Performance evaluation of CSP power tower plants schemes using supercritical carbon dioxide Brayton power block

Abstract

Supercritical Carbon Dioxide (sCO2) Brayton cycle power blocks are among the most promising candidates to improve and replace current heat-to-electric conversion technology, both for fossil, nuclear and renewable power generation at utility-scale. Concentrated Solar Power (CSP) based in sCO2 cycles also represent a potentially successful solution aiming to integrate higher efficiency power cycles in CSP plants for increasing efficiency and lowering the Levelized Cost Of Electricity (LCOE). Efficiency improvement potential of sCO2 power blocks seems clear for fossil and nuclear power plants by directly operating at higher temperatures than current subcritical steam Rankine cycles. However, for CSP it is not yet evident whether or not sCO2 power blocks could actually improve LCOE mainly due to cost uncertainty related to high temperature materials and power block components. Indeed, even improving plant efficiency is a challenge itself, since operating at higher temperatures increases heat losses in the receiver and reduces its efficiency. This work builds on top of previous studies which analyzed sCO2 power cycle concepts for CSP, performing a detailed modelling for all plant subsystems and imposing realistic design constraints, thus undertaking a rational approach for identifying the best sCO2 scheme candidates for the next-gen CSP Plants. Since current and future CSP Plant concepts must integrate large Thermal Energy Storage (TES) to provide dispatchable power to the grid, plant schemes considered in this work also include large TES. Also, multi-tower schemes have been considered, aiming at solar field downsizing and so leading to a better efficiency and modularity in the solar field and receiver subsystems. Results show that sCO2-based CSP plants operating at high temperatures (700°C) can reach a remarkably net efficiency increase of ∼20% over the subRC baseline case operating at 565°C in the best case. Also, for regular molten salts sCO2-based schemes operating at 565°C, the net efficiency can reach a substantial increase of ∼13% over the subRC case under certain conditions. Notwithstanding, results also show large dependency of the plant efficiency with ambient conditions and off-design operation, which can easily jeopardize any improvement and the feasibility of sCO2-based CSP plants in some locations.