Techno-economic benefits of augmenting solar technologies into an existing geothermal plant in Türkiye

Geothermal–solar hybridization is evaluated for the 80 MW el Kizildere 2 (KZD2) triple-flash geothermal power plant with a binary ORC bottoming cycle in Türkiye. This paper develops a high-resolution simulation model validated against 2023 operational data and assesses three solar augmentation pathways: (i) PV to offset auxiliaries, (ii) concentrating solar thermal (CST) via parabolic trough collectors (PTC), and (iii) PTC with indirect molten-salt thermal energy storage (PTC + TES). Economic performance was evaluated under both a fixed feed-in tariff (FiT) and an open-market framework using normalized hourly prices derived from 2016–2020 market data. PV offsetting auxiliary consumption increases net electricity production by up to 7.4%. For CST cases, dominant gains arise from using solar heat to preheat the cooler KZD1 supplementary stream such that the combined inlet mass flow and temperature approach design conditions. The selected PV + PTC hybrid configuration increases annual electricity generation by 17.5%, with a levelized cost of additional electricity (LCOAE) of 3.61 c$/kWh, while PV + PTC+TES raises the annual yield by 28.0%, at an LCOAE of 7.27 c$/kWh. The increase in open-market revenue slightly exceeds FiT outcomes due to alignment with higher-priced hours (17.5% vs. 18.4% for PV + PTC; 28.0% vs. 28.7% for PV + PTC+TES). Mixed-framework results indicate discounted payback within five years for PV + PTC when the FiT remains applicable for five years, followed by an open-market scenario with a $100/MWh ceiling, while higher ceiling prices strengthen the case for TES. Overall, PV + PTC emerges as the most cost-effective near-term option, with TES adding value under price volatility and improved dispatch strategies.