Techno-Economic Analysis of Hybrid Concentrating Solar Power Systems

This thesis presents the outcomes of techno-economic studies of power generation using hybrid Concentrating Solar Power (CSP) systems, in particular, the Hybrid Solar Receiver Combustor (HSRC). The HSRC technology consists of a device that integrates a combustor into a tubular solar cavity receiver to enable a schedulable firm supply of electricity. Two innovative configurations of the HSRC were investigated; one operating with conventional combustion while the other operating with Moderate or Intense Low-oxygen Dilution (MILD) combustion. The HSRC was developed to lower the overall cost of renewable electricity generation by reducing the installed capital cost, fuel consumption and parasitic losses of a conventional hybrid Concentrating Solar Power (CSP) plant. The HSRC technology was also developed to provide a firm supply of electricity with lower emissions relative to current state-of-the-art hybrid CSP systems. The thesis presents an assessment of the HSRC, which was based on operation with conventional combustion, with an analytical model that calculates the heat transfer, mass flow rates and energy into and out of the device. A systematic investigation of the influence of controlling parameters on the performance of the device was undertaken. The performance of the HSRC was analysed with a pseudo-dynamic model that accounts for variations in CSP input using historical solar data from sites in USA and Australia. The thermal efficiency of the HSRC was found to be similar to a conventional system of two stand-alone systems, namely; a solar-only cavity receiver and a conventional natural gas boiler, also termed Solar Gas Hybrid (SGH). Additionally, it was found that the HSRC system benefits from the reduction in start-up and shut-down losses, incurred by a backup boiler, and a decrease in parasitic losses due to the integration of solar and combustion in one device. The HSRC was estimated to reduce the overall Levelised Cost of Electricity (LCOE) by up to 17% relative to the SGH system. The sensitivities to key parameters of the LCOE were also assessed, and the results were found to be highly influenced by the price of the fuel (natural gas). In addition, configurations of the HSRC that enable it to operate in the conditions required for MILD combustion were also identified. This is desirable as the combustion regime is known to offer greater compactness, lower NOx emissions, and potential fuel savings due to higher and more uniform heat transfer relative to current state-of-the-art combustion systems. Operating in this combustion regime resulted in a more compact device and an estimated LCOE reduction of up to 4% relative to the HSRC operating with conventional combustion for the same reference receiver size of 30MWth. This thesis also evaluated the potential to lower the cost of hybrid CSP systems by modularising selected components (e.g. heliostat, tower and receiver) in a CSP plant. It was found that the energy losses in a system of small-sized modules employing molten salt as its heat transfer fluid are dominated by electrical trace heating due to the increased in piping length relative to their larger receiver counterpart. However, this can be reduced by a significant amount using alternative heat transfer fluids with a lower melting point such as sodium. In addition, for modularisation to be cost effective, access to alternative, lower-cost manufacturing methods is required. Specifically, the benefit of standard learning rates is insufficient to lower the LCOE on its own.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 201