In Concentrated Solar Power (CSP) plants, thermal energy storage (TES) systems commonly use several materials to store and manage thermal energy efficiently. The primary materials include:
Molten Salts
- Current Use: Molten salts, typically a mixture of sodium nitrate (NaNO3) and potassium nitrate (KNO3), are widely used in CSP plants. These salts serve both as the heat transfer medium and for thermal energy storage. They are particularly suited for power tower CSP systems, where they are heated to about 565°C and then stored in insulated tanks.
- Advantages: Molten salts have minimal heat transfer limitations, making them suitable for direct integration in power towers. However, they require large insulated tanks due to their relatively low stored energy density.
Synthetic Oils (Heat Transfer Fluids)
- Current Use: In parabolic trough CSP systems, synthetic oils are used as heat transfer fluids (HTFs). These oils are heated by sunlight reflected onto the collectors and then transfer their heat to a storage medium, often molten salt, via a heat exchanger. This setup is necessary because the storage salt has a high freezing point and is not suitable for use directly in the solar field.
Phase Change Materials (PCMs) for Latent Heat Storage
- Emerging Use: Phase change materials store thermal energy during their phase transitions (e.g., solid to liquid). They offer high energy density storage in a smaller volume compared to sensible heat storage but are more expensive and technically challenging to integrate into CSP systems.
Thermochemical Materials
- Future Prospects: Thermochemical storage involves storing energy in chemical bonds. This approach has the potential for high energy densities and long storage durations but is still in its early stages due to technical challenges and material degradation over cycles.
These materials play critical roles in enabling CSP systems to provide reliable and dispatchable renewable energy.
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