Concentrated solar power, or CSP, is a renewable energy technology that uses mirrors to collect and focus sunlight into a small area. Instead of turning light directly into electricity like a solar panel, CSP first turns sunlight into heat. That heat can then be used to make steam, spin a turbine, and drive an electric generator.
CSP matters because it can produce large amounts of power in sunny regions and can store heat for use after sunset.
In a tower system, hundreds or thousands of mirrors called heliostats track the Sun and reflect sunlight toward a receiver at the top of a tall tower. A heat-transfer fluid, often molten salt, absorbs energy in the receiver and reaches very high temperatures. The hot fluid transfers thermal energy to water, producing steam that spins a turbine connected to a generator.
Thermal storage tanks can keep the hot fluid available so the plant can generate electricity even when clouds pass or nighttime begins.
Key Facts
- CSP tower systems use heliostats to reflect sunlight to a receiver on a central tower.
- Energy flow: sunlight to thermal energy to mechanical energy to electrical energy.
- Power from sunlight can be estimated by P = IA, where I is solar irradiance and A is collecting area.
- Thermal energy stored in a fluid is Q = mcΔT.
- A turbine-generator converts spinning motion into electrical energy by electromagnetic induction.
- Molten salt is often used because it can store large amounts of heat at high temperature.
Vocabulary
- Concentrated solar power
- A renewable energy method that uses mirrors or lenses to focus sunlight and produce high-temperature heat.
- Heliostat
- A movable mirror that tracks the Sun and reflects sunlight toward a fixed target.
- Receiver
- The part of a CSP tower that absorbs concentrated sunlight and transfers the energy to a working fluid.
- Heat-transfer fluid
- A liquid or gas that carries thermal energy from one part of a system to another.
- Thermal storage
- A system that stores heat energy so it can be used later to produce electricity.
Common Mistakes to Avoid
- Thinking CSP works the same way as photovoltaic solar panels is wrong because CSP uses sunlight to make heat first, while photovoltaic panels convert light directly into electricity.
- Forgetting that mirrors must track the Sun is wrong because a fixed mirror would stop aiming reflected sunlight at the receiver as the Sun moves across the sky.
- Assuming all collected sunlight becomes electricity is wrong because energy is lost during reflection, heat transfer, steam production, turbine motion, and electrical generation.
- Ignoring thermal storage is wrong because one major advantage of CSP is that stored heat can help supply electricity when sunlight is weak or absent.
Practice Questions
- 1 A heliostat field has a total mirror area of 20,000 m2 and receives solar irradiance of 900 W/m2. If 70% of the sunlight reaches the receiver, what power reaches the receiver?
- 2 A molten salt tank contains 800,000 kg of salt with specific heat capacity 1500 J/(kg·°C). How much thermal energy is stored when its temperature increases by 250°C?
- 3 Explain why a CSP plant with thermal storage can be more useful to an electric grid than a CSP plant without storage, even if both receive the same sunlight during the day.