*5.2. Revision of the Strucure*

The minimization of total costs of the distribution system development in relation to one year (installation and operating RES and energy storages) is the objective function. Simulations are performed using a network consisting of eleven nodes, where the node number one represents the transmission system and the rest of the nodes represent the distribution system. In nodes 2–11, generation units and ES can be connected. The connection between nodes is represented by resistance and line capacities. The generation from RES is calculated as a product of the RES rated power, current power utilization level (according to the generation profile), number of units and minus energy curtailment. It is also possible that energy can be stored in an energy storage, which is connected to the nodes.

#### **6. Results**

This section provides the simulation results presented in two parts that compare approaches to the development of distribution systems. The first part displays capacity structure for each scenario and the second one displays the overall cost of system development. In each part, the results consist of three charts that present the results for a different share of energy from RES in total demand. All of the results are obtained using FICO®Xpress v. 8.6. optimization software and all graphs are created using Microsoft Excel 365.

Based on Figures 4–6, it can be seen that additional tools to RES sizing and allocation, like energy curtailment (EC) allocation or energy curtailment, allows a user to install more wind turbines, which are the cheapest renewable energy sources, without violating grid technical standards. Energy storages shift energy from one moment to another, which prevents the over-generation from RES. Energy curtailment, on the other hand, fits the generation profile to demand.

**Figure 4.** Structure of capacity for main scenarios—1.

**Figure 5.** Structure of capacity for main scenarios—2.

**Figure 6.** Structure of capacity for main scenarios—3.

Based on Figures 7–9 (all costs are compared to the highest one which is for 50% share for RES with RES sizing and allocation only), it can be observed that the combination of RES sizing and allocation and another additional tool reduces the overall cost of the distribution system development (at least 12% for 30% share). It can also be seen that, together with an increasing share of energy from RES in total demand, the energy curtailment became more efficient than energy storages.

**Figure 7.** Costs for main scenarios—1.

**Figure 8.** Costs for main scenarios—2.

**Figure 9.** Costs for main scenarios—3.

In Table 4, computation time and the number of variables are displayed for each of the analyzed scenarios.


**Table 4.** Computation time and number of variables.
