Utility-scale photovoltaic power plants (PVPPs) are gradually being enabled to provide frequency control ancillary services (FCAS) to the grid, which typically requires them to operate in a deloaded condition to maintain an active power reserve (or generation headroom). The unpredictable nature of solar irradiance, primarily due to fast-moving and intermittent cloud cover, can potentially result in rapid variations in the plant output, making it more challenging to determine its maximum power po