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How does concentrated solar power work?

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Quick answer

Concentrated solar power focuses sunlight with mirrors onto a receiver, heating oil or molten salt to several hundred degrees. That hot fluid boils water into steam, which spins a turbine and generator just as in a fuel-burning plant. Spare heat can be stored in insulated salt tanks to keep producing electricity after dark.

Concentrated solar power uses mirrors to focus sunlight onto a small receiver, heating a fluid to hundreds of degrees and using that heat to make steam that drives a turbine. Because heat is easier to store than electricity, many plants keep hot molten salt to generate power after sunset.

Step by step

  1. Motorised mirrors follow the Sun across the sky and reflect its direct rays onto a fixed receiver.
  2. The concentrated light heats a fluid such as synthetic oil or molten salt flowing through the receiver.
  3. Some of the hot fluid goes to insulated storage tanks, while the rest heads to a heat exchanger.
  4. In the heat exchanger the hot fluid boils water into high-pressure steam without the two mixing.
  5. The steam spins a turbine connected to a generator, and the cooled fluid returns to the receiver.

Key things to understand

  1. Large fields of curved or flat mirrors track the Sun and reflect direct sunlight onto a narrow receiver.
  2. In trough plants a pipe along each mirror's focal line heats synthetic oil to roughly 390 °C.
  3. In tower plants thousands of flat mirrors aim at a central receiver that can heat molten salt to around 565 °C.
  4. The hot fluid passes through a heat exchanger that boils water into steam for a conventional turbine and generator.
  5. Insulated tanks of hot molten salt store heat for hours, letting the plant keep generating through the evening.

Labelled diagram

  1. Heliostat mirrors

    Thousands of tracking mirrors reflect direct sunlight onto one central point.

  2. Tower receiver

    Concentrated light heats molten salt flowing through tubes at the tower top.

  3. Hot salt tank

    Insulated storage holds heated salt for use later, including after sunset.

  4. Steam generator

    Hot salt boils water into high-pressure steam through a heat exchanger.

  5. Turbine and generator

    Steam spins the turbine, and the generator sends electricity to the grid.

How a solar tower turns sunlight into electricity

Real-world examples

  • The Noor Ouarzazate complex in Morocco combines trough and tower plants with molten salt storage for evening demand.
  • The Andasol trough plants in southern Spain store heat in salt tanks that can run the turbine for hours after sunset.
  • Near Mount Abu in Rajasthan, a solar thermal plant uses large dish reflectors to raise steam for electricity.
  • Several plants in Chile's Atacama Desert use towers because the region gets some of the strongest sunlight on Earth.

Common mistake

✗ Myth: Concentrated solar power is just a big version of rooftop solar panels.

✓ Fact: It works on a different principle: mirrors create heat, and a steam turbine turns that heat into electricity. Rooftop panels convert light to electricity directly with no moving parts or steam.

People also ask

How does concentrated solar power produce electricity?
Mirrors focus sunlight onto a receiver where a fluid such as oil or molten salt is heated to hundreds of degrees. That hot fluid passes through a heat exchanger to boil water into steam, and the steam spins a turbine connected to a generator. The cooled fluid then cycles back to collect more heat.
What are the types of concentrated solar power?
The main designs are parabolic troughs, which focus light onto a pipe; solar power towers, where flat mirrors aim at a central receiver; linear Fresnel systems using long flat mirror strips; and parabolic dishes that focus light onto a single point. Troughs and towers make up most commercial plants worldwide.
Why is concentrated solar power not more common?
Photovoltaic panels have become much cheaper and work even in hazy or cloudy climates, while concentrated solar needs strong direct sunlight, large land areas and complex steam equipment. Its main advantage is built-in heat storage, so it remains attractive in sunny deserts that need power into the evening.
How is concentrated solar power different from solar panels?
Solar panels convert light directly into electricity using semiconductor cells. Concentrated solar power converts light into heat first, then uses that heat to spin a steam turbine, which allows cheap thermal storage but needs strong direct sunlight.
Why does concentrated solar need clear skies?
Mirrors can only focus direct beam sunlight, not the scattered light that comes through clouds or haze. That is why plants are built in deserts and dry plateaus with many cloudless days, such as Morocco, Spain, Chile and Rajasthan.
Why is molten salt used for heat storage?
A mixture of sodium and potassium nitrate stays liquid over a wide temperature range and holds a lot of heat per tonne. It is cheap, does not burn, and can sit in insulated tanks for hours with only small losses.
Can concentrated solar run at night?
Yes, if the plant has thermal storage. During the day some hot salt is diverted into a storage tank, and after sunset it is pumped through the steam generator so the turbine continues running for several more hours.

Part of the guide: Energy & Electricity at Home →