From its commissioning in 2006 to the present, the Spanish Control Centre for Renewable Energies (CECRE) has been a worldwide pioneer and reference centre in the integration of renewable energies in the electrical system. In the last 15 years, CECRE has allowed a high penetration of renewable energies in Spanish electrical system by means of the supervision and control of renewable facilities, while ensuring the power supply security. This paper defines the bases of renewable energy operation in CECRE and introduces forecasting systems for renewable energies. Furthermore, this paper describes the participation of renewable energies in balancing services and congestion management. Finally, new challenges for Spanish transmission system operator (TSO) are presented for the integration of renewable energies along with the energy transition and decarbonization.