Molten salt storage helps a concentrated solar power plant make electricity even when sunlight is not available. In these plants, mirrors called heliostats focus sunlight onto a receiver at the top of a tower, heating a liquid salt mixture to a very high temperature. The hot salt acts like a thermal battery because it stores energy as heat instead of storing it as electricity.
This matters because it can shift solar power from sunny hours to evening and night demand.
Key Facts
- Thermal energy stored can be estimated by Q = mcΔT.
- Power delivered over time is P = E/t, where E is energy and t is time.
- Molten salt storage keeps energy as heat, not as chemical energy like a battery.
- A common nitrate salt mixture can operate from about 290 °C in the cold tank to about 565 °C in the hot tank.
- In a CSP tower plant, heliostats reflect sunlight to a receiver, and the receiver transfers heat to the salt.
- Stored heat makes steam in a heat exchanger, and the steam spins a turbine connected to a generator.
Vocabulary
- Molten salt
- Molten salt is a salt mixture heated until it becomes liquid and can carry and store thermal energy.
- Concentrated solar power
- Concentrated solar power is a method of using mirrors to focus sunlight and produce high-temperature heat for electricity generation.
- Heliostat
- A heliostat is a mirror that tracks the Sun and reflects sunlight toward a fixed receiver.
- Heat exchanger
- A heat exchanger is a device that transfers thermal energy from one fluid to another without mixing them.
- Thermal energy storage
- Thermal energy storage is the process of saving energy as heat so it can be used later.
Common Mistakes to Avoid
- Thinking the molten salt burns like a fuel. This is wrong because the salt is mainly a heat storage and heat transfer material, not a substance being consumed for energy.
- Confusing molten salt storage with an electric battery. This is wrong because molten salt stores thermal energy, while batteries store energy chemically and release it as electricity.
- Assuming the plant stops producing power immediately at sunset. This is wrong because hot salt can continue heating water into steam after sunlight is gone.
- Using Q = mcΔT without matching units. This is wrong because mass, specific heat, and temperature change must use compatible units to get energy in joules.
Practice Questions
- 1 A molten salt tank contains 2.0 x 10^6 kg of salt with specific heat capacity 1500 J/(kg·°C). If the salt cools from 565 °C to 290 °C, how much thermal energy is released?
- 2 A CSP plant uses stored heat to deliver 100 MW of electric power for 8.0 hours. How many joules of electrical energy are delivered during that time?
- 3 Explain why a molten salt storage system can make a solar power plant more useful to the electric grid than a solar plant with no storage.