Hermann-Josef Wagner

Cumulative energy demand for selected renewable energy technologies

Calculation of Cumulative Energy Demand (CED) of various energy systems and the computation of their Energy Yield Ratio (EYR) suggests that one single renewable energy technology cannot be said to be the best. Due to the difference in availability of renewable energy sources, their suitability varies from place to place. Wind energy converters, solar water heating systems and photovoltaic systems have been analysed for different types of locations. Comparing the general bandwidth of performance of these technologies, however, the wind energy converters tend to be better, followed by solar water heating systems and photovoltaic systems.Since a major part of the methodology of findingCED is very close to that of life cycle assessment and also because of the dominance of environmental impacts caused by the energy demand in the entire life cycle of any product or system, it is suggested that theCED can be used as an indicator of environmental impacts, especially in the case of power producing systems. Keywords: Cumulative energy demand; life cycle assessment; energy yield ratio; photovoltaics; solar water heating; wind energy Abbreviations: CED — Cumulative Energy Demand; EYR — Energy Yield Ratio; LCA — Life Cycle Assessment; Photovoltaics — PV; WEC — Wind Energy Converters

Introduction to wind energy systems

— This article presents the basic concepts of wind energy and deals with the physics and mechanics of operation. It describes the conversion of wind energy into rotation of turbine, and the critical parameters governing the efficiency of this conversion. After that it presents an overview of various parts and components of windmills. The connection to the electrical grid, the world status of wind energy use for electricity production, the cost situation and research and development needs are further aspects which will be considered.

Optimization of Dispersed Energy Supply —Stochastic Programming with Recombining Scenario Trees

The steadily increasing share of wind energy within many power generating systems leads to strong and unpredictable fluctuations of the electricity supply and is thus a challenge with regard to power generation and transmission. We investigate the potential of energy storages to contribute to a cost optimal electricity supply by decoupling the supply and the demand. For this purpose we study a stochastic programming model of a regional power generating system consisting of thermal power units, wind energy, different energy storage systems, and the possibility for energy import. The identification of a cost optimal operation plan allows to evaluate the economical possibilities of the considered storage technologies.

Economics and Policy Issues

The economics of power generation using wind energy systems depends upon the capacity utilization factor. Higher initial cost is offset by lower operating cost due to free availability of the source of energy. For locations that have relatively lower utilization factors, several promotional policy measures are adopted by different countries. A feed-in tariff system is adopted by countries like Germany, whereas a net-metering system is adopted by India for promoting the use of wind energy. Other schemes, such as time dependent rates and quota systems, are used by other countries. For encouraging the investment in the wind sector, various countries worldwide have adopted tools like the capacity credit scheme, Clean Development Mechanism, exemption of import duty, accelerated depreciation, and income tax rebate.

Physics of Wind Energy

Wind velocity increases with height, its rate depending on the type of terrain. The energy content of wind depends on the third power of its velocity, and the area through which it is passing. Conversion of wind power to rotation of turbine depends on the geometry of the blades with respect to the incoming wind velocity vector. The rotation of blades is governed by the basic principles of aerodynamics. The ratio of the circumferential velocity of blade tip to the velocity of wind is defined as the tip-speed ratio. This ratio has a strong influence on the coefficient of power or efficiency of conversion, which has an upper limit of 59.25 % as per the Betz’s theorem.

Components of a Wind Energy Converter

Rotor blades, gear box, generator and tower are the main components of a wind energy converter. Glass fiber reinforced plastic blades are preferred in modern turbines due to less weight and more strength. Hydrodynamic gear boxes may offer efficiency related advantage over conventional design. Synchronous as well as asynchronous generators are both used in wind energy converters. Depending upon the height of converter, the type of tower is chosen out of a simple pole or lattice tower to a modern tubular steel tower are concrete tower. Other components, such as yaw mechanism and anemometer, also play an important role in the efficient operation of a wind turbine, whereas foundation, vibration measurement, and brakes are important for its safe operation.

Life Cycle Assessment of a Wind Farm

Life Cycle Assessments is an important tool for industry and policy makers, used to determine the actual emissions of a product or technology throughout its whole life cycle. In case of energy production systems or power plants, analysis of energy required to produce the materials and processes; emissions resulting from various processes for materials production and processes resulting into their Cumulated Energy Demand and Global Warming Potential become important parameters when making decisions on further research, development and deployment of any technology. The method of carrying out such analysis is explained in this chapter through a case study.

Planungswerkzeug zur Energie- und CO2-Einsparung in Kommunen

Durch nationale sowie internationale CO2-Minderungs- und Effizienzsteigerungsziele stellt sich auch fur Stadte, in denen ca. 73 % der Bevolkerung wohnt, die Frage, wie diese Ziele moglichst kostengunstig erreicht werden konnen und welche Masnahmen gefordert werden sollten. Vor diesem Hintergrund ist es wichtig, die Fragestellung zu untersuchen, welche Potenziale durch die energetische Gebaudesanierung im Gesamtsystem Stadt unter Berucksichtigung der Kosten erschlossen werden konnen, um daraus gezielt Energiedienstleistungen abzuleiten. Dazu wurde ein Planungswerkzeug zur Abbildung des stadtischen Energiebedarfs im Gebaudesektor und der daraus resultierenden CO2-Emissionen entwickelt, um anschliesend mittels Parametervariationen Einsparpotenziale identifizieren und priorisieren zu konnen.

Assessment of Film Drop Release From Liquid Pools by an Empirical Correlation Approach

The present work deals with the topic of wet resuspension, particularly with regard to the basics of film drop release from bubbles and its impact on the aerosol source term as well as with the development of an empirical correlation approach adapted to the containment code system COCOSYS at low atmosphere motion. Film drops are discharged from the lamella of a bubble during the disruption process, while the bubble is resting at the fluid surface. Besides the description of the bubble disruption process, factors which have an influence on the mass and size distribution of the drops released from the bubble lamella are discussed. To analyse the distribution of the film drops of different bubble sizes, measured film drop distributions of several bubble diameters were collected from the literature. The analysis shows that with the presence of surfactants (surface-active agents) a log-normal count distribution can be used for the approximation of the drop distribution. By the evaporation of the liquid of the released film drops the solved and/or suspended materials remain as particles. In dependence of their size the drops or particles are airborne or fall back onto the liquid pool surface. The remaining airborne drops/particles are able to contribute in the late phase of a severe accident to the source term, if they are radioactive.Copyright

Investigation of the Fission Product Release From Molten Pools Under Oxidizing Conditions With the Code RELOS

With the purpose of modeling and calculating the core behavior during severe accidents in nuclear power plants system codes are under development worldwide. Modeling of radionuclide release and transport in the case of beyond design basis accidents is an integrated feature of the deterministic safety analysis of nuclear power plants. Following a hypothetical, uncontrolled temperature escalation in the core of light water reactors, significant parts of the core structures may degrade and melt down under formation of molten pools, leading to an accumulation of large amounts of radioactive materials. The possible release of radionuclides from the molten pool provides a potential contribution to the aerosol source term in the late phase of core degradation accidents. The relevance of the amount of transferred oxygen from the gas atmosphere into the molten pool on the specification of a radionuclide and its release depends strongly on the initial oxygen inventory. Particularly for a low oxygen potential in the melt as it is the case for stratification when a metallic phase forms the upper layer and, respectively, when the oxidation has proceeded so far so that zirconium was completely oxidized, a significant influence of atmospheric oxygen on the specification and the release of some radionuclides has to be anticipated. The code RELOS (Re lease of Lo w Volatile Fission Products from Molten S urfaces) is under development at the Department of Energy Systems and Energy Economics (formerly Department of Nuclear and New Energy Systems) of the Ruhr-University Bochum. It is based on a mechanistic model to describe the diffusive and convective transport of fission products from the surface of a molten pool into a cooler gas atmosphere. This paper presents the code RELOS, i. e. the features and abilities of the latest code version V2.3 and the new model improvements of V2.4 and the calculated results evaluating the implemented models which deal with the oxygen transfer from the liquid side of the phase boundary to the bulk of the melt by diffusion or by taking into account natural convection. Both models help to estimate the amount of oxygen entering into the liquid upper pool volume and being available for the oxidation reaction. For both models the metallic, the oxidic and a mixture phase can be taken into account when defining the composition of the upper pool volume. The influence of crust formation, i. e. the decrease of the liquid pool surface area is taken care of because it yields the relevant amount of fission products released into the atmosphere. The difference of the partial density between the gas side of the phase boundary and the bulk of the gas phase is the driving force of mass transport.Copyright