A solar updraft tower is just a very tall chimney set to capture hot air rising from a covered area. The sun heats the air and it all rises up the tower, spinning electricity turbines set at the foot of the tower.

A solar tower (concentrated solar) is a container of water or other liquid (salt is often used) which is heated by a heliostat of mirrors on the ground. An array of mirrors focus the sun's rays on the top of the tower where the heated liquid is then used to generate electricity, often through steam turbines.