The uncontrollable anthropogenic greenhouse gas emissions lead to the rapid increase in the average global surface temperature. The need to mitigate climate change has been acknowledged by governments worldwide with legally binding energy and carbon emissions targets agreed under the Paris Agreement in 2015. The energy sector is one of the main emission contributors along with the transport and industry sectors. Consequently, the decarbonization of the energy sector through the development of power systems is key in achieving the global energy targets and avoid devastating environmental phenomena. Renewable power has experienced significant growth over the past two decades because of the cost reduction and financial incentives in the energy market. This thesis is focused on solar photovoltaic electricity generation and the assessment of the high penetration of solar photovoltaic power in power systems. Starting with a critical literature review on the state-of-the-art studies in power system modelling and analysis tools, system-level power flow optimisation, and techno-economic analysis of renewable integration in power systems, the thesis identifies the areas that require future work in the research domain. Furthermore, the power system of Great Britain is considered as case study to assess the impact of the integration of large-scale solar photovoltaic capacity in modern power systems by considering a system-level modelling approach, including the different generation technologies, the electrification of heating and the electrification of transport. A 29-bus simplified transmission network of Great Britain facilitates the AC Newton-Raphson load flow algorithm to evaluate 17 different energy scenarios, from 2016 to 2035, based on National Gridâs Electricity Ten Year Statement and Future Energy Scenario reports. The analysis indicates the effect of large-scale renewable integration in the Great Britainâs power system in terms of transmission network losses and transmission level voltages. The results of the thesis are expected to set the foundation for further research and publications regarding investments in power systems with high renewable generation for the provision of ancillary services and system-level benefits. Particularly, the investigation of voltage support by solar photovoltaic power is an area that can be immediately exploited based on the research.