• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 552
  • 507
  • 265
  • 1
  • Tagged with
  • 1327
  • 611
  • 590
  • 447
  • 366
  • 314
  • 275
  • 162
  • 162
  • 152
  • 147
  • 137
  • 125
  • 125
  • 125
  • 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.
51

Assessing the Life Cycle Environmental Impacts of Offshore Wind Power Generation and Power Transmission in the North Sea

Birkeland, Christine January 2011 (has links)
An integrated approach to climate and energy policy is required to meet the challenges associated with climate changes caused by anthropogenic emissions. At the same time, the demand for electricity is increasing. Wind power is considered as part of the solution in solving these challenges, as this is renewable energy. By relocating wind power production offshore, stronger winds are achieved that increases electricity production without having emissions of GHG during power production. Europe's ambitious goals and plans for development of offshore wind power development in the North Sea have also raised questions about how to integrate wind power into existing power systems in Europe. In this study the environmental impacts of offshore wind power production and development of an offshore grid in the North Sea, have been considered. To quantify the environmental impacts associated with offshore wind power generation and power transmission in the North Sea, several LCA’s have been carried out. Four LCA's were conducted, whereof three of them were analyses of various submarine cables used either in offshore wind farms or long-distance power transmission. The cables studied were; 33 kV HVAC cables used internally in offshore wind farms, 132 kV HVAC cables used to transmit power from a wind farm to the grid onshore and 450 kV HVDC cables used for long-distance power transmission between for instance countries. A fourth LCA was conducted of an entire offshore wind farm, including the inventories of the 33 kV and 132 kV cables. The emissions from a 390 MW offshore wind farm with bottom-fixed windmills, were calculated to be 20.6 g CO2 -equivalents/kWhel. Cabling constituted only 1.5 % of the total impacts to climate change from the wind farm. A larger wind farm of 9000 MW had lower estimated emissions of 19.8 g CO2 -equivalents/kWhel due to a higher electricity production. The LCA results of the 450 kV cables were used in estimating the environmental impact caused by different designs of offshore power grids in the North Sea. Several alternative grids were investigated, both with and without wind farms. For instance, a power grid in the North Sea where the two wind farms above were implemented, had estimated emissions of 84 million tonnes of CO2-equivalents throughout lifetime. This represents approximately 2% of the EU-27 countries' total GHG emissions from 2007. In addition to the quantification of environmental impacts, a qualitative discussion was conducted of the various environmental costs and benefits associated with large-scale development of power generation and transmission in the North Sea. The results from this study indicate that the expected environmental impacts from developing offshore wind farms and power grids in the North Sea are not insignificant. The positive environmental effects are large because the increased transmission capacity between power markets allows for increased development of electricity generation from intermittent renewable energy sources like wind power. Increased share of renewable energy reduces the need for power generation from fossil fuels, thus there will be an environmental gain. The study seeks to emphasize the complexity and the important aspects of the assessment of environmental impacts associated with large power systems.
52

Environmental Assessment of Scenarios for Products and Services based on Forest Resources in Norway

Grinde, Magnus January 2011 (has links)
Energy from wood biomass is one of the prioritized areas of focus in current Norwegian energy politics. The prevailing perception of bioenergy is that it is climate neutral, making this strategy appear to be an effective measure in combating climate change. Furthermore, bioenergy is considered to be relatively source of energy, and steadily increasing Norwegian forests imply huge amounts of wood available. However, not all of this wood is easily accessible with current technology and market situations (i.e. prices). As wood also is used for many other purposes, mainly construction and paper production, the bioenergy industry will have to compete with these other industries for the access to raw materials. A change in current utilization of our wood resources is in this thesis assessed in an environmental perspective in order to better understand how such a shift would influence the overall environmental impacts. First, a wood flow mapping of the current (2006) situation was carried out and applied in a ‘hybrid life cycle assessment’ model utilizing life cycle inventories which represent the industries within the Norwegian wood products sector. Then, an alternative wood flow scenario where more wood were used for bioenergy purposes, at the expense of reduced domestic paper- and wood panel production, was studied. Besides from being highly representative for Norwegian conditions, the model was developed with the intention of being able to show the breakdown of environmental impacts for both for entire sector as well as for specific products and industries. Furthermore, in contrast to the current dominant perception, recent research has pointed to the fact that the resulting greenhouse gas emissions from combustion of biomass will have a significant climate change impact even if new biomass is replanted immediately, as the gases will spend a considerable time in the atmosphere before being absorbed. This new insight may seriously influence the perceived effectiveness of bioenergy in climate change mitigation efforts. Consequently, it was considered valuable to include estimated climate change impact potentials of biogenic carbon emissions (CO2 and CH4) in this assessment. Although the developed model probably should be further refined before ultimate conclusions are made based on the assessment results, some important observations can be commented. First of all, it was clearly shown that whether or not climate change impacts from biogenic carbon emissions are considered is highly relevant to the overall climate change mitigation effect of bioenergy. Still, even when these are included there are considerable environmental gains when e.g. substituting fossil energy with wood-based bioenergy. Secondly, the results illustrate how impacts from different environmental impact categories are distributed within the wood products sector (pulp & paper production clearly being the dominant industry), within the products’ value chains and for the overall system (characterized by the impacts from paper- and heat production as well as the use of transportation fuels).
53

Hur kommer elbilar och förnybara energikällor påverka vår framtida elproduktion? / How will electric cars and renewable energy sources affect our future electric production?

Sigurd, Christer January 2010 (has links)
Att vi behöver göra något åt rådande miljösituationen är det få som tvekar på. Elbilar kommer mer och mer som ett alternativ till de konventionella fordonen och det satsas mycket på förnybara energikällor. Med en introduktion av elbilar i samhället kommer behovet av elenergi att öka. Inledningsvis kommer elbehovet endast påvekas marginellt och genom att ladda under nattetid när elkonsumtionen är låg kommer nuvarande produktion att räcka ända fram till att hälften av vår fordonsflotta är elektrifierad. När sedan antalet bilar ökar ytterligare krävs en förändring för att klara av det ökade behovet av elenergi. Med den potential våra förnybara energikällor har så visar denna rapport att det kommer klaras av gott och väl. Att köra våra elbilar på förnybar energi har också fördelen att utsläppen i princip blir lika med noll, vilket skapar mervärden. Elbilen blir inte renare än elen som den körs på är. Redan idag är en mycket stor del av vår elproduktion från förnybara energikällor. Vattenkraft står för ca 46 % av elproduktionen sett ur ett perspektiv på 11 år. Sedan finns ett planeringsmål att år 2020 ska det produceras 30 TWh från vindkraft i Sverige (idag 2,5 TWh) vilket skulle räcka som energi till både alla våra bilar samt att exportera "grön el" ut i Europa.
54

Evaluering av energieffektive tørkesystem i solrike område / Evaluation of Energy efficient Drying Systems in Sunny Areas

Øygarden, Olav January 2011 (has links)
Hovudmålet med denne rapporten har vore å evaluera moglege løysingar for energieffektive tørkesystem basert på solenergi. Gjennom litteraturstudiet vert det funne at opne system for soltørking har ei rekkje generelle problem: Store avlingstap kjem som følgje av utilstrekkeleg tørking, sopp, insekt, fuglar, gnagarar, støv og søppel, samt uventa nedbør og andre uforutsette værforhold. Lukka soltørker kan eliminera eller redusera mange av desse problema, men dei har alle det til felles at dei baserer seg på tørketemperaturar over omgjevnadstemperatur. Tørking ved relativt låge temperaturar kan vera med å bevara ei rekkje ønska kvalitetar til fersk mat. Lukka varmepumpetørker kan operera uavhengig av værforhold, gjeva tørketemperaturar under omgjevnadstemperatur, og tilbyr slik ein attraktiv moglegheit for å auka produktkvalitet og redusera øydelegging gjennom god kontroll over, og regulering av tørkebetingelsane. For å levera tørkeluft med tilstrekkeleg låg luftfuktighet, og ved temperaturar under omgjevnadstemperatur trengst det kjøling. Eit litteraturstudium er gjort kring solkjølingsteknologiar. For ei tørke med solbasert energiforsyning, vil ein naturleg konsekvens vera tidsvarierande energitilgang, og dermed tidsvarierande drift. Eit tenkt tørkesystem er difor planlagt slik at tørka går om dagen, og står stille om natta. Det er utført eksperiment med tørking av fisk, med mål om å kartlegga korleis ein slik døgnsyklus vil påverka tørkeforløpet. Hovudkonklusjonen er at ein slik syklus vil vera energisparande, men meir tidkrevjande enn tilsvarande tørking med kontinuerlig drift. Det vert også vist at tørkeprosessen går fortare ved 20°C/26%RH enn ved 10°C/50°RH.Ei tørke basert på ein standard 40-fots isolert ISO-container vert dimensjonert til å kunna tørka 122 tonn fisk (fersk vekt) årleg ved tørketemperatur 15°C, relativ fuktighet 40%, og 10 timars dagleg drift. Tørka krev 56,2kW kjøleeffekt ved 0°C, og vifteeffekt 16,3kW. Med effektbehovet kartlagt vert ulike solbaserte energiforsyningssystem vurdert. Litteraturstudiet resulterer i at ein del solkjølingsteknologiar, blant anna ejektorkjøling med CO2 som arbeidsmedium, vert vurdert som lite aktuelle for det tenkte systemet. Dei gjenverande kjøleteknologiane som vert grundigare undersøkt er dei termisk drivne teknologiane ejektorkjøling (med arbeidsmedium R134a/R11/H2O) og absorpsjonskjøling (med LiBr-vatn som arbeidspar), samt konvensjonell elektrisk driven dampkompresjon med R717-ammoniakk som arbeidsmedium. For anskaffelse av naudsynt termisk energi vert uisolerte flatplatesolfangarar, isolerte flatplatesolfangarar og vakuumrøyrsolfangarar vurdert. For anskaffelse av elektrisk energi vert solcellepanel vurdert mot termisk solfangar + varmemotor og generator. Ulike systemløysingar for å levera kjøleenergi til tørka vert så samanlikna på grunnlag av naudsynt solfangarareal, solfangarkostnad, og kjølarkostnad. Solfangarkostnaden er om lag 10 gongar høgare enn kjølarkostnaden for alle systemløysingar. Av dei undersøkte løysingane vert solcelledriven dampkompresjonskjøling funne å vera den minst kostbare og minst arealkrevjande løysinga. Ved 10 timars drift i døgnet, kan tørka drivast utelukkande frå solenergi frå 512 m2 solcellepanel til ein estimert kostnad €255.800. Vifta i tørka står for over halvparten av energibruken. Alle andre systemløysingar innebar høgare solfangarkostnader og større solfangarareal. Nest etter solcelledriven dampkompresjon ser eitt- eller to-trinns absorpsjonskjøling, driven av vakuumrøyrsolfangarar, ut til å vera det mest interessante alternativet. To-trinnsløysinga inneber litt mindre solfangarareal og –kostnader, men krev til gjengjeld eit system som tåler 145°C i forhold til eitt-trinnssystemet som går ved 90°C. Høgare temperaturar kan gjere det meir komplisert med termisk energilagring. Ved nytting av konsentrerande solfangerar kan solfangararealet i fleire av systemløysingane meir enn halverast.For klimatiske forhold og tilgjengeleg solinnstråling er det teke utgangspunkt i Mumbai, India.
55

Heating and Ventilation of Highly Energy Efficient Residential Buildings: Environmental Assessment of Technology Alternatives

Sørnes, Kari January 2011 (has links)
The aim of this study was to determine the level of environmental impact and primary energy resulting from demands placed on residential ventilation and heating systems; a conventional residential house built to the 2007 Norwegian building code with a standard heating system was compared against three technology scenarios used in a passive house of the equivalent size. Both houses have wooden framework and cladding and are projected by the Norwegian building company Norbohus. An economical evaluation of the heating systems was also done. The alternative heating option for the conventional house, Stord TEK 07, was based on current Norwegian energy consumption patterns; a combination of electricity and firewood is used to meet heating demand. This heating mix was also modeled as an option for the heating requirements of the passive house, named Stord Passive S1. Additionally, a solar collector system (Stord Passive S2) and an air-to-water heat pump (Stord Passive S3) were modeled for the passive house. Finally, a balanced mechanical ventilation system was evaluated for both buildings. The life-cycle assessment method used was the ReCiPe method and the electricity used in the operation phase was based on the Nordic electricity mix.The results of this study indicate that Stord TEK 07 has the largest emission output in relation to output of CO2-eq, presented in the impact category “Climate change”. From a life-cycle perspective, the heating system requirements of a Stord TEK 07 house are 47.5 and 45 percent higher than the renewable energy solutions of passive house scenarios S2 and S3, respectively. Total life-cycle primary energy requirements in the Stord TEK 07 house were almost twice that of the renewable solutions in the passive house. Using the Norwegian standard heating system of Stord TEK 07 in a passive house as was done in Stord Passive S1, also results in a large improvement; output of CO2-eq and use of primary energy was reduced by 34-35 percent. Stord TEK 07 has also the highest emission output in most of the other impact categories and the largest present value costs, when building constructing costs are excluded. The heat pump solution, Stord Passive S3, has the lowest impact in most categories; however, the solar collector system Stord Passive S2, had lower output of CO2-eq. Stord Passive S2 has also lower present value costs then the air-water heat pump Stord Passive S3.A balanced ventilation system with 80 percent heat recovery was studied for both the houses. The benefit of heat recovery is recognizable in all the impact categories considered. The energy consumption and potential harmful emissions resulting from the electrical energy used by fans during the life cycle far exceed the environmental impacts that result from manufacture and transportation of the ventilation unit. The study revealed that the heat-recovery system must have efficiency greater than 15 percent to achieve reduction concerning output of CO2-eq and use of primary energy for Stord TEK 07; this requirement increases to 42 percent in houses built to the passive house standard house, Stord Passive.
56

Case Study Analysis of Running Distributed Generators in Island Mode : Effects on Reliability of Supply

Hegvik, Anders January 2012 (has links)
As a consequence of increased government efforts to reduce local Norwegian CO_2-emissions the development of small distributed generators have increased. This development is assumed to continue, but at an increasing incremental cost due to the inferior profitability of remaining prospects. To maintain profitability of smaller and high cost distributed generators, cost savings must be implemented. Quality of supply is a significant factor in determining potential profitability. Hence, a significant potential in cost reduction lies in increasing quality of supply. This can be achieved by utilizing the decentralized nature of these power producers by enabling intended island operation. By enabling these generators to run in intended island mode, they are able to supply their local grid with power when fallout of the main grid or other components occurs. This increases the uptime for local customers and therefore increases quality of supply. Five different grids are modeled in PowerFactory based on collected empirical data for the evaluation of the potential for islanding in Norway. With these models different cases utilizing islanding schemes are simulated and the reliability of these configurations compared to a base case representing normal operations. The results from this analysis suggest big reductions in the reliability indices “Energy Not Supplied” and “System Average Interruption Frequency” are possible. In the thesis the reductions achieved are in the 10%-60% range of the base case. The estimated savings earned from increased reliability of supply does not justify the assumed investment needed, but the numbers are not conclusive. Better estimates of expenses and assessing other grids with better prerequisites for islanding could indicate to be profitability.
57

Implementing Hydropower Scheduling in a European Expansion Planning Model

Brovold, Sondre Heen January 2014 (has links)
This Master’s thesis proposes a method for implementing an enhanced hydropower planning formulation in a long-term expansion planning model. The motivation for this work is the important role that hydropower plays in a generation investment environment. In a time where penetration of intermittent renewable energy sources like wind and solar power is heavily increasing, new challenges in the continuous balancing of supply and demand are also introduced. Hydropower and its use of reservoirs as power batteries can respond more or less immediately to such fluctuations. As such, a detailed framework for hydropower scheduling is highly relevant.The presented implementation is carried out in an already-existing expansion planning model for Europe called EMPIRE, which is written in Mosel Xpress. This is a two-stage stochastic optimization model whose objective function is to minimize the total net present value of expected operational costs and investment costs for generation and transmission capacities.The main feature of the proposed framework involves penalization of hydropower through water values. This necessitates a complete hydropower scheduling representation where each reservoir is divided into segments which are assigned a fictitious marginal cost. The inclusion of water values enables comparability with the short-run marginal cost for competitive technologies and introduces the important aspect of conserving water for other periods of the year. Data from SINTEF Energy Research has been used for this purpose.Results from optimization runs in the time span from 2010 to 2060 for an EU 20-20-20 like policy scenario show that the original hydropower availability is too relaxed, thereby causing an overvaluation of this technology. The revamped cost representation by means of water values leads to a lower utilization of hydropower relative to the original model. An earlier deployment of solar power is carried out to replace the lower generation, with a capacity difference between the final and original models peaking at 45% in 2040. Total costs in the system are therefore increased. For both models extensive investments in intermittent renewables are taking place, amounting to 47% of the total capacity in 2060.
58

Det framtida svenska elsystemet & lönsamheten för produktionsplanering

Lindgren, Matilda, Mattsson, Pierre January 2018 (has links)
På uppdrag av Skövde Värmeverk undersöker detta examensarbete hur det svenska framtida kraftsystemet kan vara utformat genom en jämförande litteraturstudie. Det utförs också en ekonomisk utvärdering av att undvika balansavgifter med hjälp av produktionsplanering av elproduktionen för energibolagets två kraftvärmeverk. Den jämförande litteraturstudien omfattade relevanta scenariostudier, utredningar och prognoser från myndigheter och organisationer. Även litteratur om det danska och tyska kraftsystemet undersöktes för att göra en jämförelse mellan ländernas elförsörjning. Två scenarier togs fram för kostnadsbesparing med en ökad prisvolatilitet i förhållande till referensåret 2017. Ett scenario med hjälp av lägre genomsnittspriser och ett med högre genomsnittspriser. Priserna är prognostiserade årsgenomsnittspriser som har gjorts om till spotpriser på timbasis i enlighet med den variation som fanns året 2017, dock med en ökad volatilitet på 1 procentenhet per år från referensårets priser. Kostnadsbesparingen baseras på en obalans om 3MW vid alla tillfällen som spotpris och nedregleringspris har en differens. Orsaken till den schablonmässiga beräkningen är avsaknaden av den inrapporterade produktionsplanen till systemansvarig aktör och därmed den verkliga obalansen som uppstod året 2017. I detta fall är det endast nedreglering av elproduktion som utvärderats och en möjlig bränslebesparing togs därför fram. I detta fall kan alternativ dyrare värmeproduktion regleras ned om 3MW elproduktion ersätter annan värmeproduktion. Resultatet tyder på ett svenskt kraftsystem utan kärnkraft efter åren 2040 - 2050 och en fortsatt investering i det interna nätet samt i utlandsförbindelser. Ökningen av intermittent kraft, exempelvis vindkraft, väntas fortsätta och det svenska kraftsystemet har på grund av vattenkraften goda förutsättningar att hantera volatil produktion och de prisvariationer som framträder mer i system utan samma flexibilitet. Kring frågan om likheter mellan Sveriges, Danmarks och Tysklands kraftsystem är det förutsättningarna att ta sig an utmaningarna som skiljer länderna emellan. Kostnadsbesparingen för produktionsplanering av kraftvärmeverken visar ett positivt resultat som ökar vid en möjlig bränslebesparing. / On behalf of Skövde Värmeverk this paper investigates the future Swedish electricity system and its similarities to the Danish and German systems. The report also analyzes the potential economic profitability of using production planning to avoid the fee for causing imbalances on the electricity system. The analysis of the future Swedish electricity system is a comparative study of relevant literature in the subject area. The potential economic saving was analyzed by using price forecasts for annual average prices which then were modified with an increasing volatility by 1 percent unit, each following year, relative to the volatility of the reference year 2017. The result shows that the Swedish electricity system will have a lack of nuclear power by year 2040–2050, a continued expansion of wind power and good conditions to handle expected volatility in electricity prices compared to systems without the same flexibility. The result indicates that there is an economic profitability for production planning.
59

Utformning av ett miljöcertifierat flerfamiljshus av planelement / Design of an environmentally certified apartment block of prefabricated planar elements

Erlandsson, Sandra, Matrinsson, Therese January 2016 (has links)
En ökad bostadskris och allt högre miljökrav gör att Sveriges byggnadsbransch står inför en stor utmaning under den närmaste tiden. Allt fler småhusföretag känner att de vill utveckla sina produkter så att de passar bostadsmarknaden. Efter samarbete med Vimmerbyhus har ett ritningsförslag på ett prefabricerat flerbostadshus i tre våningar tagits fram. Det framtagna förslaget har även fått en miljöcertifiering inom Miljöbyggnad. Studien innehåller val av byggnadens design samt inre utformning av ytor. Sveriges lagar och krav inom ändrings- och nybebyggelse är här av stor vikt. Det ställdes också vissa krav på designen av byggnaden på grund av att planelementen byggs i fabrik för att sedan fraktas och sättas ihop på byggplatsen. En jämförelse mellan fyra olika miljöcerifieringar gjordes innan Miljöbyggnad valdes som den mest passande. Här utreddes och beräknades olika aspekter inom energi, material och inomhusklimat.
60

Utredning av störningar i en trefastransformator : An investigation of the disturbance on a three-phase transformer

Norgren, Viktor January 2016 (has links)
Allt eftersom en mer sofistikerad och optimerad elektronik utvecklas går även mer störningar ut i elnätet som påverkar annan elektronik, som även den har blivit mer känslig för störningar. För att beskriva och kontrollera hur mycket störningar som påverkar ett elsystem används benämningen elkvalité. Elkvalitén beskriver kvalitén på elen efter bestämda gränsvärden när den påverkas av störningar. De vanligaste störningarna som förekommer i ett elnät är övertoner, transienter och spänningsvariationer. Det här projektet grundar sig i en transformator som man tror går varm på grund av störningar, den ligger ute på reningsverket på Rönnskär. Transformatorns uppgift är att koppla spänningen från ett IT-isolerat system till ett direktjordat system för att kunna driva den allmänna kraften. Målen med projektet var att mäta och utreda vilka störningar som förekom samt komma upp med åtgärder för att lösa problemet. För att erhålla en djupare kunskap inom området störningar på elnätet genomfördes en fördjupad inläsning av de olika störningar som ansågs vara potentiella källor till varmgången hos transformatorn. De störningar som behandlades var övertoner, transienter och spänningsvariationer. Den mest sannolika störningen som förekom bedömdes vara övertoner, därav genomfördes mätningar mot övertoner. Övertoner är störningar på ström– och spänningskurvan vilket bland annat kan leda till effektförluster, vagabonderande strömmar och resonansproblem. Ursprunget av övertoner genereras av olinjära laster som t ex. frekvensomriktaren. Vid mätningarna användes mätinstrumentet Fluke 1735 specialiserat för övertoner. Mätningarna visade på höga strömövertoner i fas 1 på primärsidan, men på övriga faser samt sekundärsidan kunde inga bevis på övertonshalter som var skadande redovisas. Därför kunde slutsatsen dras att det var en olinjär last utifrån som skickade ut störningarna. Vid ett av mätningstillfällena utfördes även en grundlig genomgång av anläggningen samt transformatorn. Där konstaterades det att det fanns en luftspalt i transformatorns kärna, orsakat av ett fel vid tillverkningen av transformatorn. Teorin kring konsekvenserna vid ett sådant problem medförde att slutsatsen drogs att huvudkällan till varför transformatorn gick varm var luftspalten i kärnan. Eftersom det även fanns övertoner på fas 1 konstaterades att det fanns två källor till värmeökningen i transformatorn där luftspalten i kärnan anses vara mer förödande. Rekommendationerna blir därför till en början att byta ut den nuvarande transformatorn mot en ny, se över frekvensomriktarna i anläggningen samt eventuellt installera ett aktivt filter mot övertoner om prioritering är att eliminera alla övertoner.

Page generated in 0.2016 seconds