Assessment of Solar Power Tower Driven Ultra Supercritical Steam Cycles Applying Tubular Central Receivers with Varied Heat Transfer Media

Kurzfassung

In commercial power plant technology, the market introduction of ultra supercritical (USC) steam cycle power plants with steam parameters around 350bar and 720°C is the next development step. USC steam cycles are also proposed to decrease the levelized electricity costs of future solar power towers due to their highly efficient energy conversion. A 55% thermal efficiency with decreased specific investment costs is within the potential of USC steam cycles. The required process parameters can be achieved using nickel based alloys in the solar receiver, the tubing and other plant components. For solar tower applications, appropriate high temperature heat transfer media (HTM), high temperature heat exchangers and storage options are additionally required. Using the current development for molten salt power towers (Solar Tres) as a reference, several tower concepts with USC power plants were compared. The ECOSTAR methodology provided by [1] was applied for predicting the cost reduction potential and the annual performance of these power tower concepts applying tubular receivers with various HTM. The considered HTM include alkali nitrate salts, alkali chloride salts and liquid metals such as a Bi-Pb eutectic, tin or sodium. For the assessment, an analytical model of the heat transfer in a parametric 360° cylindrical, tubular central receiver was developed to examine the receiver characteristics for different geometries. The sensitivity of the specific cost assumptions for the levelized electricity costs (LEC) was evaluated for each concept variation. No detailed evaluation was done for the thermal storage, but comparable costs were assumed for all cases. The results indicate a significant cost reduction potential for the liquid metal HTM processes.