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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
131

Optimization of hydraulic drives for parabolic troughs

Nocker, Andreas January 2016 (has links)
HAWE Hydraulic SE, Munich, engineers and manufactures hydraulic drives (CSP-drives) for parabolic trough plants consisting of a compact power pack, directional and control valves, over-center valves, two cylinders and the fittings/hoses for connecting these components. Optional, but this is depending on the system and the control philosophy, also a hydralic accumulator. An optimized hydraulic drive for a parabolic trough field makes the power plant operator profit from savings at components, higher system efficiency, lower operational energy supply needs, less time spent on commissioning and first start-up, lower maintenance effort and increased life span of the drive and finally also savings on peripheral and safety devices. Many of shown proposals are even combining two or more of above mentioned advantages.
132

Latent and thermal energy storage enhancement of silver nanowires-nitrate molten salt for concentrated solar power

Maaza, Malik January 2020 (has links)
>Magister Scientiae - MSc / Phase change material (PCM) through latent heat of molten salt, is a convincing way for thermal energy storage in CSP applications due to its high volume density. Molten salt, with (60% NaNO3 and 40% KNO3) has been used extensively for energy storage however; the low thermal conductivity and specific heat have limited its large implementation in solar applications. For that, molten salt with the additive of silver nanowires (AgNWs) was synthesized and characterized. This research project aims to investigate the thermophysical properties enhancement of nanosalt (Mixture of molten salt and silver nanowires). The results obtained showed that by simply adjusting the temperature, Silver nanowires with high aspect ratio have been synthesized through the enhanced PVP polyol process method. SEM results revealed a network of silver nanowires and TEM results confirmed the presence of silver nanowires with an average diameter of 129 nm and 16 μm in length.
133

Super Grids in Africa : Could they release the economic potential of concentrating solar power?

Labordena, Merce January 2013 (has links)
The way its future power systems are designed will have significant impact on sub-Saharan Africa's (SSA) aspirations to move from low electricity consumption rates to enhance life quality and further increase economic opportunity. At present, Africa is experiencing higher economic growth rates than other continents (including Asia). And so is its need for electric power. However, all too often the options that are chosen are the ones with lowest risk and that require little coordination. In part, this is because region-wide planning, coordination and institutions are in their infancy. “Low risk” power plants typically include oil generators that can be sited close to loads, other fossil fuel power plants, and hydro plants that can easily be connected to the continent’s grid. However, hydropower production has been limited due to changes in weather and climate and socio-economic impacts. Additionally, its potential has also not been reached as large sites are far from adequate grids. A restructuring of the energy system that considers both the potential for increased geographical integration while moving gradually towards more sustainable electricity generation may hold significant promise. This work considers the potential of another renewable technology namely concentrating solar power (CSP) and connecting supply and demand centers via high voltage direct current (HVDC) power lines. Specifically, the focus is on utility-scale solar power generation to supply the needs of growing urban centers of demand. It develops a Geographic Information System-based (GIS) model with a spatial resolution of 30 arc-seconds to calculate the cost evolution of the electricity produced by different technologies of CSP plants and the costs of grid development to selected centers of demand. The results show that major SSA metropolis can benefit from distant CSP economically attractive to compete with inlaid coal-based generation. In 2010, total imports of coal exceeded 1.4 million short tons with consequent economic and environmental costs. Solar towers plants endowed with thermal storage may become a leading technology for smoothing purposes with zero fuel costs. Furthermore, Africa’s vast solar resources are far from urban centers of demand and a transmission system capable to integrate high levels of renewable energy while improving reliability of supply is required. The results of this study point to the importance of SSA centers to rely on a Super Grid approach to take advantage from CSP least-cost potential and to discontinue expensive traditional sources. Overall, solar corridors can integrate with geographically-wide wind and hydro potentials to create clean energy corridors and encourage a transition towards more sustainable energy systems.
134

Solar-driven Hydrogen Production by the use of MIEC Membranes : A Techno-Economic Assessment

Nilsson, Mattias January 2012 (has links)
This thesis comprises an assessment of a novel concept to produce high purity hydrogen using mixed oxide ion/electronic conductor (MIEC) membranes and energy provided by solar concentrators (i.e. parabolic troughs or parabolic dishes). The vision of this concept is that it will be used to produce tons of high purity hydrogen for fuel cells, which is a scarce commodity with an increasing demand from residential and transportation power generation applications. The MIEC membrane activates a steam reforming reaction between water and methane to produce hydrogen of high purity on the water side and syngas on the fuel side. Expectations are that this concept has cost advantages over other thermo-chemical water-dissociation methods, using a lower temperature and no electricity for the reaction process. The thesis’ focus is on techno-economic aspects of the concept, as part of an application process for project financing by the European Commission of Research and Innovation. The assessment in the thesis shows that the overall efficiency of the concept is expected to be very low. It also identifies the difficulties of providing stable working conditions for the concept. Suggestions to improve the concept are proposed to address the most urgent problems of the concept. These suggestions illuminate the opportunities that actually do exist to combine MIEC membranes, solar energy and thermo-chemical water splitting into a working concept. These improvements include using parabolic dishes instead of parabolic troughs, using furnaces with control systems and using a viable flow rate. The production capacity of high purity hydrogen is expected to be approximately 89 mg per minute in a membrane bundle (i.e. 150 thin membrane fibers with an oxygen permeation flux of 1 ml cm-2 min-1) if these improvements were implemented. This would imply that the studied concept needs further development to produce high purity hydrogen in quantities that could meet the shortage on the commercial fuel cell markets.
135

Techno-economic Analysis of Combined Hybrid Concentrating Solar and Photovoltaic Power Plants: a case study for optimizing solar energy integration into the South African electricity grid

Castillo Ochoa, Luis Ramon January 2014 (has links)
The cooperation between large scale Concentrated Solar Power plants (CSP) and Solar Photovoltaic (PV) parks can offer stability in power supply and enhance the capacity factor of the CSP plant intended to cover a common demand on the power system. Moreover, it can offer an investment option with lower risk. This Master thesis project presents optimum plant configurations for both technologies under the same meteorological and market conditions. The study is based in the South African electricity market and the Renewable Energy Independent Power Producer Program currently in place in the country. Using MATLAB and TRNSYS softwares, a series of detailed codes were designed in order to model both technologies energy transformation process. The main approach was to design the nominal operation point of both technologies for a given typical meteorological year data and respective technical conditions for each case. Then, a transient simulation was done in order to obtain the electricity yield. The intention was to measure the internal rate of return, levelized cost of electricity and capacity factor for each technology and the combined configuration (CSP-PV plant) under different scenarios and operation modes while a firm capacity was maintained. It was found that the plants can be economically feasible by sizing a storage unit capable of just covering the peak hours. The solar multiple sizes can vary depending on the scenario and plant configuration. Moreover, the internal rate of return increases with the capacity of the CSP in all cases. After the results were obtained, a comparison with a single CSP plant and the optimum CSP-PV plant was done in order to evaluate the performance of the proposed cooperation. Even though the internal rate of return of the CSP-PV plant was found to be within a good range for investment, the CSP-alone alternative offered always higher internal rate of return and lower levelized cost of electricity values. Nonetheless, it was found that the capacity factor of the combined configuration was favored by the integration of PV. The PV alone configuration hold the lowest levelized cost of electricity, thus considered the best option for and investment in South Africa due to its independence towards incentives. Combined PV-CSP systems were also found to be an attractive investment under the South African scheme if the CSP capacity is similar to the PV power plant.
136

Enhancing the Thermo-Economic Performance of a Direct Steam Generation Solar Tower Power Plant through the Implementation of Steam Flow Control Strategies for Flexible Operation

Ellakany, Farid January 2014 (has links)
Above 90% of the current installed concentrating solar power plants are based on conventional steam-turbine cycles. The operation of steam turbines in these plants is distinctive when compared to traditional base-load power plants. The reason goes back to the intermittent nature of solar power which, in the absence of thermal energy storage or a back-up combustion boiler, forces plant operators to shut down the turbines during night time or at times of low solar radiation. Furthermore, such intermittency often leads to undesirable off-design turbine operating circumstances, either by load variations or changes on live-steam conditions.The present study examines the influence of implementing two operating strategies dealing with steam flow control as a function of incoming solar power for enhancing the thermo-economic performance of a direct steam generation solar tower power plant. The first one consists of a simultaneous high pressure turbine stage- and feed-water preheater bypass. This strategy is used during periods in which the solar radiation is higher than nominal. On these occasions, the plant is capable of generating a larger flow of steam, which allows for an increase in the power production when inserting the additional steam in the turbine bypass. On the other hand, the second operating strategy consists of using an additional feed-water preheater when the power from the field is lower than nominal. In this way, the feed water can reach a higher temperature prior entering the boiler, which is not only beneficial during times of cloud-passages, but also during the start-up process.A dynamic model of a direct steam generation solar tower power plant has been developed following design and operation specifications of an existing reference plant. The two proposed strategies were implemented to the reference model, then a whole year worth simulation was performed for both the reference and the modified models. Lastly, the thermodynamic and economic performance of both systems was measured for the purpose of comparison, by means of using KTH in-house tool DYESOPT. Results show that the implementation of the proposed strategies can enhance the economic viability of the systems by yielding a reduction of 8.7% on the levelized cost of electricity, mainly due to allowing achieving a 12% increase in the net electricity production.
137

Solar PV-CSP Hybridisation for Baseload Generation : A Techno-economic Analysis for the Chilean Market

Larchet, Kevin January 2015 (has links)
The development of high capacity factor solar power plants is an interesting topic, especially when considering the climate and economic conditions of a location such as the Chilean Atacama Desert. The hybridisation of solar photovoltaic (PV) and concentrating solar power (CSP) technologies for such an application is a promising collaboration. The low cost of PV and dispatchability of CSP, integrated with thermal energy storage (TES), has the promise of delivering baseload electricity at a lower cost than what could be achieved with CSP alone. Therefore, the objective of this work was to evaluate whether or not a hybrid PV-CSP plant is more economically viable, than CSP alone or hybrid PV-diesel, for baseload generation. To analyse this hypothesis, a techno-economic optimisation study of a PV-CSP hybrid plant with battery storage and fossil fuel backup was performed. In doing so, a methodology for the identification of optimum solar hybrid plant configurations, given current technology and costs, to best satisfy specific location weather and economic conditions was developed. Building on existing models, for the PV and CSP components, and developing models for further hybridisation, a complete PV-CSP model was created that could satisfy a baseload demand. Multi-objective optimisations were performed to identify optimal trade-offs between conflicting technical, economic and environmental performance indicators. For the given economic and technical assumptions, CSP hybridised with fossil fuel backup was shown to provide electricity at the lowest cost and have the lowest project capital expenditure. This configuration showed a 42% and 52% reduction in the levelised cost of electricity in comparison to CSP alone and hybrid PV-diesel, respectively. It also provides a 45% reduction in CAPEX in comparison to CSP alone. PV-CSP integration increases capital costs and the cost of electricity, but reduced the use of fossil fuel backup and thereby reduced emissions, when compared to CSP with fossil fuel backup. However PV-CSP showed a 97% reduction in CO2 emissions when compared to hybrid PV-diesel. Furthermore, it showed a 35% and 46% reduction in LCOE in comparison to CSP alone and hybrid PV-diesel.
138

A Domain-Specific Design Tool for Verifying Spacecraft System Behavior

Venigalla, Sravanthi 01 December 2009 (has links)
In this report we present a graphical tool, Behavioral Analysis of Spacecraft Systems (BASS), that can be used by spacecraft designers to perform system-level behavioral analysis of small satellites. The domain-specific spacecraft meta-model is created in the visual modeling tool Generic Modeling Environment (GME) such that spacecraft designs created using the meta-model appear familiar to the spacecraft designers. Users can model scenarios that are to be verified for the design in BASS. The graphical models are assigned formal semantics facilitating the creation of formally verifiable spacecraft models. The C++ application that translates the modeling objects to equivalent mathematical representation of interest is called BASS Interpreter and is bound to the meta-model. BASS Interpreter that generates Communicating Sequential Processes (CSP) semantics for the visual spacecraft models is supported in the current work. The model-checker for CSP called Failures Divergences and Refinement (FDR) is run to explore the state-space of the spacecraft process model to comment on the design. We demonstrate the feasibilty and advantage of incorporating BASS into initial design phases of small satellite development by successfully verifying the design of Tomographic Remote Observer of Ionospheric Disturbances (TOROID).
139

Penningtvätt inom gräsrotsfinansiering efter ECSP : Bör leverantörer av gräsrotsfinansieringstjänster träffas av penningtvättsreglerna på unionsnivå? / Money laundering within crowdfunding after ECSP : Should crowdfunding service providers be obliged to follow the anti-money laundering rules on EU-level?

Hagman, Oscar January 2022 (has links)
No description available.
140

Constraint Network Satisfaction for Finite Relation Algebras

Knäuer, Simon 22 May 2023 (has links)
Network satisfaction problems (NSPs) for finite relation algebras are computational decision problems, studied intensively since the 1990s. The major open research challenge in this field is to understand which of these problems are solvable by polynomial-time algorithms. Since there are known examples of undecidable NSPs of finite relation algebras it is advisable to restrict the scope of such a classification attempt to well-behaved subclasses of relation algebras. The class of relation algebras with a normal representation is such a well-behaved subclass. Many well-known examples of relation algebras, such as the Point Algebra, RCC5, and Allen’s Interval Algebra admit a normal representation. The great advantage of finite relation algebras with normal representations is that their NSP is essentially the same as a constraint satisfaction problem (CSP). For a relational structure B the problem CSP(B) is the computational problem to decide whether a given finite relational structure C has a homomorphism to B. The study of CSPs has a long and rich history, culminating for the time being in the celebrated proofs of the Feder-Vardi dichotomy conjecture. Bulatov and Zhuk independently proved that for every finite structure B the problem CSP(B) is in P or NP-complete. Both proofs rely on the universal-algebraic approach, a powerful theory that connects algebraic properties of structures B with complexity results for the decision problems CSP(B). Our contributions to the field are divided into three parts. Firstly, we provide two algebraic criteria for NP-hardness of NSPs. Our second result is a complete classification of the complexity of NSPs for symmetric relation algebras with a flexible atom; these problems are in P or NP-complete. Our result is obtained via a decidable condition on the relation algebra which implies polynomial-time tractability of the NSP. As a third contribution we prove that for a large class of NSPs, non-hardness implies that the problems can even be solved by Datalog programs, unless P = NP. This result can be used to strengthen the dichotomy result for NSPs of symmetric relation algebras with a flexible atom: every such problem can be solved by a Datalog program or is NP-complete. Our proof relies equally on known results and new observations in the algebraic analysis of finite structures. The CSPs that emerge from NSPs are typically of the form CSP(B) for an infinite structure B and therefore do not fall into the scope of the dichotomy result for finite structures. In this thesis we study NSPs of finite relation algebras with normal representations by the universal algebraic methods which were developed for the study of finite and infinite-domain CSPs. We additionally make use of model theory and a Ramsey-type result of Nešetril and Rödl. Our contributions to the field are divided into three parts. Firstly, we provide two algebraic criteria for NP-hardness of NSPs. Our second result is a complete classification of the complexity of NSPs for symmetric relation algebras with a flexible atom; these problems are in P or NP-complete. Our result is obtained via a decidable condition on the relation algebra which implies polynomial-time tractability of the NSP. As a third contribution we prove that for a large class of NSPs the containment in P implies that the problems can even be solved by Datalog programs, unless P = NP. As a third contribution we prove that for a large class of NSPs, non-hardness implies that the problems can even be solved by Datalog programs, unless P = NP. This result can be used to strengthen the dichotomy result for NSPs of symmetric relation algebras with a flexible atom: every such problem can be solved by a Datalog program or is NP-complete. Our proof relies equally on known results and new observations in the algebraic analysis of finite structures.

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