###### Abstract
Issue 2 can be mitigated using CST as the solar resource peaks during summer. Moreover, geothermal can also make up for the deficiencies of CST and biomass, hence creating a synergistic hybridization. The addition of CST and biomass to the system will be performed through a topping cycle to the existing KZD-2 so that the topping cycle can operate at higher temperatures and pressures, compared to KZD-2, and thus, it is a better energetic use of these resources [7]. More details will be shared on the topping cycle approach in the Section 2. The synergistic hybridization and the benefits stemming from each RE technology are summarized in Table 1.  
The KZD-2 GPP is used as the case study in this paper as this paper is funded through the EU Horizon 2020 project, GeoSmart (Grant Agreement No. 818576); and through this project, access to high-quality and detailed data and insights regarding the operation procedures from the KZD-2 GPP was possible. Moreover, as the location of KZD-2 GPP has good solar and agricultural biomass resources [10; 11], it is possible to implement the underlying idea in KZD-2 as a case study. KZD-2 integrates triple flash and binary technologies in a single GPP [12]. At its design point, the flash part produces 60 MW\({}_{e}\), and the binary part produces 20 MW\({}_{e}\) of power. However, due to Issue 1, the total power output is reduced to approximately 55 MW\({}_{e}\)[12]. Thus, this study assumes that in each flash turbine, there is around 31% of _excess turbine capacity_. Non-Condensible Gases (NCGs) adversely affect the turbines and pipes [13], and since the NCG percentage of the High-Pressure Turbine (HPT) is 16.7 wt.% [12] as opposed to that of the Intermediate Pressure Turbine (IPT) 0.40 wt.% [12], the IPT is chosen for hybridization, which then feeds the Low-Pressure Turbine (LPT). A fuller explanation is given in Section 2. To the authors' best knowledge, there is no previous study in the open literature on the triple hybridization of CST, geothermal, and biomass. The primary example of an actual hybrid solar and geothermal plant is the Stillwater plant in the US [14]. This hybrid plant uses solar resources to deal with Issue 2. Separately, [PERSON] et al. analyzed a PTC-powered topping cycle using a steam Rankine cycle coupled to an existing binary GPP and showed that this strategy enabled the hybridization of an existing binary GPP without requiring changes to the binary GPP power block [15]. The present work strongly builds on the work by [PERSON] et al. that explored and assessed opportunities to hybridize geothermal with biomass [16]. In particular, the OR properties used in the present work are obtained from that paper. Moreover, [PERSON] et al. showed that the OR-driven topping cycle can generate additional power and supply additional steam flow to a GPP bottoming cycle to utilize the _excess turbine capacity_. [PERSON] et al. [17] and [PERSON] et al. [18] studied CST-biomass hybridization and showed a case where the CST and biomass parts generate steam concurrently, and those two steam flows run a shared steam turbine. A similar methodology is also used in this study. [PERSON] et al. also showed that by varying the biomass combustion rate, it is possible to generate a variable steam generation that can be used when the solar resources are insufficient, which also adds additional flexibility and dispatchability to the system [17]. As a summary, the literature review and how they affected this paper can be found on Figure 1. In light of this literature review, a hybrid system is designed on the TRNSYS environment so that a hybrid CST-biomass topping cycle is utilized by using a PTC field as the CST technology and OR as the biomass resource. This topping cycle generates additional power using a steam Rankine cycle by generating steam from the PTC and OR simultaneously. Furthermore, the excess heat from this topping cycle and energy using biomass supplies additional steam flow to the IPT of KZD-2 GPP, serving as the bottoming cycle.