A method of optimising the thermodynamic and economic performance of heliostat field within a solar tower thermal power plant has been developed. The method includes the generation of a heliostat field given a set of design variables, the assessment of its thermodynamic and economic performance, a sensitivity analysis of chosen key design variables, and a multi-objective optimisation using an evolutionary algorithm. Parameters of the former Solar One power plant in California are set as reference to illustrate the method throughout the article and to highlight potential setup improvements as well as optimal solutions under given constraints.