Rozprawy doktorskie na temat „Underground thermal storage”

Underground Thermal Energy Storage (UTES) systems are energy conservation systems used to buffer the difference between energy supply and energy demand and therefore represent an interesting alternative to energy depletion. At the same time they contribute to cut CO2 emissions by a reduction of energy demand from traditional heating/cooling systems. Even though UTES are relatively environmental friendly solutions they are not completely free of impacts on the underground. They have possible hydro(geo)logical, chemical, thermal or microbiological impacts that are obviously strongly interrelated. The risks of UTES to groundwater quality are insufficiently known, and policies to address this uncertainty are still lacking. In order to improve the understanding and knowledge of UTES techniques, this study aimed to perform a Life Cycle Analysis (LCA) on two different UTES systems: Aquifer Thermal Energy Storage (ATES) and Borehole Thermal Energy Storage (BTES). Even if at present LCA has been mainly performed on products of the industrial and building sector it can be a useful instrument to determine the sustainability of these two possible alternatives of underground exploitation.

The United States Department of Energy indicates that 97% of all homes in the US use fossil fuels either directly or indirectly for space heating. In 2005, space heating in residential homes was responsible for releasing approximately 502 million metric tons of carbon dioxide into the atmosphere. Meanwhile, the Sun provides the Earth with 1000 watts per square meter of power everyday. This document discusses the research of modeling a system that will capture and store solar energy during the summer for use during the following winter. Specifically, flat plate solar thermal collectors attached to the roof of a single family home will collect solar thermal energy. The thermal energy will then be stored in an underground fabricated Seasonal Solar Thermal Energy Storage (SSTES) bed. The SSTES bed will allow for the collected energy to supplement or replace fossil fuel supplied space heat in typical single family homes in Richmond, Virginia. TRNSYS is a thermal energy modeling software package that was used to model and simulate the winter thermal load of a typical Richmond home. The simulated heating load was found to be comparable to reported loads for various home designs. TRNSYS was then used to simulate the energy gain from solar thermal collectors and stored in an underground, insulated, vapor proof SSTES bed filled with sand. Combining the simulation of the winter heat demand of typical homes and the SSTES system showed reductions in fossil fuel supplied space heating in excess of 64%.

Coupling effects between thermal, hydraulic, chemical and mechanical (THCM) processes for rock materials are one of major issues in Geological engineering, Civil engineering, Hydrology, Petroleum engineering, and Environmental engineering. In all of these fields, at least two mechanisms of THCM coupling are considered. For an example, thermal, hydraulic, and mechanical coupling effects are important in Geological engineering and Civil engineering. The THM coupling produces effects on underground structures, since the underground structures are under influences of geothermal gradient, groundwater, gravitational stresses, and tectonic forces. In particular, underground repository of high-level nuclear waste involves all four of the THCM coupling processes. Thermo-hydro-mechanical coupling model for fractured rock media has been developed based on micromechanical fracture model [Kemeny 1991, Kemeny & Cook 1987]. The THM coupling model is able to simulate time- and rate-dependent fracture propagation on rock materials, and quantify characteristics of damage by extensile and shear fracture growth. The THM coupling model can also simulate coupled thermal effects on underground structures such as high-level nuclear waste repository. The results of thermo-mechanical coupling model are used in conducting a risk analysis on the structures. In addition, the THM coupling model is able to investigate variations of fluid flow and hydraulic characteristics on rock materials by measuring coupled anisotropic permeability. Later, effects of chemical coupling on rock materials are investigated and modified in the THM coupling model in order to develop a thermo-hydro-chemo-mechanical coupling model on fractured rocks. The THCM coupling model is compared with thermal, hydraulic, chemical, and mechanical coupling tests conducted at the University of Arizona. The comparison provides a reasonable prediction for the THCM coupling tests on various rock materials. Finally, the THCM coupling model for fractured rocks simulates the underground nuclear waste storage in Yucca Mountain, Nevada, and conducted performance and risk analysis on the repository.

The current environmental challenges that face the world put pressure on the heating market to move towards increased share of renewable energy sources as fuel. District heating (DH) is seen as an efficient solution to achieve this in dense urban areas. Thermal energy storage (TES) is seen as a solution to handle the increased amount of intermittent energy sources in the energy system. For the Swedish DH business a large-scale underground TES (UTES) is seen as an interesting solution partly for this reason and partly to utilise more residual heat and heat from under-utilised production facilities. However, the current complexity to invest in large-scale UTES is limiting the further development of DH. The purpose of this report is therefore to fill the current knowledge gap regarding factors needed to analyse an investment in large-scale UTES. An investment framework is presented to be used as decision support mainly for decision-makers in the DH business, but which can be interesting for other stakeholders in the district heating system (DHS). The main findings of the report are that there exists necessary circumstances for an investment in a large-scale UTES and that the criteria needed to evaluate an investment in large-scale UTES are either related to economy or environment. Further, the main function of a large-scale UTES is seasonal storage because this function creates the majority of the revenue. This revenue is created through storage of cheap heat during periods of low heat demand, which replaces expensive peak production during periods of high heat demand. Depending on the size of the created revenue, the large-scale UTES can be profitable as required by the DH companies. However, it is shown in the report that other factors also must be considered for the large-scale UTES to become profitable. Further, the uncertain future of DH poses a challenge for the evaluation of an investment in large-scale TES. The recommendations for further studies therefore focus on limiting these uncertainties through additional research and development.
De nuvarande miljöförändringar som världen står inför ställer krav på värmemarknaden att förändras till ökad användning av förnybara energikällor som bränsle. Fjärrvärme ses som en effektiv lösning för att åstadkomma detta i tätbebyggelse. Termiska energilager (TES) ses som en lösning för att hantera den ökande mängden intermittenta energikällor i energisystemet. För den svenska fjärrvärmen ses ett storskaligt underjordiskt TES (UTES) som en intressant lösning dels av denna anledning dels för att öka användningen av restvärme och värmen från underutnyttjade produktionsanläggningar. Hursomhelst så innebär den nuvarande komplexiteten att investera i storskalig UTES att utvecklingen för fjärrvärme begränsas. Syftet med denna rapport är därför att fylla den kunskapslucka som existerar gällande faktorer att analysera för en investering i ett storskaligt UTES. Ett investeringsramverk presenteras för att användas som beslutsunderlag för huvudsakligen beslutsfattare inom fjärrvärmeverksamheten, men som även kan vara av intresse för andra intressenter i fjärrvärmesystemet. De huvudsakliga upptäckterna från denna rapport är att det existerar nödvändiga förutsättningar för en investering i storskalig UTES och att kriterierna för utvärdering av en investering i storskalig UTES antingen är relaterade till ekonomi eller miljö. Vidare så är den huvudsakliga funktionen av ett storskaligt UTES säsongslagring eftersom denna funktion skapar lejonparten av inkomsten. Inkomsten skapas genom lagring av billig värme under perioder av låg efterfrågan på värme som ersätter dyr spetsproduktion under perioder av hög efterfrågan på värme. Beroende på storleken av den skapade inkomsten så kan ett storskaligt UTES potentiellt klara kravet på att vara lönsamt. Hursomhelst så visar denna rapport på att andra faktorer troligen också behöver tas hänsyn till för att ett storskaligt UTES ska bli lönsamt. Trots att det är nödvändigt så gör den osäkra framtiden för fjärrvärme det svårt att utvärdera en investering i storskalig UTES. Rekommendationerna för framtida studier fokuserar därför på att begränsa dessa osäkerheter genom ytterligare vetenskapligt stöd.

Mise au point d'un capteur solaire à air performant pour avoir des températures élevées du fluide caloporteur. Le sol constitue le réservoir de chaleur formant un accumulateur dans lequel sont enterrés des tuyaux qui constituent l'échangeur de chaleur.

Evaluation in situ des caracteristiques thermiques moyennes du sol, modelisation et experimentation d'un echangeur baionnette place dans un milieu solide, et elaboration d'un modele simplifie de predimensionnement pour le stockage multipuits. Resultats obtenus sur un site de 25 puits

La réduction des émissions de gaz à effet de serre provenant des énergies fossiles combinée à l'augmentation de la demande mondiale en énergie représente un défi majeur pour l'humanité. Nous ne pourrons le résoudre sans un recours massif aux énergies renouvelables. L'énergie solaire est l'une des formes renouvelables les plus abondantes et disponibles. Diverses techniques sont utilisées pour exploiter cette énergie, telles que les panneaux solaires photovoltaïques pour la production d'électricité et les capteurs solaires thermiques pour la production de chaleur. Récemment, une autre approche a émergé, celle des routes solaires, offrant à la fois des infrastructures de transport et des capacités de captation d'énergie solaire. Dans ce contexte, cette thèse propose l'étude et le développement d'un système couplant énergétiquement une chaussée à un bâtiment via un stockage thermique. Le concept repose sur la récupération de chaleur de la chaussée pendant les périodes chaudes, via un fluide caloporteur circulant dans un revêtement de chaussée drainant placé sous la couche de roulement. Cette chaleur est ensuite stockée au sein d'un stockage thermique composé de sable saturé en eau en sous-sol du bâtiment afin d'être mobilisée ultérieurement. Le chauffage et la production d'eau chaude sanitaire mettent en œuvre une pompe à chaleur. Un modèle thermique et énergétique a été développé pour l'ensemble du système. Les prédictions du modèle sont comparées aux résultats expérimentaux obtenus à l'aide d'un démonstrateur spécifiquement développé pour les besoins de l'étude. Les simulations annuelles montrent qu'il est possible de chauffer efficacement des maisons individuelles ou des petits collectifs répondants aux réglementations énergétiques actuelles en valorisant l'énergie thermique des routes avec un coefficient de performance moyen de la pompe à chaleur voisin de 6.5. Une étude de sensibilité du système a montré que la superficie du capteur, le volume du stockage et le lieu d'implantation ont une influence sur les performances du système
Reducing greenhouse gas emissions from fossil fuels combined with increasing global energy demand represents a major challenge for humanity. We will not be able to solve it without massive recourse to renewable energies. Solar energy is one of the most abundant and available forms of renewable energy. Various techniques are used to harness this energy, such as photovoltaic solar panels for electricity production and solar thermal collectors for heat production. Recently, another approach has emerged, that of asphalt solar collector, offering both transport infrastructure and solar energy capture capacities. In this context, this thesis proposes the study and development of a system energetically coupling a roadway to a building via thermal storage. The concept is based on recovering heat from the roadway during hot periods, via a heat transfer fluid circulating in a draining road surface placed under the wearing course. This heat is then stored in a thermal storage composed of sand saturated with water in the basement of the building in order to be mobilized later. Heating and domestic hot water production use a heat pump. A thermal and energy model has been developed for the entire system. The model predictions are compared to experimental results obtained using a demonstrator specifically developed for the needs of the study. Annual simulations show that it is possible to efficiently heat individual houses or small collectives meeting current energy regulations by using the thermal energy of the roads with an average coefficient of performance of the heat pump close to 6.5. A sensitivity study of the system showed that the surface area of the sensor, the storage volume and the location have an influence on the performance of the system

Realisation, mise au point et premieres utilisations d'un appareil triaxial nouveau, par l'introduction du parametre temperature. Utilisation pour prevoir le comportement thermique, hydraulique et mecanique d'un sol non sature, dans un contexte de stockage de chaleur dans le sous-sol

This diploma’s thesis analyzes the possibility of accumulation of thermal power plants in the Czech Republic. The thesis is divided into several parts. The first part describes the different types of storage power plants, the historical development of power storage for compressed air and the appropriateness of their location. The second part is devoted to the design of storage power plant for compressed air in South Moravia. In the next chapter, a calculation is made of all equipment storage power plant, including turbo-compressor, combustion chamber, combustion turbines, the volume of storage tanks and two heat exchangers. The last part is the economic analysis of the return on investment of such a project.

Bilan des differentes actions en genie solaire menee dans le cadre d'une mission de cooperation scientifique et technique effectuee au venezuela:deshumidification de l'air dans une installation qui utilise le potentiel thermique du sous-sol et l'energie solaire. Concentrateur solaire constitue de deux portions de spirales logarithmiques destine a servir de recepteur secondaire dans une installation de production de vapeur industrielle; amelioration des conditions de confort de l'environnement construit et elaboration des criteres de dessin d'un habitat climatique pour les conditions specifiques de chaque site; methode de dimensionnement d'un generateur solaire autonome avec stockage saisonnier

Etude de l'influence de densite, teneur en eau, temperature, et aussi des caracteristiques mineralogiques et des conditions physiques externes (accroissement de temperature, contrainte mecanique). Amelioration de la conductivite par additifs (graphite, quartz). Utilisation de modeles pour relier la conductivite a celles de chaque phase; bons resultats obtenus avec le modele geometrique (empirique) et le modele de porosite ellipsoidale

L’étude des phénomènes couplés thermo-hydro-mécaniques intéresse la communauté scientifique aujourd'hui confronté au problème du stockage des déchets. La modélisation est un outil essentiel pour prédire l'évolution complexe du milieu hôte et de ces déchets. Parmi les approches numériques existants, on distingue les approches de types éléments finis et les approches de type éléments distincts. Si la première, plus ancienne, a déjà donné lieu à de nombreux développement et applications, elle rend mal quelquefois la réalité du massif rocheux fracturé. Nous avons souhaité cette dernière approche en la rendant capable de modéliser les échanges thermiques convectifs liés à la circulation d'un fluide dans les fissures de roche. Nous suspectons en effet que ce phénomène peut être important si le gradient hydraulique est suffisamment élevé. Une étude bibliographique nous a permis de mettre en évidence les paramètres qui déterminent ce phénomène dont le principal est le coefficient de transfert thermique h entre la roche et le fluide. Les nombreuses formulations recensées ne sont pas totalement suffisantes à expliciter la réalité de ses effets. D’autres mesures, in situ et en laboratoire, s'avèrent nécessaires. Nous avons pu établir des expressions pour les termes d'échange thermique entre le fluide et la roche et à l'intérieur du fluide lui-même. Souhaitant donc modéliser le phénomène à l'aide d'une approche adaptée au milieu discontinu, notre choix s'est porte sur le logiciel UDEC (Universal Distinct Element Code) dont la structure permettait moyennant quelques modifications d'accueillir les développements envisagés. Les algorithmes de calcul sont basés sur les différences de vitesse entre les transferts thermiques convectifs et conductifs. Nous avons testé notre modèle dans le cas de l'écoulement d'un fluide froid entre 2 blocs. Dans le cas d'une modélisation thermohydraulique, les échanges thermiques calculés sont cohérents et s'accordent avec ceux calculés par une autre approche numérique. On observe en effet que la convection thermique croit avec l'ouverture hydraulique de la fracture, la vitesse du fluide et décroit avec sa viscosité. Des calculs thermo-hydromécaniques ont montré la nécessité d'alterner les calculs thermiques et les calculs hydromécaniques suffisamment fréquemment pour rendre compte de la réalité du couplage. Notre modèle a été utilisé à grande échelle et a permis également d'interpréter les anomalies thermiques mesurées sur le site géothermal du Cézallier

Until a few decades ago few people could imagine that the photovoltaic, solar thermal and other power based on renewable resources, will become a reality. Today people from all over the world on the contrary try at full blast derive benefit from of all possible available source. Using sunlight as a source of energy is first enforced only for small devices such as calculators for charging the battery, but now we are able to produced energy from the sun to supply people around the world. Of course it is not possible supply consumer sector plus firm only from performances renewable power supply. Therefore endeavour is derive benefit from classical energy production at the same time with others power supply. The basic components of photovoltaic and solar thermal power are panels. The panels are made of different materials in different shapes and sizes. During production, the resulting effect looks in addition to costs associated with production. For photovoltaic and solar thermal power plant requires sufficient sunlight. The sunshine has biggest intensity on south of ours planets. Therefore endeavour is build lump these power station just in stand with bigger intensity sunshine. One of them is just Cyprus, too.

The objective of this PhD thesis is to create a Unit Commitment and Economic Dispatch (UCED) modelling tool that can used to simulate the deterministic performance of a power system with thermal and renewable generators and energy storage technologies. The model was formulated using mixed integer programing (MIP) on GAMS interface. A robust commercial solver by IBM (CPLEX) is used as solver. Emphasis on the development of the tool has been given on the following aspects. a) Technical impacts of Variable Renewable Energy (VRE) integration. The UCED model developed in this thesis is a high resolution short-term dispatch model. It captures the variability of VRE power on the intra-hour level. In addition the model considers a large number of important real world, system, unit and policy constraints. Detailed representation of a power system allows for a realistic estimation of maximum penetration levels of VRE and the related technical impacts like cycling of generators (part-loading and number of start-ups). b) CO2 emissions. High levels of VRE penetration can potentially increase consumption of fuel in thermal units per unit of electricity produced due to increased thermal cycling. The dispatch of units in the UCED model is based on minimizing system wide operational costs the most important of those being fuel, start-up costs and the cost of carbon. Fuel consumption is calculated using technical data from Input/Output curves of individual generators. The start-up cost is calculated based on times the generator units have been off and the energy requirement to bring the unit back to hot state. Thus dynamic changes on fuel consumption can be captured and reported. c) Technical solutions to facilitate VRE integration. VRE penetration can be facilitated if appropriate solutions are implemented. Energy storage is an effective way to reduce the impact of RE variability. The UCED model includes an integrated Mixed Integer Linear (MILP) compressed air energy storage (CAES) simulation sub-model. Unlike existing CAES models, the new “Thermo-Economic” (TE) CAES model developed in this thesis uses technical data from major CAES manufacturers to model the dynamic effect of cavern pressure on both the compression and expansion sides during CAES operation. More specifically the TE model takes into account that a) a compressor discharges at a pressure equal to the back-pressure developed in the cavern at each moment, b) the speed of charging can be regulated through inlet guide vanes; higher charging speed can take place at the expense of additional power consumption, c) the maximum power output during expansion can be limited by the levels of cavern pressure; there is a threshold pressure level below which the maximum output decreases linearly with pressure. Since it uses actual power curves to simulate CAES operation, the TE model can be assumed to be more accurate than conventional Fixed Parameter (FP) models that don’t model dynamic effects of cavern pressure on CAES operation. The TE model in this thesis is compared with conventional FP models using historical market prices from the Irish electricity market. The comparison was based on the ability of a CAES unit to arbitrage energy for making profit in the Irish electricity market. More specifically a “Base” scenario was created that included the operation of a 270MW CAES unit with technical characteristics obtained from a major CAES manufacturer and assumed discharge time of 13hr. Various sensitivities on discharge time, natural gas prices and system marginal prices (SMPs) were modeled. An additional scenario was created to show the benefit on CAES profitability if the unit participated in both the energy and ancillary services markets. All scenarios were modeled using both the TE and FP CAES models. The results showed that the most realistic TE model returns around 15% less profitability across more scenarios. The reduction in profitability grows to around 30% when the cavern volume (discharge time) is reduced to half (6 hours). The latter is related to the sensitivity of the TE model on cavern pressure that is being built faster when the volume is reduced. A CAES unit won’t get a positive net present value (NPV) in Ireland under any scenario unless SMPs are greatly increased. Thus, it was shown that that existing FP CAES models overestimate CAES profitability. More accurate models need to be used to estimate CAES profitability in deregulated markets. Additionally, it might deem necessary to create additional markets for energy storage units and increase the possible revenue sources and magnitude to facilitate an increase of storage capacity worldwide. The second step of analysis involved the integration of the CAES and UCED models. The UCED model developed in this thesis was validated and applied using data from the Irish grid, a power system with more than 50 thermal generators. A vast of existent data was used to create a mathematical model of the Irish system. Such data include technical specifications and variables of thermal generators, maintenance schedules and historical solar, wind and demand data. The validation exercise was deemed successful since the UCED model simulated utilization factors of 45 out of 52 generators with an absolute difference between modeled and actual results on utilization factors of less than 6% (the absolute differences are called Delta in this thesis). In addition the results of validation exercise were compared with the results of a similar exercise where PLEXOS was the modelling tool and it was found that the results of the two models were similar for the vast majority of generators. More specifically, the PLEXOS model results showed higher deltas for the coal-fired generators compared to the UCED model. On the other hand the UCED model, reported higher delta values for peat-fired generators. The results of the PLEXOS model were slightly better for the gas-fired generators while both models reported deltas nearly zero for all oil and distillate-fired generators. Finally the model was applied to study the benefits of energy storage in Ireland in 2020 when wind penetration is expected to reach 37% of total demand. The analysis involved the development of two groups of 3 scenarios each. In the first group the main scenario also called the “Reference” was used to simulate the short-term unit (30 min step) commitment within the Irish system without storage. The results of the reference scenario were compared with two additional scenarios that assumed the existence of one 270MW CAES unit in Northern Ireland by 2020 (again the first scenario involved the TE and the second the FP CAES model). The results showed –when using the TE model- that the inclusion of one 270MW CAES unit in AI can help reduce wind curtailment by 88GWh, CO2 emissions by 150,000 tonnes and system costs by € 6 million per year. If an FP model had been used instead the reductions would be: wind curtailment by 108GWh, CO2 emissions by 270,000 tonnes and annual system costs by €13 million. Two main conclusions can be obtained from the specific set of results. The first conclusion is that storage units have a financial benefit over the whole system. Thus, when a CAES unit operates to minimize the costs of the whole system can incur substantially more benefits compared to if the CAES unit operated to maximize the individual unit’s profits as in the case presented earlier. The benefits of storage over the whole system should be accounted to make policy decisions and create incentives for investors to increase energy storage capacity in national grids. The second important conclusion is that existing CAES FP models overestimate the ability of a CAES unit to facilitate VRE penetration. More accurate TE models should be used to assess a unit’s capability to increase system flexibility. A second group of scenarios was created to simulate the benefit of CAES at even higher VRE penetration levels. In the second group the “Reference” scenario again, assumed no storage however, wind production was increased by 25%. Again the “Reference” was compared with two additional scenarios that assumed integration of 3x270MW=810MW of storage capacity in AI (one scenario used the TE model and the other the FP). The results for the TE model show that each of the 3 CAES units reduces wind curtailment by 188,000MWh, total system costs by €29 million and CO2 emissions by 180,000 tonnes. The same reductions for the FP model are 217,000MWh of wind curtailment, €25.6 million on total system costs and 180,000 tonnes of CO2. Thus, the results of the second group of scenarios show that as the installed capacity of both CAES and wind increases in Ireland a) the system-wide benefits of CAES increase and b) the differences on results between the TE and FP models become much smaller.