This paper investigates the local complementarity of three types of renewable sources (solar, wind and tidal). One of the main drawbacks of non-conventional renewable energy sources is their intermittent nature. Wind energy depends on the wind speed, which varies throughout the day. The generation of photovoltaic solar energy is strongly affected by clouds, that cause an abrupt drop of power to less than 50% of its rated capacity. In contrast, tidal energy is characterized by a high degree of predictability. This article raises important features of local complementarity of these renewable sources. These properties can be exploited to improve the firm power of isolated microgrids, leading to a variety of beneficial operational consequences. The contributions and conclusions presented here are supported by case studies and real data measured in the coastal region of northern Brazil.