• Energy Research

In the eve of power system decarbonization, the balancing mechanisms are becoming crucial to maintain continuous operation of the system. The stochastic nature of wind and solar units requests more balancing energy and it affects prices on both energy and balancing markets. This paper will try to address correlation between stochastic system variables and balancing energy volumes and prices. System variables observed are: consumption, wind and solar generation, net consumption and net consumption error.

Battery energy storage systems (BESS) and renewable energy sources are complementary technologies from the power system viewpoint, where renewable energy sources behave as flexibility sinks and create business opportunities for BESS as flexibility sources. Various stakeholders can use BESS to balance, stabilize and flatten demand/generation patterns. These applications depend on the stakeholder role, flexibility service needed from the battery, market opportunities and obstacles, as well as regulatory aspects encouraging or hindering integration of storage technologies. While developed countries are quickly removing barriers and increasing the integration share of BESS, this is seldom the case in developing countries. The paper identifies multiple case opportunities for different power system stakeholders in Croatia, models potential BESS applications using real-world case studies, analyzes feasibility of these investments, and discusses financial returns and barriers to overcome.

This is the second paper of a two-paper series on smart e-mobility. The concept defined in the first paper is further elaborated and mathematically formulated in here. A case study is conducted to evaluate the differences between the proposed electric-vehicle-based and the existing charging-station-based emobility systems. Each of the four issues identified in the first paper are individually examined and omission of corresponding constraints are analyzed and quantified.

In the light of power system decarbonization, electric vehicles are becoming an important tool to bridge the gap between traditional and low- carbon power systems. If aggregated, electric vehicle’s fleet can provide flexibility to system operator. Recent literature defines aggregators as electric vehicle charger aggregators which collides with the conventional way of observing electric vehicles, as stationary chargers with connected loads/vehicles. This paper observes them as mobile batteries, not chargers. Therefore, new concept of electric vehicle battery aggregator has been defined which exploits their mobility. Battery aggregator has more information about vehicle’s behavior and can maximize their flexibility provision regardless when and where they charge. New concept brings benefits to all system participants from electric vehicle owners, aggregators, and system operators to society altogether.

Ancillary services used for active power balancing are called balancing services or operating reserves and their provision is vital for maintaining power system frequency at the nominal value. In a deregulated environment, where generation is unbundled from transmission and distribution operations, independently owned generating companies may elect to provide operating reserves. However, it is not easy to calculate the exact cost of reserve provision and, therefore, bid for it accurately. Although the cost efficiency of reserve provision can be improved by co‐optimising energy and reserve markets, generating companies can still encounter monetary losses caused by the provision of reserve. Currently, these losses are compensated based on ex‐post calculations. Hence, current energy and reserve prices do not adequately factor in the ex‐post compensation caused by reserve provision. This study proposes an energy and reserve co‐optimisation with an explicit consideration of two compensation mechanisms, i.e. lost opportunity and uplift payments. The problem is structured as a bilevel model. The upper level is a mixed‐integer unit commitment problem and the lower level is a continuous economic dispatch problem. The case study shows that the proposed model increases market efficiency.

As the share of integrated renewable energy sources (RES) increases, traditional operation principles of the power systems need to change in order to maintain reliable and secure service provision, on one hand, and minimal cost and environmentally friendly electricity generation on the other. The challenge of alleviating additional uncertainty and variability brought by new sources to the system operation is seen as defining both flexibility capacities and flexibility requirements through provision of multiple services. In this context the role of emerging technologies, such as electric vehicles (EV) and energy storage (ES), is recognized through their active participation in providing both energy and reserve service. This paper elaborates on the benefits of active EV participation in multiple system services through various charging strategies. The presented mixed integer linear programming (MILP) unit commitment problem (UC) considers the capability of EV to provide primary, secondary and tertiary reserve as well as energy, however the focus is put on the benefits of EV providing spinning reserve services. The results clearly show benefits of multiple EV role to that of providing energy only. In addition the paper analyses multiple power systems, with regards to their energy mix, and recognizes how integration of EVs reflects on power system flexibility through metrics expressed as operational cost, environmental benefits and reduced wind curtailment.

Integration of renewable energy sources as one of the pillars of the power system decarbonization efforts is making a significant progress. However, large shares of renewables require additional flexibility to keep the system stable. Battery storage was identified as one of the solutions to restore the grid balance in short timeframes, from day-ahead to real time. Currently, the research community is trying to find an adequate technology for longer duration energy storage. Hydrogen, as an energy carrier, appears as a good choice for such task. Apart from hydrogen energy storage potential, it can also be used to implement power-to-gas technology able to mitigate renewable energy curtailment through the process of electrolysis. The produced hydrogen gas can be either used to partially decarbonize the natural gas grids or simply sold as hydrogen fuel. The main novelty of this paper is the creation of a mathematical model of a renewable power plant coupled with a battery storage and a hydrogen facility for trading in three day-ahead energy markets, i.e. electricity, natural gas and hydrogen, plus in the power balancing market subject to the imbalance settlement mechanism. This approach enables a long-term profitability analysis of different renewable, battery and hydrogen architectures (hydrogen energy storage, power-to-gas and their combination) and their participation in different markets. The results indicate that the battery energy storage provides balancing services to the transmission system operator almost exclusively, while it never provides balancing for its own imbalance needs, since this option is less financially attractive. The electrolyzer and the fuel cell operate at least one third of the year, depending on the observed case, and often provide a reserve. When considering the hydrogen market, the electrolyzer operates almost the entire year due to lucrative hydrogen prices. Both the battery storage and the hydrogen tank perform arbitrage in the day-ahead market, where the battery optimizes its operation on an hourly basis (short-term) and the hydrogen tank on a daily basis (medium- to long-term).