Sweden’s municipalities are leading the green energy transition, in this study, a techno-economic evaluation was done for a number of carbon neutral scenarios for Växjö municipality’s future energy system, situated within Sweden’s projected energy demand development in 2030 and 2050. The municipality’s partially decentralized energy system relies heavily on interconnected electricity supply from the national grid, and fuels imports from other parts of Sweden. It was a matter of question: in which ways will future demand changes induce supply changes, and whether a future carbon neutral energy system will be less costly in a sustained-electricity supply condition? To answer this, a balanced energy reference system for the municipality was created from an actual energy balance, using an hour-by-hour dynamic energy analysis tool EnergyPlan. Afterward, a future energy demand projection for Växjö was stemmed from the Swedish Energy Agency (SEA) sustainable future scenarios for Sweden, based on an average inhabitant energy demand. Modelling results for Växjö carbon neutral scenarios showed that Växjö energy system will be sufficient to supply future heat demand but not electricity demand, nor transport and industrial fuels. While in the short-term being carbon neutral is more economically attainable without changes in electricity supply technologies, a projected electricity price and consumption increase, change the outcomes for a carbon neutral scenario based on Intermittent Renewable Energy (IRE) to be less costly in the long term.

[pt] O aumento da penetração de fontes de energia intermitentes é uma realidade dentro da matriz energética brasileira. A utilização em larga escala de energia renovável diminui a flexibilidade operativa com a redução da inércia equivalente sincronizada no sistema, podendo colocar em risco a segurança e a qualidade do suprimento de energia dos sistemas elétricos de potência com a diminuição da capacidade de regulação de frequência. Com expectativas de crescimento acentuado, surgem os dispositivos de armazenamento de energia (Energy Storage Devices – ESD) como uma alternativa viável para contornar essas dificuldades, principalmente quando se trata de um sistema de potência isolado. Nesta dissertação, avalia-se o comportamento dinâmico do sistema elétrico do estado de Roraima, através de uma metodologia desenvolvida para quantificar a penetração de energia renovável intermitente em sistemas isolados. Avalia-se também como a utilização de dispositivos de armazenamento de energia podem contribuir para o controle de frequência, observando as vantagens que tais dispositivos podem acarretar nesse sistema. A construção do Mapa de Decisão pode auxiliar as análises tanto na etapa de planejamento como na fase de programação e operação dos sistemas. Nas simulações realizadas foi possível constatar que a utilização de ESD pode promover um aumento significativo na penetração de usinas renováveis intermitentes, como eólica e solar fotovoltaica, em sistemas de potência isolados / [en] The increase in the penetration of intermittent energy sources is a reality within the Brazilian energy matrix. The large-scale use of renewable energy decreases the operational flexibility with the reduction of the equivalent inertia synchronized in the system, which can endanger the safety and quality of the energy supply of electric power systems with the reduction of the frequency regulation capacity. With expectations of sharp growth, energy storage devices (ESD) appear as a feasible alternative to overcome these difficulties, particularly when it comes to an isolated power network. In this dissertation, the dynamic assessment of the electrical system of the state of Roraima is evaluated, using a methodology developed to quantify the penetration of intermittent renewable energy in isolated systems. It is also evaluated how the use of energy storage devices can contribute to frequency control, observing the advantages that such devices can bring to this system. The construction of the Decision Map can assist the analyses during the planning, programming and operation phases. In the simulations carried out, it was possible to verify that the use of ESD can promote a significant increase in the penetration of intermittent renewable plants, such as wind and solar photovoltaic, in isolated power systems.

The growing share of installed wind power in the Swedish electricity system has caused concerns whether the available regulating power will be sufficient. Several studies have examined the need of regulating power using both statistical and modelling approaches. However, there is a risk that some aspects of the short-term regulation of hydropower might have been missed. By using one of Vattenfall’s hydropower planning tools, the short-term operation of The Lule River has been simulated with an increasing penetration of wind power. The tool includes detailed models of reservoirs, generating units including efficiency curves and start/stop costs. By introducing a day-by-day simulation with a seven-day window price forecast, updated with a new wind forecast for each iteration, a 21-days scenario has been simulated. Transmission limits are disregarded and the thermal production is reduced with the average wind production. To quantify and compare the regulation capacity, the regulation factor is introduced. It reflects the ability to utilise high-price hours and considering that the need of regulating power for the short-term perspective is reflected in the price it will also reflect the regulation capacity. It is shown that the regulating factor is correlated to the discharge factor,whichis the relation between the maximum discharge to the average statistical discharge for a plant. A high discharge factor provides the flexibility to utilise the fluctuations in price. The discharge factor is adapted to the plants placement in the reach, accounting for both reservoirs located upstream and downstream, especially for The Lule River which has been designed to regulate for the fluctuations in the load. The flexibility required by the rest of the Nordic rivers is quantified for future studies. It is concluded that The Lule River is able to meet some of the fluctuations of wind power production due to the overcapacity ininstalled power. The production can, at the expense of decreased efficiency of the generating units, alter the production to suit a more fluctuating price.It is important to emphasise that The Lule River alone cannot balance a large penetration of wind power. To fully take into account the effects of a large penetration of wind power the study must be expanded to include more scenarios. The study should include different types of hydrological prerequisites and the seasonal variations in power production as well as additional rivers.

Cette étude s’intéresse à la conception systémique intégrant simultanément les questions de dimensionnement et de gestion optimale de l'énergie. Le système étudié concerne un procédé de pompage intégrant un processus de dessalement d’eaux saumâtres alimenté par des sources de puissance hybrides renouvelable incluant un minimum de stockage électrochimique. Ce cas d’étude appartient à une classe typique de systèmes autonomes alimentés par des sources intermittentes dont profil de puissance a une forme "donnée" : « selon les conditions climatiques (ensoleillement, vent), avec un minimum de stockage d’électricité, la puissance offerte doit être convertie ou stockée hydrauliquement sous peine d’être gaspillée ». L'influence des conditions d'environnement et la robustesse du processus d’optimisation est enfin aussi discutée dans cette thèse. Deux types de modèles mathématiques, dynamiques et quasi-statiques, sont mis en œuvre pour décrire l'ensemble du dispositif. Le système est tout d’abord modélisé dynamiquement par Bond Graphs. Pour une simulation plus rapide, plus adaptée à l’optimisation globale du système, un modèle quasi-statique est créé pour être simulé dans l'environnement Matlab. Pour de tels dispositifs, étant donné une certaine puissance offerte au fil du vent et du soleil, trouver le point optimal de fonctionnement à chaque période consiste en un partage de puissance entre les sous systèmes de pompage et de traitement de l’eau : ce processus est plutôt complexe compte tenu des non linéarités (courbes rendement – puissance) et de la présence de nombreuses contraintes relatives aux limitations de puissance des pompes, aux conditions de niveau des réservoirs, ainsi qu’aux limitations de pression et de débit dans les processus hydrauliques (pompes osmoseur). Nous montrerons qu’il n’est pas si trivial de choisir une fonction objectif qui assure simultanément la performance et la robuste du système vis-à-vis des conditions d’environnement : une fonction objectif robuste quel que soit le profil de puissance des sources est ainsi proposée pour mettre en œuvre une gestion optimale de l’énergie. Le problème d’optimisation étant posé sous forme standard, consistant en la maximisation d’une fonction objectif sous contraintes, des approches d’optimisation efficaces par programmation non linéaire sont employées. La question du dimensionnement et son couplage à la gestion énergétique est finalement étudiée. En particulier, l’intérêt de la modularité des systèmes, considérant plusieurs pompes connectées en parallèle pour la même fonction, est investigué. / This study focuses on systemic design, integrating simultaneously issues of sizing and optimal energy management. The system under study consists of a pumping process including a brackish water desalination system fed by hybrid renewable power sources with minimum electrochemical storage. Such a device belongs to the class of “autonomous systems” supplied by intermittent sources whose power profile has a “given” waveform: “with minimum electrical storage, power has to be converted, stored in water tanks, or wasted following climatic (sun, wind) conditions”. Influence of environment conditions and robustness of the optimization process is then also discussed in this thesis. Both dynamic and quasi static models are implemented for representing the whole system. The device is firstly modeled dynamically by Bond Graph methodology. For faster simulations, which are more suitable for system optimization, a quasi static model is created to be simulated in the Matlab environment. For such systems, given a certain source power, finding optimal operation point at each period consists of a power sharing between all pumping devices: it is a complex process with huge nonlinearities (efficiency vs power curves) and with many constraints as for the limitation of pump powers, tank level conditions, or pressure and flow limitations in hydraulic network and pumping devices. It is not so trivial to define an objective function which ensures system performance and robustness versus environment conditions: a convenient objective function, whatever the input power profile, is then proposed to implement the optimal management. The optimization problem being mathematically expressed, consisting of objective function maximization under constraints, efficient optimization methods by non linear programming are implemented. The issue of sizing and its coupling with system management efficiency is finally studied. In particular, the interest of modular operation with several pumps connected in parallel is also concerned in this research.

Introducing more intermittent renewable energy sources in the energy system makes the role of balancing power more important. Furthermore, an increased infeed from intermittent renewable energy sources also has the effect of creating lower and more volatile electricity prices. Hence, investing in balancing power is prone to high risks with respect to expected profits, which is why a good representation of electricity prices is vital in order to motivate future investments. We propose a stochastic multi-factor model to be used for simulating the long-run dynamics of electricity prices as input to investment valuation of power generation assets. In particular, the proposed model is used to assess the impact of electricity price dynamics on investment decisions with respect to balancing power generation, where a combined heat and power plant is studied in detail. Since the main goal of the framework is to create a long-term representation of electricity prices so that the distributional characteristics of electricity prices are maintained, commonly cited as seasonality, mean reversion and spikes, the model is evaluated in terms of yearly duration which describes the distribution of electricity prices over time. The core aspects of the framework are derived from the mean-reverting Pilipovic model of commodity prices, but where we extend the assumptions in a multi-factor framework by adding a functional link to the supply- and demand for power as well as outdoor temperature. On average, using the proposed model as a way to represent future prices yields a maximum 9 percent overand underprediction of duration respectively, a result far better than those obtained by simpler models such as a seasonal profile or mean estimates which do not incorporate the full characteristics of electricity prices. Using the different aspects of the model, we show that variations of electricity prices have a large impact on the investment decision with respect to balancing power. The realized value of the flexibility to produce electricity in a combined heat and power plant is calculated, which yields a valuation close to historical realized values. Compared with simpler models, this is a significant improvement. Finally, we show that by including characteristics such as non-constant volatility and spiky behavior in investment decisions, the expected value of balancing power generators, such as combined heat and power plants, increases. / I takt med att fler intermittenta förnyelsebara energikällor tillför el i dagens energisystem, blir också balanskraftens roll i dessa system allt viktigare. Vidare så har en ökning av andelen intermittenta förnyelsebara energikällor även effekten att de bidrar till lägre men också mer volatila elpriser. Därmed är även investeringar i balanskraft kopplade till stora risker med avseende på förväntade vinster, vilket gör att en god representation av elpriser är central vid investeringsbeslut. Vi föreslår en stokastisk flerfaktormodell för att simulera den långsiktiga dynamiken i elpriser som bas för värdering av generatortillgångar. Mer specifikt används modellen till att utvärdera effekten av elprisers dynamik på investeringsbeslut med avseende på balanskraft, där ett kraftvärmeverk studeras i detalj. Eftersom huvudmålet med ramverket är att skapa en långsiktig representation av elpriser så att deras fördelningsmässiga karakteristika bevaras, vilket i litteraturen citeras som regression mot medelvärde, säsongsvariationer, hög volatilitet och spikar, så utvärderas modellen i termer av årlig prisvaraktighet som beskriver fördelningen av elpriser över tid. Kärnan i ramverket utgår från Pilipovic-modellen av råvarupriser, men där vi utvecklar antaganden i ett flerfaktorramverk genom att lägga till en länkfunktion till tillgång- och efterfrågan på el samt utomhustemperatur. Vid användande av modellen som ett sätt att representera framtida priser, fås en maximal över- och underprediktion av prisvaraktighet om 9 procent, ett resultat som är bättre än det som ges av enklare modellering såsom säsongsprofiler eller enkla medelvärdesestimat som inte tar hänsyn till elprisernas fulla karakteristika. Till sist visar vi med modellens olika komponenter att variationer i elpriser, och därmed antaganden som används i långsiktig modellering, har stor betydelse med avseende på investeringsbeslut i balanskraft. Det realiserade värdet av flexibiliteten att producera el för ett kraftvärmeverk beräknas, vilket ger en värdering nära faktiska realiserade värden baserade på historiska priser och som enklare modeller inte kan konkurrera med. Slutligen visar detta också att inkluderandet av icke-konstant volatilitet och spikkarakteristika i investeringsbeslut ger ett högre förväntat värde av tillgångar som kan producera balanskraft, såsom kraftvärmeverk.