A three-dimensional analysis of natural convection in a toroidal loop—the effect of Grashof number

A three-dimensional, numerical analysis of natural convection in a closed, toroidal loop has been performed. The results show that the flow is strongly three-dimensional, and that streamwise flow reversal and cross-stream secondary motion exist; similar flow phenomena have been experimentally observed. The strengths of the flow reversals and secondary motion are shown to increase with increasing Grashof number. The impact which these three-dimensional effects have on the friction factor, the Nusselt number, the buoyancy force, and the average axial velocity, are discussed.     

The future of the European electricity system and the impact of fluctuating renewable energy – A scenario analysis

The ongoing transformation of the European energy system comes along with new challenges, notably increasing amounts of power generation from intermittent sources like wind and solar. How current objectives for emission reduction can be reached in the future and what the future power system will look like is, however, not fully clear. In particular, power plant investments in the long run and power plant dispatch in the short run are subject to considerable uncertainty. Therefore an approach is presented which allows electricity market development to be assessed in the presence of stochastic power feed-in and endogenous investments in power plants and renewable energies. To illustrate the range of possible future developments, five scenarios for the European electricity system up to 2050 are investigated. Both generation investments and dispatch as well as utilization of transmission lines are optimized for these scenarios and additional sensitivity analyses are carried out.     

Energy demand in the fifteen European Union countries by 2010 —: A forecasting model based on the decomposition approach

This paper develops a forecasting model based on the complete decomposition method. The forecasting model allows the trend effect, the rebound effect and dematerialization/materialization to be estimated. To demonstrate the model, a case analysis of the probable energy demand in the 15 European Union (EU) countries up to 2010 has been made. The results show that the aggregate energy demand in the 15 EU countries by the end of 2010 will have increased from 258 to 426 Mtoe compared to the 1997 level, and dematerialisation will have increased from 73 to 225 Mtoe.     

Reconstruction of a heat exchanger network under industrial constraints — the case of a crude distillation unit

Heat exchanger network retrofit using a pinch based approach is presented. In this approach, the criterion of minimum sensitivity of heat exchanger to fouling effects is accounted for. The present paper introduces this criterion without explaining its details that are described in the literature. A summary is given of HEN reconstruction in a crude distillation unit processing 4.2 million ton crude oil per year. While the total heat quantity of hot streams is 110 MW, the heat recovery in the existing HEN is 60 MW. Using Pinch Analysis, the target value of heat recovery at ΔT_min=10 K was determined at 91 MW. Measurements were carried out on the existing HEN with the aim to determine the influence of fouling effects on the heat transfer in the exchangers. Taking local constraints including fouling into account, HEN reconstruction was proposed. The heat savings in the reconstructed HEN was estimated at 75 MW.     

Influence of Lubricant on the Nucleate Boiling Heat Transfer Performance of Refrigerant—A Review

This review provides an overview of the lubricant on the heat transfer performance pertaining to nucleate boiling. It appears that the effect of individual parameter on the heat transfer coefficient may be different from study to study. This is associated with the complex nature of lubricant and some compound effects accompanying the heat transport process. Some important effects such as oil concentration, heat flux, geometric configuration, saturation temperature, thermodynamic and transport properties, miscibility, foaming, and additional surface active agent are reported and discussed. In general, the heat transfer coefficient is impaired provided the oil concentration is sufficient high (e.g., >7%), and this is applicable to smooth and structured tubes. But normally structured tubes tend to suffer more from lubricant, yet this is especially conspicuous when the size of the reentrant channel is small. On the other hand, foaming and partial miscibility seem to benefit the heat transfer coefficient.     

A Multi—Criteria Decision Making Procedured for the Analysis of an Energy System

In the course of improving and/or designing an energy system,either purely economic criteria,although theoverriding criteria,or purely energy-based criteria,although the emphasized criteria,can not separately handlereal-world situations in a satisfactory manner.The economic effectiveness and the energy efficiency mustbe considered simultaneously to demonstrate the conflicting and non-commensurable characteristics of thesemultiple criteria.An iterative and interactive approach to formulating and solving non-linear multi-criteria decision makingproblems for the analysis of an energy system is proposed.It allows the decision maker(DM)to learn fromthe available information and dynamically change his mind.Criterion functions can be treated as objectivefunctions,as constraints or as something in between by the DM.After a series of iterations and interactiveprocedures,a preferred solution can be made among the non-inferior sets considering thermodynamic criteriaand economic criteria simultaneously.A simple example for design of a heat exchanger is used to illustrate theprocedure.     

A 2D analysis of stability of bioconvection in a fluid saturated porous medium — estimation of the critical permeability value

The main purpose of this paper is to perform a 2D stability analysis of bioconvection in a suspension of motile gyrotactic microorganisms in a fluid saturated porous medium and to obtain an analytical expression for the critical permeability of the porous medium. Recent numerical investigation by Kuznetsov and Jiang [1] suggests that permeability is a very important parameter for bioconvection in porous media. Their numerical results indicate that for small permeability bioconvection is stable (the microorganisms swim in the upward direction), while for large permeability it is unstable (variations of density are enhanced and macroscopic fluid circulation is induced). In the present investigation, a simple but elegant criterion of stability of the bioconvection is obtained. This criterion gives the critical permeability of the porous medium through the cell eccentricity, average swimming velocity, fluid viscosity, and other relevant parameters.     

Effect of Guide Vanes on the Performance of a Variable Chord Self—Rectifying Air Turbine

INTRODUCTIONWiththeconventionalenergyresourceslikelytogetexhaustedinafewdecades,theinexhaustiblesourcesofenergyhavetotaketheirplace.Alternateenergyfromtheoceanisattractingtheattelltionoftheresearchersinrecentyearsduetoitsperennialavailabilityandminimumhealthhazards.Ofthemanypossibleformsofoceanenergy,waveenergyispromising.Waveenergyisanalternateformenergy,whichispollutantfreeandinnearfutureitislikelytobeeconomicallyviable.Countrieswhicharesurroundedbyseaandpossessremotelysituatedislandcom…     

Performance analysis for the part-load operation of a solid oxide fuel cell–micro gas turbine hybrid system

In this paper, the performance evaluation of a solid oxide fuel cell (SOFC)–micro gas turbine (MGT) hybrid power generation system under the part-load operation was studied numerically. The present analysis code includes distributed parameters model of the cell stack module. The conversions of chemical species for electrochemical process and fuel reformation process are considered. Besides the temperature distributions of the working fluids and each solid part of cell module by accounting heat generation and heat transfers, are taken into calculation. Including all of them, comprehensive energy balance in the cell stack module is calculated. The variable MGT rotational speed operation scheme is adopted for the part-load operation. It will be made evident that the power generation efficiency of the hybrid system decreases together with the power output. The major reason for the performance degradation is the operating temperature reduction in the SOFC module, which is caused by decreasing the fuel supply and the heat generation in the cells. This reduction is also connected to the air flow rate supplement. The variable MGT rotational speed control requires flexible air flow regulations to maintain the SOFC operating temperature. It will lead to high efficient operation of the hybrid system.     

Optimal design of feed-in-tariffs to stimulate renewable energy investments under regulatory uncertainty — A real options analysis

Feed-in-tariffs (FITs) are widely used as policy instruments to promote investments in renewable energy sources (RES). While FITs are often regarded as the most effective RES support scheme, regulators around the world continuously review their FIT schemes in the light of budget constraints and evolving policy goals. We assess the impact of adjustments to FIT schemes by quantifying the relationship between FIT levels, i.e., the guaranteed amount paid per quantity of electricity produced and the propensity to invest in RES. Through a regime switching model, we quantify the impact of regulatory uncertainty induced by regulators considering moves from a FIT scheme to a more market-oriented regulatory regime. Our focus is on market-independent, fixed FITs, the dominant scheme in Europe receiving increasing attention globally. We find that RES investment projects under market-independent, fixed FIT schemes become now-or-never decisions and derive FIT thresholds required to induce investment. We show that uncertainty regarding future regulatory regimes delays or even reduces investment activity for FIT levels near electricity market prices and high probabilities of an imminent regime switch.     

Drivers and barriers to the diffusion of energy-efficient technologies—a plant-level analysis of the German steel industry

The paper aims at explaining why large-scale energy-intensive industries—here the German iron and steel industry—had a period of slow uptake of major energy-efficient technologies from the mid 1990s to mid 2000s (Arens and Worrell, 2014) and why from the mid 2000s onwards these technologies are increasingly implemented again. We analyze the underlying factors and investment/innovation behavior of individual firms in the German iron and steel industry to better understand barriers and drivers for technological change. The paper gives insights on the decision-making process on energy efficiency in firms and helps to understand how policy affects decision-making. We use a mixed method approach. First, we analyze the diffusion of three energy-efficient technologies (EET) for primary steelmaking from their introduction until today (top-pressure recovery turbine (TRT), basic oxygen furnace gas recovery (BOFGR), and pulverized coal injection (PCI)). We derive the uptake of these technologies both at the national level and at the level of the individual firm. Second, we analyze the impact of drivers and barriers on the decision-making process of individual firms whether or not they want to implement these technologies. Economics and access to capital are the foremost barriers to the uptake of an EET. If the expected payback period exceeds a certain value or if the company lacks capital, investments in EET seem not to happen. But even if an EET is economically viable and the company has access to capital, investments in EET might not be realized. Policy-induced prices might have strengthened the recent diffusion of TRT. We found indications that in a limited number of cases, policy intervention was a driving factor. Technical risks and imperfect information are only marginal factors in our cases. Site-specific factors seem to be important, as site-specific factors shape the economics of the selected EET.     

Comparison and analysis of the emissions of a small non-road spark-ignition engine operating under different alcohol–gasoline blended fuels

In this experimental study we focused our interest on comparing the effect of lower and higher molecular mass alcohol–gasoline-blended fuels on the regulated emissions emitted by a small non-road spark-ignition engine. Twenty-one test fuels were used in this experimental study that included gasoline as a reference as well as low and high molecular mass alcohol–gasoline blends containing 5%, 10%, 20% and 40% v/v. In exhaust gases that originated from alcohol gasoline test fuels, low CO/HC and high CO₂/NO_x emissions were observed as the total percentage of alcohol in the blend increased. Methanol–gasoline blends seemed to achieve good combustion efficiency, but the engine will require a catalytic converter against high NO_x emissions. Butanol–gasoline blends in several cases gave lower emissions in comparison with the ethanol and propanol–gasoline blends. Finally, the pentanol–gasoline blends showed exactly the same emission patterns as those of neat gasoline.     

A new look at the FDI–income–energy–environment nexus: Dynamic panel data analysis of ASEAN

The main focus of this paper is to estimate the effects of foreign direct investment (FDI) inflows, income and energy consumption on CO₂ emissions using panel data of five ASEAN countries over 1981–2010. The results based on the pooled mean group (PMG) estimator of dynamic panels show that FDI tends to increase CO₂ emissions, supporting evidence of the pollution haven hypothesis. We also find that income and energy consumption have a detrimental impact on reducing CO₂ emissions.     

How large is the effect of financial incentives on electric vehicle sales? – A global review and European analysis

Plug-in electric vehicles (PEV), both as battery electric vehicles and plug-in hybrid vehicles have noteworthy potential to reduce global and local emissions. However, several barriers still hinder a fast market diffusion of this new technology. Governments around the world have implemented monetary and non-monetary policies to accelerate PEV market diffusion. Their effectiveness is established in the literature, yet the effect size has been only scarcely estimated empirically and only for the US. Here, we review econometric studies on the effect size of purchase incentives and analyse data on PEV sales from 32 European countries from 2010 to 2017 with respect to the effect of financial incentives. We apply panel data regressions and control for other factors such as income and fuel prices. We find energy prices and financial incentives to influence PEV adoption positively. The range of point estimates for the effect of incentives is 5–7% relative sales share increase in different model specifications. Methodologically, the inclusion of a trend variable proved important to capture overall changes in the diffusion of this new technology. Our findings indicate that financial incentives have an impact on PEV sales and thus can facilitate their diffusion.     

Global Energy Interconnection: an innovative solution for implementing the Paris Agreement—the significance and pathway of integrating GEI into global climate governance

There has been great concern in the international community as to whether the Paris Agreement will effectively maintain the average global temperature increase below 2 °C from pre-industrial levels. When the nationally determined contributions (NDC) of the various state parties are added, it is clear that a gap remains. Thus, UNFCCC COP21 called upon all state parties and non-state actors to take additional actions to reduce emissions beyond NDCs in order to eliminate this gap. Against the background of energy consumption transformation and climate governance, Global Energy Interconnection (GEI), which features an innovative combination of advanced technologies such as clean energy, global connectivity, and ultra-high voltage transmission, offers a new option for global prosperity and growth with fewer emissions, lower economic costs, and a safer climate. However, it takes time for the international community to fully recognize, accept, and support GEI and the relevant organizations. Therefore, GEI organizations should take the initiative to reach out to the international climate governance system based on its characteristics of multiple tiers, circles, and poles enabling exchange of technology, funding, and projects in order to win widespread support for GEI and facilitate joint implementation. Only in this way will GEI bring further economic, social, and environmental benefits.     

Applying resource efficiency principles to the analysis of EU-27 bioenergy options by 2020 – Findings from a recent study for the European Environment Agency

The Renewable Energy Directive sets a target for the European Union (EU) to consume 20% of its final energy from renewable sources by 2020 and further targets are under discussion. EU renewable energy targets will lead to a substantial increase in the demand for bioenergy. As for other sectors, it is important, therefore, to apply the principles of the EU Resource efficiency roadmap to bioenergy production: producing more output with less material input and minimising adverse environmental impacts during the entire production life cycle. This paper uses that concept to analyse the most resource efficient ways for reaching the 2020 bioenergy targets (as set out in National Renewable Energy Action Plans).Scenario analysis with three different storylines is used to model environmental and land use implications plus total bioenergy potential and GHG reductions in 2020 from the agricultural, forest, and waste sectors. These storylines vary in environmental ambition level and economic and political assumptions and explore plausible bioenergy development paths. They show substantial variance in terms of environmental impact and the GHG efficiency between different bioenergy pathways.The modelling shows that under Storyline 1 bioenergy targets of the National Renewable Energy Action Plans would be achieved with CO₂ eq emissions of 44 kg GJ⁻¹, i.e. 62% less GHG emission than if the energy were generated using fossil fuels. In contrast, stricter environmental constraints in Storyline 3 lead to a substantially lower CO₂ eq burden of 25 kg GJ⁻¹, which represents an 80% reduction compared to fossil fuels.     

Energy from waste incineration — a state of the art emissions review with an emphasis on public acceptability

The emissions performance of today's, well run state of the art energy from waste incinerators (EfWI) is compared with those which were operational in the early 1990s and the substantial improvements highlighted. Dioxin reduction improvements are analysed. Claimed health effects of emissions are scrutinized and shown to be groundless. The ‘emerging’ technologies of pyrolysis or gasification are discussed and their emissions performance compared with best practice EfWI. It is shown that there is little to draw between these contrasting energy recovery options. The role of MSW recycling is scrutinized and it is concluded that EfWI and practicable recycling and composting can work together as part of a truly integrated waste management strategy.     

Economic assessment of virtual power plants in the German energy market — A scenario-based and model-supported analysis

The energy transition (“Energiewende”) in Germany will result in a substantial transformation of the energy supply system. Virtual power plants are expected to be important components of the new intelligent energy infrastructure. They aggregate beside different types of distributed generation units also active consumers and storage technologies in order to integrate these in a profit-maximising, system-stabilising, and sustainable way. The assessment of the economic performance of virtual power plants requires a scenario-based and model-supported analysis. In this relation, future energy market conditions are simulated using the scenario methodology. Starting from the year 2015, three scenarios have been identified that illustrate alternative energy developments in Germany by 2030. Based on these scenarios, the additional revenues potential of the modeled virtual power plant is identified when compared to an independent and non-market-oriented operation mode of distributed energy resources. According to the model results, revenues of the VPP can increase by 11% up to 30% in the analyzed scenarios in 2030 due to the market-oriented operation mode. Nevertheless, the amount and composition vary depending on technology-specific subsidies, temporary nature of power demand and price structures in the energy market. Fluctuating renewable energies are expected to benefit from the market-oriented operation mode in the virtual power plant, especially through the EEG direct marketing. The selective and regulated shutdown of renewable energies in times of negative electricity prices may lead to further cost savings. The utilization of temporary price fluctuations in the spot market and the demand-oriented provision of control power offer high additional revenue potential for flexible controllable technologies such as battery storage, biomethane as well as combined heat and power units. Finally, the determination of the long-term profitability of a virtual power plant still requires a full-scale cost–benefit analysis. For this holistic approach, the model results provide a reliable scientific basis.