Novel hybrid solar tower-gas turbine combined power cycles using supercritical carbon dioxide bottoming cycles

Abstract

In this study, two novel hybrid solar power tower-gas turbine combined power cycles are proposed, in which two supercritical CO2 (s-CO2) power cycles connected in series are driven by waste energy from a gas turbine cycle partially driven by a solar power tower. The solar power tower system provides a high-temperature thermal energy up to 1223 K. Each of the two novel schemes consists of a combined cycle with configuration 1 combining an s-CO2 recompression cycle and an s-CO2 recuperative cycle as bottoming cycles. Configuration 2 replaces the recompression cycle with an s-CO2 partial cooling cycle. Another objective is to evaluate the suitability of the two novel configurations against two conventional combined cycles including a bottoming steam Rankine cycle driven by a single-pressure heat recovery steam generator (HRSG) and dual-pressure HRSG. A thermodynamic and economic analysis is conducted for the plants, all sized at 50 MWe, and found that while configuration 1 has the lowest overall cycle efficiency of 0.4608, it exhibits the lowest levelized cost of electricity (LCOE) of $83.16/MWh, due to its compact components. The highest overall cycle efficiency of 0.5066 is obtained for the configuration that employs a bottoming steam Rankine cycle with dual-pressure HRSG, which exhibits an LCOE of $85.08/MWh. Transient analysis of the cycle configuration 1 further highlighted a high solar share over 0.652 during the month of June. A sensitivity analysis examined the effect of the maximum and minimum pressures and the compressor inlet temperature of the two bottoming s-CO2 cycles, and design direct normal irradiance (DNI) on power plant performance, required field size, and LCOE. The lowest LCOE of $80.90/MWh for configuration 1 is realized when the compressor inlet temperatures approach 308 K for both s-CO2 cycles. Increasing the design DNI levels corresponds to a significant decrease in LCOE but results in lower solar shares.