Increasing variable renewable generation penetrations will cause increased cycling operation for conventional generating plants. Not all of these plants are necessarily well suited to such operation. Traditional long-term generation planning frameworks often neglect these operational characteristics and therefore do not reflect the operational constraints and costs associated with cycling of generating plants. Using a detailed generation dispatch model in PLEXOS, this study assesses the potential impact of short-term operational constraints and costs on future ‘high renewable’ generation portfolios obtained from a long-term portfolio planning framework. A case study of the Australian National Electricity Market (NEM) with different renewable penetrations, ranging from 15% to 85%, suggests that the technical and cost impacts associated with the operational constraints modelled are moderate even at high renewable penetrations. The extent of the impacts also depends particularly on the level of carbon price and the mix of generation technologies within the portfolios.