Abstract: A controlled heating method of a process fluid through concentrating solar thermal plant and heat carrier system where the solar heat available from solar plant is transmitted to a heat carrier stream constituted by air and it is eventually integrated with post firing fuel stream; the heat carrier stream constituted by hot air and post-firing flue gas stream is circulated via a duct circuit through a heat exchanger with the process fluid to allow reaching final required process fluid temperature; the post-firing contribute is determined by an automatic control system which controls in continuous the process fluid temperature and adapt the firing contribute during the different operating phases of the concentrating solar plant.