The paper gives a mathematical description for the heat conduction proceeding on the plane surface of a solar collector’s absorber divided into three parts for each of which the Laplace equation with boundary conditions is formed. Applying definite approximations the authors have completely described mathematically the heat conduction process initiating in the plane part of a collector’s absorber, then passing to a tube and from the tube to the liquid flowing through it. In all the three absorber’s parts the process is considered stationary, independent of time, and, therefore the temperature field is obtained in spatial coordinates.