Onshore wind and solar-photovoltaic-based electricity are expected to drive most of the global growth in renewable energy sources capacity until 2020. This creates a challenge for properly modelling such intermittent variable resources since: (i) their availability varies spatially and temporally and (ii) thus, their integration in power systems is determined by the configuration of transmission grids. Large energy system models usually adopt simplified approaches for modelling wind and solar photovoltaic (PV) deployment and the power grid. This paper uses the recently developed TIMES-Brazil optimisation model to study the role of transmission bottlenecks in cost-effective long-term deployment of wind and solar power in the Brazilian energy system up to 2050. The model explicitly models the grid infrastructure of 29 regions in Brazil differentiated according to existing power plants, wind and solar availabilities, future RES potentials and power demand. Three different scenarios (Free Trade, Simplified Trade and Detailed Trade), with increasingly more detail in modelling electricity transmission lines, were tested. Findings show that a more detailed transmission infrastructure significantly affects capacity deployments and electricity prices. The grid connecting the North and South of Brazil was found to be the most important bottleneck affecting the deployment of solar in the country.