Energy Return Research Articles

A combined assessment of the energy, economic and environmental performance of a photovoltaic system in the Italian context

Policymakers are increasingly moving towards greater investments in research in the renewable energy sector, in order to reduce costs, making private investment affordable, so as to accelerate the achievement of grid parity. This evidence boosts for investigating the way the convenience of investing in a solar photovoltaic (PV) system, in Italy, is unrelated to any form of public incentive. Under this perspective, this paper is focused upon designing a residential 3 kW PV system and providing a full set of indicators for the assessment of its multi-dimension performance in an holistic, integrated approach. Particularly, energy and environmental indicators, likewise the Energy Payback Time (EPBT), Energy Return on Investment (EROI) and Environmental Impact Mitigation potential (EIMP) allowed the authors to measure some of the relevant sustainability-related issues of a residential PV system. Those were found to be equal to 1.35 years, 7.05 and 23,215 kg CO2 eq, respectively. Whereas, the authors used the Levelized Cost of Energy (0.15064 €/kWh), the Net Present Value (€ 2881), and the Payback Period (8.26 years), to evaluate the economic and financial feasibility of the PV system modelized. The variations of EPBT and EROIEL with respect to solar radiation and the efficiency of the PV system and LCOE to discount rate and initial investment cost have been investigated through a sensitivity analysis.

Offshore floating photovoltaic system energy returns assessment—A life cycle energy analysis-based perspective

<abstract> <p>Researchers have long regarded photovoltaics (PV) as a poor energy return (ER) compared to fossil fuels. Although the latter's energy-return-on-investment (EROI), like oil, coal, and gas, are above 25:1 at the primary, they are about 6:1 at the final stage. Following the technology creation, it is essential to investigate whether the solar module technology innovation affects the ER. Much literature delivers the ERs of fossil fuels and PV. However, it does not address the life cycle analysis or life cycle energy analysis (LCEA) assessments. This paper, employing time-series and LCEA analyses, performs an ER evaluation of the 181-MWp global most extensive offshore floating PV (OFPV) in a 30-year life cycle at Changhua Coastal Industrial Park, Taiwan. The results show that the energy payback time (EPBT) is about one year. The EROI is about 29.8, which is superior or complies with the upper limits of previous studies under the same insolation. The approach proposed in this study should help future PV stations' ER analysis and clarify whether the innovation benefits from improving the system's performance. The results also assist in investors' decision-making regarding deploying PV projects in the future.</p> </abstract>

Sensitivity of lower-limb joint mechanics to prosthetic forefoot stiffness with a variable stiffness foot in level-ground walking

This paper presents the effectsof the Variable Stiffness Foot (VSF) on lower-limb joint mechanics in level-ground walking. Persons with transtibial amputations use lower-limb prostheses to restore level-ground walking, and foot stiffness and geometry have been shown to be the main factors for evaluating foot prostheses. Previous studies have validated the semi-active and stiffness modulation capabilities of the VSF. The core aim of this study is to investigate the mechanical effects of adjusting stiffness on knee and ankle mechanics for prosthetic users wearing the VSF. For this study, seven human participants walked with three different stiffnesses (compliant, medium, stiff) of the VSF across two force plates in a motion capture lab. Linear mixed models were utilized to estimate the significance and coefficients of determinations for the regression of stiffness on several biomechanical metrics. A stiffer VSF led to decreased ankle dorsiflexion angle (p < 0.0001, r2 = 0.90), increased ankle plantarflexor moment (p = 0.016, r2 = 0.40), increased knee extension (p = 0.021, r2 = 0.37), increased knee flexor moment (p = 0.0007, r2 = 0.63), and decreased magnitudes of prosthetic energy storage (p < 0.0001, r2 = 0.90), energy return (p = 0.0003, r2 = 0.67), and power (p < 0.0001, r2 = 0.74). These results imply lower ankle, knee, and hip moments, and more ankle angle range of motion using a less stiff VSF, which may be advantageous to persons walking with lower-limb prostheses. Responsive modulation of the VSF stiffness, according to these findings, could help overcome gait deviations associated with different slopes, terrain characteristics, or footwear.

Green hydrogen assessment of generation and storage potential from solar and wind energy shedding in Honduras

Honduras relies on fossil fuels and reservoir hydroelectric power plants to maintain the stability of the national electrical network. Due to the intermittency of renewable resources, solar and wind power plants cannot provide stability to the national electrical network. Renewable plants in the country that use variable renewable resources such as wind and solar have energy shedding controlled by the National Dispatch Center of Honduras to maintain a safe electrical system. Energy shedding can be defined as non-generated energy as a result of power limitations in renewable plants. This energy shedding can be used for green hydrogen production, which can displace fossil fuel technologies, bring stability to the national electrical network, and contribute to the decarbonization process of the country. In this research, sixteen green hydrogen Power-to-Power plants were sized using cumulative energy generation curves built with energy shedding data held by the National Dispatch Center of Honduras. A cost-benefit analysis was used as a decision criterion for the sizing of the hydrogen plants. The annual green hydrogen and energy production by electrolyzers and fuel cells, and the potential for carbon dioxide emission mitigation was estimated. The energy return on investment of each plant was calculated to analyze the harnessed energy in the hydrogen system.Page layout

A passive dorsiflexing ankle prosthesis to increase minimum foot clearance during swing.

The biological ankle dorsiflexes several degrees during swing to provide adequate clearance between the foot and ground, but conventional energy storage and return (ESR) prosthetic feet remain in their neutral position, increasing the risk of toe scuffs and tripping. We present a new prosthetic ankle intended to reduce fall risk by dorsiflexing the ankle joint during swing, thereby increasing the minimum clearance between the foot and ground. Unlike previous approaches to providing swing dorsiflexion such as powered ankles or hydraulic systems with dissipative yielding in stance, our ankle device features a spring-loaded linkage that adopts a neutral angle during stance, allowing ESR, but adopts a dorsiflexed angle during swing. The ankle unit was designed, fabricated, and assessed in level ground walking trials on a unilateral transtibial prosthesis user to experimentally validate its stance and swing phase behaviors. The assessment consisted of three conditions: the ankle in an operational configuration, the ankle in a locked configuration (unable to dorsiflex), and the subject's daily use ESR prosthesis. When the ankle was operational, minimum foot clearance (MFC) increased by 13mm relative to the locked configuration and 15mm relative to his daily use prosthesis. Stance phase energy return was not significantly impacted in the operational configuration. The increase in MFC provided by the passive dorsiflexing ankle prosthesis may be sufficient to decrease the rate of falls experienced by prosthesis users in the real world.

A low-power ankle-foot prosthesis for push-off enhancement.

Passive ankle-foot prostheses are light-weighted and reliable, but they cannot generate net positive power, which is essential in restoring the natural gait pattern of amputees. Recent robotic prostheses addressed the problem by actively controlling the storage and release of energy generated during the stance phase through the mechanical deformation of elastic elements housed in the device. This study proposes an innovative low-power active prosthetic module that fits on off-the-shelf passive ankle-foot energy-storage-and-release (ESAR) prostheses. The module is placed parallel to the ESAR foot, actively augmenting the energy stored in the foot and controlling the energy return for an enhanced push-off. The parallel elastic actuation takes advantage of the amputee's natural loading action on the foot's elastic structure, retaining its deformation. The actuation unit is designed to additionally deform the foot and command the return of the total stored energy. The control strategy of the prosthesis adapts to changes in the user's cadence and loading conditions to return the energy at a desired stride phase. An early verification on two transtibial amputees during treadmill walking showed that the proposed mechanism could increase the subjects' dorsiflexion peak of 15.2% and 41.6% for subjects 1 and 2, respectively, and the cadence of about 2%. Moreover, an increase of 26% and 45% was observed in the energy return for subjects 1 and 2, respectively.

The Dynamic Impact of Covid-19 Pandemic on Environment-friendly Energy Industry

Most of the current research on green energy and the pandemic focuses on how green investments changed after the epidemic and how the pandemic affected the local economy. The correlation between the rate of return on green energy and the number of confirmed cases in China and the rest of the globe is the main topic of this research. The daily cumulative confirmed Covid-19 cases in China and the rest of the world, and daily price of green energy are used as time series variables. They are daily data from the end of January 2020 to the end of July 2022. The study's findings largely show how the price of green energy has changed in relation to the pandemic's progression. A VAR (12) model makes a forecast on how the pandemic, which is expected to become stationary after the tenth period, would affect the price of green energy. The ARMA-GARCH model's findings demonstrate a statistically significant negative correlation between the price of green energy and the number of verified cases. In other words, compared to the pandemic, the price of green energy is lower. The pandemic has had no impact on the rate of return of green energy throughout the specified period, though.

ANALYSIS OF THE PROSPECTS OF THE IMPLEMENTATION OF HYDROGEN ENERGY IN THE ENERGY BALANCE OF COMPANIES IN THE AVIATION INDUSTRY

Hydrogen energy technologies, such as hydrogen storage of energy from renewable sources of electricity, by storing hydrogen as a battery for autonomous and distributed generation and refueling for hydrogen transport, are actively being introduced into the transport industry of developed countries. The transport industry of Ukraine is inextricably linked with the energy industry and has its own characteristics. World experience shows that the introduction of the latest technologies in the transport sector definitely gives a number of unambiguous bonuses for further stable development. Meanwhile, the objects of the transport industry of Ukraine have significant territories that are technologically not involved in the agricultural industry and cannot be used for the development of the cultural and social sphere. In turn, the objects of the transport industry of Ukraine make up its transport infrastructure and are located throughout the territory of Ukraine. Today, hydrogen energy includes a set of technologies for production, transportation, accumulation and use of the universal secondary energy carrier – hydrogen. Thus, in the concept of hydrogen energy, hydrogen complements the most important secondary energy carrier – electricity, the energy use of hydrogen is determined by the possibility of environmentally clean production of electricity and long-term storage with the minimization of losses, including in large volumes. The development of renewable energy, which receives energy from variable natural resources of solar and wind energy, as well as the active implementation of technologies of distributed generation and “smart” networks stimulate the urgency of solving the problem of long-term energy storage. The approach is also designed to settle the issue of the use of wind turbines and SPPs in power supply systems by stabilizing the return of the electric energy generated by them to the network. Undoubtedly, WPPs and SPPs can be connected to the network if necessary, meanwhile, using the proposed approach there is an opportunity to reduce the loss of energy obtained from natural sources and to use it rationally and efficiently. In the conditions of aviation industry enterprises, it is relevant and possible to introduce into the general structure of power supply systems based on renewable energy sources. The proposed approach to the introduction of hydrogen energy in the conditions of aviation industry enterprises allows to effectively use sources of electrical energy based on renewable energy sources both in autonomous power supply systems and to integrate them into existing power supply systems

Increasing the manoeuvrability of power units of the thermal power plants due to applying the hydrogen-oxygen systems

The article describes a method for providing additional peak power of a power-unit with help of an additional energy circuit involving a peak turbine and a hydrogen–oxygen system for energy storage and generation. This method is described on the example of K-300-240 turbine power unit. The proposed technical solutions result in the nominal, most economical mode of a power-unit operation during a day. Consequently, the specific fuel consumption is decreased, and reliability of equipment operation is increased. We have developed the technology for high-pressure gases generating that is realized in the membrane-less electrolysers. Thus, there is no need in the use of expensive and energy-intensive compressor equipment for the energy storage systems. That means that the cost of power unit modernization is reduced. Taking into account the environmental and economic factors, the use of hydrogen–oxygen systems for energy storage at the power generating enterprises provides a value of the energy return coefficient that is practically the same as for hydro-storage power plant. But capital costs of power unit modernization are significantly lowered and negative impact on the environment is minimal.

The causal relationship between green finance and geopolitical risk: Implications for environmental management

This study investigates the time-varying causal relationship between geopolitical risk and green finance during the period of 1 March 2012–February 16, 2022. By using the novel time-varying causality testing framework, our findings shed light on the nexus between geopolitical risk and green finance in informing environmental management decisions. First, we find that time heterogeneity does exist in the causal relations between geopolitical risk and green finance. Second, geopolitical risk has a more prolonged impact on the volatility of green bonds and renewable energy than the return. Yet, geopolitical risk tends to influence the return of clean energy more persistently than volatility. Third, we observe that geopolitical risk has a more sustained impact on the return and volatility of renewable energy than clean energy. This might be due to the distinct nature of the production of clean energy and renewable energy, thereby providing implications for effective environmental management. Lastly, this paper demonstrates that the impact of geopolitical risk on the return of European clean energy has diminished since the onset of 2015. The volatility of the European clean energy sector is not affected by global geopolitical risk, underscoring the necessity of promoting the development of this sector to reduce the dependence on fossil fuels and enhance energy independence.

A clustering approach to analyse the environmental and energetic impacts of Atlantic recipes - A Galician gastronomy case study

The definition of the term gastronomy encompasses both the knowledge of food and its handling, preparation and consumption. Beyond a sense of cultural identity and tradition, gastronomy also represents a pole of tourist attraction. This is the case of Galicia, a region in north-western Spain. Within this framework, local dishes, which include distinctive elements of the Atlantic diet, have gained popularity. This research delves into the sustainability of 60 Galician recipes by performing a hierarchical cluster analysis to study their carbon footprint, the energy return on investment ratio and cost.The life cycle assessment methodology was followed to account for the carbon footprint and the energy return on investment ratio of the recipes. The scope was bounded to the cradle-to-fork phases through the life cycle: production of the ingredients, transport, and meal preparation. The functional unit selected was one serving of a Galician meal.The results suggest that the recipes could be classified into three main groups according to the presence of a greater or lesser amount of animal-based products. Cluster 1 comprises 10 meat recipes. Cluster 2 encompasses 31 recipes rich in fish with some vegetables and moderate consumption of red meat and dairy products. Cluster 3 includes 22 vegetable-based recipes. The higher the portion of animal products in the recipes (mainly red meat), the higher the costs and carbon footprint and the lower the energy return on investment ratio. Conversely, plant-based recipes tend to reduce greenhouse gases emissions and increase cost competitiveness and energy efficiency indicators.Based on this study, the food service could promote eco-labelling that support and certify restaurant menus. This research could also provide transformative climate education for sustainable food for consumers, giving advice to improve food-based dietary guidelines in Spain.

Systematic Assessment of Prosthesis Stiffness on User Biomechanics Using the Lower Leg Trajectory Error Framework and Its Implication for the Design and Evaluation of Ankle-Foot Prostheses.

Advances in understanding the effects the mechanical characteristics of prosthetic feet on user biomechanics have enabled passive prostheses to improve the walking pattern of people with lower limb amputation. However, there is no consensus on the design methodology and criteria required to maximize specific user outcomes and fully restore their mobility. The Lower Leg Trajectory Error (LLTE) framework is a novel design methodology based on the replication of lower leg dynamics. The LLTE value evaluates how closely a prosthetic foot replicates a target walking pattern. Designing a prosthesis that minimizes the LLTE value, optimizes its mechanical function to enable users to best replicate the target lower leg trajectory. Here, we conducted a systematic sensitivity investigation of LLTE-optimized prostheses. Five people with unilateral transtibial amputation walked overground at self-selected speeds using five prototype energy storage and return feet with varying LLTE values. The prototypes' LLTE values were varied by changing the stiffness of the participant's LLTE-optimized design by 60%, 80%, 120%, and 167%. Users most closely replicated the target able-bodied walking pattern with the LLTE-optimized stiffness, experimentally demonstrating that the predicted optimum was a true optimum. Additionally, the predicted LLTE values were correlated to the user's ability to replicate the target walking pattern, user preferences, and clinical outcomes including roll-over geometries, trunk sway, prosthetic energy return, and peak push-off power. This study further validates the use of the LLTE framework as a predictive and quantitative tool for designing and evaluating prosthetic feet.

Multi-Keel Passive Prosthetic Foot Design Optimization Using the Lower Leg Trajectory Error Framework

Abstract People with lower-limb amputation in low- and middle-income countries (LMICs) lack access to adequate prosthetic devices that would restore their mobility and increase their quality of life. This is largely due to the cost and durability of existing devices. Single-keel energy storage and return (ESR) prosthetic feet have recently been developed using the lower leg trajectory error (LLTE) design framework to provide improved walking benefits at an affordable cost in LMICs. The LLTE framework optimizes the stiffness and geometry of a user’s prosthesis to match a target walking pattern by minimizing the LLTE value, a measure of how closely a prosthetic foot replicates a target walking pattern. However, these low-cost single-keel prostheses do not provide the required durability to fulfill International Standards Organization (ISO) testing, preventing their widespread use and adoption. Here, we developed a multi-keel foot parametric model and extended the LLTE framework to include the multi-keel architecture and durability requirements. Multi-keel designs were shown to provide 76% lower LLTE values, compared with single-keel designs while withstanding ISO fatigue and static tests, validating their durability. Given their single-part 2D extruded geometries, multi-keel feet designed with the extended LLTE framework could be cost-effectively manufactured, providing affordable and durable high-performance prostheses that improve the mobility of LMIC users.

Quantitative impact assessment of temperature on the economics of a rooftop solar photovoltaic system.

This paper analyzes the economics of a grid-interactive rooftop solar photovoltaic (PV) system and the impact of the temperature on it. The analysis related to energy metrics, lifecycle costing, and environmental economics was performed considering the PV system's life as 30years. The system economics is also compared at different conditions like theoretical, temperature-corrected, and real electricity generation data. The parameters like energy payback time (EPBT), energy return on energy invested (EROI), and lifecycle conversion efficiency are determined as 5.95years, 5.04, and 0.078, respectively, based on actual generation. The unit electricity cost of the rooftop PV system was estimated as INR 5.37 at the 5% interest rate. The electricity cost varies with the interest rate variation and operation system life. The results show a reduction in overall economic performance on the increase in module temperature. The effect of temperature on the economics of the system is presented in terms of the per degree rise of module temperature. One degree increase of module temperature 8.5days in EPBT of the PV system increases, and INR 0.021 increases in the unit cost of electricity considering a reference temperature 25°C. A PV system has environmental benefits by reducing greenhouse gas emissions, which are also affected by the rise of module temperature. The system lost INR 355.93 in carbon credits at an increase of one-degree module temperature.

The Energy Return on Investment of Whole-Energy Systems: Application to Belgium.

Planning the defossilization of energy systems while maintaining access to abundant primary energy resources is a non-trivial multi-objective problem encompassing economic, technical, environmental, and social aspects. However, most long-term policies consider the cost of the system as the leading indicator in the energy system models to decrease the carbon footprint. This paper is the first to develop a novel approach by adding a surrogate indicator for the social and economic aspects, the energy return on investment (EROI), in a whole-energy system optimization model. In addition, we conducted a global sensitivity analysis to identify the main parameters driving the EROI uncertainty. This method is illustrated in the 2035 Belgian energy system for several greenhouse gas (GHG) emissions targets. Nevertheless, it can be applied to any worldwide or country energy system. The main results are threefold when the GHG emissions are reduced by 80%: (i) the EROI decreases from 8.9 to 3.9; (ii) the imported renewable gas (methane) represents 60 % of the system primary energy mix; (iii) the sensitivity analysis reveals this fuel drives 67% of the variation of the EROI. These results raise questions about meeting the climate targets without adverse socio-economic impact, demonstrating the importance of considering the EROI in energy system models.

Bioenergy recovery potential from upflow microaerobic sludge blanket reactor fed with swine wastewater

This paper reports the bioenergy recovery potential inherent to swine wastewater (SWW) when treated in an upflow microaerobic sludge blanket reactor (UMSB) operating with different oxygen loads. The UMSB reactor performance was compared with the one achieved with an upflow anaerobic sludge blanket (UASB) reactor that worked as a control. The biogas production was measured on a lab scale and used to estimate the UMSB reactor self-sufficiency energy. The highest methane yield achieved in the UMSB reactor was 228.6 NL kgCOD−1 d−1 at an organic loading rate (OLR) of 12.2 kgCOD m−3d−1 (HRT of 10 h). Both OLR and air dose increase generated methane dilution in the biogas, which reduced the possibility of electrical energy recovery. Nevertheless, the results showed that the UMSB reactor was self-sufficient and had energy efficiency at the 12 h HRT with doses of 0.17 and 0.25 LO2 Lfeed−1d−1 and at the 10 h HRT with a dose of 0.25 LO2 Lfeed−1d−1. The UMSB reactor achieved an energy return on investment (EROI) of 11.6–18.7, showing a potentially viable alternative for power generation.

Life cycle carbon, energy, water, and landuse footprints of agricultural residue-based biojet fuel in Bangladesh

Biojet fuel is a low carbon alternative to fossil jet fuel. There is limited literature on life cycle environmental performance of biojet fuel from 2nd generation biomass feedstocks. This work (i) assesses biojet fuel potential from rice, wheat, jute and potato residues in Bangladesh, and (ii) conducts farm to factory gate attributional Life Cycle Assessment of biojet fuel. Different scenarios suggest Bangladesh can produce 1074 to 2548 million liters of biojet fuel annually, with 1810 million liters per annum being the most optimistic potential. This is 4.5 times higher than the current jet fuel demand of the country. Carbon, energy, and landuse footprints of biojet fuel are lower than fossil jet fuel, however, water footprint is higher. Energy Return on Investment (EROI) of biojet fuel ranges from 1.60 to 1.78. The results will contribute to UN SDGs 7 & 13 and biojet fuel development in Bangladesh.

Implications on EROI and climate change of introducing Li-ion batteries to residential PV systems

In this study, we investigate the sustainability aspect of residential PV installations combined with batteries — with a focus on EROI (Energy Return On Invested Energy) and CO2 reduction potential. We pay special attention to situations where an excess of photovoltaic power generation is not allowed to be fully fed into the distribution grid and has to be (partly) curtailed. To this extent, we estimate the impact of residential solar batteries in three different European countries: Switzerland, Norway, and Spain. The combined EROI (PV coupled with battery) was shown to be greater for all battery sizes up to 30 kWh compared to a scenario where excess PV production would be curtailed, with Spain’s EROI almost doubling from around 8 for the case of no battery to 15 for an 18 kWh battery. For Switzerland and Norway, the EROI is improving by about 50% to 11 and 9, respectively, with the ideal size being smaller at 12 kWh. Optimal battery sizes were also calculated for different curtailment thresholds, which are set to increase in the coming years due to higher PV penetration in national power grids. Residential solar batteries were demonstrated to be a viable addition in all geographical settings from a Net Energy Analysis point of view. When considering CO2-equivalent emission reduction potential of a PV plus battery system, the local grid’s CO2 intensity is decisive, increasing the benefit in countries such as Spain and Switzerland, but worsening overall impacts in Norway for oversized batteries.

Sustainability of waste-to-hydrogen conversion pathways: A life cycle thinking-based assessment

Waste-derived hydrogen (H2) has been identified as a clean energy source which could simultaneously abate greenhouse gas (GHG) emissions and avert municipal solid waste (MSW) from being deposited in perpetual landfills. In this study, four waste-to-hydrogen processes – gasification, pyrolysis, integrated pyrolysis-gasification, and landfill bioreactor technology – are studied with MSW as feedstock. Following technological evaluations, life cycle assessment and life cycle costing are performed for different scenarios and configurations to evaluate their environmental footprint, levelized cost of H2, and energy return on investment. Finally, multicriteria decision-making was applied using the VIKOR method under four weighting schemes to evaluate the four processes under varying decision-making contexts. Gasification results in the highest H2 outputs and energy returns, whereas pyrolysis produces the lowest levelized cost due to its biochar by-product formation. Nevertheless, all four technologies proved to be performing optimally under different weightings of environmental, economic, and social elements, suggesting the versatility of the waste-to-hydrogen concept and its suitability to be applied in various decision-making contexts. The results and novelties of this study would contribute toward planning and investment decision-making in sustainable H2 production and clean energy.

Evolution of the conceptualization of hydrogen through knowledge maps, energy return on investment (EROI) and national policy strategies

In order to address Climate Change and energy dependency challenges, hydrogen (H2) is emerging as a promising energy carrier. Studies related to its production have conceptualized it as green (GH2), clean, renewable (RH2), ecological, and sustainable (SH2). The aim of this research is to deepen the understanding of the GH2 concept and to state boundaries between different terms. To reach this objective, a bibliometric analysis of publications indexed in SCOPUS is launched. Also, in order to assess the potential of renewable energy sources (RES) for GH2 production, a review of the meta-analysis literature on the Energy Return on Energy Invested (EROI) ratio as regards these RES is performed. Additionally, an analysis of main national strategies on GH2 is launched. Results indicate that the GH2 concept is gaining remarkable relevance, while the keyword maps show no significant differences between SH2, RH2 and GH2. EROI reveals low average values for the different biomass energy production processes. For their part, GH2 national strategies focus mainly on solar and wind technologies, albeit leaving the door open to biomass, where EROI could become an adequate metric to guide these strategies towards a low carbon energy path. Although the role of biomass may become fundamental in this energy transition process, given its low EROI values and considering that it is not a totally clean RES, it should be indexed as RH2, but not always as GH2. Finally, a proposal that guides a more appropriate use of the term GH2 is made.Graphical abstract