Numerical design and simulation of CSP multi-tower solar heliostat field.

In power tower systems, the heliostat field is one of the essential subsystems in the plant due to its significant contribution to the plant’s overall power losses and total plant investment cost. The design and optimisation of the heliostat field is hence an active area of research, with new field improvement processes and configurations being actively investigated. In this thesis, a different configuration of a multi-tower field is explored. This involves adding an auxiliary tower to the field of a conventional power tower Concentrated Solar Power (CSP) system. The methodology for the auxiliary towers positioning were based on the region in the field which has the least effective reflecting heliostats. The multi-tower configuration was initially applied to a 50MWth conventional field in the case study region of Nigeria. The results from an optimised multi-tower field, achieved through MATLAB Genetic Optimisation, show a marked increase in the annual thermal energy output and mean annual efficiency of the field over a typical conventional field. The efficiency and thermal energy output become even more pronounced in optimised multi-tower fields with two auxiliary towers. For the given thermal field power, the gain recorded in the thermal energy output could not offset the additional costs from the presence of additional towers and receivers in the field. However, in much larger fields a higher number of weaker heliostats were witnessed in the field. The auxiliary towers in the field thus provides an alternate aim point for the weaker heliostat, thereby considerably cutting down on some optical losses, which in turn gives rise to higher energy output. At 400MWth, the one auxiliary tower multi-tower field configuration provides both a lower LCOH and a higher field efficiency over a single conventional power tower field with similar thermal field output power. The thesis goes further to explore and develop methods in which the field layout generation methodologies in multi-tower fields can be improved. The Auxiliary Tower with Subfield Configuration (ATS) and Heliostat Repositioning Configuration (HRC). The addition of auxiliary tower has already shown to hold much potential in large plants. ATS and HRC further show that the same intended field thermal power output can be reached with a lesser LCOH and a higher field efficiency when compared to both conventional fields and optimised multi-tower fields of similar thermal ratings. These field improvement strategies were then applied to an existing field, the Gemasolar plant in Sevilla Spain, as a case study in order to further highlight their applications. In this work, multi-towers have shown that in large solar fields, a clear advantage over the conventional fields exists by proving a higher field efficiency and thermal energy output. Multi- tower fields have thus shown to provide a viable alternative to conventional fields and equally provide the potential to change the way power tower fields are being built in the future.