Impact of Time-of-Delivery Schemes on Optimum Solar Hybrid Power Plants- A Techno-Economic Study

Abstract: Analyses concerned with identifying optimal plant configurations of solar power plants can be expanded by implementing payment schemes where prices are unknown but daily occurring payment multipliers in the form of Time-of-Delivery (TOD) factors are known by enhancing the impact of financial conditions in optimal designs through the use of financial models. The hybridisation of solar technologies such as CSP with TES with photovoltaics (PV) and battery energy storage systems (BESS) have also been shown to offer promising synergies in terms of economy and design. The purpose of the present thesis was therefore to measure the impact of applying different TOD approaches on optimal plant configurations of combined PV-CSP, CSP-only plants as well as combined PV-BESS plants in the chosen market of California, United States. Multi objective optimisation studies was then carried out aimed at minimising capital expenditures (CAPEX) as well as a benchmark Power Purchase Agreement (PPA) tariff defined using a financial model. This allowed the impact of two identified TOD approaches from the local utilities Southern California Edison (SCE) and Pacific Gas & Electric (PG&E) to be evaluated for an identified case aimed at supplying power during peak demand periods in the state, which involved the development and implementation of a dynamic dispatch strategy allowing day-by-day determination of CSP plant dispatch. The main results show that the impact of varying the TOD factor during the day has little to no effect on optimal PV-BESS plants due to the minimisation of BESS in such a design caused by the high cost of integrating such a component, which disfavoured it in relation to the optimisation objectives. Simultaneously, the impact was noticeable on optimal PV-CSP and CSP-only plants where the low variability in TOD factor between the early-daytime Off-Peak period, and the early-afternoon On-Peak daily periods in the SCE case caused the PV-CSP plant to feature a small CSP plant and comparatively large PV plant while the CSP-only design featured a large design. The high variability between the early-daytime "Shoulder" period and the late-afternoon "Peak" period in the PG&E tariff scheme instead caused very similar PV-CSP and CSP-only designs, with the main difference that small amounts of PV were integrated in the former, resulting in comparable but lower PPA tariff value despite the increase in CAPEX. Overall, PV-only designs scored the lowest average PPA tariff values, while the highest power output during the peak demand periods was achieved by the CSP-only plants. However, the second best performance of the combined PV-CSP optimal plants in terms of the PPA tariff suggests that PV-CSP hybridisation is a feasible option in the studied market moving forward, especially if future cases involves requirements of firm power output as a technical objective together with financial objectives.