The efficiency of a two-tank direct thermal energy storage (TES) system compared to other configurations depends on design and operational parameters:
Efficiency Comparison with Thermocline Systems
- Equivalent energy output: Studies show nearly identical annual ORC energy production (~0.92 GWh/year) between two-tank direct, indirect, and thermocline systems under similar conditions.
- Cost advantages: Thermocline systems may require less storage material, but two-tank direct systems in certain configurations achieve ~45% lower investment costs and ~48% lower levelized storage costs compared to two-tank indirect setups due to simplified architecture and reduced material requirements.
- ORC compatibility: Both systems exhibit comparable power block efficiency in CSP-ORC plants, with hexamethyldisiloxane often preferred as the working fluid in two-tank direct systems for higher thermal stability.
Comparison with Single-Tank or Indirect Systems
- Flexibility vs. efficiency: While single-tank designs (e.g., thermocline) reduce physical footprint, two-tank direct systems offer simpler temperature stratification management, critical for maintaining ORC heat input consistency.
- Thermal losses: Indirect systems using heat exchangers introduce additional efficiency drops compared to direct configurations, especially in smaller-scale applications.
Key Trade-offs
- Cost vs. complexity: Two-tank direct systems balance moderate upfront costs with operational simplicity, whereas thermocline systems require advanced controls to manage thermal stratification decay.
- Scalability: Two-tank designs are more adaptable to hybridization (e.g., solar-biomass cogeneration) due to modularity.
For medium-scale CSP-ORC plants, two-tank direct systems often achieve similar energy output to alternatives but with lower lifetime costs, making them economically preferable despite comparable thermodynamic efficiency.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-does-the-efficiency-of-a-two-tank-direct-system-compare-to-other-systems/
