Wind Turbine Design for a Hybrid System

Abstract

The global issue on global warming leads nations to reduce their carbon emission, and one way to do it is by decarbonising the power system and employing higher penetration of renewable energy technology. However, due to the variable nature of renewable energy, their integration to the power system poses challenges to the utilities and system operators. Hybrid power system, due to its feature of complementary generations, serves as one of the option to answer the integration issues. This research studies the optimisation of a hybrid power system, consisting of a wind turbine and solar PV, by designing the wind turbine that operates in such systems. The design approach of the wind turbine design emphasises the complementary generation feature of the hybrid power system, which is conducted by optimising the wind generation for times when the output power from the solar PV are low. Thus, the wind turbine design considers the diurnal and seasonal variation. The diurnal turbine design is optimised for the night-time, and the seasonal turbine design is optimised for the low solar irradiance season. The wind turbine design is focused on the conceptual design phase with the objective of rotor diameter optimisation that generates electricity with the lowest cost. The cost function employed is taken from the NREL mass and cost model with additional adjustment, due to the different scaling approach. The data for the design process is obtained from a case study to represent real generation data, and the chosen location is Muppandal, India. The research aims to identify the impact of the specific operational conditions on the design parameters and the design result. Subsequently, the impact on the system performance is observed by modelling the hybrid power system in different topologies that include zero-curtailment, grid-constrained and demand load-supplying topology. The result on the site condition indicates that the affected important design parameters include wind speed distribution, wind shear profile and turbulence intensity. The research limits the analysis only on the wind speed distribution and the wind shear profile. The site condition analysis of the case study indicates that the diurnal variation of the wind speed distribution is similar to the full-year wind speed distribution and the seasonal variation that consider the season with low solar irradiance coincide with the low wind speed season. In zero-curtailment topology, higher wind speed distribution leads to smaller optimum rotor diameter and vice versa. In the grid-constrained and demand load supplying topology, larger rotor diameter suffers from curtailment due to the limited grid capacity and low demand load level. This condition leads to the shifts of optimum rotor diameter to the smaller rotor. The level of curtailment is higher in the demand load-supplying topology due to the overall lower evacuation capacity. When the night-time design and low-wind speed period design is fully operated in a year, the wind turbines are not operating at its optimum, and higher cost of electricity is expected. This result implies the higher cost for designs that correspond to the diurnal and seasonal variation. The storage system is applied to save the curtailment of wind energy. The result of this analysis suggests that the relationship between the amount of saved curtailment and the capacity of the storage is linear for higher storage capacity (<10%) and non-linear at lower storage capacity. It is found that the first few additions of storage yield the most cost-efficient of curtailment saving. The cost and benefit analysis of the storage system also indicates that the current cost of the storage technology is not compensated by the benefit of evacuating the curtailment.