How Power Tower Works
Power towers use large, flat mirrors called heliostats to reflect sunlight onto a solar receiver at the top of a central tower. In a direct steam power tower, water is pumped up the tower to the receiver, where concentrated thermal energy heats it to around 1,000 degrees Fahrenheit. The hot steam then powers a conventional steam turbine. In this case, the medium that transfers heat from the receiver to the power block is steam. Some power towers use molten salt in place of the water and steam. That hot molten salt can be used immediately to generate steam and electricity, or it can be stored and used at a later time.
In power tower CSP systems, numerous large, flat, sun-tracking mirrors, known as heliostats, focus sunlight onto a receiver at the top of a tall tower. A heat-transfer fluid heated in the receiver is used to generate steam, which, in turn, is used in a conventional turbine generator to produce electricity.
A large power tower plant can require thousands of computer-controlled heliostats that move to maintain point focus with the central tower from dawn to dusk. Because they typically constitute about 50% of the plant's cost, it is important to optimize heliostat design; size, weight, manufacturing volume, and performance are important design variables approached differently by developers to minimize cost.