Solar Updraft Towers generate electricity from solar radiation. Underneath a large translucent collector roof, air is heated by solar radiation. Due to the difference in density between the warm air inside the collector and the cold air outside, it flows radially to a tube open at the bottom in the center of the collector and rises inside it. The air flow drives a turbine with generator installed at the base of the tube and generates electricity. Optionally, continuous 24-hour operation can be guaranteed by closed water hoses laid out under the roof to release the heat stored during the day at night. A 50 kWel prototype was built in Manzanares (Spain), designed for a trial period of about three years. Our prototype supplied energy for seven years, proving the functionality and operational reliability of this type of solar thermal power plant.