We present the results of the quantitative analysis of the temperature and concentration dependences of the thermopower in Bi-based HTSC-samples of Bi2Sr2Ca|_;(YcCu20>, (x = 0 + 0.5) and Bi2Sr2_,cKxCaCu20J, (x = 0 + 0.4) compositions on the basis of three different models of the electron transport. The parameters of the energy spectrum and charge-carrier system in investigated samples were determined and a character of their changes with increasing impurity contents was analyzed. Potassium in the Bi2Sr2....xKxCaCu20;), system is proposed to introduce additional states into the conduction band.