OPTIMIZING THE STRUCTURE OF A HYBRID WIND-SOLAR POWER PLANT FOR BETTER UTILIZATION OF THE APPROVED TRANSMISSION NETWORK CONNECTION CAPACITY

Wind power plants (WPP) and photovoltaic power plants (PVPP) have a relatively small average annual capacity factor (CF), so they require significantly larger installed power in comparison to thermal power plants which are phasing out in the process of decarbonizing electricity generation. On the other hand, transmission network (TN) needs to be dimensioned based on the maximal power a power plant (PP) injects into the electric power system (EPS). For this reason, massive WPP’s and PVPP’s connection requires new transmission capacities (transmission lines, switching stations and transformer stations) which will enable evacuation of their generating power. Due to the small CF of renewable energy sources (RES), transmission capacities are underutilized, which increases RES development costs, and thereby the price of the electrical energy generated by these sources also increases. The underloaded high voltage transmission lines bring surpluses in generated reactive power, which causes the emergence of overvoltages in transmission network and jeopardize system reliability. The development of TN has significant negative influence on the environment, first of all due to the space occupied by the corridors of high voltage transmission lines, but also due to the high voltage hazard and acustic and electromagnetic pollution. The complementarity of time profiles of these sources makes them suitable for the development of hybrid PPs, i.e. the integrated solar and WPPs which have a single point of connection (POC) to the TN. Such objects can be, both in technical and regulatory aspects, treated as a single PP which time generation profile corresponds to the sum of generating powers of PV systems and wind generators. These PPs have a relatively small number of hours during which the injected powers equal to the sum of installed powers of PV systems and wind generators occur because the probability of occurrence of strong winds at the same time as high insolations is small. This fact enables us to optimize the required injection power approved for the POC to significantly smaller value than the sum of installed powers on inverter terminals of photovoltaic systems and wind generators. This way utilization of TN infrastructure can be significantly improved in comparison to the independent operation of PVPP and WPP. The current regulation requires new RES PPs to install the balancing capacities which installed power and energy capacity depend on the approved power at the POC of the PP to the TN [1]. The development of hybrid wind-solar PPs can reduce the required approved connection power, and thereby the also the required balancing capacity of the PP which reduces specific costs of the PP development. In this paper, a model for optimizing the installed powers of WPP and PVPP for the given value approved power at the POC to the TN in order to achieve, for certain level of unused energy of the PP, the maximal total annual energy the PP injects into the network.