In the face of a fully renewable energy DC sending-end system that may appear in the future, the challenge of how to effectively suppress the random fluctuations and uncertainties of wind power and photovoltaic to meet the DC transmission demands poses a great challenge to the operation and scheduling of the sending-end system. At the same time, the rapid development of concentrating solar power, which has excellent regulation capability, has opened up new ways to solve these problems. However, concentrating solar power capacity needs to meet the demand for DC transmission in numerous operating scenarios of renewable energy. And how to reasonably allocate concentrating solar power capacity to suppress the random volatility and uncertainty of wind and photovoltaic, so as to meet the DC transmission demands is an urgent issue to be studied. Therefore, this paper proposes a method to optimise the configuration of concentrating solar power capacity for fully renewable energy delivery systems to meet the demand for DC transmission. Firstly, a typical operation scenario of the fully renewable energy system is delineated. Then, based on the regulation model of the concentrating solar power plant, a scenario analysis method is introduced to describe the uncertainty of the operation scenario. A model is constructed for the optimal configuration of the concentrating solar power capacity of the fully renewable energy sending-end system with the objective of satisfying the DC transmission demands, and the optimal configuration method of the concentrating solar power capacity is proposed. Finally, the effectiveness of this capacity configuration method for concentrating solar power is verified by means of a case.