The microgrids can function as a single controllable system in a grid-connected or islanded operation mode. The transition from grid-connected mode to islanded mode can result in microgrid excess generation or demand, which must be spilled or curtailed. This paper proposes an optimization model for optimizing the microgrid operations accounting for distributed energy resources (stochastic generation and time-varying demand), as well as microgrid operation constrains. The objective is to minimize the microgrid operational costs considering the classical generation capacities and exchanged power with the upstream grid, as well the operational constraints. The analyzed microgrid is composed of a thermal engine, a photovoltaic system, an electrochemical storage system, critical and interruptible loads. The deterministic and stochastic optimization model were formulated, and each optimization model is tested in various case studies considering the different operational states of the microgrid
This paper analyses the impact on renewable energy sources integrated into the Romanian power system on the electrical network operation considering the reduction of electricity consumption with respect to the 1990s. This decrease has led to increased difficulties in integrating the renewable energy sources into the power system (network reinforcements), as well as issues concerning the balance of production/consumption. Following the excess of certain proportions of the energy mix, intermittent renewable energy sources require the expansion of networks, storage, back-up capacities and efforts for a flexible consumption, in the absence of which renewable energy sources cannot be used or the grid can be overloaded. To highlight the difficulty of connecting some significant capacities installed in wind power plants and photovoltaic installation, the paper presents a case study for Dobrogea area that has the most installed capacity from renewable energy sources in operation.
In the last years, the conducted studies for connecting renewable energy sources with small installed capacity to the electrical grid highlighted the importance of the grid characteristics and on the technical conditions required for the equipments. The operation of wind farms in the electrical system is restricted by its capacity to absorb the produced power and to ensure the required adequacy. The propagation of voltage fluctuations in the electrical system, where wind farms are connected, is of high importance in order to assess their power quality impact
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