Abstract: An inflatable solar concentrator comprising an elongate hollow member of relatively thin flexible material inflatable to an upright position in which it is generally in the form of a cone convergent from its upper to its lower end. The inflated member has a substantially transparent top of a material which transmits incident solar radiant energy, and a highly reflective inner conical surface which reflects downwardly and thereby concentrates the radiant energy. A rigid collar on the lower end of the member has a passage through it in communication with the interior of the member for supply of gas under pressure into the member to inflate it and for exit of gas from the member to collapse it. The member is mounted with its lower end above a heat absorbing surface for impingement on the surface of concentrated radiant energy.