###### Abstract  
The usage of fossil fuel in the energy sector is the primary factor for global GHG emissions, so it is crucial to better utilize RE sources. One way to do that is to hybridize RE technologies to make up for their deficiencies while enabling a more synergistic power production. This study utilizes such an approach to hybridize the KZD-2 Geothermal Power Plant (GPP) with CST and biomass in the southwest region of Turkiye. The main motivation is to address the two main issues of GPPs--excess turbine capacities happening over the operating years and decreasing performance during hot summer months--while also increasing the flexibility of KZD-2. A topping cycle of CST-biomass is added utilizing a PTC field as the CST technology and olive residual biomass combustion as the biomass technology. The hybrid plant is simulated on TRNSYS, and the energetic data show that it is possible to generate more than 20 MW\({}_{\rm e}\) of additional power during sunny and clear sky conditions while also increasing the Capacity Factor (CF) from 69% to 74-76%. Moreover, the financial results show that the resulting LCOAE is 81.19 USD/MWh, and the payback period is five or nine years for using the YEKDEM incentive or the spot market prices, respectively. C 2024 17 5336 10.3390 12.  
replenished [4]. As the brine enthalpy decreases, the generated steam's enthalpy at the turbine inlet also decreases as manifested by lower temperatures, pressures, and, most importantly, lower mass flow rates. Hence, as GPPs age, they often increasingly have steam mass flow rates that are lower than their design point, which leads to _excess turbine capacities_ [4]. A second challenge with GPPs, especially those using Dry Cooling Towers (DCTs) as opposed to Wet Cooling Towers (WCTs), is their output tends to decrease during times of high ambient temperature due to higher condenser temperatures [5]. Since hot ambient temperatures tend to occur during the summer, the output from GPPs tends to be minimal on hot summer days. In contrast, solar energy resources tend to peak during the summer but are not available at night. Like geothermal, Concentrated Solar Thermal (CST) is a thermal energy source that uses a power block to convert heat into electricity. As an energetic opportunity, the combustion of biomass resources from agricultural waste streams can provide a thermal energy source that is flexible (i.e., it can be ramped up and down) and dispatchable (i.e., it can be turned on and off) without the need for thermal or electrical energy storage. As a challenge, agricultural waste streams tend to experience large seasonal variations that coincide with harvesting [6]. In summary, CST, geothermal, and biomass are all renewable thermal energy sources that have different strengths and weaknesses and use a power block to convert heat into electricity. The aim of this work is to develop and assess novel strategies to synergistically hybridize geothermal with CST and biomass to increase the performance of GPPs [7]. In particular, in this paper, one such hybridization scenario is presented, which involves the Kizildere-2 (KZD-2) Geothermal Power Plant (GPP), owned and operated by Zorlu Energy and located in the Southwest of Turkiye, with the addition of CST and olive residual (OR) biomass to exploit the strengths and compensate for the weaknesses of each technology and improve the overall performance of the existing GPP. The issues with GPPs can then be summarized below. 1. Issue 1: Excess turbine capacities. 2. Issue 2: Performance decreases during summer. The CST technology used in this study is the Parabolic Trough Collectors (PTCs), whereas the biomass source used is the local OR. The reasoning behind these selections is given later in the literature review. OR is found mainly between October and February when olives are harvested [8; 9]. OR can also add additional flexibility as the combustion rate can be varied when needed. Issue 1 can be addressed by supplying additional steam flow to the GPP turbines to utilize the excess turbine capacity.