The current benchmark for CSP is the molten salt tower. The next generation of CSP plant should keep the general architecture of the current benchmark – namely the molten salt tower with its direct storage – but should operate at higher temperatures in order to downsize its solar field through higher efficiency. Solid particles are the best candidate today to replace the molten salt as storage medium. They are used as both storage medium and heat transfer fluid that works as an in-tube upward bubbling fluidized bed in the solar receiver.
Next-CSP is a project funded by the European Union’s H2020 program that aims at developing a new concept of particle solar receiver and validating it with a 1.2 MWe demonstration plant. The project also includes the study of a future utility-scale plant based on the concept in order to assess its technical and economic feasibility. This paper outlines the preliminary design of such a 150 MWe Next-CSP plant. Cost estimates were made with reasonable uncertainties to make design choices but are not dealt with in this paper.
The plant is designed as a peaker that generates power during the evening. Due to inherent limitations of the concept, the solar receiver is a cavity one with a limited thermal output, which makes a multi-tower configuration mandatory. Our plant has six towers, each one with one receiver. Bucket elevators were chosen to lift the particles from ground level to the receivers. The layout of the whole solar island was optimized to minimize the cumulated length of the network that horizontally conveys the particles between the storage system and the six towers. The chosen layout, named “Vertical Star”, allows for a cumulated length of 4.0 km, which is still very challenging in terms of Capex and thermal losses. Continuous-flow conveyors and proper design limit the thermal losses to 5%.
The power cycle is an externally-heated gas turbine operated in combined cycle. Whilst the bottoming steam cycle is standard, the gas turbine features a double reheat in order to achieve a combined cycle efficiency approaching 50%. The heat exchangers that provide the heat from the particles to the gas turbine are numerous (ten) and bulky.
To conclude, the deployment of a utility-scale Next-CSP plant can realistically be envisioned; however, some technical challenges must be dealt with carefully, especially the thermal losses of the solar receiver and the particle conveying network.
