(also known as “central tower” power plants or “heliostat” power plants) capture and focus the sun’s thermal energy with thousands of tracking mirrors (called heliostats).A tower resides in the centre of the heliostat field.The heliostats focus concentrated light on a receiver which sits on top of the tower. Within the receiver, the concentrated sunlight heats molten salt to about 540 o C. The heated molten salt then flows into a thermal storage tank where it is stored, maintaining 98% thermal efficiency, and eventually pumped to a steam generator. The steam drives a standard turbine to generate electricity. This process, also known as the “Rankine Cycle” is similar to a standard coal-fired power plant, except it is fuelled by clean and free solar energy. The advantage of this design above the parabolic trough design is the higher temperature. Thermal energy at higher temperatures can be converted to electricity more efficiently and can be more cheaply stored for later use. Furthermore, there is less need to flatten the ground area. In principle, a power tower can be built on a hillside. Mirrors can be flat and plumbing is concentrated in the tower. The disadvantage is that each mirror must have its own dual-axis control, while in the parabolic trough design one axis can be shared for a large array of mirrors.
