A solar power tower is a renewable energy machine that turns concentrated sunlight into electricity. Instead of using one solar panel at a time, it uses hundreds or thousands of mirrors spread across a field. These mirrors, called heliostats, aim sunlight at a receiver on top of a tall tower.
The intense light creates high temperatures that can drive a power plant without burning fuel.
Key Facts
- Solar power input on a mirror is P = IA, where I is solar irradiance and A is mirror area.
- If mirror reflectivity is r, reflected power is Preflected = rIA.
- Thermal efficiency is ηthermal = useful heat output / solar power input.
- Electrical efficiency is ηelectric = electric power output / solar power input.
- A heliostat rotates on two axes so it can reflect sunlight toward the receiver as the Sun moves.
- Thermal energy storage lets some solar power towers generate electricity after sunset.
Vocabulary
- Heliostat
- A heliostat is a movable mirror that tracks the Sun and reflects sunlight toward a fixed target.
- Receiver
- The receiver is the part at the top of the tower that absorbs concentrated sunlight and converts it into heat.
- Solar irradiance
- Solar irradiance is the power of sunlight arriving on each square meter of surface, usually measured in W/m².
- Heat transfer fluid
- A heat transfer fluid is a liquid or gas that carries thermal energy from the receiver to another part of the power plant.
- Thermal storage
- Thermal storage is a system that saves heat, often in molten salt, so electricity can be generated later.
Common Mistakes to Avoid
- Assuming the mirrors make electricity directly is wrong because heliostats only reflect light, while electricity is produced later by a heat engine and generator.
- Forgetting reflectivity losses gives an overestimate of power because real mirrors absorb and scatter some of the sunlight.
- Pointing all mirrors straight at the Sun is wrong because each mirror must be angled so reflected rays meet at the tower receiver.
- Ignoring the Sun’s motion leads to the wrong design because heliostats must continuously rotate to keep the reflected beam on the receiver.
Practice Questions
- 1 A heliostat has an area of 40 m² and receives solar irradiance of 900 W/m². If its reflectivity is 0.90, how much power does it reflect toward the tower?
- 2 A solar power tower receives 120 MW of reflected solar power at the receiver. If the overall electric efficiency is 25 percent, what electric power output is produced?
- 3 Explain why a solar power tower can be easier to connect to thermal energy storage than a field of ordinary photovoltaic panels.