| 1. |
- Lindroth [formerly Tyrberg], Simon, 1979-
(författare)
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Buoy and Generator Interaction with Ocean Waves : Studies of a Wave Energy Conversion System
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- On March 13th, 2006, the Division of Electricity at Uppsala University deployed its first wave energy converter, L1, in the ocean southwest of Lysekil. L1 consisted of a buoy at the surface, connected through a line to a linear generator on the seabed. Since the deployment, continuous investigations of how L1 works in the waves have been conducted, and several additional wave energy converters have been deployed. This thesis is based on ten publications, which focus on different aspects of the interaction between wave, buoy, and generator. In order to evaluate different measurement systems, the motion of the buoy was measured optically and using accelerometers, and compared to measurements of the motion of the movable part of the generator - the translator. These measurements were found to correlate well. Simulations of buoy and translator motion were found to match the measured values. The variation of performance of L1 with changing water levels, wave heights, and spectral shapes was also investigated. Performance is here defined as the ratio of absorbed power to incoming power. It was found that the performance decreases for large wave heights. This is in accordance with the theoretical predictions, since the area for which the stator and the translator overlap decreases for large translator motions. Shifting water levels were predicted to have the same effect, but this could not be seen as clearly. The width of the wave energy spectrum has been proposed by some as a factor that also affects the performance of a wave energy converter, for a set wave height and period. Therefore the relation between performance and several different parameters for spectral width was investigated. It was found that some of the parameters were in fact correlated to performance, but that the correlation was not very strong. As a background on ocean measurements in wave energy, a thorough literature review was conducted. It turns out that the Lysekil project is one of quite few projects that have published descriptions of on-site wave energy measurements.
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| 2. |
- Svensson, Olle, 1967-
(författare)
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Experimental results from the Lysekil Wave Power Research Site
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents how experimental results, from wave power research performed offshore at the Lysekil research site, were obtained. The data were used to verify theoretical models as well as evaluate the feasibility of wave power as a future sustainable energy source.The first experiments carried out at the research site was the measurement of the force in a line where one end was connected to a buoy with a diameter of 3 m and the other end to a set of springs with limited stroke length. The system is exposed to high peak forces compared to average forces. The maximum measured force in the line, when the buoy motion is limited by a stiff stopper rope is ten times the average force in that particular sea state.The experiment performed on the first wave energy converter tested at the Lysekil Research Site is described. The infrastructure of the site is presented where the central connection point is the measuring station. The key finding is that it is possible to transform the motions of ocean waves into electrical energy and distribute it to land.Many wave energy converters must be interconnected if large amounts of energy are to be harvested from the waves. The first submerged substation intended for aggregation of energy from wave power converters is described, with focus on the measurement and control system placed inside the substation. During this experiment period the generators were equipped with many different sensors; these measurements are explained in the thesis.The system that aggregates power from the studied wave energy converter is regularly exposed to peak power of up to 20 times the maximum average output from the converter.Vertical and horizontal movement of the buoy has been measured in different ways. The result is that the vertical displacement of the buoy can be measured with a simple accelerometer circuit but it is much more complicated to measure the horizontal displacement. A special method for measuring the horizontal displacement has been implemented by measuring the strain in the enclosure and the force in the line.
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| 3. |
- Acuña, José, 1982-
(författare)
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Distributed thermal response tests : New insights on U-pipe and Coaxial heat exchangers in groundwater-filled boreholes
- 2013
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Konstnärligt arbete (övrigt vetenskapligt/konstnärligt)abstract
- U-pipe Borehole Heat Exchangers (BHE) are widely used today in ground source heating and cooling systems in spite of their less than optimal performance. This thesis provides a better understanding on the function of U-pipe BHEs and Investigates alternative methods to reduce the temperature difference between the circulating fluid and the borehole wall, including one thermosyphon and three different types of coaxial BHEs.Field tests are performed using distributed temperature measurements along U-pipe and coaxial heat exchangers installed in groundwater filled boreholes. The measurements are carried out during heat injection thermal response tests and during short heat extraction periods using heat pumps. Temperatures are measured inside the secondary fluid path, in the groundwater, and at the borehole wall. These type of temperature measurements were until now missing.A new method for testing borehole heat exchangers, Distributed Thermal Response Test (DTRT), has been proposed and demonstrated in U-pipe, pipe-in-pipe, and multi-pipe BHE designs. The method allows the quantification of the BHE performance at a local level.The operation of a U-pipe thermosyphon BHE consisting of an insulated down-comer and a larger riser pipe using CO2 as a secondary fluid has been demonstrated in a groundwater filled borehole, 70 m deep. It was found that the CO2 may be sub-cooled at the bottom and that it flows upwards through the riser in liquid state until about 30 m depth, where it starts to evaporate.Various power levels and different volumetric flow rates have been imposed to the tested BHEs and used to calculate local ground thermal conductivities and thermal resistances. The local ground thermal conductivities, preferably evaluated at thermal recovery conditions during DTRTs, were found to vary with depth. Local and effective borehole thermal resistances in most heat exchangers have been calculated, and their differences have been discussed in an effort to suggest better methods for interpretation of data from field tests.Large thermal shunt flow between down- and up-going flow channels was identified in all heat exchanger types, particularly at low volumetric flow rates, except in a multi-pipe BHE having an insulated central pipe where the thermal contact between down- and up-coming fluid was almost eliminated.At relatively high volumetric flow rates, U-pipe BHEs show a nearly even distribution of the heat transfer between the ground and the secondary fluid along the depth. The same applies to all coaxial BHEs as long as the flow travels downwards through the central pipe. In the opposite flow direction, an uneven power distribution was measured in multi-chamber and multi-pipe BHEs.Pipe-in-pipe and multi-pipe coaxial heat exchangers show significantly lower local borehole resistances than U-pipes, ranging in average between 0.015 and 0.040 Km/W. These heat exchangers can significantly decrease the temperature difference between the secondary fluid and the ground and may allow the use of plain water as secondary fluid, an alternative to typical antifreeze aqueous solutions. The latter was demonstrated in a pipe-in-pipe BHE having an effective resistance of about 0.030 Km/W.Forced convection in the groundwater achieved by injecting nitrogen bubbles was found to reduce the local thermal resistance in U-pipe BHEs by about 30% during heat injection conditions. The temperatures inside the groundwater are homogenized while injecting the N2, and no radial temperature gradients are then identified. The fluid to groundwater thermal resistance during forced convection was measured to be 0.036 Km/W. This resistance varied between this value and 0.072 Km/W during natural convection conditions in the groundwater, being highest during heat pump operation at temperatures close to the water density maximum.
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| 4. |
- Davidsson, Simon, et al.
(författare)
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A review of life cycle assessments on wind energy systems
- 2012
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Ingår i: The International Journal of Life Cycle Assessment. - : Springer Science and Business Media LLC. - 0948-3349 .- 1614-7502. ; 17:6, s. 729-742
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Forskningsöversikt (refereegranskat)abstract
- PurposeSeveral life cycle assessments (LCA) of wind energy published in recent years are reviewed to identify methodological differences and underlying assumptions.MethodsA full comparative analysis of 12 studies were undertaken (10 peer-reviewed papers, 1 conference paper, 1 industry report) regarding six fundamental factors (methods used, energy use accounting, quantification of energy production, energy performance and primary energy, natural resources, and recycling). Each factor is discussed in detail to highlight strengths and shortcomings of various approaches.ResultsSeveral potential issues are found concerning the way LCA methods are used for assessing energy performance and environmental impact of wind energy, as well as dealing with natural resource use and depletion. The potential to evaluate natural resource use and depletion impacts from wind energy appears to be poorly exploited or elaborated on in the reviewed studies. Estimations of energy performance and environmental impacts are critically analyzed and found to differ significantly.Conclusions and recommendationsA continued discussion and development of LCA methodology for wind energy and other energy resources are encouraged. Efforts should be made to standardize methods and calculations. Inconsistent use of terminology and concepts among the analyzed studies are found and should be remedied. Different methods are generally used and the results are presented in diverse ways, making it hard to compare studies with each other, but also with other renewable energy sources.
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| 5. |
- Johansson, Björn, 1975, et al.
(författare)
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Evaluation and Calculation of Dynamics in Environmental Impact Assessment
- 2013
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Ingår i: IFIP Advances in Information and Communication Technology. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1868-4238 .- 1868-422X. - 9783642403514 ; 397:1, s. 135-141
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Konferensbidrag (refereegranskat)abstract
- In ten years customers will select products not only based on price and quality but also with strong regard to the product value environmental footprint, including for example the energy consumed. Customers expect transparency in the product realization process, where most products are labeled with their environmental footprint. Vigorous companies see this new product value as an opportunity to be more competitive. In order to effectively label the envi-ronmental impact of a product, it is pertinent for companies to request the envi-ronmental footprint of each component from their suppliers. Hence, companies along the product lifecycle require a tool, not only to facilitate the computing of the environmental footprint, but also help reduce/balance the environmental impact during the lifecycle of the product. This paper proposes to develop a procedure that companies will use to evaluate, improve and externally advertise their product’s environmental footprint to customers.
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| 6. |
- Kilkiş, Şiir
(författare)
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A net-zero building application and its role in exergy-aware local energy strategies for sustainability
- 2012
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904 .- 1879-2227. ; 63:SI, s. 208-217
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Tidskriftsartikel (refereegranskat)abstract
- Based on two case studies, this paper explores the nexus of exergy, net-zero targets, and sustainable cities as a means of analyzing the role of exergy-aware strategies at the building and district level. The first case study is a premier building in Ankara that is ready to meet the net-zero exergy target. It is also the first building in Turkey to receive the highest Platinum rating in Leadership in Energy and Environmental Design. A net-zero exergy building (NZEXB) is a building that has an annual sum of net-zero exergy transfer across the building-district boundary. This new target is made possible by lowered annual exergy consumption, (AEXC), and increased on-site production from a bundle of sustainable energy technologies. The modeled results of the building indicate that the reduced AEXC of 60 kW h/m 2 yr is met with on-site production of 62 kW h/m 2 yr. On-site production includes PV and building integrated PV, a micro-wind turbine, combined heat and power, GSHP, and solar collectors. Diversified thermal energy storage tanks further facilitate the exergy supply to meet with the exergy demand. The results of this case study provide key lessons to structure an energy value chain that is more aware of exergy, which are up-scalable to the district level when the bundle of sustainable energy technologies is zoomed out across a larger spatial area. These key lessons are then compared with the second case study of two districts in the south heating network of the city of Stockholm, which was the European Green Capital in 2010. The levels of exergy match in these districts of Stockholm, namely the districts of Högdalen and Hammarby, is found to be 0.82 and 0.84, respectively. However, there remain several bottlenecks for these districts to reach net-zero targets at the community level. The paper concludes that the NZEXB case study has much to offer as a "building block" to reform the way energy is converted and managed and in this way, to structure an exergy-aware energy value chain for greater sustainability in green cities of the future.
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| 7. |
- Grip, Carl-Erik, et al.
(författare)
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Possibilities and problems in using exergy expressions in process integration
- 2011
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Ingår i: Proceedings of the World Renewable Energy Congress 2011 (WREC 2011), 9-13 May, Linköping.. - Linköping : Linköping University Electronic Press. ; , s. 1605-1612
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Konferensbidrag (refereegranskat)abstract
- Industrial energy systems are complicated networks, where changes in one process influence its neighboring processes. Saving energy in one unit does not necessarily lead to energy savings for the total system. A study has been carried out on the possibility to use the exergy concept in the analysis of industrial energy systems. The exergy concept defines the quality of an amount of energy in relation to its surrounding, expressing the part that could be converted into work. The study consists of literature studies and general evaluations, an extensive case study and an interview study. In the latter it was found that non technical factors are major obstacles to the introduction of exergy.
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| 8. |
- Ackermann, Thomas
(författare)
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Introduction
- 2012
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Ingår i: Wind Power in Power Systems, Second Edition. - : Wiley. ; , s. 1-5
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Bokkapitel (refereegranskat)
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| 9. |
- Vikström, Hanna, 1985-, et al.
(författare)
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Lithium availability and future production outlooks
- 2013
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 110:10, s. 252-266
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Tidskriftsartikel (refereegranskat)abstract
- Lithium is a highly interesting metal, in part due to the increasing interest in lithium-ion batteries. Several recent studies have used different methods to estimate whether the lithium production can meet an increasing demand, especially from the transport sector, where lithium-ion batteries are the most likely technology for electric cars. The reserve and resource estimates of lithium vary greatly between different studies and the question whether the annual production rates of lithium can meet a growing demand is seldom adequately explained. This study presents a review and compilation of recent estimates of quantities of lithium available for exploitation and discusses the uncertainty and differences between these estimates. Also, mathematical curve fitting models are used to estimate possible future annual production rates. This estimation of possible production rates are compared to a potential increased demand of lithium if the International Energy Agency’s Blue Map Scenarios are fulfilled regarding electrification of the car fleet. We find that the availability of lithium could in fact be a problem for fulfilling this scenario if lithium-ion batteries are to be used. This indicates that other battery technologies might have to be implemented for enabling an electrification of road transports.
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| 10. |
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Systems Perspectives on Electromobility 2013
- 2013
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Samlingsverk (redaktörskap) (refereegranskat)abstract
- The transportation of goods and people is at the heart of the industrial society.Yet transportation relies heavily upon oil – a scarce fossil fuel that contributes toclimate change and local air pollution. The term ‘electromobility’ refers to an alternativetransportation system based on vehicles propelled by electricity. Electromobilityis increasingly seen as favourable in that it could circumvent problems relatedto both oil and biofuels whilst meeting our mobility needs and desires. However,the virtue of electromobility is not uncontested and a range of issues come to thefore. Are electric vehicles energy efficient? Are they safe? How much greenhousegas is emitted in the production of electricity and advanced vehicle components?Will battery production lead to new resource problems? Will electromobilitypromote or hinder the diffusion of renewable energy? Will driving patterns shapeor be shaped by new types of vehicles? Is electromobility suitable for cars but notfreight transport? How is technical knowledge for electromobility produced andby whom? Is the automotive industry up to the challenge? Is there a need for newbusiness models and governmental policy support (or both) to stimulate marketdemand for electric vehicles?There is no simple answer to these questions. However, studying electromobilityfrom different systems perspectives can help to resolve these complex issues.Systems Perspectives on Electromobility 2013 is composed of fifteen chaptersthat address different topics related to the immensely important issue of whether– and to what extent – our transport systems can and should be energised byelectricity. The book is far from complete, but we hope it may be a useful startingpoint for future discussions and debates.
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