Lake breeze-driven effects on cloudiness over furnas hydropower reservoir: their implications for floating photovoltaic energy

Abstract

Brazil's energy sector experienced a significant blackout on August 15, 2023, due to voltage instability caused by inconsistencies wind and solar forecasts. From April 2024 to March 2025, Brazil curtailed 18.3 TWh yr-1 of wind and solar energy, equivalent to 2.6% of total electricity generation. Wind curtailment accounted for 11.9% of total wind generation, and solar for 6.3%. Curtailment for reliability reasons (CNF) reached 8.3 TWh yr-1, corresponding to 45.5% of the total curtailed energy. To overcome this energy curtailed, hydro and thermopower are dispatched to stabilize the system. A promising alternative has been the installation of floating PV modules on flooded areas of hydropower plants (HPP) reservoirs. A multi-source observational approach was used to evaluate the influence of the lake-breeze (LB) circulation on cloud cover over the Furnas HPP reservoir, Brazil. Moreover, this study employs a GIS-based approach, leveraging geophysical data, to assess PV potential in both on-reservoir (over the water surface) and off-reservoir (over land) areas. A simplified hydro-PV hybrid model simulates water level dynamics under various implementation scenarios, demonstrating significant water savings and reduced seasonal variability. Seasonally, the on-reservoir weather mast recorded higher solar irradiance than the off-reservoir masts. This difference was more pronounced during the afternoon of the dry season (5.3-12.7%), when the Furnas reservoir reaches critical water levels. Economic feasibility is evaluated using the Levelized Cost of Energy (LCOE), revealing that FPV systems, despite a higher LCOE (US$56.8/MWh) and superior capacity factor (17.7%) compared to land-based systems (US$49.7/MWh, 16.5%), offer improved long-term performance. Off-reservoir PV potential is estimated at 82 km², while on-reservoir potential reaches 251 km². Additionally, a floating PV system transforms unused flooded areas into productive energy sites, preserving land for agriculture and commercial activities. Keywords: Curtailment; Furnas HPP; hybrid system; floating photovoltaic system; lake-breeze.