Nowadays Ukraine demonstrates the highest in the world rates of signing contracts for the future connection of the RSE, but this creates great risks for the outdated energy system. The key factor is that according to the information of the National Commission for State Regulation of Energy and Public Utilities (NCSREPU), in the first quarter of 2018, 159.4 MW of generating capacities were put into operation – 54 objects of energy sector (2.4 times exceeds the generating capacities, put into operation during the same period of 2017). Objects of WPS and PVS represent 92 % of the generation capacities, put into operation and average single capacity of the energy sector objects is 3 MW. The installed capacity of WPS and PVS in Ukraine as on the middle of 2019 totally is 3653 MW these capacities have minor impact on the electric energy balance. Their deviations from the planned generation are compensated by the power cycling.
System operation in the research stresses that solar power plants and wind stations from the point of view of the stable energy supply are not reliable. Deviations from the planned daily curve is more than 450 MW at the installed capacity of
1217 MW. One more specific feature, regarding the installation of the renewable sources of energy is their non-uniform distributions on the territory of Ukraine. Thus, availability of one powerful source of up to 3 MW or several less powerful up to
0.5 MW sources, connected to one substation on the distributed electric grid (DEG) give the possibility to consider DEG as the local electric system (LES).
Especially urgent for the distributed electric grids is the problem of the reliable and sustainable energy supply. According to the decision of National Commission for State Regulation of Energy and Public Utilities (NCSREPU) of 12.06.2018 "On the approval of the procedures of the provision of the standards of energy supply quality and consumers compensation in case of the standards inobservance”, the index is determined that qualitatively characterizes the level of the electric grid reliable operation.
But taking into consideration the rates of RSE generation capacities increase, in particular PVS, it is expedient to carry out the analysis of the defined indices change in the conditions of its increase.
Unstable charter of the renewable sources of energy operation influences the operation modes of the electric grids. Instability of PVS generation is compensated by the power, supplied to DEG from the energy system. That is why, the conditions of DEG mode balancing influence the operation modes of electric energy system. In present conditions the centralized system of energy supply is responsible for the balance provision. However, changes in the mechanism of the energy market of Ukraine operation gradually take place, these changes make the owners of RSE work according to the preset schedule, in particular, introduction of penalties for in observance of the contracted daily generation schedule. For the operation according to the preset schedule, first of all, it is necessary to study the potential possibilities of the generation sources regarding the coverage of the load curve.
On the base of the statistic generation data, if the power plant operates, or on the base of the forecast data of energy generation if the power plant is not put into operation, the output information for the determination of the reserve power which must be maintained to provide the balance reliability of DEG or determination of the storage capacity, can be obtained.
The problem of determining the optimal capacity of the drive is complicated by the fact that, first, when solving it, it is necessary to take into account not only its life cycle but the number of charge / discharge cycles; third, to control the depth of discharge parameter. To date, the further increase of renewable energy sources is impossible without the use of balancing tools, and since the specificity of generating renewable energy sources is dispersed throughout the territory of Ukraine, so the storage also needs to be installed directly near the imbalance sources. However, as of today, the cost of the drive is quite high, so it would be advisable to calculate its technical and economic characteristics for a group of stations in one region, or connected to a single substation. This approach will reduce the losses in the electricity grids and improve the quality of electricity.
In the given research new solution of the actual scientific-applied problem, aimed at the improvement of energy supply reliability can be obtained, this solution is based on the transmission of the supply from the source with the ensnared generation curve on the buses of the photovoltaic power plant and determination of the storage unit capacity for the photovoltaic power plant in the conditions of the introduction of new energy market.
