Optimisation in operating strategies for concentrating solar power plants

Abstract

This research paper emanates from a directive of Eskom, South Africa’s power utility, to acquire a more full understanding of the technical, financial, and operational aspects of running a plant that is built on concentrating solar central receiver technology. Eskom owns the supply chain of electricity, this includes generation, transmission, distribution and management of the electric grid. The power utility identified the need to understand the operating capabilities of such plants within the South African electric grid. Therefore, to demonstrate the role and value Concentrated Solar Power (CSP) with storage offers to the electric grid, an array of operating strategies was identified during the design phase of Eskom’s Solar-1 project. These operating strategies explored in this paper are; Maximising Power Generation, Maximise Plant Revenue, Minimise Energy Dumping and Optimise Electric Grid (base load, peaking and auxiliary services). A Typical Meteorological Year (TMY) data set for the case study plant situated in Upington, South Africa is used to obtain the annual performance of the plant. In the ‘Maximise Power Generation’ operating strategy the developed model increases the power block efficiency by 1.8% utilising part-load operational optimisation instead of running the turbine at full load until depletion of the hot storage tank. This is achieved by reducing the total annual turbine stops by 50% to only 176 stops. The thermal energy saved from start-up of the power block is utilised for power generation instead. Results from the ‘Base Load’ operating strategy reduces the turbine stops by 85% to only 52 stops annually. Therefore, increasing the turbine online hours to 94.5%. The results from the ‘Minimise Energy Dumping’ operating strategy shows that it is possible to reduce energy dumping from 4.0% to 2.7% by effectively optimising the dispatch from the hot storage tank at selected times and increasing the power block output to 110%. As a result, an additional 7.4% of electric energy is generated from this saving. Under the ‘Optimise Electric Grid’ operating strategies, the complementary services of CSP to other non-dispatchable power generation technologies such as wind and photovoltaics are investigated. CSP with storage has the potential to increase the utilisation factor of distribution substations in grid constrained areas within the grid. This opportunity greatly increases the market of CSP and emphasises the value of thermal storage. However, plant design optimisation is required for this operating strategy as it greatly affects the plant performance of the case study plant. Although CSP with storage demonstrates continuous reliable power delivery to the electric grid it also provides complementary services to non-dispatchable generating technologies.