Brazilian electricity production is subject to considerable hydrological risks due to a large share of hydropower production. A long drought has caused a crisis in the electricity system in 2014 implying high operational costs and a high amount of carbon-intensive power production. A further expansion of the Brazilian electricity system is therefore necessary to guarantee security of supply, in particular when considering the projected growth in demand. We assess how high shares of renewable electricity production can be maintained in the Brazilian system, while reducing hydrological risks. We focus on a longterm perspective and simulate 36 years of renewable power production from meteorological data, assessing the statistical characteristics of different portfolios and, using an optimization model, balancing monthly supply and demand in different technological portfolios. The uncertainty in the operation of that portfolio is compared to a hydro-only scenario. Results indicate that adding both, solar PV and wind to the system, will decrease the need for thermal power backup and the risk of loss of load, as total variability of renewable supply decreases significantly in comparison to a scenario that adds only hydropower to the system. Solar PV has a slight advantage over wind power in decreasing supply risks. (C) 2016 Elsevier Ltd. All rights reserved.