The efficiency of thermal energy storage (TES) systems varies significantly depending on the type of storage medium used, as well as the method of storage (sensible heat, latent heat, or thermochemical storage). Here is a detailed breakdown of how different storage mediums influence TES efficiency:
Sensible Heat Storage
- Mediums: Common sensible heat storage media include water, oils, molten salts, sand, and engineered bricks.
- Efficiency Range: Sensible heat storage systems typically show efficiencies between 50% and 90%, depending on the materials’ thermodynamic properties and insulation quality.
- Examples:
- Water and oils were used in first-generation TES systems due to their high specific heat and chemical stability but are limited to low to moderate temperature applications (below ~250°C) due to their low boiling points.
- Molten salts allow for higher operating temperatures (280°C to ~600°C), enabling better efficiency in concentrated solar power and industrial heat applications.
- Newer third-generation TES systems use particle-based materials like sand or special bricks that can operate at temperatures greater than 1000°C, yielding higher efficiencies in industrial heat processes, though they require thermally stable containment.
- Energy Density: Sensible heat storage typically has lower energy density (around 10-50 kWh/m³), which can limit storage capacity per volume.
Latent Heat Storage (Phase Change Materials – PCM)
- Mediums: Materials that store energy by changing phase—such as ice, paraffin waxes, salts, or other solids/liquids.
- Efficiency Range: Latent heat storage offers higher efficiency, generally 75% to 90%, due to the large enthalpy change during phase transitions without significant temperature change.
- Advantages: PCMs can store more energy per volume than sensible heat storages (approximately 100 kWh/m³), can maintain a stable temperature while discharging, and are useful for precise temperature-control applications.
- Limitations: PCMs typically serve a narrow temperature range and cannot handle very high temperatures above 1000°C.
Thermochemical Storage (TCS)
- Mediums: Storage based on reversible chemical reactions.
- Efficiency Range: Can approach 75% to nearly 100% efficiency, with higher energy density (up to 250 kWh/t) and stable heat storage over long durations without losses.
- Application: Promising for long-term and high-temperature storage but currently mostly under research and demonstration stages.
Advanced and Emerging Thermal Storage Technologies
- Packed-bed TES with hot air and pebbles/copper slags have demonstrated over 90% thermal efficiency at temperatures around 800°C. Recent innovations in flow design (radial flow packed beds) have reduced pressure drops and parasitic energy losses, further improving effective efficiency and making these systems more commercially viable.
- ThermalBattery™ (high-performance concrete based) technology claims efficiencies over 98%, with advantages including long service life, near-zero performance degradation, continuous multi-day discharge capacity, and environmental benefits due to recyclable materials.
Summary Comparison
| Storage Medium/Type | Operating Temperature Range | Efficiency Range | Energy Density (kWh/m³ or kWh/t) | Typical Applications | Key Advantages/Disadvantages |
|---|---|---|---|---|---|
| Water/Oils (Sensible Heat) | Up to ~250°C | 50% – 70% | ~10 – 50 kWh/m³ | Residential heating, low-temp industrial | Low cost, stable but limited to low temps |
| Molten Salts (Sensible Heat) | 280°C to ~600°C | 70% – 85% | ~100 kWh/m³ | CSP plants, higher-temp industrial heat | Higher temp, moderate efficiency |
| Particle-based (Sand/Bricks) | >1000°C | Up to ~90%+ | High (variable) | Industrial heat decarbonization | High temp resistant, large scale, thermal stability required |
| Phase Change Materials (PCM) | Narrow temp range (~0-250°C) | 75% – 90% | ~100 kWh/m³ | Precise temp control, building HVAC, cold storage | High density, stable temp, limited temp range |
| Thermochemical Storage (TCS) | >300°C | 75% – ~100% | Up to 250 kWh/t | Long-term storage, industrial processes | High density, long storage, still developing |
| ThermalBattery™ (Concrete) | Variable (~100s °C) | Over 98% | Not specified | Industrial heat, renewable integration | Very high efficiency, robust, recyclable |
| Packed-bed (Pebbles/Copper slag) | ~800°C | Over 90% | Not specified | Industrial heat, solar thermal storage | High efficiency, low parasitic losses |
Conclusion
The efficiency of thermal energy storage systems varies primarily with the storage medium’s thermophysical properties and operating temperature:
- Sensible heat storage efficiency improves with higher temperature and better insulation but generally maxes out below 90%.
- Latent heat storage (PCMs) offers higher efficiencies and energy densities but is limited to specific temperature ranges.
- Thermochemical storage potentially offers the highest efficiency and energy density but is less mature.
- Emerging materials like particle beds and ThermalBattery™ technologies are pushing efficiencies above 90% and 98%, respectively, with additional benefits like scalability, material availability, and environmental sustainability.
These efficiencies must be balanced with cost, scalability, and application needs for the best practical TES solution.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-does-the-efficiency-of-thermal-energy-storage-systems-vary-with-different-storage-mediums/
