An atmospheric impact assessment of water-based hydrogen production methods: Sustainability evaluation

The potential for mitigating greenhouse gas emissions and minimizing yield losses using the negative pressure irrigation system

A life cycle analysis (LCA) and technoeconomic analysis (TEA) are developed for a next generation solid oxide electrolyzer (SOE) converting water into hydrogen (H2) and oxygen (O2). The LCA quantifies the expected change in environmental impacts with the displacement of current technologies competing with SOEs. The TEA calculates the expected future life cycle cost of producing extremely pure H2 and O2.Approach:To develop these analyses, Gaia collaborates closely with a world-leading developer of SOE technology, OxEon Inc (formerly Ceramatec Inc.). To execute this research, Gaia works closely with the SOE developer to identify and analyze SOE cell, stack, and system engineering performance data. Gaia then develops and deploys custom computer models and data sets that include, but are not limited to, chemical engineering process plant designs of SOEs and detailed LCA and TEA models. Gaia also builds on existing U.S. DOE modelling tools, such as the Argonne National Laboratory full life-cycle model, the Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model; the H2A H2 production analysis model; and existing DOE high temperature electrolysis case studies.1: Life cycle analysis (LCA)Modelling results indicate that the environmental impacts of SOEs can be substantially lower than competing technologies generating H2 and O2. For example, greenhouse gas (GHG) emissions are calculated to be significantly lower for H2 generated via SOEs, compared with H2 generated via steam methane reforming (SMR) of natural gas. (SMR of natural gas produces ~95% of H2 generated in the U.S. today, and is by far the most commercially prevalent process for generating H2.) Modelling results indicate an ~80% or greater decline in GHGs with a switch from natural gas SMR to SOE for H2 production. Results indicate that the primary factors influencing this comparison of GHG emissions from SOE vs. natural gas SMR include, but are not limited to,(1) the SOE stack and system electricity usages (kWh_electric/kg H2),(2) the SOE stack and system heat usages (kWh_thermal /kg H2),(3) the carbon footprint of the electricity input source to the SOE (kg carbon /kWh_electric), and(4) the carbon footprint of the thermal input source to the SOE (kg carbon /kWh_thermal).In addition to GHGs, this analysis also considers life cycle air pollution emissions and solid waste streams.2: Technoeconomic analysis (TEA)Modelling results indicate that the life cycle economics of SOEs can be substantially lower than competing technologies generating H2 and O2. For example, results indicate that, under certain conditions, SOEs can be expected to produce H2 at < $2/kg H2. $2/kg H2 is the DOE Hydrogen and Fuel Cell Technologies Office’s (HFTO) H2 production cost target. Results indicate that the primary cost drivers influencing the levelized cost of H2 from SOEs include, but are not limited to,(1) the sales price attained for the high-purity O2 generated by the SOE system;(2) the efficiency with which the system coverts input electricity into H2 and O2 (i.e. SOE system electricity usage rates, and including stack and balance of plant (BOP) efficiencies);(3) the efficiency with which the system coverts input heat into H2 and O2 (i.e. SOE system heat usage rates, and including stack and BOP efficiencies);(4) the price of the electricity purchased as an input to the SOE;(5) the price of the external heating purchased as an input to the SOE stack;(6) the SOE stack power density;(7) the SOE stack, balance of plant (BOP) and system capital costs;(8) SOE stack and system lifetimes;(9) the operating capacity factor; and(10) operations and maintenance costs.This work also quantifies the impact of R&D improvements to the SOE on reducing levelized costs. This work evaluates both near-term and far-term advanced SOE cases. R&D and higher manufacturing production rates are estimated to reduce the uninstalled SOE system capital costs from about $840/kWe in the near-term to about $640/kW in the far-term. Between near and far-term cases, the efficiency with which the system coverts input electricity into H2 and O2 is estimated to increase from about 37.61 kWh_e/kg H2 in the near-term to 35.1 kWh_e/kg H2 in the far-term. Consequently, the levelized cost of H2 is estimated to be ~$3 /kg H2 in the near-term, based on a 2.5¢/kWh electricity price, and < $2 /kg H2 in the far-term, based on 2¢/kWh electricity.This work was supported in part by the U.S. Department of Energy (DOE) prime contract number DE-EE0007645 via a subcontract.

Membraneless Electrolyzers for Low-Cost Hydrogen Production in a Renewable Energy Future

Livestock farming is of major economic relevance but also severely contributes to environmental impacts, especially greenhouse gas (GHG) emissions such as methane (CH4; particularly from ruminant production) and nitrous oxide (N2O; mainly from manure management and soil cultivated for feed production). In this study, we analyse the impact of GHG emissions from Austrian livestock production, using two metrics: a) the commonly used global warming potential (GWP) over 100 years (GWP100 in CO2-equivalents, CO2-e), and b) the recently introduced metric GWP*, which describes additional warming as a function of the timeline of short-lived GHG emissions (unit CO2 warming equivalents, CO2-we). We first compiled the sectoral (i.e. only direct emissions without upstream processes) GWP100 for different livestock categories with a focus on dairy cattle, beef cattle and pigs in Austria between 1990 and 2019. We also estimated product-related (i.e. per kg carcass weight or per litre of milk) GWP100 values, including upstream processes. We then calculated the corresponding GWP* metrics, both sectoral and product-related, and compared them with the GWP100 values. Decreasing livestock numbers and improved production efficiency were found to result in strong sectoral emission reductions from dairy production (–32 % of GWP100 from 1990 to 2019) and from pigs (–32 % CO2-e). This contrasts with low reductions from other livestock categories and even increases for cattle other than dairy cows (+3 % CO2-e), mainly due to rising suckler cow numbers. Allocated results per kg milk and kg body mass show quite similar results. Using the GWP* metric, the climate impacts of Austrian livestock production are less severe. When assuming constant management and emission intensity over a period of at least 20 years, the CO2-we (GWP*) is almost 50 % less than CO2-e (GWP100) per kg Austrian raw milk due to the different impacts of the short-lived CH4. A similar trend applies to an average cattle carcass (-40 % warming impact). The emission reductions of the shrinking Austrian livestock population represent an important contribution to a climate-neutral agriculture: The CH4 reductions of livestock production during the past 20 years reduce the current total Austrian CO2-we by 16 %. Continuous CH4 reduction, as we show it here for Austrian livestock, is an effective option to tackle the climate crisis in the short term. It shall be stressed that a relatively low GWP* should not be interpreted as a concession for further CH4 emissions but as an actual reduction of (additional) warming.

Refrigerant significantly influences the performance of air-conditioning and refrigeration system as well as it has some environmental issues that need to be considered before selection. These systems can be made eco-friendly, if it is powered by solar energy or low-grade thermal energy and they use environment-friendly refrigerants. In this chapter, low GWP (global warming potential) refrigerants have been explored for the domestic air-conditioning applications. Refrigerants with high GWP are mostly used in environment control applications such as heating, ventilation, air-conditioning (HVAC), and refrigeration systems. Some refrigerants contribute to significant environmental issues and the Montreal Protocol and Kyoto Protocol have been signed to address the threats of ozone layer depletion and global warming potential. To fulfil the commitments of Kyoto Protocol, meanwhile, governments in many countries instituted phase-out plan for the use of environmentally harmful gasses in heat pump systems. For instance, EU MAC Directives, F-gas regulation, and Japan METI directives, which clearly declared their target year to use new refrigerant of GWP below 150 for mobile air conditioner and GWP below 750 for the residential air conditioner. Research interest has been stimulated to find alternative refrigerants with low or ultra-low GWP for energy conservation and environmental sustainability. Hydrofluoroolefins (HFOs) have a very low environmental impact, and thus HFOs are considering as potential candidates to replace the hydrofluorocarbon (HFC) refrigerants such as R410A, a near-azeotropic mixture of difluoromethane (R-32) and pentafluoroethane (R-125) and is commonly used refrigerant in air-conditioning applications. The limited number of pure fluids sometimes cannot meet the excellent heat transfer criteria due to their low volumetric capacity and moderate flammability or toxicity. Mixing of HFOs and HFCs refrigerants, in this case, allows the adjustment of the most desirable properties of the refrigerant by varying the molar fraction of the components. Different combination of mixture presented here cannot be claimed as the best mixture, but it might be a good choice for further study. This chapter focuses on the research trend in finding low GWP refrigerants and its application in different heat pump system considering the system performance, safety, and the overall environmental impact. The conventional vapor compression system, thermally driven adsorption system, and sorption-compression hybrid system have been taken into consideration.

Optimizing irrigation management sustained grain yield, crop water productivity, and mitigated greenhouse gas emissions from the winter wheat field in North China Plain

Producing H2 and O2 propellants from icy regolith in the permanently shadowed regions (PSR) of the moon requires development of integrated robust electrolysis systems that operate in cryogenic environments. High-temperature solid-oxide electrolysis (SOXE) stack technology for water splitting with an optimized balance-of-plant to recuperate heat can provide high-purity H2 (after cooling and drying) and O2 (after cooling) for use as rocket propellant. SOXE steam electrolysis can require below 45 kWhelec kgH2 -1, less than alkaline and PEM liquid H2O electrolyzers. However, to achieve these energy advantages, SOXE systems require efficient upstream steam generation and compression, heat recuperation, and water recovery from the H2 product. In this study, optimization of a 3.5 kWelec lab-scale system reveals that the ability of OxEon’s stack technology to operate at steam-utilizations e H2O > 95% can provide a system that meets the target of 45 kWhelec kgH2 -1.The SOXE stack utilizes stabilized zirconia electrolytes similar to the MOXIE (Mars Oxygen In-Situ Resource Utilization Experiment) system and operates at a steady 800ºC. This high operating temperature requires efficient thermal integration and balance-of-plant components to minimize system energy and mass for operation in the PSRs ‘cryo-vac’ conditions, where temperatures can reach as low as 40 K. Figure 1a illustrates the process diagram showing the steam generator, compressor, cathode and anode heat recuperators for heat recovery, and a H2 cooler/dryer for exhaust H2O recovery. Passive radiative coolers for lunar operation prepare the O2 and H2 product streams for liquification. To optimize the system operation, a MATLAB-based process model calculates the performance of the integrated component system model and is called by the MATLAB optimization toolbox to minimize specific power w sp under constraints that maintain reasonable system mass. Optimization variables in this study included SOXE stack H2O utilization e H2O; SOXE stack anode electrochemical compression DP a; steam generator vapor outlet temperature T vap; and compressor pressure ratio P rat. The SOXE cell operated at the thermoneutral voltage (V tn » 1.28 V/cell @ 800℃). BOP power demands included the compressor, SOXE steam preheater, insulation heaters, and supplemental electric heating for the steam generator. Optimization for the 3.5 kWelecSOXE system indicates that the biggest benefit for w sp comes from high eH2O, which reduces freezing required to recover water in the H2 passive cooler. e H2O of 95% with lower T vap around 85℃ and low P rat (around 2.00) provides a path for achieving the target w sp < 45 kWhelec kgH2 -1 . Figure 1

Crop intensification is often thought to increase greenhouse gas (GHG) emissions, but studies in which crop management is optimized to exploit crop yield potential are rare. We conducted a field study in eastern Nebraska, USA to quantify GHG emissions, changes in soil organic carbon (SOC) and the net global warming potential (GWP) in four irrigated systems: continuous maize with recommended best management practices (CC‐rec) or intensive management (CC‐int) and maize–soybean rotation with recommended (CS‐rec) or intensive management (CS‐int). Grain yields of maize and soybean were generally within 80–100% of the estimated site yield potential. Large soil surface carbon dioxide (CO2) fluxes were mostly associated with rapid crop growth, high temperature and high soil water content. Within each crop rotation, soil CO2 efflux under intensive management was not consistently higher than with recommended management. Owing to differences in residue inputs, SOC increased in the two continuous maize systems, but decreased in CS‐rec or remained unchanged in CS‐int. N2O emission peaks were mainly associated with high temperature and high soil water content resulting from rainfall or irrigation events, but less clearly related to soil NO3‐N levels. N2O fluxes in intensively managed systems were only occasionally greater than those measured in the CC‐rec and CS‐rec systems. Fertilizer‐induced N2O emissions ranged from 1.9% to 3.5% in 2003, from 0.8% to 1.5% in 2004 and from 0.4% to 0.5% in 2005, with no consistent differences among the four systems. All four cropping systems where net sources of GHG. However, due to increased soil C sequestration continuous maize systems had lower GWP than maize–soybean systems and intensive management did not cause a significant increase in GWP. Converting maize grain to ethanol in the two continuous maize systems resulted in a net reduction in life cycle GHG emissions of maize ethanol relative to petrol‐based gasoline by 33–38%. Our study provided evidence that net GHG emissions from agricultural systems can be kept low when management is optimized toward better exploitation of the yield potential. Major components for this included (i) choosing the right combination of adopted varieties, planting date and plant population to maximize crop biomass productivity, (ii) tactical water and nitrogen (N) management decisions that contributed to high N use efficiency and avoided extreme N2O emissions, and (iii) a deep tillage and residue management approach that favored the build‐up of soil organic matter from large amounts of crop residues returned.

There are many cropping systems followed in Bangladesh for enhancing cropping intensity and increasing crop production, but greenhouse gas (GHG) emission from agricultural fields are mostly reported on country basis. In order to estimate of GHG emission from agriculture fields, Cool Farm Tool Beta-3 was used to determine total GHG from selected cropping systems. It was found that non-rice based cropping system had lower global warming potential (GWP) than rice based cropping systems. Among the rice based cropping systems, Onion-Jute-Fallow, Jute-Rice-Fallow, Wheat-Mungbean-Rice and Maize-Fallow-Rice systems are relatively more suitable for reducing GHG emission and subsequent GWP. There are spatial variations in CH4 emissions and the higher amounts were found in Mymensingh and Dinajpur districts in Bangladesh. In 2013–14, about 1.56 Tg year−1 CH4 emissions took place from paddy field in Bangladesh. Further study is required for validation and suggesting suitable mitigation strategies to check the GHG emission in Bangladesh.

The equipment for chilling or freezing food consumes much energy. Therefore, there is a need to reduce the energy consumption. Also, to contribute to reduce the greenhouse gas (GHG) emissions, it is necessary to replace conventional refrigerants which affect Global Warming because of high Global Warming Potential (GWP). Hence, there is a need for the use of alternative refrigerants with lower GWPs. Therefore, in this study, the potential of the non-freon refrigerant GF-08, which consists of hydro-carbons, as an alternative refrigerant was evaluated. The use of GF-08 for chilling and freezing storage systems was evaluated. The eco-benefits of GF-08 in comparison to the conventional refrigerant (R404A) was evaluated by developing a theoretical simulation model. A demo-test using a refrigerator in a restaurant was conducted to validate the simulated result. This result showed that performance differences depend on different operating conditions of temperature. Based on the simulation model, the benefits considering the energy reduction was evaluated. The reduction of the annual energy consumption, and the environmental impact of GF-08 using the life cycle assessment (LCA) methodology were estimated. The use of GF-08 reduced the annual energy consumption by 28.6% and the GHG emissions by 27.1 % in comparison to the R404A.

Life-cycle analysis of flow-assisted nickel zinc-, manganese dioxide-, and valve-regulated lead-acid batteries designed for demand-charge reduction

Solid-oxide electrolysis (SOEC) systems coupled to pressurized vaporization provides an efficient pathway to produce H2 and O2 at specific energy > 50 kWhelec/kgH2 from icy regolith in the permanently shadowed regions. The high-temperature nature of SOEC (> 700 °C) places a significant burden on the balance of plant, both for heat recovery in incoming flows and for exhaust effluent cooling/drying to achieve high purity O2 and H2 [1]. Process simulations of a scaled-up SOEC fuel production system has been benchmarked against demonstration experiments in a vacuum chamber of an SOEC system using an OxEon Energy SOEC stack with balance of plant components. These simulation tools include discretized down-the-channel models of the SOEC stack as well as HX for H2 during with exhaust heat and unreacted H2O recovery indicate that YSZ-electrolyte stacks can reliably operate reliably around thermo-neutral voltages (≅1.29 V/cell) at 800 °C with sustained mean current densities above 0.3 A/cm2. The current study explores how modeling of the benchmarked lab-scale system that produces ≅ 0.083 kgH2/h and 0.66 kgO2/h informs the design and simulation of a larger SOEC system to support ISRU of lunar water for future lunar operations.Scale up of SOEC production of 20 kgH2/h and 160 kgO2/h for lunar applications requires the identification of an SOEC unit stack and the deployment of many SOEC stacks in conjunction with common steam generators and exhaust recuperators and dryers. To date, SOEC stack technology as developed by OxEon and others has in generally been limited to individual cells on the length scales of 10 × 10 cm, and such cell sizes provide ≅ 1.0 gH2/h at targeted current densities of 0.3 A/cm2. Ten 200-cell stacks can support the 20 kgH2/h, and this study explores the performance of such a multi-stack SOEC system coupled to a common balance of plant for providing pressurized steam inputs and cooling and drying of the product H2 and O2 in lunar operations. The benchmarking experimental work demonstrated that stacks and single-stack balance-of-plant can achieve specific H2-production energy below 50 kWhelec/kgH2, and scale-up modeling of the multi-stack system shows how much this specific energy drops with various process designs and sizes. Optimal designs and operating conditions are also formed by qualitative assessment of stack and heat exchanger reliability, availability, and maintainability during operation in the cryovacuum environment that characterizes the permanently shadowed craters near the lunar poles. The previous SOEC system design was further complicated by the need to recycle H2 from the exhaust of the electrolyzer during the warmup of the stack in order to avoid oxidization of its partial-nickel cathode. As such, the team has undergone redesign of the stack and balance-of-plant (illustrated in Figure 1) to perform SOEC system analysis for the upcoming technology development push, as well as detailed architecture studies for scaled-up demonstration of this technology on the Moon.The simulation models for multi-stack SOEC system with a pressurized steam generator displacing the compressor-less operation has explored the sensitivity of system mass and specific energy for a range of operating parameters. kWhelec/kgH2, The scaled-up operation for a SOEC stack and balance of plant simply using a similarly sized SOEC stack from the benchmark studies reveals how increased SOEC stack temperature to 850 °C can improve specific energy down to close to 45 kWhelec/kgH2 but at the expense of stack life. The common balance of plant steam generator, recuperator, O2 cooler, and H2 dryer in Fig. 1 at scale can enable higher current densities and reduced BOP losses for a 20 kgH2/h H2 production. This study illustrates the potential of SOEC operation to offer a viable solution toward H2 and O2 production for lunar operations.. Figure 1

A review of life cycle greenhouse gas (GHG) emissions of commonly used ex-situ soil treatment technologies

The hydrogen (H2) economy is seen as a crucial pathway for decarbonizing the energy system, with green H2—i.e., obtained from water electrolysis supplied by renewable energy—playing a key role as an energy carrier in this transition. The growing interest in H2 comes from its versatility, which means that H2 can serve as a raw material or energy source, and various technologies allow it to be produced from a wide range of resources. Environmental impacts of H2 production have primarily focused on greenhouse gas (GHG) emissions, despite other environmental aspects being equally relevant in the context of a sustainable energy transition. In this context, Life Cycle Assessment (LCA) studies of H2 supply chains have become more common. This paper aims to compile and analyze discrepancies and convergences among recent reported values from 42 scientific studies related to different H2 production pathways. Technologies related to H2 transportation, storage and use were not investigated in this study. Three environmental indicators were considered: Global Warming Potential (GWP), Energy Performance (EP), and Water Consumption (WF), from an LCA perspective. The review showed that H2 based on wind, photovoltaic and biomass energy sources are a promising option since it provides lower GWP, and higher EP compared to conventional fossil H2 pathways. However, WF can be higher for H2 derived from biomass. LCA boundaries and methodological choices have a great influence on the environmental indicators assessed in this paper which leads to great variability in WF results as well as GWP variation due credits given to avoid GHG emissions in upstream process. In the case of EI, the inclusion of energy embodied in renewable energy systems demonstrates great influence of upstream phase for electrolytic H2 based on wind and photovoltaic electricity.

Lowland rice cultivation is a major contributor to agricultural greenhouse gas (GHG) emissions. Managing water and fertilizer is important GHG emissions. This paper evaluated GHG emissions of rice production under contrasting water regimes, i.e., continuous flooding (CF) versus alternate wetting and drying (AWD), with six nitrogen fertilizer combinations: no nitrogen (F1), urea 175 kg ha-1 (F2), urea 350 kg ha-1 (F3), urea 262.5 kg ha⁻¹ + manure 3 tons ha-1 (F4), urea 525 kg ha⁻¹ + rice straw 3 tons ha-1 (F5), and urea 175 kg ha⁻¹ + manure 3 tons ha-1 + biochar 0.6 tons ha-1 (F6). The field experiments were conducted at Bogor Regency, West Java, Indonesia, using a randomized complete block design with three replications. Growth, yield components, and GHG emissions were observed in this study throughout the growing season. Results showed AWD reduced CH₄ emissions by 30% but increased N₂O by 43% compared to CF, yielding a net 23% lower global warming potential (GWP). Organic-amended treatments (F6) maintained yields equivalent to conventional fertilization while showing numerically lower GWP. The independent effect of the water regime and the nitrogen fertilizer combinations implies that the best level of biochar and manure combined with AWD has the most promising prospect of maintaining rice yield while reducing GHG emissions.