Optimal Photovoltaic Integration for Offsetting Temperature-Dependent Auxiliary Electricity Demand in an Air-Cooled Geothermal Power Plant

Air-cooled binary geothermal power plants experience increased auxiliary demand and reduced net output during hot operating periods. This study develops a grid-connected photovoltaic (PV) sizing framework for an operating approximately 25 MW plant in the Menderes Massif, Türkiye. A measured 8760 h plant-wide auxiliary-load series, calculated from the plant’s 2025 SCADA gross and net electrical-output records, was used directly as the demand input in MATLAB (R2026a) and HOMER Pro (version 3.18.4). NASA POWER provided hourly ambient-temperature and solar-irradiance data. MATLAB performed hourly dispatch, a 0–5 MW capacity sweep in 0.25 MW increments, lifecycle-cost analysis, and sensitivity analysis, while HOMER Pro provided an independent cross-platform comparison. Under the adopted 2025 scenario assumptions (PV CAPEX of $733/kW and an auxiliary-offset electricity value of $0.10/kWh), the minimum Net Present Cost (NPC) occurred at 4.50 MW. This configuration supplied 6199 MWh/year directly to the auxiliary loads, corresponding to 31.4% of the 19,764 MWh annual auxiliary demand. The selected 5 MW engineering design increased direct PV utilization to 6592 MWh/year and the renewable fraction to 33.4%, while avoiding approximately 3032 t CO2/year under the adopted displacement-accounting convention. Its NPC was $19.539 million, only approximately $27,000 (0.14%) higher than the 4.50 MW minimum-NPC configuration identified within the evaluated capacity grid, with a simple payback of approximately 7.36 years. Sensitivity analysis further showed that the economically preferred PV capacity is conditional on the auxiliary-electricity value, PV CAPEX, and discount rate rather than representing a universal optimum.