A method to integrate collected solar thermal energy into the feedwater system of a Rankine cycle power plant is disclosed. This novelty uses a closed loop, single phase fluid system to collect both the solar heat and to provide the heat input into the feedwater stream of a regenerative Rankine cycle. One embodiment of this method of integrating solar energy into a regenerative Rankine power plant cycle, such as a coal power plant, allows for automatic balancing of the steam extraction flows and does not change the temperature of the feedwater to the boiler. The concept, depending on the application, allows for the spare turbine capacity normally available in a coal plant to be used to produce incremental capacity and energy that is powered by solar thermal energy. By “piggybacking” on the available components and infrastructure of the host Rankine cycle power plant, considerable cost savings are achieved resulting in lower solar produced electricity costs.