Abstract: An air curtain control system for a solar thermal receiver comprising: at least one air jet (505) arranged to produce a continuous planar air curtain (507) over at least a portion of a receiver aperture 509 of a solar thermal receiver, an air flow control device (517) for controlling a speed of air flow out of the air jet (505), at least one angular control device (503) for controlling an angle of the air curtain (507) relative to the receiver aperture 509, and a system controller (501) arranged to control the air flow control device (517) and angular control device (503) to isolate the receiver aperture (509) from ambient elements external to the receiver aperture (509).