The focus of this research was to create and characterize high temperature alumina and nitrate salt eutectic nanofluids for use in thermal energy storage (TES) systems. The nitrate eutectic was originally used in the TES system demonstrated as part of the Solar Two power tower and is currently employed as the TES material at Andasol 1 in Spain. Concentrations of alumina nanoparticles between 0.1% and 10% by weight were introduced into the base material in an effort to create nanofluids which would exhibit improved specific heat capacity to reduce the $/kWht thermal energy storage system costs. The composite materials were created using an aqueous mixing method in which both the nanoparticles and nitrate eutectic were placed into solution using acidic water. This solution was then sonicated in an ultrasonic bath in an effort to reduce nanoparticle agglomeration and to improve homogeneity. After boiling off the excess water, the nanoparticle-nitrate eutectic composite was recovered for characterization. The thermal properties of both the composite and base materials were characterized using the differential scanning calorimetry techniques outlined in ASTM E 1269. The created nanofluids were not stable and did not offer a cost-effective alternative to the current nitrate eutectic TES material. Despite these setbacks, a positive correlation between alumina concentration and nanofluid specific heat was demonstrated. Additionally, the specific heat capacities of the created nanofluids exceeded that predicted by the current theoretical models. These findings suggest that further work in the field of high temperature nanofluids for use in TES systems is warranted.

In this thesis proposals for different designs of a borehole thermal energy storage (BTES) have been developed for the building DN-huset in Stockholm, Sweden. To build a BTES results in savings in energy costs by approximately 44 %, i.e. 2 million Swedish crowns annually. Furthermore, a BTES would reduce the annual environmental impact with roughly 75-157 tonnes of CO2 equivalents per year, depending on how the electricity consumption’s environmental impact is estimated. The payback period is about 11 years, including the warm-up period that is necessary before commissioning the BTES. The savings in environmental impact and operating costs are a result of energy being reused. During the summer heat is stored in the bedrock beneath the building for retrieval about half a year later in the winter, when there is a heating demand. In addition to developing proposals for different BTES designs the thesis also examines the influence of certain design parameters, conservative choices and operating conditions.

Total produced energy in the world is mostly consumed as thermal energy which is used for space or water heating. Currently, more than 85% of total thermal energy consumption is supplied from fossil fuels. This high consumption rate increases the depletion risk of fossil fuels as well as causing a tremendous release of hazardous gases such as carbon dioxide, carbon monoxide, sulfur oxides, nitrogen oxides and particulate matter that effects both environment and human health. Those drawbacks force humankind to search for new technologies, like renewables, to reduce fossil fuel dependency on thermal energy production. Thermal energy storage in adsorbent beds is one of the resulting technologies. Adsorption is an exothermic process in which a fluid (adsorbate) diffuses into the pores of a porous solid material (adsorbent) and trapped into the crystal lattice. In this system, exothermic adsorption of water vapor from air is carried out by using hybrid adsorbent of activated alumina and zeolite. In previous studies, through literature review, this adsorbent was selected to be the most efficient adsorbent for this process due to its high water adsorption capacity, high heat of adsorption, and stability [Dicaire and Tezel, 2011]. In this study, previous studies started on this project was confirmed and pursued by trying to increase the efficiency of the process and confirm the feasibility and applicability of this system in larger scales. In this thesis, various zeolite and activated alumina hybrid adsorbents with varying zeolite compositions were screened to find the most efficient adsorbent for thermal energy storage process that gives the highest energy density. Then, existing small column was replaced with a new one, which is 16 times bigger in volume, in order to confirm the feasibility of this process at larger scales. Applicability of on-off heat release in adsorption process was also investigated by conducting several on-off experiments at different on-off time periods. Moreover, exothermic adsorption process was modeled by doing mass and energy balances in the column, water accumulation balance in the pellets, and energy balance in the column wall. Validity of this model was confirmed by comparing it with experimental results at different column volumes, and at different volumetric flow rates. Finally, an overall plant design, capital cost and thermal energy price estimations were done for adsorption thermal energy storage plants for different storage capacities and payback periods.

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In hot climate areas, the electrical load in a building spikes, but not by the same amount daily due to various conditions. In order to cover the hottest day of the year, large cooling systems are installed, but are not fully utilized during all hot summer days. As a result, the investments in these cooling systems cannot be fully justified. A solution for more optimal use of the building cooling system is presented in this dissertation using Cool Thermal Energy Storage (CTES) deployed at a district level. Such CTES systems are charged overnight and the cool charge is dispatched as cool air during the day. The integration of the CTES helps to downsize the otherwise large cooling systems designed for the hottest day of the year. This reduces the capital costs of installing large cooling systems. However, one important question remains - how much of the CTES should be charged during the night, such that the cooling load for the next day is fully met and at the same time the CTES charge is fully utilized during the day. The solution presented in this dissertation integrated the CTES with Photovoltaics (PV) power forecasting and building load forecasting at a district level for a more optimal charge/discharge management. A district comprises several buildings of different load profiles, all connected to the same cooling system with central CTES. The use of forecasting for both the PV and the building cooling load allows the building operator to more accurately determine how much of the CTES should be charged during the night, such that the cooling system and CTES can meet the cooling demand for the next day. Using this approach, the CTES would be optimally sized, and utilized more efficiently during the day. At the same time, peak load savings are achieved, thus benefiting an electric utility company. The district presented in this dissertation comprises PV panels and three types of buildings – a mosque, a clinic and an office building. In order to have a good estimation for the required CTES charge for the next day, reliable forecasts for the PV panel outputs and the electrical load of the three buildings are required. In the model developed for the current work, dust was introduced as a new input feature in all of the forecasting models to improve the models' accuracy. Dust levels play an important role in PV output forecasts in areas with high and variable dust values. The overall solution used both the PV panel forecasts and the building load forecasts to estimate the CTES charge for the next day. The presented method was tested against the baseline method with no forecasting system. Multiple scenarios were conducted with different cooling system sizes and different CTES capacities. Research findings indicated that the presented method utilized the CTES charge more efficiently than the baseline method. This led to more savings in the energy consumption at the district level. / Doctor of Philosophy / In hot weather areas around the world, the electrical load in a building spikes because of the cooling load, but not by the same amount daily due to various conditions. In order to meet the demand of the hottest day of the year, large cooling systems are installed. However, these large systems are not fully utilized during all hot summer days. As a result, the investments in these cooling systems cannot be fully justified. A solution for more optimal use of the building cooling system is presented in this dissertation using Cool Thermal Energy Storage (CTES) deployed at a district level. Such CTES systems are charged overnight and the cool charge is dispatched as cool air during the day. The integration of the CTES helps to downsize the otherwise large cooling systems designed for the hottest day of the year. This reduces the capital costs of installing large cooling systems. However, one important question remains - how much of the CTES should be charged during the night, such that the cooling load for the next day is fully met and at the same time the CTES charge is fully utilized during the day. The solution presented in this dissertation integrated the CTES with Photovoltaics (PV) power forecasting and building load forecasting at a district level for a more optimal charge/discharge management. A district comprises several buildings all connected to the same cooling system with central CTES. The use of the forecasting for both the PV and the building cooling load allows the building operator to more accurately determine how much of the CTES should be charged during the night, such that the cooling system and CTES can meet the cooling demand for the next day. Using this approach, the CTES would be optimally sized and utilized more efficiently. At the same time, peak load is lowered, thus benefiting an electric utility company.

The increasing demand for energy in combination with a greater awareness for our environmental impact have encouraged the development of sustainable energy sources, including materials for energy storage. Latent heat thermal energy storage by the use of phase change material (PCM) have become an area of great interest. It is a reliable and efficient way to reduce energy consumption. PCMs store and release latent heat, which means that the material can absorb the excess of heat energy, save it and release it when needed. By introducing soy wax as a biobased PCM and apply it on textile, one can achieve a thermoregulation material to be used in buildings and smart textiles. By replacing the present most used PCM, paraffin, with soy wax one cannot only decrease the use of fossil fuel, but also achieve a less flammable material. The performance of soy wax PCM applied on a textile fabric have not yet been investigated but can be a step towards a more sustainable energy consumption. The soy wax may also broaden the application for PCM due to its low flammability. The aim is to develop an environmental friendly latent heat thermal energy storage material to be used within numerous application fields.

Concentrating solar power plants can integrate cost-effective thermal energy storage systems and thereby supply controllable power on demand, an advantage against other renewable technologies. Storage integration allows a solar thermal power plant to increase its load factor and to shift production to periods of peak demand. It also enables output firmness, providing stability to the power block and to the grid. Thus, despite the additional investment, storage can enhance the performance and economic viability of the plants. However, the levelized cost of electricity of these plants yet remains higher than for other technologies, so projects today are only viable through the provision of incentives or technology-specific competitive bid tenders. It is the variability of the solar resource, the myriad roles that storage can assume, and the complexity of enhancing the synergies between the solar field, the storage and the power block, what makes the development of adequate policy instruments, design and operation of these plants a challenging process. In this thesis a comprehensive methodology for the pre-design and analysis of concentrating solar power plants is presented. The methodology is based on a techno-economic modeling approach that allows identifying optimum trade-off curves between technical, environmental, and financial performance indicators. A number of contemporary plant layouts and novel storage and hybridization concepts are assessed to identify optimum plant configurations, in terms of component size and storage dispatch strategies. Conclusions highlight the relevance between the sizing of key plant components, the operation strategy and the boundaries set by the location. The interrelation between critical performance indicators, and their use as decisive parameters, is also discussed. Results are used as a basis to provide recommendations aimed to support the decision making process of key actors along the project development value chain of the plants. This research work and conclusions are primarily meant to set a stepping stone in the research of concentrating solar power plant design and optimization, but also to support the research towards understanding the value of storage in concentrating solar power plants and in the grid. / Koncentrerad solkraft erbjuder möjligheten att integrera kostnadseffektiv termisk energilagring och därmed behovsstyrd kraftkontroll. Detta är en viktig fördel jämfört med andra förnybara energiteknologier. Lagringsintegration tillåter solkraftsanläggningar att öka sin lastfaktor och skifta produktion till tider med största efterfrågan. Vidare möjliggör lagring fast elproduktion vilket leder till förbättrad nät- och kraftturbinstabilitet. Därför kan termisk lagring öka anläggningsprestanda och ekonomiskt värde trots ökande initiala kapitalkostnader. I termer av specifik elproduktionskostnad (LCOE) ligger koncentrerade solkraftsanläggningar med lagring fortfarande högre än andra kraftteknologier och anläggningsprojekt blir endast lönsamma genom subventionsmodeller eller teknologispecifika konkurrensutsatta anbudsförfaranden. Att hitta adekvata policylösningar och optimala design och operationsstrategier är en utmanande process eftersom det gäller att hitta rätt balans mellan variabel solinstrålning, lagring av energi och tid för produktion genom optimal design och operation av solmottagarfält, kraftblock och lagringskapacitet. I denna avhandling presenteras en omfattande metodik för pre-design och analys av koncentrerande solkraftverk. Metodiken baseras på en tekno-ekonomisk modelleringsansats som möjliggör identifiering av optimala avvägningssamband för tekniska, ekonomiska och miljöprestanda indikatorer. Metodiken tillämpas på ett antal moderna anläggningslayouter  och lagrings- och hybridiseringskoncept för att identifiera optimal kraftanläggningsdesign i termer av komponentprestanda och lagringsanvändningsstrategier. I slutsatsen poängteras relevansen av att hitta rätt storlek på nyckelkomponenter i relation till lagringsstrategi och randvillkoren som ges av konstruktionsläget för optimal ekonomisk och miljömässig prestanda. Resultaten används för att formulera rekommendationer till nyckelaktörer i beslutsprocessen genom hela kraftanläggningens värdekedja från politisk beslutsfattare till anläggningsingenjör. Forskningen och slutsatserna i detta arbete skall i första hand ta ett steg framåt för optimering och design av solkraftsanläggningar men även tillhandahålla en metodik för utvärdering av lagringslösningar och dess specifika värde för solkraftsanläggningar och elnätet. / <p>QC 20160829</p>

Concentrated solar power (CSP) has the potential of fulfilling the world’s electricity needs. Parabolic-trough system using synthetic oil as the HTF with operating temperature between 300 and 400o C, is the most matured CSP technology. A thermal storage system is required for the stable and cost effective operation of CSP plants. The current storage technology is the indirect two-tank system which is expensive and has high energy consumption due to the need to prevent the storage material from freezing. Latent heat storage (LHS) systems offer higher storage density translating into smaller storage size and higher performance but suitable phase change materials (PCMs) have low thermal conductivity, thus hindering the realization of their potential. The low thermal conductivity can be solved by heat transfer enhancement in the PCM. There is also lack of suitable commercially-available PCMs to cover the operating temperature range. In this study, a hybrid cascaded storage system (HCSS) consisting of a cascaded finned LHS and a high temperature sensible or concrete tube register (CTR) stages was proposed and analysed via modelling and simulation. Fluent CFD code and the Dymola simulation environment were employed. A validated CFD phase change model was used in determining the heat transfer characteristics during charging and discharging of a finned and unfinned LHS shell-and-tube storage element. The effects of various fin configurations were investigated and heat transfer coefficients that can be used for predicting the performance of the system were obtained. A model of the HCSS was then developed in the Dymola simulation environment. Simulations were conducted considering the required boundary conditions of the system to develop the best design of a system having a capacity of 875 MWhth, equivalent to 6 hours of full load operation of a 50 MWe power plant. The cascaded finned LHS section provided ~46% of the entire HCSS capacity. The HCSS and cascaded finned LHS section have volumetric specific capacities 9.3% and 54% greater than that of the two-tank system, respectively. It has been estimated that the capital cost of the system is ~12% greater than that of the two-tank system. Considering that the passive HCSS has lower operational and maintenance costs it will be more cost effective than the twotank system considering the life cycle of the system. There is no requirement of keeping the storage material above its melting temperature always. The HCSS has also the potential of even lower capital cost at higher capacities (>6 hours of full load operation).

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2015-10-26T16:14:39Z No. of bitstreams: 1 Jutaí Juarez Estrázulas_.pdf: 1716303 bytes, checksum: ac095da5508e03eaab20ab1008f22067 (MD5) / Made available in DSpace on 2015-10-26T16:14:39Z (GMT). No. of bitstreams: 1 Jutaí Juarez Estrázulas_.pdf: 1716303 bytes, checksum: ac095da5508e03eaab20ab1008f22067 (MD5) Previous issue date: 2015-06-12 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Inúmeras aplicações residenciais, comerciais e industriais voltadas ao gerenciamento térmico tem seus custos operacionais reduzidos quando um sistema de armazenamento de energia térmica é incorporado. Tal tipo de sistema pode, por exemplo, absorver energia térmica oriunda de fonte solar, de reaproveitamento de calor de processo industrial ou mesmo proveniente de energia elétrica (nos horários em que esta é menos onerosa), e liberá-la em um horário em que estas fontes de calor não estejam presentes e em que a energia elétrica, se utilizada, seria mais onerosa.Os PCMs (Phase Change Materials), devido ao seu alto calor latente de fusão, são materiais que representam uma alternativa viável à implementação de sistemas de armazenamento de energia térmica. No entanto, inúmeros PCMs ainda não tiveram suas características e propriedades fluidodinâmicas investigadas suficientemente. Assim, este trabalho apresenta um estudo numérico da mudança de fasede PCMs da família RT,em cavidades cilíndricas, visando o armazenamento térmico de energia através de calor latente (LHTES). O estudo foi realizado através de simulação numérica por CFD, com o software ANSYS Fluent. O modelo numérico adotado é bidimensional e é composto pelas equações da conservação da massa, quantidade de movimento e energia. Além destas, foi utilizada a técnica de modelamento entalpia-porosidade. A malha computacional é do tipo hexaédrica, com refinamento junto às paredes da geometria e na região de interface entre o PCM e o ar. O modelo implementado foi validado com resultados numéricos e experimentais da literatura, obtendo-se bons resultados. Foi avaliado o processo de fusão de cinco diferentes tipos de PCMs (RT 4, RT 35, RT 35HC (alta capacidade), RT 55 e RT 82), cada um deles com três intervalos de temperatura (T=10, 20 e 30 °C).Além disto, para T=10 ºC, os PCMS RT 27, RT 35, RT 35 HC e RT 82 foram testados para cinco diferentes valores de constante C (Mushy Zone), totalizando trinta diferentes situações. Paraos PCMs RT 4, RT 35, RT55 e RT82, aumentando-se o T de 10 oC para 20 oC e de 10 oC para 30 oC, para frações líquidas entre 0,4 e 0,8, a redução média dos tempos de fusão foide, aproximadamente, 55,8% e 71,8% e os incrementos médios no fluxo de calor foram de 63% e 111 %, respectivamente. Para o RT35HC, as reduções médias nos tempos de fusão foram de 51,6% e de 67,8%, para a mesma faixa de fração líquidae mesmos T. O RT35HC, quando comparado com o RT 35, possui calor latente de fusão 41,1% maiore os seus tempos de fusão são entre 100% à 134% superiores, dependendo do T utilizado. / Several residential, commercial and industrial applications focused on thermal management have their operating costs reduced when a thermal energy storage system is incorporated to them. This type of system can provide, can, for example, absorb thermal energy from solar source, heat reuse from industrial process or even from electrical power (during the time this is less expensive) and release it at a time that these heat sources are not present and the electrical power, if used, would be more expensive.The Phase Change Materials (PCMs), due to their high latent heat of fusion, are materials that represent a viable alternative to the implementation of thermal energy storage systems. However, many PCMs have not had their characteristics and fluid dynamics properties sufficiently investigated. Thus, this paper presents a numerical study of RT phase change materials family, inside cylindrical cavities, aiming at the thermal energy storage trough latent heat (LHTES). The study was conducted through a CFD numerical simulation, with ANSYS Fluent software. The numeric model adopted is two-dimensional and is composed by mass conservation, movement amount and energy equations. In addition, the enthalpy-porosity modeling technique was used. The computational mesh is hexaedric, with refinement along the walls of geometry and at the interface area between the PCM and air. The model was validated with numerical and experimental results available in the literature, achieving good results. The fusion process of five different PCMs (RT 4, RT 35, RT 35 HC (high capacity), RT 55 and RT 82) was evaluated, each one of them with three temperature ranges (T= 10, 20 e 30 °C). Furthermore, for T=10 °C, the PCMs RT 27, RT 35, RT 35 HC and RT 82 were tested for five different values of C constant (Mushy Zone) totaling thirty different situations. For PCMs RT 4, RT 35, RT 55 and RT 82, increasing T from 10 oC to 20 oC and from 10 oC to 30 oC, for liquid fraction between 0,4 and 0,8, the average reduction in fusion time were, approximately, 55.8% and 71.8% and the average increase in heat flow were 63% and 111% respectively. For RT 35 HC, the average reductions in fusion time were 51.6% and 67.8% for the same liquid fraction range and same T. The RT 35 HC, when compared to RT 35, has latent heat of fusion 41.1% greater and its fusion times are between 100% to 134% greater, depending on T used.