Life Cycle Net Energy Research Articles

Solar-Driven Upgrading of Biomass by Coupled Hydrogenation Using in Situ Photoelectrochemically Generated H2

Green H2 has been recognized as an important element in efforts to decarbonize our fossil fuel-dependent society. One approach to produce green H2 is solar water splitting in a photoelectrochemical (PEC) device. Solar-to-hydrogen (STH) efficiencies of up to 30% have been demonstrated1 but studies have shown that this approach still results in a relatively high levelized cost of hydrogen (LCOH) of ~10 US$ per kg of H2.2-3 This is ca. one order of magnitude higher than that of hydrogen produced via steam methane reforming (SMR), which forms the bulk of the currently produced H2. A possible solution is to incorporate an upgrading process of biomass feedstock that generates valuable chemicals into the solar water splitting device. This is expected to not only decrease the overall LCOH but also introduce an alternative renewable pathway in chemical manufacturing. In this study, we propose the concept of solar-driven hydrogenation of biomass-derived feedstock. Photoelectrochemically generated H2 in our solar water splitting device is coupled in situ with the homogenously catalyzed hydrogenation of itaconic acid (IA) to methyl succinic acid (MSA). IA has been identified by the US Department of Energy as one of the twelve building blocks that possess the potential to be transformed subsequently into several high-value bio-based chemicals or materials.4 MSA is a valuable chemical compound with an estimated global market size of up to ~15,000 tonnes, whose derivatives are ubiquitously used as solvents in cosmetics,5 polymer synthesis,6 binders in powder coatings,7 and organic synthesis, especially for pharmaceutical synthesis.8-9 Our coupled hydrogenation approach—performed in the PV-electrolyzer and PEC configurations using III-V PV cells and BiVO4-based photoelectrode, respectively—successfully demonstrate solar-driven H2-to-MSA conversion efficiencies as high as 60%. In comparison to the non-coupled approach (i.e., direct hydrogenation), our coupled system offers synergistic benefits in terms of prolonged durability and a higher degree of flexibility toward other important chemical transformation reactions. In addition, life-cycle net energy assessment and technoeconomic analysis results show that adding the coupled hydrogenation process significantly lowers the energy payback time and the LCOH, respectively, to a point that is competitive even with SMR-produced H2. Further implications and optimization potentials of the coupled PEC hydrogenation approach will be discussed. References Kim, J. H.; Hansora, D.; Sharma, P.; Jang, J.-W.; Lee, J. S., Toward practical solar hydrogen production – an artificial photosynthetic leaf-to-farm challenge. Chem. Soc. Rev. 2019, 48 (7), 1908-1971.Shaner, M. R.; Atwater, H. A.; Lewis, N. S.; McFarland, E. W., A comparative technoeconomic analysis of renewable hydrogen production using solar energy. Energy Environ. Sci. 2016, 9 (7), 2354-2371.Pinaud, B. A.; Benck, J. D.; Seitz, L. C.; Forman, A. J.; Chen, Z.; Deutsch, T. G.; James, B. D.; Baum, K. N.; Baum, G. N.; Ardo, S.; Wang, H.; Miller, E.; Jaramillo, T. F., Technical and economic feasibility of centralized facilities for solar hydrogen production via photocatalysis and photoelectrochemistry. Energy Environ. Sci. 2013, 6 (7), 1983-2002.Werpy, T.; Petersen, G. Top value added chemicals from biomass: volume I--results of screening for potential candidates from sugars and synthesis gas; National Renewable Energy Lab., Golden, CO (US): 2004.Richard, H.; Muller, B. Use of a 2-methylsuccinic acid diester derivative as solvent in cosmetic compositions; cosmetic compositions containing the same. WO2012119861A3, 2012.Verduyckt, J.; De Vos, D. Method for the production of methylsuccinic acid and the anhydride thereof from citric acid. WO2018065475A1, 2017.Mijolovic, D.; Szarka, Z. J.; Heimann, J.; Garnier, S. Powder coating useful as a coating agent, and for coating metallic- and non-metallic surfaces, comprises a binder comprising methyl succinic acid. DE102011080722A1, 2012.Okabe, M.; Lies, D.; Kanamasa, S.; Park, E. Y., Biotechnological production of itaconic acid and its biosynthesis in Aspergillus terreus. Appl. Microbiol. Biotechnol. 2009, 84 (4), 597-606.Willke, T.; Vorlop, K.-D., Biotechnological production of itaconic acid. Appl. Microbiol. Biotechnol. 2001, 56 (3), 289-295.

Life cycle net energy assessment of sustainable H2 production and hydrogenation of chemicals in a coupled photoelectrochemical device

Green hydrogen has been identified as a critical enabler in the global transition to sustainable energy and decarbonized society, but it is still not economically competitive compared to fossil-fuel-based hydrogen. To overcome this limitation, we propose to couple photoelectrochemical (PEC) water splitting with the hydrogenation of chemicals. Here, we evaluate the potential of co-producing hydrogen and methyl succinic acid (MSA) by coupling the hydrogenation of itaconic acid (IA) inside a PEC water splitting device. A negative net energy balance is predicted to be achieved when the device generates only hydrogen, but energy breakeven can already be achieved when a small ratio (~2%) of the generated hydrogen is used in situ for IA-to-MSA conversion. Moreover, the simulated coupled device produces MSA with much lower cumulative energy demand than conventional hydrogenation. Overall, the coupled hydrogenation concept offers an attractive approach to increase the viability of PEC water splitting while at the same time decarbonizing valuable chemical production.

Life cycle net energy and global warming impact assessment for hydrogen production via decomposition of ammonia recovered from source-separated human urine

Decomposition of ammonia derived from source-separated human urine is a renewable approach for hydrogen production. Life cycle net energy analysis and global warming impact of scaled-up hydrogen production via this technique are studied in this paper. Ammonia decomposition processes, including fixed-bed reactors with Ru/Al2O3 and Ni/Al2O3 as catalyst options are simulated using the Aspen Plus software, and the results are compared with published data for validation. The life cycle net energy indicators are assessed for three scenarios of ammonia generation: conventional air stripping, microbial fuel cell, and electrochemical cell methods at a unit basis of 1000 kg of H2 production. Results show that the microbial fuel cell process is more energy-efficient and emits lower greenhouse gases. The net energy ratio of the microbial fuel cell method is 1.38, and 1.12, for Ru/Al2O3 and Ni/Al2O3, respectively. A comparative assessment of ammonia generation and decomposition options for environmentally-benign hydrogen production is discussed.

Process Simulation Integrated Life Cycle Net Energy Analysis and GHG Assessment of Fuel-Grade Bioethanol Production from Unutilized Rice Straw

For the life cycle scenario of bioethanol production from unutilized rice straw, the life cycle stage of paddy rice cultivation can be excluded with a zero-inventory allocation rule, i.e., rice straw with no applied valorization in current practice. This study evaluates the life cycle net energy analysis and greenhouse gas (GHG) assessment for a scaled-up bioethanol production plant using unutilized rice straw as the feedstock. The process simulation technique is integrated to model a scaled-up production plant to produce bioethanol at 99.7 vol% purity from unutilized rice straw, and the simulation results are retrieved to calculate inventory data for the life cycle assessment (LCA). The simulated mass flow and energy flow results are comparable with that of real plants, reported in the published literature, which validates the process simulations in this study. Including energy generation using waste flows in the process (i.e., wastewater and solid residues), the life cycle net energy analysis results show a net energy gain of 7804.0 MJ/m3 of bioethanol with a net renewable energy gain of 38230.9 MJ/m3 of bioethanol that corresponds to a net energy ratio of 1.20 and renewability factor of 5.49. The life cycle GHG assessment exhibits a net global warming potential of 584.8 kg CO2 eq/m3 of bioethanol. The effect of system boundary expansion up to the end-of-life stage as gasohol (E10), the sensitivity of the key process parameters, and the economic benefit via valorization of unutilized rice straw are further analyzed and discussed.

The greenhouse gas emissions’ footprint and net energy ratio of utility-scale electro-chemical energy storage systems

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-CO2eq for sodium-sulfur, 625–659 kg-CO2eq for lithium-ion, 749–803 kg-CO2eq for valve-regulated lead-acid, 742–806 kg-CO2eq for nickel–cadmium, and 800–963 kg-CO2eq 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.

Life cycle net energy and greenhouse gas emissions of photosynthetic cyanobacterial biorefineries: Challenges for industrial production of biofuels

The net energy ratios (NERs) and greenhouse gas (GHG) emissions of a Photosynthetic Cyanobacterial Biorefinery (PSBR) were evaluated using a Life Cycle Assessment (LCA) approach. This study assessed engineered cyanobacterium cultures in which biosynthetic biofuels are directly secreted. Biofuels researched in this study include bisabolane, a biosynthetic substitute for D2 diesel; heptadecane, a substitute for diesel; and ethanol, a substitute for gasoline. Results demonstrate that cyanobacteria-based ethanol has higher yields, lower NER, and lower GHG emissions than bisabolane and heptadecane products in Synechocystis sp. PCC6803. By performing a sensitivity analyses of the life cycle NER and GHG emissions responses of the system, we derived the improvements in system biology, metabolic engineering, and process engineering that would be required to minimize the environmental impacts at an industrial scale. The NER and GHG emissions of the biofuel products were found to be the most sensitive to organism-level biofuel productivities, the energy consumption of vapor compression and distillation, and the energy consumption of culture mixing. This LCA will serve as a baseline for stakeholders; including policy makers, cyanobacterial refineries, and researchers, to establish the goals to engineer cyanobacteria and sustainable bioprocesses.

Net energy benefits of carbon nanotube applications

Implementation of carbon nanotubes (CNTs) in various applications can reduce material and energy requirements of products, resulting in energy savings. However, processes for the production of carbon nanotubes (CNTs) are energy-intensive and can require extensive purification. In this study, we investigate the net energy benefits of three CNT-enabled technologies: multi-walled CNT (MWCNT) reinforced cement used as highway construction material, single-walled CNT (SWCNT) flash memory switches used in cell phones and CNT anodes and cathodes used in lithium-ion batteries used in electric vehicles. We explore the avoided or additional energy requirement in the manufacturing and use phases and estimate the life cycle net energy benefits for each application. Additional scenario analysis and Monte Carlo simulation of parameter uncertainties resulted in probability distributions of net energy benefits, indicating that net energy benefits are dependent on the application with confidence intervals straddling the breakeven line in some cases. Analysis of simulation results reveals that SWCNT switch flash memory and MWCNT Li-ion battery cathodes have statistically significant positive net energy benefits (α=0.05) and SWCNT Li-ion battery anodes tend to have negative net energy benefits, while positive results for MWCNT-reinforced cement were significant only under an efficient CNT production scenario and a lower confidence level (α=0.1).

Time-valued net energy analysis of solar kilns for wood drying: A solar thermal application

This paper describes a LNEA (life-cycle net energy analysis) for solar thermal applications with particular reference to two typical greenhouse-type solar kilns (Oxford and Boral) for wood drying. The analysis included the simulation of future flows of OE (operational energy), and the assessment of EE (embodied energy) for the two kilns over an expected service life of 20 years. The OE streams associated with the drying of a hardwood species (Eucalyptus pilularis) were estimated by solving a solar kiln model, while a LCA (life cycle assessment) model was used for the assessment of EE components. The key objective of this paper was to carry out a time-valued net energy analysis for two significantly different kiln designs. This approach of evaluating the energy-intensive facilities (e.g. solar kilns) is novel, and may result in a robust framework for further performance/design optimization study of solar kiln designs. Based on the chosen life-cycle performance parameters, the Oxford kiln was generally found to be more productive and energy efficient than the Boral kiln for hardwood drying in Australia.

Multi-Objective Optimization Design for Indirect Forced-Circulation Solar Water Heating System Using NSGA-II

In this study, the multi-objective optimization of an indirect forced-circulation solar water heating (SWH) system was performed to obtain the optimal configuration that minimized the life cycle cost (LCC) and maximized the life cycle net energy saving (LCES). An elitist non-dominated sorting genetic algorithm (NSGA-II) was employed to obtain the Pareto optimal solutions of the multi-objective optimization. To incorporate the characteristics of practical SWH systems, operation-related decision variables as well as capacity-related decision variables were included. The proposed method was used to conduct a case study wherein the optimal configuration of the SWH system of an office building was determined. The case study results showed that the energy cost decreases linearly and the equipment cost increases more significantly as the LCES increases. However, the results also showed that it is difficult to identify the best solution among the Pareto optimal solutions using only the correlation between the corresponding objective function values. Furthermore, regression analysis showed that the energy and economic performances of the Pareto optimal solutions are significantly influenced by the ratio of the storage tank volume to the collector area (RVA). Therefore, it is necessary to simultaneously consider the trade-off and the effect of the RVA on the Pareto optimal solutions while selecting the best solution from among the optimal solutions.

(Invited) Life-Cycle Net Energy Assessment of Large-Scale Hydrogen Production Via Photoelectrochemical Water Splitting

The Joint Center for Artificial Photosynthesis (JCAP) aims to find a cost-effective method to produce fuels for transportation and feedstocks using only sunlight, water, and carbon dioxide as inputs. Development of such a technology offers the possibility of widespread sources of environmentally benign, energy rich chemicals across the globe. Although still at an early stage, solar-driven water splitting to produce hydrogen is the most mature artificial solar-to-fuel conversion approach. Moreover, there is sufficient information from photoelectrochemical (PEC) water-splitting prototypes designed and developed by JCAP and others to perform an assessment of whether large scale application of this approach would be advantageous from a net energy production point of view. Here we report a prospective life-cycle net energy assessment of a hypothetical large-scale PEC-based hydrogen production facility, assuming energy output equivalent to 1 GW continuous annual average (610 metric tons of H2per day) [1]. We determine essential mass and energy flows required to support such production [2], and use heuristic methods to conduct a preliminary engineering design of the facility. We then develop and apply a parametric model describing system-wide energy flows associated with the production, utilization, and decommissioning of the facility. Based on these flows, we calculate and interpret life-cycle net energy metrics for the facility. We find that under base-case conditions (10% solar-to-hydrogen (STH) conversion and 10 year PEC cell life span) the energy payback time is 8.1 years, the energy return on energy invested (EROEI) is 1.7, and the life-cycle primary energy balance over the 40 years projected service life of the facility is +500 PJ. The most important model parameters affecting the net energy metrics are the STH conversion efficiency, the life span of the PEC cells, and the embodied energy of several components of the PEC cell. We discuss the sensitivities of these and other parameters, and highlight recent work indicating promising ways to improve the net energy metrics. Results suggest that a strong program of research into improved materials and methods to process the materials will have a high impact on the feasibility of this technology.

A simplified method for optimal design of solar water heating systems based on life-cycle energy analysis

Significant energy mismatch exists in solar water heating systems as the time and amount of solar energy supply are usually different from that of hot water demand. Using a hot water storage tank can reduce or eliminate such mismatch in short term while it is difficult to avoid this mismatch in long term. In many optimal design and life-cycle analysis methods, the energy mismatch is ignored which causes the system performance to be overestimated and also misleads the optimal design of the system. This paper presents a simplified method for optimizing the key parameters of solar water heating systems based on life-cycle energy analysis. This optimal method considering the energy mismatch phenomenon can be implemented through two steps. In the first step, a simplified energy model based hourly energy matching different components of the system, is developed for determining the operating performance of system with different solar collector areas and water storage volumes. In the second step, the law of diminishing marginal utility is employed to determine the optimum size of the system. The optimum size is identified when the maximal life-cycle net energy saving is achieved. A case study on the application of the proposed method in a building is presented as well.

Life-cycle net energy assessment of large-scale hydrogen production via photoelectrochemical water splitting

This article reports the first prospective life-cycle net energy assessment of a gigawatt-scale photoelectrochemical (PEC) hydrogen production facility.

Assessment of the biomass energy potentials and environmental benefits of Jatropha curcas L. in Southwest China

Jatropha curcas L. (JCL) is believed to be the most promising tree species used to produce biodiesel in China. Due to its abundant marginal land resource and good meteorological conditions, Southwest China is the major region to develop JCL. With Southwest China being taken as the study area in this paper, multi-factor comprehensive analysis is used to identify marginal land resources suitable to JCL plantation and make suitability assessment, thus obtaining their spatial distribution, suitability degree and total amount. With life cycle analysis (LCA), the life cycle net energy and greenhouse gas emission reduction capacity of marginal land resources with different suitability degrees used to produce biodiesel are investigated. Based on the research results, the life cycle model is expanded to obtain the potentiality of total net energy production and greenhouse gas emission reduction of large-scale plantation of JCL in southwest China. The results show that the area of land resources suitable and moderately suitable for JCL plantation is 1.99 × 106 ha and 5.57 × 106 ha, respectively. If all of these land resources are put into use, the maximum net production potential of biodiesel from JCL would be 1.51 × 108 GJ/a, and the total greenhouse gas emission reduction capacity 1.59 × 107 t/a in Southwest China.

Net Energy Payback and CO2 Emissions from Three Midwestern Wind Farms: An Update

This paper updates a life-cycle net energy analysis and carbon dioxide emissions analysis of three Midwestern utility-scale wind systems. Both the Energy Payback Ratio (EPR) and CO2 analysis results provide useful data for policy discussions regarding an efficient and low-carbon energy mix. The EPR is the amount of electrical energy produced for the lifetime of the power plant divided by the total amount of energy required to procure and transport the materials, build, operate, and decommission the power plants. The CO2 analysis for each power plant was calculated from the life-cycle energy input data. A previous study also analyzed coal and nuclear fission power plants. At the time of that study, two of the three wind systems had less than a full year of generation data to project the life-cycle energy production. This study updates the analysis of three wind systems with an additional four to eight years of operating data. The EPR for the utility-scale wind systems ranges from a low of 11 for a two-turbine system in Wisconsin to 28 for a 143-turbine system in southwestern Minnesota. The EPR is 11 for coal, 25 for fission with gas centrifuge enriched uranium and 7 for gaseous diffusion enriched uranium. The normalized CO2 emissions, in tonnes of CO2 per GWeh, ranges from 14 to 33 for the wind systems, 974 for coal, and 10 and 34 for nuclear fission using gas centrifuge and gaseous diffusion enriched uranium, respectively.

The Potential for Fusion Power to Mitigate U.S. Greenhouse Gas Emissions

This study summarizes a recent life-cycle net energy analysis (NEA) on a modern natural gas turbine power plant for comparison against DT fusion and conventional technologies (coal, fission, and wind). The NEA results are used as the basis for developing a life-cycle greenhouse gas (GHG) emission rate. The GHG emission rate for DT fusion is 9 metric tonnes of CO2 equivalent emitted per gigawatt electric hour produced (T/GWeh). This rate compares favorably against gas turbine (464 T/GWeh) and conventional coal (974 T/GWeh), and competitively against fission (15 T/GWeh) and wind (15 T/GWeh). The implications of this research for U.S. GHG mitigation are discussed. In evaluated scenarios, the installed nuclear and renewable capacity in the U.S. must quadruple by 2050 to maintain a Kyoto based emission target, with fusion and/or other renewable sources comprising 43-59% of U.S. capacity.