Exergetic sustainability indicators for a high pressure hydrogen production and storage system

This study examines the exergetic sustainability effect of PEM electrolyzer (PEME) integrated high pressure hydrogen gas storage system whose capacity is 3 kg/h. For this purpose, the indicators, previously used in the literature, are taken into account and their variations are parametrically studied as a function of the PEME operating pressure and storage pressure by considering i) PEME operating temperature at 70 °C, ii) PEME operating pressures at 10, 30, 50 and 100 bar, iii) hydrogen gas flow rate at 3 kg/h and iv) storage pressure between 200 and 900 bar. Consequently, the results from the parametric investigation indicate that, with the ascent of storage pressure from 200 to 900 bar at a constant PEME operating pressure (=50 bar), exergetic efficiency changes decreasingly between 0.612 and 0.607 while exergetic sustainability between 1.575 and 1.545. However, it is estimated that waste exergy ratio changes increasingly between 0.388 and 0.393 while environmental effect factor between 0.635 and 0.647. Additionally, it is said that the higher PEME outlet pressure causes the higher exergetic sustainability index, the lower environmental effect factor, the lower waste exergy output, the higher exergetic efficiency. However, the higher storage pressure causes the lower exergetic efficiency, the higher waste exergy output, the higher environmental effect factor and the lower exergetic sustainability index. Thus, it is recommended that this type of the system should be operated at higher PEME outlet pressure, and at an optimum hydrogen storage pressure.     

The sustainability of ethanol production from sugarcane

The rapid expansion of ethanol production from sugarcane in Brazil has raised a number of questions regarding its negative consequences and sustainability. Positive impacts are the elimination of lead compounds from gasoline and the reduction of noxious emissions. There is also the reduction of CO₂ emissions, since sugarcane ethanol requires only a small amount of fossil fuels for its production, being thus a renewable fuel. These positive impacts are particularly noticeable in the air quality improvement of metropolitan areas but also in rural areas where mechanized harvesting of green cane is being introduced, eliminating the burning of sugarcane. Negative impacts such as future large-scale ethanol production from sugarcane might lead to the destruction or damage of high-biodiversity areas, deforestation, degradation or damaging of soils through the use of chemicals and soil decarbonization, water resources contamination or depletion, competition between food and fuel production decreasing food security and a worsening of labor conditions on the fields. These questions are discussed here, with the purpose of clarifying the sustainability aspects of ethanol production from sugarcane mainly in São Paulo State, where more than 60% of Brazil's sugarcane plantations are located and are responsible for 62% of ethanol production.     

Pumped storage systems introduction in isolated power production systems

The present paper investigates the introduction of pumped storage systems (PSS) in isolated power production systems with high thermoelectric production and wind energy rejection.The introduced PSS aims at:

• the maximisation of the wind energy penetration and

• the minimisation of the energy production cost.

In former studies, the introduction of PSS in power production systems aims at the power demand peaks saving. In the present study, the PSS storage-production procedure is accomplished without any predefined schedule. Energy is stored whenever:

• wind energy is rejected and

• the thermal generators that burn cheap heavy fuel oil do not operate at their nominal powers.

Furthermore, the production of the thermal generators that burn expensive diesel oil is substituted during the power demand peak hours.Two case studies for Crete and Rhodes are accomplished. An iterative procedure is performed, in order to calculate the optimum pumps and hydro turbines nominal powers in both islands. The optimisation criterion is the energy production specific cost minimisation.The PSS introduction in Crete yields to almost 10% annual electricity production cost reduction. The annual wind energy rejection is nullified. The investment payback period may be less than 5 years.The PSS introduction in Rhodes leads to a 1.85% annual electricity production cost reduction. The PSS project does not exhibit attractive economic indexes.Conclusively, isolated power production systems with energy production specific cost higher than approximately 0.05€/kW h seem to be appropriate for PSS introduction, following the operation algorithm of the present paper.     

Assessment of sustainability indicators for renewable energy technologies

The non-combustion based renewable electricity generation technologies were assessed against a range of sustainability indicators and using data obtained from the literature. The indicators used to assess each technology were price of generated electricity, greenhouse gas emissions during full life cycle of the technology, availability of renewable sources, efficiency of energy conversion, land requirements, water consumption and social impacts. The cost of electricity, greenhouse gas emissions and the efficiency of electricity generation were found to have a very wide range for each technology, mainly due to variations in technological options as well as geographical dependence of each renewable energy source. The social impacts were assessed qualitatively based on the major individual impacts discussed in literature. Renewable energy technologies were then ranked against each indicator assuming that indicators have equal importance for sustainable development. It was found that wind power is the most sustainable, followed by hydropower, photovoltaic and then geothermal. Wind power was identified with the lowest relative greenhouse gas emissions, the least water consumption demands and with the most favourable social impacts comparing to other technologies, but requires larger land and has high relative capital costs.     

Energy indicators for tracking sustainability in developing countries

Due to the fact that human activities and most sustainability issues are closely related to energy use, the energy system is a sound framework for providing lead indicators for sustainable development. Common energy-economic models enable the estimation of future states of the energy system. An energy system-based lead indicator set can be used to develop consistent and coherent future indicator estimates and to track sustainability, a clear advantage over existing sets.     

Assessing the impact of techno socioeconomic factors on sustainability indicators of microhydro power projects in Indonesia: A comparative study

A review of electricity access projects in rural areas reveals a number of unsustainable features. Each rural area can be very different with regard to the socioeconomic conditions and the dynamics between society and technology. This research is a comparative study to assess the impact of techno socioeconomic factors on the sustainability of two microhydro power projects. The assessment of sustainability projects was based on sustainable development indicators for rural electrification, considering technical, economic, social, environmental and institutional sustainability. The indicators were investigated through a survey. The results show that both projects performed poorly in the economical dimension and positively in other dimensions. The education background of microhydro power project-Rimba Lestari clients was relatively better than those of microhydro power project-Mendolo, in which the earlier project has higher sustainability in the institutional, social, and environmental dimensions. If the income of clients is better, microhydro power project-Mendolo, this would give better economic sustainability.     

The energy forestry production systems

When growing and using energy forests a long chain of steps is taken: choice of site, site characterization, amelioration, choice of plant material and spacing, land preparation, planting, management, harvest and handling, transport, conversion, production of hot water and electricity.

The economics of energy forestry must be improved to make the whole concept viable. Although the economics need strengthening, it has been agreed that energy forestry is one of the most promising alternatives to cereal crops on farm land. There are two main ways to improve the economics: to increase production of stemwood per area and time, and to lower the costs of production. Good achievements along these routes have been reached over the last three years. Improving each step in growing is being achieved gradually. Lowering the costs is a more stepwise process, for example as was the case when a modified maize harvester proved to work surprisingly well as an energy forestry harvester.

Introductary work done during the three-year period indicates that expert systems or decision support systems may play an important role to share and use the knowledge on energy forestry production systems. For immediate use, a handbook on how to grow short rotation forests has been made published.     

Key strategies of hydrogen energy systems for sustainability

Here we conduct a parametric study to investigate the effects of hydrogen energy utilization on the global stability and sustainability. In this regard, in order to derive the hydrogen energy based sustainability ratio, the green energy based sustainability ratio, as developed earlier, is modified to come up with a new parameter, namely “hydrogen energy utilization ratio through non-fossil fuels”. We take actual historical data from key sources to determine the role of hydrogen energy for sustainability and make some future projections as the road map for hydrogen economy. In addition, an illustrative example on the hydrogen energy based sustainability ratio is presented by considering green energy sources such as solar, wind, hydro and nuclear to make hydrogen economy more environmentally benign and sustainable. It is found that hydrogen energy based global stability and sustainability ratios increase with the rise of hydrogen energy utilization ratio. The best results for hydrogen energy based sustainability ratio are obtained for the highest hydrogen energy impact ratios between 73.33% and 100%. In case of 10% of hydrogen energy utilization ratio, hydrogen based sustainability ratios for year 2010 are, respectively, determined to be 0.21%, 0.23%, 0.25%, 0.27% and 0.29% in 2.92% of hydrogen based global stability ratio by depending on the hydrogen energy impact ratios (=73.33%$=73.33\%$, 80%, 86.67%, 93.33% and 100%). In case of 20% of hydrogen energy utilization ratio, the hydrogen energy based sustainability ratios are found to be 1.09%, 1.19%, 1.28%, 1.38% and 1.48% in 7.41%, respectively. The results are really encouraging in a way that hydrogen economy appears to be one of the most significant players for better sustainability.     

Environmental sustainability assessment of bio-ethanol production in Thailand

Bio-ethanol is playing an important role in renewable energy for transport according to Thai government policy. This study aims to evaluate the energy efficiency and renewability of bio-ethanol system and identify the current significant environmental risks and availability of feedstocks in Thailand. Four of the seven existing ethanol plants contributing 53% of the total ethanol fuel production in Thailand have been assessed by the net energy balance method and Life Cycle Assessment (LCA). A renewability and net energy ratio portfolio has been used to indicate whether existing bio-ethanol production systems have net energy gain and could help reduce dependency on fossil energy. In addition, LCA has been conducted to identify and evaluate the environmental hotspots of ‘cradle to gate’ bio-ethanol production. The results show that there are significant differences of energy and environmental performance among the four existing production systems even for the same feedstock. The differences are dependent on many factors such as farming practices, feedstock transportion, fuel used in ethanol plants, operation practices and technology of ethanol conversion and waste management practices. Recommendations for improving the overall energy and environmental performance of the bio-ethanol system are suggested in order to direct the bio-ethanol industry in Thailand towards environmental sustainability.     

Complex chemical systems with power production driven by heat and mass transfer

In this paper, we investigate power production in complex multireaction systems propelled by either uncoupled or coupled multicomponent mass transfer. The considered system contains two mass reservoirs, one supplying and one taking out the species, and a power-producing reactor undergoing the chemical transformations characterized by multiple (vector) efficiencies. To establish a suitable basis for these efficiencies, an approach is applied that implements balances of molar flows and reaction invariants to complex chemical systems with power production. Reaction invariants, i.e., quantities that take the same values during a reaction, follow by linear transformations of molar flows of the species. Flux balances for the reacting mixture may be written down by equating these reaction invariants before and after the reactor. Obtained efficiency formulas are applied for steady-state chemical machines working at the maximum production of power. Total output of produced power is maximized at constraints which take into account the (coupled or uncoupled) mass transport and efficiency of power generation. Special attention is given to non-isothermal power systems, stoichiometric mixtures and internal dissipation within the chemical reactor. Optimization models lead to optimal functions that describe thermokinetic limits on power production or consumption and extend reversible chemical work W_rev to situations in which reduction of chemical efficiencies, caused by finite rates, is essential. The classical thermostatic theory of reversible work is recovered from the present thermokinetic theory in the case of quasistatic rates and vanishing dissipation.     

Bio-fuels production and the environmental indicators

The paper evaluates the role of the bio-fuels production in the transportation sector in the world, for programs of greenhouse gases emissions reductions and sustainable environmental performance. Depending on the methodology used to account for the local pollutant emissions and the global greenhouse gases emissions during the production and consumption of both the fossil and bio-fuels, the results can show huge differences. If it is taken into account a life cycle inventory approach to compare the different fuel sources, these results can present controversies. A comparison study involving the American oil diesel and soybean diesel developed by the National Renewable Energy Laboratory presents CO₂ emissions for the bio-diesel which are almost 20% of the emissions for the oil diesel: 136 g CO₂/bhp-h for the bio-diesel from soybean and 633 g CO₂/bhp-h for the oil diesel [National Renewable Energy Laboratory—NREL/SR-580-24089]. Besides that, important local environmental impacts can also make a big difference. The water consumption in the soybean production is much larger in comparison with the water consumption for the diesel production [National Renewable Energy Laboratory—NREL/SR-580-24089]. Brazil has an important role to play in this scenario because of its large experience in bio-fuels production since the seventies, and the country has conditions to produce bio-fuels for attending great part of the world demand in a sustainable pathway.     

Sustainability indicators for the assessment of nuclear power

Electricity supplies an increasing share of the world’s total energy demand and that contribution is set to increase. At the same time, there is increasing socio-political will to mitigate impacts of climate change as well as to improve energy security. This, in combination with the desire to ensure social and economic prosperity, creates a pressing need to consider the sustainability implications of future electricity generation. However, approaches to sustainability assessment differ greatly in their scope and methodology as currently there is no standardised approach. With this in mind, this paper reviews sustainability indicators that have previously been used to assess energy options and proposes a new sustainability assessment methodology based on a life cycle approach. In total, 43 indicators are proposed, addressing the techno-economic, environmental and social sustainability issues associated with energy systems. The framework has been developed primarily to address concerns associated with nuclear power in the UK, but is applicable to other energy technologies as well as to other countries.     

The analysis of some nuclear power integrated systems

This paper define the concept of the nuclear power integrated system as a fast-thermal one. the integration with three successive fast reactor generations is considered: first reactor genertion—LMFBR(PuO₂); second reactor generation-LMFBR(CPu); and third reacator generation—GCFBR(PuO₂). A time interval of [0, 40] years is considered and the time evolution of the integrated system is followed under the following circumstances: a time delay of 15 years in the case of the first reactor generation, 20 years in the case of the second reactor generation and 25 years in the case of the third reactor generation. By applying the mathematical model of integrated systems an analysis of the three nuclear power integrated systems is made and many important conclusions of interest to decision makers are also drawn.     

A novel multicriteria sustainability investigation of energy storage systems

Affordable, clean, efficient, flexible, and reliable energy storage is an important component of sustainable energy systems. There are several studies in the literature concentrating on improving the sustainability performance of energy storage systems from economic and technical perspectives. However, a comprehensive performance investigation of energy storage systems that take economic, environmental, social, and technical criteria into account is still needed. For that reason, in the present study, it is aimed to perform a complete assessment and analysis of the sustainability of energy storage systems for residential applications in communities and cities. Pumped hydro, conventional batteries, high‐temperature batteries, flow batteries, and hydrogen are the selected energy storage systems. In order to handle the vagueness and ambiguity during the assessment and to eliminate the perceived hesitancy in the decision makers' preferences, an innovative method, a hybrid hesitant fuzzy multicriteria decision‐making (MCDM) methodology composed of hesitant fuzzy analytic hierarchy process (HFAHP) and hesitant fuzzy technique for order preference by similarity to ideal solution (HFTOPSIS), is utilized to assess the sustainability of the selected systems. In this study, four different performance criteria: economic (power cost and energy cost), environmental (pollutant emissions, area requirement, wastewater quality, and solid waste production), social (safety, accessibility, ease of use, and public acceptance), and technical (efficiency, storage capacity, cycling limit, and performance degradation) are taken into consideration. The performance evaluation results indicate that technical performance has the highest influence and social performance has the lowest influence when evaluating the sustainability of the selected energy storage systems. And hydrogen has the highest sustainability performance compared with the other selected energy storage options.     

Energy sustainability from analysis of sustainable development indicators: A case study in Taiwan

As Taiwan has a dense population and only limited natural resources, the government began actively establishing a Taiwan's sustainable development indicators (TSDI) system in 2003, which was developed with reference to the Pressure–State Response (PSR) framework to evaluate the progress towards sustainability. Energy is a very important factor in leading to sustainable development at the national level. However, there are only two indicators concerning the energy sustainability in the TSDI system. This paper summarizes the current status of energy supply, energy consumption, carbon dioxide (CO₂) emissions and renewable energy production since the year 2000. The updated information on the TSDI was also addressed and analyzed to imply the progress towards energy sustainability during 2000–2008. Finally, the weighted-sum method was proposed to make an analysis of energy sustainability from Taiwan's renewable energy production, showing that this country has experienced a significant progress toward energy sustainability in recent years.     

Personal power systems

The lack of compact, efficient, human compatible, lightweight power sources impedes the realization of machine-enhanced human endeavor. Electronic and communication devices, as well as mobile robotic devices, need new power sources that will allow them to operate autonomously for periods of hours. In this work, a personal power system implies an application of interest to an individual person. The human-compatible gravimetric energy density spans the range from 500 to 5000 Wh/kg, with gravimetric power density requirements from 10 to 1000 W/kg. These requirements are the primary goals for the systems presented here. The review examines the interesting and promising concepts in electrochemical, thermochemical, and biochemical approaches to small-scale power, as well as their technological and physical challenges and limitations. Often it is the limitations that dominate, so that while the technology to create personal autonomy for communications, information processing and mobility has accelerated, similar breakthroughs for the systems powering these devices have not yet occurred.

Fuel cells, model airplane engines, and hummingbird metabolism, are three promising examples, respectively, of electrochemical, thermochemical, and biochemical power production strategies that are close to achieving personal power systems' power demands. Fuel cells show great promise as an energy source when relatively low power density is demanded, but they cannot yet deliver high peak powers nor respond quickly to variable loads. Current small-scale engines, while achieving extraordinary power densities, are too inefficient to achieve the energy density needed for long-duration autonomous operation. Metabolic processes of flying insects and hummingbirds are remarkable biological energy converters, but duplicating, accelerating, and harnessing such power for mobility applications is virtually unexplored. These challenges are significant, and they provide a fertile environment for research and development.     

Environmental and sustainability aspects of hydrogen and fuel cell systems

Discussed in this paper are current environmental problems, potential solutions to these problems, possible future hydrogen energy‐utilization patterns for better environment and sustainable development through life cycle assessment (LCA), and how the principles of thermodynamics via exergy can be beneficially used to evaluate hydrogen and fuel cell systems and their role in sustainable development. Throughout the paper current and future perspectives of hydrogen and fuel cell systems based on exergetic, LCA and sustainability aspects development are considered. The results will likely be useful to scientists, researchers and engineers as well as policy and decision makers. Two case studies on the LCA aspects of hydrogen and fuel cell systems are presented to highlight the importance of the hydrogen and fuel cell systems and show that these can help achieve better environment and sustainability. Copyright © 2006 John Wiley & Sons, Ltd.     

Developing a sustainability framework for the assessment of bioenergy systems

The potential for biomass to contribute to energy supply in a low-carbon economy is well recognised. However, for the sector to contribute fully to sustainable development in the UK, specific exploitation routes must meet the three sets of criteria usually recognised as representing the tests for sustainability: economic viability in the market and fiscal framework within which the supply chain operates; environmental performance, including, but not limited to, low carbon dioxide emissions over the complete fuel cycle; and social acceptability, with the benefits of using biomass recognised as outweighing any negative social impacts. This paper describes an approach to developing a methodology to establish a sustainability framework for the assessment of bioenergy systems to provide practical advice for policy makers, planners and the bioenergy industry, and thus to support policy development and bioenergy deployment at different scales. The approach uses multi-criteria decision analysis (MCDA) and decision-conferencing, to explore how such a process is able to integrate and reconcile the interests and concerns of diverse stakeholder groups.     

The sustainability of sugarcane-ethanol systems in Guatemala: Land, labour and law

Since 2010, Guatemala has been exporting ethanol, principally to European markets. This means that Guatemalan biofuel has been certified sustainable, although this is deeply contested with NGO reports drawing attention to the negative impacts of ‘agrofuels’, particularly for marginalised communities. Guatemala therefore provides an excellent case study for examining not only the impacts of increased global demand for biofuels, but also whether sustainability, as conceptualised by the European Union's Renewable Energy Directive, can capture those issues that are salient to the Guatemalan context. Drawing on more than eighty qualitative, in-depth interviews, this paper finds that the bloc's governance framework for biofuels fails to capture many of the issues that matter most to local people in Guatemala, namely land access, trade unions and compliance with the law. This paper argues that the current framework therefore runs the risk of exacerbating the plight of Guatemala's already marginalised rural communities.