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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.
1

Dispatchable operation of multiple electrolysers for demand side response and the production of hydrogen fuel : Libyan case study

Rahil, Abdulla January 2018 (has links)
Concerns over both environmental issues and about the depletion of fossil fuels have acted as twin driving forces to the development of renewable energy and its integration into existing electricity grids. The variable nature of RE generators assessment affects the ability to balance supply and demand across electricity networks; however, the use of energy storage and demand-side response techniques is expected to help relieve this situation. One possibility in this regard might be the use of water electrolysis to produce hydrogen while producing industrial-scale DSR services. This would be facilitated by the use of tariff structures that incentive the operation of electrolysers as dispatchable loads. This research has been carried out to answer the following question: What is the feasibility of using electrolysers to provide industrial-scale of Demand-side Response for grid balancing while producing hydrogen at a competitive price? The hydrogen thus produced can then be used, and indeed sold, as a clean automotive fuel. To these ends, two common types of electrolyser, alkaline and PEM, are examined in considerable detail. In particular, two cost scenarios for system components are considered, namely those for 2015 and 2030. The coastal city of Darnah in Libya was chosen as the basis for this case study, where renewable energy can be produced via wind turbines and photovoltaics (PVs), and where there are currently six petrol stations serving the city that can be converted to hydrogen refuelling stations (HRSs). In 2015 all scenarios for both PEM and alkaline electrolysers were considered and were found to be able to partly meet the project aims but with high cost of hydrogen due to the high cost of system capital costs, low price of social carbon cost and less government support. However, by 2030 the price of hydrogen price will make it a good option as energy storage and clean fuel for many reasons such as the expected drop in capital cost, improvement in the efficiency of the equipment, and the expectation of high price of social carbon cost. Penetration of hydrogen into the energy sector requires strong governmental support by either establishing or modifying policies and energy laws to increasingly support renewable energy usage. Government support could effectively bring forward the date at which hydrogen becomes techno-economically viable (i.e. sooner than 2030).
2

Sharing Surplus Energy at Gränby Sports Field : A case study investigating the possibilities for sharing thermal surplus energy from the ice rinks at the sports field

Waldenfjord, Rebecca, Abrahamsson, Linnea, Engström, Karolina January 2021 (has links)
This project aimed to investigate the existence of thermal surplus energy from the ice rinks at Gränby Sports Field, Uppsala. Furthermore, a secondary goal was to suggest a distribution system for sharing the potential surplus energy. To fulfil the purpose, each ice rink was modelled in the software IDA ICE. The following ice rinks were considered: buildings A and B, building C and the bandy arena. Data regarding the total heat and cold consumption for each building was collected from the owner, Uppsala kommun Sport- och rekreationsfastigheter AB, and was used to validate the simulation results from the building models. The results from IDA ICE were presented in graphs that illustrate each ice rink’s total heat and cold consumption, surplus energy and energy balance. However, the results from the models in IDA ICE were not validated within a deviation of a maximum of 10% when compared to the data from Uppsala kommun Sport- och rekreationsfastigheter AB. Hence, the results were analyzed on a general level, which showed that there was a greater need for heating during wintertime, with certain peaks during the coldest months, whereas the cooling is maintained at a relatively stable level throughout the year, but with a slightly greater need in the summer. Further on, there was an identified surplus energy from the ice rinks, in terms of waste heat from the refrigeration systems. During the summer there was a greater amount of surplus heat generated, caused by the greater cooling demand. Due to not being able to validate the models, complementary calculations of the yearly surplus heat were made with data from Uppsala kommun Sport- och rekreationsfastigheter AB. The surplus heat was 1 200 MWh for buildings A and B, 497 MWh for building C and 1 492 MWh for the bandy arena. No surplus cold was identified within the ice rinks. The suggested solution for sharing the surplus energy is to implement seasonal thermal storage, due to the similar characteristics in heating and cooling demand for the ice rinks. The stored surplus energy could cover the ice rink’s peaks in heating demand during winter, which is an energy-efficient way would reduce purchased heat from the district heating grid. For further studies, it is of great interest to identify the possibilities of implementing a distribution system similar to the fifth generation district heating as well as seasonal storage, to possibly enable a direct share of energy between all the buildings within the sports field.
3

A Comparative Study of the Perceptions of Elementary School Administrators, Teachers, and Students Regarding recess and Free Play in the Public School.

Banner, Amy Bennett 07 May 2005 (has links) (PDF)
According to recent studies, the number of schools that have severely limited or eliminated recess and free-play opportunities is on the rise across the nation. School officials cite the increasing levels of state and federal pressure to perform on standardized tests as the primary reason for this shift away from the playground. The threat of lawsuits and safety concerns are also listed as factors in this change of policy. The purpose of this mixed methods study was to examine the perceptions of directors of schools, supervisors, principals, assistant principals, teachers, and students regarding recess and free play in three East Tennessee school systems. Representative schools were chosen from each system and examined. In addition, results from standardized test scores as provided by the state of Tennessee were examined for the selected schools. The findings of this study revealed that directors, supervisors, principals, teachers, and students were in favor of recess and stated that offering recess and free-play opportunities provided some benefit to students. Even so, two schools in the study had chosen to limit recess and free-play opportunities to varying degrees whereas the third school maintained a policy of recess breaks. In examining the test data, the two schools that had limited recess were found to have lower test scores than the school that had maintained the integrity of recess. Other factors could attribute to the lower scores. The findings did reveal that limiting recess appeared to offer no significant gain in scores just as providing recess did not appear to cause any decrease in test scores. Stakeholders interviewed expressed the perception that the benefits of having recess outweighed any potential threat of time lost in the classroom. Recommendations for further research include repeating this study in other school settings on a larger scale to see if the same results are realized.

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