Publication Date

2012

Journal

Sandia National Laboratories

Department

Mechanical Engineering

Abstract

Dish-Stirling systems have been demonstrated to provide high-efficiency solar-only electrical generation, holding the world record at 31.25%. This high efficiency results in a system with a high possibility of meeting the DOE SunShot goal of $0.06/kWh. Current dish-Stirling systems do not incorporate thermal storage. For the next generation of non-intermittent and cost-competitive solar power plants, we propose a thermal energy storage system that combines latent (phase-change) energy transport and latent energy storage in order to match the isothermal input requirements of Stirling engines while also maximizing the exergetic efficiency of the entire system. This report takes an initial look at the technical advantages of dish Stirling with storage as well as the technical challenges, in order to make a preliminary estimate as to the technical feasibility of such a system. We find that a storage system using metallic eutectic phase change storage results in a feasible physical embodiment, with mass, volume, and complexity suitable for 25kWe dish Stirling systems. The results indicate a system with 6 hours of storage and a solar multiple of 1.25 provides the optimum impact to LCOE and profit. Further, for no negative impact on LCOE, the optimal storage system may cost as much as $82/kWhth or $33k/dish, a substantial departure from the SunShot goals for tower systems. The storage system also is shown to have substantial structural benefits to the dish design. In addition, there may be benefits in terms of capacity payments or failure-to-deliver penalties. A dish storage system design must take into account the value placed on storage by the PUC or utility.

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