupled with nanoparticles and ultrasound is also discussed for enhanced biohydrogen generation from food waste.

The Palm Oil industry is growing faster, as the global demand for its products greatly overcomes its production. As palm oil production increases, also does its effluent, Palm Oil Mill Effluent (POME). POME is a complex effluent, which is not toxic, but due to its elevated organic content, it is considered extremely polluting. Generally, POME is submitted to both physical and chemical treatments before being discarded into receiving streams or other water bodies. This process might be costly for the industry and there 98is no income from effluent treatment, therefore another destination for this effluent is desirable. As an alternative, this residue could be exploited as raw material in biological processes, specially hydrogen and methane production, due to the presence of carbohydrates, lipids and proteins that might be metabolized during the dark fermentation process. Hydrogen can be used in different industries, such as chemical, biochemical and food industries. Methane is an important combustible, which could substitute natural gas and hydrogen as a very promising fuel. This review approaches sustainable and renewable processes for POME exploitation as raw material for renewable energy production.

Wet torrefaction (WT) is a sustainable subcritical water pretreatment technology to upgrade moist biomass into hydrochar solid fuel with superior fuel properties with the avoidance of energy-intensive conventional thermal drying. In order to obtain a holistic understanding of WT processing system, this review has comprehensively discussed recent advances in WT of biomass to produce high quality solid fuel and its subsequent thermochemical applications. This review has not only summarized distinct advantages of WT over dry torrefaction of biomass with high moisture content but also clarified the similarities and differences between WT and hydrothermal carbonization. According to structures and chemical compositions of components therein, four representative categories of diverse biomass materials were selected to describe the influence of intrinsic nature of biomass on fuel quality of hydrochar derived from WT. Furthermore, this article has attempted to figure out the inherent relationship between WT conditions and fuel properties with respect to operating conditions (e.g. temperature, pressure, and residence time), biomass to water ratio, acids and additives, torrefaction atmosphere, and heating techniques. Three conventional thermochemical applications of wet-torrefied biomass have been extensively reviewed to reveal that WT could benefit energy recovery from wet biomass in terms of improved quality of ultimate energy carriers and obviously reduced pollutants emissions. Nevertheless, critical concerns associated with optimization of operating cost, minimization and controlling of pollutants emissions, re-design of industrially applicable reactor, and system integration with downstream applications have been pointed out in order to make WT technology more environmentally and commercially viable.

This study investigated activated sludge (AS) dewatering and reuse for solid biofuel by novelty combining and a low H2O2 dose and pulse ultrasonication followed by torrefaction to achieve zero-waste with the supernatant also recycled for nutrient supply to the AS unit. Mass and volume reduction rates are employed to evaluate the AS dewatering efficiency, and the biochar characteristics were systematically evaluated using higher heating value (HHV), mass and energy yield, proximate and ultimate analyses, and combustibility. The energy return on investment (EROI), greenhouse gas (GHG) emissions, and cost-effectiveness of the proposed technology were also systematically evaluated. Results showed that the mass and volume reduction rates of AS using an H2O2 concentration of 0.8 % with ultrasonication at 70 W for 20 s was higher than 50 % and promoted the release of protein and carbohydrate content in the supernatant. Torrefaction of residual AS produced biochar with HHV of 17.8–18.4 MJ/kg. The biochar with 57.4 % less GHG emissions than burning bituminous coal, high EROI (4.7–7.3), but a low fuel ratio. Thus, we propose co-firing 10–20 % biochar with coal to enhance the FRs to that of bituminous coal while simultaneously mitigating GHG emissions. The production cost of biochar was 56.3 % lower than the traditional AS disposal cost. Therefore, the proposed technology is environmentally and economically friendly and can solve sludge disposal problems, produce biochar with reasonable cost for renewable energy, mitigate global warming, and recover supernatant as a nutrient feedstock. It is worth developing practical applications in this field.

Bioethanol is one of the most promising and eco-friendly alternatives to fossil fuels, which is produced from renewable sources. Although almost all the current fuel ethanol is generated from edible sources (sugars and starch), lignocellulosic biomass (LCB) has drawn much attention in recent times. However, the conversion efficiency as well as ethanol yield of the biomass differs greatly with respect to the source and nature of LCB, primarily due to the variation in lignocellulosic content. Two major polysaccharides in LCB, namely, cellulose and hemicellulose firmly link to lignin and form a complex lignocellulosic network, which is highly robust and recalcitrant to depolymerization. For this reason, generation of ethanol from LCB requires a complicated conversion process that has made it commercially non-competitive. As attempts to exploit LCBs into commercial ethanol production, recent research efforts have been devoted to the techno-economic improvements of the overall conversion process, in addition to screen out promising feedstocks. This review paper presents an overview on the diversity of biomass, technological approaches and microbial contribution to the conversion of LCB into ethanol.

The high energy and silica contents of rice husks make them attractive for use in renewable energy and green chemical strategies. This review comprehensively discussed the potential route of rice husk utilization to energy and bio-silica simultaneously which is still lacking to investigate. The ash content in the dry rice husk could be up to 25 wt% and the high silica content in the rice husk ash could reach 99.77 d b. wt%. About 1 tonne/h of rice husk combustion could produce about 600–700 kWh of averaged net electricity so that it can be employed to support a small and simple power plant. Apart from that, applying acid leaching as a pretreatment before rice husk ash extraction with NaOH could achieve bio-silica with 98% recovery, 99.7% purity, and 400.69 m2/g surface area. Rice husk combustion in a suspension combustor seems to be appropriate to maintain the low combustion temperature at 700 °C in order to prevent the crystalline silica formation in the rice husk ash. The combustion efficiency is very high with 0.8% of unburnt carbon content in the ash as well as CO and NOx emissions are below 250 ppm. This review reveals that the industrial-scale for energy and amorphous bio-silica production from rice husk through a suspension combustor with optimized operating parameters emerges as a future prospect. It can lead to sustainability and self-reliance on chemicals and energy sectors, of which there are many research and development challenges to overcome.

Commercial production of jet fuel from biobased feedstocks is still encumbering, mainly due to their high production cost and competition with food resources. Pennycress oilseed is a potential jet fuel feedstock which can be supplied at a lower price compared to similar oilseeds, such as soybean and canola. However, the techno-economics of pennycress-based jet fuel production needs to be evaluated. The objective of this study was to assess the technical feasibility and costs of hydroprocessed renewable jet fuel (HRJ) production from pennycress. The production capacity was considered to be 18.9 million L/yr (5 million gal/yr). The analysis considered pennycress grain handling and conditioning, oil extraction and conversion to HRJ and byproducts, i.e., LPG, naphtha and green diesel, through hydroprocessing technology, as well as pennycress meal processing as boiler fuel and wastewater treatment. Total investment for establishing the HRJ biorefinery at the selected capacity was estimated to be 90.8 million USD. Minimum selling price (MSP) of HRJ was estimated to be 1.2 USD/L, which was comparable to the MSP of HRJ from similar oilseeds, including soybean and canola. It could also be further reduced by supplying pennycress grain at a lower price, increasing the oil content and increasing the production capacity of the biorefinery. The outcomes of this research would help establish the performance targets needed to reach the economic viability of HRJ production from pennycress at the commercial scale.

Hydrogen (H2) is an effective, environmentally friendly and renewable source of fuel that can be produced during dark- and photo-fermentation by different facultative and obligate anaerobic and purple bacteria and microalgae. This product is known as biohydrogen. It has the advantage of variable yield at low temperature (for mesophiles growing best at moderate temperature) and relatively low production cost, if compared with thermochemical methods. To develop fermentative H2 production biotechnology using cheap carbonaceous by-products and utilization of organic wastes, the selection or construction of effective bacterial strains and optimization of technology process conditions are required. Here we review recent new data that have been obtained with Escherichia coli, Clostridium beijerinskii, Rhodobacter sphaeroides and other bacteria. Activities of [Ni-Fe]-hydrogenases of dark-fermentative bacteria and [Mo]-nitrogenase and [Ni-Fe]-hydrogenase of photo-fermentative species have been examined after growth with different carbon sources, using pure cultures, as well as co-culture and mixed-cultures technologies. Importantly, H2 production from cheap and readily available substrates like crude glycerol or different industrial, agricultural and other carbon-based wastes by bacteria is a sustainable technology. Consequently further approaches and strain-improvement could increase H2 production in a cost-effective way, and they will lead to both small- and large-scale H2 production. Moreover, they will provide significant economic and environmental benefits for renewable and sustainable energy supply in the near future.

The gradual shift of transportation fuels from oil based fuels to alternative fuel resources and worldwide demand for energy has been the impetus for research to produce alcohol biofuels from renewable resources which focus on utilizing simple sugars from lignocellulosic biomass, the largest known renewable carbohydrate source as an alternative. Currently, the usage of bioethanol and biodiesel do not cover an increasing demand for biofuels. Hence, there is an extensive need for advanced biofuels with superior fuel properties. Biobutanol is regarded to be an excellent biofuel compared to bioethanol in terms of energy density and hygroscopicity, could be produced through acetone-butanol-ethanol (ABE) fermentation process. Even though the ABE fermentation is one of the oldest large-scale fermentation processes, biobutanol yield by anaerobic fermentation remains sub-optimal. For sustainable industrial scale of biobutanol production, a number of obstacles need to be addressed including choice of feedstock, low product yield, product toxicity to strain, multiple end-products and downstream processing of alcohol mixtures plus the metabolic engineering for improvement of fermentation process and products. Studies on the kinetic and physiological models for fermentation using lignocellulosic biomass provide useful information for process optimization. Simultaneous saccharification and fermentation (SSF) with in-situ product removal techniques have been developed to improve production economics due to the lower biobutanol yield in the fermentation broth. The present review is attempting to provide an overall outlook on the discoveries and strategies that are being developed for biobutanol production from lignocellulosic biomass.

Based on their environmental benefits, microalgae are currently the most favorable renewable biofeedstock materials for biodiesel production. However, the possibility of an economically viable production system using microalgae is still technology-driven, not yet market-driven due to its higher production cost. Accordingly, to establish industrial manufacturing systems for microalgal biodiesel, it is critical to develop technology for its cost-effective production. Here, we propose some novel molecular strategies, which have not been attempted for microalgal biodiesel production and are conducive to cost-effective production of biodiesel from microalgae. These include genetic manipulation strategies for higher biomass yield and extracellular production of free fatty acids, triacylglycerol, and fatty acid ethyl ester (biodiesel) with high quality, which could be exploited as a breakthrough technology for the cost-efficient production of microalgal biodiesel.

This paper maps the availability of deforested and degraded land in the state of Para in the eastern Amazon and discusses the feasibility of using this land for the expansion of palm crops for biod ...

Biodiesel can be considered as the optimum alternative fuel for diesel fuel in Iran. Biodiesel is an environmentally friendly fuel and has the potential to provide comparable engine performance results. The biodiesel production potential from oil seeds such as canola, soybean, cotton, seasem, olive, sunflower, safflower, almond, corn, coconut, walnut and hazelnut in Iran is investigated in this paper. In Iran, oil seeds are not commonly used for energy application. This is because; more than 90% of the edible oil for human consumption is being imported. To contribute to the fuel supply, renewable energies such as oil seeds to be an attractive resource for biodiesel production, this paper aims to cover several perspectives on the size of the biodiesel oil seeds resource in Iran. Oil seeds are harvested every year in Iran. Around 1 million ha of land from 20 states are estimated to be potential land for growing of oil seeds. There are approximately 3.67 MT (million ton) of oil seeds crops in Iran that can potentially produce 721 ML (million liter) of biodiesel every year. Canola, cotton and soybean are the most favorable biodiesel production source. Based on the results, it can be concluded that production of biodiesel from the seed oils can ideally replace about 2% of total diesel fuel consumption in Iran. By managing this, an B2 (2% biodiesel and 98% diesel) can be an optimum alternative fuel for compressed ignition engine since there is no major engine modification required to use biodiesel.

Resource depletion and mitigation of climate change are the driving forces to find alternatives to fossil fuels. Seaweeds (macroalgae) have been considered as a promising alternative source of biofuels due to higher growth rates, greater production yields and a higher rate of carbon dioxide fixation, than land crops. A comparatively easily depolymerized structure, lack of need of arable land and no fresh water requirement for cultivation, make seaweed a potential feedstock for gaseous biofuel production. Biomethane potential of seaweed is greatly dependent on its chemical composition that is highly variable due to its type, habitat, cultivation method and time of harvest. Saccharina latissima and Laminaria digitata are the highest biomethane yielding Irish brown seaweeds. Seaweed harvested in July (northern hemisphere) was estimated to give gross energy yields in the range 38–384 GJ ha−1 yr−1; higher values are dependent on innovative cultivation systems. An integrated model is suggested where seaweed can be co-digested with other feedstock for the sustainable production of gaseous fuel to facilitate EU renewable energy targets in transport.

The importance of lignocellulosic biomass as important bioresources that can be utilized in many forms has increased in the last few decades. Cassava peels, a lignocellulosic biomass discarded during cassava processing, are commonly found in the tropics and several other countries around the world due to the popularity of cassava as an important calorie source. Interestingly however, a lot of energy deprived, oil dependent countries are also amongst the highest producer of this biomass. Hence, this review explores the suitability of cassava peels as a lignocellulosic biomass substrate for the production of bioethanol. Special consideration to the properties of the biomass drive the conceptualized plant design while conditions for optimal production and salient economic considerations are discussed. A cellulosic biorefinery of this type is expected to help in harnessing the presently improperly managed agricultural processing byproduct with a view to reducing dependence on fossil fuels, which are totally non-renewable and have damaging effects on the environment especially in developing countries.

Rapid economic growth in Asia and especially in China, will lead to a huge increase of food waste (FW) production that is expected to increase by 278–416 million tonnes. Among various waste management practices, anaerobic digestion (AD) is a useful method to transform food waste, producing renewable energy/biofuel and bio-fertilizers. This review aims to investigate some of the key factors in proposing FW for anaerobic digestion, with particular reference to China and South East Asian countries. Food waste shows variable chemical composition and a high content of biodegradable material (carbohydrates, protein and lipid). This composition led to consistent biogas production that was reported, as average for Chinese FW, of 480 ± 88 LCH4 kg−1 VS (n = 42). Since these data are higher than those reported for energy crops (246 ± 36 LCH4 kg−1 VS), this makes FW a good candidate to substitute for energy crops, avoiding food-energy conflicts. FW co-digestion with different substrates improved total bio-methane production (on average), from 268 ± 199 mL g−1 VS to 406 ± 137 mL g−1 VS. Food waste pretreatment, also, seems to be very useful in increasing total biogas production. Physical and thermal treatments were the best, increasing biogas production by 40% and 30%, respectively. Techno-economic evaluation seems to indicate the feasibility of substituting EC with FW for producing biogas and reducing total biomass costs. To achieve this, separate collection sources need to be put into place, assuring high FW quality to promote a Circular Economy approach in FW management.

Biomass pretreatment is an essential step prior to several thermochemical conversion processes. Wet torrefaction, a biomass pretreatment method in hydrothermal media or hot compressed water at temperatures within 180–260 °C, has been receiving a lot of attention because it possesses some advantages over other pretreatment methods. Apart from the undoubted benefits of upgrading biomass fuels to closer to coal properties, wet torrefaction has the capacity to work with wet or even extremely wet biomasses and enhance the ash removal from the biomass. The technology has recently attracted great interest from both academic groups and industrial companies. This review aims at providing a comprehensive overview of recent research and development activities in the field with focus on improvements in the chemical, physical and fuel properties of the solid product after wet torrefaction. Moreover, a brief introduction to dry torrefaction, a more conventional thermal pretreatment of biomass in the absence of oxygen under atmospheric pressure and in a temperature range of 200–300 °C, is also given and compared with wet torrefaction. Main differences in the properties of the solid products from the two torrefaction methods are also discussed.

The importance of renewable energy technologies was presented with focus on biomass energy as the favorable renewable energy option for rural communities. Agricultural and forest residues were considered the major sources of biomass in rural communities which can sustainably contribute towards meeting the energy demand of rural people for direct heat applications through the production of biomass briquette. The effect of palm oil mill sludge as a binding agent on the properties of sawdust briquette was investigated. Palm oil mill sludge was mixed with sawdust using 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100% of the weight of compacted the sawdust sample. The experimental results showed that the increased addition of palm oil mill sludge into sawdust had a significant effect (p

Interest is growing in the production of biohydrogen from algae through dark fermentation, as alternative to fossil fuels. However, one of the limiting steps of biohydrogen production is the conversion of polymeric carbohydrates into monomeric sugars. Thus, physical, chemical and biological pretreatments are usually employed in order to facilitate carbohydrates de-polymerization and enhancing biohydrogen production from algae. Considering the overall process, biohydrogen production through dark fermentation leads generally to negative net energy balances of the difference between the energy produced as biohydrogen and the direct ones (heat and electricity) consumed to produce it. Thus, to make the overall process economically feasible, dark fermentation of algae must be integrated in a biorefinery approach, where the outlets are valorized into bioenergy or value added biomolecules. The present study reviews recent findings on pretreatments and biohydrogen production through dark fermentation of algae looking at the perspectives of integrating side streams of dark fermentation from algal biomass, according to a biorefinery approach

Brunei Darussalam is located near the equator in the Borneo Island. Abundant rain, humidity and sunshine have created one of the largest rain forests in the world. Seven samples of sawdust taken from this rainforest and were analyzed for their fuel value and environmental impact. Among the seven variety of variety of wood investigated, one was soft, two were light, and four were of the hard type. Properties, such as wood density, ash content and elemental composition of plants were assessed and correlated with the calorific value. This was evaluated in relation to their properties and environmental impact when burned. It was revealed that the sawdust with the highest calorific value does not necessarily constitute the best option as fuel, if elemental composition is taken into account. The variation in wood density, calorific value, ash content and elemental composition of C, N and S along with their indirect impact on the environment are discussed in this paper.

Biodiesel, a renewable fuel has a great potential in fulfilling an ever-increasing transport fuel demand. The enzymatic conversion process of feedstock oil to biodiesel is greener when compared to the conventional approach of chemical conversion due to mild reaction conditions and less wastewater generation. Lipases obtained from various microbial sources have been widely applied as catalysts for the conversion of oil to biodiesel. Biodiesel and glycerol obtained by enzymatic conversion have shown a higher purity as compared to that obtained by other conversion techniques. Enzymatic conversion of oil to biodiesel is less energy intensive because of milder reaction conditions and fewer purification steps involved in processing. Lipases, due to their catalytic efficiency and specificity, have emerged as a great tool for converting a wide range of feedstock oils to biodiesel. This manuscript presents an overview of the use of enzymatic conversion for making biodiesel production sustainable and environmentally-friendly. The constraints of enzymatic conversion are the high cost of the enzyme and its inhibition by alcohol and glycerol. The possible solutions to overcome these constraints are discussed. Recent advances to develop an effective process for enzymatic conversion of feedstock oils into biodiesel are critically evaluated. Prospective and challenges in scaling up of this technology are also discussed.

This paper evaluates life cycle energy analysis of molasses based ethanol (MOE) in Nepal. Net energy value (NEV), net renewable energy value (NREV) and energy yield ratio are used to evaluate the energy balance of MOE in Nepal. Total energy requirements in sugarcane farming, cane milling and ethanol conversion processes are estimated and energy allocation is made between co-products (molasses and sugar) as per their market prices. The result shows negative NEV (−13.05 MJ/L), positive NREV (18.36 MJ/L) and energy yield ratio (7.47). The higher positive value of NREV and energy yield ratio reveal that a low amount of fossil fuels are required to produce 1 L of MOE. However, negative NEV reveals that the total energy consumption (both fossil and renewables) to produce the ethanol is higher than its final energy content. Nevertheless, the renewable energy contribution amounts to 91.7% of total energy requirements. The effect of the increased price of molasses and reduced energy consumption in the sugarcane milling and ethanol conversion are found to be significant in determining the energy values and yield ratio of MOE. In addition, there are clear measures that can be taken to improve efficiency along the production chain. Finally, energy security, scarcity of hard currency for importing fossil fuels and opportunities for regional development are also strong reasons for considering local renewable energy options in developing countries.

Using different types of renewable energy sources considering their uncertainties causes numerous challenges for minimizing the operation cost and maximizing the reliability of system. Hence, stochastic programming is an essential tool to consider the system uncertainties. This paper presents a day-ahead energy management system to decrease the operation cost and increase the reliability of a Microgrid considering a number of challenges for supporting electrical and thermal loads. In the proposed method, micro-CHP units, renewable energy sources, auxiliary boiler and energy storage system are all responsible for supplying the electrical and thermal loads. The problem is formulated as a multi-objective optimization problem. Moreover, the influence of considering the electrical energy storage system as a non-ideal battery with charge/discharge efficiency less than 1 is investigated. Also, demand response programs are provided based on load shifting contracts to consumers. A scenario-based approach is used to cover the uncertainties of renewable energy sources, market price and electrical load. Besides, this paper considers both islanding and grid-connected modes of Microgrid and investigates the influence of demand side management on operation cost and reliability in both modes. The capability of the proposed algorithm is analyzed by simulation results of a 3-feeder Microgrid.

Propelled by the actual demand from the renewable energy industry, the progress of literature on quantitative forecasting models during the past years is extensive. Research provides a vast output of papers on wind speed, wind power, solar irradiance and solar power forecasting models, accompanied by models for energy load and price forecasting for short-term (e.g. for the intraday trading schemes available at many market places) to medium-term (e.g. for day-ahead trading) usage. While the models themselves are, mostly, rather sophisticated, the statistical evaluation of the results sometimes leaves headroom for improvement. Unfortunately, the latter may occasionally result in the rejection of papers. This review aims at giving support at this point: It provides a guide on how to avoid typical mistakes of presenting and evaluating the results of forecasting models. The best practice of forecasting accuracy evaluation, benchmarking, and graphically/tabularly presenting forecasting results is shown. We discuss techniques, examples, guide to a set of paragon papers, and clarify on a state-of-the-art minimum standard of proceeding with the submission of renewable energy forecasting research papers.

To lower the cost of electricity produced, advanced high-efficiency power cycles operating at temperatures above 600 °C (such as the supercritical CO2 Brayton cycle) are presently being developed for use in both nuclear and concentrating solar power (CSP) plants. Incorporating thermal energy storage into CSP plants allows renewable energy to be generated while simultaneously providing reliability and stability to the grid. Sensible energy storage using molten nitrate salts is used in the majority of CSP plants. However, nitrate salts decompose at around 600 °C, hence an alternative storage medium is required to support the development of next generation high-efficiency CSP plants. Because of practical experience with molten salt storage in the two-tank configuration in industry, continuing to use fluid media is an attractive option, although thermal storage is also possible with other types of storage media (e.g. solids and phase change materials). This paper critically reviews options for energy storage in fluids that are stable over 600 °C. The focus is on three alternative molten salts — fluorides, chlorides and carbonates — which are assessed based on their thermophysical properties and cost. A brief review of liquid metal and molten glass storage options is included for completeness. Corrosion of containment materials is an important consideration in the choice of storage media, because if exotic materials are required, the cost of the storage tanks can dominate the overall storage cost. Therefore, this paper includes a summary of the main corrosion issues relating to containment of the more promising storage fluids considered herein, identifying possible tank materials and corrosion mitigation options.

WOS: 000463342600001 In this research, we aim at exploring the influence of renewables on industrial production (Ip) in the US by following continuous wavelet coherence and partial continuous wavelet coherence analyses. To this end, we observed the co-movements between, biofuels and Ip, solar and Ip, wind and Ip, geothermal and Ip, wood and Ip, and, waste and Ip in the US for the monthly period from January 1989 to November 2016. The primary motivations behind this research are twofold. Firstly, it attempts to reach the co-movements, if exists, between renewables' consumption and industrial production by following time domain and frequency domain analyses. Secondly, it aims at observing the potential co-movements between renewable energy sources (geothermal, solar, wind, biofuels, wood, and, waste) and Ip by adding some control variables (fossil fuels, total biomass etc.) into the wavelet models to understand clearly the responses of the industrial production to the impulses in renewables in both short term and long term periods. The paper hence eventually reveals significant effects of geothermal, wind, solar, biofuels, wood, and, waste on US industrial production in short term cycles and long term cycles. Thereby, following this paper's results of continuous wavelet analyses which depict the impact of renewables on US economy at 1-3-year frequency and 3-8-year frequency for the time period from January 1989 to November 2016, one might provide policy makers with relevant current and future efficient renewables' energy policy for the US and other countries which have similar structures with the US.

Geothermal energy piles (GEPs) are an environmentally friendly energy source which utilise the low-grade heat energy present in the shallow earth surface to provide heating and/or cooling to the supported structures e.g. buildings. The heat is extracted from or injected into the ground through the circulation of heat carrier fluid that flows in energy loops attached to the reinforcement cage of the pile foundation elements. Utilising the GEP system to achieve building thermal comfort need has proven to be environmentally sustainable, economically viable, and with great social benefits. This paper presents an extensive review of literature on the principles behind the different design considerations, current available design standards, and government legislation for installing the GEP system. Furthermore, the behaviour of the energy pile under working loads was found to be influenced by the magnitude of the heat energy extraction and injection rate. In addition, case studies from several countries around the world including Austria, Switzerland, Australia, UK, Spain, Hong Kong, USA, Japan, China and South Korea which highlights the practicality of the system installation, its associated benefits, limitations and overall energy performance were presented and discussed. Moreover, factors such as thermal conductivity, thermal diffusivity, specific heat capacity, groundwater flow, soil moisture content, number and configuration of energy loops, pile length and diameter have positive implication on the energy performance of the system. This paper found that the GEP system, if appropriately designed and carefully installed, provides a viable alternative in terms of an energy source with a positive energy footprint on the environment.

The demand for reduction of greenhouse gases, the need for a decreased dependence on fossil fuel, and the increasing penetration of the renewable energy sources are changing the world's electrical energy production. The island of Crete in Greece possesses great potential when it comes to wind and solar energy. Currently, a large amount of wind energy is often being curtailed in Crete, due to the technical minima of the existing thermal units, the inherent fluctuating power output of the wind turbines and the electricity demand profile. Electrical energy storage is recognized as an underpinning technology to have great potential in overcoming these challenges. There are many different ways to store the surplus energy and convert it back to electrical energy when it is needed. The aim of the present paper is the investigation of the role that energy storage can play in the further development of renewable energy sources in non-interconnected islands via considering the energy storage technologies of compressed air energy storage, pumped hydroelectric storage and sodium – sulfur batteries. This paper examines the solution of electrical energy storage in curtailment exploitation. A review over the above energy storage technologies is carried out and a comparative analysis is performed for the case study of Crete. Each storage technology is techno-economically evaluated using actual data. Finally, a parallel comparison of the examined storage systems’ levelized cost of energy is presented and conclusions are drawn. The compressed air energy storage system appears to be more favorable, having the lowest levelized cost of energy of the examined systems studied at 0.21 €/kWh, while contributing 105.59 GWh of electrical energy to the island's grid per year. For the examined case study, compressed air energy storage system appears to be almost 20% and 50% cheaper in terms of levelized cost of energy in comparison with pumped hydro storage and batteries respectively.

Renewable energy targets announced in 2014 present an opportunity to reform Indonesia's electricity sector which is dominated by fossil fuels. In this paper we discuss Indonesia's current renewable energy policies and future outlook for achieving the targets. This paper serves as a literature review of Indonesia's changing energy policy landscape, as part of a broader research investigating renewable energy targets and the role of the private sector. Despite Indonesia's wealth of renewable energy resources, numerous studies have identified multiple constraints to the development of renewable energy, including geographical, institutional and investment factors. Influential groups are calling for the Indonesian Government to put in place a clear policy framework that facilitates private sector investment. Therefore, interventions to facilitate investment in energy infrastructure in Indonesia must address the monopolised power market system that oversees a changing, complex malaise of electricity pricing regulations which make investment risky and uncertain. This study will enrich the existing literature on renewable energy policy which emphasises the importance of engaging the private sector. It is based on a rigorous qualitative assessment of Indonesia's changing policy that affects the progress of the renewable energy targets. The lessons from Indonesia's experience may provide insights for policymakers notably in developing countries.Keywords: energy in Indonesia, private sector investment, renewable energy

The energy consumption in buildings accounts for a significant proportion of total energy and carbon emissions over the world. To reduce the building energy consumption and achieve sustainable development of buildings, nearly zero energy buildings (NZEBs) have attracted widespread attention as a future building energy target. This paper reviews energy-efficient measures (EEMs) and renewable energy technologies (RETs) in NZEBs and discusses the application and suitability of the key technologies, i.e. minimizing the energy demand in NZEBs by EEMs and adopting RETs to meet the remaining energy needs. EEMs contain efficient thermal insulation system, high-performance window system, good airtightness and fresh air heat recovery system. RETs are composed of solar photovoltaic/thermal (PV/T) system, air source heat pump system (ASHP), ground source heat pump system (GSHP), and wind power. In addition, this paper emphasizes further research works, which involve life cycle energy analysis (LCEA), meteorological parameters change, intelligent building operation management (IBOM) system, energy storage system and social policy issues. This paper will provide some references for the further development of NZEBs in different climatic regions in China.

Due to the massive entrance of new renewable energies such as wind or solar, hydraulic turbines have to work far from its designed point and withstanding multiple transients, such as starts and stops, that shorten the useful life of the machine and cause fatigue damages. The present paper reviews the complex problem of fatigue in Francis turbines particularly focused on the experimental data available for static and dynamic stresses. For this purpose, many researches, which include different Francis turbines covering a wide range of design head and power, have been considered. The experimental stresses characteristics measured with strain gauges installed on the turbine runner and obtained from previous works have been analyzed for the different operating conditions and transient states occurring in the normal life of actual Francis units. The actual computational capabilities and techniques typically used to estimate such stresses have been discussed in detail. Potential future techniques to simplify complex strain measurements on the turbine runner, computational and statistical methods to estimate turbine stresses are reviewed in this paper. Finally, the relative damage of the different operating conditions and useful life estimation of the turbine, based on past strain measurements of the runner, are addressed.

Increasing energy demand, high energy cost and global warming issues require energy-intensive industries to make sincere efforts to improve energy efficiency. The energy consumption data available for different industries suggests that pulp and paper industry accounts for a significant share. Amongst various procedures to make paper, Kraft recovery process is majorly employed that yields weak but lignin-rich black liquor as a byproduct. Black liquor is one of the emerging biomass energy resources with a strong potential to be used as a biofuel for generating steam/energy to operate the process units, thereby, ensuring process self-sufficiency and sustainability. A Multi-Stage Evaporator (MSE) is needed to concentrate it but suffers from being the most energy consuming unit among all. This piques our interest to explore various energy reducing schemes or configurations used previously for MSE and to report previous research endeavors in the area of steady–state, dynamic modeling and simulation of such processes. It is noted that steady-state and transient behavior analysis together with an efficient controller design may significantly contribute in eliminating or troubleshooting problems to ensure both energy savings and product quality. The article highlights that such an analysis and effective solutions of developed models, due to their non-linear complex nature, are highly dependent on the nature of the algorithm employed. Attempts to design control techniques to enable efficient process control and to eliminate process uncertainties have suffered limitations not only due to inherent inefficiency of control techniques but also due to insufficient underlying knowledge or inappropriate modeling of system transience. With this perspective in mind, advanced and intelligent control techniques and their influence on process/energy transience and optimization have been reviewed. Here, we propose that it is very essential to maintain sufficient prudence in selecting an appropriate simulation, optimization and control algorithm to ensure a sustainable production.

With nearly 70% of the world population expected to live in cities by 2050, assessing the sustainability of urban systems, both existing and future ones, is becoming increasingly relevant. Making cities more sustainable is a global priority, which is highlighted by ‘Sustainable Cities and Communities’ being listed as one of the Sustainable Development Goals (SDG) adopted by United Nations Member States in 2015. This Virtual Special Issue (VSI) explores the implementation and assessment of policies and technologies that contribute to the transition to a sustainable, energy efficient and regenerative society. We organized the issue according to four main research themes: 1) Renewable Energy Systems (i.e., different types of systems, qualitative assessments and public acceptance); 2) Sustainable Built Environment (which includes construction, operation and refurbishment); 3) Multi-Scale Models (considering urban sustainability transition from building to districts, or cities and regions to multi-country comparisons and their scaling across different countries); and 4) Governance and Policy (climate change mitigation and adaptation plans/policies that are reported across countries, urban services and infrastructures). This paper serves two purposes. The first is to provide an analysis about patterns, correlations and synergies found across the different topics that have been addressed over the last 20 years in the literature about cities’ sustainability paths. A bibliometric analysis and a contingency matrix show the degree of correlation between scientific journals and main topics addressed by published articles. Secondly, the paper acts as an Editorial to the VSI, introducing the wealth of research articles and topics included in it. Both the bibliometric analysis and the papers published in this VSI demonstrate the interconnectedness of energy consumption, pollutant emissions and the competition for finite resources. The aim is to present advances and challenges of this exciting and ever-evolving research field to inform and guide future studies of urban sustainability.

The electricity market is being increasingly challenged by new trends, such as the high penetration of intermittent renewables and the transformation of the consumers’ energy space. To accommodate these new trends and improve the performance of the market, several modifications to current market designs have been proposed in the literature. Given the vast variety of these proposals, and focusing on the short-term timescale within the context of European electricity markets, this paper provides a comprehensive investigation of the modifications proposed in the literature as well as a detailed assessment of their suitability for improving market performance under the continuously evolving electricity landscape. To this end, first, the barriers present in current market designs hindering the fulfilment of an efficient performance are identified. Then, the different market solutions proposed in the literature, which could potentially mitigate these barriers, are extensively explored. Finally, a taxonomy of the proposed solutions is presented, highlighting the barriers addressed by each proposal and the associated implementation challenges. The outcomes of this analysis show that even though each barrier is addressed by at least one proposed solution, no single proposal is able to address all the barriers simultaneously. In this regard, a future-proof market design must combine different elements of proposed solutions to comprehensively mitigate market barriers and overcome the identified implementation challenges. Thus, by thoroughly reviewing this rich body of literature, this paper introduces key contributions enabling the advancement of the state-of-the-art towards increasingly efficient electricity markets.

To stop the spread of COVID-19, governments have implemented confinement measures unprecedented in modern society. One of the main consequences has been the paralysis of commercial and industrial sectors worldwide, primary electricity consumers. This paper examines the impact of these measures on the electricity sector through a literature review accompanied by fieldwork on the impact of COVID-19 in Ibero-America and its energy regulatory response. First, we will review the causes of the reduction in electricity demand due to the confinement measures and their technical and financial consequences in the electricity sector. Second, we will examine the impact of COVID-19 on the wind and solar PV energy sectors, mainly affected by the paralysis of production and export of materials and components. Third, we will revise the regulatory measures implemented by the countries to avoid the interruption of electricity supply to households. This paper will end by reviewing economic recovery plans and their relationship to the energy transition. Although there are no fundamental differences between developed and developing countries in their regulatory reaction to this crisis in the energy sector, there are significant differences in economic recovery planning. While developed countries aim for a green economic recovery and the creation of green jobs, developing countries are allocating least resources to social protection and general economic stimulus programs, postponing climate objectives. In Latin America, this adds to the high levels of debt faced by utilities and the possible resurgence of social crises that were stopped by the COVID-19 outbreak, making a green recovery even more difficult., Graphical abstract Image 1

Energy systems are quickly evolving through the development of new technologies and the emergence of new operational and market design paradigms. In particular, the global push for sustainability is driving the transition towards a pronounced redesign. In fact, renewable energy integration is occurring at a massive scale, and several other exciting developments are finding their place in modern energy systems, such as distributed energy resources, demand response, energy storage technologies, and local energy markets. In this dynamic context, the process of energy policy design and implementation has found new challenges, and in supporting this key process, expansion planning models and tools can play an essential role. For example, these models can be employed to estimate the impact of a multitude of policy instruments. Thus, there is a wide interest in these tools and a variety of such models, as evidenced by a rich literature and a fast-paced evolution of this research area. Motivated by this, this work presents a comprehensive and up-to-date review on expansion planning models and tools with emphasis on their application to energy policy analysis. In particular, this paper reviews the most significant policy instruments, with an emphasis in renewable energy integration, the optimization models that have been developed for expansion planning, and existing decision-support tools for energy policy analysis. Finally, this paper also discusses the trends in the literature and the most pressing current challenges in the development and use of expansion planning models for energy policy analysis.