With global climate change as the main driver, there is an increase towards including more variable renewable energy (VRE) sources in the electricity mix. Energy production from utilizing the photovoltaic effect, or PV power, is increasing rapidly and is visioned to cover 5 – 10 % of Sweden’s electricity demand in 2040. In addition to rooftop PV production, large- scale PV production in the form of ground-mounted PV parks is gaining ground. A higher share of VRE in the power system creates new challenges as to uphold the power system stability. For a PV park owner, achieving a preferable economic outcome is also a challenge, as the variable electricity output may not match electricity demand. Therefore, combining a PV park with an energy storage, which can store the PV production energy, is seen as a favorable solution. This way, the variability of the electricity production can be reduced and the stored energy in the battery can be used for services benefitting both the PV park owner and the power grid. This study aims to explore the economic potential of combining a PV park with an energy storage. This is achieved by simulating a lithium-ion (Li-ion) battery storage combined with PV production modeled after a 3.5 MW PV park located in Fyrislund, Uppsala. Five cases with individually differing approaches are simulated, exploring how so-called service stacking can be applied with a battery. The investigated services included in the cases are 1) lowering the cost of connecting the PV park to the power grid, 2) lowering the cost of feeding in energy to the power grid, 3) increasing the revenue of selling electricity on the Nord Pool spot market, 4) increasing the revenue by performing energy arbitrage, 5) increasing the revenue by participating in the primary frequency regulating markets to help stabilize the 50 Hz grid frequency. The cases are evaluated by calculating the net present value (NPV) of the system over 10 years with an annual discount rate of 5 %. Battery capacities ranging from 0.1 MWh/0.1 MW to 8 MWh/2 MW are tested. The system configuration achieving the highest NPV occurs when all services are performed, and a 0.13 MWh/0.1 MW battery is used. This NPV is also higher than the NPV when not including a battery in the system. Conclusions include that the spot price impacts the choice of battery capacity to a high extent and that the battery investment cost motivates using a smaller-sized battery.

Le placement de production (UC pour unit commitment) est une famille de problèmes d'optimisation qui déterminent l’état et la puissance de consigne des groupes de production pour satisfaire la demande électrique à moindre coût. Traditionnellement, une contrainte de sûreté détermine un certain volume de capacité raccordée disponible, appelé la réserve, destinée à gérer l'incertitude. Néanmoins, dans les petits systèmes la contrainte de réserve fixe peut entraîner dans certains cas une violation du critère N-1 bien que le volume de réserve minimale soit respecté. Plus récemment, la part croissante de production variable à partir de sources renouvelables (ENR) peut conduire à des programmes d’appel qui ne garantissent plus la sûreté même dans les grands systèmes.Pour y faire face, différentes techniques d'atténuation des impacts ont été proposées telle que la révision des modèles de placement de la production pour inclure une meilleure représentation de la dynamique du système. Cette sous-famille des problèmes UC est formellement définie dans ces travaux comme le problème FCUC (frequency constrained unit commitment). Elle vise à maintenir la fréquence au-dessus d'un certain seuil, et éviter ainsi le délestage par sous-fréquence (DSF).La première partie de ces travaux identifie les défis dans la formulation du problème FCUC. D’une part, la contrainte de fréquence est fortement non-linéaire par rapport aux variables de décision du problème UC. D’autre part, elle est difficile à approcher par des fonctions analytiques. La simulation séquentielle d'un modèle UC classique et d’un modèle de réponse primaire de la fréquence est alors proposée. L’intérêt d’une formulation plus fidèle de la contrainte de sûreté est donc révélé. La deuxième partie de ces travaux étudie l'impact des ENR sur la réponse primaire de la fréquence. Le besoin de formuler des modèles de FCUC plus précis est mis en avant.La troisième partie des travaux examine le coût, les bénéfices et les limitations des modèles FCUC, basés sur des contraintes indirectes sur certains paramètres dynamiques des unités de production. Il est montré que, bien que l'application de contraintes de sécurité indirectes assure la sûreté dans certains pas horaires, l'effet inverse peut apparaître à un autre instant. Ainsi, l’efficacité des leviers dépend fortement du point de fonctionnement du système. Il en est de même pour le coût de la solution. Cette étude met en évidence la nécessité de nouvelles méthodes pour traiter correctement la contrainte sur le creux de fréquence afin d'assurer l'optimalité et efficacité de la solution.Finalement, la quatrième partie des travaux offre une nouvelle formulation du problème FCUC suivant une approche de décomposition de Bender. La décomposition de Bender sépare un problème d'optimisation avec une certaine structure en deux parties : le problème maître et le problème esclave. Dans le cas du FCUC, le problème maître propose des plans de production candidats (états des groupes) et le problème esclave assure le respect des contraintes de fréquence par le biais d'un modèle de plans sécants. Les résultats de simulation montrent que la représentation plus précise du creux de fréquence au niveau du problème esclave réduit le risque de DSF et le coût de la sécurité par rapport à d'autres modèles de FCUC. / The Unit Commitment problem (UC) is a family of optimisation models for determining the optimal short-term generation schedule to supply electric power demand with a defined risk level. The UC objective function is given by the operational costs over the optimisation horizon. The constraints include, among others, technical, operational and security limits. Traditionally, the security constraints are given by the requirement of a certain volume of on-line spare capacity, which is called the reserve and is meant to handle uncertainty, while preventing the interruption of power supply. It is commonly specified following a static reliability criterion, such as the N-1 rule.Nevertheless, in small systems the fixed, and a priori defined, reserve constraint could entail a violation of the N-1 criterion, although the reserve constraint was met. More recently, the increasing share of variable generation from renewable sources (V-RES), such as wind and solar, may lead to UC solutions that no longer ensure system security. Therefore, different impact mitigation techniques have been proposed in literature, which include the revision of UC models to provide a better representation of the system dynamics. This subfamily of UC models is formally defined in this work as the frequency constrained UC problem (FCUC), and aims to keep the frequency above a certain threshold, following pre-defined contingencies, by adding enhanced security constraints. In this work this topic is addressed in four parts.The first part identifies the main challenge of formulating the FCUC problem. Indeed, the frequency minimum, also called the frequency nadir, constraint is strongly non-linear on the decision variables of the UC model. Moreover, the behaviour of the frequency nadir regarding the binary decision variables is hard to approximate by analytical functions. Thus, a sequential simulation approach is proposed, based on a classic UC model and a reduced order model of the primary frequency response. The potential benefits of a smarter allocation of the primary reserve is revealed.The second part of this work investigates the impact of V-RES sources on the primary frequency response. The underlying processes that lead to the increase of the Under-Frequency Load Shedding (UFLS) risk are thoroughly discussed. The need of formulating more accurate FCUC models is highlighted.The third part of this work examines the cost/benefit and limitation of FCUC models based on indirect constraints over certain dynamic parameters of the generating units. A methodology is proposed that assesses the effectiveness and optimality of some existing V-RES impact mitigation techniques, such as the increase of the primary reserve requirement, the prescription of an inertia requirement, the authorisation of V-RES dispatch-down or the consideration of fast non-synchronous providers of frequency regulation services. This study showed the need for new methods to properly handle the frequency nadir constraint in order to ensure optimality, without compromising the optimisation problem’s tractability.The fourth part of this work offers a new formulation of the FCUC problem following a Bender’s decomposition approach. This method is based on the decomposition of an optimisation problem into two stages: the master and the slave problems. Here, the master problem deals with the generating unit states and the slave problem handles the frequency nadir constraints through a cutting plane model. Simulation results showed that the more accurate representation of the frequency nadir in the slave problem reduces the risk of UFLS and the security cost, with respect to other FCUC models, such as those based on inertia constraints. In addition, the optimality of the global solution is guaranteed; although the convergence of the master problem is slow, due to the well-known tailing off effect of cutting plane methods.

In order to handle the mismatch between photovoltaic (PV) electricity production and household electricity use, battery storage systems can be utilized. However, the profitability of PV-battery systems in Sweden is poor, and economic incentives for households to invest in such systems are therefore missing. Hence, it is important to improve the profitability to increase the number of PV-battery installations. The aim of this thesis is to investigate the techno-economic potential of a PV-battery system offering ancillary services, more specifically the primary frequency regulation FCR-N. Five cases of residential PV-battery installations are investigated: the first with a PV system only, the second with a PV-battery system to store surplus PV electricity, and the three other cases with PV-battery systems with the ability to regulate the grid through FCR-N to varying degrees. The results show that providing FCR-N with a PV-battery system offers a substantial techno-economic potential for the system owner. By using available battery capacity for FCR-N, the payback time for a PV-battery system can be shortened significantly. With a battery price of EUR 570 per kWh (VAT excluded) and a discount rate of 2%, the payback time for the entire system can decrease from 32 to 9 years if the battery is used for FCR-N regulation. Furthermore, the payback time for a battery storage can be shortened with FCR-N. Calculated with respect to the economic added value of a battery and with a discount rate of 5%, the payback time can decrease from over 100 years to 4 years.

The aim of master´s thesis is analysis of utilization of large-capacity battery energy storage systems, used in cooperation with facility Červený mlýn to supply ancillary services to ČEPS, a.s.. In the first part, categorisation of ancillary services is presented. Within the categorisation technical and legislative requirements on subjects providing individual services are defined, the overview of ancillary services providers is listed and the mechanisms of ancillary services procurement are elucidated. The thesis continues with an overview of accumulation technologies used in high-capacity application around the world and in Czech republic. Subsequently three technologies are presented – Li-Ion, NaS and VRB, which are considered as suitable technological solutions for given application. The last part of thesis deals with specification of parameters of the accumulation system, with selection of installation site within the facility and with description of operating modes while providing ancillary services. In order to evaluate the investment from an economic point of view, a model of sensitivity analysis is created and described and its outputs are presented and discussed at the end of the thesis.