Results 1 - 10 of 2052
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[en] The Kitaev-Heisenberg model is source of a topological quantum spin liquid with Majorana fermions and gauge flux excitations as fractional quasiparticles. The material -RuCl is composed of weakly van der Waals bound honeycomb layers of edge sharing RuCl octahedra which has recently emerged as a prime candidate for realising such physics. We studied -RuCl by means of thermal transport measurements, a valuable tool to probe elementary excitations of systems with low dimensional spin structure. While the in-plane, longitudinal heat transport is governed by heat conduction of phonons that strongly scatter off the magnetic excitations present in the system, studying the thermal Hall effect (Rhighi-Leduc effect) opens up a new path towards detecting a direct contribution of unconventional magnetic excitations to entropy transport. We have observed a sizeable transversal heat conductivity , the agreement of which with the theoretical predictions for the pure Kitaev model being suggestive of heat transport by fractionalised quasiparticles in -RuCl.
[en] Ongoing climate change affects complex and long-lived infrastructures like electricity systems. Particularly for decarbonized electricity systems based on variable renewable energies, there is a variety of impact mechanisms working differently in size and direction. Main impacts for Europe include changes in wind and solar resources, hydro power, cooling water availability for thermoelectric generation and electricity demand. Hence, it is not only important to understand the total effects, i.e., how much welfare may be gained when accounting for climate change impacts in all dimensions, but also to disentangle various effects in terms of their marginal contribution to the potential welfare loss. This paper applies a two-stage modeling framework to assess RCP8.5 climate change impacts on the European electricity system. Thereby, the performance of two electricity system design strategies - one based on no anticipation of climate change and one anticipating impacts of climate change - is studied under a variety of climate change impacts. Impacts on wind and solar resources are found to cause the largest system effects in 2100. Combined climate change impacts increase system costs of a system designed without climate change anticipation due to increased fuel and carbon permit costs. Applying a system design strategy with climate change anticipation increases the cost-optimal share of variable renewable energy based on additional wind offshore capacity in 2100, at a reduction in nuclear, wind onshore and solar PV capacity. Compared to a no anticipation strategy, total system costs are reduced.
PurposeIn this paper, we summarize the discussion and present the findings of an expert group effort under the umbrella of the United Nations Environment Programme (UNEP)/Society of Environmental Toxicology and Chemistry (SETAC) Life Cycle Initiative proposing natural resources as an Area of Protection (AoP) in Life Cycle Impact Assessment (LCIA).
MethodsAs a first step, natural resources have been defined for the LCA context with reference to the overall UNEP/SETAC Life Cycle Impact Assessment (LCIA) framework. Second, existing LCIA methods have been reviewed and discussed. The reviewed methods have been evaluated according to the considered type of natural resources and their underlying principles followed (use-to-availability ratios, backup technology approaches, or thermodynamic accounting methods).
Results and discussionThere is currently no single LCIA method available that addresses impacts for all natural resource categories, nor do existing methods and models addressing different natural resource categories do so in a consistent way across categories. Exceptions are exergy and solar energy-related methods, which cover the widest range of resource categories. However, these methods do not link exergy consumption to changes in availability or provisioning capacity of a specific natural resource (e.g., mineral, water, land etc.). So far, there is no agreement in the scientific community on the most relevant type of future resource indicators (depletion, increased energy use or cost due to resource extraction, etc.). To address this challenge, a framework based on the concept of stock/fund/flow resources is proposed to identify, across natural resource categories, whether depletion/dissipation (of stocks and funds) or competition (for flows) is the main relevant aspect.
ConclusionsAn LCIA method—or a set of methods—that consistently address all natural resource categories is needed in order to avoid burden shifting from the impact associated with one resource to the impact associated with another resource. This paper is an important basis for a step forward in the direction of consistently integrating the various natural resources as an Area of Protection into LCA.
[en] As more variable renewable energy (VRE) such as wind and solar are integrated into electric power systems, technical challenges arise from the need to maintain the balance between load and generation at all timescales. This paper examines the challenges with integrating ultra-high levels of VRE into electric power system, reviews a range of solutions to these challenges, and provides a description of several examples of ultra-high VRE systems that are in operation today.
[en] Despite the increasing attention on renewable energy, still there is limited empirical analysis about its determinants especially in developing countries. In this paper, we investigate the determinants of diversification of nonhydro renewable energy sources such as wind, solar, geothermal, biomass and waste using an extensive data set covering more than 100 developing countries from 1980 to 2010. We explore several estimation techniques such as negative binomial regression and Poisson pseudo-maximum likelihood estimation. Controlling for time and regional variations, results show that higher per capita income, implementation of renewable energy policy, advances in technological innovation and improvement in human capital promotes diversification of nonhydro sources of renewable energy. However, financial development showed no robust evidence of its effect on the diversification. Similarly, high dependence on foreign sources of fuel, increasing world market price for crude oil and increasing population will push developing countries to diversify sources of nonhydro renewable energy. In contrast, the local abundance of hydropower, high production of fossil fuel, development aid and foreign direct investment do not contribute to diversification. Results highlight salient information in drawing the roadmap for further diffusion of renewable energy in developing countries. This suggests that policy makers should exert consistent effort in integrating renewable energy in the country's energy mix. (orig.)
PurposeSport utility vehicles typically have lower fuel economy due to their high curb weights and payload capacities as well as their potential to cause serious environmental impacts. In light of this fact, a life cycle assessment is carried out in this study to assess their cradle-to-grave environmental impacts for life cycle phases ranging from manufacturing to end-of-life recycling.
MethodsA hybrid economic input-output life cycle assessment (EIO-LCA) method is used in this research paper to estimate the environmental impacts (greenhouse gas emissions, energy consumption, and water withdrawal) of sport utility vehicles. This life cycle assessment is also supplemented with a sensitivity analysis, using a Monte Carlo simulation to estimate the possible ranges for total mileage of operation and fuel economy, and to account for the sensitivity of the EIO-LCA output.
Results and discussionThe operation phase is the major contributor to the overall life cycle impact of sport utility vehicles in each fuel/power category. Furthermore, among the selected vehicles in this study, the battery electric vehicle has the lowest greenhouse gas emissions (77.2 tonnes) and the lowest energy consumption (1046.8 GJ) even though the environmental impact indicators for the battery manufacturing process are significantly large. The plug-in hybrid vehicle, on the other hand, demonstrates an optimal performance between energy use and water withdrawal (1172.9 GJ of energy consumption and 1370 kgal of water withdrawal). In addition, all of the fuel-powered vehicles demonstrated similar environmental performances in terms of greenhouse gas emissions, which ranged between 100 and 110 tonnes, but the hydrogen fuel cell vehicle had a significantly large water withdrawal (2253.2 kgal).
ConclusionsSince the majority of the overall impact stems from the operation of the vehicle in question, their complete elimination of tailpipe emissions and their high energy efficiency levels make battery electric vehicles a viable green option for sport utility vehicles. However, there are certain uncertainties beyond the scope of this study that can be considered in future studies to improve upon this assessment, including (but not limited to) regional differences in source of electricity generation and socio-economic impacts.
[en] Ocean thermal energy conversion (OTEC) is a form of power generation, which exploits the temperature difference between warm surface seawater and cold deep seawater. Suitable conditions for OTEC occur in deep warm seas, especially the Caribbean, the Red Sea and parts of the Indo-Pacific Ocean. The continuous power provided by this renewable power source makes a useful contribution to a renewable energy mix because of the intermittence of the other major renewable power sources, i.e. solar or wind power. Industrial-scale OTEC power plants have simply not been built. However, recent innovations and greater political awareness of power transition to renewable energy sources have strengthened the support for such power plants and, after preliminary studies in the Reunion Island (Indian Ocean), the Martinique Island (West Indies) has been selected for the development of the first full-size OTEC power plant in the world, to be a showcase for testing and demonstration. An OTEC plant, even if the energy produced is cheap, calls for high initial capital investment. However, this technology is of interest mainly in tropical areas where funding is limited. The cost of innovations to create an operational OTEC plant has to be amortized, and this technology remains expensive. This paper will discuss the heuristic, technical and socio-economic limits and consequences of deploying an OTEC plant in Martinique to highlight respectively the impact of the OTEC plant on the environment the impact of the environment on the OTEC plant. After defining OTEC, we will describe the different constraints relating to the setting up of the first operational-scale plant worldwide. This includes the investigations performed (reporting declassified data), the political context and the local acceptance of the project. We will then provide an overview of the processes involved in the OTEC plant and discuss the feasibility of future OTEC installations. We will also list the extensive marine investigations required prior to installation and the dangers of setting up OTEC plants in inappropriate locations.
[en] In this research work, the contribution of functional energy storage technologies to fulfill the energy policy triangle (economic viability, environmental sustainability, and security of supply) is investigated for up to the year 2030. It is noted that the aspect of economic viability should consider both the system and the stakeholder perspectives. Besides classical storage technologies like pumped hydro storage, heat storage for the flexibilisation of combined heat and power (CHP) in district heating systems, Power2Heat, Power2Gas as well as flexibilisation of load in industrial processes and households are taken into account. The term ''Functional Energy Storage'' encompasses all these technologies. Firstly, wherever they can offer an added value, all use cases for storage are analysed. The analysis of the use cases show that through changes in market design, on one hand, demand for flexibility can be reduced whereas on the other hand, it can also allow for the access to more flexibility. Hence, changes in market design can also contribute to security of supply. Subsequently, the added value of storage technologies is evaluated with the help of an energy system model (''ISAaR'' = Integrated Simulation model for plant deployment and expansion planning with Regionalization). Within this model, unit commitment and expansion of units are simulated using linear programming. To identify differences between the system and stakeholder perspectives, taxes and fees that are incurred during operation of the units are taken into account for the stakeholder perspective whereas they are not for the system perspective. The energy system is modelled with an hourly resolution at the transmission level. Germany consists of 20 knots, Austria 8 knots and the other European countries each constitute one knot. All the weather dependent input data was based on meteorological data from the year 2012. For the system perspective, the used scenarios vary by means of grid and consumption of electrical energy. In Germany, the expansion of renewable energy sources is taken from the German grid development plan 2015. However, for onshore wind power production, timelines which result in full load hours of newly installed units of 3000 instead of 2000 are used. The given expansion path of renewables by the grid development plan leads towards a 75 % share of renewables by the year 2030. This is markedly more than what was stated in the coalition contract to form the federal government of Germany in 2013 (55 % by 2035). Simulation results show that until the year 2030, Power2Heat in district heating systems with a capacity of more than 8 GW, and the flexibilisation of load in industrial processes are all very cost effective from the system point of view. Though up to 8 TWh of curtailment is avoided by storage commitment, CO2-Emissions increase. This can be attributed to an increase of operation hours of base load power plants. When taxes and fees are considered in modelling the stakeholder perspective, both the expansion and deployment of storage are reduced. This drives additional costs of up to several hundred million euros whereas at the same time, CO2-Emissions are lowered by a small amount.
[en] Relativistic mean-field (RMF) models with density dependent (DD) couplings have been used successfully to describe finite nuclei and nuclear matter. They usually assume a dependence of the nucleon-meson couplings on the so-called vector density that is derived from the baryon current. A dependence on other densities, in particular the scalar density, was not really explored although suggested in early introductions of the DD-RMF approach. In this contribution, properties of nuclei, the corresponding equations of state (EoS) and symmetry energies of different DD-RMF models are compared using DD couplings of various functional form and dependence on vector and scalar densities. They are obtained by fitting the same set of nuclear observables. The choice of the dependence changes the EoS and the characteristic nuclear matter parameters. Problems of some of the models are identified.
[en] Globally, the use of renewable energy sources is increasing significantly, despite a comparatively low energy price level. Among other things, this development is driven by energy self-sufficiency efforts, the continued fall in prices for some renewable energy options (primarily photovoltaic, wind), rapid and fast-growing energy and especially electricity demand in many emerging economies and, at least in some OECD countries, the current climate protection efforts. Also some options for the use of regenerative energies (for example, cooking energy from solid biomass) have been used globally in global energy management traditionally for centuries; For example, biogenic solid fuels are still an integral part of rural energy supply. In total, 2017 saw the use of so much energy from renewable energies as never before in human history. This applies in addition to the biomass for providing in particular thermal energy primarily for the generation of electrical energy. Electricity generation plants based on hydropower, biomass, wind and solar radiation, among other things, accounted for roughly half of the world's newly installed annual electricity output in 2017 and were responsible for around one fifth of electricity generation globally. In contrast, the provision of heat and fuel from renewable energies continued to show a below-average increase in 2017 as well. In the coming years, the different options for the use of regenerative energies should continue to be used; the absolute and relative highest growth is expected to continue to be provided by photovoltaics and wind energy.
[de]Global nimmt die Nutzung des erneuerbaren Energieangebots trotz eines vergleichsweise geringen Energiepreisniveaus deutlich zu. Diese Entwicklung wird unter anderem getrieben von Energieautarkiebestrebungen, den weiter fallenden Preisen bei einigen Optionen zur Nutzung regenerativer Energien (primaer Photovoltaik, Wind), der in vielen Schwellenlaendern schnell und stark wachsenden Energie- und insbesondere der Stromnachfrage sowie - zumindest in einigen OECD-Staaten - den laufenden Klimaschutzbestrebungen. Auch werden einige Optionen zur Nutzung regenerativer Energien (zum Beispiel Kochenergie aus fester Biomasse) global energiewirtschaftlich relevant traditionell seit Jahrhunderten genutzt; beispielsweise stellen biogene Festbrennstoffe bis heute einen integralen Bestandteil insbesondere der laendlichen Energieversorgung dar. Insgesamt wurde damit 2017 so viel Energie aus erneuerbaren Energien genutzt wie niemals zuvor in der Menschheitsgeschichte. Dies gilt neben der Biomasse zur Bereitstellung insbesondere thermischer Energie primaer fuer die Erzeugung elektrischer Energie. Stromerzeugungsanlagen unter anderem auf der Basis von Wasserkraft, Biomasse, Wind und Solarstrahlung trugen 2017 mit rund der Haelfte zur jaehrlich weltweit neu installierten elektrischen Leistung bei und waren global fuer etwa ein Fuenftel der Stromerzeugung verantwortlich. Demgegenueber zeigte die Waerme- und Kraftstoffbereitstellung aus erneuerbaren Energien auch 2017 nach wie vor einen nur unterdurchschnittlichen Anstieg. Auch in den kommenden Jahren duerften die unterschiedlichen Optionen zur Nutzung regenerativer Energien weitergehend genutzt werden; das absolute und relative hoechste Wachstum wird voraussichtlich weiterhin von der Photovoltaik und der Windenergie erbracht.