The use of solar heat for industrial applications is of growing interest in the academic and governmental areas. The development of thermal integration techniques, design approaches for minimum cost of solar collector fields and its operation are fundamental to motivate the interest of the process industries. About the design of a solar field, the investment and pay-back period are fundamental for decision making, therefore, cost minimisation is of paramount importance. The present work deals with the minimisation of the total cost of a network of solar collectors using a multi-objective optimisation approach. The optimisation approach uses a new cost equation for flat plate solar collectors and a validated thermal model. The optimisation model is solved in a Mat-Lab GAMS platform. It is found that tube diameter, the tube length and collector width, are the variables that most impact the total cost, and in the case of solar networks, the number of collectors in series to achieve a fixed temperature. With respect to commercial geometries, the cost of the optimised designs is 41 % cheaper.