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Sandia National Laboratories (SNL) worked with the National Renewable Energy Laboratory (NREL) and the University of Connecticut, under the National Laboratory R&D competitive funding opportunity, to demonstrate key thermal energy storage (TES) system components for dish Stirling power generation.

Approach

Schematic of a circular CSP dish showing arrows modeling the movement of vapor and condensation between the dish and the heat pipe receiver on the front and heat pipe transport to a rear-mounted PCM and engine.
The research team demonstrated a TES system that combines latent heat transport and latent heat storage, providing up to 6 hours of storage on a 25-kWe dish Stirling system. The end product of this project is a representative subscale test device with a recommended phase change material (PCM), heat pipe input and output specifications, and systems-level design guidance for integration into a high-performance dish Stirling system. The effort focused on several development areas:

  • Solar heat pipe receiver performance and life design and testing
  • PCM selection, characterization, and basic compatibility
  • PCM compatibility with shell materials
  • PCM freeze-thaw and thermal transport modeling
  • PCM interface design, development, and optimization
  • Systems-level proof-of-concept hardware testing
  • Systems-level modeling and optimization

Innovation

In this dish Stirling design, the storage and the engine are both moved to the rear of the dish. This placement provides more optimum balance of the dish system, reduces cantilevered weight, and allows closing of the "pedestal gap," leading to a more efficient structural design. The size and duration of the proposed TES system enables utility-scale dish Stirling systems to have the same ability to dispatch power when needed and allow dish Stirling systems to produce power into the evening and nighttime, similar to other forms of concentrating solar power (CSP) technology with storage. Combining TES with dish Stirling systems, which are currently the highest efficiency CSP technology, enhances this technology's ability to meet the CSP SunShot goals.

Conclusions

  • A robust high performance heat pipe was developed and demonstrated, with operation extending nearly 20 times the duration of prior high performance felt wick heat pipes. This may have application in other thermal management fields such as electronic cooling, as well as high temperature applications in the nuclear industry as well as tower-based solar projects. 
  • A high performance metallic PCM was identified and synthesized in significant volumes. Such a PCM may be useful in high temperature solar systems with near-isothermal heat input, such as a multi-stage reheat sCO2 engine on a dish or a tower. 
  • Several potential coatings were identified and tested for protection of the PCM containment. For the ternary CuMgSi PCM, thermal spray coatings of alumina or an aluminum/magnesium spinel were promising, with a transition layer to control CTE mismatch issues. These coatings need further development and testing to confirm compatibility. 
  • The benefit of storage on a dish Stirling system was clearly identified and demonstrated in analytical models, laying a foundation for future development. The operating performance of the dish Stirling systems, in particular the high conversion efficiency, leads to a high allowable cost for the storage apparatus relative to tower systems with Rankine steam cycles under 600°C. 

Publications, Patents, and Awards

 

Learn about other DOE competitive awards for concentrating solar power research that are in progress.