A source-grid-load cross-area coordinated optimal dispatch model based on IGDT and a wind-photovoltaic-photothermal system is suggested to handle the problem of renewable energy consumption under large-scale wind power and photovoltaic grid connections. Firstly, the peak flexibility of a wind-photovoltaic-photothermal co-generation system is investigated to improve the utilization rate of wind and solar resources. To increase the model’s efficiency and accuracy, the alternating direction multiplier method (ADMM) is used. Finally, arithmetic examples are utilized to examine and contrast how the system dispatch cost changed under risk-averse and risk-seeking strategies. It also examines how the installed ratio of concentrated solar power plants affects the overall cost of the system. The findings demonstrate that the suggested model may achieve a coordinated optimization of the source, grid and load while lowering system operation costs.