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Abstract: Global warming, energy security, and the rising costs of oil have added a greater driving force to the development of feasible alternatives to petroleum-based transportation fuels. In parallel, wastes and wastewater generated from various industries should be avoided or converted to energy more in the future in order to reduce environmental problems and provide additional sources of energy. In this aspect, biogas plant is an effective option where gas is produced biologically by the fermentation of animal dungs, sewage, and agricultural residues. To utilize biogas as a transportation fuel, raw biogas has to undergo two major processes: cleaning and upgrading, to achieve natural gas quality. The upgraded biogas (so called bio-methane or bio-CNG) is considered green fuel with respect to environment, climate, and human health. However, the resulting bio-CNG from the processes still needs to be evaluated in terms of greenhouse gas emissions and energy aspects. This paper presents the integrated life cycle energy and environmental assessment of compressed bio-methane gas (CBG or bio-CNG) generated from cassava starch wastewater treatment plant in Thailand. The functional units were set to be 1 MJ of bio-CNG and 1 km of vehicle driven. The system boundary covered six main steps: digestion, purification and upgrading, compression, distribution, refueling, and combustion. The energy analysis result showed that the net energy ratio was higher than one, indicating a net energy gain. For the greenhouse gases aspect, the results showed that the biogas production and biogas upgrading step had the highest impact due to methane loss and high energy consumption. Comparing with other fuels, the global warming potential of bio-CNG was lower than those of fossil-based CNG and gasoline. [Copyright &y& Elsevier]

Abstract: A variety of researchers have constructed and presented lifecycle assessments of the microalgae-to-biofuel process, however, inconsistencies in system boundary definitions and high-level process modeling have led to a wide range of results. This study integrates engineering process models validated through experimental and modeling research to perform an environmental assessment of four microalgae-to-biofuel production scenarios leveraging the Argonne National Laboratory GREET model. The baseline scenario consists of a down flow open pond growth system, three phase de-watering step (settling, dissolved air flotation, and a centrifuge), hexane extraction and nutrient recovery using anaerobic digestion. The net energy ratio (NER), defined as energy consumed over the produced energy, and greenhouse gases (GHG) for the baseline scenario are 0.7MJMJ−1 and −41.7gCO2-eq MJ−1 respectively. Three alternative scenarios are also evaluated: 1) Improved microalgal productivity, 2) supercritical CO2 extraction, and 3) no nutrient recycle. This research shows that supercritical CO2 extraction is neither currently energetically- nor environmentally favorable and that nutrient recycle plays an integral role in achieving favorable NER and GHGs. The study highlights on the systems level, two findings related to the NER; 1) the NER is minimally impacted with increased productivity and 2) increasing microalgae lipid content detrimentally affects the NER which is attributed to the reduction in the total energy that can be captured by the anaerobic digester. [Copyright &y& Elsevier]

The internally illuminated photobioreactor (IIPBR) design has been shown to be more efficient in utilizing the incident light energy than the externally illuminated designs. This study evaluated (i) optimal sparging of the IIPBR with CO2-enriched air (CEA) to enhance biomass productivity; and, (ii) single-stage and two-stage operation of the IIPBR to enhance lipid productivity. Growth data from two algal cultures-Scenedesmus sp. and Nannochloropsis salina, cultivated in an 18-L prototype version of the IIPBR were used to establish the optimal conditions for the two goals in terms of the energy ratio. Based on the optimized results under sparging with CEA, the energy ratio in the IIPBR in the first stage with Nannochloropsis salina was at least 6 times higher due to optimal performance of the IIPBR at lower energy input than typical literature results for other PBR designs, whereas the energy ratios in the second stage were comparable to literature results. [Copyright &y& Elsevier]

• Life cycle assessment of utility-scale solar energy is performed. • Upstream production and assembly are the most emission-intensive life cycle stages. • Energy use during production and plant lifetime are the most sensitive parameters. • The system shows a net energy production with a net energy ratio up to 6.6. • The life cycle GHG emissions range from 98.3 to 149.3 g CO 2 eq /kWh. Grid-connected utility-scale solar PV has emerged as a potential pathway to ensure deep decarbonization of electricity in regions with fossil fuel-dominated energy mixes. Research on utility-scale solar PV projects mainly focuses on assessing technical or economic feasibility. Environmental performance assessments of large-scale solar applications are scarce. There is limited information on the greenhouse gas (GHG) emissions and energy footprints of utility-scale solar energy systems. Earlier studies conducted on small-scale solar systems have limited application in the grid system. We developed a comprehensive bottom-up life cycle assessment model to evaluate the life cycle GHG emissions and energy profiles of utility-scale solar photovoltaic (PV) system with lithium-ion battery storage to provide a consistent electricity supply to the grid with peak load options. We conducted a case study for a fossil fuel-based energy jurisdiction, Alberta (a western province in Canada). The results of the energy assessment show that raw material extraction, production, and assembly of solar panels are the key drivers, accounting for 53% of the total consumption. Energy consumed during battery manufacturing is responsible for 28%. The system shows a net energy production with a mean net energy ratio as high as 6.6 for two-axis sun tracking orientation. The life cycle GHG emissions range from 98.3 to 149.3 g CO 2 eq /kWh with a mean value of 123.8 g CO 2 eq /kWh. The largest emissions contribution is due to the manufacturing of batteries, 54% of the total emissions. The solar PV system offers a mean energy payback time of 3.8 years (with a range of 3.3 to 4.2 years). The results are highly sensitive to the expected lifetime of the system, the panel's peak wattage, and process energy consumption at various life cycle stages. [ABSTRACT FROM AUTHOR]

This study is an experimental determination of the energy return on investment (EROI) for algal biocrude production at a research facility at the University of Texas at Austin (UT). During the period of this assessment, algae were grown at several cultivation scales and processed using centrifugation for harvesting, electromechanical cell lysing, and a microporous hollow fiber membrane contactor for lipid separation. The separated algal lipids represent a biocrude product that could be refined into fuel and the post-extraction biomass could be converted to methane. To determine the EROI, a second-order analysis was conducted, which includes direct and indirect energy flows, but does not include energy expenses associated with capital investments. The EROI for the production process evaluated here was significantly less than 1, however, the majority of the energy consumption resulted from non-optimized growth conditions. While the experimental results do not represent an expected typical case EROI for algal fuels, the approach and end-to-end experimental determination of the different inputs and outputs provides a useful outline of the important parameters to consider in such an analysis. The Experimental Case results are the first known experimental energy balance for an integrated algal biocrude production facility, and as such, are expected to be helpful for setting research and development priorities. In addition to the Experimental Case (based on direct measurements), three analytical cases were considered in this work: (1) a Reduced (Inputs) Case, (2) a Highly Productive Case, and (3) a Literature Model. The Reduced (Inputs) Case and the Highly Productive Case speculate the energy use for a similar system in an improved, commercial-scale production setting. The Literature Model is populated with relevant data that have previously been reported in the literature. For the Experimental Case, Reduced Case, Highly Productive Case, and Literature Model, the estimated second-order EROI was 9.2 × 10, 0.074, 0.22, and 0.35, respectively. These results were dominated by growth inputs (96%, 89%, 87%, and 61% of the total energy requirement, respectively). Furthermore, the EROI was adjusted using quality factors that were calculated according to the price of each input, yielding a quality-adjusted EROI that parallels a partial financial return on investment analysis. For the Experimental Case, the Reduced Case, and the Highly Productive Case, the quality-adjusted EROI was 9.2 × 10, 0.013, and 0.36, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A new process evaluation methodology of microalgae biodiesel has been developed. Based on four evaluation criteria, i.e. the net energy ratio (NER), biodiesel production costs, greenhouse gases (GHG) emission rate and water footprint, the model compares various technologies for each step of the process, from cultivation to oil upgrading. An innovative pathway (hybrid raceway/PBR cultivation system, belt filter press for dewatering, wet lipid extraction, oil hydrotreating and anaerobic digestion of residues) shows good results in comparison to a reference pathway (doubled NER, lower GHG emission rate and water footprint). The production costs are still unfavourable (between 1.94 and 3.35€/L of biodiesel). The most influential parameters have been targeted through a global sensitivity analysis and classified: (i) lipid productivity, (ii) the cultivation step, and (iii) the downstream processes. The use of low-carbon energy sources is required to achieve significant reductions of the biodiesel GHG emission rate compared to petroleum diesel. [Copyright &y& Elsevier]

Abstract: In the current scenario of depleting energy resources, increasing food insecurity and global warming, Jatropha has emerged as a promising energy crop for India. The aim of this study is to examine the life cycle energy balance for Jatropha biodiesel production and greenhouse gas emissions from post-energy use and end combustion of biodiesel, over a period of 5years. It’s a case specific study for a small scale, high input Jatropha biodiesel system. Most of the existing studies have considered low input Jatropha biodiesel system and have used NEB (Net energy balance i.e. difference of energy output and energy input) and NER (Net energy ratio i.e. ratio of energy output to energy input) as indicators for estimating the viability of the systems. Although, many of them have shown these indicators to be positive, yet the values are very less. The results of this study, when compared with two previous studies of Jatropha, show that the values for these indicators can be increased to a much greater extent, if we use a high input Jatropha biodiesel system. Further, when compared to a study done on palm oil and Coconut oil, it was found even if the NEB and NER of biodiesel from Jatropha were lesser in comparison to those of Palm oil and Coconut oil, yet, when energy content of the co-products were also considered, Jatropha had the highest value for both the indicators in comparison to the rest two. [Copyright &y& Elsevier]

Abstract: This study investigates the energy and environmental aspects of producing biohydrogen for bitumen upgrading from a life cycle perspective. Three technologies are studied for biohydrogen production; these include the Battelle Columbus Laboratory (BCL) gasifier, the Gas Technology Institute (GTI) gasifier, and fast pyrolysis. Three different biomass feedstocks are considered including forest residue (FR), whole forest (WF), and agricultural residue (AR). The fast pyrolysis pathway includes two cases: truck transport of bio-oil and pipeline transport of bio-oil. The net energy ratios (NERs) for nine biohydrogen pathways lie in the range of 1.3–9.3. The maximum NER (9.3) is for the FR-based pathway using GTI technology. The GHG emissions lie in the range of 1.20–8.1kgCO2 eq/kg H2. The lowest limit corresponds to the FR-based biohydrogen production pathway using GTI technology. This study also analyzes the intensities for acid rain precursor and ground level ozone precursor. [Copyright &y& Elsevier]

Abstract: One necessary criterion for a biofuel to be a sustainable alternative to the petroleum fuels it displaces is a positive net energy balance. This study estimated the net energy ratio (NER), net energy balance (NEB), and net energy yield (NEY) of small-scale on-farm production of canola [Brassica napus (L.)] and soybean [Glycine max (L.)] biodiesel in the upper Midwest. Direct and embodied energy inputs based on well-defined system boundaries and contemporary data were used to estimate the energy requirement of crop production, oil extraction, and biofuel processing. The NER of canola biodiesel was 1.78 compared with 2.05 for soybean biodiesel. Canola biodiesel had a NEB of 0.66 MJ MJ−1 of biofuel compared with 0.81 MJ MJ−1 for soybean biodiesel. The NEY of soybean biodiesel was 10,951 MJ ha−1, less than canola biodiesel which had a NEY of 11,353 MJ ha−1. Use of soybean as a biodiesel feedstock was more energetically efficient than canola primarily due to reduced nitrogen fertilizer requirement. In terms of energetic productivity, canola was a more productive biodiesel feedstock than soybean due to its higher oil content. A best-case scenario based on optimal feedstock yields, reduced fertilizer input, and advanced biofuel processing equipment suggested that potential gains in energetic efficiency was greater for canola than soybean. According to our results, small-scale on-farm biodiesel production using canola and soybean can be an energetically efficient way to produce energy for on-farm use. [Copyright &y& Elsevier]

The present article deals with the study of environmental impacts of using biodiesels derived from jatropha, karanja, and neem tree using an energy life-cycle analysis approach. To evaluate the energy consumption during the life cycle of jatropha, karanja, and neem biodiesel as fuel for compression ignition (CI) engine, a cradle-to-grave analysis is carried out. Net energy ratio is calculated for each biodiesel by the ratio of the energy output of the system in the form of fuel energy delivered to the compression ignition engine and the cumulative energy demand of the system. Net energy ratios for jatropha, karanja, and neem biodiesel life cycles are R1 = 1.2325, R2 = 1.6425, and R3 = 1.6479, respectively. Life-cycle energy ratio of biodiesels shows that all the three fuels are renewable. It is concluded from the study that all biodiesels have higher output than inputs in terms of energy. [ABSTRACT FROM AUTHOR]

Abstract: Most renewable energy sources depend to some extent on use of other, non-renewable sources. In this study we explore use of diesel fuel in producing and transporting woody biomass in the state of New Hampshire, USA. We use two methods to estimate the diesel fuel used in woody biomass production: 1) a calculation based on case studies of diesel consumption in different parts of the wood chip supply chain, and 2) to support extrapolating those results to a regional system, an econometric study of the variation of wood-chip prices with respect to diesel fuel prices. The econometric study relies on an assumption of fixed demand, then assesses variables impacting supply, with a focus on how the price of diesel fuel affects price of biomass supplied. The two methods yield similar results. The econometric study, representing overall regional practices, suggests that a $1.00 per liter increase in diesel fuel price is associated with a $5.59 per Mg increase in the price of wood chips. On an energy basis, the diesel fuel used directly in wood chip production and transportation appears to account for less than 2% of the potential energy in the wood chips. Thus, the dependence of woody biomass energy production on diesel fuel does not appear to be extreme. [Copyright &y& Elsevier]

Abstract: This study analyzes the energy balance of a bioethanol production system from high-yield rice plant in Japan. Two systems are considered in which rice is converted to ethanol: one in which cellulose feedstocks, straw and husk, are used for cogeneration (scenario 1), and the other in which they are converted to ethanol, and byproducts such as lignin and unreacted holocellulose are used for cogeneration (scenario 2). Energy input in the agricultural process including transportation is estimated to be 52.3GJ/ha from an Input Output Table. The heating values of produced rice and cellulose feedstocks are 120.7GJ/ha and 162.3GJ/ha, respectively. The net energy balance (NEB) of scenario 1 is 129.2GJ/ha, which produces 3.6kL/ha of ethanol and 9420kWh/ha of external electricity. On the other hand, NEB of scenario 1 is 11.7GJ/ha, which produces 7.1kL/ha of ethanol. Both NEBs are positive, but NEB of scenario 2 is much higher than that of scenario 1. An acid hydrolysis technology of cellulosic biomass applied to scenario 2 needs a large amount of heat energy for sulfuric acid recovery. If an enzyme hydrolysis of cellulosic biomass is developed, there is a possibility of improving NEB of scenario 2. [Copyright &y& Elsevier]

Abstract: Jatropha curcas L. has been considered as a potential feedstock for biodiesel production in several tropical countries. Two Jatropha plantation models currently being considered in Thailand, a perennial plantation for 20 years and annual harvesting, are compared vis-à-vis the energy benefits. The advantage of the perennial plantation is that fruit yield is low in the first 2 years but stabilizes after the second year; thus, the biodiesel production is maximized. On the other hand, the biodiesel yield for annual harvesting is low but substantial energy is gained from the wood which can be used for power production. The overall energy output from the annual system is about twice that of the perennial system whereas the biodiesel production is less than half. The energy values of both the systems are high and the net energy ratios as high as 6–7 indicating a substantial energy benefit. [Copyright &y& Elsevier]

Abstract: For hydrogen to be a viable energy carrier, it is important to develop hydrogen generation routes that are renewable like biohydrogen. Hydrogen can be produced biologically by biophotolysis (direct and indirect), photo-fermentation and dark-fermentation or by combination of these processes (such as integration of dark- and photo-fermentation (two-stage process), or biocatalyzed electrolysis, etc.). However, production of hydrogen by these methods at commercial level is not reported in the literature and challenges regarding the process scale up remain. In this scenario net energy analysis (NEA) can provide a tool for establishing the viability of different methods before scaling up. The analysis can also be used to set targets for various process and design parameters for bio-hydrogen production. In this paper, four biohydrogen production processes (dark-fermentation, photo-fermentation, two-stage process and biocatalyzed electrolysis) utilizing sugarcane juice as the carbon source, are compared with base case method steam methane reforming (SMR) on the basis of net energy ratio, energy efficiency and greenhouse gas (GHG) emissions. It was found that when by-products are not considered, the efficiencies of biological hydrogen processes are lower than that of SMR. However, these processes reduce GHG emissions and non-renewable energy use by 57–73% and 65–79%, respectively, as compared to the SMR process. Efficiencies of biohydrogen processes increase significantly when by-products are considered hence by-products removal and utilization is an important issue in biological hydrogen production. [Copyright &y& Elsevier]

Although several studies have found biodiesel to be a renewable source of energy, there has been a claim that it is not. This article investigates models used to calculate the net energy ratio (NER) of biodiesel production to point out the reasons for the contradictory results, compares their strengths and weaknesses, and proposes a uniform model for interpretation of the final result. Four commonly referenced models were compared for their assumptions and results. The analysis revealed that the most significant factors in altering the results were the proportions of energy allocated between biodiesel and its coproducts. The lack of consistency in defining system boundaries has apparently led to very different results. The definitions of NER used among the models were also found to be different. A unified model is proposed for biodiesel energy analysis to answer the renewability question. Using the unified boundary, a range of probable NERs was calculated using bootstrapping. The mean NER on a mass basis was 2.55 with a standard deviation of 0.38. The economic sustainability ratio (ESR) is defined as the monetary value ratio of biodiesel to biodiesel's share of the energy inputs. The average ESR was found to be 4.43 with a standard deviation of 0.6. [ABSTRACT FROM AUTHOR]

We estimate the energy content, the operational energy inputs, and the net energy ratio (NER) of an industrial tubular photobioreactor used for the photosynthetic production of by microalgae. The NER is the dimensionless ratio of the chemical energy output (higher heating value) to the total primary energy input into the system. The calculated output of the photobioreactor is based on a range of algal photosynthetic generation efficiencies, and on the application of standard theory for tubular solar collectors. For small diameter reactors the mixing energy is large, and can reduce the NER by a third or more, compared to bigger diameters. For a tubular photobioreactor, low-density polyethylene (LDPE) film and glass have significantly higher NERs than rigid polymers such as polymethyl methylacrylate (acrylic). Using a hypothetical improved microalgal generation efficiency of 5%, an NER can be obtained for LDPE film and for glass. For mechanical and assembly reasons LDPE film is the material of choice. These results show that photobiological hydrogen could be a viable generation technology, if tight constraints on energy inputs are met. [Copyright &y& Elsevier]

Microgrids—generating systems incorporating multiple distributed generator sets linked together to provide local electricity and heat—are one possible alterative to the existing centralized energy system. Potential advantages of microgrids include flexibility in fuel supply options, the ability to limit emissions of greenhouse gases, and energy efficiency improvements through combined heat and power (CHP) applications. As a case study in microgrid performance, this analysis uses a life cycle assessment approach to evaluate the energy and emissions performance of the NextEnergy microgrid Power Pavilion in Detroit, Michigan and a reference conventional system. The microgrid includes generator sets fueled by solar energy, hydrogen, and natural gas. Hydrogen fuel is sourced from both a natural gas steam reforming operation and as a by-product of a chlorine production operation. The chlorine plant receives electricity exclusively from a hydropower generating station. Results indicate that the use of this microgrid offers a total energy reduction potential of up to 38%, while reductions in non-renewable energy use could reach 51%. Similarly, emissions of CO2, a key global warming gas, can be reduced by as much as 60% relative to conventional heat and power systems. Hydrogen fuels are shown to provide a net energy and emissions benefit relative to natural gas only when sourced primarily from the chlorine plant. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Bottom-up life cycle assessment models were developed for battery storage systems. • Life cycle greenhouse gas (GHG) emissions of five battery storage systems were evaluated. • Four different stationary applications of batteries were examined. • The Li-ion has the highest net energy ratio (NER) and lowest GHGs in all applications. Electro-chemical batteries are widely used in portable devices and transportation, but they can also be used in the electricity grid for various applications. The assessment of the environmental impacts of electro-chemical storage systems for stationary use has received little attention. In this study, data-intensive, bottom-up life cycle assessment models were developed to assess the life cycle net energy ratios (NERs) and greenhouse gas (GHG) emissions of utility-scale stationary applications of five electro-chemical energy storage systems: sodium-sulfur, lithium-ion, valve-regulated lead-acid, nickel–cadmium, and vanadium redox flow. Four stationary application scenarios were considered: bulk energy storage, transmission and distribution (T&D) investment deferral, frequency regulation, and support of voltage regulation. The Li-ion storage system has the highest NER and lowest GHG emissions in every scenario. The life cycle GHG emissions range from 715 to 784 kg-CO 2 eq for sodium-sulfur, 625–659 kg-CO 2 eq for lithium-ion, 749–803 kg-CO 2 eq for valve-regulated lead-acid, 742–806 kg-CO 2 eq for nickel–cadmium, and 800–963 kg-CO 2 eq for vanadium redox flow per MWh of electricity delivered, depending on the application scenario. The results are highly influenced by the operation phase that involves charging the batteries. Lithium-ion and sodium-sulfur storage systems are the most suitable for all the application scenarios because of their longer cycle lives and higher energy densities. [ABSTRACT FROM AUTHOR]

There is considerable research effort being made to improve the efficiency of solar cells. Perovskite architectures that use titanium dioxide nanorods as electron transport layers are among technologies that have been proven to have enhanced efficiency. However, assessments of the life cycle environmental performances of such nanorod-based perovskite solar cells are limited. In this study, a cradle-to-grave life cycle assessment is conducted to evaluate the environmental footprints in terms of energy payback time, greenhouse gas (GHG) emissions, and the net energy ratio of this architecture. Unlike most studies that focus on the life cycle of the cell processing, this study extends the scope to include the balance of the system (BOS) and to evaluate the environmental effects of reusing important components such as fluorine-doped tin oxide glass and the gold layer, which appear to significantly impact energy consumption and associated GHG emissions. The energy payback time is calculated to be 0.97 − 0.41 + 0.78 years and the life cycle GHG emissions to be 181. 5 − 82 + 170 g CO 2 eq/kWh of electricity produced for a solar system. The net energy ratio is 3.1, indicating the system is a net energy generator. The assembly life cycle stage, comprising the panel production, BOS and mounting of solar panels, generates the most GHG emissions and the contribution from the cell fabrication stage is second. It was observed that the embodied GHG emissions for fluorine-doped tin oxide glass and gold contribute just 4% of the total GHG emissions associated with the perovskite solar cell for a three-time reuse case. • Cradle-to-grave LCA of TiO 2 nanorod-based perovskite solar cells is performed. • The life cycle GHG emissions are 181. 5 − 82 + 170 g CO 2 eq per kWh of electricity. • The energy payback time is calculated to be 0.97 − 0.41 + 0.78 years. • The system is a net energy generator with a net energy ratio of 3.10. [ABSTRACT FROM AUTHOR]

Research efforts have investigated a range of system designs for algae growth and conversion into biofuels. The economic feasibility and environmental impact of these systems are frequently evaluated through techno-economic analyses (TEA) and life-cycle assessment (LCA), which typically determine the levelized cost of fuel production in gallons of gasoline equivalent (MFSP, in $-gge−1), global warming potential (GWP, in g CO 2 -eq-MJ fuel −1), and net energy ratio (NER, unitless). While the outputs from these models seem comparable, the results often conceal the impact of a large number of assumptions inherent to the modeling, limiting direct comparisons. As such, a direct comparison of the modeling results as published can be misleading due to differences in critical assumptions and/or foundational methodology. This work applies harmonization methodology to several sustainability assessment studies found in the literature with the goal of enhancing comparability through implementation of a standard set of assumptions. For the economic evaluation, two harmonization efforts were performed: the first focused on harmonizing productivity, economic assumptions, and cost year for the entire growth to product process; the second compared only downstream fuel conversion technologies by fixing the biomass cost, thereby removing the uncertainty of upstream-growth assumptions. For LCA, harmonization focused on productivity and system boundary. The results of these efforts show a decrease of 43% in the range of reported fuel prices and minimal redcution in the range of LCA results. Both TEA and LCA harmonization efforts then investigated the impact of productivity by simulating a range of biomass productivity values (12.5, 25, and 50 g-m−2 day−1). The work reveals limitations to both the economic and environmental benefits of productivity improvements past approximately 35 g-m−2 day−1. Results highlight the need to redirect research efforts not only to increase productivities, but also to other areas where investments can make a greater impact in terms of economic viability and environmental impact. • Harmonization of algal sustainability assessments over the past decade • Diminishing sustainability returns for productivities above 25–35 g m−2 d−1 • Net energy ration (NER) is the most transparent metric for assessment. [ABSTRACT FROM AUTHOR]

The net energy ratio (NER) of microalgae biofuels depends fundamentally on assumptions of operational energy demand and biomass yield. However, for the NER calculation, it has not previously been considered that these parameters are related. This study derives a correlation between these values from published experimental data on flat plate photobioreactors and uses it to calculate the NER. The found correlation is adapted to outdoor conditions, and the energy demand throughout the life cycle for cultivation and biogas production is added. Results show that an asymptotic correlation between the aeration rate and the photosynthetic efficiency hampers net energy output. Maximising the biomass output requires a disproportionately high aeration rate, and thus operational energy demand. Best NER is obtained at low aeration rates, however the biomethane yield at these rates cannot compensate for the total energy demand throughout the life cycle. A NER of 3.6 is calculated. Sensitivity analysis on further technological improvements, such as more efficient energy supply, reduces the NER to 1.8. A comparison of assumptions from seven previous life cycle analyses demonstrates that NER below one results from incomplete system boundaries, or unrelated parameters for operational energy demand and biomass yield. Our findings help to explain contradictory results in previous studies, and will improve the quality of future NER analyses. [ABSTRACT FROM AUTHOR]

• Parabolic trough collector used as intensification tool for enhanced biodiesel production. • CaO catalyst packed column reactor is also used in combination. • Temperature reached around 95 °C in 20 min in day time. • Yield up to 95.84% obtained by recirculating batch reactions. • Net energy ratio and energy efficiency indices were analyzed for various conditions. Waste cooking oil was converted to biodiesel using a parabolic trough collector using solar radiations as a heating source and a parabolic trough collector as an intensifier. Calcium oxide (CaO) derived from seashells was used as a catalyst in order to boost the rate of the reaction. Temperatures of almost 95 °C were reached using this collector although the temperature was limited to below 78.4 °C in order to prevent the vaporization of ethanol. The influence of different parameters on the reaction was analyzed. The maximum yield was found to be 95.84%, obtained under conditions of 180 LPH reactant flow rate, 300 rpm stirring speed, 60 minutes reaction time, 9:1 ethanol to oil ratio and 90 cm catalyst bed height. The composition and properties of the biodiesel were found to be in accordance with literature and ASTM and BIS norms. The energy efficiency of the process was analyzed by net energy ratio (NER). The net energy efficiency index (NEEI) was obtained from the ratio of NER of the solar method to the conventional method. NEEI of the process was found to be 4.16, thereby making the process a highly promising method of biodiesel production. [ABSTRACT FROM AUTHOR]

• 1-ha microalgal plant based on novel photobioreactor design has NER of 3.0. • Integrated PV module produces energy excess to requirements for plant operation. • NER for novel photobioreactor comparable to agricultural biofuel crops. • Spectral selection and PV technologies result in standalone operation. • Novel photobioreactor offers energy and water sustainable production of microalgae. The need for thermal regulation in microalgal photobioreactors is a significant impediment to their large-scale adoption. The energy costs associated with thermal regulation alone can easily result in a negative energy balance. Self-sustaining photovoltaic powered photobioreactors that do not require cooling systems provide an opportunity to maximize biomass productivity, generate local electricity, reduce thermal regulation requirements, and significantly improve the energy balance of the system. Net energy analysis of a spectrally-selective, insulated-glazed photovoltaic photobioreactor (IGP) with an integrated capability for renewable electricity generation used to cultivate Nannochloropsis sp. without freshwater-based cooling resulted in a net energy ratio of 2.96, a figure comparable to agricultural bio-oil crops such as Jatropha and soybean. Experimental data from pilot-scale operation of this novel photobioreactor producing Nannochloropsis biomass under outdoor conditions was extrapolated to a 1-ha IGP installation. Annual biomass productivity reached 66.0-tons dry weight ha−1, equivalent to overall energy output of 1696.2 GJ ha−1. The integrated semi-transparent photovoltaic panels generated an additional 1126.8 GJ ha−1 yr−1 (313.0 MWh ha−1 yr−1). Energy demands from plant building materials, machinery, fertilizers, plant operations, and biomass harvesting constituted total energy input with a combined value of 707.3 GJ ha−1 yr−1. Comparison with a conventional photobioreactor requiring passive evaporative cooling showed novel photobioreactor had a 73% greater net energy ratio. Nannochloropsis cultivation in IGP system ensured co-production of lipid and protein of 34.7 and 25.7-tons ha−1 yr−1, respectively. These results suggest that this novel photobioreactor could be a viable and sustainable biomass production technology for mass microalgal cultivation. [ABSTRACT FROM AUTHOR]

• Algal consortium cultivated outdoor in wastewater without using external energy. • Average biomass productivity of 3.48 ± 0.44 gm−2 d−1 under natural conditions. • Biomethane vs biocrude yield for different energy conversion routes compared. • Net Energy Ratio (Hydrothermal liquefaction) > Net Energy Ratio (anaerobic digestion). • Existing bottlenecks in algal biofuels feasibility discussed with possible solution. Real-time studies highlighting the actual bottlenecks of microalgae-based biofuels are needed to overcome the limitations of assumption-based approach. In the present study, an algal consortium consisting of Chlorella pyrenoidosa and Phormidium, was cultivated in municipal wastewater under outdoor conditions in a pilot scale (100 L) attached biofilm reactor during January-February 2018. No energy was used to maintain the cultivation conditions (temperature, light intensity/duration). After 6 days of hydraulic retention time, the consortium showed 53–87% reduction in the nutrients' concentrations of the selected wastewater. Consistent biomass productivity of 3.48 ± 0.44 g m−2 d−1 was observed, and its biochemical composition showed that it was rich in lipids (35.20 ± 0.63% of total solids). The wastewater grown algal biomass was subjected to anaerobic digestion at 37 °C for 30 days and hydrothermal liquefaction at 27 bars and 230 °C for 20 min to produce biomethane or biocrude, respectively. On performing the biomethane potential assay, a cumulative biomethane production of 346.59 ± 5 mL g−1 VS was observed. The theoretical methane production and stoichiometric methane potential calculated for the biomass was 504 mL g−1 VS and 591 mL g−1 VS, respectively, showing a digestibility of 58.5%. Hydrothermal liquefaction of the wastewater grown biomass gave biocrude yield of 43 ± 2% (dried biomass basis) rich in aldehydes/ketones/fatty acids. Net energy ratios for the two processes were compared. Net energy ratio for algal cultivation integrated with anaerobic digestion was found to be 0.007 and for that with hydrothermal liquefaction was found to be 0.08, proving it to be a more energy efficient process. [ABSTRACT FROM AUTHOR]

Abstract: Biodiesel from palm oil has been considered for partial substitution of diesel fuel for transportation in Thailand. The Thai government recently has set up a production target of 8.5million liters per day of palm oil-based biodiesel by 2011. The aim of this study is to investigate the energy consumption of palm methyl ester (PME) production in Thailand using a life cycle approach compared to other possible oil crops for biodiesel production including jatropha and coconut. The main contributors to the energy use are cultivation, oil production, transesterification and transportation. Taking into account only fossil fuel or petroleum inputs in the production cycle, the energy analysis provides results in favour of PME in Thailand. The net energy balance (NEB) and net energy ratio (NER) of PME and co-products are 100.84GJ/ha and 3.58, respectively. The NER of PME without co-products is 2.42, which is still higher than one indicating a favourable result. The results are important in selecting an appropriate feedstock for biodiesel production and this study will support policy makers in the energy sector to make informed decisions vis-à-vis promotion of oil palm plantation for biodiesel. This will also support the Thai government in its policy to promote the use of indigenous and renewable sources for transportation fuels. [Copyright &y& Elsevier]